Rockwell Space Shuttle Challenger

Text by Divan Muller
Photographs courtesy of NASA

The mere mention of the name ‘Challenger’ conjures up images of an exploding Space Shuttle. However, there is so much more to the Challenger story than its widely publicized, tragic ending.

This is a brief history of Orbiter OV-099 – NASA’s most loved Space Shuttle.

The early years

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. 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 acted 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 the Challenger as a Structural Test Article (STA), called STA-099. This meant that the 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 the 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.

Challenger

The improved construction method of the Challenger’s airframe made it considerably lighter than the Columbia, resulting in its capacity to carry heavier payloads. Astronauts preferred flying in the Challenger as its flight deck was much more spacious and its instrument panels were not as cluttered as those on the Columbia. In fact, the 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, the 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 practise to have a crew of seven onboard the craft, whilst 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 the 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 the 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 Space Shuttle flight begins with the STS (Space Transportation System) resting on a launch platform. The biggest component is the external fuel tank, to which the orbiter (Space Shuttle) is attached. The external tank provides fuel (liquid hydrogen and liquid oxygen) to the Space Shuttle’s three main engines. Two white SRBs (Solid Rocket Boosters) are responsible for the Shuttle’s initial acceleration and can be seen on either side of the external tank. At the end of the launch countdown, the Space Shuttle’s three main engines ignite. 2.64 seconds later, the two SRBs ignite, providing more thrust for the next two minutes than 140 Boeing 747 engines. As the Shuttle leaves the launch platform in its wake, it rolls 120° to the right, whilst accelerating at 3Gs. 124 seconds after lift off, the Shuttle is 45 km above the ground and explosive bolts separate the SRBs from the external tank. At 129 km altitude the Shuttle will have exceeded Mach 15. Just less than nine minutes after lift off, the external tank is released from the Shuttle and disintegrates as it falls back to Earth. The two SRBs descend to the Atlantic Ocean with parachutes and will be refurbished and reused in future STS missions. Once in orbit, the Shuttle uses orbital manoeuvring systems and reaction control systems to alter its attitude.

At 300 km altitude, the Shuttle orbits the Earth once every hour and a half at a speed of 15 200 kts. This is where mission specialists start completing the mission’s objectives. These objectives range 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 is its Remote Manipulator System (RMS). A highly trained RMS operator uses this robotic arm to store or unload cargo and to assist astronauts in conducting ‘extra vehicular activities’ (space walking). On Earth, the RMS arm weighs just over 400 kg, but in space it can move large objects weighing as much as 30 tons. ‘Manned Manoeuvring Units’ with vectoring thrusters allow astronauts to move around outside the orbiter, without the need to be tethered to the spacecraft. Astronauts can 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 has to prove that it is 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, help to make the programme financially viable. NASA claims that each dollar they spend returns at least $2 in benefits.

Having completed orbital operations, the Shuttle has to slow down in order to quite literally ‘fall’ out of orbit. Once the cargo bay’s doors have been shut, the Shuttle manoeuvres into a tail-first attitude – flying backwards. The Shuttle’s orbital manoeuvring engines then fire a three minute burst, slowing the Space Shuttle down, to the extent that it starts to descend. The commander quickly has to correct the orbiter’s attitude to a nose-first 30° angle of attack. The thermal protection tiles start to heat up as the Shuttle enters the Earth’s atmosphere at a speed of 14 000 kts. The heat causes the surrounding air to ionize (become electrically charged), causing a communications blackout that lasts up to the point where the orbiter slows down to Mach 6. At 200 000 ft the Shuttle’s aerodynamic control surfaces become more effective. Finally, after gliding the spacecraft to the landing strip or runway, the Shuttle touches down at about 190 kts.

Tragic ending

The Challenger’s tenth and final mission took place on 28 January 1986, at the Kennedy Space Centre at Cape Canaveral (Florida, USA). The crew of seven included Christa McAuliffe, a teacher, who was to become the first private citizen to fly into space. Half a second into the flight, an SRB released a puff of grey smoke. Cameras detected eight more puffs during the next two seconds. 65 seconds after the launch, flames mixed with hydrogen from the external tank. Ten seconds later, this lead to a massive explosion and the end of the Challenger’s illustrious career. A subsequent inquiry found that an O-Ring (pressure seal) in the right-hand SRB had been damaged by extreme cold temperatures during the mission’s preparation stages. The Challenger exploded at an altitude of 46 000 ft. at a speed of Mach 1.92.

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.”