Suborbital refuelling

Might be a difference between the old .xls and the newer .xlsx ?
 
I completely concur with steelpillow - I'd just like to add that the tradeoff of airbreathing runway takeoff vs. rocket powered vertical liftoff from dedicated infrastructure likely has no definite answer (yet?), but will probably depend on variables like vehicle and fleet size, mission frequency, etc. Personally, I'd like to keep the flying vehicle as simple as possible, meaning for example a minimum of on board propulsion elements, especially if one of them is only good for a small part of the velocity spectrum, and rather put a little more complexity into the ground infrastructure, where it is not mass critical and at all times readily accessible for maintenance, checkouts, etc. As steelpillow has shown with his brilliant wire analogy, you really don't have a fundamental performance difference between classical staging and refueling schemes. Ultimately, I'd rather put a little more mass in stage connectors, if that allows me to eliminate at least one potential in flight risk event in the form of suborbital mating. I realize the military has different perceptions of acceptable risk, but I'd rather try to emulate the paradigm of commercial aviation.
 
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We must remember that one does not need a flock concept to indulge in a little suborbital refuelling. Simply fitting some tankage and a fuelling lock to a SpaceShipTwo, just enough to make a rendezvous with a big beast of a tanker in LEO, might be a practical way to increase the useful mission payload of almost any spaceplane.
I'd be interested to see more about the scenarios that NASA studied.
 
Hi,
I know zero about rockets and stuff, just a bit about planes...
So basically, it would be something that takeoff like a regular plane from a runway, using jet engines. It would have a rocket engine (or more?), but would takeoff with tanks (almost ?) empty for these.
Then another vehicle of the same kind would takeoff the same way, but with the rocket fuel tanks full.
The two would meet at the highest possible halt (using only the jet engines ?), and the one with full tanks would transfer rocket fuel to the one with empty tanks.
They then separate, and the first vehicle, now with full tanks, would boom his rocket and go in orbit…
Ok cool, but then if the second vehicle can reach up there with full tanks to refuel the first one, why doesn't it just fires his own rocket engine and get orbited ?
I miss something :D told you, I know zero about rockets...

btw Archibald, try zipping these .xls. maybe would work.
 
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Galgot you got it mostly right. Just that they use the rockets to go halfway to orbit and practice a little rocket propellant transfer between them high there. The tanker make the orbiter La courte echelle, as we say in french.
Because as far as SSTO and Earth orbit go - without a tanker 95% of the mass is the tank contains, fuel and oxidizer to reach 9 km/s.
A 1000 mt rocket-only SSTO would have to weight only 50 mt with the tanks empty otherwise no orbit.
The tanker assistance along the way to orbit allows to relax that insane number.
 
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I tried to track down the sparse history of aerial / in-flight refueling applied to reusable rockets. Will post a brief summary and some documents.
 
steelpillow said:
Might be a difference between the old .xls and the newer .xlsx ?
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I found a converter and aparently, it worked... linking a whole bunch of converted spreadsheets. Hurray, it WORKS !!! :cool:

Please provide feedback.

What I've found is that the optimal mass / PMF for the rocketplane is
- 18 mt with empty tanks
- 120 mt with the tanks full
- Propellant Mass Fraction is 0.85
There is no point in going larger since what matters first and foremost is the PMF. Doubling the mass brings little improvement. For the record, 120 mt is the mass of a Tu-22M Backfire, the heaviest supersonic twin jet ever build (AFAIK).
 
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galgot said:
Hi,
I know zero about rockets and stuff, just a bit about planes...
So basically, it would be something that takeoff like a regular plane from a runway, using jet engines. It would have a rocket engine (or more?), but would takeoff with tanks (almost ?) empty for these.
Then another vehicle of the same kind would takeoff the same way, but with the rocket fuel tanks full.
The two would meet at the highest possible halt (using only the jet engines ?), and the one with full tanks would transfer rocket fuel to the one with empty tanks.
They then separate, and the first vehicle, now with full tanks, would boom his rocket and go in orbit…
Ok cool, but then if the second vehicle can reach up there with full tanks to refuel the first one, why doesn't it just fires his own rocket engine and get orbited ?
I miss something :D told you, I know zero about rockets...
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It's vaguely like that but there are some important differences. The problem that it attempts to solve is the fuel mass ratio (FMR) demand for a single stage to orbit (SSTO) vehicle, typically a re-usable spaceplane. Any given rocket engine needs so much fuel that the weight of the tank limits its performance to sub-orbital, never mind any payload.
Conventionally we get round this by discarding used tankage and the associated engine power along the way, in what is called a step-rocket. The last of these stage separations almost invariably happens in the suborbital flight phase, in space but still travelling way too slow.
For a re-usable spaceplane, the equivalent would be a composite aircraft, something like White Knight Two plus SpaceShipTwo fuelled on amphetamines. Or, perhaps, a larger "three-series" pair with the "SpaceShipThree" payload being "OrbiterOne".
But instead, why not convert a second SpaceShipTwo to carry a fuel supply as its payload, launch it alongside, rendezvous with the one carrying the real payload just as they run out of fuel in suborbital flight, and transfer the extra fuel across? It's just air-to-air refuelling without the air. (OK you need a liquid-fuelled SpaceShip for this but the principle is there).
The "flock" concept is just a way to do this using a single standardised spacecraft design, so you can get rid of the massive WhiteKnight by doing multiple in-flight refuellings, in the same way as the RAF got the odd Vulcan bomber as far as the Falkland Islands. Space rockets are much the same as planes, only they run out of air half way.
Hope this helps.
 
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Incidentally, how does it compares with present and future RLVs ?

Compared to Skylon
Pros
No need for SABRE, precooler. Can works without LH2 if needed or different props. Simpler engines (rockets and turbofans). Quieter at liftoff (Skylon will thunder at 160 dB), uses more begnin propellants closer from those of airlines (although H2O2, I know: meh. At least kerosene).
Note that the rocketplane can compete with Skylon 40 000 pounds to orbit in two different ways
- suborbital refueling if LOX/LH2 is used with a small LOX transfer
- non suborbital refueling: just put a Centaur stage on the back of the rocketplane
The vehicle does not end up trapped in LEO but could fly higher (the turbofans are easier to protect than the Sabres, the vehicle is merely 40% the size and length and mass of Skylon).
Cons
Needs a second vehicle flying with the first. The suborbital refueling manoeuver is a leap into the unknown, admittedly. Also it needs a pilot, unlike Skylon which is automated.

Compared to Falcon 9R / New Glenn
Pros
The system is fully reusable. Payload matches if 3-FLOC or 4-FLOC. Can land at airports.
Cons
Harder to reach GTO / GEO except with orbital refueling.

Compared to BFR/BFS
Pros
As far as suborbital P2P passenger transport goes - the rocketplane can land at airports. Starship is bound to platforms offshore. Aborts are safer because wings and turbofans.
Cons
Payload is much, much smaller and fractioned. No question about this. 8-FLOC payload is huge but overall it is impractical and unbalanced. Can't land on Mars although can still access cislunar space. Much less passengers, obviously.
 
Thks for these explanations.
Are you sure it needs a pilot ? We are not far from seeing refueling drones in the USN. Ok , at that speed and height, it's never been done. But this is typically the kind of thing computers would maybe do better than a human ?
 
What is sure is that a pilot is not needed to dump an expendable stage in suborbital flight (Skylon-Fluyt, XS-1, AFRL TSTO...) So an unmanned variant could still be build. For example the Mk.1 keroxide bird could carry an expendable rocket stage on its back - either high energy LOX/LH2 or low-energy - solid-fuel, storable, kerolox (think Block D or Briz-M). Fact is that performance - payload to orbit - would actually be superior to the suborbital refueling scheme, for a simple reason. Expendable upper stages are optimized for the job of hauling things into orbit. The two major caveats are a) they are difficult to reuse and b) the rocketplane don't go into orbit by itself. Which doesn't mean it is unuseful. An expendable upper stage once it reaches orbit can become a prop depot.

As for suborbital refueling... IDK if the manoeuver could be automated. My current feeling (reinforced a little by this thread up and downs :p) is that the manoeuver is already tricky and controversial enough, if I insist it might be automated, I'm dead meat.

Much like everything else related to this concept, the motto is: build experience, build confidence, then improves the system.
 
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steelpillow said:
Archibald said:
then the massive FLOC effect happens
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Now shorten the wires to zero, i.e. clamp the whole flock together. Are you seriously suggesting that the act of clamping massively changes the efficiency? Or that efficiency is a function of wire length?
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Clamped (form one single body):

at separation you have 1/2mv² conservation

With m1 let say being 2*m2 you 'll get 1/2m2v2² = 1/2m1v1² hence 1/2v2²=2*1/2v1²

this to get v2²=2v1² hence v2=v1 * 2^0.5 = 1.414v1

Wire linked (two body):
the wire position is only dependent of each body speed and this is not reciprocal.
The kinetic energy is not transmitted (only the work) and the speed of each vehicles depends only from their individual contribution. The tow effect don't gains from mass reduction but from the raw power of the "tug". So if in effect, you'll get a simplified structural work, in reality to offset 1/1414= 30% per stage of free efficiency is a burden to take at risk.
 
Archibald said:
Incidentally, how does it compares with present and future RLVs ?

Compared to Skylon
Pros
No need for SABRE, precooler. Can works without LH2 if needed or different props. Simpler engines (rockets and turbofans). Quieter at liftoff (Skylon will thunder at 160 dB), uses more begnin propellants closer from those of airlines (although H2O2, I know: meh. At least kerosene).
Note that the rocketplane can compete with Skylon 40 000 pounds to orbit in two different ways
- suborbital refueling if LOX/LH2 is used with a small LOX transfer
- non suborbital refueling: just put a Centaur stage on the back of the rocketplane
The vehicle does not end up trapped in LEO but could fly higher (the turbofans are easier to protect than the Sabres, the vehicle is merely 40% the size and length and mass of Skylon).
Cons
Needs a second vehicle flying with the first. The suborbital refueling manoeuver is a leap into the unknown, admittedly. Also it needs a pilot, unlike Skylon which is automated.

Compared to Falcon 9R / New Glenn
Pros
The system is fully reusable. Payload matches if 3-FLOC or 4-FLOC. Can land at airports.
Cons
Harder to reach GTO / GEO except with orbital refueling.

Compared to BFR/BFS
Pros
As far as suborbital P2P passenger transport goes - the rocketplane can land at airports. Starship is bound to platforms offshore. Aborts are safer because wings and turbofans.
Cons
Payload is much, much smaller and fractioned. No question about this. 8-FLOC payload is huge but overall it is impractical and unbalanced. Can't land on Mars although can still access cislunar space. Much less passengers, obviously.
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Archibald, I cannot help but notice that you *still* studiously avoid a full and fair quantitative comparison to a parallel staged fully reusable winged rocket powered TSTO sized for the same mission parameters, launch/landing modes, and orbital payload and based on the same technology level in terms of propellant combination, dry mass fractions, etc.
 
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you are inventing hidden biases, really things that don't exist. I feel I have been honest and transparent. What, I've made my calculations available, recognized the weaknesses compared to present, ongoing RLV systems in development. I'm not saying it is the best thing since bread come in slices: nor that it will kill or replace all the aforementioned RLVs. That thing has potential, that's all.
 
I see no hidden bias, just an honest engineer's request for hard information. It is now plain that no such analysis exists. Many of the claims made by Archibald are wholly unsupportable and that does not do the more credible ones any good at all.
For example I now understand that his specific proposal carries a couple of turbofans into orbit. That raises alarm bells. The whole point of SABRE is to get rid of them, so claiming them as a plus point over SABRE really does need some real and credible explanation. I'd back the analytical thoroughness of Alan Bond's team over unsubstantiated statements any day.
 
Archibald said:
you are inventing hidden biases, really things that don't exist. I feel I have been honest and transparent. What, I've made my calculations available, recognized the weaknesses compared to present, ongoing RLV systems in development. I'm not saying it is the best thing since bread come in slices: nor that it will kill or replace all the aforementioned RLVs. That thing has potential, that's all.
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I take extreme umbrage at your claim of bias - I am actually asking (and implicitly trusting) you for an *unbiased* quantitative comparison of your concept to another well established and documented RLV concept based on a lot of the same technologies and principles. You have qualitatively compared a so far purely fictional concept to designs under actual (in the case of Skylon, at least partial) hardware development. If you truly believe your idea is superior, why are you so recitent to quantitatively compare it with another often postulated configuration that is at the same current level of hardware development (i.e. zero)? If your idea has potential, as you say, it is simply fair to ask whether there are other solutions out there that have more potential. I believe that to be the case. You may not be interested in creating a truly optimized solution, but I am. The goal is not to come up with something "cool", but something reliable and practical.
 
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steelpillow said:
I see no hidden bias, just an honest engineer's request for hard information. It is now plain that no such analysis exists. Many of the claims made by Archibald are wholly unsupportable and that does not do the more credible ones any good at all.
For example I now understand that his specific proposal carries a couple of turbofans into orbit. That raises alarm bells. The whole point of SABRE is to get rid of them, so claiming them as a plus point over SABRE really does need some real and credible explanation. I'd back the analytical thoroughness of Alan Bond's team over unsubstantiated statements any day.
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Steelpillow, while, as you say, apparently no comparative analysis exists as yet, Archibald should have no problem at all to adapt his spreadsheet to create one. I wholly concur with you that for a launch vehicle turbofans are more of a necessary(?) evil (e.g. for winged RTLS boosters with high staging Mach numbers, but even there Musk has demonstrated that rocket tossback works like a charm in practice) than an advantage.
 
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For your info Buran was to carry Su-27 turbofans in orbit. NOT OK GLI but the real vehicle. They were removed some days before the lone 1988 flight.
 
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Archibald said:
For your info Buran was to carry Su-27 turbofans in orbit. NOT OK GLI but the real vehicle. They were removed some days before the lone 1988 flight.
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The fact that Buran successfully completed its one and only orbital flight without any turbofans (or turbojets, for that matter) on board (as did the Space Shuttle for more than 130 times, by the way) should tell you something.
 
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... and again : Discussion should be run by adressing arguments, not people, who made them.
No " you have ...", "you are ..." and so on.
If someone says, he has calculations, etc., about a certain theme, but doesn't come up with them,
though repeatedly called on, others certainly will draw their conclusions, but there's no need to do
this publicly.
This discussion somehow got out of control, perhaps the participants (ALL participants !) would deign
to reconsider their personal behaviour and wording ?
Please, consider this a warning !
 
Jemiba: fair enough and well noted. Let's this one cool down a little. I have not much to add to the discussion, btw.
 
martinbayer said:
*please* don't put words in my mouth/writing - I never claimed that aerial refueling was risky for airline passengers, but simply observed it wasn't done *at all*. Likewise, I expect future aerospace passenger operations to be done with a minimum amount of vehicle interactions, because the more, the messier.

Martin
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martinbayer said:
Hello Randy,

thanks for explicitly stating that you think suborbital refueling might only be of interest for a military niche application! I think that puts that concept squarely into a box that excludes civilian/commercial applications (which I expect and hope will dwarf any other space endeavors in the future), just like aerial refueling is used nowadays by the military only, but by exactly none of any and all commercial airlines anywhere around the globe.
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Commercial A2A is not done currently but it has been studied and suggested for various reasons of late:

And considering how big a business it has become worldwide, (https://www.bloomberg.com/press-rel...h-672-million-in-2024-says-stratview-research) as long as commercial operations would not directly impact military requirements...

As for commercial future passenger operations numerous studies have shown such is getting to the point where we need a major change in how we do things if the market keeps growing. The main problem of course is we have a huge infrastructure build up to do thing the way we do them :)

Passenger and frankly even 'regular' access for cargo to orbit can change a lot depending on what works and what doesn't. Yes the military is the main point of interest TODAY but that doesn't preclude commercial interest. Especially if the military ends up paying for large chunks of the research and development process.

Your points about the oh so difficult resolution of various stages firing in parallel were successfully resolved for the Space Shuttle decades ago, so this is just an engineering issue we already well know how to address. You state that rocket powered HTHL systems are considered to be always behind airbreathing HTHL concepts specifically due to the operational and physical issues with rocket powered horizontal take off, so why do you advocate horizontal launch for an inflight refueling architecture? And if you assume airbreathers, would you be willing to accept them for one concept but not the other, and if so, why? Whether airbreathers are preferable for horizontal takeoff or not, that question clearly affects the identical tanker concept twice as much as an optimized non-identical TSTO, or at least the same as in a clone bimese stage version. My personal conclusion is that airbreathers excel at steady state flight at subsonic, supersonic, and perhaps even hypersonic flight, while rockets shine at pure acceleration, which is at the heart of any space launch mission. I can relate to the cat dominance issue though .

Martin
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Jet engine airbreathing was specific to the concept and that so they could operate out of nominally "standard" airports where a pure rocket vehicle cannot. Point of fact I DO except other HTHL airbreathing concepts such as TSTO's based on various engines which are good accelerator engines through low-hypersonic speeds. If we're being technical I've been impressed by VTHL/VL airbreathing boosters as well it just depend on the mission and engine capabilities.

As my current T-shirt note:
"Dogs have Owners, Cats have Staff" :)

steelpillow said:
RanulfC said:
steelpillow said:
Arthur C Clarke remarked back in 1947 that once you reach low Earth orbit you are halfway to anywhere [in the Universe].
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AhhhHEM there mister, want to correct that before Bob comes down from heaven and set you straight?
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Well, OK it was 1950 and maybe the phrase "halfway to anywhere" might have come later, but I refer you to his Interplanetary Flight, Temple Press, 1950, page 15:
"The necessary speed to maintain a stable orbit at any distance from the Earth ... is about 7.9 km/sec (18,000 m.p.h.) This is less than the corresponding escape velocity in a ratio 1:√2."
Since e=½mv^2, the kinetic energy to reach LEO is half that to reach escape velocity. In practice some extra energy is needed to climb to orbit so the kinetic energy equation is an approximation to the practical launch, but the difference is relatively small. Even if the craft is refueled in LEO (as Archibald sensibly suggests), that fuel has already been given a lot of expensive kinetic energy to get up there. The velocity delta from LEO to escape may be less, but the total energy cost still has to be found. I accept that in this scenario, the "second" fuel load which I observed is needed for escape has already been burned by the tanker.
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"Escape"? I only got as far as LEO. I would suppose the idea is one orbiter brings up the actual 'cargo' and a second (and likely third or more) orbiter brings up propellant for an escape trajectory. Note these don't have to actually rendezvous with the cargo orbiter but would be better to drop off in an orbital propellant depot where the out-bound orbiter would stop to top-off.

Many thanks to you and Archibald for your own contributions here, very informative. However I still find unsupported claims lurking. Every engineer knows that in a chain of 100 links, if one link fails the whole chain fails.
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And every maintenance person I've ever met knows very well that of those 100 links the Engineers were so clever to identify, WE end up dealing with hundreds or additional links and systems they didn't consider. And OUR job is to keep them running despite all that :) And specifically if your engineers have done their job right no "one" link will every be the single failure point. It might take down a subsystem but it won't cause a total failure or at least not one that is a total disaster. Finally you have to face the fact that there WILL be failures and try and reduce them to being as survivable as possible. You won't get everything of course but that shouldn't stop you from trying..

  • "Operationally if the notional TSTO fires all engines on launch and has propellant cross-feed to separation then the analogy works but that has its own issues to deal with. (Exhaust plume interaction and aerodynamic and hydraulic stress' for example)" is an excellent description of the Space Shuttle. It cannot be seen as damning criticism.
  • "Your abort options are greater since you don't have to worry about separating a mated pair of vehicles should something go wrong." Setting aside the SRB (which ran counter to Von Braun's dictum never to use solid fuel), I cannot recall a step-rocket launch where escape separation ever failed. And if something goes wrong with the sub-orbital refueling, you do have to separate.
  • "I saw you mentioned that you'd like to 'see' this in operation before believing it might work?" No, I said I'd like to see the numbers.
  • An open runway vs a dedicated launch facilities, eh? The runway may be simpler to engineer but the craft itself is a heck of a lot more complex with its wings, airbreathing engines, retractable undercarriage and other flight systems. Again, directly comparable quantitative analyses of the whole system lifecycle (air traffic control, safe fuel storage, so many peripheral activities are involved) are needed before one can accept the best answer. I am not prepared to commit based on speculative arguments alone.
  • Composite vs refueling? Refueling a jet fighter in mid-Atlantic is done because the jet is not equipped for composite carriage. By contrast the Short Mayo of the interwar period was a transatlantic composite flying boat, Mercury a modified Empire class flying boat, Maia a dedicated mail-carrying floatplane. It was done that way because in-flight refueling was deemed overly expensive. Not even commercial freight uses in-flight refueling today, it is nothing to do with passenger safety, it is just too expensive. Using the qualitative example of the jet fighter optimized for combat to try and justify the economics of in-flight refueling is absurd.
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1) That wasn't 'damning' criticism but noting how difficult and frankly dangerous such operations were. We knew this but did it anyway. "In-line" is frankly always safer and THAT isn't saying as much as one might hope. Note the Shuttle/Buran system is not being considered for future launch operations for many of those reasons. More integrated shapes and assemblies are possible of course but you still have to consider the stress' along the entire trajectory from aerodynamic and other stresses. But what if you don't HAVE to for launch? Is it not worth examining?

2) Note Von Braun though he didn't LIKE SRB's eventually (as he did for "balloon" structural tanks like the Atlas and Centaur) came around on the supposed cost and utility of SRBs so far as to approve and help design the ones to be used on the Advanced Saturn-V concepts and later the Shuttle SRBs. His opposition was later vindicated when Solid propellant never achieved its promised cost goals or reliability rating but he still felt they had a place. Now having said that let's address the abort issue. You note:
"I cannot recall a step-rocket launch where escape separation ever failed." What about the Titan's, Delta's, Atlas's and other rocket that failed and lost their payloads? I'll grant that we should continue to ensure passenger escape is possible but we should also ensure that the cargo can be saved as well if possible.

Second you wrote "And if something goes wrong with the sub-orbital refueling, you do have to separate." Yes, under minimal stress and no aerodynamic loading. Turnover, reenter, and return to base to fix the problem. Unlike a step booster which has to be designed to do such maneuvers at the highest acceleration and peak aerodynamic loading.

3) "See" as in see if the rendezvous and transfer works as planned because it's the key to the idea. I'd also agree on the 'numbers' but I'll point out that the "numbers" for SCramjets have 'worked' since the mid-50s and they still have issues actually flying economically today :) Numbers are good for your initial pass but you need some practical data to boot. My suggestion, (though I don't think I brought it up with Archibald for some reason :) ) was to build a couple of air-powered 'proof-of-concepts' for the rendezvous and quick-dock platforms and test them in a vertical wind tunnel. It's crude but readily available.

4) You won't commit over a purely speculative concept that is passionately argued by believers? Shocked! I Shocked sir that you would be so cold hearted and unwilling to simply believe the Earth is Flat... Er, sorry that is Vaccines cause aut.... Wait what was I arguing again? :) Seriously at this point the idea IS speculative and one reason for putting it out there is to have discussions such as this to refine the idea and define the needed trade spaces. As for the quantitative comparisons aircraft, while not spacecraft and vice-versa CAN and have been shown to be capable of orbital performance with the right design and operations. In this case we're trying to tie it as close as we can to the existing and very deeply paid for "aircraft" support and servicing infrastructure, which should greatly reduce the operations and support costs for the concept compared to a "standard" TSTO. Specifically since it uses standard airbreathing engines for launch and landing which makes it vastly more capable of interfacing with that existing infrastructure than most TSTO concepts. I don't WANT you to 'commit' but to question and then let me know if my answers address your points :)

5) Composite versus refueling is a very basic and quite generic 'analogy' to the concepts as the environment and operations would be vastly different. In-flight refueling was still very crude but it WAS used on occasion for long distance flights. (Imperial Airways had in fact done some testing with the then current "best" system but found it to complex and cumbersome so they tested the Mayo/Mercury concept and then went BACK and installed several air-to-air systems on their flying boats :) As I pointed out above while we don't have any in use today it has been seen by the industry that there is a very good chance it WILL be used in the future as an economic system even if they "only" use a slightly improved system that what we have today.

None of these niggles is a technical engineering showstopper, but I do seriously doubt the economics of it.
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I take solace in the fact that "many" seriously doubted the actual economics of reuse of rocket stages until it was proven :) The problem was many of those were less conversant with the actual operations and maintenance costs of both expendable and reusable rocket stages. I'm thinking neither you nor Martin will have that issue which makes getting you input that much more important :)

On the plus side, I would note the incredible speed with which a Formula One racing car gets refueled during a pit stop, something like 3.9 seconds including attachment, transfer and detachment. Fortunately perhaps, a spaceplane does not need all four tyres changing at the same time.
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Jettison the takeoff gear and use brand new tires on the landing gear. Hmmm, or stop by "Cloudbase" (https://en.wikipedia.org/wiki/Cloudbase) for a quick pit-stop? ("Did I not tell you to go BEFORE the spaceflight?") I was surprised by how short a time was needed to transfer a single propellant with modern A2A equipment but It's looking like my notes WERE on the malfunctioning laptop and not on my main computer :( I still have some hope for them being mixed into my other note sets but I REALLY have to go through my notes and get them organized! Weren't computers supposed to HELP in that respect not throw up their metaphorical hands and go sulk in a corner? A couple of terabytes of 'files' scattered over a couple different computers and hard drives with thousands of 'notes' files I mean how hard could it be? (And why is my work computer now making whimpering sounds?) I mean it's not like I'm asking it to look over my hand-written, (which even "I" have issues trying to read) notes or anything...

Randy :)
 
martinbayer said:
I completely concur with steelpillow - I'd just like to add that the tradeoff of airbreathing runway takeoff vs. rocket powered vertical liftoff from dedicated infrastructure likely has no definite answer (yet?), but will probably depend on variables like vehicle and fleet size, mission frequency, etc. Personally, I'd like to keep the flying vehicle as simple as possible, meaning for example a minimum of on board propulsion elements, especially if one of them is only good for a small part of the velocity spectrum, and rather put a little more complexity into the ground infrastructure, where it is not mass critical and at all times readily accessible for maintenance, checkouts, etc. As steelpillow has shown with his brilliant wire analogy, you really don't have a fundamental performance difference between classical staging and refueling schemes. Ultimately, I'd rather put a little more mass in stage connectors, if that allows me to eliminate at least one potential in flight risk event in the form of suborbital mating. I realize the military has different perceptions of acceptable risk, but I'd rather try to emulate the paradigm of commercial aviation.
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Actually the idea IS to emulate the paradigm of commercial aviation as much as possible, hence the use of 'standard' airbreathing engines and avoiding the use of highly specialized and specific launch infrastructure, (and frankly landing as well since a 'glider' doesn't inteact well with standard air traffic) by using the deeper, and broader air traffic system infrastructure. The airbreathing populsion system is used to move the vehicle from the "airport" to a place where it can light off it's rocket engine freely. At any point it can also be used to 'abort' to an alternative airport or emergency airstrip. Similarly when the vehicle is back from orbit and moving back towards a landing it has an airbreathing engine so that it does not interfere with the standard air traffic flow and take a place in the que for landing and servicing.

I'm going to point out that Steelpillow's "wire analogy" isn't really brilliant as it begins with the assumption that the vehicles have to be physically interconnected as the basis for the analogy. It's the 21st Century my dear sir have you never heard of 'wireless' operations? :) (Must have missed where FLOC came in, sigh, going back to read after this post)

Because that is what it would be. You specifically do NOT have a physical connection between the vehicle because doing so reduces their efficency and adds mass to the system. They ARE 'wirelessly' connected of course and are aware and constantly updated on each others position and because you don't have those 'physical' connections you also don't deal with the stress and aerodynamics that come along with them. They ONLY come together in order to transfer propellant beyond that they are seperate vehicles for the whole flight.

Yes there's some serious questions over SSTO capability and operational advantages, lord knows I'm one of the ones who doubts the rosy picture the advocates paint :) But as I noted before they DO have some points and they can be applied to near-SSTO vehicles as well. It is a unitary airframe that does not have to be 'integrated' with another airframe for launch and only 'interacts' above the nominal atmosphere in a free-fall arc. TPS, structure and other systems are lighter and easier to maintain this way. As a space station delivery vehicle the airbreathing engines give it unlimted range and endurance compared to a pure rocket powered vehicle, (and that's before we look into such engines as the turb-ram-rocket or Supercharged Ejector Ramjet for two examples) so chasing and matching a particular stations ground-track is vastly easier. Unitary means no ground mateing/demateing and associated support systems, while it may be more complex it will likely be smaller (which will cost less) and easier to work on. (Ya, tell that to the tech who has to be shoved into panel D-1A to rewire cannon plug CR-21 on his back with all the tools and wire sitting on his chest and only about 3 inches to work with... No, what makes you think I've had to do something like that? :) ) As a near-SSTO it doesn't have to be as optimized and light weight as an SSTO does and bonus it likely carries more playload as well. Probably not as much as an optimized TSTO vehicle but then again, (and this may be just me) but I'm pretty sure that taking 10,000lbs into space once a week or more can have more effect on some costs than going once a month with 100,000lbs specifically for things like space station support supplies. Twice a week is better an four times a week even more so of course.

Blackhorse in its original incarnation wasn't really even a 'near-SSTO but had some similar advantages, funny thing was both Zubrin and Clapp actually missed some opportunites and concepts because they stuck so close to the initial concept. The basic idea of the sub-orbital refueling concept accepted that both Blackhorse vehicles would remian the same but really the fact that they added airbreathing engines in and of itself had a more far reaching effect than they assumed.

Randy
 
galgot said:
Hi,
I know zero about rockets and stuff, just a bit about planes...
So basically, it would be something that takeoff like a regular plane from a runway, using jet engines. It would have a rocket engine (or more?), but would takeoff with tanks (almost ?) empty for these.
Then another vehicle of the same kind would takeoff the same way, but with the rocket fuel tanks full.
The two would meet at the highest possible halt (using only the jet engines ?), and the one with full tanks would transfer rocket fuel to the one with empty tanks.
They then separate, and the first vehicle, now with full tanks, would boom his rocket and go in orbit…
Ok cool, but then if the second vehicle can reach up there with full tanks to refuel the first one, why doesn't it just fires his own rocket engine and get orbited ?
I miss something :D told you, I know zero about rockets...
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Both vehicles, (they aren't really "planes" and more like spaceships with some "airplane" bits on them :) ) use airbreathing jets to take off from a pretty standard runway. (You're going to run into some noise issues if you use military jet engines but high-bypass turbofans are pretty big and get 'draggy' at high speeds) They both have "full" propellant tanks for the rockets and fly to a spot where they can both light off the rocket engines and climb into a sub-orbital trajectory.

Note one vehicle has a payload bay full of payload for orbit the other has a propellant tank in its payload bay and both are equipped with a rendezvous and attachment system with active seeking and connections. Think of it as a couple of flexible booms with active sensors and wireless comunications systems. The second vehicle (tanker) COULD use the propellant to reach orbit... But it carried the propellant to do so instead of any payload so what was the point? If it transfers the propellant to the vehicle that IS carrying a payload but not the extra propellant then THAT vehicle can now reach orbit WITH the payload. :)

They both fire the rockets and shut down the jets and climb into 'space' (over 90 miles) moving around Mach 8 or so. They they manuver towards each other where the automatic systems of the booms take over and move them into rendezous position and begin propellant transfer. (Takes less than 60s seconds to do it all) They then detach and the 'tanker' vehicle drops back into the atmosphere while the "orbiter" fires the rockets again to achieve orbit.

steelpillow said:
It's vaguely like that but there are some important differences. The problem that it attempts to solve is the fuel mass ratio (FMR) demand for a single stage to orbit (SSTO) vehicle, typically a re-usable spaceplane. Any given rocket engine needs so much fuel that the weight of the tank limits its performance to sub-orbital, never mind any payload.
Conventionally we get round this by discarding used tankage and the associated engine power along the way, in what is called a step-rocket. The last of these stage separations almost invariably happens in the suborbital flight phase, in space but still travelling way too slow.
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Quick nit: First not the Last of the stages is suborbital :)

For a re-usable spaceplane, the equivalent would be a composite aircraft, something like White Knight Two plus SpaceShipTwo fuelled on amphetamines. Or, perhaps, a larger "three-series" pair with the "SpaceShipThree" payload being "OrbiterOne".
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Ugh there are SEVERAL other concepts you could have used rather than a kludge like that? StratoLaunch for example is planning on launching a three -barrel, (three rocket bodies mated together) TSTO where the first two liquid stages fire upon leaving the aircraft and the upper stage once those burn out. Launcher One in fact is a step-rocket, (https://en.wikipedia.org/wiki/LauncherOne) being a two-stage kerosene/lox powered rocket.

What this is is two seperate vehicle that start our seperate and only come together to transfer propellant well above the effective atmosphere and in free-fall conditions.

But instead, why not convert a second SpaceShipTwo to carry a fuel supply as its payload, launch it alongside, rendezvous with the one carrying the real payload just as they run out of fuel in suborbital flight, and transfer the extra fuel across? It's just air-to-air refuelling without the air. (OK you need a liquid-fuelled SpaceShip for this but the principle is there).
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Well you hit the original X-15 concept on the head there though they did look at possibly using only one B-52 the required modifications and mass for the high speed (Mach-6) flights proved one B-52 could not carry the load. While I admit that such an idea DOES off-load the engines and standard kerosene jet fuel off the Spaceship's you now have to recovery the 'tanker' as a glider AND serioulsy build up the second Spaceship one to handle orbital speeds. So neither one is a "Spaceship" anymore. (Keep in mind the design isn't compatabile with orbital flight, you need a whole different design to accomplish that) As you note the FLOC concept does this a LOT more than just once and frankly I've got doubts over multiples even being needed.

Putting jet engines on the vehicles themselves solves a ton of issues that the opeational plan for WK2/SS2 has with using any 'standard' airport for both launch and landing. (It can do the former but landing has to be a different place because of the traffic flow pattern) Good basic explination but I'd add the extra bit to keep in straight...

As to the "need" for airbreathing engines lets keep in mind that's an operational choices that impacts where you can launch and land at. Neither Buran or the Space Shuttle carried them but then again neither of them could take off or land from anything like a 'normal' runway, nor could they interface with commercial air traffic. Both had to have cleared airspace from first movemnt to wheels stop, whereas this can, (as long as you keep in mind noise regulations and safety which in this case is similar to launching a hazerdous cargo jet rather than a 'space launch' since that takes place far outside normal 'traffic' lanes) litterally take off and land at any airport with a sufficent runway and infrastructure to support it. (I don't see this going out of any airport inside or with flight path ONLY over a city but there's a lot of places that's not an issue)

While you don't need to have any 'boosting' of the engine power that's not to say you can't. Afterburners are of course a thing though they will further limit the places you can operate from due to noise regulations. And then there's what's now known as "Water Injection Pre-Compressor Cooling" (https://nas.nasa.gov/assets/pdf/papers/Mehta_U_February2015.pdf) where you inject water into the jet inlet to cool and compress the air volume and which both increases thrust, ("up to twice" normal thrust output, NASA studies mention this as a MINIMUM) and also the standard jet engine Mach range (from say 1.5 to 3 or 4) due to compressor face heating. This would push the vehicles up to speeds beyond Mach-2 and altitudes over 65,000ft BEFORE they light the rockets. If you were using LOX as an oxidizer you could inject some into the intake to further cool the incoming air and help stablize engine operations up to 80,000ft and speeds in excess of Mach-3. (In a climb don't forget) Otherwise you'd need a supplmental tank for the LOX but since you have to add the water tanks and injection system it's better to do so from the begining and adjust vehicle size from there.

Randy
 
steelpillow said:
We must remember that one does not need a flock concept to indulge in a little suborbital refuelling. Simply fitting some tankage and a fuelling lock to a SpaceShipTwo, just enough to make a rendezvous with a big beast of a tanker in LEO, might be a practical way to increase the useful mission payload of almost any spaceplane.
I'd be interested to see more about the scenarios that NASA studied.
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Well it depends since a "tanker in LEO" isn't suborbital :) The main issue with looking at the NASA studies, (other than your usual NTRS issues that is :) ) is they are spread out and not usually very well keyworded to things like "Aerial" or "sub-orbital" propellant transfer as a seperate concept. I first heard about NASA looking at the idea from several sources, (these forums IIRC being one) as an alternative or add-on to the LARC "Spacejet" studies. Both the military and NASA agreed that the general idea of Blackhorse was sound and workable so they must have based that on something. Zubrin and Clapp made note that doing so suborbitally was easier and less stressful and they agreed as well.

Still trying to catch up with what the FLOC is going on as it were :)

Randy
 
Archibald said:
thanks RanulfC for his explanations... he is far better at arguing / quoting / nailing a point - than myself (short temper doesn't help, welcome to my Greta Thunberg side).

that the sub-orbital refueling is going to lose in several categories from the simple fact it's an odd concept and seems operationally complex. Having said that there's an operational and logistical reason it keeps cropping up in military circles along with "Blackhorse" like concepts. The actual 'best' choice is often customer rather than concept driven
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bingo. I fully agree with that point of view. What I'm suggesting in my papers is that rocketplane has plenty of niches it could fill.

the whole thing is an evolutive family of rocketplanes.
evolutive by oxidizer changes and also by adding birds into the flock : 2 to 3, 3 to 4 and eventually 8.
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Ok so we're clear here, "Flock" as in squadron/group/company not FLOC as in, well, whatever the original FLOC (Ahh found it "Fleet Launched Orbital Craft" here https://selenianboondocks.com/2008/01/an-insane-but-interesting-idea-fleet-launched-orbital-craft/) stood for where you have dozens of vehicles performing 'hookups' along the trajectory...

Archibald said:
and that's why I suggest to use plain old turbofans for an airliner-style liftoff - and nothing else. The RASV shows that exotic ground assist systems are unwelcome at air bases and airport. They need and want F-16 or 737 ground ops.
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Well that's one thing but it depends on the airframe and thrust requirements. I tend to use a fully fueled "Blackhorse" (http://www.ai.mit.edu/projects/im/magnus/bh/analog.html) your takeoff weight is higher, so then is your gear mass and wing area needed. Doable but tricky.

Archibald said:
This. My papers mentions that point. Going from Earth surface to Earth orbit takes an horrible delta-v of 9 km/s. By comparison, Earth escape is 3 km/s, lunar orbit is 4 km/s and lunar surface, 6.5 km/s.
Now follow my reasoning.
Since the rocketplane is build for suborbital REFUELING, then the refueling gear can be used a second time once in a stable Earth orbit. Orbital propellant depot, here we go. Filled with kerosene and H2O2, which don't boiloff with time, unlike cryogens.
Let's suppose we fill the tanks to the brim. See my calculations up thread: total delta-v of the Mk.1 with the tanks full is 6100 m/s. Now if you refill the tanks completely, you regain these 6100 m/s.
So the question is, how far can you go from LEO with a delta-v of 6100 m/s ? see above. You can nearly land on the Moon. You can certainly go in and out of lunar orbit (4km/s +1 km/s TEI), returning via a mix of propulsive braking (1km/s left) and aerobraking.

In the end the most exciting aspect of the system is that, with only two refuelings (first one, partial, in suborbital flight, second one, complete, in orbit) you can fly all the way from Earth surface to cislunar space.
And with a third refueling in cislunar space, you can make the roundtrip from lunar orbit to surface to orbit (2.5 km/s down, 2.5 km/s up). Landing on the Moon Starship style, like a vertical tail-sitter, on throttled down rocket power.

Three refuelings, same rocketplane all the way from Earth surface to Moon surface.

What's more, since the delta-v to Earth escape (3 km/s) and lunar orbit (4 km/s) are so much smaller than ascent to orbit (9 km/s) then the payload rise accordingly. The hardest segment is ascent to orbit, and that's where payload suffer the most. By contrast, payload from LEO to cislunar space can be huge. It is a matter of getting out of Earth deep gravity well, or at least to the edge of it. We are living at the bottom of a steep gravity well.
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Yes it's possible but the main question is why you'd want to? It's much like using Starship to go from the surface of Earth to Mars and then back again. You CAN but why would you really want to since it is not very efficent to do so? You could in 'theory' take one all the way to Mars but... You'd run out of life support long before you got there :)

Low Earth Orbit is a destination for some good reasons. As In noted this would work quite well as a space station supply vehicle bringing up consumables and some small amount of passerngers per flight. Pushing the destination further out requires more propellant transfers and more systems and supplies when it's not really needed.

Randy
 
steelpillow said:
I see no hidden bias, just an honest engineer's request for hard information. It is now plain that no such analysis exists. Many of the claims made by Archibald are wholly unsupportable and that does not do the more credible ones any good at all.
For example I now understand that his specific proposal carries a couple of turbofans into orbit. That raises alarm bells. The whole point of SABRE is to get rid of them, so claiming them as a plus point over SABRE really does need some real and credible explanation. I'd back the analytical thoroughness of Alan Bond's team over unsubstantiated statements any day.
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SABRE doesn't actually get rid of the 'turbofans' though and that was the point of the exercise. Back in the dark ages of space and high speed flight it was "assumed" (by aero-engineers) that liquid rocket engines had to have "liquid" to feed the pumps for those rocket engines. Funny thing was during the studies for making liquid oxygen in flight one sub-contractor discovered that you could feed 'deep cooled' but not 'liquid' oxygen/air into a turbopump and feed it at rocket engine pressures. This was ignored because it wasn't what those who were running the studies were interested in. Alan Bond re-discovered this later on and used it to develop what would eventually become the SABRE but it still uses a fan and turbo-compressor system like a jet engine, it just feeds it directly into a rocket engine.

SABRE therefor can't operate out of any conventional airport and must have a specialized and therefore expensive infrastrcuture built to support and maintain it. Thus the Air Force and others have been more interested in deep cooling for TSTO (and mostly military) purposes since they are not bothered by the lack of commonality with commercial air operations. If you don't have the rockets directly linked to the deep-cooled turbojet system, (and there have been many suggestions for systems to do so) then you have a very efficent turbjet accelleator as I've noted above with the capability of getting up to high altitude and high mach speed but the downside is you've used a lot of hydrogen fuel to do so. (Not nearly as much as if you'd gone with liquid air/oxygen but more than if you'd fed it all directly into the rockets from the start) Yet this has both economic and operational advantages,(which Bond himself has stated ARE issues with both the RB545 and SABRE and more 'sovlable' in LAPCAT) since it can be better integrated into the existing commercial and military air traffic systems. Loud turbo jets are still only turbojets whereas rockets will never fly from an 'airport' on their own.

The idea raises "alarm bells" but it shouldn't since the idea address' several well known issues with cycles like SABRE. It of course has some dsadvantages in that you have a seperate engine that is mostly 'dead' weight' for part of the flight but they can and do operate during parts of the flight where rockets are at a distinct disadvantage.

martinbayer said:
Steelpillow, while, as you say, apparently no comparative analysis exists as yet, Archibald should have no problem at all to adapt his spreadsheet to create one. [b[I wholly concur with you that for a launch vehicle turbofans are more of a necessary(?) evil (e.g. for winged RTLS boosters with high staging Mach numbers,[/b] but even there Musk has demonstrated that rocket tossback works like a charm in practice) than an advantage.
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Martin, could I suggest there actually IS some "bias" on Steelpillow's and your part? I mean it's litterally right there in bold above, you "assume" that turbofans would be a 'neccessary-evil' for a winged RTLS booster, but fail to grasp the original intent and concept of using them to takeoff from a runway and fly to a point, return from orbit and fly right back to that runway INCLUDING operational things like stacking in a holding pattern and taxing off the runway after landing to the hanger. Please don't take offense over the suggestion but I've seen it quite often in the cases where people DO have bias' (and we all do of course) but fail to grasp that theirs might be having a larger effect than the think they do.

I'm going to have to download the spreadsheets at home but let's keep in mind that we all have assumptions and bias' that color our outlooks and we need to keep calm and acknowledge them while also compesnating for them to arrive at a better understanding.

Randy
 
ranulfc : I declare you my advocate and ambassador, altogether. If I were Greta Thunberg then you would be Samantha Smith. In a nutshell: as far as pasionaria and crusaders goes, you win persuasively, I lose in anger. ROTFL
 
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Yes it's possible but the main question is why you'd want to? It's much like using Starship
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The answer is in the question. SpaceX influenced me. Note that Starship needs 1100 mt of methalox to go anywhere beyond LEO. My little rocketplane "only" needs 100 mt of keroxide, 11 times less and it doesn't boil off. It is a mass small enough, manageable, a complete refueling is worth considering to go higher. Another motivation to do that is the GTO / GEO / TLI delta-v (2.5 km/s to 4 km/s) are really a joke or a walk in the park compared to ascent to orbit (9 km/s).
 
RanulfC said:
Steelpillow's "wire analogy" isn't really brilliant as it begins with the assumption that the vehicles have to be physically interconnected as the basis for the analogy.
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I will just say that in the thought experiment, the wires are very obviously there to illustrate a point and not to be part of a practical design, instead to be taken as sufficiently thin to be of negligible weight and drag. Martinbayer had no trouble in appreciating this, so I do not see it as an obscure issue. That others need it stating astonishes me, I fear that constructive dialogue loses the common basis in language that makes it possible. So I regret that there is little point in responding to all the recent misunderstandings of Martinbayer's and my critiques, not to mention SABRE, per se.

I would also remind folks that a mildly insulting remark accompanied by a smiley is still an insult, and in the wake of the recent administrative redactions and warnings, this is perhaps even less appropriate than usual.
 
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And then there's what's now known as "Water Injection Pre-Compressor Cooling"
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bouncing off this...

Marti Sarigul-Klinj nicely quantified delta-v gain from an optimal air-launch. Altitude: 45000 ft. Angle of attack: 30 degrees. Then there is the mothership / carrier aircraft own speed and the delta-v boost it provides
- Mach 0.95 brings a benefit of 1100 m/s
- Mach 2 carrier aircraft, 1600 m/s
- Mach 3 carrier aircraft, 2000 m/s
So one can see the boost is somewhat non-linear. I personally decided Mach 0.95 and 1100 m/s was good enough, hence CFM56, LEAP, big, quiet turbofans for my rocketplane.
YET
toying with my spreadsheets I ALSO realized that a delta-v gain of 500 m/s and 900 m/s was useful, too. So, another path of evolution for that rocketplane might be to swap the subsonic turbofans (stopping at mach 0.95) for high-speed engines. Thanks to RanulfC and a decade spent at Nasaspaceflight.com, three engines come to mind
- MIPCC
- J-58
- SERJ (Supercharged Ejector Ramjet)
The goal being to delay ignition of the rocket from Mach 0.95 to Mach 3 (MIPCC & J-58) or even Mach 4.5 (SERJ). And reap the benefits of airbreathing (to you, Skylon !) WITHOUT renouncing to suborbital refueling, of course.

Unfortunately going past Mach 2.5 opens the usual *hypersonic* can of worms -"kinetic heating needs something better than light alloys. Titanium, Carbon fiber, Rene 41 superalloy" - the usual enchillada known since 1955 at least.

Mach 2 is also an option and there there are plenty of excellent, powerful engines, all the way from Olympus 593 to F119 including NK25 and NK32 from the Tupolev bombers.

What matter is thrust, as in liftoff T/W ratio. Below 0.15 it becomes difficult to get a supersonic heavy aircraft off the ground.

Which bring us to another fascinating aspect of that rocketplane: the many ways of improving the system
- change the propellants to get a better specific impulse
OR
- add one or two rocketplanes into the FLOC
OR
- change the rocket ignition speed from Mach 0.95 to Mach 3 or even Mach 4.5 by swapping the engines
OR
- use an expendable upper stage OR KST Astroliner towing-by-a-747 OR Black Colt subsonic-refueling OR Andrew Space Gryphon air distillation plant into LOX

There are so many clever ideas that coalesce around that rocketplane, it is mind-boggling.

It is that flexibility and growth potential I like so much.
 
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steelpillow said:
RanulfC said:
Steelpillow's "wire analogy" isn't really brilliant as it begins with the assumption that the vehicles have to be physically interconnected as the basis for the analogy.
Click to expand...
I will just say that in the thought experiment, the wires are very obviously there to illustrate a point and not to be part of a practical design, instead to be taken as sufficiently thin to be of negligible weight and drag. Martinbayer had no trouble in appreciating this, so I do not see it as an obscure issue. That others need it stating astonishes me, I fear that constructive dialogue loses the common basis in language that makes it possible.
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Which is why I threw in the line about "wireless" AND the smiley face, I apologize about the confusion over the whole analogy because as I noted I'd missed the move to FLOC, (I literally read it flock for some reason) FLOC is a whole 'nother kettle of fish and I'd like to set it aside if we could. My confusion was trying to apply it to the original concept of two vehicle operations. I'd thought FLOC was "flock" of vehicle pairs or something. (Besides the "wireless" comment was just begging to be made) Again apologies.

So I regret that there is little point in responding to all the recent misunderstandings of Martinbayer's and my critiques, not to mention SABRE, per se.
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I thought that my responses were adequate to my understanding of your critiques, I thought I also explained why some of those decisions and considerations were chosen and the valid reasons to support them. If I am misunderstanding please help me understand what I am misunderstanding and understand it correctly, that's all I ask.

I would also remind folks that a mildly insulting remark accompanied by a smiley is still an insult, and in the wake of the recent administrative redactions and warnings, this is perhaps even less appropriate than usual.
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I try humor where I can and it doesn't always work. (Case in point)

On the other hand, I just read two posts by you and Martin where you claim no hidden bias’s and then go on to prove they exist along with certain assumptions on your part that while I admit are due to lack of comparative analysis of the design, also assume that answers if any from such an analysis will support your assumptions and bias'. Ok can I, personally get a list of what we want to compare, with what other system and what the basic assumptions for each concept are?

While I feel I may have a grasp on these questions the place where the current conversation is makes me think I do not.

ON assumptions and biases let me address this:
Archibald said:
ranulfc : I declare you my advocate and ambassador, altogether. If I were greta thunberg then you would be samantha smith. In a nutshell: as far as pasionaria and crusaders goes, you win persuasively, I lose in anger. ROTFL
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I... I... You... How... Ok, wait a second, deep breaths and let them out, confusion and anger pass with each breath, I am calm... OH HELL I'M NOT!

Seriously, I KNOW we've been no enough forums for you to have read my personal bias/assumption/truism that "Airplanes are not spacecraft and Spacecraft are not Airplanes and you're going to make me your "advocate and ambassador" for a concept that comes very close to overturning my truism? Having to sit on MY biases and assumptions is hard enough pal, you do NOT get to throw me to lions, (unless they prefer being designated Tigers or Bears, and lets stick with land based large predators because there at least I'm not terrain/environment disadvantaged like sharks or such) and once we get some questions and requests I can parse, (correctly) lets have you plug them in and see if we can get some answers ok? :)

I’m NOT mad I’m just having issues with suppressing (while allowing them to peek through to keep me honest) my own issues to rationally discuss something like this and I need all the help I can get. IF you feel angry or snippy take a break and send it to me in an IM and we’ll work on it but please don’t abandon me :)

And if anyone else doesn’t understand why this may be hard for me I spent several intense months making notes and defining concepts for various ways to get a “Blackhorse” vehicle into orbit from a more or less ‘standard’ runway “like” and airplane and then another few months trying to figure out why I wasn’t just calling it an “airplane” anyway

Randy
 
And speaking of MY biases and assumptions:
Archibald said:
The answer is in the question. SpaceX influenced me. Note that Starship needs 1100 mt of methalox to go anywhere beyond LEO. My little rocketplane "only" needs 100 mt of keroxide, 11 times less and it doesn't boil off. It is a mass small enough, manageable, a complete refueling is worth considering to go higher. Another motivation to do that is the GTO / GEO / TLI delta-v (2.5 km/s to 4 km/s) are really a joke or a walk in the park compared to ascent to orbit (9 km/s).
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There's the problem right there though, influance and insperation are good things but not to a point where it overrides logic and practicality. Never mind what Starship 'needs' it turns out it's not very efficent doing such flights. Your vehicle needs less 'propellant' but carries far less payload AND would carry even less in this case because it needs extended life support, conumables and extra systems like landing legs.

Seriously why is it everyone has this tendency to proclaim they want space travel to be like "whatever equivilant Terrestrial transport system" and then promplty toss aside how that actually works and why in favor of doing everything with one vehicle, "just because" they can?

Airplanes takeoff and land at airports
Busses arrive and leave bus depots, or designated stops
Trains load, unload and service at train stations and depots
Trucks go from warehouse to commercial or residential building where they load, unload and transfer
Ships go in and out of ports where they load, unload, transfer and resupply.

Spaceships take off from the surface of the Earth, go into LEO where they get refueled, and then they go to the surface of another world, refuel, takeoff and fly back to Earth where they land, so the 'same' right? Wrong.

The above terrestrial transporation systems have had centurires for the most part to oprimized and perfect the transporation of goods and people around the world and while new technologies and systems have come along to supplement them in some roles and surplant them in others the very core elements remain and one very important economic and operational point is that NO ONE SYSTEM does it all. And there's a damn good reason for this.

Transport systems are optimized for economics and payload if you will and they make money by moving stuff from one place to another. An often overlooked part of this is they do NOT make money if they are sitting still or in transit. Ship, aircraft, tractor-trailer rig, or spacecraft doesn't matter if you're parked you are loosing money. Now you can't be in motion all the time, (though there have been numerous concpets for every transporation system including spacecraft to try and keep you in motion constantly lets not go there just yet) but this is 'planned' in as planned servicing and support periods. So at an airport you have planes landing and taking off in very short increments, (which is why spacecraft won't be allowed because they distrupt this flow) and even when loading and unloading there are time limits and schedules to keep so a plane has to be unloaded in a certain timeframe, serviced, reloaded and ready for pushback in a very short time. While the timeframes are a bit different for each form of transporation the overall and operational effect is the same.

Starship and this concept take a perfectly viable "tranport" and tie it up for long periods of time doing jobs that would be vastly better suited for vehicle built to do those jobs. There's some justification for doing it all with one ship early on but this rapidly becomes less economic.
The sequence shouldn't be: fly into orbit with payload/passengers and then wait while propellant is brought up to you, fly to the destination and then set down, unload passengers and carg and then wait while propellant is again provided for you so you can fly back to Earth, reenter and then land at which point you THEN go into maintenance and servicing for your next flight.

It SHOULD be that your surface to LEO transport, (my preference is Ground-To-Orbit because who doesn't like a GTO refrence) carries its payload into LEO where it rendzvous with a space station or Transfer Vehcle and hands over the payload. It then loads any down-bound payload and departs back to Earth. (Where it will be ready to fly again very soon) The Transfer Vehicle is already full of propellant from an orbital depot, (every other flight for the GTO vehicle is likely delivering propellant to this depot) and only awaiting payload and/or passengers before it departs. Once loaded it boosts out of orbit and on towards its destination. For the Moon its a couple of days in transist for Mars up to 6 or more months. Arriving it unloads payload/passengers at a Gateway where it takes on return-bound payload/passengers and propellant and once loaded it departs. From the Gateway landers depart with payload and passengers to one or more surface stations and then come back bearing propellant and payload for the next Transfer Vehicle.

Would you need a 'specalized' vehicle for each leg? Probably not since you could use varients of the same airframe mold line to accomplish each step. They key and heart is you ALWAYS have payload in motion and no vehicle rides 'dead-head' at any destination or depot. By adding transfer vehicle varients that are automated and take 'longer' but less propellant intensive trajectories you can probably delivery Martian propellant to Cis-Lunar space for a price that may be cheaper than delivered from Earth.

So no, the 'answer' isn't a valid one. Just because you CAN do something never forget to ask IF you should, WHY you should, and if it adds any real value to the system as a whole :)

Randy
 
The main issue with looking at the NASA studies, (other than your usual NTRS issues that is :) ) is they are spread out and not usually very well keyworded to things like "Aerial" or "sub-orbital" propellant transfer as a seperate concept. I first heard about NASA looking at the idea from several sources, (these forums IIRC being one) as an alternative or add-on to the LARC "Spacejet" studies. Both the military and NASA agreed that the general idea of Blackhorse was sound and workable so they must have based that on something. Zubrin and Clapp made note that doing so suborbitally was easier and less stressful and they agreed as well.
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Well said. I can tell you I spent a helluva amount of time on Google books (yes, Google books) whacking my brain around the many ways of saying "ravitaillement en vol" in English language - and combining that with the words"rocket" "suborbital" and the like.

I finally dug some interesting bits here and there, but the overall story is extremely fractioned and scattered.

There was more or less four phases
- Phase 1: Aerospaceplane, HIRES, and that X-15 thing. Involving General Dynamics and one of their engineers, Richard A. Nau.
- Phase 2: Richard A. Nau, of GD Triamese fame, got a couple of papers (in 1967 and 1976) over his Aerospaceplane experience... including HIRES.
- Phase 3 "Mister Tripropellant" Robert Salkeld made a brief foray into aerial refueling circa 1973. This led to NASA Langley Spacejet, and USAF / Boeing RASV. The later two dragged on from 1976 to 1991.
- Phase 4: Mitchell Burnside Clapp, 1993.

That's all I could find, plus a "shazam" nugget thanks to this forum: Atmospheric Rendezvous Study, 1971-72.

Basically a Langley veteran and colleague of John "LOR" Houbolt, John Dexter Bird, got the idea of launching the Shuttle Flyback Booster, alone, to meet and catch a descending Shuttle orbiter at 1.5 km/s (no kidding !).
The reasoning being: no 747 SCA needed, baby !
The flyback booster would catch the orbiter midair, dock it on its back, and fly it back to the launch site. Crucially, John Bird deemed the catching manoeuver as achievable. Note that the ascending booster and the descending orbiter are not only different vehicles BUT they come from OPPOSITE directions. In the case of my rocketplane the vehicles and trajectories are identical and paralel.
 

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Your vehicle needs less 'propellant' but carries far less payload AND would carry even less in this case because it needs extended life support, conumables and extra systems like landing legs.
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Sure. Ascending to orbit takes merely 10 minutes, Soyuz / Progress speed to ISS in 3 to 6 hours, but going to the Moon takes 3 days and Apolloactually spent 11 days.
So you have a point there.
Now let me explain some details.
First, the crew is two guys in an austere U-2 like cockpit. Okay, but 11 days in that ? no way. Well, in this case, let's put a spacehab in the payload: a camper module for the two guys. It will eat into the payload, however. Fair enough.
What payload, by the way ?
If my rocketplane goes into a TLI, then it act as a kind of "downrated S-IVB" booster stage, with two huge caveats a) no LH2 and b) all the dead weight of the rocketplane around the rocket stage.
I readily accept this.
I just note, however, that (as I said earlier) a 3 km/s TLI is a walk in the park compared to ascent to orbit so the payload, even with all the flaws above, is surprisingly huge.
Briefly, that keroxide Mk.1 rocketplane: it painstakingly haul a miserable 12 000 pounds to 9 km/s with the assistance of a "tanker twin".
Yet, if refueled to the brim in LEO via a propellant depot, then it recovers its entire 6 km/s max delta-v. On a 3 km/s TLI, the result is a HUGE payload to cislunar, 70 000 pounds or even more.

Of course an entirely different matter is to get that 70 000 pound payload into LEO first !!!! But once there, nudging it into a TLI is like a walk in the park.

The deal is to use that rocketplane as a "poor's man S-IVB" - admittedly, it is completely suboptimal in that role YET even "suboptimal" means 1/3 of the S-IVB payload to cislunar. Now had the S-IVB orbited alone, without any payload, by a Saturn V, it would weight 120 mt in LEO. The basic rule of thumb with LH2 TLI stages is that "they can push their own mass through TLI"
Hence a 120 mt S-IVB could have pushed a 120 mt payload to TLI.
Now my rocketplane even if it is a *very shitty TLI stage* (no question about that) still can boost 1/4th of the S-IVB payload - 120 / 4 = 30 mt.

I'm not kidding you: I did the maths.

the basic rocketplane delta-v equation is 981*327*ln(120/18) = 6100 m/s.
Now "burden" the rocketplane with 30 mt of payload...
981*327*ln(150/48) = 3655 m/s
Not enough to enter lunar orbit (4100 m/s) but more than TLI (3115 m/s) and enough to reach EML-1 or EML-2. Returning via aerobraking or propulsive braking.
 
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RanulfC said:
I thought that my responses were adequate to my understanding of your critiques, I thought I also explained why some of those decisions and considerations were chosen and the valid reasons to support them. If I am misunderstanding please help me understand what I am misunderstanding and understand it correctly, that's all I ask.
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OK, but please take them one at a time and not all in one message.

Also I am not immune to misunderstandings. I had gained the impression that FLOC was one particular proposal for a flock system, am I wrong?
 
steelpillow said:
RanulfC said:
I thought that my responses were adequate to my understanding of your critiques, I thought I also explained why some of those decisions and considerations were chosen and the valid reasons to support them. If I am misunderstanding please help me understand what I am misunderstanding and understand it correctly, that's all I ask.
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OK, but please take them one at a time and not all in one message.
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But, but my relationship with verbosity, what will it think of me if I don't use it every chance I get, will it still respect me in the morning?
Seriously I'll try and it may help that I may be getting some "blog" relief since I've been invited to do collaborative postings.
(If/When I suppose we'll see)

Also I am not immune to misunderstandings. I had gained the impression that FLOC was one particular proposal for a flock system, am I wrong?
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No, not for the FLOC proposal itself, ("Fleet Launched Orbital Craft" here https://selenianboondocks.com/2008/01/an-insane-but-interesting-idea-fleet-launched-orbital-craft/) which had dozens of vehicles acting like self propelled "drop tanks" and was a bit of a mess both organizationallly and operationally in addition to having issues with most of the rendezvous NOT being exo-atmospheric due to the nature of the system. I mean you COULD and both the original paper and the one I linked point that out but it's limited returns over time and the "time" and losses it incures makes it pretty clear why no one takes it too seriously. It IS a crazy workable idea but it's not really a valid one for the usage. But FLOC isn't what we're discussing per-se.

Two (2) vehicles launch one with payload and one with propellant and fly to a sub-orbital, exo-atmospheric rendzvous, where they transfer propellant and one flies home while the other goes to orbit with the payload. If I'm reading Archibald right what he's suggesting beyond that is you could do the same thing but the 'payload' on the next orbiter is propellant to refuel the on-orbit vehicle so it can go further. Lets leave that one aside for the moment :)

Randy
 
RanulfC said:
martinbayer said:
I completely concur with steelpillow - I'd just like to add that the tradeoff of airbreathing runway takeoff vs. rocket powered vertical liftoff from dedicated infrastructure likely has no definite answer (yet?), but will probably depend on variables like vehicle and fleet size, mission frequency, etc. Personally, I'd like to keep the flying vehicle as simple as possible, meaning for example a minimum of on board propulsion elements, especially if one of them is only good for a small part of the velocity spectrum, and rather put a little more complexity into the ground infrastructure, where it is not mass critical and at all times readily accessible for maintenance, checkouts, etc. As steelpillow has shown with his brilliant wire analogy, you really don't have a fundamental performance difference between classical staging and refueling schemes. Ultimately, I'd rather put a little more mass in stage connectors, if that allows me to eliminate at least one potential in flight risk event in the form of suborbital mating. I realize the military has different perceptions of acceptable risk, but I'd rather try to emulate the paradigm of commercial aviation.
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Actually the idea IS to emulate the paradigm of commercial aviation as much as possible, hence the use of 'standard' airbreathing engines and avoiding the use of highly specialized and specific launch infrastructure, (and frankly landing as well since a 'glider' doesn't inteact well with standard air traffic) by using the deeper, and broader air traffic system infrastructure. The airbreathing populsion system is used to move the vehicle from the "airport" to a place where it can light off it's rocket engine freely. At any point it can also be used to 'abort' to an alternative airport or emergency airstrip. Similarly when the vehicle is back from orbit and moving back towards a landing it has an airbreathing engine so that it does not interfere with the standard air traffic flow and take a place in the que for landing and servicing.

I'm going to point out that Steelpillow's "wire analogy" isn't really brilliant as it begins with the assumption that the vehicles have to be physically interconnected as the basis for the analogy. It's the 21st Century my dear sir have you never heard of 'wireless' operations? :) (Must have missed where FLOC came in, sigh, going back to read after this post)

Because that is what it would be. You specifically do NOT have a physical connection between the vehicle because doing so reduces their efficency and adds mass to the system. They ARE 'wirelessly' connected of course and are aware and constantly updated on each others position and because you don't have those 'physical' connections you also don't deal with the stress and aerodynamics that come along with them. They ONLY come together in order to transfer propellant beyond that they are seperate vehicles for the whole flight.

Yes there's some serious questions over SSTO capability and operational advantages, lord knows I'm one of the ones who doubts the rosy picture the advocates paint :) But as I noted before they DO have some points and they can be applied to near-SSTO vehicles as well. It is a unitary airframe that does not have to be 'integrated' with another airframe for launch and only 'interacts' above the nominal atmosphere in a free-fall arc. TPS, structure and other systems are lighter and easier to maintain this way. As a space station delivery vehicle the airbreathing engines give it unlimted range and endurance compared to a pure rocket powered vehicle, (and that's before we look into such engines as the turb-ram-rocket or Supercharged Ejector Ramjet for two examples) so chasing and matching a particular stations ground-track is vastly easier. Unitary means no ground mateing/demateing and associated support systems, while it may be more complex it will likely be smaller (which will cost less) and easier to work on. (Ya, tell that to the tech who has to be shoved into panel D-1A to rewire cannon plug CR-21 on his back with all the tools and wire sitting on his chest and only about 3 inches to work with... No, what makes you think I've had to do something like that? :) ) As a near-SSTO it doesn't have to be as optimized and light weight as an SSTO does and bonus it likely carries more playload as well. Probably not as much as an optimized TSTO vehicle but then again, (and this may be just me) but I'm pretty sure that taking 10,000lbs into space once a week or more can have more effect on some costs than going once a month with 100,000lbs specifically for things like space station support supplies. Twice a week is better an four times a week even more so of course.

Blackhorse in its original incarnation wasn't really even a 'near-SSTO but had some similar advantages, funny thing was both Zubrin and Clapp actually missed some opportunites and concepts because they stuck so close to the initial concept. The basic idea of the sub-orbital refueling concept accepted that both Blackhorse vehicles would remian the same but really the fact that they added airbreathing engines in and of itself had a more far reaching effect than they assumed.

Randy
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Frankly, with a launch vehicle I would absolutely *NOT* want to be married/tied down to the current ATC/ATM system - as an aside, I honestly think it is near a breaking point. I can easily envision an alternative future system where in order to be certified any aerospacecraft needs to have some kind of AI onboard that continuously coordinates with all other aircraft in a local area to avoid collisions. Heck, if small feathered animals that quite literally only have bird brains consistently manage to avoid bumping into one another while zigzagging in three dimensions in tight swarm formations, don't try to tell me that technology can't hack that soon, espicially looking at the synchronized massive swarm flights of current UAVs. I dream of a world where the job of an air traffic controller has about the same professional prospects as a buggy whip manufacturer (well, not quite, since from NYC Central Park to Amish country there actually still are buggies around, but you get the point).

Looking at the track record of the Space Shuttle, I am perfectly comfortable with a gliding return from space. I also continue to believe that trying to make a launcher look like an aircraft just to use existing infrastructure is not the best overall compromise, and I really don't see a need to go to orbit from say an airstrip at Winslow-Lindbergh Regional Airport near Winslow, AZ (I've been there years ago for a brief flight test campaign of a small black helicopter [fun!], since it has an average of only about four aircraft arriving or departing on any given day).

As far as I understand it, steelpillow's whole point of the wire thought experiment was to show that it really *doesn't* notably encumber any two or more vehicle concept - at least that was my takeaway. YMMV, of course. Personally, I vastly prefer some small mass "inefficiency" of a staged system over adding a significant risk event like free fall rendezvous, docking, and propellant transfer. Once again, I take it you hold a different view, but I don't see any advantage in "only" coming together for that, since it means now you have to ensure the temporary connection is established safe and secure during a very limited period of time in flight instead of being able to check it out without time pressure and under easy accessibility on the ground. To tie in with your military background, how difficult, complicated and time consuming is it these days to strap a missile to a fighter (two separate air vehicles mated on the ground with in flight separation) while both are safely on the ground? I hazard to guess we really do have two *very* different visions of aerospace transportation.

I also think your remark above about airbreathing engines giving a launch vehicle "unlimited (*really*???) range and endurance" is based on a fundamental misconception - the job of a reusable launch vehicle is to get to orbit (and back) as quickly and efficiently as possible, not to dawdle in the atmosphere. Once you are in orbit, you can have *all* the range and endurance you want, as the X-37B continues to demonstrate. And like any other vehicle in history (cars/trucks, boats/ships, airplanes... the list goes on), any RLV, including any TSTO (or SSTO, if you can get one working) can be scaled to nearly *any* payload, be it 10 klbs, 100 klbs, or (at least in case of vertical take off launch vehicles, hehe :D) 1000 klbs, so I guess maybe you emphasize smaller payloads because HTHL vehicles have some inherent growth limitations there and try to turn lemons into lemonade.

Martin
 
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