Dumb question: why don't they launch rockets from the tops of mountains?
Being close to the equator is more important. And mountains that could be used to construct a base are not so high.
Paul Allen's new rocket-launching plane
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Re: Paul Allen's new rocket-launching plane
#42Earlier quoted context omitted.
Is 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.
It 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…
Cool, I was totally unaware of this "prior art". Thanks!
Re: Paul Allen's new rocket-launching plane
#43The really interesting question - does the modest increase in initial velocity and altitude with a boost out of the lower atmosphere make it practical to build a Single Stage To Orbit rocket? If they can, then it's an impressive achievement. If not, then it doesn't really seem worth the trouble.
Re: Paul Allen's new rocket-launching plane
#44IANARS but this plane should give the remaining stage(s) four advantages: 1. +230m/s orbital velocity [1] 2. +9km launch altitude [1] 3. can launch in more weather conditions 4. 1st stage can abort mid-launch without loss of payload. Of these, the most important is the increase in launch altitude, because that means stage 2 launches in air of greatly decreased density, leading to the following efficiencies: A. a vacu…
You can also fly towards the equator before the launch for more boost. Further from the Earth's axis.
For example Cape Kennedy is 28 degrees north. If you fly to the equator, you get another 200 m/s.
Depends a bit to which orbit you're launching though.
Another good thing is flexibility if you are more constrained by launch windows in a stationary launch location. Hard to explain.
Re: Paul Allen's new rocket-launching plane
#45It seems like air launch doesn't buy you a whole lot, but it turns out that a small win on delta-v can result in a fairly big win on payload. This might seem counter-intuitive, but you have to remember that in orbital class rockets, payload is only 5% or so of total mass at take-off.
Re: Paul Allen's new rocket-launching plane
#46Since the Orbital ATK Pegasus already exists and already has a customised plane it launches from, can we assume launching Pegasus is just phase 1 for this plane? If that's all it's going to do there would be no point. So presumably this has capabilities the current Pegasus launch plane doesn't have, and eventually we'll see it launching something like a Pegasus XL Plus? Do we have any indication how big a rocket this thing can carry?
Also, I wonder how this compares in capability to the XS-1 currently under development, which will be a vertically launched first stage rocket that can fly back for a runway landing.
Edit: just found the link below from last year on Space.com.
http://www.space.com/32680-stratolaunch-rocket-vulcan-aerosp...
Re: Paul Allen's new rocket-launching plane
#47Dumb question: why don't they launch rockets from the tops of mountains?
Rockets require cryogenic fuels, workers and large launch complexes. In contrast, Everest is a mere 9km and the first stage of a rocket will take it to something along the lines of 100km at 2000m/s. It is much easier just to throw more fuel in the first stage (or move to the equator) than try and relocate around the relatively smooth surface of Earth.
Re: Paul Allen's new rocket-launching plane
#48IANARS but this plane should give the remaining stage(s) four advantages: 1. +230m/s orbital velocity [1] 2. +9km launch altitude [1] 3. can launch in more weather conditions 4. 1st stage can abort mid-launch without loss of payload. Of these, the most important is the increase in launch altitude, because that means stage 2 launches in air of greatly decreased density, leading to the following efficiencies: A. a vacu…
Is 4. really doable? Would have thought landing while carrying a fully fueled rocket might be pretty high risk.
Re: Paul Allen's new rocket-launching plane
#49This is awesome but a little bit scary. Interesting that they didn't physically connect the tail wings at all, I wonder what stresses and torques the main wing will endure under maneuvering or turbulence. I assume all the control surfaces are computer controlled to synchronize and minimize that, but from the perspective of an ignorant observer, looks a little fragile.
Re: Paul Allen's new rocket-launching plane
#50IANARS but this plane should give the remaining stage(s) four advantages: 1. +230m/s orbital velocity [1] 2. +9km launch altitude [1] 3. can launch in more weather conditions 4. 1st stage can abort mid-launch without loss of payload. Of these, the most important is the increase in launch altitude, because that means stage 2 launches in air of greatly decreased density, leading to the following efficiencies: A. a vacu…
The primary advantage of airplane launch is that you can fly to into a launch window for an orbital rendezvous. Otherwise you'd have to wait for the target's orbit to be just right w/respect to the launch site, or do a long orbit matching process.
This is very useful if say you want to very quickly and quietly launch something towards another satellite.
People are making comparisons with the Spruce Goose, but the Glomar Explorer may be a better analogy.