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The Air Force is looking for designs for reusable first stage boosters for two-stage-to-orbit >(TSTO) systems. Then it might be able to be used for this purpose. Most likely you would use >kerosene fuel for this since dense fuels are more suitable for first stages.
NK-33.
http://www.astronautix.com/engines/nk33.htm
Atlantis.
http://www.astronautix.com/craft/atlantis.htm
Lox/Kerosene.
http://www.astronautix.com/props/loxosene.htm
and the oxidizer to fuel ratio of the NK-33 of 2.8 to 1 we can calculate the propellant load that >can be carried as about 300,000 kg. You would need at least 3 of the NK-33's to lift this fuel >load, orbiter and second stage.
The tank weight of kerosene/lox is typically around 1/100th of the propellant weight so around, >3,000 kg. Then the empty weight of the reconfigured orbiter would be 68,600kg + 3*1,222kg + >3,000kg = 75,266kg. And the fully fueled weight of this stage would be 375,266kg.
I mentioned before converting the space shuttle orbiter into a first
stage use would actually be quite important. I discuss this below.
I.)Weight savings by removing unneeded components.
II.)Replacement of the Ares I first stage by the reconfigured shuttle.
III.)Costs saving by private commercial financing rather than "cost-
plus" contracts.
I.) I wanted to get some shuttle component weights to estimate the
weight savings we could make by removing systems that would not be
needed for a suborbital or first stage use. The Astronautix page on
the Shuttle Atlantis gives its "Heat Shield Mass" as 12,100 kg (26,600
lb).
However, Astronautix is sometimes inaccurate. So I found this report
after a web search:
Thermal Protection System Sizing and Selection for RLVs Using the
Sentry Code.
http://www.sei.aero/eng/papers/uploads/archive/AIAA-2006-4605.pdf
It gives on page p. 11 a weight of 17,910 lbs for the thermal
protection tiles and panels but notes other hardware for the TPS
amounts to 4,600 lbs. for a total of 22,510 lbs., 10,232 kg. I'll use
this value for the shuttle TPS.
I've been informed by someone who did a study for the Air Force's
"Reusable Booster System" program that for first stage use at low
hypersonic speeds an aluminum frame would require minimal thermal
protection. See the slides from pages 5 and 7 of this report on the
Air Force's RBS program:
Spacelift Development Plan.
http://www.acq.osd.mil/nsso/conference/briefs/HampstenSDP%20Public%20Release.ppt
So I'll subtract off the 10,232 kg TPS weight from the 75,266 kg dry
weight I got for a reconfigured orbiter, to get a 65,034 kg dry
weight.
This NASA page says a saved weight of 450 lbs off the OMS system
amounted to 10% of its weight:
OMS/RCS PODS.
http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/sts_coord.html#sts_oms_pods
So I'll remove the OMS system to save 4500 lbs, 2,000 kg, bringing
the dry weight now to 63,035 kg.
This page gives the left payload bay door weight as 2,375 lbs. and
the right as 2,535 lbs., and both doors containing radiator systems at
an additional weight of 833 lbs each:
PAYLOAD BAY DOORS.
http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/stsref-toc.html#payload_bay_doors
These won't be needed so removing these would save 6,576 lbs, 2,990
kg, bringing the dry weight to 60,000 kg.
The Buran showed it's possible for the shuttle to have a completely
automated ascent and descent, so I'll remove the life support
components from the mass to use the orbiter as an unmanned first
stage. For lack of any other reference on the mass of these components
I'll subtract off the numbers given on the Astronautix Atlantis page
of "Crew Seats and Provisions" as 750 kg and "Environmental Control
System" as 2,500 kg, for a total saving of 3,250 kg, bringing the dry
weight to 56,750 kg.
Probably the fuel cells and the tanks to hold the on board LOX and
LH2 for the fuel cells could be removed, since as a first stage its
flight would only last minutes rather than the days of a manned
orbiter flight. For such short flights, lightweight batteries or
electrical generators powered by the engines would suffice. This page
gives the fuel cell's oxygen tank weight as 201 lbs. and the hydrogen
tank weight as 216, and says there are a maximum of 5 pairs of tanks:
POWER REACTANT STORAGE AND DISTRIBUTION.
http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/sts-eps.html#sts-eps-prsd
I'll take the total fuel cell's tank weight as 2,085 lbs, 948 kg.
There are three fuel cells each weighing about 120 kg, for a total of
360 kg. So I'll subtract off 1,308 kg from the dry weight to bring it
to 55,442 kg.
II.) The manned space program is in a quandary now because of the
ballooning costs overruns on the Ares I system that was supposed to
act as the next manned transportation system. The primary difficulty
was the Ares I first stage boosters. Originally the development cost
was set at $1.8 billion dollars, though fixes to for example the
excessive vibration generated undoubtedly has increased that cost:
Aug. 10, 2007
NASA Awards First Stage Contract for Ares Rockets.
"WASHINGTON - NASA has signed a $1.8 billion contract with Alliant
Techsystems, known as ATK, located near Brigham City, Utah, for the
design, development, testing, and evaluation of the first stage of
the
Ares I and Ares V launch vehicles."
http://www.nasa.gov/home/hqnews/2007/aug/HQ_C07036_Ares_first_stage.html
Moreover, weight growth and a short fall in the delta-V delivered by
this first stage drove costly adjustments of the upper stage as well.
My point is adapting the shuttle or the Buran for first stage use
would vastly reduce the cost for a first stage. You would have then
several options for manned flight all of which would be cheaper than
using the Ares I first stage solid motors and all of which would allow
a return to space at a faster time scale than the original Ares I
plan.
I'll give a calculation that you could still carry the planned upper
stage and payload of the Ares I with the reconfigured shuttle as first
stage. This page gives the specifications of the Ares I:
Space Launch Report - Ares I.
http://www.spacelaunchreport.com/ares1.html
The gross weight including payload is given as 912,660 kg and the
gross weight of the first stage as 732,550 kg. So the gross weight of
the Ares I second stage plus payload is 180,110 kg.
Then the gross weight for the 55,442 kg dry weight of the
reconfigured shuttle, plus 300,000 kg propellant load, plus 180,110 kg
second stage and payload is 535,552 kg, 1,178,214 lbs. But the 3 NK-33
engines I was suggesting to use only put out a total of 1,018,518 lbs.
of thrust at sea level. For this purpose you would need a fourth
NK-33. The dry weight is now 56,664, the gross weight is 536,774 kg,
1,180,903 lbs., and the sea level thrust of the 4 engines is 1,358,024
lbs.
Using the average Isp of the NK-33 as the midpoint of the sea level
and vacuum Isp's at 315 s, the achieved delta-V would be 315*9.8*ln
(536,774/(56,664+180,110)) = 2,527 m/s, comparable to the equivalent
delta-V, speed + altitude, provided by the Ares I first stage. The
achieved delta-V is actually higher than this since the rocket spends
most of the time at high altitude, where the Isp is closer to the
vacuum value.
Note that if you want to increase the delta-V, the space occupied by
the crew compartment is now empty. This gives an additional 74 cubic
meters that could be used for propellant, which amounts to 74,000 kg
additional lox/kerosene propellant that could be carried.
Then we could still use the planned upper stage of the Ares I while
having a significantly lower development cost and per launch cost of
the now reusable first stage. Still the time when we could reach
flight status would be dependent on the development of the upper
stage. However, we don't need to use the large Ares I upper stage and
Orion capsule if we just want manned flight. I'll show in a following
post we could get a smaller and reusable manned upper stage at a much
lower cost also than the Ares I upper stage and Orion capsule, that
will also allow a much quicker return to manned flight.
III.) I wish also to argue however that for these methods, for the
reconfigured shuttle/Buran first stage and smaller reusable manned
upper stage, we don't want to use the standard procurement methods
with the "Old Space" aerospace companies. Robert Zubrin has some
insightful observations about the "cost-plus" government contracts
that the large aerospace companies get in his book, [u]Entering Space:
Creating a Spacefaring Civilization[/u].
In the chapter, "The Age of the Dinosaurs" referring to the "Old
Space" companies, he first comments that high launch costs drive the
tendency to make satellites be highly reliable which drives the cost
for the satellite higher. And conversely if your satellite is already
very expensive, say a $1 billion Air Force satellite, then there is
little incentive to reduce launch costs since at that satellite price
a launch cost of $100 million or zero makes little difference.
Then Zubrin says:
"Beyond these considerations stands the government contracting system
known as "cost plus," which has been in place for some time now in the
United States. According to the people who invented this system, it is
essential that corporations be prevented from earning excessive
profits on government contracts. Therefore, rather than negotiate a
fixed price for a piece of hardware and allow the company to make a
large profit or loss on the job depending on what its internal costs
might be, regulators have demanded that the company document its
internal costs in detail and then be allowed to charge a small fixed
percentage fee (generally in the 10 percent range) above those costs
as profit. This system has served to multiply the costs of government
contracting tremendously, so much so that it has produced public
scandals when news leaks out about the military paying $700 for a
hammer or a toilet seat cover."
[u]Entering Space[/u], by Robert Zubrin, p. 24.
Then I'm suggesting that the "New Space" companies rather than going
through the usual "cost-plus" financing from the government could
purchase a shuttle/Buran on their own and develop the manned reusable
upper stage on their own with the idea of making a profit. I'm arguing
the development cost of this reconfigured first stage and the small
upper stage would be so low that this can be profitable both for
satellite launch and for now fully orbital space tourism.
Bob Clark
