[HN Gopher] Stratolaunch reveals its first hypersonic design for...
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Stratolaunch reveals its first hypersonic design for high-altitude
flights
Author : belter
Score : 36 points
Date : 2022-05-31 14:32 UTC (8 hours ago)
(HTM) web link (www.space.com)
(TXT) w3m dump (www.space.com)
| Gravityloss wrote:
| What is the flight profile and purpose of the vehicle?
|
| If it's hypersonic atmospheric cruise, then it would be for
| weapons development as there's no civilian use for that
| technology.
|
| Satellites are launched first up and then horizontally outside
| the atmosphere.
| dotnet00 wrote:
| The primary motivation is probably weapons, but experience with
| hypersonic flight should also help with reusable rocketry,
| which I think may be relevant since they mention that the next
| iteration of the vehicle is intended to be fully reusable. If
| only intended for weapons, making the vehicle fully reusable
| doesn't seem too relevant.
| mandevil wrote:
| I don't think that necessarily tracks: having a test-bed be
| reusable can mean you get more flights, can carry more
| payloads, and study many different things. Which for
| exploring something as complex as hypersonic flight, has
| obvious attractions. The research vehicle that has done the
| most study of hypersonic flight to-date is almost certainly
| the North American X-15, which did 199 flights over 9 years,
| and it was fully reusable and not related to a weapon in any
| way.
|
| This presumes, of course, that the cost of turn-around for
| reflight is <<< the cost of building a new one. This is
| obviously true for normal airplanes but was probably only
| barely true for the Space Shuttle. So there is a continuum
| here, a point where the between-flight inspection and
| cleaning costs do loom large enough to not be worth it.
| belter wrote:
| "Air Force secretary hints at military space applications for
| Stratolaunch super-plane" (2017)
|
| https://www.geekwire.com/2017/air-force-secretary-highlights...
| lmm wrote:
| Most rocket launches start accelerating horizontally either as
| soon as they've cleared the thickest part of the atmosphere, or
| right from the start. If you can energy you can impart to a
| satellite with an air-breathing stage, you can save an
| exponential amount of fuel on the final rocket stage.
| xcskier56 wrote:
| This is a common theory, but if you look at the math of the
| rocket equation, a very large percentage is for pure
| horizontal velocity, with a small percentage of gravity
| losses for getting from the surface to the orbital altitude,
| an even smaller percentage are losses due to aerodynamic
| drag.
|
| I haven't done the math, but in general, the benefit of
| something like stratolaunch is much less than you'd expect
|
| Here's a great (but complicated) reddit post on this topic:
|
| https://www.reddit.com/r/KerbalAcademy/comments/63nzq6/how_d.
| ..
| mandevil wrote:
| The reason that there are plenty of rocket first stages and
| basically no air-breathing first stages that go to orbit is
| that, essentially, this isn't true. OSC Pegasus and Virgin
| LauncherOne are the only exceptions, and both are only good
| for very tiny payloads and accordingly have very limited
| flight numbers- compare the less than 50 total across both
| launchers to the 150 for just the already retired Delta II
| rocket (which entered service at basically the same time as
| Pegasus, is why I chose it). The only real use case that I
| can see for air launch is that they can be fully launch
| azimuth independent for launches from within US territory, so
| there can be some sort of responsive launch capability (read:
| military wants to launch something immediately). Other than
| that one use case, it's hard to see what air-breathing
| engines bring to the table for space-flight.
|
| Payload size is clearly a massive problem because airplanes
| are so volume limited. But there is another issue here:
| heating. In order for an air-breathing engine to provide
| useful thrust, you have to have enough air for it to breathe.
| That pretty much requires you to now have to deal with
| aerodynamic heating, which is a thing that most rockets try
| very very hard to ignore on launch.
|
| The most prominent air-breathing to orbit attempt going right
| now, Skylon, seems to be viewed generally pretty skeptically
| by most people in the space community, from what I can tell.
| And even then, the log-line is different: instead of separate
| jet engines and rocket engines, the idea is to have a rocket
| engine that can make a mediocre jet engine for some portion
| of the flight. Most people outside RE don't think this idea
| will work very well (I recall people who ran the numbers
| pointing out that HOTOL- the program that Skylon grew out of-
| would actually have significantly more payload if it had just
| rocket engines) but Bond and co. continue on, with very small
| budgets, the sort of budgets suitable for long-shot
| technology development. Thus, it appears that the people who
| control the purse strings generally agree that this has a low
| chance of working out, even if it is worth trying.
| trhway wrote:
| So far nothing could beat just increasing the size of the
| first stage. Simplicity and weight as any air breathing
| hardware brings in weight and complexity. Even the simplest
| and my favorite approach - air augmentation - could not be
| made so far (beside a small USSR surface-to-air missile).
|
| Also with the size of the rocket the proportional air
| breathing machinery power scales between linear and square
| while rocket mass cubically, so a useful air breathing on say
| a Starship is hard to imagine.
| jccooper wrote:
| It's a hypersonic testbed. Which basically means DoD, though I
| suppose if you came along with a civilian usecase they wouldn't
| hang up the phone.
| mrtri wrote:
| 8bitsrule wrote:
| Apart from military uses, Stratolaunch (owned by a PE firm) seems
| a solution looking for a problem.
|
| The homepage says "Together with our customers, we are advancing
| one of our country's most important priorities." I wonder what
| that might be.
| boardwaalk wrote:
| I like to see innovation in aerospace, but there seems to be a
| lot of either solution searching for a problem or problems I'd
| rather not see solved (weaponry). This is one of them. Spinlaunch
| is another (the Gs). Astra is yet another ("launch anywhere" =
| military use).
|
| IMO the things to watch are reusability (SpaceX, Rocket Lab),
| mass/efficiency (SpaceX), 3D printed components (Relativity and
| others to a lesser extent) and humans long-term in space beyond
| LEO (NASA I guess? SpaceX makes noises but doesn't seem to want
| to be the one to solve the hard problems here).
|
| tl;dr I think Stratolaunch is "cool" but not particularly
| interesting.
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