Stratolaunch

[blackstar]

So this aircraft is equipped to top off the tanks of a rocket carried under the wing?

Probably not. But it would hardly be rocket science to modify it. Think of it as an option in case a cryogenically-fuelled payload comes along.

In other words, no.

 

[steelpillow]

You seem to be assuming they'll use a single-stage rocket.

No, I make no such assumption. You are evidently arguing against something I have not said.

Don't forget that an air launch is a much lower-gee affair than a rocket launch. The F9 is a poor comparison because it is a relatively high-gee rocket system and therefore inherently more efficient than say the Shuttle. You just do those sums, and see how F9 fares as a low-gee launch platform!

Oh, and I'm sure that the bureaucracy is capable of catching up with the reality, should the need arise. Why are you so down on the whole idea that you have to invoke tickboxes?

 

[steelpillow]

So this aircraft is equipped to top off the tanks of a rocket carried under the wing?

Probably not. But it would hardly be rocket science to modify it. Think of it as an option in case a cryogenically-fuelled payload comes along.

In other words, no.

But a tad more informative.

 

[Hobbes]

Don't forget that an air launch is a much lower-gee affair than a rocket launch. The F9 is a poor comparison because it is a relatively high-gee rocket system and therefore inherently more efficient than say the Shuttle. You just do those sums, and see how F9 fares as a low-gee launch platform!

When designing a rocket, G levels are set to be as high as possible without damaging the payload. This is done to reduce gravity losses: at lower acceleration, you spend more time at suborbital speeds and your launch will ultimately cost more fuel.
Whether you launch at 0 m/s or 300 m/s doesn't change that.
Check the user guide for the air-launched Pegasus rocket for instance, G-forces at stage burnout are 9G for the first stage (much higher than the F9, by the way).

Oh, and I'm sure that the bureaucracy is capable of catching up with the reality, should the need arise.

It's not a matter of bureaucracy. Dropping a spent rocket stage on someone's head is a surefire way to bankrupt your business. I don't see Stratolaunch buying an MPA to scout their last-minute-changed landing zone, so they have to use the existing legal mechanism of NOTAMs, which take a while to result in a cleared area.

 

[Zoo Tycoon]

Steelpillow
Your claim that up to ten percent of a cryogenic propellant is lost at time of burn out due to evaporation – Ref Text Book “Modern Engineering for Design of Liquid –Propellant Rocket Engines” by Dieter K Huzel, page 146 Para 5.3, quotes “Rate of oxidizer evaporation in the tank as 1.6lb/s” for a relatively large 4 engine powered LOX/RP1 stage. This is about four/five orders less than your claim so please can you provide a referable source to support your claim.

Every aircraft I’ve ever come across has had operating limits, e.g. crosswind limits, hot/high limits, contaminated surface limits, etc. So it makes no difference how good the weather is at the desired launch location, if the weather at airfield is outside of operating limits, the mission doesn’t get flown. I guess in theory you could say the planning could be more flexible but that’s making the assumption that airports are really going to accept a 0.1 - 0.2 kilo ton bomb siting on their main runway, which if it goes bang would be a single point failure for their entire revenue income. An airport with population living under the flight path I reckon will be an automatic exclusion.

Others and myself cannot understand how an air launch reduces the max flight g, in particularly considering the additional pitch up which inherently occurs after release. Maybe you could provide a referable source to support your claim which can explain it better.

Your claim that that automatic loading of cryogenic propellant in flight is “not rocket science”;- the USAF blew up seven ICBM’s (Titan 1 and Atlas) complete with their silo’s during operational propellant loading exercises. (Although according to Dieter’s data above, it’s unnecessary so not worth the risk)

Why these concepts get developed?
When it comes to developing technology cash is king. Just because an entrepreneur is mega wealthy doesn’t automatically mean they has a good understanding of even simple physic’s or will even listen to the advice of someone that does;- they’re notorious for going with their “gut” combined with a dogmatic, get on with it attitude. Once cash is being spent and loyal people are on the payrole, they become very vulnerable to the “Emperor’s New Clothes” situation. This has been responsible for a good number of spectacular white elephants in years gone by.

However enticing that the thought that a commercial airliner can achieve 10% of the altitude required for orbit, it’s an inescapable fact that it only has a tiny fraction of the required orbital energy. This is best illustrated by the orbital mass fraction of the vehicle at zero V, which is barely different for both methods.

 

[sferrin]

Don't forget that an air launch is a much lower-gee affair than a rocket launch. The F9 is a poor comparison because it is a relatively high-gee rocket system and therefore inherently more efficient than say the Shuttle. You just do those sums, and see how F9 fares as a low-gee launch platform!

When designing a rocket, G levels are set to be as high as possible without damaging the payload.

Why is the Delta IV Heavy so damn slow? I swear, by the time it reaches Mach 1 the Space Shuttle would have already shed it's boosters.

 

[Hobbes]

Off the cuff as I haven't studied this: compromised design because they wanted to reuse the Delta IV core?

 

[Archibald]

Don't forget that an air launch is a much lower-gee affair than a rocket launch. The F9 is a poor comparison because it is a relatively high-gee rocket system and therefore inherently more efficient than say the Shuttle. You just do those sums, and see how F9 fares as a low-gee launch platform!

When designing a rocket, G levels are set to be as high as possible without damaging the payload.

Why is the Delta IV Heavy so damn slow? I swear, by the time it reaches Mach 1 the Space Shuttle would have already shed it's boosters.

Because the RS-68 are LH2 engines of far lower thrust than SRBs. SRBs are brute force and raw power. The difference is similar to a 300 hp sport car and a 300 hp diesel truck. SRB are rather sport car, they go fast but are pretty short lived or short range. LH2 starts slowly but once at max power, it rules the skies.

 

[sferrin]

Don't forget that an air launch is a much lower-gee affair than a rocket launch. The F9 is a poor comparison because it is a relatively high-gee rocket system and therefore inherently more efficient than say the Shuttle. You just do those sums, and see how F9 fares as a low-gee launch platform!

When designing a rocket, G levels are set to be as high as possible without damaging the payload.

Why is the Delta IV Heavy so damn slow? I swear, by the time it reaches Mach 1 the Space Shuttle would have already shed it's boosters.

Because the RS-68 are LH2 engines of far lower thrust than SRBs. SRBs are brute force and raw power. The difference is similar to a 300 hp sport car and a 300 hp diesel truck. SRB are rather sport car, they go fast but are pretty short lived or short range. LH2 starts slowly but once at max power, it rules the skies.

I'm not asking HOW (I'm aware of the differences in T/W between the two) I'm asking WHY. If the G levels should be as high as possible why did they go so low with the Delta IV.

 

[steelpillow]

@Zootycon
I don't have refs to hand but boiloff of H2 is far higher than that of LOX. See here for a suggestion of 300-500 Kg/min, around 10 times the number given by Huzel. Also, H2 is far lighter, so that weight represents a much bigger proportion of the total load. That's possibly where a couple of orders went. If I am still way out then maybe I am a bit dated - standards of insulation have improved over the years.

Your arguments against cryo fuel safety apply equally to rockets. Stratolaunch is not intended to operate from airports, for one thing it is too big to fit. The UK has pencilled in a couple of spaceports where cryo beasts may safely hog the departure lounge, I believe the US already has several. Plane takeoffs are less disrupted by weather than rocket launches. Sorry, but all that airport spiel is just a non-argument.

A plane does not reduce gee in and of itself, nobody is saying it does. What it does do is allow you to reduce max gee up to first stage separation* without hanging a massive booster stage from its own skyhook.

You need an example of reliable in-flight cryo transfer? Try the Space Shuttle.

* Just to be clear, I count a launch aircraft as a first stage.

 

[steelpillow]

talk about a heateddebate (runs for cover)

Just you wait 'til we start talking re-entry shielding ;D (ducks under said shielding)

 

[Hobbes]

A plane does not reduce gee in and of itself, nobody is saying it does. What it does do is allow you to reduce max gee up to first stage separation* without hanging a massive booster stage from its own skyhook.

* Just to be clear, I count a launch aircraft as a first stage.

What you don't seem to grasp is that "reduce max gee up to first stage separation" is not necessary. No launch vehicle experiences its peak G-load at speeds between 0 and 300 m/s, it experiences peak G-load at burnout of the first rocket stage.

 

[steelpillow]

A plane does not reduce gee in and of itself, nobody is saying it does. What it does do is allow you to reduce max gee up to first stage separation* without hanging a massive booster stage from its own skyhook.

* Just to be clear, I count a launch aircraft as a first stage.

What you don't seem to grasp is that "reduce max gee up to first stage separation" is not necessary. No launch vehicle experiences its peak G-load at speeds between 0 and 300 m/s, it experiences peak G-load at burnout of the first rocket stage.

I think you will find my remarks consistent with that.

 

[Hobbes]

Then why offer that point as an advantage of air launch?

 

[steelpillow]

Then why offer that point as an advantage of air launch?

Because it reduces the size of the skyhook you need for the first rocket stage, if you are going for a low-gee trajectory. Have you done your low-gee sums on the Falcon 9 yet?

 

[Zoo Tycoon]

An anonymously posted spiel on an Internet chat room is not a reliable technical reference.

 

[steelpillow]

So having the lightest weight skyhook on an air launch is an advantage over not needing such a thing on a vertical launch?

No. The air launch allows a reduction in the amount of rocket fuel that needs to be carried, to support the longer-period trajectory of a lower-gee orbital injection. The "skyhook" is a metaphor to try and get across the fundamental significance of time spent under both gravity and rocket power. You are not stupid, you know that very well. I fear you deliberately misread my statements in order to wind me up. That is disgusting of you.

Maybe by now you realize that he's not really a serious poster. Look at all the claims he made. They're all just... not serious.

Don't be absurd. I have answered every confused query with technically correct detail. Some of you have misunderstood what I wrote and others have questioned it, but it is you who are now totally losing the plot.

To recap. Somebody asked why people went in for launch aircraft like Stratolaunch. I attempted to answer that query. Whether the protagonists of launch aircraft are ultimately right or wrong, that is what they have argued, from Eugene Sanger to the Mriya-HOTOL composite to Pegasus to WhiteKnight to Stratolaunch. In explaining their case I have been subject to aggressive questioning, seemingly wilful misunderstanding, and now outright ridicule. I am sorry, but that is not acceptable.

 

[Hobbes]

If I came across as aggressive, I apologize. That was not my intent.

You made some claims that seemed optimistic or incorrect to me, based on my understanding of the physics involved, so I wrote some posts disagreeing with what you said. Those posts are my attempt to get a better understanding of what's going on, and I wrote them with the understanding that I might turn out to be incorrect.
Similarly, any misunderstandings on my part were genuine. I'm not in the habit of arguing to wind somebody up.

I tend to take people literally, so when you mentioned 'Skyhook' the thought that that might be a metaphor didn't cross my mind.

 

[Hobbes]

Cryogenic liquid fuel boiloff is one reason. Approx 10% of any LOX/LH2 fuel load will boil off during the initial stages of launch and its tankage is just dead weight. A mothership can keep it topped up, allowing the later-stage tanks to be 10% smaller. That allows a significantly bigger payload and/or higher orbit.

I found some boiloff calculations for the Shuttle external tank.

0.2 kg per second of LH2. 720 kg per hour loss. 106.26 tonnes - 6 days.
0.1 kg per second of LOX. 360 kg per hour loss. 629.34 tonnes - 73 days.

During the initial filling of the tank, boiloff is a lot higher: only 56% of the supplied LOX makes it into the tank, the rest is lost as boiloff during filling (cooling the tank from ambient to LOX temperature) and other waste. But once the tank is full and at equilibrium temperature, boiloff is 0.3 ton/hour for the Shuttle ET (which contains 600 tons of LOX). For a smaller rocket the boiloff will be higher, but we're quite a few orders of magnitude away from 10% boiloff in a few minutes.

 

[steelpillow]

@Hobbes,
Ah, found my problem. The 10% relates to the boiloff from a cryo rocket being carried for a nominal 1 hr to its drop site by a launch plane. It is not directly comparable to even a low-gee vertical rocket stage. It also assumes a higher rate of heat loss ca. 500 W/m2, which is out of date as I began to suspect. Was from a conversation I had many years ago during the HOTOL era.
The 100 W/m2 transfer rate in the study you draw on looks around half what it should be at any reasonable atmospheric pressure, judging by the sources it cited, so that may explain the rest of the gap.
Overall you appear to be a lot more right than I was. I hope that clears this one up.

My other comments stand.

 

[Zoo Tycoon]

Steelpillow
I made very polite request for you to support your case with good technical sources or a reference which explains it clearly, but failed to do this, instead responding with a ref made to an anonymous person on a chat room (which was an order of magnitude difference to your original claim???), more unsupported opinions, dismission of my suggestion with a profanity, jargon? (The wiki description of a Skyhook is nothing like yours), insults, claims of victimisation and final name dropping.

Apologies ? I never intended to be aggressive or wind you up....Maybe you need to consider your conduct.

 

[Jemiba]

So, back to topic, please, and maybe for a while at least, thinking twice, what a post can mean to others.
Such a discussion hasn't to be free of humour or irony, but those stylistic devices can quite easily be misunderstood.

 

[overscan (PaulMM)]

My understanding of the economics of air launch is it is advantageous primarily for small payloads, where atmospheric drag is a relatively big factor. Drag is proportional to surface area so simple geometry makes it less important to large rockets due to scaling between area and volume. I've not studied it in any detail however.

 

[Byeman]

Cryogenic liquid fuel boiloff is one reason. Approx 10% of any LOX/LH2 fuel load will boil off during the initial stages of launch

Not true at all. There is little to not boil off in the short time from launch to orbit.

 

[Byeman]

1. Operational flexibility is another. You can fly round inconvenient weather patterns to find an open window, not have to wait for it to come to you. You can fly to an optimal launch spot and add a few mph in the optimal direction: different orbits are best reached in different ways and you are not tied to one spaceport's way. You can resupply and relaunch quickly, reducing the number of launchers needed to support a busy schedule.

2. Economy of operation is yet a third. Several of those flexibility options also offer significant cost savings and/or heavier payloads. More significantly,

3. if you have a delicate payload such as space tourists, your gee force is severely limited and a rocket must waste an age hanging in the sky burning gargantuan amounts of fuel.

4. Substituting aerodynamic lift for the thirstiest flight segment offers equally gargantuan cost savings. It's not so important if you can pile on those gees for a robust payload, a rocket first stage then makes a lot more sense.

1. No, still limited to a launch range. And no, resupply and relaunch is not a given nor proven.

2. No, none of those provide cost savings nor heavier payload. Replacing the L1011 with a solid motor as in Taurus provides more performance.

3. Not true. Vertical rockets are not g limited. Horizontal flight put more loads on payloads.

4. Unproven.

Not one of your statements is backed by data.

 

[fredymac]

Air launch doesn’t seem to provide an obvious advantage but you have 2 new business startups pursuing this architecture with serious money. There are also examples of air launched ballistic missiles and targets. Something must be advantageous about this approach and I would be very surprised if trade studies vs ground launch hadn’t been analyzed before money was committed.

The altitude advantage appears to be minor. Compared to the eventual orbital altitude, the removal of 6 miles seems trivial. Launch speed has the same issue of being so low compared to the final orbital velocity. The lower air friction at high altitude might be useful but rockets tend to lift off slowly during their initial climb out so I wouldn’t think it would amount to very much.

At the rudimentary level, for a ground launched rocket to reach the altitude/velocity of an air launch, it would have to expend the fuel to power maximum thrust for 15 to 30 seconds. If you remove the fuel/tankage structure/engine power margin to do this, just how much do you gain?

 

[steelpillow]

Not one of your statements is backed by data.

Nor are any of yours. Eugene Sanger, B.Ae, Pegasus, Scaled Composites, Virgin Galactic and Stratolaunch have all thought your views to be rubbish. I am inclined to agree with them.

 

[Byeman]

Air launch doesn’t seem to provide an obvious advantage but you have 2 new business startups pursuing this architecture with serious money. There are also examples of air launched ballistic missiles and targets. Something must be advantageous about this approach and I would be very surprised if trade studies vs ground launch hadn’t been analyzed before money was committed.

The altitude advantage appears to be minor. Compared to the eventual orbital altitude, the removal of 6 miles seems trivial. Launch speed has the same issue of being so low compared to the final orbital velocity. The lower air friction at high altitude might be useful but rockets tend to lift off slowly during their initial climb out so I wouldn’t think it would amount to very much.

At the rudimentary level, for a ground launched rocket to reach the altitude/velocity of an air launch, it would have to expend the fuel to power maximum thrust for 15 to 30 seconds. If you remove the fuel/tankage structure/engine power margin to do this, just how much do you gain?

The mobility is the advantage. There is a slight benefit for lower atmospheric density for the motor, the added altitude is negligible.

 

[steelpillow]

Air launch doesn’t seem to provide an obvious advantage but you have 2 new business startups pursuing this architecture with serious money. There are also examples of air launched ballistic missiles and targets. Something must be advantageous about this approach and I would be very surprised if trade studies vs ground launch hadn’t been analyzed before money was committed.

The altitude advantage appears to be minor. Compared to the eventual orbital altitude, the removal of 6 miles seems trivial. Launch speed has the same issue of being so low compared to the final orbital velocity. The lower air friction at high altitude might be useful but rockets tend to lift off slowly during their initial climb out so I wouldn’t think it would amount to very much.

At the rudimentary level, for a ground launched rocket to reach the altitude/velocity of an air launch, it would have to expend the fuel to power maximum thrust for 15 to 30 seconds. If you remove the fuel/tankage structure/engine power margin to do this, just how much do you gain?

That's all about right. According to the HOTOL technical manager, air-launching it would have saved around 10-15% overall (and much of that due to topping-up boiloff), but of course that has to be offset against the carrier craft. I suspect that air-launching a rocket would probably save less, as the structure has to be strengthened to resist sagging under gravity (whereas a spaceplane like HOTOL is already strengthened).
The amount you gain is heavily dependent on the excess thrust of the engines, i.e. the acceleration or gee force they impart after separation. For a high-gee, solid-fuel system like Pegasus it might actually be bigger than its vertical-launch equivalent.

 

[blackstar]

Not one of your statements is backed by data.

Nor are any of yours. Eugene Sanger, B.Ae, Pegasus, Scaled Composites, Virgin Galactic and Stratolaunch have all thought your views to be rubbish. I am inclined to agree with them.

There's an old saying that on the internet, nobody knows you're a dog. But you have to be careful, because on the internet, you could actually be arguing with somebody who flies rockets for a living...

 

[blackstar]

1-Air launch doesn’t seem to provide an obvious advantage but you have 2 new business startups pursuing this architecture with serious money.

2-There are also examples of air launched ballistic missiles and targets.

3-Something must be advantageous about this approach and I would be very surprised if trade studies vs ground launch hadn’t been analyzed before money was committed.

1-Even in the recent past there were many more such proposals, but they haven't gotten funding. So two startups with funding doesn't prove the success of this model. Let's see if they are launching customers ten years from now.

2-There are no operational air-launched ballistic missiles. But that's a different set of issues. Ballistic missiles don't have to make money, they just have to work. And air-launching a ballistic missile has some operational drawbacks. In order to reduce vulnerability, you have to keep the plane in the air a lot, and that's expensive. These operating schemes have just never worked out, but they've been evaluated numerous times.

3-Well, in the case of Stratolaunch it appears to be primarily an ego-driven project. A rich guy wanted the biggest airplane in the world and he wanted it to launch rockets. It's just like owning a really large yacht. The fact that they've gotten this far without a rocket is an indication of how much the circle doesn't close on this approach.

Virgin is a different case, and in some ways a more logical one. They're using a surplus 747 that they were going to write off anyway. Virgin already has maintenance and other logistics infrastructure to maintain this plane, so it's not like they have to pay somebody else to do it, They can also keep some of their related costs low, like having the pilots fly regular revenue flights until needed for a launch mission. That helps to keep the cost of the airplane low. Now is it going to be low enough to make them profitable (all other things considered)? We don't know. The carrying cost for the plane (meaning how much they are going to have to spend every year just to keep the plane flying) is still going to cost some serious cash. And they're going to have to be innovative on the rocket and payload processing side. I'd like to see them succeed, because it's a cool idea. But we should all be honest and admit that air-launch is very much a niche and there's no reason to believe that any of these efforts will succeed.

 

[TomcatViP]

Don't forget that their aircraft is certified so they can fly it anywhere, anytime (but without payload) to meet customer launch site expectations easily. So basically they will have a global business soon or latter.

The drawbacks is that as a civilian airliner, maintenance will prove to be higher with a lot of systems non-relevant for the mission. Stratolaunch have only a modern tailored composite airframe to sustain which certainly would prove to cost less per pound in orbit.

 

[Mark Nankivil]

Don't forget there are costs for ground based operations - whether you own the launch site and infrastructure or lease/rent it. All part of the cost analysis but the ground option is not free.

Enjoy the Day! Mark

 

[blackstar]

Don't forget that their aircraft is certified so they can fly it anywhere, anytime (but without payload) to meet customer launch site expectations easily. So basically they will have a global business soon or latter.

I doubt that they will be able to take the rocket to any foreign country they want for launching purposes. The rocket is on the munitions list.

 

[Byeman]

Not one of your statements is backed by data.

Nor are any of yours. Eugene Sanger, B.Ae, Pegasus, Scaled Composites, Virgin Galactic and Stratolaunch have all thought your views to be rubbish. I am inclined to agree with them.

Another statement lacking data for support.
And just because they are doing something doesn't mean they are right or never supports your claim.
Sanger built anything. B.Ae hasn't done anything air launched. Pegasus is the most expensive per lb of payload for any launch vehicle. Scaled Composites isn't producing orbital vehicle. Stratolaunch is a plane looking for a mission.

BTW, my statements are backed by data. They just point out where yours lacked data.

Also, your logic is flawed. Just because somebody comes up with a paper concept does not mean it is good, viable or workable. There are thousands of paper concepts like Sea Dragon, ROMBUS, Orion, etc.

 

[Byeman]

Nor are any of yours. Eugene Sanger, B.Ae, Pegasus, Scaled Composites, Virgin Galactic and Stratolaunch have all thought your views to be rubbish. I am inclined to agree with them.

So you also like to beat dead horses too?


Actually, anything I said would not be "rubbish" to them. They would understand what I said and would agree.

 

[XP67_Moonbat]

I'm gonna have to go with Byeman on this... Beating a dead horse here.

StratoLaunch at sunrise, for your trouble.

 

[Archibald]

Not one of your statements is backed by data.

Nor are any of yours. Eugene Sanger, B.Ae, Pegasus, Scaled Composites, Virgin Galactic and Stratolaunch have all thought your views to be rubbish. I am inclined to agree with them.

There's an old saying that on the internet, nobody knows you're a dog. But you have to be careful, because on the internet, you could actually be arguing with somebody who flies rockets for a living...

ROTFLMAO, as they say.

 

[ADVANCEDBOY]

Does anyone know when is the first flight due? They promised to take it airborne by the end of the summer. The summer is over. The bird is still taxiing.
P.S. I hope it doesn`t break in half. For such long fuselages to be joined only by a single skinny wing , I am concerned. Especially when dealing with torsional forces. The rear wing and the rudder are very far away from the central wing and if rudders or ailerons are used to compensate air flows on one side , it will exert huge loads on the central wing where it is joined to each of the fuselages. Just a wild guess.

 

[Flyaway]

Stratolaunch Reveals Hypersonic Testbed Concepts