Space Shuttle program

NASA's Space Shuttle program is an ongoing endeavor, started in the early 1970s, that had created the world's first reusable spacecraft, and the first spacecraft capable of carrying large satellites both to and from (low) Earth orbit. Each shuttle is designed for a projected lifespan of 100 launches. One of the main purposes of the program was to construct and service a space station. With the International Space Station this purpose is now a reality.

The Space Shuttle consists of four main components:

• the reuseable orbiter itself
• a large expendable external fuel tank (ET) containing liquid oxygen and liquid hydrogen (in inner tanks at the forward and aft side, respectively) for the three main engines of the orbiter; it is discarded 8.5 minutes after launch at an altitude of 109 kilometers and breaks up in the atmosphere; the pieces fall in the ocean and are not recovered)
• a pair of reusable solid-fuel rocket boosters (SRB); the propellant consists mainly of ammonium perchlorate (oxidizer, 70 % by weight), aluminum (fuel, 16 %); they are separated two minutes after launch, at a height of 66 km, and have parachutes; after falling in the ocean they are recovered.

Other statistics:

• Space Shuttle stack height: 56.14 meters (184.2 feet) tall
• Orbiter alone: 37.23 meters (122.17 feet) long
• Wingspan: 23.79 meters (78.06 feet)
• Weight at liftoff: 2,041,166 kilograms (4.5 million pounds)
• Weight at end of mission: 104,326 kilograms (230,000 pounds)
• Maximum cargo to orbit: 28,803 kilograms (63,500 pounds)
• Orbit: 185 to 643 kilometers (115 to 400 statute miles)
• Velocity: 27,875 kph (17,321 mph)

Space Shuttle Atlantis transported by a Boeing 747, 1998 (NASA)

Space Shuttle Columbia during takeoff, 1981 (NASA)

Shuttles

• test vehicle not suitable for earth orbit:
  • Enterprise
• lost in accidents (see below):
  • Challenger
  • Columbia
• in use:
  • Atlantis
  • Discovery
  • Endeavour

The Shuttle decision

NASA had conducted a series of paper-projects throughout the 1960s on the topic of reusable spacecraft to replace their expedient "one-off" systems like the Mercury, Gemini, and Apollo. Meanwhile the Air Force had a continuing interest in smaller systems, and were involved in their own project called Dynasoar[?]. In several instances groups from both worked together to investigate the state of the art.

With Apollo effort winding down in the second half of the 1960s, NASA started looking to the future of the space program. They envisioned an ambitious program consisting of a large space station being launched on huge boosters, served by a reusable logistics "space shuttle", both providing services for an eventual manned mission to Mars.

However reality was to interject and NASA found themselves with a rapidly cut budget. Instead of looking at their future as a whole, they instead attempted to save as many of the individual projects as possible. The mission to Mars was quickly eliminated, but a station and shuttle continued on. Eventually only one of them could be saved, so it stood to reason that a low-cost shuttle system would be a better bet, because without it a station would never be affordable.

A number of designs were proposed, but many of them were complex and varied widely in their systems. An attempt to re-simplify was made in the form of the "DC-3" by one of the few people left in NASA with the political clout to pull it off, Maxime Faget[?], who had designed the Mercury capsule among others. The DC-3 was a small craft with a 20,000lbs (or less) payload, a four-man crew, and limited manuverability. At a minimum, the DC-3 provided a baseline "workable" (but not terribly advanced) system by which other systems could be compared for price/performance tradeoffs.

The final defining moment was when NASA, in desperation to see their only remaining project saved, went to the Air Force for its blessing. NASA asked that the AF place all of their future launches on the shuttle instead of their current expendable launchers (like the Titan II), in return for which they would no longer have to continue spending money upgrading those designs -- the shuttle would provide more than enough capability.

The Air Force relucantly agreed, but only after demanding a much greater increase in capability to allow for launching their projected upcoming spy satellites. These were quite large and weighed an estimated 40,000 lbs, flown to a polar orbit (which requires more capacity to get to). And since the AF also wanted to be able to abort after a single orbit (as did NASA), the spacecraft would also require the ability to manuver to either side of its orbital track to adjust for the launching point rotating away from it while in polar orbit - in a 90 minute orbit Vandenberg would move over 1,000 miles, whereas in a "normal" equatorial orbit NASA needed the range would be less than 400.

The result was that the simple DC-3 was clearly out of the picture because it had neither the cargo capacity nor the cross-range the Air Force demanded. In fact all existing designs were far too small, as a 40,000 lbs delivery to polar orbit is similar to a 65,000 lbs delivery to a "normal" 28 degree equitorial orbit. In fact any design using simple straight or fold-out wings was not going to meet the cross range requirements, so any future design would require a more complex delta wing.

Worse, any increase in the weight of the upper portion of the shuttle, which had just occurred, requires an even bigger increase in the capability of the lower stage it uses to launch it. Suddenly the two-stage system grew in size to something larger than the Saturn V, and the cost to develop it skyrocketed.

While all of this was going on, others were suggesting a completely different approach to the future. They stated that NASA was better off using the existing Saturn to launch their space station, supplied and manned using modified Gemini capsules on top of the Air Force's newer Titan II-M. The cost of development for this looked to be considerably less than the shuttle alone, and would have a large space station in orbit earlier.

The answer within those groups dedicated to the shuttle was to show that as long as you have enough launches, the development cost of the system would be overwhelmed by the cost of the rockets you would otherwise throw away. One factor that needs to be considered is inflation though, and in the 1970s this was high enough that the payback from the development had to happen very quickly or that money would never pay for itself. In other words you needed a fairly high launch rate to make the system work.

But there was no way that a space station or Air Force loads could demand such rates (roughly 1 to 2 per week), so they went further and suggested that all future launches would take place on the shuttle, once built. In order to do this the cost of launching the shuttle would have to be lower than any other system with the exception of the very small, which they ignored for practical reasons, and very large, which were rare and terribly expensive anyway.

With a baseline project now gelling, NASA then started to work though the process of obtaining stable funding for the five years the project would take to develop. Here too they found themselves increasingly backed into a corner.

With the budgets being pressed by inflation at home and the Vietnam war abroad, the govornment generally couldn't care less about NASA and were looking to make further deep cuts. But with a single long term project on the books, there wasn't much they could do in terms of cutting whole projects -- the shuttle was all that was left, cut that and there would be no NASA by the 1980s.

Instead they looked to reduce the year-to-year costs of development to a stable figure. That is, they wished to see the development budgets spread out over several more years. This is somewhat difficult to do, you can't build half a rocket. The result was another intense series of redesigns in which the re-usable booster was eventually adbandoned as impossible to pay for. Instead a series of simpler rockets would launch the system, and then drop away for recovery. Another change was that the fuel for the shuttle itself was placed in an external tank instead of the internal tanks from the pervious designs. This allowed the larger payload bay in an otherwise much smaller craft, although it also meant throwing away the tankage every time.

The last remaining debate was over the nature of the boosters. NASA had been looking at no less than four solutions to this problem, one a development of the existing Saturn lower stage, another using "dumb" pressure-fed liquid fuel engines of a new design, and finally either a large single solid rocket, or two (or more) smaller ones. The decision was eventually made on the smaller solids due to their lower development costs. While the liquid fuel systems provided better performace, delivery capability to orbit is much more a function of the upper-stage performance and weight than the lower. The money was simply better spent elsewhere.

Shuttle development

The shuttle program was launched on January 5, 1972, when President Richard M. Nixon announced that NASA would proceed with the development of a reusable low cost space shuttle system.

The project was already to take longer than originally anticipated due to the year-to-year funding caps. Nevertheless work started quickly and several test articles were available within a few years.

Most notable among these was the first complete Orbiter, originally to be known as Constitution. However a massive write-in campaign on the part of fans of the TV show Star Trek convinced the White House to change the name to Enterprise. Enterprise was rolled out on September 17, 1976 and later conducted a very successful series of landing tests which was the first real validation of the gliding abilities of the design

The first fully functional shuttle orbiter was the Columbia, which was delivered to Kennedy Space Center on March 25, 1979, and had its first launch on April 12, 1981, with a crew of two. Challenger was delivered to KSC in July 1982, Discovery was delivered in November 1983, and Atlantis was delivered in April 1985. Challenger was destroyed in an explosion during launch in January 1986 with the loss of all seven astronauts on board, and the orbiter Endeavour was built as a replacement and delivered in May 1991. Columbia was lost, with all seven crew, in a re-entry mishap on February 1, 2003.

The Shuttle in retrospect

Whilst the shuttle has been a reasonably successful launch vehicle, it was unable to meet its goals of radically reducing flight launch costs, as each mission costs on the order of 500 million dollars rather than initial hopes of $10 to $20 million.

Although the design is radically different than the original NASA needs, the project was still supposed to meet the upgraded AF goals as well as be much cheaper to fly in general. What went wrong?

One issue appears to be inflation. During the 1970s the US suffered from the worst inflation in modern history, driving up costs by about two times by 1980. In contrast, the rate between 1990 and 2000 was only 34% in total. This has the effect of magnifying the development costs of the shuttle tremendously.

However this doesn't explain the high costs of the continued operations of the shuttle. Even accounting for inflation the launch costs on the original estimates should be about 100 million today. To explain this you have to look at the operation details of maintaining and servicing the shuttle fleet, which turned out to be tremendously more expensive than anticipated.

When originally conceived the shuttle was to operate similar to an airliner. After landing the Orbiter would be checked out and start "mating" to the rest of the system (the ET and SRBs) and be ready for launch in as little as two weeks. Instead this sort of turnaround in fact takes (typically) months. This is due, in turn, to the continued "upgrading" of the inspection process as a result of the Challenger explosion. Even simple tasks now require unbelievable amounts of paperwork.

The result is a massively inflated manpower bill. There are 25,000 workers in shuttle operations (perhaps an older number), so simply multiply any figure that you choose for an average annual salary, divide by six (...launches per year), and there you have it.

The lessons of the shuttle have been seen as different depending on who you ask. In general however, future designers look to systems with only one stage, automated checkout, and in some cases, overdesigned low-tech systems.

Perhaps the most annoying aspect of the shuttle system is to consider the Air Force participation. While the blame rests solely at the feet of NASA for getting them involved in the first place, it was the Air Force requirements that certainly drove the system to be as complex and expensive as it is today. Ironically neither NASA nor the Air Force got the system they wanted or needed, and the Air Force eventually threw in the towel and returned to their older launch systems and abandoned their Vandenburg shuttle launch plans.

Shuttle description

The Space Shuttle consists of four main components; the reuseable orbiter itself, a large expendable external fuel tank, and a pair of reusable solid-fuel booster rockets. The fuel tank and booster rockets are jettisoned during ascent. The longest the shuttle has stayed in orbit in a single mission is 17.5 days, on mission STS-80 in November 1996.

The Space Shuttle system has had numerous improvements over the years.

The Orbiter has changed its thermal protection system several times in order to save weight and ease workload. The original silica-based ceramic tiles need to be inspected for damage after every flight, and also soak up water and thus need to be protected from the rain. The later problem was initially fixed by spraying the tiles with Scotchgard, but a custom-solution was later purchased. Later many of the tiles on the cooler portions of the Shuttle were replaced by large blankets of insulating material instead, which means huge areas (notably the cargo bay area) no longer have to be inspected as much.

Internally the Shuttle remains largely similar to the original design, with the exception that the avionics continues to be improved. The original systems were "hardened" IBM 360 computers connected to analog displays in the cockpit similar to contemporary airliners like the DC-10. Today the cockpits are being replaced with "all glass" systems and the computers themselves are many times faster. In addition several improvements have been made for safety reasons after the Challenger explosion, including a crew escape system for use in situation that require the Orbiter to "ditch".

The Space Shuttle Main Engines[?] have had several improvements to enhance reliability and power. This is why during launch you may hear curious phrases such as "Go to throttle-up at 106%". This does not mean the engines are being run over-limit. The 100% figure is the power level for the original main engines.

The external tank[?] was originally painted white to protect the insulation that covers much of the tank, but improvements and testing showed that it was not required. This saves considerable weight, and thereby increases the payload the orbiter can carry into orbit. Additional weight was saved by removing some of the internal "stringers" in the hydrogen tank which proved to be unneeded in flight. The resulting "light weight external tank" has been used on the vast majority of shuttle missions.

And, of course, the SRBs have undergone improvements as well. Notable is the adding of a third O-ring seal to the joints between the segments, which occurred after the Challenger accident.

A number of other SRB improvements were planned in order to improve performance and safety, but never came to be. These culminated in the considerably simpler, lower cost and better performing Advanced Solid Rocket Booster which was to have entered production in the early to mid 1990s, but was later cancelled to save money. In addition the Air Force developed their own much lighter single-piece design using a new filament-wound system, but this too was cancelled.

Shuttle accidents

Two shuttles have been destroyed, both with the loss of all astronauts on board:

• Challenger - lost 73 seconds after lift-off, January 28, 1986
• Columbia - lost during re-entry, February 1, 2003: see Space Shuttle Columbia disaster

see also Shuttle Buran

External links

• Orbiter Vehicles (http://science.ksc.nasa.gov/shuttle/resources/orbiters/orbiters)
  
• NASA Human Spaceflight - Shuttle (http://spaceflight.nasa.gov/shuttle/) Current status of Shuttle missions