Stratolaunch: General Company and Development Updates and Discussions

[baldusi]

Sorry, but isn't the B-52 already doing this?

[rdale]

Sorry, but isn't the B-52 already doing this?

I've never heard of a B52 launching space missions, do you have any examples?

[Danderman]

The 45 minute climb to altitude prior to launch is going to generate a lot of boiloff for an LH2 fueled vehicle.

[jongoff]

The 45 minute climb to altitude prior to launch is going to generate a lot of boiloff for an LH2 fueled vehicle.

Depends strongly on the design, and amount of applied engineering cleverness...

~Jon

[Jim]

Sorry, but isn't the B-52 already doing this?

I've never heard of a B52 launching space missions, do you have any examples?

First 5 Pegasus missions.  Also, some might say the X-15 missions where the pilot earned astronaut wings.

[rdale]

So it "did it" - that's far different that "doing it"

[simonbp]

Just for reference WRT masses, the mass of a loaded Delta IV first stage is 226 tonnes, while the Atlas V first stage masses 307 tonnes. They have almost the same total delta v, so that's a mass savings of 26%. That's pretty significant, and much more than to account for the extra mass from a recovery system.

LH2 certainly has its issues (not least engine availability), but for a recoverable system, I think they'll have to go there to keep the first stage mass down.

[truth is life]

Huh?  wrong, that capability exists now, with current aircraft.  Stratolaunch isn't anything new.    The Stratolaunch aircraft is not going to be sold to just anyone.

Well, I know about Airborne Minuteman (C-5s carrying Minuteman missiles around and dropping them out the back for launch--there was even a demonstration) and Skybolt, but I didn't know anyone had an operational Air Launched Ballistic Missile?

[Jim]

Huh?  wrong, that capability exists now, with current aircraft.  Stratolaunch isn't anything new.    The Stratolaunch aircraft is not going to be sold to just anyone.

Well, I know about Airborne Minuteman (C-5s carrying Minuteman missiles around and dropping them out the back for launch--there was even a demonstration) and Skybolt, but I didn't know anyone had an operational Air Launched Ballistic Missile?

Change  capability to ability

[fatjohn1408]

One benefit of airlaunch is the low aerodynamic drag once at altitude. This can greatly diminish hydrolox's drag penalty. The drag experienced near sea level occurs when under turbofan power so isn't expensive.

To be fair, lower aerodynamic drag would open up the possibility of designing a much less slender kerolox launcher. Near circular tanks would lead to significant construction mass reductions.

This effect is very important when looking to other launch assist concepts such as that of XCORīs lynx, where release conditions would be so fast and high that the assisted vehicle would better be a single stage. In this scenario each pound saved in construction mass would add a pound to payload capability.

Another problem with the LH2 density is that there is only a limited space beneath the wings, so a hydrolox launcher of the same mass as the kerolox launcher would be three times as long. Imagine the bending load the rocketīs hull has to withstand.

[Robotbeat]

I think you mean "nearly spherical" not "near circular" tanks.

It's true that spherical tanks would, in "spherical cow land," have a better mass fraction for a pressure vessel. (And spherical tanks also would need less insulation for a given boil-off rate... not counting aerodynamics there). Whether there's a real benefit after everything is taken into account is a lot more difficult question to answer. There's also "ease of manufacturing" and "ease of transportation" considerations.

[mmeijeri]

I'm with Jim.

A wise default choice in general, but I wonder if we know enough to make a pronouncement either way. Is it obvious that one is superior to the other? I don't even know which way I would bet if I had to. Same with kerolox + hydrolox as with Atlas vs all hydrolox as with Delta. Which is better? Conventional wisdom says kerolox is better for first stages, so you could say Atlas is more technically capable, but how much economic benefit comes from having identical propellant combinations on both stages? And what about all kerolox as with Falcon? In the end only experience and markets can tell us what is best overall, and the answer may be different for various niches.

[mmeijeri]

I think the anti-LH2 bent that a lot of people have in New Space is somewhat amusing.

I find it amusing to hear there is an anti-LH2 attitude in New Space. In my experience if anything they're preaching the gospel of LH2, not bad-mouthing it. At the same time they are practicing less challenging things for now, and haven't even moved far beyond pressure-fed systems as far as I know.

To be fair I've never used anything much worse than LOX myself (though I have many friends who have LH2 experience and few of them think it's the devil-juice that some make it out to be).

We must travel in different circles. I've never heard anyone describe LH2 as devil juice. It's a standard industrial commodity.

[Tcommon]

I think the anti-LH2 bent that a lot of people have in New Space is somewhat amusing.

I find it amusing to hear there is an anti-LH2 attitude in New Space. In my experience if anything they're preaching the gospel of LH2, not bad-mouthing it. At the same time they are practicing less challenging things for now, and haven't even moved far beyond pressure-fed systems as far as I know.

To be fair I've never used anything much worse than LOX myself (though I have many friends who have LH2 experience and few of them think it's the devil-juice that some make it out to be).

We must travel in different circles. I've never heard anyone describe LH2 as devil juice. It's a standard industrial commodity.

Yah, this argument has gotten 'entertaining'. LH2 has advantages and disadvantages. They should be dispassionately discussed. But when I  mentioned the months of Shuttle delays caused by Hydrogen leaks, one of its disadvantages, there seemed to be a lot of emotions.

"devil-juice" ... Never heard that one before

[mmeijeri]

"devil-juice" ... Never heard that one before

Sounds like a more appropriate term for hydrazine or NTO.

[Robotbeat]

I think the anti-LH2 bent that a lot of people have in New Space is somewhat amusing.

I find it amusing to hear there is an anti-LH2 attitude in New Space. In my experience if anything they're preaching the gospel of LH2, not bad-mouthing it. At the same time they are practicing less challenging things for now, and haven't even moved far beyond pressure-fed systems as far as I know.

To be fair I've never used anything much worse than LOX myself (though I have many friends who have LH2 experience and few of them think it's the devil-juice that some make it out to be).

We must travel in different circles. I've never heard anyone describe LH2 as devil juice. It's a standard industrial commodity.

Join the ARocket mailing list.

We're talking about the little New Space folk, many who have lots of experience in the amateur realm.

[mmeijeri]

Join the ARocket mailing list.

I have, but maybe I need to read more closely.

Anyway, back to Stratolaunch. I don't think we've seen any indication they are planning for LH2. SpaceX has also stopped talking very much about moving beyond kerolox and to the degree they still do they're talking about LOX/CH4, not LH2.

[Jim]

I think the anti-LH2 bent that a lot of people have in New Space is somewhat amusing.

I find it amusing to hear there is an anti-LH2 attitude in New Space. In my experience if anything they're preaching the gospel of LH2, not bad-mouthing it. At the same time they are practicing less challenging things for now, and haven't even moved far beyond pressure-fed systems as far as I know.

To be fair I've never used anything much worse than LOX myself (though I have many friends who have LH2 experience and few of them think it's the devil-juice that some make it out to be).

We must travel in different circles. I've never heard anyone describe LH2 as devil juice. It's a standard industrial commodity.

Yah, this argument has gotten 'entertaining'. LH2 has advantages and disadvantages. They should be dispassionately discussed. But when I  mentioned the months of Shuttle delays caused by Hydrogen leaks, one of its disadvantages, there seemed to be a lot of emotions.

Because you are blatantly wrong, again.
LH2 is not difficult to deal with and your example didn't nothing to disprove it.  Have you worked with LH2 or any other propellant?

[Tcommon]

Yah, this argument has gotten 'entertaining'. LH2 has advantages and disadvantages. They should be dispassionately discussed. But when I  mentioned the months of Shuttle delays caused by Hydrogen leaks, one of its disadvantages, there seemed to be a lot of emotions.

Because you are blatantly wrong, again.

OK, Jim. The Shuttle didn't have months and months of delays over Hydrogen leaks. Wouldn't want you to get worked up or lose any sleep over the truth, would we?

[Lee Jay]

LH2 is not difficult to deal with and your example didn't nothing to disprove it.

I'm sure it's more difficult than room-temperature liquids.  Heck, any knucklehead can fill a container at the pump and re-fill their Kerosene heater.

But that leads me to a question.  Which liquids commonly used in rocketry are harder to handle than LH2?  I would think the Hypergols certainly are, probably a good number of the oxidizers, and maybe even liquid helium.  Is that correct, Jim?  Any others?