STS - Space Transportation System

by Jeanette Cain

In 1981, the Space Transportation System made its first test flight. The STS, or the better known space shuttle, consisted of an orbiter with three main engines, 2 solid boosters, an external tank, and the cargo, which was carried in the orbiter's payload bay. The main engines received propellant (fuel) for the journey from the external tank. When the orbiter returns to Earth, it lands on a long runway. The main engines start at 0.12-second intervals, then the solid rocket boosters start up. Once the bolts, which were holding the STS down, are released, the OMS, orbital maneuvering system, will put the orbiter into its correct orbit, but only after discarding the tank and boosters. The OMS, with the help of the thrusters, position the orbiter for correct re-entry and landing.

What has the space shuttle accomplished? It carried the Spacelab space station, and provides launching for probes and satellites. The STS also has a platform that is used for repairs, or construction, when in orbit. The shuttle orbiter is a space plane, and the STS will carry one orbiter. Although it may carry one, it may choose from one of four-the Discovery, Atlantis, Columbia, or Endeavour. Any one of these orbiters have the ability to carry seven crew members, and the capacity for at least a 10-day flight. Its cabins hold a flight deck, middeck, and a lower deck, which holds life-support equipment.

The solid rocket boosters send the orbiter into a 45 km altitude, which boosters have been made for the purpose of 20 flights. After the flight, the rocket boosters will be recovered from the ocean, and refurbished for the next mission. When the STS is grounded, the boosters will support its entire weight. The boosters are connected to the orbiter by the external tank when the shuttle is launched into orbit. The external tank also holds the liquid hydrogen fuel and the liquid oxygen. However, after each flight the external tank will be discarded.

As the orbiter re-enters the Earth's atmosphere it encounters heat friction. The friction may range from 300o Centigrade and 1,500o Centigrade. The orbiter was designed with a thermal protector, or protective coating, which will prevent the orbiter from melting and burning up on its re-entry. Manufacturers designed different protection types to shield different parts. The edges of the nose tip and the wings will acquire the hottest temperatures. Approximately 70% of these surfaces are covered in tiles capable of absorbing heat between 370o Centigrade and 1,260o Centigrade. Since the tiles are capable of slow transference of heat, heat is prevented from reaching the orbiter.

A tragedy most everyone remembers: the Challenger explosion on January 28, 1986. It was caused by the failure of a joint between two segments of the boosters, and all crew members were killed. The hot gases had burned through the booster casing that hit the external tank, causing it to split. With the liquid hydrogen burning so excessively, the Challenger had broken apart within 15 seconds.

There have been more successes than failures. The Discovery orbiter placed the Hubble Space Telescope in its orbit on the mission from April 24 through the 29th in 1990. The Atlantis orbiter placed the Galileo probe into position for an upper stage to boost it on its journey to Jupiter.

Sources:
1. Editors. Secrets of the Universe. International Master Publishing: US. 1999

2. Couper, Heather and Nigel Henbest. Space Encyclopedia DK Publishing, Inc.: NY 1999