Space Transportation System
The roots of the space shuttle go back to the mid 1960's when the US Air Force did studies on a transportation system to support large military space stations. NASA was thinking about space stations, lunar bases, and missions to Mars. Because of the costs involved, none of this was to be. Even the idea of a shuttle was threatened unless costs could be contained. Total costs for the shuttle program were about $199 billion (in 2010 US ollars).
The Air Force also had military plans for space. However, the X-20 (DynaSoar) was replaced by the MOL (Manned Orbiting Laboratory), which in turn was cancelled over fears that it would duplicate much of Skylab. The Air Force was stung over these developments. An agreement between NASA and the Air Force would prompt the Air Force to give political support to the threatened space shuttle in turn for military use of the new system. As such, many of the Air Force's requirements had to be met in the shuttle design.
The go ahead for the space shuttle was received in August 1972. The shuttle was to be a joint effort between the Air Force and NASA, and was to reduce the cost of launching satellites into space by building a reusable vehicle in place of the expendable launch vehicle (ELV). The shuttle would be used for both civilian and military purposes. Military satellites could be placed into polar orbit by launching the shuttle from Vandenberg Air Force Base in California.
The shuttle, being a manned vehicle, inherited the costs of Houston's Manned Space Flight Center. With its own cost overruns and launch costs, it is actually cheaper to use ELV's. Not only did development costs run over, so did weight. The final system came in about 20% heavier than forecasted. Oddly enough, much of the extra weight came from the Air Force requirements for payload size and landing maneuverability. This made launches from Vandenberg impossible. After the Challenger disaster, the Air Force withdrew its involvement in the shuttle.
Prime contractors for the shuttle are: the orbiter - North American Rockwell; orbiter engines - Rocketdyne Division of North American Rockwell; solid booster rockets - Thiokol; and the external fuel tank - Martin Marietta.
Not all of the shuttle system is reusable. The orbiter comes in and lands as a glider and can be prepared for the next flight. The solid rocket boosters are jettisoned and parachute into the ocean for recovery. They are then dismantled and refurbished for another flight. The external fuel tank is expendable and not reused. In theory, each orbiter could withstand up to 100 flights. The X-30, a proposed replacement for the space shuttle, was killed in the early 1990's.
Initial hopes set the cost of each mission in the range of (US)$10 to (US)$20 million. Allowing for inflation, that would equate to about (US)$100 million today. During its lifetime, the shuttle incurred costs totalling (US)$209.1 billion (2006 dollars). That includes development and operational costs. On average, each of the 135 missions cost in excess of (US)$1.5 billion. Turn around time between flights was initially planned to be about two weeks. In the end, it typically took several months.
The Endeavour, built in 1991 to replace the Challenger, cost (US)$1.7 billion. That is just the cost for the orbiter, not the entire shuttle system (orbiter, three main engines, external tank, and two solid rocket boosters).
The shuttle launch criteria is varied and complex. Listed here are some of the major points which must be met. For a more comprehensive explanation of the criteria, read NASA release 103-96.
- Launch may not occur if the temperature is 35° F or colder.
- The temperature cannot exceed 99° F for 30 consecutive minutes.
- Peak wind speed is 30 knots. When the wind direction is between 100 degrees and 260 degrees, the maximum wind speed may be as low as 24 knots.
- Winds in the solid rocket booster recovery area must be forecasted not to exceed 26 knots, no seas to exceed Sea State 5 (8-13 feet).
- There can be no precipitation at the launch site.
- There can be no reports of lightening within 10 nautical miles of the flight path for 30 minutes prior to launch.
- Launch is not permitted through cloud types known to contain hazardous electric fields.
- Direct visual observation must be possible to 8000 feet.
- Suitable weather must be reported from Trans-Oceanic Abort Landing Sites (TAL).
- Maximum of 50% cloud coverage below 8000 feet.
- Visibility of 5 miles or greater.
- Peak cross winds cannot exceed 15 knots (12 knots at night).
- Headwind cannot exceed 25 knots.
- Tailwind cannot exceed 10 knots average, 15 knots peak.
- No thunderstorm, lightening, or precipitation within 30 nautical miles of the landing site.
- Turbulence must be less than or equal to moderate intensity.
More information can be obtained from the WorldSpaceFlight.com addendums pages.
Once the shuttle has landed, the crews must power down all the systems and wait for ground crews to clear the area of toxic fumes and gases with special fans. This can take from ½ hour to a hour. The gases come from a gas turbine (powered by the decomposition of hydrazine and used to move steering and flight controls and wheel brakes) and an ammonia-water evaporator used to cool equipment during descent.