Space Shuttle Programme

A. A spacecraft is a vehicle that travels through space. Spacecraft include robotic or unmanned space probes as well as manned vehicles. The term is sometimes also used to describe artificial satellites, which have similar design criteria. The term spaceship is generally applied only to spacecraft capable of transporting people.

B. A spacesuit has at times been called a miniature spacecraft or spaceship, emphasizing its purpose of keeping its wearer alive while traveling in the vacuum of outer space.

C. NASA's Space Shuttle, officially called Space Transportation System (STS), is the United States' manned launch vehicle. It is partly reusable, and is the world's first spacecraft to be designed with this capacity. It is used to carry large payload to various orbits, for crew rotation of the International Space Station (ISS), and to carry out servicing missions. Each shuttle was designed for a projected lifespan of 100 launches.

D. The program started in the late 1960s and has totally dominated NASA's manned operations since the mid 1970s. Use of the Space Shuttle will be focused on completing the assembly of the International Space Station in 2010, and it will then be retired.

E. The Space Shuttle consists of four main components:

· the reusable Orbiter Vehicle (OV), with a large payload bay and three main engines (used while the external fuel tank is attached) and an orbital maneuvering system with two smaller engines (used after the external tank has been disposed of)

· a large expendable external fuel tank (ET) containing liquid oxygen and liquid hydrogen for the three main engines of the orbiter; it is jettisoned 8.5 minutes after launch at an altitude of 109 kilometers and breaks up in the atmosphere upon reentry; 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) and aluminum (fuel, 16 %); they are separated two minutes after launch at a height of 66 km and are recovered after landing in the ocean, their fall slowed by parachutes.

F. The Shuttle has a large payload bay taking up much of its length. The payload bay doors have heat radiators mounted on their inner surfaces, and so are kept open while the Shuttle is in orbit for thermal control. Thermal control is also maintained by adjusting the orientation of the Shuttle relative to Earth and Sun. Inside the payload bay is the Remote Manipulator System, a robot arm used to retrieve and deploy payloads. Since the arm is a crucial part of the Thermal Protection Inspection procedures now required for shuttle flights, it will likely be included on all future flights.

G. 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 they also soak up water and thus need to be protected from the rain. Later many of the tiles on the cooler portions of the Shuttle were replaced by large blankets of insulating felt-like material, which means huge areas no longer have to be inspected as much.

H. 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. The computers use the HAL/S programming language. In addition to the " glass cockpit" 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. With the coming of the Space Station, the Orbiter's internal airlocks are being replaced with external docking systems to allow for a greater amount of cargo to be stored on the shuttle mid-deck during Station resupply missions.

I. For STS-1 and STS-2 the external tank was not painted. This saved 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. STS-91 saw the first flight of the " super light weight external tank". This version of the tank is made of the Aluminum-Lithium alloy. It weighs 7, 500 lb (3.4 t) less than the last run of light-weight tanks. As the Shuttle cannot fly unmanned, each of these improvements has been " tested" on operational flights. 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.

Comprehension Check

1. Complete the scheme according to the content of the text: