The Space Shuttle: How NASA’s reusable rocket was ‘beyond the state of the art’
When NASA’s Space Shuttle Columbia blasted off from Cape Canaveral on 12 April 1981, it was the most advanced, state-of-the-art flying machine ever built. In his new book Into The Black, aviation expert Rowland White recaptures the historic moments leading up to the daring maiden flight, using interviews, NASA oral histories, and recently declassified material, to piece together the dramatic untold story. Here he explains the main challenges NASA faced in building a winged rocket plane the size of an airliner, that would be capable of flying to space and back before preparing to fly again…
When work on the Space Shuttle got underway in the early 1970s, the programme’s lead engineer described the technologies required as ‘beyond the state of the art.’ It’s difficult to overemphasise the scale of the task that NASA had set itself to make it work. Previous space missions had carried crews of up to three astronauts inside a cramped capsule that returned to Earth beneath parachutes, then retired to museums. The Space Shuttle was the size of an airliner and had to be reusable. Alongside the Space Shuttle, the Apollo designs were like bicycles; the minimum required to carry people to their destination and back. By comparison, the reusable Space Shuttle was like Han Solo’s Millennium Falcon; a freighter capable of carrying crews of seven and their cargo that was ‘the fastest ship in the galaxy’.
To build it, NASA faced three potentially showstopping challenges. They needed:
1) The highest performance rocket engine ever built
2) The biggest heatshield ever designed
3) The first completely computerised flight control system
And it all had be used over and over again.
Work on the Shuttle’s main rocket engines began first. Together, the three engines mounted in the tail of the Orbiter developed over half a million kilograms of thrust. On their own, each of the Rocketdyne RS-25 engines generated 37 million horsepower – or the same as nearly 40,000 Bugatti Veyrons. They consumed fuel at a rate that would empty an average family swimming pool in just twenty five seconds. And at the heart of each engine was a device called a turbopump. Not much bigger than the engine of an average family car, the turbo pump had to spin at a rate of 36,000 revolutions per minute, at pressures of nearly 600 kg/cm2, and at power levels of 75,000 horsepower. By comparison, the engines that drove the Titanic generated just 55,000 horsepower and were spread over an area half the size of a football pitch.
Next was the Shuttle’s heatshield. The bottom of the earlier Apollo capsule was the size of a large dining table. The area needing protection on the Shuttle was more like a tennis court. And when it came to re-entering the Earth’s atmosphere, that made a vast difference to the numbers NASA had to contend with. The kinetic energy carried by the 85-ton Space Shuttle travelling at 17,500 mph was roughly the same as that of a Nimitz class aircraft carrier displacing 100,000 tons; if, that is, it was travelling at over 500 mph. When, on re-entry, the Shuttle made contact with the atmosphere, most of that energy was converted to heat, generating temperatures in a shockwave pushed out ahead of the Shuttle flight path that, at over 3000 degrees Celsius, were similar to those found on the surface of the sun.
Just to compound the problem, the Shuttle’s heat shield, unlike those of the little Apollo capsules, had to be reusable. And as unlikely as it sounds, NASA’s thoughts turned to sand, or rather silica fibres made from sand. Silica fibres were mixed with water then baked to produce ceramic tiles as light as balsa wood. Unlike metal, the silica tiles were such low conductors of heat that within seconds of being removed from a furnace, and while the center was still glowing red hot, they could be picked up by their edges with unprotected fingers. Each Shuttle was covered in a mosaic of over 30,750 of these individually shaped and numbered tiles.
The last major challenge was the flight control system. In earlier aircraft, the pilot’s controls in the cockpit were directly connected to the control surfaces on the wings and tail. But that wasn’t going to work for the Space Shuttle. Such were the extremes of the Shuttle’s performance that, without the help of computers, it would be unflyable. So computers were used to interpret the pilot’s control imputs. And yet each of the computers offered just 104K of memory. It wouldn’t have got you far playing Grand Theft Auto. Even an average smartphone today offers over 150,000 times more memory.
For the Apollo moon missions NASA had designed a tailor made guidance computer. It was an unprecedented undertaking and resulted in a computer which simply refused to fail. Building, though, had been dauntingly expensive in terms of time, money and effort. For the Shuttle NASA decided to use an off-the-shelf computer. Or, rather, they used four of them. They calculated that if they used four synchronised computers, they could expect catastrophic computer failure to cause the loss of a Shuttle just once in every 250 million flights. Still not entirely happy to trust those odds, NASA also included a fifth, back-up computer, programmed in isolation by a different company. If the main computers carried a fatal software bug the uncontaminated computer – known as the ‘landing in suitcase’ could be plugged in to bring the Shuttle home.
But for all the research and testing that went into the Shuttle it was, at the time of the first launch in 1981, untried. It would be the first and last time in history that any spacecraft had been flown for the first time with a crew on board. As astronaut John Young, the Commander of the mission, said before the flight: ‘Anyone who sits on top of the largest hydrogen-oxygen fueled system in the world, knowing they’re going to light the bottom, and doesn’t get a little worried, does not fully understand the situation’. After a perfect landing three days later he raved ‘This is the world’s greatest all-electric flying machine’. And it was.
Into the Black, published by Bantam Press, is available now.
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