The Mega-Module Path to Nowhere (Or: How to Eliminate Human Space Flight With an HLV)
The recent Ad Astra Online article by John Strickland, "The Mega Module Path to Space Exploration (Or: How to Use an HLV)" is a sad reflection of old-school thinking. His argument for heavy lift is the same approach adopted in the 1960's, which made Project Apollo a costly dead end.
Strickland calls for NASA to "to go for the largest available booster which can be created at a reasonable cost." On the surface, that seems reasonable--who could be against reasonable cost? But Strickland never bothers to quantify the cost of those super-boosters and mega-modules or what "reasonable" cost is. As Robert Heinlein said, if you can't say it in mathematics, it isn't science; it's opinion.
The Saturn V cost about $2 billion per flight, in 2005 dollars. NASA estimates it will cost $10 billion to develop its big Shuttle-derived Heavy Lifter. After that, we can expect each launch to be about the same cost as the Saturn V. This expense is due to high capital costs (expensive infrastructure to support such super-boosters) and high labor costs (due to the huge workforce needed to launch them). Furthermore, NASA's Shuttle-derived HLV will use explosive solid rocket motors that require careful handling, which may drive costs up even more. (The late Dr. Wernher Von Braun emphatically rejected the use of solids on the Saturn rockets.)
Common wisdom in the aerospace community is that larger rockets will be cheaper than smaller rockets. Yet, common wisdom has failed to reduce the cost of human spaceflight--why?
"Common wisdom" is based on the payload fraction--a larger rocket can carry more payload for each pound of liftoff weight. So, a larger rocket should cost less per pound of payload. That argument's fine, as far as it goes, but it ignores other factors. Most of the liftoff weight is propellant, and rocket propellants typically cost pennies per pound. For current systems, propellant cost is less than 1% of launch costs, so optimizing for mass fraction alone doesn't produce low cost.
We need to look at capital and labor costs, which account for 99% of launch costs. With expendable rockets, there's a certain amount of capital that's expended with each launch--the rocket itself--but there's also a huge amount of fixed capital, in the form of launch pads, vehicle assembly buildings, factories, etc. The size and cost of the launch and manufacturing facilities depends on the size of the rocket.
Basic business theory says that when you have a large capital investment, you should use it as often as possible to get the maximum productivity out of it. If you're going to invest in a launch pad, for example, you ought to use it as often as you can. Yet, Strickland calls for just the opposite--"avoiding multiple launches." That means the pads and other facilities will be underutilized. In principle, a launch pad can be used at least twice a week. (The late Dr. Max Hunter launched two Thors from the same pad within 48 hours.) Yet, NASA's plan calls for it to launch just three heavy lifters per year.
Assume two expendable rockets, Hoss and Little Joe. Hoss can launch 100-tons. Little Joe can launch only 10 tons. Hoss requires $6 billion worth of launch pads, roadways, hangars, etc. Little Joe requires only $600 million worth of launch facilities. If you launch Hoss three times a year for 10 years, the amortized cost of those launch facilities will be $6,000,000,000/30 = $200,000,000 per flight, or $2,000,000 per ton of payload. To do the same job with Little Joe requires at least 10 times as many flights. Let's call it 12 times, to allow for Hoss's more efficient payload fraction. So, Little Joe must be launched 36 times a year. So, the amortized cost of launch facilities over 10 years will be $600,000,000/360 = about $1,670,000 per flight or $167,000 per ton of payload.
Labor costs show similar advantages for Little Joe compared to Hoss. Hoss might require 5 times as many workers to assembly, checkout, and prepare for launch. Hoss is launched only three times a year, but you have to keep the team together between flights. So, each worker must be paid 4 months wages for each flight. Little Joe, on the other hand, is launched about once every 10 days, so workers only get 10 days wages for each flight. Annual labor costs for Hoss are 5 times what they are for Little Joe, to deliver the same payload.
There's more. The Little Joe crews are launching 36 rockets a year. The Hoss crews are only launching 3 rockets a year. So, the Little Joe crews are a lot more practiced in their jobs. The more often you do something, the more efficient you become. Economists call this "the learning effect." If you perform a task twice as often, efficiency generally improves 10-20%. The Little Joe crews are practicing their jobs 12 times as often, so their efficiency should be at least 30% better.
These factors lead to a single, inescapable conclusion. The most important factor effecting launch costs is not the size of the rocket. It's the flight rate.
The advocates of great big rockets point to 747s as evidence for economies of scale favoring large vehicles. But smaller jets like the 737 carry far more passengers, with virtually the same economy per seat-mile. Airlines know that economy scales most strongly with flight rate, not aircraft size. 747s operate only on major routes where there's enough demand to fill a 747 on a daily basis. When you consider these factors, it's little wonder that a Planetary Society group headed by Mike Griffin wrote that "present launch costs of $9-11K per kg will continue for the next 40 years" when they recommended the super-booster/mega-module architecture. Their assessment is a classic example of a self-fulfilling prophecy.
There is not enough demand to fly a heavy-lift vehicle on a daily basis, or a weekly basis, or even a monthly basis. Nothing in NASA's plans, or the plans of private industry, even comes close. Someday, when we are launching thousands of tons of payload every day, heavy lift vehicles will make sense. Until then, vehicles should be sized appropriately for current demand.
But what about right now--what options does NASA have?
Space Adventures and its Russian partners are offering circumlunar flights for an estimated $100 million per flight. For the cost of developing a Shuttle-derived super-booster, NASA could buy 100 circumlunar flights from Space Adventures. Or, if you assume a lunar landing is five times as hard as a circumlunar trip, they might buy 20 Moon landings for the same price. If Russian hardware is not politically acceptable, Boeing and Lockheed could develop systems to use their existing Delta and Atlas rockets, using the multiple launch techniques once proposed for the Lunar Gemini program.
Even a strident advocate of heavy lift like Dr. Robert Zubrin has acknowledged that low-cost missions could be done with current vehicles. In "The Case for Mars" he writes that "even if Energia or other Russian launch vehicles (such as Proton...) are not available or allowed, the mission still doesn't have to cost that much. Current launch costs using existing US boosters such as Titan's, Atlas's, or Delta's is about $10,000 per kilogram. At these rates... launching the entire 300 (metric) tonnes would cost $3 billion. Add that to the $1 billion for hardware development, and once again we find a total cost of less than $5 billion."
With orbital rendezvous and docking (proven long ago in the Gemini program and many times since in Apollo, Skylab, Mir, and ISS), we can build space structures far larger than the piddly little 100-ton "mega-modules" Strickland writes about. With existing expendable launch vehicles, NASA could send humans to the Moon and Mars and do it *sooner* than the current timetables call for.
At the same time, NASA can leave the door open for the future. Consider, for a moment, a small reusable launch vehicle, like the Space Van proposed by Len Cormier of Third Millennium International. The Space Van could carry a crew of two plus 8 passengers or a ton of cargo into orbit, for less than $500,000 per flight.
Just one Space Van, flying five times a week, 50 weeks a year could launch 250 tons a year. That's more mass than two of Strickland's "mega-modules," at a cost of $125 million instead of $4 billion. A fleet of 12 Space Vans could launch 1500 tons a year -- the equivalent of 15 Skylabs or 15 Strickland mega-modules -- plus 3200 human beings.
Cormier believes the Space Van could be developed for $200 million. That seems amazingly low by expendable launch vehicle standards, but there's good reason to believe he's in the right ball park. Remember, this is a small vehicle, and there's some evidence that reusable vehicles are cheaper to develop than ELVs. A large part of development is testing; reusable vehicles are cheaper to fly, so they should also be cheaper to flight test. In the 1960's, General Dynamics did a study of the X-15 and the Atlas A, reusable and expendable vehicles of similar performance. They found that a piloted, reusable vehicle was more complex but also 40% cheaper to develop.
SpaceShipOne provides another example. The flight test program included 66 flights of the first stage (White Knight) and 17 flights of the upper stage (SpaceShipOne). If these had been expendable stages, Scaled Composites would have had to build a total of 83 stages to complete the same test program. If each expendable stage cost $5 million, the total program would have cost nearly half a billion dollars. Because both vehicles were reusable, Scaled was able to complete the flight test program for only $25 million.
Of course, a first-generation RLV like Space Van might not pan out. Many new vehicles are not quite right on the first attempt--the de Havilland Comet airliner, for example. But, even if it takes two or three generations for developers to get it right, the cost would still be a fraction of the $10 billion needed to develop NASA's super booster.
NASA could encourage the development of such vehicles by designing its lunar and Mars missions around a modular, open architecture, with many small components that can be easily moved between vehicles. In the short term, this would allow NASA to negotiate better prices from competing launch vendors. In the long term, it would allow NASA to take advantage of new vehicles that don't exist and may not even be envisioned today.
Or, NASA can mortgage its future by tying itself to "mega-modules" that can be launched only by giant super boosters, which only the government can afford to develop.
Ultimately, the choice comes down to what kind of future we want to have. Mr. Strickland promotes heavy lifters as a way to avoid multiple launches and develop orbital fuel depots with "no permanent human crew needed." I prefer to reduce the cost of space access so that we can have human crews. I want to see a future where we have a lot *more* launches and a lot *more* people in space.
NASA's proposed lunar architecture would allow three moonshots a year, with four astronauts on each flight. This is just 12 flight opportunities per year, down drastically from the Shuttle program. It's no secret that NASA's contemplating astronaut layoffs. What kind of message does that send to America's young people, who have been told to study hard, excel in math and science, so they can grow up to become astronauts?
Small reusable vehicles can revolution access to space the way microcomputers revolutionized access to computing. NASA can help enable a vibrant future where thousands of people travel into space every year -- or it can cling to the super-boosters and mega-modules of the "mainframe" era, in which case the NASA manned space program will continue its slow downward spiral. As a classic science fiction movie asked, "All the universe, or nothing--which shall it be?"
Edward Wright is president of X-Rocket LLC, a company specializing in spaceflight services, training, and education.
NOTE:The views of this article are the author's and do not reflect the policies of the National Space Society.
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