MAB, part 8

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A series about the Microwave Airbreathing Booster- except with a twist.  This one discusses an option that leaves the airbreather out.

Speculation alert.  Some new ideas to kick around.

You know something?  I wonder if there is some sort of objection amongst the upper muckety mucks to airlaunching upper stages.  Is it because it is felt to be unsafe?  Or is it inelegant in their opinion?  Or is it possible that nobody thought of it?  Personally, I think everything has been thought of at least once.  It just hasn't been implemented.  Thus, the thought that there is an objection to this idea at a high level.

Yet the Shuttle was an ungainly looking thing sitting on top of that big fuel tank.  What the heck.

The idea is to turn a plane into a rocket of sorts and fly it high enough to get above the atmosphere, and then you could release a LH2/LOX powered rocket and it would get to orbit.

Maybe it could even get to orbit easily.  You wouldn't even have to get to hypersonic speed for the release.  Just get above the atmosphere.  The reason being that the lower atmosphere gets in the way of efficient rocket performance.  You save a lot of mass by airlaunching.  Mass is your big enemy in a rocket design.

Take the Falcon 9.  The final payload of this rocket is only 2% of the "wet mass" on the launch pad.  If that's all you can get to orbit, it behooves us to use a lot less mass, don't you think?   Just getting to 30k feet as the Stratolaunch is slated to do actually saves a lot of weight.  If you got to 100k ft in altitude, it may make your engines almost as good as in a vacuum.  Your final wet mass for your rocket stage can be much less than a conventional setup.

Now, a 747 plane by itself can't do an airlaunch that good.  But a modified one with more powerful engines might.  Let's say an altitude of 100k feet would be high enough, and your rocket plane can get there.  What else do you need?

I figured an ISP of 427 for the LH2/LOX rocket would be enough performance.  If you could get to a high enough altitude in order to get an ISP of that much, then you would be able to get to orbit.  You could use J2X rocket engine or Aerospike engine.  Either one would be able to do it as long as you are far enough out of the atmosphere.

Note:  For the purposes of the discussion, I am adding 8500 lbs for a space capsule and 5000 lbs more for engines than the S4B (Saturn) used.  Also, I am adding 40% extra mass on top of the upgraded S4B's mass in order to  to make the rocket reusable.  You could add some wings, wheels, and a heat shield.  The assembly would sit on top of the rocket plane as the Shuttle did on a 747.  It would fly up to 100k feet then be released at a subsonic speed.  Also, if a 747 cannot do this, there would be a plane that could be designed that would.


What if you used rocket engines instead of 747 jet engines on a 747?  To put it another way, what if you replaced the jet engines with rocket engines?  The guys doing the Stratolaunch took the 747's engines and put them on their design.  What if you used the airframe instead, and not the engines?

The 747 uses 4 engines, which are rated at about roughly 50k lbf thrust each.  A single rocket engine will beat that.

But if you did a "clean sheet" design of such a plane, maybe you could make it go supersonic, or even hypersonic.  The point is to get a horizontal launch to horizontal landing capability with your airlauncher.

Another thought:  What if you put Spaceship One  on top of the stack instead of a Gemini capsule?  If launched without fuel, the spacecraft doesn't weigh all that much.  Even less than the Gemini.  What if you take the engines out and beefed it up a little and put a heat shield on it?  Could you get the mass down to a similar weight to a Gemini?  If so, it could land on a runway.  That's the point.

Update:

Did you ever wonder how much fuel it takes just to get to supersonic speed on a Falcon 9 launch?  It must be a lot because it took 1 minute and 10 seconds to reach supersonic speed according to the announcer in the cots resupply video on Wikipedia.

That's 70 seconds of all out thrust.  Lots of fuel going out there and lots more of it has to be used because of that fact.

If you just go supersonic to start with, you save a lot of fuel.

The point that I'm making is that you don't really want to launch at sea level with a vertical launch.  It guarantees a much bigger rocket.

Update:

Ninth post in this series is here.