Flights of the ‘Death Star’

by Chris Bergin

John Young called it the ‘Death Star’. Behind the dark humour, however, lay real concern for the then-chief of NASA’s astronaut corps. Even with an increasingly confident outlook on the Shuttle’s capabilities at the dawn of 1986, Young instinctively knew that the STS-61F and 61G flights would be two of the riskiest ever attempted by the reusable spacecraft.

Fellow astronauts Rick Hauck and Dave Walker, who would command the two missions, echoed his concern. “As with any flight,” Hauck said in a January 2004 interview, “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 of disaster”.

The loss of Challenger during ascent and Columbia upon re-entry have demonstrated how fine the line is between triumph and tragedy; a line – and risk – that every astronaut knows and accepts before climbing aboard. Yet Hauck and Walker’s flights, both scheduled to occur a few days apart in May 1986, would carry additional danger. This was partly due to the important scientific payloads their crews would truck into low-Earth orbit – a probe called Ulysses to explore the Sun’s poles on Hauck’s flight, followed by a spacecraft dubbed Galileo to study Jupiter on Walker’s mission – which were both equipped with controversial nuclear powerplants.

Needless to say, the implications of a launch accident and the consequences of depositing highly-radioactive plutonium dioxide across eastern Florida did not bear thinking about. The risk, though, was compounded still further by the fact that, attached to the base of each nuclear hot potato in the Shuttles’ payload bays was a thin-skinned, liquid-fed rocket that many astronauts and even managers had condemned as unsafe and unacceptable for use in conjunction with a manned spacecraft. Measuring 30 feet long and 14 feet wide, it was called the Centaur-G Prime and, for Rick Hauck, it was his baby.

Furthermore, just like a baby, it was both temperamental and unpredictable.

“I was assigned to be the Astronaut Project Officer for Centaur, an upper-stage rocket that’s very thin-skinned,” he said. “It’s pressure-stabilised, which means if it’s not pressurised, it’s going to collapse by its own weight. If it were not pressurised, but suspended, and you pushed on it with your finger, the tank walls would ‘give’ and you’d see that you’re flexing the metal!” Nicknamed a ‘balloon tank’ because its rigidity thus depended on being fully-pressurised, the Centaur had long been viewed warily by NASA, whose general safety rule of thumb on the Shuttle dictated that no single failure should be capable of endangering the spacecraft or its crew.

The Centaur-G Prime did more than that. Much of its pressure-regulation hardware, disturbingly, was non-redundant – without a backup facility – and, worse, a failure of its internal bulkhead had the potential to rupture both its volatile liquid oxygen and hydrogen tanks. Additionally, it was recognised that the sheer mass of its propellants, which totalled close to 45,000 pounds, could cause ‘sloshing’ and a myriad of other controllability problems that could hinder Hauck or Walker if the need arose to make an emergency landing shortly after liftoff.

In spite of the hazards, the Centaur’s key advantage was that, pound for pound, its liquid propellants provided considerably more oomph to push large payloads out of low-Earth orbit and en-route to other planets than solid-fuelled rockets could achieve. It was also well-known that liquid-fed boosters generally produced a much ‘gentler’ thrust than the notoriously harsh impulse of solids.

Still, the safety concerns rightly overshadowed and ultimately overwhelmed these benefits. “The Shuttle was obligated to launch Ulysses and Galileo,” explained Hauck, “and [NASA] needed the most powerful rockets they could have [and] at some point the decision was made to use the Centaur, which was never meant to be involved in human spaceflight. That’s important because rockets that are associated with human spaceflight have certain levels of redundancy and certain design specifications that are supposed to make them more reliable.

“Clearly, Centaur did not come from that heritage, so, Number One, that was going to be an issue in itself, but Number Two is [that] if you’ve got a Return to Launch Site abort or transatlantic abort and you’ve got to land, and you’ve got a rocket filled with liquid oxygen [and] liquid hydrogen in the cargo bay, you’ve got to get rid of [it], so that means you’ve got to dump it while you’re flying through this contingency abort. To make sure that it can dump safely, you need to have redundant parallel dump valves, helium systems that control the dump valves [and] software that makes sure contingencies can be taken care of.

“Then, when you land, here you’re sitting with the Centaur in the bay that you haven’t been able to dump all of it, so you’re venting gaseous hydrogen out this side [and] gaseous oxygen out that side and this is just not a good idea!” To support the new rocket on 61F and 61G, both Challenger and Atlantis underwent a series of lengthy modifications – costing around five million dollars apiece – which included extra plumbing to load and vent the Centaur’s propellants and control panels in the flight deck to monitor its performance. As NASA’s newest orbiter, Atlantis had been made Centaur-capable during her initial construction and was destined to spend the first few months of 1986 out at Pad 39A undergoing validation tests of the new hardware.

Following her return from 51L on February 3rd 1986, Challenger was expected to receive the Centaur modifications before being transferred to Pad 39B, while sister ship Discovery was earmarked for similar upgrades to support Department of Defense missions from Vandenberg Air Force Base in California. During typical, pre-launch loading operations, the liquid propellants would have been fed through plumbing ‘tapped into’ the Shuttle’s main propulsion system feedlines. Emergency dumping vents were situated on either side of the aft fuselage and close to the vertical stabiliser tailfin, none of which filled Hauck or Walker with confidence due to the risk of leakages or explosions.

In fact, doubts over the reliability of the Centaur-G Prime flying aboard the Shuttle had already, in the autumn of 1981, obliged NASA to cancel it and opt to place Ulysses and Galileo onto ‘safer’ – though less powerful – solid-fuelled Inertial Upper Stage (IUS) boosters. For the exceptionally-large Galileo, which comprised both a Jupiter orbiter and atmospheric-entry probe, the swap from Centaur to IUS meant that its journey time to the giant planet would almost double to four-and-a-half years and most likely require the mission to be split into two ‘halves’.

Predictably, Galileo’s pricetag soared as a result, peaking at close to a billion dollars, until Congress pressed NASA in late 1982 to resume work on the Shuttle-borne Centaur and reduce the Jupiter travel time to around two-and-a-half years. Not only Galileo, but also Ulysses, required close encounters with the giant planet – the latter as a means of altering its trajectory to rendezvous with the Sun’s poles – and both missions were duly allocated to the same, week-long launch window in mid-May 1986. Hauck’s crew would liftoff from Pad 39B aboard Challenger on the 15th, followed by Walker’s team from adjacent Pad 39A aboard Atlantis on the 20th.

The two flights each had scarcely an hour available to them in which to launch and, in order to minimise weight, both would carry just four astronauts: Hauck was joined by Pilot Roy Bridges and Mission Specialists Mike Lounge and Dave Hilmers, while Walker’s crewmates were Pilot Ron Grabe and Mission Specialists Norm Thagard and James ‘Ox’ van Hoften. Additionally, the two-day-long Death Star flights were headed for lower-than-normal, 105-nautical-mile-high orbits because, said Hauck, “you need the performance to get the Centaur up because it was so heavy”.

Throughout the second half of 1985 and into the spring of 1986, in addition to their rigorous training regimes, Hauck and Walker found themselves frequently questioning their own judgement over how many potential failure modes and problems they could live with. “In early January 1986,” Hauck recalled, “we were working an issue to do with redundancy in the helium actuation system for the liquid oxygen [and] liquid hydrogen dump valves and it was clear that the [Shuttle management] was willing to compromise on the margins in the propulsive force being provided by the pressurised helium. We were very concerned about it.

“We had discussions about it with the technical people, but we went to a [review] board to argue why this was not a good idea to compromise on this feature. The board turned down the request. I went back to the crew office and said to my crew, in essence, ‘NASA is doing business differently from the way it has in the past. Safety is being compromised and, if any of you want to take yourself off this flight, I will support you’. Two or three weeks later, Challenger blew up. Now, there is no direct correlation between my experience and Challenger, but it seemed to me that there was a willingness to compromise on some of the things that we shouldn’t compromise on”.

Years later, Hauck remained undecided as to whether or not he would have refused, himself, to fly 61F, but admitted that the Shuttle management were taking unacceptable risks in the months leading up to Challenger’s fateful launch. Only days after the tragedy, any lingering doubts were resolved for him. The Kennedy Space Center’s Safety Office refused to approve advanced processing of the first Centaur-G Prime, citing “insufficient verification of hazard controls” from both NASA and the booster’s contractor, General Dynamics. Additional safety concerns, and cost overruns to the tune of $100 million, ultimately led to the project’s cancellation in June 1986.

Fortunately, a few years later, the Galileo and Ulysses missions went ahead, reverting to the less-powerful IUS to get them successfully – though not without incident, and requiring considerably longer journey times – to their celestial targets. History has shown us that both achieved considerably more than expected and truly revolutionised humanity’s understanding of both our parent star and our planetary big brother, Jupiter.

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