The space shuttle Discovery landed safely at Edwards Air Force Base in California on Tuesday. The eagerly awaited return to flight of the orbiter, more than two years in the making, was meant to signal the start of several more years of operation by the ageing shuttle fleet. But even before Discovery landed, NASA began pushing plans to replace it with a new class of spacecraft and launchers. Clearly the shuttle’s days are numbered, and its end may come far sooner than many expect.
This urgency stems in part from the problems Discovery encountered during its flight. Seconds after its launch on 26 July, several large chunks of insulating foam broke off from the giant external fuel tank. For NASA, it was a chilling moment of déjà vu: precisely the same problem fatally damaged Columbia’s wing during launch in January 2003. As it re-entered Earth’s atmosphere, superheated air flowed into the wing and destroyed the shuttle, killing its seven crew members.
Fortunately for Discovery’s crew, the foam chunks that broke off during its launch flew harmlessly away from the orbiter. But the mission’s travails weren’t over. Newly installed cameras on the shuttle detected that two small pieces of ceramic filler had come loose from between the orbiter’s thermal tiles during the launch, and were jutting out by a couple of centimetres. Concerned that the protruding material could cause unacceptable friction during re-entry at speeds of more than 22,000 kilometres per hour, astronauts Stephen Robinson and Soichi Noguchi removed them in a gruelling six-hour space walk.
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Then NASA found a loose piece of insulating blanket near Discovery’s nose-cone. Engineers considered another space walk to repair it, but decided that the loose blanket did not pose an unacceptable risk.
Notwithstanding Discovery’s seat-of-the-pants success, NASA has grounded its shuttles until it figures out why foam pieces are still falling, despite it having spent more than $200 million since the Columbia disaster to eliminate such problems.
It is unclear when the shuttle will fly again. NASA will be hard-pressed to get the Atlantis orbiter ready for the next launch window in early September. Some critics are already saying that even the last opportunity this year, in early November, will be a stretch. While NASA’s new chief Michael Griffin has not conceded defeat on getting another shuttle flying this year, he has noted that Discovery’s crew and that of the International Space Station, which is serviced by the shuttle, explored what could be done to “pre-position the station for a longer gap between flights, should there be one”.
“NASA needs to find out why foam is still falling despite it having spent more than $200 million on the problem”
The as yet unfinished ISS can easily survive longer gaps between flights. But without the shuttle, its construction cannot be completed. And while some say the ISS’s poor scientific returns mean it should be abandoned, they acknowledge that politics are likely to keep it aloft at least for a while.
“There is no question that into Mike Griffin’s inbox has fallen a set of challenges that result from years of myopic decision-making from previous regimes,” says Courtney Stadd, a former senior NASA administrator who worked with Griffin’s immediate predecessors, Dan Goldin and Sean O’Keefe, and helped Griffin when he moved into the job. “A glaring example is the design of the station that made it so highly dependent on the space shuttle.”
Whether the space station is terminated or not, it is clear that NASA is steadily moving towards ending the shuttle’s reign. Griffin’s team has been aggressively pursuing the possible retirement of at least one of the three remaining shuttle orbiters within the next year or so. And gone are the days when NASA talked about conducting another 28 flights to complete the ISS; the most now being discussed is 20, and it is possible the shuttle will fly as few as 12 times, according to many estimates.
Its fate will depend on how fast NASA develops its replacement, the Crew Exploration Vehicle. The CEV is an essential component of what NASA calls “the Vision” – its plan, initiated by President George W. Bush in January 2004, to return humans to the moon no later than 2020 and send them on to Mars soon afterward.
In April this year, Griffin charged an internal team with reassessing and redefining the CEV requirements. The results of the Exploration Systems Architecture Study will be released in the next few weeks. But Griffin is already talking about some choices that NASA has made. In a news conference on 29 July, well before Discovery landed, he said that the launch system for the CEV would almost certainly be derived from space shuttle hardware. It will consist of a configuration of the shuttle’s solid rocket boosters (SRBs) for the new vehicle’s lower stage, and a liquid-fuelled upper stage derived either from the shuttle’s main engines or possibly the reliable J-2 engines from the Saturn V rocket that powered the Apollo missions to the moon.
Griffin said that the crew and cargo will ride on top of the fuel and engines, not alongside as with the shuttle. “As long as we put the crew and valuable cargo up above wherever the tanks are, we don’t care what they shed,” Griffin said, referring to the shuttle’s foam problem. “They can have dandruff all day long.”
While putting crew and cargo over the stack eliminates some problems, the idea of having people sitting atop a solid rocket booster will raise some eyebrows. The shuttle’s SRBs have always generated impassioned debate: though they are still among the most economical and powerful booster rockets around, they have drawbacks. Solid fuel boosters cannot be shut down once ignited. Anyone who remembers the 1986 explosion of the shuttle Challenger will recall the image of an SRB corkscrewing skywards at full power even after the orbiter and external fuel tank had been destroyed. Despite this, NASA now appears to be convinced that subsequent improvements have made the SRBs among the safest rockets in the world.
“As long as we put the crew and valuable cargo up above wherever the tanks are, we don’t care what they shed”
Using this architecture, details of which have been reported in US newspapers including The Orlando Sentinel, NASA will develop two new launchers: one for crew and one for cargo. This will bring NASA back in line with one of the long-standing principles in space flight, which is to keep cargo and crew missions separate; combining them has been one of the most contentious aspects of the shuttle.
The crew launcher will be able to lift 25 tonnes into low Earth orbit, which roughly matches what the shuttle can do. The cargo launcher will have a lifting capacity of 100 tonnes or more, putting it in the same class as the now defunct Saturn V and Russia’s mothballed Energia.
While Griffin and others at NASA have officially revealed nothing about the CEV itself, żěè¶ĚĘÓƵ has learned of some decisions already taken that will likely shape its design. Notably, it will be a capsule, not a winged vehicle with lift like the shuttle. Most aerospace engineers blame much of the shuttle’s temperamental performance on the decision to make it as plane-like as possible. This led to a need for more challenging thermal protection and aerodynamic engineering, and produced a vehicle that becomes an ungainly glider on approach and landing. Not surprisingly, the pilots nicknamed it the “flying brick”.
Capsules have many advantages for human space flight. They are generally safer, more robust in flight, and cheaper to develop and maintain. But the CEV could look quite different from the gumdrop-shaped Apollo capsules or the more spherical Russian Soyuz. Advances in areas ranging from aerodynamics to materials may result in a capsule that is sleeker and more capable of adapting to different missions. Unlike Apollo, the CEV will likely touch down on dry land, probably in the western US, using a combination of parachutes and retrorockets, much like Soyuz.
Crew capacity for the first CEV is still an open question. Ultimately, NASA wants it to carry six people, the desired complement for a mission to Mars. But the immediate priority is to develop a vehicle capable of servicing the ISS, for which the minimum would be only three people. NASA now has to decide whether to go for broke and develop a six-person vehicle, which could cost more and take longer, or start with a three-person vehicle and scale up later.
“Advances in areas from aerodynamics to materials may result in a capsule that is sleeker and more adaptable”
NASA is aiming for a first CEV flight by 2011, a year after the planned retirement of the shuttle. This is a massive advance in schedule from the plan announced by President Bush, which called for a CEV debut flight in 2015. But Griffin is determined to narrow, if not altogether eliminate, the gap between the shuttle’s retirement and the CEV’s debut. Plans released earlier this year, when O’Keefe was still administrator, envisaged NASA selecting its contractor to build the CEV in 2008. Under Griffin, the selection is scheduled for early next year.
NASA spokesman Michael Braukus says there is a simple reason for wanting to get the CEV into orbit as soon as possible after the shuttle’s final flight: “Without an active CEV, the United States would be without a human-rated spacecraft.” That would leave NASA embarrassingly dependent on the space programmes of other countries, notably Russia.
But it remains unclear whether the gap can be eliminated completely. Griffin and NASA are working against the tide of recent history. After the shuttle was announced by President Nixon in 1972, it didn’t see first flight until 1981, several years later than anticipated. As for the most recent would-be shuttle replacements, both the Reagan-era National Aerospace Plane and the Clinton-era X-33 burnt billions and never flew.
To hedge his bets, Griffin has been manoeuvring to clear the way for NASA to purchase more Soyuz flights after the existing contract expires in April 2006. NASA is currently barred from buying more Soyuz missions by the Iran Nonproliferation Act of 2000, which bans the purchase of certain Russian high technology until Russia proves it is not helping Iran with its nascent nuclear programme. But in the 29 July news conference Griffin said that he is working with Congress and the White House to “get an exemption” to the act that would allow NASA to continue using Russian spacecraft to service the ISS. “We hope for and expect a successful outcome,” he said.
“Without a human-rated craft, NASA would be embarrassingly dependent on the space programmes of other countries”
As for getting the CEV and the new launchers off the drawing boards and into space, Griffin can look to the past and take heart from one major programme that did run to plan and schedule. That was Saturn V – and it took humans to the moon.
