The concept of sending a reusable aircraft into space is much older than most people realize. In fact, aeronautical experts had been contemplating ways of sending aeroplanes into space even before the Second World War. But it was only with the introduction of the X-Planes that constructing a reusable spacecraft seemed possible. When Chuck Yeager’s Bell X-1 first broke the sound barrier in 1947, the stage was set for succeeding X-Planes to break more speed and altitude records. The hypersonic X-15 was undoubtedly the most significant research platform. It was responsible for many major scientific breakthroughs, particularly in developing technology, such as reaction control systems, that would later be used extensively in Space Shuttles. Interestingly, Joe Engle (who had flown sixteen X-15 flights) later served as commander on two Space Shuttle missions. US President Nixon finally approved the Space Shuttle programme in 1972, in spite of the cost of the Vietnam War, which was a considerable burden in itself. After evaluating several design plans, NASA awarded the Space Shuttle contract to Rockwell International, which had also been responsible for building the famous Apollo modules.
Whilst NASA’s first Space Shuttle, Columbia, was already operational, NASA announced the requirement for a lighter weight airframe design. For this purpose, Rockwell built Challenger as a Structural Test Article (STA), called STA-099. This meant that Challenger would be used almost exclusively to test how a lighter airframe would react to intense heat and stress, by being subjected to months of vibration and thermal testing. In other words, STA-099 would never leave the ground. Later in the programme, budget cuts forced NASA to reduce the number of operational orbiters in its intended fleet of Space Shuttles. The only way to maintain its capability in space, was to refurbish and upgrade Challenger from an STA to an Orbiter Vehicle (OV). Challenger OV-099 blasted off for the first time on 4 April 1983, soon earning the reputation of being NASA’s most reliable, popular and capable space orbiter.
The improved construction method of Challenger’s airframe made it considerably lighter than Columbia, resulting in its capacity to carry heavier payloads. Astronauts preferred flying in Challenger as its flight deck was much more spacious and its instrument panels were not as cluttered as those of Columbia. In fact, Challenger was the first Space Shuttle to be equipped with HUDs (Head Up Displays) and became the first shuttle to carry a crew of five. As a matter of interest, Challenger was also the first Shuttle to have a female crew member as well as the first to have an African American as part of the crew.
Later on, it became normal practice to have a crew of seven onboard the craft, while the maximum number of the crew was eight. However, in an emergency there would be sufficient space for ten people. In theory, it would be possible for a two-man crew to fly a shuttle into orbit, in order to rescue eight crew members of a stranded orbiter.
Programme managers used Challenger more often than other shuttles, as it could be prepared for the next flight in less time than other orbiters. This was mainly due to its incredible reliability. The first spacewalk of the Space Shuttle programme took place during Challenger’s maiden flight. During its third mission, it became the first orbiter to launch and land at night. Challenger was also the first Space Shuttle to land at Kennedy Space Centre. In short, every Challenger mission became a groundbreaking flight.
A typical mission
A typical Space Shuttle flight began with the STS (Space Transportation System) resting on a launch platform. The biggest component was the external fuel tank, to which the orbiter (Space Shuttle) was attached. The external tank provided fuel (liquid hydrogen and liquid oxygen) to the Space Shuttle’s three main engines. Two white SRBs (Solid Rocket Boosters) were responsible for the Shuttle’s initial acceleration and could be seen on either side of the external tank. At the end of the launch countdown, the Space Shuttle’s three main engines would ignite. 2.64 seconds later, the two SRBs would ignite, providing more thrust for the next two minutes than 140 Boeing 747 engines.
As the shuttle left the launch platform in its wake, it would roll 120° to the right, while accelerating at 3 Gs. 124 seconds after lift off, the Shuttle would be 45 km above the ground with explosive bolts separating the SRBs from the external tank. At 129 km altitude, the shuttle exceeded Mach 15. Just less than nine minutes after lift off, the external tank was released from the shuttle and disintegrated as it fell back to Earth. The two SRBs descended to the Atlantic Ocean with parachutes and would be refurbished and reused in future STS missions. Once in orbit, the Shuttle used orbital maneuvering systems and reaction control systems to alter its attitude.
At 300 km altitude, the shuttle orbited the Earth once every hour and a half at a speed of 15,200 kts. This is where mission specialists started completing the mission’s objectives. These objectives ranged from launching, repairing or retrieving satellites to conducting Spacelab experiments and providing a ‘shuttle service’ to the International Space Station. The shuttle’s most important tool was its Remote Manipulator System (RMS). A highly trained RMS operator used this robotic arm to store or unload cargo and to assist astronauts in conducting ‘extra vehicular activities’ (space walking). On Earth, the RMS arm weighed just over 400 kg, but in space it could move large objects weighing as much as 30 tons. ‘Manned Maneuvering Units’ with vectoring thrusters allowed astronauts to move around outside the orbiter, without the need to be tethered to the spacecraft. Astronauts could literally spacewalk up to a distance of 90 metres away from the shuttle, to retrieve an object.
Interestingly, in order to finance the Space Shuttle programme, NASA continuously had to prove that it was a good investment to keep these spacecraft operational. Fees charged for placing, repairing and retrieving commercial satellites, as well as maintaining military satellites with strategic importance, helped to make the programme financially viable. NASA claimed that each dollar they spent returned at least $2 in benefits.
Having completed orbital operations, the shuttle had to slow down in order to quite literally ‘fall’ out of orbit. Once the cargo bay’s doors had been shut, the Shuttle maneuvered into a tail-first attitude – flying backwards. The Shuttle’s orbital maneuvering engines then fired a three minute burst, slowing the Space Shuttle down, to the extent that it started to descend. The commander quickly had to correct the orbiter’s attitude to a nose-first 30° angle of attack. The thermal protection tiles would then start to heat up as the Shuttle entered the Earth’s atmosphere at a speed of 14,000 kts. The heat would cause surrounding air to ionize (become electrically charged), causing a communications blackout that lasted up to the point where the orbiter slowed down to Mach 6. At 200,000 ft the Shuttle’s aerodynamic control surfaces became more effective. Finally, after gliding the spacecraft to the landing strip or runway, the Shuttle would touch down at about 190 kts.
During the disaster, liquid oxygen and hydrogen from Challenger's collapsing fuel tank resulted in a huge fireball. Aerodynamic forces tore Challenger apart and it plummeted into the ocean.
US President Ronald Reagan summed up the Challenger story beautifully in his Address to the Nation. “I know it is hard to understand, but sometimes painful things like this happen. It's all part of the process of exploration and discovery. It's all part of taking a chance and expanding man's horizons. The future doesn't belong to the fainthearted. It belongs to the brave. The Challenger crew was pulling us into the future, and we'll continue to follow them.”