4 ms·
The less air you are pushing the cheaper it is to achieve that delta-V
by tejtm 9y ago
The less air you are pushing the cheaper it is to achieve that delta-V
- Analemma_ 9y agoIs it really that dramatic a difference? I suppose it must be, if they're building it, but it's strange that no one has done this before if it really helps.
- jacquesm 9y agohttps://en.wikipedia.org/wiki/Stargazer_(aircraft) https://en.wikipedia.org/wiki/Stargazer_(aircraft)
- tejtm 9y agoThey have been doing it all along, just in reverse. Those heat shields glowing red hot and ablating away is pretty dramatic. That is pushing very thin air at (sub?) orbital delta-V
- desdiv 9y agoOrbital ATK has been doing air launch to orbit[0] since 1990 with their Pegasus rocket. They've had three dozen successful launches since then[1]. [0] https://en.wikipedia.org/wiki/Air_launch_to_orbit https://en.wikipedia.org/wiki/Air_launch_to_orbit [1] https://en.wikipedia.org/wiki/Pegasus_(rocket)#Launch_history https://en.wikipedia.org/wiki/Pegasus_(rocket)#Launch_histor...
- muricula 9y agoVirgin Galactic's White Knight is a very similar aircraft. It was used to launch SpaceshipOne which one the x prize. The article doesn't mention it but this new plane is the logical extension of the White Knight. https://en.m.wikipedia.org/wiki/Scaled_Composites_White_Knight_Two https://en.m.wikipedia.org/wiki/Scaled_Composites_White_Knig...
- hinkley 9y agoThere's a reason they are very similar: http://www.scaled.com/projects/stratolaunch http://www.scaled.com/projects/stratolaunch
- mikeash 9y agoIt is a pretty big difference. In vacuum you want a huge nozzle to extract as much energy as possible from the engine's exhaust. In atmosphere, there's a limit to how large the nozzle can be before the exhaust flow separates from the sides and you get asymmetric thrust or worse. Since the nozzle can only be optimized for one particular altitude, that means that rockets which launch from sea level spend a good portion of their ascent with a smaller nozzle than they'd like to have. By launching from high altitude they can be significantly more efficient. As others noted, this has been done before, but it's not too common. I think that's mainly because rockets need to be really, really big to get a decent-sized payload to orbit. Launching from an aircraft would let them be a bit smaller, but they still need to be huge. Pegasus (the one currently in use) is a small rocket and can only orbit a small payload. This plane is designed to carry about 500,000lbs of rocket. For comparison, a fully loaded Falcon 9 is about 1.2 million pounds, and that's only a medium-sized rocket when it comes to orbital launchers. Amusing aside: in the 1970s, the US Air Force tested the feasibility of air-launching ICBMs. The test was carried out by loading a Minuteman ICBM into a C-5 Galaxy transport, flying it over the ocean, and then essentially shoving the missile out the back door and lighting it up. In this case, the advantage wasn't efficiency or payload, but rather the ability to move ICBMs around to make it more difficult to destroy them in a first strike. They decided it wasn't worth all the trouble in the end.
- Analemma_ 9y agoCool, I was totally unaware of this "prior art". Thanks!
- savoytruffle 9y agoHere's a remarkable official USAF film from 1974 about the air-launched Minuteman. Really amazing. https://www.youtube.com/watch?v=8b8LLcdBaQc https://www.youtube.com/watch?v=8b8LLcdBaQc
- arethuza 9y agoThere was also the cancelled Skybolt ALBM from the early 1960s: https://en.wikipedia.org/wiki/GAM-87_Skybolt https://en.wikipedia.org/wiki/GAM-87_Skybolt