Tuesday, November 29, 2011

SSTO: A Spaceship for the Rest of US


A Spaceship for the Rest of US

NSS Policy Paper (1992)

by Allen Sherzer


Space is an important and growing segment of the U.S. economy. The U.S. space market is currently over $5 billion per year, and growing. U.S. satellites, and to a lesser degree U.S. launch services, are used throughout the world and are one of the bright stars in the U.S. balance of trade.

The future is even brighter. The space environment promises new developments in materials, drugs, energy, and resources, which will open up whole new industries for the United States. This will translate into new jobs and higher standards of living not only for Americans but for the rest of the world's people.

Standing between us and these new industries is the obstacle presented by the high cost of putting people and payloads into space. This paper addresses the reasons why access to space is so expensive and how those costs might be reduced by looking at the problem in a different way.

Finally, this paper will describe a radical new spacecraft currently under development. Called Single Stage to Orbit (SSTO), it promises to greatly reduce costs and increase flexibility.

Access to Space: Expensive and Dangerous

Access to space today is very expensive, complex, and dangerous With U.S. expendable launchers like Atlas, Delta, and Titan, it generally costs about $3,000 to $8,000 to put a pound of payload into low Earth orbit (LEO). In addition, U.S. expendables require extensive ground infrastructure to do final assembly and payload integration and complex launch facilities to actually launch the rocket. Finally, despite all the extra care and effort, they don't work very well and even the best launchers fail about 3% of the time (would you go to work tomorrow if there was a 3% chance of your car exploding?).

Even the U.S. Space Shuttle, which was supposed to give the U.S. routine low cost access to space, has failed. A Shuttle flight costs about $500 million (roughly $10,000 per pound to LEO). Even going full out, NASA can only launch each Shuttle about twice a year (for a total of eight flights).

The effects of these high costs go deeper than the price tag for the launches themselves. Space equipment is much more expensive than comparable equipment meant for use on Earth, even when tasks are similar and the Earthly environments are harsh. The difference is that space equipment must be as lightweight as humanly possible and must be as close as humanly possible to 100% reliability. Both of these extra requirements are ultimately problems of access to space: if every extra pound costs thousands of dollars, and replacing or repairing a failed satellite is impossibly expensive, then efforts to reduce weight and improve reliability make sense. Unfortunately, they also greatly increase price.

With equipment so expensive, obviously building extra copies is costly, and launching them is even worse. This encourages space projects to try to get by with as few satellites as possible. Alas, this can backfire: when something does go wrong, there isn't any safety margin...as witness the U.S.'s shortage of weather satellites at this time. Expensive access to space not only produces costly projects, it produces fragile projects that assume no failures, because safety margins are too expensive. Lamentably, failures do happen.

Finally, although research in space holds great promise for new scientific discoveries and new industries, it is progressing at a snail's pace, and companies and researchers often lose interest early. Why? Because effective research requires better access to space. Scientific discoveries seldom come as the result of single experiments: even when a single experiment is crucial, typically there is a long series of experiments leading up to it and following through on it. And getting the "bugs" out of a new industrial process almost always requires a lot of testing. But how can such work be done if you only get to fly one experiment every five years? Good researchers and innovative companies often decide that it's better to avoid space research, because it costs too much and takes too long. The ones who haven't abandoned space research are looking hard at buying flights on Russian or Chinese spacecraft: despite technical and political obstacles, they can fly their experiments more often that way.

People excuse this because it has always been this way and so probably always will be (after all, this is rocket science). But there are a lot of reasons to think that it needn't be so complex and expensive.

Spacecraft are complex, expensive, and built to aerospace tolerances but they are not the only products of that nature we use. A typical airliner costs about the same as a typical launcher. It has a similar number of parts and is built to similar tolerances. The amount of fuel a launcher burns to reach orbit is about the same as an airliner burns to go from North America to Ausralia. Looked at this way, it would seem that the cost of getting into orbit should be much closer to the $1500 it takes to get to Australia than to the $500 million dollars plus it takes to put an astronaut up.

Why the differences in cost? Largely they are due to different solutions to the same problems. Some of these differences are:

1. Throw away hardware. A typical expendable launch vehicle costs anywhere from $50 to $200 million to build (about the cost of a typical airliner) yet it is used one time and then thrown away. Even the 'reusable' Space Shuttle throws away most of its weight in the form of an expendable external tank and salvageable solid rocket motors. This is the single biggest factor in making access to space expensive.

Airlines use reusable hardware and fly their aircraft several times every day. This allows them to amortize the cost of the aircraft over literally thousands of passenger flights. The entire Shuttle fleet flies only eight times a year, while many airliners fly more than eight times per day.

2. Redundant Hardware and Checks. Since expendable launchers are used one time and then thrown away, they cannot be test-flown; huge amounts of effort therefore go into making sure they will work correctly. Since the payloads they launch are typically far more expensive than the launcher (a typical communication satellite can cost three times the cost of the launcher) millions can be and are spent on every launch to obtain very small increases in reliability. This is well beyond the point of diminishing returns and sometimes results in greater harm. For example, a couple of years ago a Shuttle Orbiter was almost damaged when it was rotated from horizontal to vertical with a loose work-platform support still in its engine compartment. The support should have been removed beforehand...and three signatures said it had been.

Airliners, since they are reusable and can also be tested before use, thus are able to be built to more relaxed standards without sacrificing safety. The exact same aircraft flew to get to your airport and it is likely that any failure would already have been noticed. In addition, aircraft are built with redundancy so they can survive malfunctions; launchers usually are not. Most in-flight failures of airliners result, at most, in delays and inconvenience for the passengers; most in-flight failures of launchers result in complete loss of launcher and payload.

3. Pushing the Envelope on Hardware. Current launchers tend to use hardware that is run all the time at the outside limit of its capability. This may be fine for expendable launchers which are used one time and don't need to be repaired for reuse. But this has also tended to carry over to the Shuttle which, for example, operates its main engines at around 100% of its rated thrust (this is like driving your car 55 MPH in first gear all the time). Because the hardware is used to its limit every time, it needs extensive checkout after every flight and frequent repair.

Airliners tend to be much more conservative in their use of hardware. Engines are used at far less than their full rated thrust and airframes are stressed for greater loads then they ever see. This results in less wear and tear which means they work with greater reliability and fewer repairs.

4. Labor Requirements. For all of the reasons given above, existing launchers require vast amounts of human labor to fly. The efforts of about 6,000 people are needed to keep the Shuttle flying. This represents a huge expense and is amortized only over eight or so Shuttle flights every year.

Airliners are far more streamlined and, for the reasons given above, don't need nearly as many people. A typical airliner only has 150 people supporting it, including baggage handlers, flight crews, ticketing people, and administration. Since the cost of those 150 people are amortized over thousands of flights per year, the cost per flight is very low.

Our current launchers are expensive and complex vehicles. Yet the fact that we routinely use vehicles with similar cost and complexity for far less cost indicate that the causes of high launch costs lie elsewhere. If we looked at the problem in a different way, we could try to build launchers the same way Boeing builds airliners. The next section will describe just such a launcher and how it is being built.

A Spaceship that Runs Like an Airliner: SSTO

For a long time, some launcher designers have realized that designing launchers the way airliners are designed would result in lower costs. Several designs have been proposed over the years and they are generally referred to as Single Stage to Orbit (SSTO) launchers.

1. Single Stage to Orbit (SSTO). Unlike an existing launcher which has multiple stages, a SSTO launcher has only one stage. This results in far lower operational costs and are key to reusability. Conventional launchers need expensive assembly buildings to stack the stages together before going to the launch pad. An SSTO only has one stage, so these facilities are not needed. This means that the only infrastructure needed to launch a SSTO is a concrete pad and a fuel truck.

2. Built for Ease of Use. SSTO vehicles are built to be operated like airliners. They can fly multiple times with no other maintenance needed other than refueling. If a problem is discovered, all components can be accessed with ease (by design). The defective Line Replaceable Unit (LRU) is replaced and launch can occur with only a short delay. If the problem is more complex or other maintenance is needed, the SSTO is towed to a hanger where the easy accessibility of parts insures rapid turnaround.

3. Standard Payload Interface. Payloads need access to services like power, cooling, life support, etc., while waiting for launch. The interfaces which provide these services are not standardized, adding cost and complexity to existing launchers. In effect, part of the launcher must be redesigned for each and every launch. SSTOs, however, would be designed with standard payload interfaces. This allows payload integration to occur hours before launch instead of weeks before launch. (Although in all fairness, the makers of expendable launchers are also slowly moving in this direction).

4. Built to be tested. Unlike expendables, SSTO vehicles do not have to be perfect the first time. Like airliners, they can survive most failures. Like airliners, they can be tested again and again to find and fix problems before real payloads and passengers are entrusted to them. Even when a failure does occur with a real payload aboard, usually neither the vehicle nor the payload will be lost. The reliability of SSTO vehicles should be close to that of airliners -- a loss rate of essentially zero -- and far better than the 3% loss rate of existing launchers.

SDIO Single Stage Rocket Technology Program

Recent advances in engine technology and materials have made most critics believe that the technology is now available to build a SSTO. In 1989, SDIO recognized the potential of this approach and commissioned a study to assess its risk. The study concluded that a SSTO vehicle is possible today. As a result of this study, SDIO initiated the Single Stage Rocket Technology Program (SSRT). The goal of the three phase SSRT program is to build a SSTO, thus providing routine cheap access to space.

Phase I consisted of four study contracts to develop a baseline design for a SSTO. General Dynamics and McDonnell Douglas proposed vehicles which both take off and land vertically (like a helicopter). Rockwell proposed a vehicle which takes off vertically but lands horizontally (like the Space Shuttle does today). Finally, Boeing proposed a vehicle which both takes off and lands horizontally (like a conventional aircraft).

In August 1991, SDIO selected the McDonnell Douglas vehicle (dubbed Delta Clipper) for Phase II development, and contracted for the construction of a 1/3 scale prototype vehicle called DC-X. This prototype is currently under development and should begin flying in April, 1993.

DC-X will provide little science data but a wealth of engineering data. It will validate the basic concepts of SSTO vehicles and demonstrate the ground and maintenance procedures critical to any successful orbital vehicle.

Phase III of the program will develop a full scale prototype vehicle called DC-Y. DC-Y will reach orbit with a substantial payload, hoped to be close to 20,000 lbs, and demonstrate total reusability. In addition, McDonnell Douglas will begin working with the government to develop procedures to certify Delta Clipper like an airliner so it can be operated in a similar manner.

Phase III was scheduled to begin in September of 1993 but SDIO will not be able to fund the Phase III vehicle. There is some interest in parts of the Air Force and it is hoped that they will fund DC-Y development. It will be a great loss for America if they do not.

After Phase III, it will be time to develop an operational Delta Clipper launcher based on the DC-Y. At this point government funding shouldn't be needed any longer and the free market can be expected to fund final development.


If a functional Delta Clipper is ever produced it will have a profound impact on all activities conducted in space. It will render all other launch vehicles in the world obsolete and regain for the United States 100% of the western launch market (half of which has been lost to competition from Europe and China). It will allow the United States to open up a new era for mankind, and regain our once commanding lead in space technology.




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