Ahoy, Space Ahead!
I pray for one last landing
On the globe that gave me birth;
Let me rest my eyes on the fleecy skies
And the cool, green hills of Earth.
Robert A. Heinlein; "The Green Hills of Earth"
n a clear blue February morning, 200,000 feet above Texas, members aboard the Columbia were getting ready for re-entry after a 16-day space mission dedicated to quest of scientific knowledge. Members went about routine checks and tasks and exhanged paltry, mundane conversation as they began to feel the first effects of gravity. Commander Rick Husband aboard the Columbia joked about the view outside, "Looks like a blast furnace, you definitely don't want to be outside now." Eleven minutes later, the words acquired a cruel twist, as the space shuttle disintegrated and the seven members aboard the spacecraft were reduced to debris. As NASA investigators piece begin the painful and protracted task of piecing the debris together, it is an extraordinary tribute to the seven spacefarers aboard the demand for scuttling manned space exploration, has not been raised despite the multitude risks and variables involved in mankind's odyssey into space.
The Columbia tragedy should not belie the fact that the extraordinary success rate of America's space program has been largely attributed to its pioneering space shuttle technology. Until the Apollo space program, NASA used one-shot disposable rockets used to place astronauts and equipment in outer space. This was an expense that even NASA with its deep pockets could ill-afford. Thus began a search for a reliable, but less expensive, rocket, that was reusable which culminated in the idea of a reusable space shuttle that could launch like a rocket but deliver and land like an airplane.
NASA carried out the design, cost and engineering studies on the space shuttle and in 1972, President Nixon announced that NASA would develop a reusable space shuttle or space transportation system (STS). The shuttle consisted of an orbiter attached to solid rocket boosters and an external fuel tank and was covered with insulating ceramic tiles that could absorb the heat generated during re-entry without harming the astronauts. NASA built a working orbiter called the Enterprise to test the aerodynamic design, but not to go into outer space. The Enterprise flew several flight and landing tests, where it was launched from a Boeing 747 and glided to a landing at Edwards Air Force Base in California.
NASA then went the whole hog and eventually built four shuttles namely Columbia, Discovery, Atlantis and Challenger. The first flight was in 1980 with the space shuttle Columbia, piloted by astronauts John Young and Robert Crippen. Columbia performed admirably and thus pioneered a series of highly successful flights by the other shuttles.
Disaster struck in 1986, as the shuttle Challenger was destroyed when a flame from a leaky joint on one of the solid rocket boosters ignited the fuel in the external fuel tank. The Challenger exploded and the entire crew was lost. The shuttle program was suspended for several years, while the reasons for the disaster were investigated and corrected.
Once the Challenger disaster was put behind, a new shuttle, Endeavour, was built to replace Challenger in the shuttle fleet. NASA has designed each space for 100 missions and, they have flown only about one-fourth of their expected lifetime. Thus even though things may look bleak in the aftermath of the Columbia tragedy, NASA's tryst with space is by no means over.
Let's take a look at the major components of a typical space shuttle. The space shuttle consists of the following major components:
Two solid rocket boosters (SRB) - vital for the launch
Engines- provides thrust for the launch
External fuel tank (ET) - carries fuel for the launch
Orbiter - carries astronauts and payload
Orbital Manoeuvring System - controls the orbiter
An archetypal space shuttle mission follows these major stages:
- Getting into orbit
- Functioning in the orbit
- Re-entry
- Landing
To lift the shuttle from the launch pad to the orbit, which can range from 185 to 643 km above the earth, the shuttle uses the following components:
- Solid rocket boosters (SRB)
- Engines of the orbiter
- External fuel tank (ET)
- Orbital Manoeuvring System (OMS)
The SRBs are solid rockets that provide 71 per cent of the thrust needed to lift the space shuttle off the launch pad. The orbiter has three main engines, which provide the remainder of the thrust (29 percent) to lift the shuttle off the pad and into orbit. The External Fuel Tank stores the fuel for the main engines. The ET is made of aluminium and aluminium composite materials. It has two separate tanks inside, the forward tank for oxygen and the aft tank for hydrogen, separated by an intertank region. The two orbital manoeuvring systems' (OMS) are used to place the shuttle into final orbit, to change the shuttle's position from one orbit to another, and to slow the shuttle down for re-entry.
Once the shuttle is in space the next challenge to be tackled is to live and work in space. The shuttle orbiter is the area where the astronauts reside and it must be able to provide water, light, food supply, wastes removal, temperature control, atmosphere control and other essentials for survival. The other major functionalities that shuttle orbits must provide are Communications and Tracking, Navigation, Electrical power generation and Information Exchange. In brief the shuttle orbiter should enable the astronauts to accomplish their mission objectives be it launching or retrieving satellites or conducting experiments.
The Columbia tragedy has turned the spotlight on the risks associated with re-entry and landing of a space shuttle. Re-entry and landing of a space shuttle is a highly complicated undertaking for which a number of things should go exactly right. First, the orbiter must be manoeuvred into the proper position. When the space crew receives the command to come home the crew fire the RCS thrusters to turn the orbiter tail first. Then the crew slows the orbiter down so that it begins to fall back to earth. During that time, the crew fires the RCS thrusters to pitch the orbiter over so that the bottom of the orbiter faces the atmosphere at about 40 degrees and is moving nose first again.
The orbiter, which hurtles down at a speed of 28,000 km/h will hit air molecules and build up heat of about 1650 degrees C from friction. To shield it from this extreme heat, the orbiter is covered with ceramic insulating materials. These materials have a high heat capacity and are designed to absorb large quantities of heat without increasing their temperature very much.
On re-entry, the orbiter will be able to fly like an airplane. The orbiter will make a set of banking turns to slow its descent speed as it begins its final approach to the runway. When the orbiter is about 600 m from the ground the pilot deploys the landing gear and the orbiter touches down. The commander brakes the orbiter and the speed brake on the vertical tail opens up. A parachute is deployed from the back to help stop the orbiter.
The Columbia never touched the ground. The reasons for tragedy need to be uncovered but certainly its not the beginning of the end.
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