On Nov 19, 2009, at 11:15 AM, Andrew Crystall wrote:
On 19 Nov 2009 at 8:19, Bruce Bostwick wrote:
Oh, and while we're talking about STS .. why is it, exactly, that
NASA
has been dropping all of those ET's back into the atmosphere to burn
up, after spending the $10k/pound to get them up there, and not
saving
them on-orbit as construction material?
One of my my *major* bugbears with the way the entire program's been
run, actually. They've hauled up the ISS *inside* the shuttle. I have
yet to hear any convincing explination either.
For reference, the volume of the ET's LOX tank alone is very roughly
3500m^3. The current ISS habitable volume is 358m^3.
Exactly. Why waste all that material if you *have it in orbit with
you*? All they'd have to do is delay releasing the tank until after
the OMS burns, and maybe compensate for the change in thrustline with
some RCS torque if they can't gimbal the OMS engines. At most, they'd
have to bolt an auxiliary propulsion module on it with enough delta-V
to get it to a storage orbit. Trivial, given that the cost of getting
it up to transfer orbit has already been paid.
That being said, what I really wish someone would propose is sending a
robot propulsion/navigation system out to a conveniently sized nickel/
iron asteroid, bring it home, and park it in an orbit high enough to
keep it from decaying for the foreseeable future (and any orbit with a
perigee higher than a few hundred miles qualifies for that),
preferably one that doesn't spend too much time in the van Allen
belts, and set up an automated smelter, foundry, and mill on/in it
that can build structural components on-orbit, without ever having to
lift them up from earth. And, if there's a surplus, make periodic
drops to the surface.
Did I mention that steel parts made in a vacuum are incredibly strong,
mainly because they don't have any of the oxide inclusions and other
contaminants that are unavoidable in the same parts made in an air
atmosphere? ;)
*That* would be a good application for VASIMR and other high-
efficiency engine technologies ..
The stack geometry of the STS is one of the most insane
things I've ever seen, and I'm quite frankly impressed that they've
only had two LOV/C's and not many more, especially in the pre-51L
days.
I'm not convinced that for carrying Humans, Ares is going to be much
safer. Yes, I've heard the arguments. Still not entirely convinced,
and it's still an extremely expensive launch vehicle - for the price,
they'd be better just using proven Russian lifters.
There's still the question of transporting hardware to the launch
site, which if we were using Russian launch systems would involve
either shipping all that hardware to Baikonur (and a greatly expanded
fleet of Super Guppies and all the infrastructure to support them), or
setting Canaveral up to launch Protons, which would involve shipping
them here and building an entire new pad structure (and possibly major
modifications to the VAB high bays) and fitting out MLP's to support
them. And building a UDMH/N2O4 infrastructure at the new pad, to
boot. Nasty stuff, those two. Worth taking the tour of the Titan II
Museum in AZ to hear just how nasty.
[And the Russian systems haven't always been all that safe. There's a
blast scar at Baikonur, from an N-1 crash in the 60's that pretty much
wrecked all the pad infrastructure they had at the time, that was
clearly visible from orbit for at least 20 years. (That was from the
one that shut down all but one of its first stages a couple of hundred
feet up, and fell back onto the pad. The blast from it had enough of
an overpressure to flatten all the surrounding buildings and buckle
the tanks on the one remaining N-1 that hadn't been launched yet.
Which is why the USSR never landed on the moon.) The Protons are a
much more mature system, especially now, granted, but a lot of the
legacy systems were USSR-built and .. well, let's just say they cut a
few corners here and there.]
And you know what? If you come up with a propulsion system that's
more efficient than binary-fuel combustion from onboard fuel and
oxidizer,
Well - I'm sure you're aware that SpaceShipOne sucessfully used a
N2O/HTPB Hybrid rocket engine. And I'm with Pournelle's contention
that if you gave Rutan a billion, he'd have a working reuseable
Spaceplane which could reach a reasonable orbit inside three years.
(And honestly, he could of done so for at least a decade).
Pournelle is probably just about right, there.
It all comes down to a) developing enough thrust (and/or lift) to get
out of the part of the atmosphere where you're having to expend most
of your energy pushing air out of the way (one reason RP1/LOX worked
so much better for first stages early on), and b) putting in enough
deltaa-V, fast enough, to get to a high enough apogee to be able to
burn one last time to bring the perigee up above drag altitude. What
Rutan did come up with is actually very close to the concept I had in
mind -- carry the ship up to high stratospheric altitudes at
relatively high airspeed with turbojets (Isp = about 3000 s), maybe
boosting thrust at high altitude with MIPCC, and then launch it using
a rocket (Isp = 300-500 s depending on chemistry).
"When you mention that we want five debates, say what they are: one on
the economy, one on foreign policy, with another on global threats and
national security, one on the environment, and one on strengthening
family life, which would include health care, education, and
retirement. I also think there should be one on parts of speech and
sentence structure. And one on fractions." -- Toby Ziegler
_______________________________________________
http://mccmedia.com/mailman/listinfo/brin-l_mccmedia.com
