A guess? The extra capacity could be used for boost-back. A Mach-10 staging is more suited to Global Strike than space launch, but if you stage the space launch at Mach-6 the extra propellant and capability can be used for RTLS purposes.sferrin said:
Randy
DSE said:
Actually a lot of the RBCC systems (such as SERJ) tend to have comparable if not better T/W than either standard rockets or air-breathing engine. But you have to "want" those factors associated with an "Air-Augmented-Rocket" or they get lumped in with other "AB" systems and dumped.
It seems we keep getting pulled off-track trying to overuse the Air-Breathing systems (NASP) or trying to reach to far for technologies that are not ready for "prime-time" play as though they were. (SCramjet) Tack on the various "optimization" efforts that loaded on systems like LACE and SCram-LACE (Seriously, you're going to LIQUIFY incoming HYPESONIC air? Why? Just because it makes the "numbers" look so good? And yes that was the "sad" part that WAS pretty much the only reason...) choosing the wrong engine design, the wrong fuel, decide that computers are so good you don't NEED a flying hypesonic lab because you can design and build it in the computer and then build only one or two "proof-of-principle" sub-scale models and flight test them. After all what could possibly go wrong?sferrin said:
It's really no wonder we've had the issue we have had. Build-it, fly-it, break-it, figure out what went wrong, then build it again, etc repeat as needed MAY be more expensive than what we're doing now but the real world record shows as a method it has a much higher success and completion record. That should be saying a lot if anyone is actually paying attention.
Randy
RanulfC said:
Not any one I've seen detailed flight hardware designed under honest terms past a conceptual design. The Aerojet Strutjet was the basis for the ISTAR engine given the three oem designs brought to the program. However, when the RC3 team worked it's detail design in earnest its weight ballooned horribly.
RanulfC said:
SERJ is a paper engine and in this case, at least to me, the reference to it appears to be a case of the kettle calling the pot black.
RanulfC said:
No argument here! In fact just this week I pointed out to management the fact of how limited design cycle experience is killing off the ability to actually learn and progress in these areas. I began working this field in the pre-teaming days of NASP. Coming from a completely different field I took seriously to learning the lessons of the past and continue in this adventure today. However, unfortunately, I can't say this for many of the people who have entered into this area in the past 10-15 years. Similarly, I find people have become way too specialized to a fault without having even the a basic grasp of the overall problem and even worse, no desire to learn. If they can't google it, it doesn't exist.
See Below, but frankly strutjet never made all that much sense to me.DSE said:
Mardquart built several variations of the SERJ engine including a small scale "flight-weight" H2O2/Kerosene test engine and an LH2/LOx powered one as well as dozens of lab engines using various fuels. They were petty eager to move to a flight test program but NASA was more interested in the DuPont engine and the military lost interest in high speed interceptors.
And if you don't know or aren't "sure" what you're looking for there is little chance you'd find anything anyway. Worse from what I've been seeing even if someone stumbles across information or data about a system they thought was "new" as soon as they find out it is from more than 20 years ago the trend is to dismiss it because "if it worked they would have used it then" so something must be wrong, why bother?
Randy
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True, and, not to sound argumentative, but twin-stage long-range rockets are always more efficient than single staged ones as well, however in many cases we just build single staged one (AIM-54, AIM-120).Orionblamblam said:
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Though in the first test flight of the new version of the Falcon 9, the F9 v1.1, they did not stably "land" the first stage, SpaceX is optimistic they can solve the problem to get a reusable first stage:
SpaceX Hit Huge Reusable Rocket Milestone with Falcon 9 Test Flight (Video)
By Mike Wall, Senior Writer | October 17, 2013 02:01pm ET
http://www.space.com/23230-spacex-falcon9-reusable-rocket-milestone.html
SpaceX also plans to transition the half-scale Grasshopper VTVL test vehicle to a full scale Falcon 9 first stage:
Final flight of Grasshopper v1.0 sets new record.
By Brian Dodson
October 14, 2013
http://www.gizmag.com/grasshopper-retires-altitude-record/29384/
This article says this "Grasshopper 2", as it were, would have all 9 engines of the regular F9 first stage. However, discussions on other forums have said it would only have 3 engines. That would make sense since on stage return, you are using at most 3 engines, and moreover this way, you would not be risking an expensive 9 copies of the Merlins during these Grasshopper test flights.
Still, in point of fact there would be an advantage of using all 9 engines on this first stage Grasshopper, and with a full propellant load. In November, 2012 Elon Musk gave a lecture in London at the Royal Aeronautical Society.
http://www.youtube.com/watch?v=wB3R5Xk2gTY
About 30 minutes in, he gave the propellant fraction of the new Falcon 9 v1.1 as around 96%, or perhaps 95.5%. The 96% propellant fraction number gives a 25 to 1 mass ratio. But at an Isp of 311 s for the Merlin 1D, the rocket equation gives a delta-v of 311*9.81ln(25) = 9,800 m/s. Since the delta-v to orbit is only about 9,100 m/s, this would allow a significant amount of payload.
Then using the 9 engines and the full propellant load on the F9 first stage would allow in fact not just a VTVL test vehicle, but in fact a fully reusable and fully orbital vehicle.
Amusingly, about 36 minutes into Elon's lecture someone asks a question about what he sees as the next big breakthrough in rockets after full reusability. Elon thinks for awhile and can't come up with an answer. He finally jokes maybe warp drive. Ironically, he already has the next big advance: a reusable SSTO.
Bob Clark
SpaceX Hit Huge Reusable Rocket Milestone with Falcon 9 Test Flight (Video)
By Mike Wall, Senior Writer | October 17, 2013 02:01pm ET
http://www.space.com/23230-spacex-falcon9-reusable-rocket-milestone.html
SpaceX also plans to transition the half-scale Grasshopper VTVL test vehicle to a full scale Falcon 9 first stage:
Final flight of Grasshopper v1.0 sets new record.
By Brian Dodson
October 14, 2013
http://www.gizmag.com/grasshopper-retires-altitude-record/29384/
This article says this "Grasshopper 2", as it were, would have all 9 engines of the regular F9 first stage. However, discussions on other forums have said it would only have 3 engines. That would make sense since on stage return, you are using at most 3 engines, and moreover this way, you would not be risking an expensive 9 copies of the Merlins during these Grasshopper test flights.
Still, in point of fact there would be an advantage of using all 9 engines on this first stage Grasshopper, and with a full propellant load. In November, 2012 Elon Musk gave a lecture in London at the Royal Aeronautical Society.
http://www.youtube.com/watch?v=wB3R5Xk2gTY
About 30 minutes in, he gave the propellant fraction of the new Falcon 9 v1.1 as around 96%, or perhaps 95.5%. The 96% propellant fraction number gives a 25 to 1 mass ratio. But at an Isp of 311 s for the Merlin 1D, the rocket equation gives a delta-v of 311*9.81ln(25) = 9,800 m/s. Since the delta-v to orbit is only about 9,100 m/s, this would allow a significant amount of payload.
Then using the 9 engines and the full propellant load on the F9 first stage would allow in fact not just a VTVL test vehicle, but in fact a fully reusable and fully orbital vehicle.
Amusingly, about 36 minutes into Elon's lecture someone asks a question about what he sees as the next big breakthrough in rockets after full reusability. Elon thinks for awhile and can't come up with an answer. He finally jokes maybe warp drive. Ironically, he already has the next big advance: a reusable SSTO.
Bob Clark
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RGClark said:
What makes you say that?
As has already repeatedly been pointed out to you, for any foreseeable technology level and combination, a fully reusable TSTO designed for the same mission in terms of orbit and payload as a fully reusable SSTO will be notably smaller and cheaper, so what would be the "big advance" beyond full reusability?
Martin
RGClark said:
Wrong. There are no facts in this post. the SSTO as a viable payload delivery vehicle is a fallacy.
the nonsense of a reusable orbital SSTO claimed by the poster is a a pipe dream since it doesn't include the mass for landing legs, deorbit propellant or TPS for reentry.
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This is incorrect. Falcon 9 first stage cannot survive re-entry from orbit.RGClark said:
AFAIK, the big penalty of reusing the first stage was not the extra fuel need for landing, but the non-optimal staging. The first stage would need to separate earlier to survive the subsequent aerodynamic braking.
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martinbayer said:
A three stage system would also carry more payload than a two stage. Despite that, nobody says a two stage system has no value. By the same token a single stage can have value in lower cost and simplicity for smaller payloads and in regards to reusability.
Note that you don't just all of sudden create an entire new multi-stage system to handle smaller payloads. SpaceX could get a smaller 5,000 kg payload capacity launcher by restarting the Falcon 5, but they are unlikely to do so. If the SSTO version does indeed have a 5,000 kg payload then SpaceX would already have a cheaper launcher than the full Falcon 9 to handle smaller payloads. Sure, the full F9 could carry more payload, but as far as the small satellite owner is concerned that's just wasted capacity that he doesn't need.
Another consideration is the rather large loss of payload quoted by Elon Musk for a reusable two stage system. He stated it would be about 40%. Quite key is that a large component of this significant loss in payload is due to the need to get the first stage back to the launch pad, not even the stage that gets to orbit. With the single stage launcher you don't have that problem.
Elon Musk on SpaceX’s Reusable Rocket Plans.
By Rand Simberg
February 7, 2012 6:00 PM
http://www.popularmechanics.com/science/space/rockets/elon-musk-on-spacexs-reusable-rocket-plans-6653023
Bob Clark
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AdamF said:
The break up of the previous Falcon 9 first stages on reentry was due to the fact that they were tumbling. Note that the recent launch of the F9 v1.1 followed the usual trajectory because it was only going to "land" on the water. And the first stage did at least survive the reentry.
It turns out the greatest aerodynamic stress occurs lower down in the atmosphere not high up when the vehicle is moving at near orbital speed. This is because of the exponential drop off in air density with altitude.
Also, the change in the staging point for the reusable two stage system is not coming from the need to reduce aerodynamic stress, but from the need to get the first stage back to the launch site. This is because the usual Mach 10 staging would take it too far down range. This is proven by the fact the recent flight of the F9 v1.1 did fly the usual trajectory, as it did not have to return to the launch site.
Bob Clark
RGClark said:
Wrong again and also the recent flight was not proof since it was not a normal payload and had excess performance. Internet searching is not a substitute for an education or knowledge in rocket science.
martinbayer
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RGClark said:
While three stage RLVs have been looked at, see for example here http://www.rocketpunk-manifesto.com/2009/09/three-stages-to-orbit.html, in reality there are engineering approaches and approximations to determine the optimum number of stages from a mass point of view, such as discussed at some length at www.aai.ee/~vladislav/Astronautics_Lecture8.pps. - feel free to do your own math. In addition to these considerations for constant stage structural ratios, additional smaller (upper) stages typically tend however to be specifically heavier due to scaling effects and therefore offer even more progressively diminishing returns in terms of performance. Translating the basic mass properties into cost characteristics certainly adds complexity to the assessment, but well designed TSTOs can leverage commonalities and design repeats with respect to propulsion and structures, all the way up to potential bimese (or, like the BAC MUSTARD, even trimese) designs, and result in lower costs than SSTOs. Return to launch site (which by the way is not really a firm requirement, since the booster could also land downrange and be ferried back to the launch site by various means - this is where the "full *and fast* reusability" in Musk's quote comes in) would certainly impact the design, but due to their staging TSTOs are inherently more resilient in their performance with respect to suboptimal design parameters. Turning the extremely limited payload capability of an SSTO (if existent at all) from a vice into a virtue by declaring it a system well suited for small payloads, because the postulated (and hence as yet completely undemonstrated) performance in relation to its size is underwhelming, is however a rather strange logic indeed. But even if it were feasible to adapt an existing system like the Falcon 9, the fact that Elon Musk, who, judging by his career to date, seems to be somewhat familiar with what makes sense in a business context and certainly has proven that he is no stranger to how to succeed in rocket science as well, apparently does not really consider turning the Falcon 9 into any sort of an SSTO, but instead seems to be thinking of a TSTO, should less bewilder you than give you reason to pause and question your own assumptions. Note that in the quote you refer to Musk states at the end that "Even taking into account the payload reduction for reusability (of a Falcon derived TSTO), the improvement is therefore theoretically over a hundred times." Unless you have a source to prove that the quoted 40% payload reduction is indeed specifically due in large part to the booster stage RTLS maneuver rather than the added masses for structural strengthening and recovery systems (which would impact an SSTO to a dramatically higher extent than a TSTO), I remain highly skeptical of that assertion.
Martin
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martinbayer said:
The quote from Popular Mechanics strongly implies a large portion of the loss in payload is coming from the need to return to launch site, due to the large reserve of propellant needed. There is no need to retain as much propellant if you just allow it to continue on its trajectory and only allow enough thrust to cancel its vertical speed.
Moreover, as suggested in the animations released by SpaceX of a reusable full Falcon 9, the first stage would not need TPS, which is also supported by the reduced speed for the first stage for the reusable TSTO version. It would need landing legs. However as you know every kilo of dry mass added to a first stage only subtracts a fraction of a kilo from the payload capability. This is variously estimated as 1/5th to 1/10th that of the added mass. So the landing legs being a fraction of the first stage dry mass, would result in an even smaller amount of the payload capability being lost.
In regards to the question of the economic feasibility of the SSTO, in that video at the Royal Aeronautical Society I cited, Elon mentions the propellant fraction might be 95.5% instead of 96%. In that case the payload capability would be reduced. Using some estimates for the propellant and dry masses of the F9 first stage, that small difference in propellant fraction could reduce the payload of the expendable SSTO version to 3,000 kg. And it would be even less with a reusable version. It may be a reusable version, which Elon wants to focus on, would not be economical. However, considering the rather low Isp of the Merlin 1D, and that much higher Isp engines (Russian) exist, this raises the possibility we could have a reusable SSTO if we did use such more efficient engines.
Just doing a test flight of the expendable F9 SSTO, even if the payload was only 3,000 kg would be worthwhile to just remove the mindset that a SSTO of any type, reusable or not, could not carry significant payload.
Bob Clark
RGClark said:
No, they won't waste the time or effort since it is not viable, the payload would not be within a magnitude of 3000kg. You are forgetting fairing, avionics, payload adapter. But then again, it might be a good idea since it would disprove the nonsense that you have been spamming the internet with.
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RGClark said:
Taking your assertion of SSTO feasibility for the moment at face value, you are apparently falling prey to the fallacy that if an SSTO were feasible, it would automatically be superior to a TSTO built with the same technologies for the same mission requirements (as opposed to the one off 'demonstrator' you postulate for a payload niche). If you actually impartially do the math, you will quickly discover that this is NOT the case. What you propose is at best a stunt that, as you concede, is more aimed at psychological impact than actually producing an optimized system with a sustainable business case. As an analogy, consider that it is conceivable that it might be possible to build supersonic airships with today's technologies. While indubitably this might be considered 'cool' in some circles, it would however by no means automatically imply that the resulting system would be economically or operationally superior to existing supersonic heavier than air planes. Just because something *can* be done doesn't automatically mean it makes sense to do it.
Martin
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Byeman said:
www.youtube.com/watch?v=sSF81yjVbJE
Bob Clark
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Byeman said:
To do an experiment is always a good idea regardless of the motivation!
Bob Clark
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martinbayer said:
The estimates for the payload of the Falcon 9 v1.1 first stage as SSTO I'm getting from Dr. John Schilling's Launch Vehicle Performance Calculator:
http://www.silverbirdastronautics.com/LVperform.html
SpaceX, irritatingly, has not released the propellant loads and dry masses for the individual stages of either version of the F9, just the total gross masses. This is in contrast to the other launch providers at least among the Western ones. Perhaps these numbers will be released when SpaceX is launching commercial payloads on a regular basis.
The propellant mass for the F9 v.1.1 has been estimated in the range of 400 metric tons (mT). If the 96% propellant fraction is right that would put the dry mass at 16.6 mT. If the 95.5% value is right, the dry mass would be 18.8 mT.
Enter the selected numbers for the propellant load and dry mass into the Calculator. For the thrust and Isp values, Schilling says use the vacuum values as the Calculator takes into account the reduction at sea level. The SpaceX page on the F9 v1.1 gives the total vacuum thrust of the first stage as 6,672 kN. The vacuum Isp for the Merlin 1D has been reported as 311 s.
Among the options, select "No" for the "Restartable Upper Stage" option, otherwise the payload will be reduced. Use the default altitude of 185 km. And select Cape Canaveral as the launch site, at a 28.5 degree orbital inclination to match the site latitude. Then I got in the range of 5,000 kg for the 96% propellant fraction case, and in the range of 3,000 kg for the 95.5% case.
But for an economical SSTO, you really should use altitude compensation. This will greatly increase the payload for the SSTO, but its usefulness goes beyond that. Even for a two stage vehicle using altitude compensation on the first stage can increase the payload. The increase will not be as pronounced as for the SSTO case but it will be significant.
Try using the Schilling Calculator where you use the Merlin Vacuum's Isp of 340 s. I think you'll be surprised by the answer.
Bob Clark
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quellish said:
There have been cited two different numbers on the net for the number of engines for the next version of the Grasshopper, either three or nine. As I said I find three to be more likely. But it may very well be at later tests they would use the full 9 engines. Since propellant cost is a minor component of the cost of a launch they could also use a full propellant test of such a full-up Grasshopper.
Bob Clark
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RGClark said:The estimates for the payload of the Falcon 9 v1.1 first stage as SSTO I'm getting from Dr. John Schilling's Launch Vehicle Performance Calculator:
http://www.silverbirdastronautics.com/LVperform.html
SpaceX, irritatingly, has not released the propellant loads and dry masses for the individual stages of either version of the F9, just the total gross masses. This is in contrast to the other launch providers at least among the Western ones. Perhaps these numbers will be released when SpaceX is launching commercial payloads on a regular basis.
The propellant mass for the F9 v.1.1 has been estimated in the range of 400 metric tons (mT). If the 96% propellant fraction is right that would put the dry mass at 16.6 mT. If the 95.5% value is right, the dry mass would be 18.8 mT.
Enter the selected numbers for the propellant load and dry mass into the Calculator. For the thrust and Isp values, Schilling says use the vacuum values as the Calculator takes into account the reduction at sea level. The SpaceX page on the F9 v1.1 gives the total vacuum thrust of the first stage as 6,672 kN. The vacuum Isp for the Merlin 1D has been reported as 311 s.
Among the options, select "No" for the "Restartable Upper Stage" option, otherwise the payload will be reduced. Use the default altitude of 185 km. And select Cape Canaveral as the launch site, at a 28.5 degree orbital inclination to match the site latitude. Then I got in the range of 5,000 kg for the 96% propellant fraction case, and in the range of 3,000 kg for the 95.5% case.
But for an economical SSTO, you really should use altitude compensation. This will greatly increase the payload for the SSTO, but its usefulness goes beyond that. Even for a two stage vehicle using altitude compensation on the first stage can increase the payload. The increase will not be as pronounced as for the SSTO case but it will be significant.
Try using the Schilling Calculator where you use the Merlin Vacuum's Isp of 340 s. I think you'll be surprised by the answer.
Bob Clark
I don't see any accounting for masses that would be required to turn a first stage into even an expendable SSTO (e.g. avionics and payload adapter and fairing) and would reduce the actual payload in your considerations. But you also still have conveniently neglected to outline what the dramatic advantage of an SSTO over a TSTO is supposed to be. Once again, just because it might be doable doesn't mean it would be automatically superior.
Martin
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martinbayer said:
You'll have to plug in the the 340s Isp of a Merlin with altitude compensation to see the benefits of a reusable SSTO. Hint: a rule of thumb among propulsion engineers is that an increase of 10% in Isp corresponds to an approx. 100% increase in payload.
Then because of the large 40% loss in payload for a reusable TSTO because of the need to return the first stage to the launch site, the reusable SSTO could wind up carrying more payload than the reusable TSTO because of the much smaller loss of payload due to reusability.
Bob Clark
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RGClark said:
Once again, you have to compare both an SSTO and a TSTO on an equal basis and objectively calculate the metrics, i.e. a TSTO will also benefit from altitude compensation. One hint: in order to do a true apples to apples comparison, it is *NOT* sufficient to simply take snippets from web sites and throw them into the discussion - you actually have to *do the math* in equal depth for both cases and not simply rely on internet 'rules of thumb' (I think at one point you claimed that you were teaching math at an east coast US university, so that really shouldn't be asking for too much). As I said before, those 40% you quote are in all likelihood only in small part attributable to the RTLS maneuver of a TSTO booster, so your postulation above is most probably invalid (and no, I *don't* consider a quote from Popular Mechanics that in your interpretation "strongly implies" something as anything near to a reliable, let alone authoritative statement). But even if it were true, as I already stated previously, RTLS is not really a hard requirement, and even if THAT were the case, that number *still* would only characterize the difference of a reusable TSTO to an expendable one, but says *NOTHING* about how either reusable or expendable SSTOs would compare to corresponding TSTOs. I generally don't concur with too much that Orionblamblam puts forth, but much earlier in this thread he states in a response to you that "Any technology that would make SSTO practical would make a fully reusable TSTO substantially cheaper than the SSTO", and I couldn't agree more. I'm confident that once you work your way competently and 'sine irae et studio' through the associated calculations you will see the light, too. If not, I would be eminently curious to review your associated work and more than happy to point out the flaws and errors in your logic and calculations.
Martin
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martinbayer said:
That is the entire point of doing the calculation on the launch calculator. You won't see how advantageous a SSTO can be until you see for yourself how large the increase in payload is when you use altitude compensation.
The two stage vehicle will also have its payload increased by using altitude compensation, which is why altitude compensation should be developed whether or not you think SSTO's are worthwhile. However, the increase in payload for the SSTO is far greater both in percentage and absolute terms. So the TSTO that uses altitude compensation might only have, say, 25% more payload than the SSTO that uses altitude compensation, instead of having multiple times more.
In that case even for an expendable, the SSTO would better on the cost per kilo scale.
Bob Clark
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martinbayer said:
Perhaps Popular Mechanics misquoted Elon, but Rand Simberg's background is in engineering and I don't consider that likely for such a simple idea. Or perhaps Elon was simply wrong, but there really is no other way to interpret what is stated there:
Elon Musk on SpaceX’s Reusable Rocket Plans.
By Rand Simberg
February 7, 2012 6:00 PM
http://www.popularmechanics.com/science/space/rockets/elon-musk-on-spacexs-reusable-rocket-plans-6653023
I would be happy to discuss how much payload likely would be subtracted for the reusable SSTO and TSTO cases based on a common understanding of how much the expendable SSTO with altitude compensation could carry derived from simulations such as Dr. Schilling's Launch Vehicle Performance Calculator.
Bob Clark
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RGClark said:
Very well, then tell me what the exact *absolute* numbers for launch mass, dry mass and payload mass are that you postulate/obtain when running the launch calculator for an SSTO vs. a TSTO with the same structural and propulsion technology assumptions for both. Remember though that both vehicles should be defined for the same payload mass and target orbit, so you might have to iterate and tweak your initial vehicle size assumptions a bit. Saying things like "the TSTO that uses altitude compensation *might* (my emphasis) only have, say, 25% more payload than the SSTO that uses altitude compensation" make me suspect you really *haven't* run a true comparison yet, but once you're ready to present your results, I'll be more than happy to discuss them with you. Quoting various percentages without providing the base numbers is however pretty meaningless. Once we have agreed on the mass properties for both vehicles, we can then proceed to run them through an open source cost model and settle this argument. I'm looking forward to seeing your mass breakdowns for both systems - feel free to choose the payload mass and orbit you want to design both vehicles to, as long as they're consistent. It looks however like the launch calculator is really geared towards ELVs and does for example not support propulsive RTLS options, but I think an RLV comparison for VTHL concepts would be representative. I look forward to seeing your findings.
Martin
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RGClark said:
Actually, I would be more than happy to discuss *ABSOLUTE* payload, launch mass and dry mass numbers as well as associated specific transportation cost for the expendable and reusable SSTO and TSTO cases based on a common understanding of what the specific consistent technology assumptions and mission requirements are.
Martin
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DSE,
thanks for the heads up - I guess I still hoped for some insight and logic on his part. But with a little searching I came across a thread called 'An SSTO as "God and Robert Heinlein intended"'on the Orbiter Forum http://orbiter-forum.com/showthread.php?t=15509 that eerily parallels the discussion in this thread. He starts it by discussing how to turn the SpaceX Falcon 1 into an SSTO and then goes on to other existing or planned launchers to claim how they could be turned into SSTOs as well. When people bring TSTOs into the discussion, he mostly ignores them. Some of the arguments brought to his attention are almost verbatim the same as me and others made here. A few examples of responses to his posts:
"There you see a strong misconception. This world works like that: You make the claims, you do the math to prove them. you can ask people for help, that is ok and if you are polite and not start commanding people around (which you have a tendency for), people will help you with your problems. We are not your employees here, and we also have no moral obligation to prove your wild claims. Most people here don't believe in SSTOs, because they can experimentally see how much better even a reusable TSTO already is."
"Ergo - SSTO is possible but makes no sense with current technology."
"Personally my opposition of SSTOs has nothing to do with insisting that it can't be done, it's about SSTOs not being practical. Don't get me wrong, I see the benefits of an SSTO system... but those benefits are not worth it if they come at a cost that is simply too high."
"You have always only done very simple analyses of things. Going back to my first post, for example: you have never done an analysis of a complete, operational system, as it would exist in reality (apart entirely from unbridled internet speculation). Neither have you done a complete analysis of two different systems- i.e. an SSTO and TSTO, and compared them."
"RGClark, I suggest (and not out of jest or sarcasm) that you do a simple cost comparison between a reusable TSTO and reusable SSTO. The conditions are that you have to show your work, and cite proper sources (i.e. NASA studies and technical papers, AIAA studies, etc) and not just things like space news websites. You cannot make baseless, referenceless and dubious claims (i.e. 'with modern materials, this can be reduced by half'). You have to show the reasoning behind the methods you use and your assumptions."
"RGClark, you never actually bother to answer tough questions (like my SSTO vs TSTO challenge). It seems you pick up on a sort of 'buzzword' (for example, "SSTO can cut costs to $100/kg", "private development can be 1/10th the cost of government development" or soforth) and keep on repeating it (in a manner that harkens the term 'stuck record') whenever someone challenges your claims or asks you to properly substantiate them. "
"The issue is the economics. Just because something is physically possible doesn't mean it is economically worth doing. Yes, if you use lightweight tankage and high performance engines, you can get an SSTO... it could work and fly to orbit, but that isn't the issue."
"In your quest to prove that SSTO is not magically impossible, you totally and entirely gloss over the economic aspect. The issue isn't whether you can build an SSTO or not, but rather: if your SSTO costs twice as much as a TSTO design, why bother with the SSTO at all?"
"The main problem that remains to be proven from RGClark: Can a fully reuseable SSTO be in any sense superior to a fully reuseable TSTO? Nobody doubts that the rocket equation permits finding numbers that make a SSTO possible."
"You still didn't show concrete numbers for a complete system. You still just mention parts and materials, but never combine them into one system."
"The main issue here is the economics- and in specific, the economics of an SSTO compared to a TSTO (since you have to justify the concept you are supporting compared to its competitors). And this analysis in the full sense is far more in-depth than any of the math you've done here."
"If SSTO were as advantageous, and as possible to make happen with SpaceX hardware, as you make it out to be, then SpaceX would be actively pursuing SSTO vehicles. All indications are that they aren't. It doesn't make sense."
"WAY before a reusable SSTO would be competitive, a reusable TSTO will be competitive - and by the pure mathematics, any TSTO will have to be encrusted with diamonds and studded with adamantine (And get exceptional images of travelling dwarves by forgotten beast bone), before a SSTO with the same technology will be more cost-effective."
So you're right, I can see that people already have unsuccessfully raised all these valid arguments before. Looks like there is sadly no reason to expect this time it might be different.
Martin
thanks for the heads up - I guess I still hoped for some insight and logic on his part. But with a little searching I came across a thread called 'An SSTO as "God and Robert Heinlein intended"'on the Orbiter Forum http://orbiter-forum.com/showthread.php?t=15509 that eerily parallels the discussion in this thread. He starts it by discussing how to turn the SpaceX Falcon 1 into an SSTO and then goes on to other existing or planned launchers to claim how they could be turned into SSTOs as well. When people bring TSTOs into the discussion, he mostly ignores them. Some of the arguments brought to his attention are almost verbatim the same as me and others made here. A few examples of responses to his posts:
"There you see a strong misconception. This world works like that: You make the claims, you do the math to prove them. you can ask people for help, that is ok and if you are polite and not start commanding people around (which you have a tendency for), people will help you with your problems. We are not your employees here, and we also have no moral obligation to prove your wild claims. Most people here don't believe in SSTOs, because they can experimentally see how much better even a reusable TSTO already is."
"Ergo - SSTO is possible but makes no sense with current technology."
"Personally my opposition of SSTOs has nothing to do with insisting that it can't be done, it's about SSTOs not being practical. Don't get me wrong, I see the benefits of an SSTO system... but those benefits are not worth it if they come at a cost that is simply too high."
"You have always only done very simple analyses of things. Going back to my first post, for example: you have never done an analysis of a complete, operational system, as it would exist in reality (apart entirely from unbridled internet speculation). Neither have you done a complete analysis of two different systems- i.e. an SSTO and TSTO, and compared them."
"RGClark, I suggest (and not out of jest or sarcasm) that you do a simple cost comparison between a reusable TSTO and reusable SSTO. The conditions are that you have to show your work, and cite proper sources (i.e. NASA studies and technical papers, AIAA studies, etc) and not just things like space news websites. You cannot make baseless, referenceless and dubious claims (i.e. 'with modern materials, this can be reduced by half'). You have to show the reasoning behind the methods you use and your assumptions."
"RGClark, you never actually bother to answer tough questions (like my SSTO vs TSTO challenge). It seems you pick up on a sort of 'buzzword' (for example, "SSTO can cut costs to $100/kg", "private development can be 1/10th the cost of government development" or soforth) and keep on repeating it (in a manner that harkens the term 'stuck record') whenever someone challenges your claims or asks you to properly substantiate them. "
"The issue is the economics. Just because something is physically possible doesn't mean it is economically worth doing. Yes, if you use lightweight tankage and high performance engines, you can get an SSTO... it could work and fly to orbit, but that isn't the issue."
"In your quest to prove that SSTO is not magically impossible, you totally and entirely gloss over the economic aspect. The issue isn't whether you can build an SSTO or not, but rather: if your SSTO costs twice as much as a TSTO design, why bother with the SSTO at all?"
"The main problem that remains to be proven from RGClark: Can a fully reuseable SSTO be in any sense superior to a fully reuseable TSTO? Nobody doubts that the rocket equation permits finding numbers that make a SSTO possible."
"You still didn't show concrete numbers for a complete system. You still just mention parts and materials, but never combine them into one system."
"The main issue here is the economics- and in specific, the economics of an SSTO compared to a TSTO (since you have to justify the concept you are supporting compared to its competitors). And this analysis in the full sense is far more in-depth than any of the math you've done here."
"If SSTO were as advantageous, and as possible to make happen with SpaceX hardware, as you make it out to be, then SpaceX would be actively pursuing SSTO vehicles. All indications are that they aren't. It doesn't make sense."
"WAY before a reusable SSTO would be competitive, a reusable TSTO will be competitive - and by the pure mathematics, any TSTO will have to be encrusted with diamonds and studded with adamantine (And get exceptional images of travelling dwarves by forgotten beast bone), before a SSTO with the same technology will be more cost-effective."
So you're right, I can see that people already have unsuccessfully raised all these valid arguments before. Looks like there is sadly no reason to expect this time it might be different.
Martin
R
RGClark
Guest
DSE said:
It's a matter of math. It's commonly said SSTO's need some new technology or maybe even nuclear engines to carry significant payload. In truth, the fact that the exact opposite is the case can be proven by anyone who takes the time to run the rocket equation. It's actually easy to accomplish.
For instance according to SpaceX their side boosters for the Falcon Heavy will have a 30 to 1 mass ratio. With altitude compensation the Merlin can get 340 s Isp. What does the rocket equation say the delta-v will be in that case? Note how well above this value is than the delta-v needed to reach orbit.
Bob Clark
R
RGClark
Guest
martinbayer said:
I discussed the numbers for the 311 s Isp SSTO case in post #184. For the 340 s Isp SSTO case that uses altitude compensation just change the Isp number from 311 s to 340 s. You'll see the payload goes up multiple times.
For the TSTO case, a problem again is that SpaceX has not provided the propellant and dry mass numbers for the upper stage of the Falcon 9 v 1.1. An estimate puts the propellant mass in the range of 70 metric tons (mT). But what about the dry mass? It is quite likely the upper stage won't have as good a mass ratio as the first stage because it will undergo greater acceleration as propellant is burned off. This will require it to have a stronger and therefore heavier structure. I took the dry mass as an estimate as 7 mT. You can try different propellant and dry mass combinations you feel are more accurate if you wish.
Using these numbers for the upper stage, when I changed the Isp for the first stage from 311 s to 340 s the payload for this TSTO went up less than 25%.
Bob Clark
R
RGClark
Guest
martinbayer said:
No one has yet done the calculation of how high the payload can be when you use altitude compensation on a launcher with the high mass ratio's of SpaceX, either from just plugging in to the rocket equation or using Dr. Schilling's performance calculator. The assumption is simply made that it HAS to be small without actually running the numbers.
I could say what numbers I'm getting but people would believe it more when they do the calculation themselves.
Bob Clark
R
RGClark
Guest
Archibald said:
The problem is the simple calculation of the altitude compensation case hasn't been done. Then the fiction is maintained that SSTO's can't carry significant payload. How can you compare the SSTO case to the TSTO case if all you know about the payload in the SSTO case is "it's some small amount"?
The story has been told about Galileo attempting to show the defenders of the Earth-centered universe the Moons of Jupiter through the telescope to support the Heliocentric view. They refused to look.
Bob Clark
