'Whatever Was Needed': Remembering the Hair-Raising Rise to Orbit of STS-93

After two false starts, Columbia rises to orbit at 1:21 a.m. EDT on 23 July 1999. Photo Credit: NASA

Almost two decades ago, on 23 July 1999, the first woman ever to lead a space mission was launched aboard shuttle Columbia to deliver NASA’s $1.5 billion Chandra X-ray Observatory into a highly elliptical orbit. Chandra represented the third in a quartet of “Great Observatories”—which also includes the Hubble and Spitzer telescopes, together with the long-since-deorbited Compton Gamma Ray Observatory—to be delivered to space for studies of our astronomical backyard across virtually the entire electromagnetic spectrum. The demands for Commander Eileen Collins, Pilot Jeff Ashby and Mission Specialists Catherine “Cady” Coleman, Steve Hawley and Michel Tognini on STS-93 were high, with a shuttle launch long regarded as the most hazardous phase of the flight. Not until Columbia actually left the pad, however, did they realize how hazardous it really was.

Led by Commander Eileen Collins, the STS-93 crew emerges into the glare of television lights on the night of 22 July 1999. Photo Credit: Joachim Becker/SpaceFacts.de

STS-93 met with many delays before finally settling on 20 July 1999 for its launch. However, on that morning, the countdown was halted at T-7 seconds, when high concentrations of hydrogen were detected in the shuttle’s aft compartment. It was a particularly dangerous moment, coming milliseconds before the ignition of the three Space Shuttle Main Engines (SSMEs), and might have triggered a risky on-the-pad abort and additional delays. The cause of the problem was traced to a hydrogen “spike”, which a sharp-eyed launch controlled spotted peaking briefly at 640 parts per million, double the maximum allowable “safe” level.

Launch was rescheduled for 22 July. However, this second attempt also seemed cursed with misfortune, with lightning strikes recorded within 3 miles (5 km) of Pad 39B at the Kennedy Space Center (KSC) in Florida. If Columbia did not launch by the 23rd, the mission would be stood down until at least mid-August. The countdown was held at T-5 minutes, in the hope that conditions might improve. When they did not, the second attempt was scrubbed and the clock recycled for a third attempt in the small hours of the following morning.

The STS-93 crew poses with a model of the Chandra X-Ray Observatory. From left to right are Eileen Collins, Steve Hawley, Jeff Ashby, Michel Tognini and Catherine “Cady” Coleman. Photo Credit: NASA

In the late evening of the 22nd, Collins and her crewmates—clad in their bulky orange pressure suits—again clambered aboard Columbia and their patience was rewarded when STS-93 sprang from the pad at 1:21 a.m. EDT on the 23rd. “We have ignition…and liftoff of Columbia, reaching new heights for women and X-ray astronomy,” exulted the launch commentator, but unknown at the time was a serious problem brewing in the shuttle’s engines. An igniter plug dislodged at liftoff, striking the interior of the nozzle and damaging a hydrogen chamber coolant tube. Then, five seconds after departing the pad, Collins and Ashby were startled by a voltage drop on one of the electrical buses, which caused one of two backup controllers on two of the three SSMEs to abruptly shut down. The third engine was unaffected and, by the fortune of providence, all three performed nominally, boosting Columbia into a 155-mile-high (250 km) orbit. The STS-93 crew went on to complete their five-day mission, successfully deploying Chandra to begin its voyage of discovery.

However, the launch scare was significant. On no other shuttle mission had a crew come so perilously close to executing a risky Return to Launch Site (RTLS) abort and, had the main engines’ primary controllers also failed, an SSME shutdown was likely…and that would have obliged Collins to await the separation of the twin Solid Rocket Boosters (SRBs), flip Columbia, fly “backwards” at ten times the speed of sound, then head west, jettison the bulbous External Tank (ET) and guide the orbiter down to the Shuttle Landing Facility (SLF) at the Cape. More critically, she and Ashby would have done all this under a cloak of darkness, several hours before Florida sunrise.

As circumstances transpired, Columbia completed a safe landing in the hours of darkness at the end of her mission. But had the launch phase turned out differently, Collins and Ashby might have been forced to complete a night landing on the back of a risky Return to Launch Site (RTLS) abort. Photo Credit: NASA, via Joachim Becker/SpaceFacts.de

“We were prepared for that,” she remarked after the mission. “We were listening for the engine performance data calls on ascent. The crew would have been ready to do whatever was needed.” Fortunately, Columbia made it safely into space, but was traveling some 14.8 feet/sec (4.5 meters/sec) slower than expected. Although this discrepancy was tiny in view of her 17,400 mph (28,000 km/h) orbital velocity, it was enough for puzzled engineers to question whether there might have been a 4,000-pound (1,800 kg) shortfall in the liquid oxygen pumped into the ET before liftoff. NASA confirmed on 24 July that the loading of propellants had been done correctly, although it would become part of the investigation into the electrical short.

Analysis of still video imagery during the STS-93 ascent also revealed another problem: a leak of hydrogen gas from one of the SSMEs. The images, particularly those from cameras mounted on Pad 39B, revealed a narrow, bright area inside the nozzle of the right-hand engine, possibly indicative of a weld-seam breach in one of more than 1,000 stainless steel hydrogen recirculation tubes. Although Wayne Hale, in his capacity as Mission Operations Director, stressed that few conclusions could be made until the engine was back on Earth, he speculated that the leak might account for the “missing” liquid oxygen. As hydrogen was lost at a rate of 2.2 pounds (1 kg) per second, the main engine controllers compensated by guzzling oxygen at a higher rate.

It had been one of the most hazardous ascents in shuttle history and would lead directly to the grounding of the rest of the fleet for the next six months. Not until December 1999 would another crew—embarking on a time-sensitive mission to repair another Great Observatory, the Hubble—voyage into orbit once more.





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3 comments to ‘Whatever Was Needed’: Remembering the Hair-Raising Rise to Orbit of STS-93

  • Scott FW

    The whole article and particularly that hydrogen recirculation tube thing brings to mind this from Air & Space Magazine in January 2012 by Tom Mueller of SpaceX, “There are a thousand things that can happen when you go to light a rocket engine, and only one of them is good.”

  • Robert Waltrers

    I saw on TV that hard to launch missionr

  • Hari

    1999 was a tough year. In addition to this close call the infant ISS was left at the mercy of space junk when a debris avoidance maneuver was aborted by Zarya’s computer. The Cape was spared a direct hit by Hurricane Floyd, but real misfortune came with the loss of both the Mar Climate Orbiter and Mars Polar Lander. The world also lost Pete Conrad in an accident on the 30th anniversary of Apollo 11.

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