After a whirlwind two days, the time came to put the Shuttle to its ultimate test: knifing through the atmosphere, subjecting some of the tiles to thermal extremes up to 3,000 Celsius and performing an unpowered, 'deadstick' landing at Edwards Air Force Base in California. Although the last few minutes, from passing subsonic in the low atmosphere to the runway, had been rehearsed using Enterprise, the 45 minutes from the de-orbit burn of the OMS engines, through the searing heat of reentry and the complex aerodynamic turns needed to 'bleed-off' Columbia's speed and align her for touchdown, were largely unknown.
To play things safe, NASA opted to use the wide expanse of dry lakebed at Edwards, deep in the Mojave Desert, for the first four test flights. This would provide Young and Crippen with a more forgiving runway and greater margins for error, although it was hoped that when the Shuttle became fully operational and its aerodynamic performance was better understood, precision landings on a narrower concrete runway at KSC would become the norm. Four hours before landing, at around 2:00 pm on 14 April, the crew closed and latched the payload bay doors for the last time.
Twenty minutes before the onset of the de-orbit burn that would drop Columbia out of space and into the upper reaches of the atmosphere, the astronauts oriented their spacecraft tail-first, and switched on two of the three Auxiliary Power Units (APUs). These essentially controlled the Shuttle's flight surfaces and hydraulics during re-entry. Fifty-three hours and 28 minutes into the mission, at 5:28 pm, as Columbia flew over the Indian Ocean, the OMS engines ignited in the vacuum, slowing her and beginning her perilous, high-speed glide home.
The burn, which lasted two-and-a-half minutes, was reported in typical matter-of-fact fashion by Young, who told Capcom Joe Allen, ''Burn went nominal.''
''Nice and easy does it, John. We are all riding with you.'' Allen's words echoed not only the prayers of the men and women in Mission Control, but also countless observers across the world.
Minutes later, Columbia was turned so that its nose was pitched 'up' at a 39-degree angle, and Young and Crippen removed the safing pins from their ejection seats and overhead hatches and switched on the third APU. As the spacecraft entered the denser portion of the atmosphere, the tracking station in Guam noted increasing amounts of static and the crew reported seeing the yellowish-orange bursts of Columbia's pulsing thrusters reflected in their cockpit windows. Travelling at close to 25,750 km/h, the spacecraft hurtled onwards, the colour of ionised atmospheric gases outside turning from light pink to pinkish-red, then reddish-orange, reminiscent of the inside of a blast furnace.
During this time, the public-affairs commentator at Mission Control reeled off a steady stream of updates: ''We will be out of communication with Columbia for approximately 21 minutes. No tracking stations before the west coast and there is a period of about 16 minutes of aerodynamic re-entry heating that communications are impossible [due to the build-up of a plasma 'sheath' around the vehicle].'' It was also during this time that the Kuiper Airborne Observatory snapped its infrared picture of the meteoric Columbia hurtling back through the atmosphere.
The aircraft had taken off from Hickam Air Force Base in Hawaii and established itself at an altitude of about 13.7 km, directly underneath Columbia's flight path, about an hour before the start of entry interface. It then recorded a single infrared image of the belly and side of the speeding spacecraft.
As they descended towards Edwards, the astronauts picked up UHF radio calls between Mission Control and one of the T-38 chase planes that would accompany the Shuttle down to the runway. ''Hello, Houston,'' called Young, ''Columbia's here. We're doing Mach 10.3 at 188 [thousand feet].'' For the majority of this time, except for the 'roll reversals' - a series of S-shaped turns used to reduce speed - the computers flew the spacecraft. Shortly after Columbia had crossed the coastline near Big Sur - to which Crippen radioed excitedly, ''What a way to come to California!'' -Young took manual control of his ship.
Still travelling at well over four times the speed of sound, the Shuttle passed, as planned, over Bakersfield, Lake Isabella and Mojave Airport, enabling the astronauts to verify by glancing out of the cockpit windows that their ground track was ''right on the money.'' Young then performed a sweeping, 225-degree turn to align Columbia with the lakebed Runway 23 at Edwards. Shortly thereafter, as their altitude dropped to around 12.2 km, he took the stick and later commented that the ship's controllability was crisp and precise.
Watching the arrival of America's first Space Shuttle from orbit were tens of thousands of people, including Larry Eichel of the Philadelphia Inquirer. His testimony perfectly illustrated the anxiety and nervous excitement of everybody awaiting the historic event: ''The Shuttle appeared far above the north-east horizon, a white dot against a cloudless blue sky. That dot was dropping so fast that to an eye accustomed to watching the more gradual descent of commercial jets, it seemed inevitable that the Shuttle would crash to the desert floor.''
As Columbia approached Edwards, the speedbrake - which flared out from the rear edge of the vertical stabiliser - was gradually retracted and was fully closed by the time the Shuttle was 600 m above the runway. Dropping at a precipitous rate, seven times steeper than a commercial airliner, it was understandable that Eichel should think it inevitable that the Shuttle was going to crash. It was at this stage, however, that Young pulled back on the stick, lifting the nose and transforming his ship at once from an apparently out-of-control falling brick into a graceful flying machine.
''The Shuttle has a very, very steep glide slope,'' said Neil Hutchinson. ''It's about eight or nine degrees. That doesn't sound very steep, but if you were in an airliner doing that, you'd think you were headed for sure death!''
Weather conditions at the landing site were almost perfect, with Capcom Joe Allen telling the astronauts that ''winds on the surface are calm''.
At 6:20:35 pm, Crippen deployed the landing gear and all six wheels were down and locked within the required 10-second time limit. Columbia touched down 22 seconds later at 342 km/h, rolling for almost 2.7 km before coming to a smooth halt. The speedbrake was opened and full-down elevons were applied, giving the astronauts an impression of considerable deceleration. ''As it touched down'', reported Eichel, ''at a speed 80 to 90 miles an hour faster than a commercial airliner does, the rear wheels nestled into the hard-packed sand, kicking a rooster-tail high into the air . . .''
The countdown to landing was echoed by both the public-affairs spokesman at Edwards and by the crew of one of the T-38 chase planes, who were the first to welcome Young and Crippen home with a resounding, ''Beautiful! Beautiful!''
Rookie astronaut John Creighton was on board a US Army helicopter at Edwards that day and he would later describe the remarkable efforts of some spectators to get a close-up view of Columbia's landing. ''All kinds of people had camped out there for several days. There was a fence there and there'd been a patrol to keep people back there. As soon as the Shuttle rolled to a stop, these people charged forward, [this] fence went down and they got motorcycles and cars that went out racing. This was about five miles away from where the Shuttle actually landed and the only way you could see [it] was with binoculars, but boy, they wanted to get an up-front view! The security folks didn't know what to do, so they told the helicopters to try to get this crowd under control. So these helicopters would swoop down in front of these on-charging group of cars. The helicopter pilots loved it. They were having a great time trying to head off all of these people!''
Post-landing analysis showed that Columbia's right-hand inboard brakes suffered higher-than-anticipated pressure, which caused a slight pull to the right just before the wheels stopped. Young compensated for this by balancing the total braking to either side of the Shuttle, maintaining a near-perfect course straight down the runway centreline, stopping at the intersection of Runways 23 and 15. One notable surprise was the sheer amount of lakebed debris - pebbles and grains of sand -kicked up by the wheels.
''Do I have to take it to the hangar, Joe?'' Young joked.
''We're going to dust it off first,'' deadpanned Allen.
Immediately after wheelstop, the astronauts unstrapped their harnesses and began safing the RCS and OMS switches before the arrival of the ground crew. When the latter arrived minutes later, they first hooked up sensitive 'sniffer' devices to verify the absence of toxic or explosive gases and attached coolant and purging lines to Columbia's aft compartment to air-condition her systems and payload bay and dissipate residual, potentially toxic fumes. Until this procedure had been completed, the ground crew operated in Self-Contained Atmospheric Protection Ensemble (SCAPE) suits. They then proceeded to roll an airport-type stairway over to Columbia's hatch.
John Young, who had remained totally cool throughout the re-entry, approach and landing, finally let his excitement get the better of him by asking the ground crew to hurry up so that he could leave Columbia. When finally allowed outside about an hour after touchdown, he bounded down the steps, checked out the tiles and landing gear and jabbed the air triumphantly with both fists. He also kicked the tyres, which gave Henry Pohl a scare.
''I was really worried about that, because those tyres have got 375 psi pressure in them,'' said Pohl, ''and I knew the brakes [and tyres] got hot, and I was afraid the tyres were going to explode. It would have been a shame to do all that flying and a terrific landing and then have a tyre blow up because you went over and kicked it!'' But Young, obviously, was over-excited. ''I've often claimed John calmed down by [the time he got outside the orbiter],'' Crippen would say later. ''You should have seen him when he was inside the cockpit!"
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