Single-stage-to-orbit

A single-stage to orbit launcher describes a as-yet theoretical class of spacecraft designed to place a load into orbit as a self-contained vehicle without the use of multiple "stages" that are destroyed or released during the flight. No actual launchers have been constructed - current launches are either performed by the Space Shuttle, which is assisted by fuel tanks that are jettisoned during the initial climb, and expendable solid rockets, or by multi-stage expendable rockets.

The continual pressure on the budget of NASA, and the huge launch costs of the Space Shuttle, a space vehicle designed to radically reduce launch costs but which conspicuously failed to do so, sparked interest throughout the 1980's in designing a successor vehicle. Several suggestions have been made, but in general they are basically more automated, smaller versions of the Shuttle.

Studies of the cost of the Shuttle all show a single problem as the root cause of its high cost -- manpower. Contrary to the original design which was an airliner-like maintenance schedule with a two-week turnaround, the delivered vehicle had to be made more and more fail-safe as various abort systems were removed from the design. In addition the policy of using the most technically advanced engines and materials (seen as a NASA duty) backfired in a number of ways.

The result is a vehicle that is taken almost completely apart after every mission. The engines are removed and rebuild, large amounts of the structure are taken off for testing, and the entire cycle takes months. Even without these problems the system still requires the various parts - the Orbiter, SRBs and ET, to be collected and assembled in the VAB, which alone takes weeks. Given that there are 25,000 people working on Shuttle operations, the payroll alone is the single biggest cost in flying.

Many in the American space community came to the conclusion that the best way to solve this problem was an entirely self-contained, reusable vehicle. The idea is that such a vehicle would require much less processing that the Shuttle, who's individual parts have to be collected back together and re-assembled.

Another advantage would be the inclusion of "all-aspect abort", meaning that the craft could abort at any point in the launch cycle, and return at least its cargo intact. The lack of such abort modes on the Shuttle is what leads to the increadible failure avoidance costs and massive overhauls.

Combine this with more reliable systems and a fully-automated maintenance system, and the cost of launch goes down considerably. If anything does need to be looked at it will tell you, and if not, add fuel and go again.

On the downside is is technically much harder to make a such a spacecraft. Staging is used beacuse is greatly reduces the total mass that flies all the way into space, the rocket is continually shedding fuel tanks and engines that are now dead weight. This increases their mass fraction and makes the overall job much easier.

Without staging the rocket needs to lift everything into orbit all the way. That means that in order for the rocket to have the same sort of mass fraction as a staged design, it must used every weight saving trick in the book. At one time this appeared to be basically impossible, but the rapid advances in materials technology and decrease in weight for auxilury systems like flight computers has slowly reduced that to "potentially possible". Its unclear today whether or not a useful SSTO can be built, although the chances get better every year.

The closest approach to a real vehicle was the unmanned DC-X technology demonstrator, originally developed by McDonnell Douglas for the Strategic Defense (anti ICBM) program office. Although the test program was not without mishap (including a minor explosion), the DC-X demonstrated without any doubt that the concept was indeed sound. A tiny crew of people worked on the machine between flights, and the craft was once turned around by six people in one day.

However the program ran out of money in the midst of its test series in a general downsizing of the SDI budget. At that point NASA took the ship for their own testing. Emmediately they decided to go against the entire program concept, and added a number of new and advanced features that were of little import to a system that is proving management goals, not technical ones. After a rebuild to include new lightweight tanks, the ship was dropped on landing and exploded. NASA declined to fix it.

ome have suggested this was a NIH issue, as NASA already had its own SSTO project underway, the X-34. However that project ran into continued cost overruns, and NASA finally gave up on it. Today there is almost no research into SSTO, much to the chagrin of everyone involved.

Note:

Many others in the industry declared that the solution to the problem is the exact opposite of SSTO. That is, make completely non-advanced rocket from off-the-shelf parts, and dump it in the ocean after it flies. However this is exactly what previous systems have done, and it appears any hope of lowering the cost by reducing the technical complexity of the individual systems is unlikely to reduce costs much at all. Most of this appeared to be based on simple engine systems using "low-tech" fuels, but this is exactly what the Russians and Chinese do, without the huge cost savings proponents claimed.