Space Shuttle SSTO?
Ruediger Klaehn
Is there any chance of converting a Space Shuttle into a SSTO or perhaps
TSTO (first stage Boeing 747 or Antonov 124) with horizontal starting
and landing? With LH2 / LO2 Fuel you get an Exhaust velocity of about
4000 m/s and therefore a weight ratio of 7.3890 to 1 for 8000 m/s
orbital speed. (The value for the exhaust velocity for LH2/LO2 engines
is from some newsgroup and therefore probably very inaccurate! If
someone knows the real value, please tell me) If you want a real
horizontal starting SSTO Shuttle, you would have to use aerospike
engines, because they have a better efficiency at high ambient
pressures, and a horizontally starting shuttle would spend quite a lot
of time in the lower atmosphere. So one would have to reduce the
unfueled weight of the shuttle to 1/7 of the fueled weight.(with a large
transportation aircraft as Stage One, you could get a higher starting
location (less air resistance), a small delta v (about 300 m/s) and a
good starting location (equator), so you could perhaps do with a weight
ratio of about 6. Perhaps this value can be achieved by converting the
Shuttle into an unmanned vehicle and therefore getting rid of the life
support systems. Because horizontal takeoff requires less g's than
vertical takeoff, one could perhaps use only one or two SSME's. If this
weight fraction cannot be achieved (does not sound too difficult to me),
One could use a nuclear engine. These have an exhaust velocity of about
8500 m/s with LH2 and therefore would require a weight ratio of 2.553.
This could certainly be done, but there would probably be some trouble
with greenpeace. Equipping a shuttle with nuclear engines would probably
be cheaper than developing a completely new SSTO based on LH2/LO2,
because most of the research has already been done in the 60s (Rover).
It would certainly be much cooler!
Ruediger Klaehn
Ken Hayashida
>Is there any chance of converting a Space Shuttle into a SSTO or perhaps
>TSTO (first stage Boeing 747 or Antonov 124) with horizontal starting
>and landing? With LH2 / LO2 Fuel you get an Exhaust velocity of about
Well, the original drawings for STS was a TSTO vehicle with a liquid
fueled, flyback booster derived from the first stage of the Saturn V.
This was a verticle takeoff system though.
But, my view is that you'd need big modifications of the airframe,
TPS, and cargo bay to support a mission profile as you are suggesting.
later he writes:
>pressures, and a horizontally starting shuttle would spend quite a lot
>of time in the lower atmosphere.
Hence, you'd need better thermal management because as you pancake
through the atmosphere at higher and higher velocities you put higher
and higher thermal loads on the vehicle.
>ratio of about 6. Perhaps this value can be achieved by converting the
>Shuttle into an unmanned vehicle and therefore getting rid of the life
>support systems.
This starts to sound like a reusable Pegasus launch vehicle. The
Pegasus is launched from a B-52 or 747 (?) and can inject payloads
into orbit.
I guess the real issue is why would you take these steps?
Henry Spencer
>Is there any chance of converting a Space Shuttle into a SSTO or perhaps
>TSTO (first stage Boeing 747 or Antonov 124) with horizontal starting
No.
Doing SSTO with horizontal takeoff and landing is virtually impossible
without some kind of cheating. The landing gear -- well, more precisely,
the takeoff gear -- is too heavy. Boeing spent years, and a lot of money,
studying the possibility, and concluded that there was just no way to do
it without some sort of fudging like sled launch. (They *did* conclude
that if you were willing to use sled launch, it could be done.) Moreover,
starting with the shuttle orbiter wouldn't be much better than starting
from scratch, and might even be worse -- the current orbiter design is
totally unsuited to this application.
As for air launch, the shuttle orbiter is much too heavy for air launch by
any existing aircraft (bearing in mind that it needs a large external tank
accompanying it, to supply fuel). This approach is workable, but only for
considerably smaller vehicles.
>With LH2 / LO2 Fuel you get an Exhaust velocity of about
>4000 m/s and therefore a weight ratio of 7.3890 to 1 for 8000 m/s
>orbital speed...
Actually, good LH2/LOX engines get 4400 m/s or thereabouts, although you
have to specify whether you are talking about sea-level or vacuum
performance. (A rocket SSTO does most of its accelerating in vacuum, but
the time spent within the atmosphere is not negligible.) However, you need
something like 9100 m/s total to reach orbit, because you lose some to air
drag and gravity losses. Wings help with gravity losses but add drag and
structural mass.
>One could use a nuclear engine. These have an exhaust velocity of about
>8500 m/s with LH2 and therefore would require a weight ratio of 2.553.
Unfortunately, there are a few problems here. There is some release of
fission products in the exhaust, which is considered unacceptable for
operation within the atmosphere nowadays. The tested nuclear-engine
designs have relatively low thrusts, and clustering them is tricky (the
reactors interact via neutrons). And to cap it off, the mass you've
gotten rid of is LOX, which is cheap, compact, and easy to deal with.
You actually need *more* LH2, which is horrendously bulky and makes it
relatively difficult to achieve good mass ratios.
>...Equipping a shuttle with nuclear engines would probably
>be cheaper than developing a completely new SSTO based on LH2/LO2,
>because most of the research has already been done in the 60s (Rover).
The research needed for LH2/LOX SSTOs has already been done. In 1982,
Boeing quoted the USAF a firm fixed price of $1.4 billion to develop a
sled-launched HTHL SSTO. Boeing does not quote fixed prices on advanced
development projects very often; they were awful damn confident that they
could do it.
I believe the SEI people were estimating more than that -- admittedly
in somewhat later dollars -- just to get operational nuclear engines,
never mind vehicles using them. It's harder than it looks; for example,
it is no longer considered acceptable to just vent the exhaust from test
engines to the atmosphere, and a scrubber system capable of handling the
exhaust from a large rocket engine is a major project in itself.
--
The Earth is our mother. | Henry Spencer
Our nine months are up... | he...@zoo.toronto.edu
Mark Grant
>Doing SSTO with horizontal takeoff and landing is virtually impossible
>without some kind of cheating. The landing gear -- well, more precisely,
>the takeoff gear -- is too heavy.
Alan Bond's Skylon design has a neat way of getting around this, though
it might count as cheating 8-)... AFAIR from his IAF paper, a very large
fraction of the mass of the landing gear is brake material to absorb the
heat generated by a last-minute abort on takeoff. So rather than using very
large brake pads, they're sized based on the landing requirements. The
vehicle also carries several tons of water which are used to cool the
brakes if it does have to abort on takeoff. Once it's at a safe altitude
and speed the water is just dumped overboard, and hence does not have to
be taken to orbit and back.
Even allowing for the partially air-breathing engines, I'm amazed by the
payload mass he's claiming for Skylon. It's something like 12 tons to LEO
with a launch mass of about 250 tons. Shame he (again AFAIR) claims it
will have a two week turnaround and require 200 people to process and
launch...
Mark
(Mark....@isltd.insignia.com)
Filip De Vos
: Ruediger Klaehn <st00...@hrz1.hrz.th-darmstadt.de> writes:
: >Is there any chance of converting a Space Shuttle into a SSTO or perhaps
: >TSTO (first stage Boeing 747 or Antonov 124) with horizontal starting
: Well, the original drawings for STS was a TSTO vehicle with a liquid
: fueled, flyback booster derived from the first stage of the Saturn V.
: This was a verticle takeoff system though.
No, that was only the third design. The original design for the Shuttle
called for two completely reusable Areo-spaceplanes: a Booster,
would carry the Orbiter piggy back.
First, it was thought that putting hydrogen tanks on board the
Orbiter would be too dangerous, so two external tanks were substituted.
The next phase was the combination of the two tanks into a single
hydrogen tank. Then came a proposal to replace the flyback booster
with a simpler design based on the Saturn V first stage.
This too was changed, to a design with two boosters flanking the ET.
In this desig, engines on the orbiter would fire at start too.
Finally, the liquid boosters were replaced with solids.
--
Filip De Vos "Flying the shuttle until 2030 assumes
that technology that doesn't work
fid...@eduserv.rug.ac.be particularly well now will work better
when it's 60 years old"
- Rich Kolker -