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Atlantis on the pad
The shuttle Atlantis on the pad on the evn of the final mission of the Space Shuttle program. What lessons from the shuttle can we carry forward to future programs? (credit: J. Foust)

Space Shuttle 2.0: What did we learn?


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The last shuttle launch is behind us and a number of articles and blogs are appearing lamenting both the end of an era and the death knell of the US space program. While the Space Shuttle was a remarkable vehicle, it’s perhaps time to revisit its original design goals, remember why we started this journey in the first place, and understand the foundation that the STS Program built for the future.

The key to commercial involvement in space is airline-like operations and high reusability. Only with a reusable, highly operational system can we get the launch costs down far enough for the average aerospace enthusiast to afford to get to orbit.

NASA’s initial goal for the Shuttle was not only to build and maintain a space station in LEO and then use this space station to assemble and launch exploration missions to the Moon and Mars, but also to support commercial operations. To accomplish this most effectively required airline-like ground operations, enabling quick turnaround, and very high flight rates (the original proposal teams all had airlines as team members). The engines were to fly 55 times before overhaul and the airframes were good for 100 flights before servicing, If these goals could be met, launch costs would fall to little more than three times the cost of propellants, travel to space would begin on a regular scheduled basis, and ultimately commercial space transportation would materialize.

The key to commercial involvement in space is airline-like operations and high reusability. Only with a reusable, highly operational system can we get the launch costs down far enough for the average aerospace enthusiast to afford to get to orbit. You can afford to own a car because General Motors makes millions of them each year, so your share of the development cost is miniscule and the production cost is covered by the price you paid, which is amortized over thousands of trips across town or to work. Operationally, a trip across town in your car costs roughly $10 or about a nickel per pound of payload. You can afford to fly across the country because the very expensive airplane you flew on was produced by Boeing by the thousands and is amortized over tens of thousands of flights, so the cost of each flight is primarily the cost of fuel, crew, and maintenance (about $250,000). A trip across the country has a price of roughly $400, or about $2 per pound of payload. In theory, an airplane-like launch system amortized over thousands of missions could have costs per flight approaching the cost of propellants, crew, and maintenance. This gets the launch down into the $2 million to $3 million range.

The Space Shuttle was originally designed to be the first fully reusable launch vehicle (RLV). The initial design had first and second stages that landed on a runway at the launch site, were turned around in less than a week (160 hours), and flew forty times a year. The cost per mission was promised at $10.5 million (in 1972 dollars), for a cost per pound to low earth orbit (LEO) of $210 per pound. Unfortunately, after the hugely successful Moon landings that helped the US win the Space Race, Richard Nixon could not continue to fund NASA at five percent of the federal budget (there was a war in Vietnam to pay for). He cut NASA to three percent of the federal budget, and this seriously limited NASA’s budget for shuttle development. To meet these budget constraints, NASA simplified the design. They replaced the large flyback booster with two water-recoverable Solid Rocket Boosters (SRBs), and the fully reusable orbiter with a partially reusable orbiter (all cryogenic propellants in a drop tank jettisoned on-orbit). They retained the new high-pressure staged combustion rocket engines. In theory, the move from fully reusable to partially reusable should have had only a small impact on turnaround time and roughly doubled the cost per mission. However, several decisions during the preliminary design and procurement process prevented the shuttle from reaching the true potential of a fully reusable and highly operational vehicle.

Even though the last Space Shuttle flight may be the end of an era, what we take away from the experience could still jumpstart commercial space travel.

The engines never reached their design goals and that worked against operability in several ways. First, the engines had to be removed and rebuilt each flight adding to cost, and secondly their lack of thrust growth capability meant that many shuttle operational features were never added, because their additional weight would take away critical payload mass. The new shuttle tile thermal protection system (TPS) proved to be hygroscopic (absorbs water out of the air), which meant each individual tile had to be waterproofed between flights, and the waterproofing compound was so highly toxic that the workers had to wear bio-isolation suits when working. The final Space Shuttle required hundreds of workers to service the vehicle, resulting in ground turnaround times averaging 87 days instead of the planned 160 hours; and instead of $10.5 million per flight, the touch labor and material costs per flight approached $200 million. The total Kennedy Space Center (KSC) cost per flight was over $500 million, or roughly $10,000 per pound.

NASA was correct in chasing the dream to achieve $210 per pound. Today, a typical trip to low Earth orbit (LEO) costs about $80 million, or about $6,000 per pound. Most of this cost is the expensive launch vehicle that gets thrown away during each launch, while the cost of propellants and launch operations is a small fraction (about 10%) of the total launch cost. If money were made available to fund development of a next generation RLV (call it Shuttle 2.0), the nonrecurring cost per vehicle (about twice the cost of an airliner), would be amortized over 100 to 200 flights, and a trip to LEO would cost about $5 million, or $250 per pound of payload. If we had an advanced RLV, the cost per vehicle could be amortized over 500 to 1,000 flights, the payload could be doubled to 20 metric tons, and a trip to LEO would cost $3 million or $75 per pound. That is low enough to be afforded as the vacation of a lifetime.

There are still many questions about the future of RLVs and commercial space transportation. Is the space tourism market big enough to support the dozens of RLVs that need to be sold to payback the development costs, and does the supply and demand of the space market provide enough revenue to operate the RLVs profitably? The airline business provides thousands of flights per year, but they show a profit only about half the time because of the large number of competitors (supply) in the market. Is the space transportation market going to be orderly, or largely uncontrolled like the air transportation market? Our hypothetical Fully Reusable Earth to Orbit System (FRETOS) is going to be more expensive to develop than a modern airliner, so additional sources of revenue for the operators are probably necessary, and previous studies have shown that additional revenue can be generated in LEO if the cost per pound drops below $500 (see the final report of Commercial Space Transportation Study published in 1993 by Boeing, General Dynamics, Lockheed, Martin, McDonnell, and Rockwell). They showed that the business opportunities were numerous and lucrative (think of a bank that operates above all banking laws), but only if the cost to orbit was low enough to support the supply and demand.

Even though the last Space Shuttle flight may be the end of an era, what we take away from the experience could still jumpstart commercial space travel.


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