SpaceX Has A Pipedream

Spaceflight Now has a recent article [Reprinted from CBS Space] on SpaceX's vision of making their boosters reusable. The simulation video is sharp. The stated intention is for direct descent and landing under rocket thrust. Sounds simple enough on the face of it but I immediately saw some flaws in the plans.

First Stage; Slant range puts the booster a long way from the launch site and variable target orbits increase possible descent points over a large arc, typically well out over the Atlantic. The sheer height of the Falcon 9 booster makes me want to install much larger landing legs [and more of them]. This is why all flyback booster designs thusfar have wings, wheeled landing gear and sometimes jet engines.

Second stage, This might actually be a bit easier than the first stage. Because the 2nd stage is itself orbital [or nearly so], one can pick the reentry point and bring it down where desired. A reentry heat shield adds a lot of weight though. At least 2 motor restarts are needed, but restarts are not that uncommon here. Need a lot of spare fuel for both the deorbit and the landing. Second stage motor nozzles are typically optimized for high altitude/vacuum operations and will be inefficient back at sea level.
I believe it was NRL that was ground testing a booster 20 or so years ago that was low-pressure [no turbo pumps] and had a variable expansion thrust bell, kinda like the "turkey feathers" on a fighter jet engine nozzle. This allowed inflight expansion ratio optimization for any altitude.

Capsule and boosters are shown returning on thrust alone. Even with thrust for landing, parachute systems would still be more economical and probably lighter for slowing and stabilizing the vehicles in an upright position instead of relying on attitude thrusters and the mains alone. Parachutes would also add some safety in case of motor failure, or at least reduce the splat.

>>>>>>
"We'll see if this works," Musk said. "But it's going to be certainly an exciting journey. And if it does work, it'll be pretty huge. If you look at the cost of a Falcon 9 ... it's about $50 (million) to $60 million. But the cost of the fuel and oxygen and so forth is only about $200,000. So obviously, if we can reuse the rocket, say, a thousand times, then that would make the capital cost of the rocket for launch only about $50,000. ... It would allow about a hundred-fold reduction in launch costs."
<<<<<<

Was Mr Musk reading that off a script???
Nobody's gonna get 1000 uses out of any booster, even if there is that large a backlog of flight contracts. Divide flight contracts by; payload production rates, vehicle refurbishment rate, available ground support, optimal launch windows... I'm sorry but I would've scoffed at 100 flights per booster. How about 10 flights each on a 5-10 booster fleet. By then; if the economics are sound, you'll be building a few replacements and/or an improved new fleet anyway.
Note that Elon says a 1000 fold reduction in booster cost relates to only a 100 fold reduction in overall launch costs. That sounds reasonable as other costs go up drastically. Additional flight systems complication, booster retransport, refurbishment, range comm/nav systems, additional facilities...manpower, manpower, manpower.

I have great respect for SpaceX and what they have accomplished. In fact I'd like to work for them, and I can't say that about most of the aerospace industry or NASA itself.

http://spaceflightnow.com/news/n1109/30spacexflyback/

Reinventing The Wheel

There's a great little article in the March '09
Air & Space magazine called; Hot Commodity
printed in the recurring section called; In the
Nuseum. I was able to access the photo online,
but not the text. Good luck if you can.
www.airspacemag.com

The NASA and contractor engineers charged with
designing the heat shield for the new NASA Orion
crew capsule found they had a problem. AVCO, the
contractor that made the original Apollo heat
shields was long gone, along with all their files.
Meanwhile, all the existing capsules are on display
and off-limits. Look but don't touch. OFFICIAL
National Treasures. I like that. It was looking
like they'd have to reinvent this wheel from scratch
though.

The right question in the right ear led to the Paul
E. Garber storage facility, owned by the National
Air & Space Museum. It's a really cool warehouse
packed with the greatest stuff. They had 5 crates
of new and used heatshield parts and samples tucked
away. The story goes on to say that the gathering
of happy scientists looked like kids on christmas
morning. Current ideas verified, impressive old
materials tech, fastening methods revealed...
A happy story as far as it goes.

I really don't mind that NASA is engaged in retro
rocket science, if it were up to me, they'd be
resurrecting the entire Saturn lift capability.
I just hope I'm not there, years from now, when
NASA is trying to relearn how to build and fly a
spaceplane.

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