Disclaimer 1: These are my personal opinions. I emphatically do NOT
speak for my employer (who probably wishes to remain anonymous--I haven't
asked) or for anyone else, real or ficticious, living or long since dead;
human, cetacean, or space alien; animal, vegetable, mineral or ethereal.
Disclaimer 2: I'm an aerospace stress analyst, not an economist or
accountant. Take what I say about cost estimation with a grain of salt.
Peter A. Taylor
Why do space launches cost so much? Specifically, why are the costs so far
out of line with the cost of seemingly comparable airplane operations? Fuel
is about 15% of the operations and maintenance (O&M;) cost of a typical
military airplane, and 38% for commercial aircraft, according to Aircraft
Design: A Conceptual Approach, 1992, by Daniel P. Raymer. Space launches
should be more energy intensive than airplane flights, so one would expect
that propellants would be a larger fraction of the total operations cost for a
launch industry that was as mature as the airline industry. Why are the
non-fuel costs orders of magnitude higher for rockets?
If you don't think the question is important, please take a look at the
Where (in space) do we go from here? or Why do we have a manned space
program? Specifically, I refer you to the discussion towards the bottom,
of the economics of an Aerobraking Orbit Transfer Vehicle (AOTV, a "space
tug"). I worked on this project, and thinking about it got me seriously upset
about the economics of the manned space program in general, and launch
vehicles in particular.
Why are space launches so expensive? I present here a list of answers I
have heard. I will discuss each of these in turn. At the end I offer my own
18 Candidate Explanations for High Launch Costs:
- # "It just does!"
- # Propellant costs.
- # "Energy costs."
- # Lack of reusability.
- # Lack of full reusability.
- # Conflicting vehicle requirements.
- # Learning curve; not enough generations of launch
- # Lack of adequate investment (solid boosters for
- # Politics I: Parasite control.
- # Politics II: Obstructionism.
- # Lack of technology I: Dry weight too high.
- # Lack of technology II: "Complexity" of multiple
stages (need SSTO).
- # Living on the edge.
- # "Ground handling and launch operations" (need
"ship and shoot" payloads).
- # Lack of intact abort capability.
- # Critical differences between rockets and
airplanes (ie. thermal problems).
- # Lack of a clear sense of direction.
- # Economies of scale.
This is not an answer. It is the stuff of which light bulb jokes are made.
It suggests that the launch industry is very mature and that no further
significant improvements are possible, which is highly implausible based on
the airplane analogy. Instead of dealing with the problem of high launch
costs, we are urged to just throw money at it and go on to other things.
Unfortunately, at current launch prices, it is hard to identify many "other
things" that are worth what they cost. Under the circumstances, I find this
sort of complacency very hard to understand.
- "It just does!"
This is silly. If it takes 100 lbs of kerosene and LOX to put a pound of
payload in orbit, with propellants on the order of $0.20/lb, this only
accounts for $20/lb. of payload, out of something like $5,000-10,000/lb. That
was the way I initially thought about the cost of the space program when I was
10 years old, so I tend to describe this as a ten-year old's view of launch
- Propellant costs.
If "energy costs" refers to the cost of energy, $/lb., all of the energy in
question comes from the chemical energy stored in the propellants, which we
have just shown is not a significant cost factor. But if "energy costs" means
energy requirements, in BTUs/lb., then how does this relate to dollars? Am I
twice as dead if I fly into the side of a mountain at 2000 mph as I am at 1000
mph? Do I need twice as many pilots if my spacecraft is flying twice as fast?
The "energy cost" doctrine depends for 99.6% of its plausibility on the
belief that labor costs are an extremely strong function of energy
requirements. But where is the basis for this belief? I have never heard of
anyone even trying to make a quantitative estimate of how labor relates to
energy. This "answer" is a cop-out. It sounds well grounded in
physics, and conveniently deflects criticism of NASA. It presents the cause
of high launch cost problem as being fundamentally unsolvable, and hence not
worthy of further serious attention. This line of reasoning is often used as
an argument for building a base on the Moon, where the "energy cost" in BTUs
per lb. of a space launch is lower, but where the man-hours of skilled labor
that account for the remaining 99.6% of Terrestrial launch costs will be
astronomically more expensive for the forseeable future. Perhaps launching
things from the Moon will be cheaper than from the Earth some day, but if so,
it is likely to have more to do with the Moon not having an atmosphere than
because of energy. In short, the "energy cost" explanation is an evasion. It
doesn't tell me anything about money. Why does orbital speed cost so much?
"Energy costs" doesn't answer the question unless we understand it in such a
way that it is blatantly false. We are back to "It just does!"
- "Energy costs."
This is much better than #2. Propellants may only cost a few cents per
pound, but aircraft typically cost between $150 and $300 per pound (Raymer).
If rockets are like very expensive airplanes, are expendable, and weigh empty
several times what the payload weighs, it is easy to see how a launch could
cost thousands of dollars per pound of payload. This was a plausible
explanation for high launch costs until the Shuttle was built, and may still
be plausible for many expendable vehicles.
- Lack of reusability.
This is an attempt to modify #4 to make sense in the light of Shuttle
experience. If the Shuttle External Tank (ET) costs $350 per pound (that
figure was from the early '80s), and weighs more than the payload, that
explains a significant fraction of the Shuttle's cost. But it is possible to
build cheap cryogenic tankage, depending on how it fits in with the rest of
the vehicle and how desperately critical the weight is. The liquid natural
gas tanks used in LNG tankers cost something like $5 per pound (early '80s
numbers), and the Atlas rocket propellant tanks cost $80 per pound (early
'80s). There is surely some truth to explanations 4 and 5, but not enough to
dismiss expendable concepts like the Big Dumb Booster and partially expendable
"drop tank" concepts out of hand.
- Lack of full reusability.
Max Faget originally wanted a Shuttle with a 10,000 lb. payload capacity and
minimal cross-range. The Air Force wanted 65,000 lbs. and large cross-range.
It was supposed to carry stuff to a space station, then it was supposed
to perform in lieu of a space station, and now it is carrying stuff
to a space station. It was required to carry large, heavy cargo and a
full load of people at the same time, safe enough for school teachers, and
carry stuff both up and down. It was supposed to be inexpensive to develop
and to operate, with the peak funding kept low. Now no one is happy.
- Conflicting requirements: "Jack of
all trades" philosophy.
The idea here is that even if airplanes and rockets are similarly
complicated, we are a whole lot better at building and flying airplanes
because we have designed, built, flown, and crashed a whole lot more of them.
This explains why the airplane fuel cost analogy doesn't apply to rockets. It
also suggests a solution: build lots of cheap X-vehicles, build small
launchers that fly often, and figure on spending lots of money on refining
many little design details over many years, in small steps.
Implicit in one version of this theory is a belief that rockets are
complicated not because of any one reason, but because of a myriad of little
details that have to be gotten right. Consequently, there is little hope for
major cost breakthroughs. Another consequence is that the cost entries on a
launch vehicle's balance sheet should be taken pretty much at face value;
there is little point in trying to "read between the lines."
A more optimistic version of this theory is that we need more diversity in our
X-vehicles more than we need large numbers of them, and there is hope for a
- Learning curve: not enough
generations of launch vehicles.
Raymer reports (p. 502) that aircraft manufacturing man-hours typically
follow learning curves between 75% and 80%. That is, doubling the number of a
particular type of aircraft built reduces the time spent on the last one to
80% of the previous time. Although these curves are meant to apply to the
construction of particular types of aircraft, one might hope that the state of
the art of operating space launchers in general would improve with experience
in an analogous way.
However, #John London (Reducing Space Mission
Cost, Wertz and Larson, Figure 4-1, Historical Trends
in Space Launch Costs) indicates that, while there was rapid progress
in reducing launch costs in the late 50s and early 60s, since 1970 the
costs have been roughly constant, between 40 and 100 man-years per ton of
payload, depending largely on vehicle size.
There may be a "chicken and egg" problem in the space launch business.
It may not be possible to amortize the investment needed to build a
dramatically cheaper launch vehicle without an enormous increase in the
size of the launch services market. And a dramatic increase in the size
of this market may not appear until decades after the prices have dropped
by an order of magnitude. If this is true, a large investment may be
required to lower costs dramatically, probably at public expense.
However, this does not mean that you can solve
an inefficiency problem by throwing money at it blindly--you might just
make things worse. How would you spend the money? There is no shortage
of launch vehicle technology "gimmicks" that would be expensive to
develop (ie. #Single Stage To Orbit), but there seems
to me to be a severe shortage of reasons for
believing that most of these gimmicks would lower costs rather than raise
costs, let alone that they would lower costs substantially.
- Lack of adequate investment.
The Shuttle was designed to use solid boosters and an expendable ET to
minimize development cost, partly at the expense of operating cost. But
current studies claim that switching to a liquid flyback booster can't be
justified based on economics, but rather improved safety. If more money
had been spent on developing the Shuttle, would that have made it an
economic success, or just a more expensive flop? Until we have a
convincing answer to the question, "How would you spend the money?" the
lack of adequate investment is not a sufficient explanation.
There is no question that the space program has what
calls a "parasite control" problem, too many people whose services are not
really required trying to use it as their meal ticket, and a political system
that prizes their votes and responds to their lobbying. But we are not trying
to explain why rocket costs are a little bit out of line with airplane costs,
we are trying to explain why they are two orders of magnitude out of line.
Does poor parasite control explain this big a discrepancy?
- Politics I: Parasite control.
I don't think it does. Political scientist John Ambler has argued that
popular democratic governments can do things efficiently if
there is sufficient political will, and as an example invoked an oil company
that was owned by the French government and operated very profitably under a
Socialist administration, which viewed it as an important milk cow needed to
support its social programs (a lecture I heard). The space program currently
has no such political will. NASA hasn't had a clear sense of direction since
Economist David Friedman suggests
(Machinery of Freedom) that functions that are performed by government
agencies typically cost a factor of two more than they cost in free markets.
Friedman is a self-described libertarian anarchist, so this figure is surely
not biased in favor of big government. Physicist Freeman Dyson (Infinite
in All Directions) suggests that the politically driven waste in
scientific programs depends in a strongly nonlinear way on the size of the
program. But I am still thinking, "factor of 2," not "200."
Let's distinguish between development and operations costs (If we can! I
have been told by an ex-boss whom I respect a great deal that the main reason
the Shuttle is so expensive is that NASA refuses to "put the pencil down," and
keeps adding or changing the requirements.). Our objective is to get the
"marginal" cost of payload in LEO (the cost of the last little bit) down to
where interesting things will happen. At that point, the development cost is
a sunk cost, so even if the development cost was regrettably high, it is too
late to back out, and so interesting things will still happen. If parasites
double our operations costs, that means we don't achieve our objective,
whereas if they double the development cost, we still get interesting things
to happen; it just takes longer and costs more, as long as we keep working on
it. So I want to focus on operations cost, and look at development parasites
only if they threaten to create problems like conflicting requirements or
inappropriate technology that will have serious operational repercussions. If
the X-33 program is mostly waste, it is an infuriating setback, but it doesn't
by itself explain why the Shuttle costs so much. On the other hand, the Space
Shuttle Main Engine (SSME) is an example where Max Faget said we needed a
"truck engine" but we got a "race car" engine instead that is very expensive
to operate. This can reasonably be attributed to parasites.
Now let's look at competition. In a free market, if there are nine
organizations with severe parasite problems and one without, I expect the
parasite-infested organizations to soon change or go out of business. I
imagine "soon" here as being on the order of a decade. Does this line of
reasoning put an upper bound on the seriousness of the parasite problem? I
think it does, at least for expendables. The launch industry is very
fragmented and political, but I think there is enough competition, both
domestic and international, that it would be clear if there were any
organization that was head and shoulders above the others in efficiency. The
Russians look good right now from a cost standpoint, but this is partly an
artifact of the state of their economy. Ariane, Sea Launch, etc. are not that
much cheaper than Atlas and Titan. Many of the organizations involved,
Boeing, Lockheed, McDonnel Douglas, etc., are quite competant at building both
economical airliners and a wide variety of sophisticated expendable military
missiles. It is not plausible that all launch vehicle operators throughout
the world should be roughly equally infested with an anomolously high level of
I note that none of the players in this market have particularly enviable
records for reliability right now. Russia has dropped Protons on Kazakstan,
Japan has given up on their H-2, Ariane is recovering from some recent
failures, and it wasn't long ago that a $1B US spy satellite was lost on a
Titan. It appears to me that the industry is at least somewhat competitive,
and tries very hard to balance cost and reliability with expendables. If they
have a vehicle with higher than 95% reliability, they cut their staff, and if
reliability goes below 95%, they increase it. NASA is laughed at for having
so many people supporting Shuttle launches, but they operate manned vehicles
and need and get higher reliability, more like 99%. It appears that "the
devil's in the details," and no one seems to have any spectacular advantage at
being able to distinguish between "parasite control" (aka "better, faster,
cheaper") and "cutting corners."
This argument isn't as strong for reusable launch vehicles (RLVs), because
there is only one current example. But if a competant venture capitalist
could find a competant aerospace contractor who thought they could build an
RLV with operating costs that were in line with airline operations, what is to
stop them from going into the launch business? At worst, they might have to
go overseas, as Kistler (Australia), Beal (Sombrero Island), and Boeing (Sea
Launch) are doing to escape some of the politics in the US. In order to
explain high launch costs, the parasite control theory has to be combined with
theories 4 (lack of reusability) and 8 (lack of adequate investment), and
probably several others. It can at most be only one piece of the
I should elaborate on the point about combining with theory 8. It may be
that Boeing thinks they could develop an RLV with low operating costs, but
that (A) it would cost a huge amount of money, (B) it could only capture a
fraction of the total launch market, (C) the current market isn't all that
huge, (D) it would take a decade or more for the market to expand to take
advantage of low prices, (E) due to knowledge problems, the customers won't
commit themselves to making the investments needed to take advantage of
radically lower costs until after the prices have already fallen, (F) the
results are uncertain, and (G) the innovations that would make their vehicle
cheap would be easily observed and imitated. Factors E, F, and G suggest that
there is enough of a "public good" problem in developing an RLV that we
shouldn't be surprised if there is a "market failure." So this combination
theory says that only RLVs can be cheap, the free market won't build them
because of too large an element of public good, and governments don't build
them because of parasites. We should also be alert to the possibilities
that the customers are doing things that have a lot of public good in them,
like quasi-religious public entertainment and medical research that can't
easily be kept secret, or that the whole manned space program simply costs
more than it's worth. But it seems to me that in any case, the parasite
control theory by itself won't take us the whole way.
This theory is similar to the parasite control theory in that it doesn't do
a credible job of explaining why all launch vehicles are expensive, but it is
useful in explaining why there isn't more competition. My favorite version of
this is that there is someone in the State Department who really doesn't like
the idea of Bubba having his own ICBM, and is quietly but deliberately trying
to discourage anyone from building any launch vehicles that aren't firmly
controlled by the US government. There are certainly some turf battles
between various Federal agencies, and a lot of the usual attempts by the
relevant agencies to control everything they can without accepting any
responsibility for anything. Another effect is paranoia or at least posturing
about espionage or technology transfer. The resulting "red tape" certainly
exists and certainly discourages groups like Sea Launch. Some NASA and Air
Force officials undoubtedly regard private companies as unwanted and
potentially very embarrassing competitors, and the large aerospace companies
that are in the best position to develop launch vehicles privately are also
dependent on govenment contracts for enough of their income to be vulnerable
to blackmail, implicit or explicit.
- Politics II:
Then there is the phenomenon of "displacement," familiar to
conservative welfare reformers, wherein the existence of a government
agency that is supposed to fix some problem tends to discourage
volunteer efforts that would otherwise be working on the same problem.
For a long time before the Clementine mission, Alan Binder was trying to
raise money from private contributors and recruit workers for a volunteer
version of Lunar Prospector. After Clementine, he was successful at
getting government money. Before Clementine, when he approached
potential contributors, he reported that they often responded that this
was a great idea, but why isn't NASA doing it? I had heard libertarians
claim that because of displacement, NASA was, on net, doing more harm
than good, but I never took that claim seriously until I heard Binder
talk of this experience.
Addendum: Andrew Beal stated in his 10-23-2000 press release regarding
the Cease of Operations of Beal Aerospace, "There will never be a private
launch industry as long as NASA and the U.S. Government choose and
subsidize launch systems." However, I greet this announcement with a
certain degree of skepticism. Beal invested how many years and how many
millions of dollars in his launch company before discovering that the
U.S. Government was funding competing schemes? A co-worker of mine
suggests instead that he got egg on his face and is looking for a
Incidently, Max Faget complained about "pharisees" rigidly enforcing
rules about things like the use of flammable materials in spacecraft
without knowing why the rules were made, and when they can safely be
relaxed. #Sellers and Milton argue on p. 70 of
Reducing Space Mission Cost that too large a Quality Assurance
(QA) bureaucracy can actually reduce quality, and it certainly raises
costs. Political pressure after a high-profile failure such as the
Challenger accident may increase the amount of QA paperwork even if it is
already too high.
Again, like the parasite control theory, political obstruction may take us
part of the way towards explaining why rockets are two orders of magnitude
more expensive to operate than airplanes, but it doesn't take us the whole
Marshall Kaplan wrote a series of articles in Launchspace, starting in
April 1999, that take what I describe as the "orthodox" view in the
aerospace business that cost is largely a function of weight. Basically,
the aerospace companies and think tanks have empirical Cost Estimating
Relationships (CER) that relate cost to empty weight and various other
parameters. Most of what I know I learned from reading a chapter in
Aircraft Design: A Conceptual Approach, 1992, by Daniel P. Raymer.
There is a different curve for each different class of aircraft (flying
boats, fighters, military transports, etc.). Kaplan is mostly concerned
with private companies wanting to amortize development costs, whereas I'm
mostly interested in operating cost. But Raymer says on p. 512,
regarding maintenence man-hours per flight hour, "MMH/FH is roughly
proportional to weight because the parts count and systems complexity go
up with weight."
- Lack of technology I: Dry
weight too high. We should develop and use advanced technology and push
it to the limit to reduce the dry weight.
On one level, these CERs are purely empirical, and one could argue that
they do not depend on an underlying "story" in order to be valid. But I
am reminded of Stephen Landsberg's criticism of econometrics, that if you
don't understand the story behind the statistics, the fact that American
football teams are statistically likely to punt the ball on fourth down
would lead one to suggest that punting would be greatly reduced by
changing the rules so that there were only three downs per possession.
Also, even if these CERs give reasonable estimates for development costs
for something like a Space Shuttle, they still don't say why the
operations costs are so far out of line with airplanes.
Common sense tells us that cost is a function of weight, but it seems
to me that common sense is talking out of both sides of its mouth here.
Apart from having to buy more material, bigger cranes, etc. to build a
bigger airplane, there is an underlying assumption which Raymer
acknowledged that cost is driven largely by complexity, and that aircraft
of the same class and weight will have the same complexity. Also,
complexity goes up with weight--a machining operation to remove weight
from a 2" thick piece of aluminum is more likely to be worth while than
from a 1" thick piece.
But common sense also tells us that if you have a part with a certain
weight that does a certain job, and you decide retroactively that it
needs to weigh less, the cost will go up. Unless you did a bad job
trading off weight and cost in the first place, the reason the part
weighs as much as it does is probably because you thought it would be too
expensive to take any more weight out. But an inexperienced cost
estimator who doesn't have a firm grip on complexity may use the CERs to
predict that a development program will be cheaper if you make it more
technically challenging by lowering the allowable weight. Shortly after
the Challenger accident, I was at a meeting to discuss crew escape
systems where this seemed to happen, and I can only presume that the cost
guy was trying to make a point that he didn't have enough information to
answer the question he was being asked.
So complexity and cost increase with increasing weight except when they
increase with decreasing weight. I want to use this sort of insight in
order to compare the costs of reusables and expendables, and between such
things as thick-wall monocoque (simple shell) propellant tanks for
pressure-fed engines, thin-wall monocoque pressure stabilized tanks for
pump-fed engines, and stiffened thin-wall designs like the Shuttle ET.
Some people might suggest that dual-fuel engines would save weight and
therefore save money. My reaction is that, at least as far as operating
cost is concerned, I don't believe that an adequate data base exists to
tell me what I want to know, I don't understand what the CERs purport to
be telling me, and I don't think I would trust them even if I did
understand them. I don't have a good enough handle on complexity, and I
don't think anyone else does, either.
The idea here is that cost is a strong function of complexity, and the
primary way to measure complexity is to count the number of stages. So we
should develop and use advanced technology and push it to the limit in order
to avoid staging rather than, for example, to reduce the dry weight of a
- Lack of technology II: Need Single
Stage To Orbit (SSTO).
My first problem with this theory is that, to me, rockets don't seem all
that complicated compared to airplanes. In particular, staging a rocket seems
rather simple compared with what an F-14 is able to do: catapult launch,
variable geometry, all-weather, aerial refuelling, combat, separation of
various external stores in non-predetermined order, and a tailhook landing at
night on a moving ship at sea. In comparison, the complexity of staging a
rocket seems more like that of changing planes in Dallas in order to fly from
Houston to Toronto. It seems far from being absurdly complicated.
My second problem is that counting the number of stages seems an absurdly
naive way of measuring complexity. How about the number of drawings needed to
build it? How about the parts count? How about the number of dissimilar
parts? How about the number of machining operations? How about dissimilar
machining operations? How about the number of pages of stress analysis
needed? How about the number of places where damage tolerance, corrosion
resistance, and fatigue life are sacrificed in favor of materials that are
just a tad lighter? What about the number of different ways that failures
could result in death? We are told that one stage is simpler than two, but it
seems very strange to me for someone to wring his hands about "complexity"
without being worried that a rocket stage with performance requirements that
are beyond anything that's ever been demonstrated might be more complicated
than a rocket stage with only half the mission velocity requirement. It's
like saying that one is less than two, therefore one Indy 500 race car is
simpler and cheaper to operate than two touring motorcycles.
My third problem with this theory has to do with what Maxwell Hunter called
"the standing army problem" in his 3-11-89 paper, "The SSX," later known as
the DC-X. The overwhelming majority of the cost of a launch vehicle is
ultimately attributable to labor, so any significant reduction in cost has to
manifest itself as someone getting laid off. Whose salary could be eliminated
if you could eliminate staging from a vehicle similar to the Space Shuttle?
Unfortunately, the only information I have on this in anecdotal. The Orbiters
typically spend on the order of 10 days in the Vehicle Assembly Building
(VAB), where the External Tank (ET) and Solid Rocket Boosters (SRB) are mated,
and 60 days in the Orbiter Processing Facility (OPF), where such things as
corrosion and Thermal Protection System (TPS) tiles are repaired. The Orbital
Maneuvering System (OMS) pods and their toxic propellants are handled
elsewhere, in the Hypergolic Maintenance Facility (HMF). An SSTO vehicle will
have more surface area of exotic TPS than a comparable two stage (TSTO)
vehicle, and at least as much OMS work. SSTO would presumably spend less time
in the VAB, but it would still need some crane work to install the payload.
The empty SSTO would be heavier, but not enough to affect the transporter
much. The launch pad might be simpler or more complicated, depending on
whether the SSTO uses dual fuel. Launch operations at KSC might be simpler.
Flight operations at JSC would be little affected. Neither SSTO nor TSTO
would have SRBs or ET. I just don't see from this how SSTO is related to
laying off a huge number of people.
Finally, I think I have a basis for skepticism in the way SSTO was sold. It
was basically The Big Lie: the SSTO promoters equated SSTO with reusability.
As Whitehead rather kindly puts it, "The concept of single stage to orbit is
widely associated with the notion of reusable launch vehicles because the
ultimate goal is to combine the two. In reality, designing for reusability
initially requires robust hardware which is too heavy to reach orbit without
staging.... Since reusability and SSTO are conflicting requirements, it is
logical to first develop these capabilities independently." (AIAA 96-3108,
Single Stage to Orbit Mass Budgets Derived from Propellant Density and
Specific Impulse, John C. Whitehead, p.9). Raymer (Aircraft Design: A
Conceptual Approach) mentions that maintainability requires access panels,
which add weight, and that sometimes the ratio of access panel surface area to
"total wetted area" is used as a figure of merit for maintainability. Some
aircraft have figures of merit as high as 0.5. Raymer mentions the F-4
Phantom as a negative example, because in order to remove the radio, which was
a common operation, one first had to remove the ejection seat, which was
frequently damaged during removal.
Addendum: Oops. I forgot to mention the two most obvious weight impacts of
reusability: the TPS and landing system (which for a VTOHL launch vehicle
includes the wings). Roughly 15% of the Orbiter's empty weight is TPS. The
wings, tail, and control surfaces are about 12% and the landing gear are about
Sometimes there are "dog and pony shows" where aerospace contractors show
off their latest technology. At one of these, shortly before Lockheed was
selected to build the X-33, I asked a Lockheed X-33 presenter how SSTO was
going to save money. The conversation quickly moved to new TPS (heat shield)
technology, built-in test equipment (BITE), payload isolation, and different
management philosophy. Why can't a two-stage vehicle use the new TPS
technology? Why can't a TSTO have BITE? Wouldn't a TSTO be less sensitive to
the weight associated with payload isolation? Why can't a different
management philosophy be applied to Shuttle? It seemed to me that he changed
the subject a lot.
Norm Augustine's Law XV states, "The last ten percent of performance
generates one-third of the cost and two-thirds of the problems."
- Living on the edge.
The basic idea here is that there are theoretical and practical limits to
the performance of a rocket stage, and that the labor cost associated with
developing and operating the stage depends strongly on how close to the limits
it is required to operate. That last little bit of specific impulse may force
me to increase the pressure in the combustion chamber dramatically. I may
have to make the nozzle much more complicated. Removing that last little bit
of weight may force me to use exotic materials that are hard to maintain and
to tailor each inch of the structure for minimum weight rather than having a
lot of common hardware. It's said that an airplane is a bunch of compromises
flying in close formation. But if I am pushing the limits of performance, I
can't afford to compromise much, and I will have to sacrifice robustness,
maintainability, ruggedness, safety, and simplicity.
Common sense suggests that there is a certain amount of overhead for even a
very low-performance rocket stage, but that it should not be costly to scale
up a low-performance propulsion system slightly. On the other hand, costs may
rise asymptotically near the limits of feasibility. As a thought experiment,
consider a simple formula that has these characteristics:
cost = minimum_cost / ( 1 - ( delta_V / maximum_delta_V ) ^
2 ) .
Suppose that maximum_delta_V was just a hair more than orbital speed, so
that you could build an SSTO launch vehicle, but just barely. Would you want
This theory suggests developing "the big dumb booster," perhaps using
pressure-fed rather than pump-fed engines. But if money is to be saved
by designing launch vehicles with two or three low performance stages
instead of one or two high performance stages, it raises the question of
why current launch vehicles live so close to the edge. Is it due to some
world-wide, quasi-religious, irrational worship of technology? Political
pressure for glamor and prestige? Are rockets phallic symbols? This
theory may be more helpful for explaining why the sole first generation
reusable launch vehicle, the Space Shuttle, is expensive than it is for
explaining why the relatively competitive expendables are.
Addendum: #John London (Reducing Space Mission
Cost, Microcosm, p. 151) describes a large (1,112,000 Newton),
pressure-fed engine built by TRW for under $100,000 in the late 1960s,
inspired by the Lunar Module Descent Engine. Despite this, London reports
(pp. 142-3) that Air Force studies in the 1980s continued to reject
pressure-fed booster concepts on the grounds that cost was expected to be a
strong function of weight. London argues (p. 144) that over-reliance on
weight-based Cost Estimating Relationships (CER) is a serious problem in the
aerospace industry in general. It also occurs to me that these CERs are
vulnerable to deliberate misuse by interested parties whose positions would be
jeopardized by any serious attempt at parasite control.
Addendum II: John Whitehead argues (AIAA 2000-3140, "Launch vehicle cost - a
low tech analysis" and -3141, "Mass breakdown of the Saturn V") that an
expendable "big dumb booster" using pressure-fed engines is incapable of
significantly reducing launch costs because the performance (payload
weight/vehicle empty weight) is just too sensitive to the propellant mass
fraction of each stage. (Naive observers of the space launch industry tend to
focus too much on specific impulse and not enough on propellant mass fraction
as a measure of performance.) Figure 4 in his -3140 paper indicates that a
modest amount of weight growth (reduction in propellant mass fraction from .9
to .77) in a 3-stage kerosene/oxygen rocket will cancel out all of the savings
associated with an order of magnitude reduction in manufacturing cost (dollars
per pound of empty vehicle weight). Launch vehicle designers are thus forced
to sacrifice reliability, in the form of less redundancy and reduced factors
of safety relative to airplanes, in order to achieve a reasonable payload
mass. This argument reinforces the belief that expendable launch vehicles
will never be cheap. Unfortunately, it also underscores the difficulty of
building a reusable vehicle that is not prohibitively heavy.
I saw a memo from early 1986 that stated that propellant cost was
insignificant, and that vehicle dry weight was secondary in importance to
"ground handling and launch operations." Things that would help include
built-in test equipment (BITE) and more automation in general during checkout,
but the emphasis in this memo, at least through my biased eyes, seemed to be
on reducing payload integration problems with the so-called "bolt-on" or "ship
and shoot" payloads. Less sensitivity to weather conditions (high altitude
winds that threaten to damage the wings during launch, and landing site
visibility) would also help.
- "Ground handling and launch
operations" (need "ship and shoot" payloads).
I am perhaps overly sensitive to payload integration problems, having been
involved in too many "coupled loads analyses," a very non-airline like
activity in which the dynamic (unsteady acceleration) loads that a payload
designer needed before he made the design are calculated by combining a
computer model of the Shuttle with one of the payload(s), after it has
been built and tested. In other words, we take a "finite element" computer
model (FEM) of the Orbiter, integrate FEM of all of the payloads that are
manifested on a particular flight, and calculate all the structural loads
specifically for that flight, perhaps several times if there are problems
resulting in changes. You may find out at the last minute that your payload
can't fly because it resonates with another payload to produce loads higher
than what you designed for, or that the Orbiter is good for. There is at
least one of these analyses per Shuttle flight, sometimes several. While the
"coupled loads" costs may be hidden in "payload development" rather than seen
as Shuttle operating costs, they are part of what makes it expensive and time
consuming to put something in space. Coupled loads analyses for transport
aircraft are normally limited to generic analyses when the aircraft are first
developed, not something to do every flight. Part of the reason for this is
that the vibration environment on rockets is dramatically worse that on
airplanes. Part of it is "living on the edge" and not wanting to add weight.
Part of it is also the way the Shuttle was designed, with the LOX tank on the
"wrong" side of the payload bay from the main engines. More standardization
among payloads would help.
Addendum: See my comments below regarding economies of scale (#18). It has
also been noted that scrubbed launches are expensive, and suggested that money
could be saved by only launching into orbits with very wide launch windows.
An example would be due East launches into equatorial orbits, for which an
equatorial launch site is always in the right plane. But Ariane launches from
Kourou into geostationary orbit provide an example of this, and as noted
above, they are only modestly less expensive than Titan or Altas launches from
Addendum II: Tom Sarafin (President,
Instar Engineering and Consulting, Inc.) writes in Doing Things Right in
I am still looking for the launch-vehicle program that is
seriously interested in breaking the mold and providing a better service to
their customers with a standard mounting adapter that includes a tunable
isolation system. The first company that succeeds in this endeavor will knock
the socks off its competition as payload developers put more emphasis on the
indirect costs of LV options.
This theory is taken directly from Maxwell Hunter's 3-11-89 paper, "The
SSX," (draft 2). Although Hunter also cites bureaucracy and various other
problems, the point of this theory is that the size of the "standing army" is
driven largely by the severity of the consequences of a failure, more than by
the complexity of the systems involved. Essentially, the lack of "continuous
intact abort capability" (safe abort during all phases of flight, including
saving the payload) forces whomever is operating a launch vehicle to maintain
an army of engineers to make sure that absolutely nothing can go wrong.
Although "lack of intact abort capability" never appears as a line item on any
budget, it indirectly drives the size of this "army," whose salaries in turn
quite visibly drive launch costs.
- Lack of intact abort
While I don't buy a lot of other things Hunter says, I tend to buy the
intact abort argument. This theory works for both expendables and reusables.
Expendables inherently lack intact abort capability, and often carry
frightfully expensive payloads, sometimes on the order of $1 billion, in
addition to the launch cost in the tens or hundreds of millions. Similarly,
the Space Shuttle Orbiters are essentially irreplacable nowadays, carry people
on board, are politically sensitive, and are vulnerable to numerous potential
catastrophic failures. If anything goes wrong with the SRBs during a Shuttle
launch, the result is catastrophic. There is also a phase during flight when
the only intact abort mode, Return To Launch Site (RTLS), requires a maneuver
that has been said to require about eight miracles. By comparison, if an
airliner has a serious failure during takeoff, the most likely result is that
schedules will get messed up and the airline may have to put people up in a
Based on this theory, it is quite conceivable that an expensive to
replace reusable vehicle without good abort capabilities could be more
expensive to operate than an expendable.
Addendum: Tom Sarafin points out in Doing Things Right in Space
that once a spacecraft has been launched, generally, if something goes
wrong, we not only can't fix it, we can't even see what's wrong with it.
This makes failures doubly (or triply) expensive.
Note also that the operations cost associated with providing
good abort capabilities is a strong function of vehicle complexity (ie.
living on the edge). Each flight controller or subsystem manager must
not only know what can go wrong in his own system, and what can be done
about it, he must also know how his system is affected by potential
failures in other people's systems.
A lot of the labor involved in operating the Shuttle is repairing the
Thermal Protection System (TPS) tiles. The thermal environment during Shuttle
reentry really is unlike anything experienced by an airliner. There have been
minor advances over the years, but major improvements seem to involve blunter
vehicle shapes, lower weight/surface area, and redesign of the underlying
- Critical differences between
rockets and airplanes (ie. thermal problems).
Another unique problem for rockets is the oxidizers. There are no nice
oxidizers. The most practical of them seems to be liquid oxygen. An
air-breathing engine works with gasseous oxygen diluted with 80% nitrogen, at
moderate pressures (ie. ten atmospheres). Liquid rocket engines use pure
oxygen at pressures an order of magnitude higher, which eventually reaches
very high temperatures (hopefully in places where it doesn't touch anything
but fuel). Apart from the thermal stress and other problems of dealing with
cryogens, it is difficult to keep oxygen from reacting with the walls of the
plumbing it is flowing through. This makes it extremely difficult if not
absolutely impossible to eliminate catastrophic failure modes, in which a
failure in one engine destroys the entire propulsion system. In an airplane,
if an engine shreds itself, you close the fuel valve. In a rocket, if an
engine shreds itself, you notify the next of kin.
Addendum, 8-10-2001: To clarify, there are two problems here. One is to
contain the blast and shrapnel from an explosion, and the other is to keep a
fire from rapidly propagating up the oxygen line. The first problem is
obviously solvable, but perhaps at a prohibitive price in terms of weight. It
was not clear to me that the second is solvable, but I have since been
informed that there are copper alloys such as monel whose fire resistance is
good enough to keep a fire contained even in pure oxygen at moderate
pressures. Again, the reason they are not used more extensively is their
In comparison, several other differences I will mention are mere nuissances.
One is the vibration environment. Good liquid rocket engines require good
mixing in the combustion chamber, which requires extreme turbulence (or at
least, that is my understanding of it). High pressure, turbulence, and
combustion lead to the nasty random vibration loads that I complained about
with regard to coupled loads analyses (along with large shocks like SRB
ignition and nosegear "slapdown").
Another nuissance is acoustics. This seems an inevitable consequence of the
shock waves that come from firing rockets with hypersonic exhaust velocities
in the atmosphere, especially near the ground. It's just one more thing to
make life difficult for spacecraft designers, especially for payloads with
large surface areas and low mass.
Other nuissances include avionics that are more complicated than an airplane
really needs, and the need for attitude control thrusters. (8-10-2001: In
retrospect, this may be a very naive view of the complexity of launch vehicle
avionics. This may be much more than a nuissance!)
Two more differences are more than nuissances, the impracticality of
evolving orbital launchers from low speed cargo rockets, and the
impracticality of incremental testing for many configurations. Airplane
developers were able to learn by building economically useful low performance
airplanes before moving on to faster and higher performance designs. But
there is very little market for a reusable cargo rocket that doesn't make it
into orbit. The process of testing a new vehicle is analogous. An airplane
can do taxi tests, then low speed flights, and gradually "expand the envelope"
to find out if there are problems before committing to performing at the
limits it was designed for. The only rocket I know of that was able to do
this was the DC-X. A VTOHL rocket that lifts off the pad is committed to
making the transition to horizontal flight in order to land safely, and has
no way to abort testing of the transition maneuver.
#Wiley Larson writes (p. 18), "Managing the DoD's and
NASA's large space programs is like trying to win a potato-sack race--with
five people each having one leg in the sack while running in different
directions, and 10 to 30 coaches and helpers are on the sidelines directing
the people in the potato sack."
- Lack of a clear sense of
This theory sounds similar to #6, conflicting vehicle requirements, but they
operate on different levels. #6 tries to explain "proximate" causes, why
particular vehicles are expensive in terms of technical conflicts. #17 tries
to explain ultimate or "root" causes on a human level, or why it is that the
technical problems were not handled well by human decision makers. For
example, if the Space Shuttle needed "truck engines," why were "race car
engines" built for it? If the purpose of the Shuttle was to dramatically
lower launch costs, why is there not a huge uproar within NASA that it failed
to accomplish its mission? If the space station is being built to do
research, why is its budget so out of proportion with the research budget? If
the Shuttle is to be the primary logistics vehicle for the space station, why
do they seem to compete with one another as research platforms more than they
complement one another as related parts of a transportation infrastructure?
Why does the space program seem to be fatally vulnerable to parasites when a
French state-owned oil company is not? Why does NASA and much of Congress
talk of private development of space launchers while other agencies seem to go
out of their way to make things difficult for Sea Launch and Kistler? Why do
volunteer organizations like the Mars Society criticize the Apollo program for
"flags and footprints" missions while pushing for very similar Mars
I am also struck by a sense that the space program is driven by cyclically
repeating fads. There is a saying at NASA that you should never put a date on
a briefing chart because it means having to do more work when you are asked to
study the exact same thing and give the same briefing three years later. I
feel like a fashion model watching hem lines rise and fall repeatedly over
many years to no apparent purpose. Inflatables have been proposed before, but
never pushed very hard. Why does a technically promising project like
Transhab (today's inflatable) with obvious long term benefits flounder for
want of a hard requirement for it in the short term? It mutates from
purporting to support a Mars mission to wanting to be a space station module,
or perhaps a hyperbaric chamber. It appears to be a solution looking for a
problem, despite a very strong feeling among the people working on it that
somebody, sooner or later, will want it, and probably sooner.
It seems to me that the lack of a clear sense of direction goes a long way
towards explaining all of these things.
The idea here is that if the number of space launches or, alternately, tons
of cargo per month were as high as the number of airline flights or tons of
cargo per month, the costs might be more directly comparable. This
explanation overlaps to a considerable extent some of the others that we have
already considered. Economies of scale result partly from increased
specialization (fewer conflicting vehicle requirements, #6), the learning
curve (#7) and the ability to amortize larger investments (#8). With a larger
market, there might also be more political muscle available to overcome
obstructionism (#10). Additional advantages can be wrung from specialization
by trained personnel or specialized equipment that can be operated nearer to
its full capacity. Also, in addition to the "learning curve" possibly
representing how vehicle designers learn from previous designs, the learning
curve definitely applies on a microscopic scale, as it was originally
intended, reducing the number of man-hours needed to get repetitive work done
on longer production runs.
- Economies of scale.
There are certainly economies of scale in the sense that aerodynamic drag is
relatively less important for larger launch vehicles. Furthermore, while
complexity may increase with size, it doesn't increase as fast as payload
capacity; if two vehicles fly equally often, the larger one should cost more
per flight, but less per pound of payload. More demand for space launches
would tend to make it easier for large launchers like Ariane 5 to find
multiple customers who want their payloads delivered at similar times into
similar orbits, and can thus share flights.
At one time it was often claimed that the Shuttle would reduce costs by
flying frequently so as to take advantage of economies of scale. Nowadays it
is generally thought the Shuttle can't fly more than about a dozen times per
year without either compromising safety or greatly increasing staffing levels
and perhaps capital investment.
However, it would appear that economies of scale are part of the reason
why Russian launch vehicles are relatively cheap--they've built a lot of
them and lifted a lot of relatively heavy satellites with relatively
short operational lifetimes. The Russian vehicles generally use
larger numbers of engines than comparable American vehicles, but fewer
different kinds. (See #London, and note the
similarity to the Microcosm Scorpius design.) Maybe the relatively
modular Russian expendable boosters really are dramatically cheaper
than Western launchers in terms of man-years per ton of payload, and not
just because of exchange rates.
But if the space launch industry were driven by economies of scale,
that would tend to make it highly monopolistic, with the larger or busier
firms much more efficient than the smaller or less busy ones. If this is
so, why is there not a shake-out of smaller or less committed firms?
There are several possible answers: Too many customers may have
incompatible requirements for payload size, orbit, and schedules,
creating a number of niche markets rather than one big monopoly. However,
there seems to be competition within the niches. There is certainly
political interference by many governments, such as subsidies for
domestic launchers and import and "technology transfer" restrictions for
foreign launchers, again resulting in a fragmented market. But again,
there is still considerable competition within the niches. Various
nations' military establishments all want to ensure that their access to space
is not subject to foreign political risks, and the US military tries to avoid
being too reliant on any one contractor. Cost is clearly a secondary issue to
the military, but I note that the US military has gone for dissimilar designs
(Atlas and Delta) rather than trying to take advantage of some economies of
scale by having competing suppliers build and operate a common design under
If economies of scale were extremely pronounced, it would be cheaper to fly
a single large vehicle than an assortment of large and small ones, even if the
large one often flew half-empty. I also note that Boeing's Sea Launch program
is using Ukrainian Zenit rockets while Boeing is simultaneously building more
One variation on the economies of scale argument is that my comment, "More
standardization among payloads would help," under Launch Operations (#14),
doesn't go nearly far enough. It is argued that very few launch
missions are ever quite the same. For any two missions on the "same" launch
vehicle, there is almost always a slightly different payload or set of
payloads, different destination orbits, or differences in payload fairings or
numbers and sizes of strap-on boosters. In this view, economies of scale
could save a lot of money, but no one is currently taking advantage of them
very effectively. The way to do this would be to design "cookie cutter"
payloads and highly standardized launch mission profiles, using only a handful
of initial "parking orbit" destinations. But like several of the other
explanations we have considered, this one invites the question, "Then why
doesn't someone do it that way?" The marginal cost of flying identical or
near-identical payloads and mission profiles does not appear to drop
spectacularly relative to dissimilar ones.
If the economies of scale in space launchers were overwhelming, there
should be more consolidation in the launch business, and the Russians and
French would have stronger advantages. The European Arianes aren't all
that much cheaper than their American competitors. It's hard to say how
much a Russian launch vehicle really costs, but if these vehicles are
judged by their failure rates, they are again only somewhat better than
their Western competitors.
There are certainly some economies of scale in the launch business, but
we need to explain two orders of magnitude cost difference between
airplanes and rockets. Economies of scale don't appear to be a
Are we near the left edge of this curve, or towards the right, near the
optimum point where the two curves cross? (This curve is qualitatively similar
to what you might find in an economics textbook, but the numbers are purely
Now I will repeat my list of theories and try to sum up my conclusions.
Remember that the original question was, "Why are the costs of space launches
so far out of line with the costs of seemingly comparable airplane
- #^ "It just does!"
- #^ Propellant costs.
- #^ "Energy costs."
- #^ Lack of reusability.
- #^ Lack of full reusability.
- #^ Conflicting vehicle requirements.
- #^ Learning curve; not enough generations of launch
- #^ Lack of adequate investment (solid boosters for
- #^ Politics I: Parasite control.
- #^ Politics II: Obstructionism.
- #^ Lack of technology I: Dry weight too high.
- #^ Lack of technology II: "Complexity" of multiple
stages (need SSTO).
- #^ Living on the edge.
- #^ "Ground handling and launch operations" (need
"ship and shoot" payloads).
- #^ Lack of intact abort capability.
- #^ Critical differences between rockets and
airplanes (ie. thermal problems).
- #^ Lack of a clear sense of direction.
- #^ Economies of scale.
I find it very difficult to take any of the first three answers seriously.
"It just does" (1) clearly does not answer the question. "Propellant costs"
(2) is an answer, but it is clearly wrong for any reasonable choice of
propellants. "Energy costs" (3) either doesn't answer the question or is
demonstrably wrong, depending on how it is interpreted.
The next two answers are a little better. "Lack of reusability" (4) may
have a lot of truth in it in the sense that expendables may never be cheap,
but if so, it still doesn't explain why a "big dumb booster" couldn't be made
relatively cheap. It also fails to explain why the Shuttle is so expensive.
"Lack of full reusability" (5) is much less plausible. While the Shuttle's
expendable External Tank is very expensive, lots of other tanks, including
"drop tanks" on airplanes, are not.
The next three answers, "Conflicting vehicle requirements" (6), not having
gone far enough on the "Learning curve" (7), and "Lack of adequate investment"
(8), are all somewhat helpful as partial explanations. They at least help
explain why the Shuttle is so expensive, but none of them are very powerful
explanations of high launch costs in general.
Similarly, the two classes of political answers, "Parasite control" (9) and
"Obstructionism" (10), are helpful partial explanations, especially if they
are combined with a belief that a considerable element of public good is
involved in the conquest of space. Parasite control is mainly helpful in
explaining the cost of the Shuttle and any proposed government-funded
replacements for it.
In my opinion, these explanations don't seem nearly powerful enough by
themselves. However, they help, and most of the people I've talked to
seem to believe that I seriously underestimate the importance of
The next three answers are oriented towards technology: "Dry weight too
high" (11), "Need Single Stage To Orbit (SSTO)" (12), and "Living on the
edge" (13). Estimates of dry weight may be useful in predicting the
development cost of certain kinds of vehicle, but it is a curve-fit story.
This dry weight "story" doesn't explain why some points lie on a curve,
it doesn't explain why space launch operations costs are so far off of
the airplane curves, and it doesn't allow me to compare a "big dumb
booster" against a lighter, more complicated design. The SSTO argument
fails too many reality checks for me to take it seriously: complicated
airplanes aren't that expensive, and staging isn't that complicated.
"Living on the edge," like several of the previous answers, is helpful.
It is especially helpful in explaining why certain vehicles such as the
Shuttle are expensive. But in order to help much in explaining high
costs throughout the entire worldwide space launch industry, it must be
combined with an explanation for why such concepts as the "big dumb
booster" are so generally out of favor, both politically and commercially.
Again, this explanation is helpful, and perhaps I underestimate the mischief
caused by the misuse of Cost Estimating Relationships (CERs).
Addendum: In retrospect, John Whitehead's "low tech analysis" answers
several of the questions I raise in my discussions of theories 11 and 13. The
big dumb booster (ie. an expendable vehicle with pressure-fed engines) is
unlikely to save very much money because of the highly nonlinear relationship
between the propellant mass fraction of a rocket stage and the resulting
vehicle's payload capacity. In other words, we are living on the edge because
we don't have a choice. This in turn answers the earlier question of why the
Cost Estimating Relationships for rockets are so different from those of
airplanes. It is economical for a rocket to live much closer to the edge than
an airplane does.
The last five answers all seem to resist categorization.
"Ground handling and launch operations" (14), is a sort of grab-bag of minor
problems, some of which can also be viewed in terms of "living on the edge" or
"learning curve" problems. This explanation is only mildly helpful.
"Lack of continuous intact abort capability" (15), is my favorite. This to
me is a plausible explanation of why neither expendables nor the Shuttle can
be operated at anything like the costs of airliners. This may not be the full
story, but it is a large piece of it.
"Critical differences between rockets and airplanes" (16) is helpful,
especially in conjunction with intact abort (15). Although the Shuttle
Orbiter's thermal protection (TPS) tiles are the first thing that comes to
mind, a more serious problem may be keeping strong oxidizers at high pressure
from reacting with metal parts in the main propulsion system. This makes
engine failures much more dangerous in rockets than in airliners.
Painfully apparent to me is "Lack of a clear sense of direction" (17).
Although this may not directly cause high costs, indirectly it goes a long way
towards explaining why we haven't solved the problems that do directly cause
Finally, we have "Economies of scale" (18). This is only mildly helpful.
I consider the lack of continuous intact abort capability (15) to be the
principal proximate cause of high launch costs. Several of the other answers
are directly helpful, but none of them seem capable of explaining nearly as
large a disparity in the costs of air travel and space travel. The learning
curve (7) and lack of direction (17) are root causes for many of these
problems. I also believe very strongly that lack of direction is largely
responsible for our having made so little progress on the learning curve.
These are the problems we should focus on in trying to reduce launch costs.
Instead, much of the attention of space futurists has focussed on "advanced
technology development." I regard this as a regrettable
Addendum (11-11-2001): In retrospect, the best root cause explanation of
high launch costs may be the highly nonlinear relationship between propellant
mass fraction and payload capacity. This makes it hard to build cheap
expendables, or to build safe reusable vehicles (rugged ones with good abort
capability and lots of redundancy) at any price. Consequently, I may have to
retreat somewhat from my criticism of "advanced technology development,"
provided that this development is aimed at reducing empty weight, or to some
extent for increasing specific impulse. My criticism of SSTO stands. I'm
convinced that expendables are not the way to go, either. For reusables, I am
still uncertain about the relative importance of weight vs. intact abort
capabilities. I still want to see more X-vehicles aimed at reusable rocket
This essay has a companion: Where (in space) do we go
from here? or Why do we have a manned space program?
If you found this article interesting, you may also be interested in the
Interviews with Max
Faget and Guy Thibodaux
The Kistler K-1 two-stage
reusable launch vehicle project
Scorpius modular expendable launch vehicle project (see their conference
Reducing Space Mission Cost, by James R. Wertz
and Wiley J. Larson, eds., Microcosm Press (Torrance,
CA) and Kluwer Academic Publishers, 1996, ISBN 1-881883-05-1. Note ch. 4
especially, "Reducing Launch Cost," by John R. London