When Challenger was lost in the skies of Cape Canaveral on 28 January 1986, it brought to an end the space shuttle’s “age of innocence” and exposed the deep flaws which plagued the fleet of reusable orbiters. In addition to the tragic loss of seven lives—Commander Dick Scobee, Pilot Mike Smith, Mission Specialists Ellison Onizuka, Judy Resnik, and Ron McNair and Payload Specialists Greg Jarvis and schoolteacher Christa McAuliffe—the world also lost an orbiter which might, a few months hence, have deployed the shuttle’s first payload to another planet. In fact, had 1986 panned out as intended, Challenger and her sister ship, Atlantis, might have flown no fewer than two missions, just a week apart, to send robotic explorers deep into the Solar System. Those two missions, fraught with risk, were targeted to launch in May 1986, 30 years ago, this month.
Thirty years ago, had history been a little more kind, Challenger and Atlantis should have stood proud at Pads 39B and 39A, primed and ready to launch their respective spacecraft to Jupiter. The first, Ulysses would employ Jupiter’s colossal gravity to slingshot it out of the ecliptic plane and explore the Sun’s polar regions, whilst the second, Galileo, would become humanity’s first mission to enter orbit around the giant planet itself. With only a handful of days available in the “launch window,” Ulysses (on Mission 61F) would have flown on 15 May and Galileo (on Mission 61G) would have followed on 20 May. Both flights would have lasted between two and four days, creating the very real possibility that one shuttle might liftoff less than 24 hours after the other had landed.
At the same time, both 61F and 61G would highlight an appalling game of Russian roulette, played with a pair of multi-billion-dollar national assets and the lives of eight of NASA’s astronauts.
“As with any flight,” said 61F Commander Frederick “Rick” Hauck in a NASA oral history, “if everything goes well, it’s not risky. It’s when things start to go wrong that you wonder how close you are to the edge.” The two missions became known as “Death Star” flights by Chief Astronaut John Young, because their risk encompassed far more than the obvious dangers associated with any other shuttle launch. Ulysses and Galileo both carried plutonium-fed nuclear generators and both would be propelled out of low-Earth orbit by a liquid-fueled rocket: the Centaur-G Prime, built by General Dynamics. Twenty-nine feet (9 meters) long and 13.1 feet (4 meters) in diameter, the Centaur was a thin-skinned “balloon tank,” depending upon full pressurization to support its weight. “If it were not pressurized,” explained Hauck, “but suspended, and you pushed on it with your finger, the tank walls would give and you’d be flexing the metal!” That said, the Centaur provided more oomph to deliver payloads toward interplanetary targets than solid rockets could achieve.
Historically, NASA’s safety rule of thumb dictated that no single failure should endanger the vehicle or its crew … but much of the Centaur’s pressure regulation hardware was non-redundant, with no backup capability. That was not all. The booster carried so much propellant—more than 36,370 pounds (16,500 kg) of volatile liquid oxygen and hydrogen—that engineers and astronauts feared it might “slosh” in the tanks and impair the shuttle’s controllability. If an emergency occurred, minutes after liftoff, necessitating a launch abort, the astronauts would have to dump the Centaur’s propellants whilst flying to a contingency landing site, either at the Shuttle Landing Facility (SLF) at the Kennedy Space Center (KSC) in Florida or at one of the Transoceanic Abort Landing (TAL) sites.
To do that in a safe manner, both Challenger and Atlantis would be fitted with redundant parallel dump valves, helium systems to control them, and software to execute the abort. The valves were located on opposite sides of the orbiter’s aft fuselage and could remove the Centaur’s entire load within 250 seconds. However, their close proximity to the orbiters’ suite of three Space Shuttle Main Engines (SSMEs) and Orbital Maneuvering System (OMS) pods raised the risk of fuel leaks or explosions.
In support of their roles on 61F and 61G, the two shuttles would have undergone extensive modifications. As well as the dump valves and associated plumbing, they would have been equipped with S-band data transmitters and flight deck controls to monitor the Centaur’s status. A Centaur Integrated Support Structure (CISS) at the aft end of the payload bay would have held the giant booster during ascent and throughout the pre-deployment checks. In mid-February 1986—had Challenger not been lost—Atlantis would have been rolled out to Pad 39B, carrying a “real” Centaur and a mockup of Galileo, for several weeks of fueling tests. She would then have returned to the Vehicle Assembly Building (VAB) for the installation of the “real” Galileo, then headed back out to Pad 39A in early April. By the middle of that same month, Challenger would have joined her on adjacent Pad 39B with Ulysses.
The result would have been only the second occasion in shuttle program history that a pair of shuttle stacks would have occupied both pads, simultaneously. In fact, the 39B complex had only newly entered operational service with the launch of tragic Mission 51L, after more than a decade of refurbishment and modification in the aftermath of its July 1975 usage for the U.S. “half” of the Apollo-Soyuz Test Project (ASTP).
As NASA’s newest orbiter—having flown her maiden voyage a few months earlier, in October 1985—Atlantis had received many Centaur modifications during her assembly and, ironically, Challenger would have undergone hers in the aftermath of 51L. Atlantis’ cargo, the Galileo spacecraft, was several times heavier than Ulysses and, in January 1986, NASA accepted a recommendation to fly with her “Phase II” SSMEs running at an as-yet-untried 109-percent of rated performance.
The crews for the two missions were announced in May 1985. Rick Hauck had previously served as the Astronaut Office’s Centaur representative and it was unsurprising that he would command the first (Ulysses) mission. He was joined on Mission 61F by Pilot Roy Bridges and Mission Specialists Mike Lounge and Dave Hilmers. Meanwhile, the crew of Mission 61G comprised Commander Dave Walker, Pilot Ron Grabe, and Mission Specialists John Fabian and James “Ox” van Hoften. By mid-September 1985, however, Fabian had resigned and was replaced by another veteran astronaut, Norm Thagard.
One of the reasons for Fabian’s departure was his conviction that NASA prized commercial respectability over operational flight safety. During his time with the 61G crew, he recalled seeing a technician clambering onto the Centaur with an untethered wrench in his back pocket and another smoothing out a weld, then accidentally scarring the booster’s thin skin with a tool. In Fabian’s mind, it was bad enough that the two shuttle missions would be carrying a volatile booster with such limited redundancy, without having the additional worry of poor quality control oversight and a lax attitude to safety.
Actually, the presence of the Centaur dictated virtually every detail of the two missions. According to the 61F Crew Activity Plan (CAP), released by NASA on 14 January 1986, Hauck’s men would launch at 4:10 p.m. EDT on 15 May. Everything aboard Challenger would have kept at a barebones minimum: from the number of astronauts—the smallest shuttle crew since STS-6 in April 1983 and a size never seen again until the last flight of the program in July 2011—to the on-board provisions and the orbital altitude itself. Both 61F and 61G would enter relatively low orbits of 105 miles (170 km), simply because they needed the SSME performance just to get the heavy Centaurs into space. Additional weight savings were achieved by cutting secondary experiments, an otherwise-empty payload bay, and even the removal of the middeck galley.
The presence of the Centaur also restricted the amount of time the astronauts had to deploy their respective payloads. Periodically, it was required to dump its boiled-off gaseous hydrogen, thereby keeping tank pressures within mandated limits. After too much time, it would have “bled” so much hydrogen that the remainder would have been insufficient to perform the requisite “burn” to begin the voyage to Jupiter. Consequently, for both 61F and 61G, mission planners scheduled just three deployment opportunities, the first occurring just seven hours after launch.
As the men with the burden of command, Hauck and Walker spent much time questioning their judgement about how many failure modes and problems they could live with. A few days before Challenger was lost, they were working an issue pertaining to the redundancy of helium actuators for the Centaur dump valves. “It was clear,” said Hauck, “that the [senior managers] were willing to compromise on the margins in the propulsive force being provided by the pressurized helium. We were very concerned about it. We went to a review board to argue this was not a good idea to compromise on this feature. The board turned down the request.” Defeated and angry, Hauck returned to the Astronaut Office and called his crew together. Safety had been compromised, he told them, and if they wanted to resign from the mission, they would do so with his full support.
Of course, none of them did so. Years later, Mike Lounge rationalized their thinking. In the bulletproof days before Challenger, NASA still rode the coattails of past glories: the Apollo lunar landings and the salvation of the Skylab space station. “We assumed we could solve all these problems,” Lounge told the NASA oral historian. As if to underline the point, the 61F crew was in a flight procedures meeting on 28 January 1986, reviewing the techniques they might need to vent the Centaur’s propellants in an abort. “Until Challenger,” Lounge added, “we just thought the things would always work.”
The second part of this article will appear tomorrow.