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/

Such a great idea...

Such a great idea, yet even Estes doesn't seem to
want to build one. WTF?
In the 1997 Estes catalog there was a kit that never
reached production. It was a model of a fly-back booster
called Star Booster. It's based on descriptions in Buzz
Aldrin's sci-fi book; Encounter with Tiber. copyright 1996
Great book by the way. I dug it up for this post and then
read it all again.

In the book, the Star Booster is built by Boeing to take
a slide-in Zenit motor/tank assembly, built under license,
in the USA. One or two of them would be attached to a
core vehicle as a strap-on like an SRB is. After using up
it's propellants, the Star Booster would seperate from the
core vehicle then glides back to an automated runway
landing near the launch site. After each flight, the Zenit
is removed for seperate servicing. When the airframe is
ready, the next available Zenit gets installed for a quick
turn-around.
BTW; Boeing really is building licensed Zenits for the
Sea Launch commercial launch program.

The Estes Star Booster model was going to be 18" long,
with a 9.5" wingspan, parachute recovery, C motors only.
By the looks, I expected it to have a cast styrofoam
fuselage over a cardboard core tube, just like the large
Shuttle Orbiter kit of the same time period.

I've been looking at the Estes Star Booster recently  with
ideas for reproducing it. I have hot-wire foam cutting
equipment, so it's not a big stretch for me to model it at
the original size or larger.  The difficult part is that not
only do I want it to glide, I want it to glide with an unfair
chunk of reload casing inside it. In short, a realistic mission
as afly-back strap-on,  boosting a level 2 size rocket.  For
the sake of balance it needs a long thin motor case.  Either
a 29/360 or 38/480+ sized case, probably EX  and burning
sugar. The big trade-off [ya can't design anything without
trade-offs] is, to maintain balance, the bigger the  model,
the longer the motor case needs to be, and  vice-versa.   
Of course, it'll glide like a brick!

For more info see;  Fly-Back Boosters, Reprised
right here at ZZakk's Lab on Monday, May 18, 2009
These 2  posts [of 3 before long] were supposed to coincide
more closely, but I'm easily distracted.

Fly-Back Boosters, Reprised

Last week, the USAF released study information concerning
lower cost, shorter lead time, access to space. I think
it's funny that the USAF was studying similar proposals
back in 1988. Amongst more familiar designs were the first
drawings I'd seen of fly-back booster systems. They add
a lot to the liftoff weight, but reusability is greatly
enhanced by not dipping the booster in salt water, like the
shuttle strap-ons. Other typical features include motor
commonality, where possible, and limited reusability.
An example would be; useing the motor[s] X number of
times in the fly-back booster, then transferring them to
the disposable core stage[s] for one last trip.

I am by no means bitching. I like these systems. However
it is somewhat amusing how history repeats itself, only at
twice the price now. There are no technical hurdles to
overcome now, and there really weren't any then either.
The Air Force isn't asking for peak performance. Larger
base capacity makes up for moderate performance coupled
with higher reliability. The difference between pro-stock
class and top-fuel dragsters or funny cars at the drag strip.

The big difference between the old fly-back system and the
new, is that with the old, it was primarily a very heavy lift
system [105,000-160,000 LB/LEO], while the new approach
is part of a fully rounded low to heavy capacity [peak 64.000
Lb/LEO] program. I like modular systems, especially when
there are enough modules to fully utilize the concept.

Stay tuned for some modular space system gripes, coming soon.