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Rosetta Down, But Not Out
Rosetta Down, But Not Out
23 Jan 2003
(Source: The Planetary Society)

By A.J.S. Rayl
Planetary Society

Rosetta -- the first mission to orbit and land on a comet - may be down, but it's definitely not out. That's the word streaming from officials of the European Space Agency (ESA), as well as scientists and engineers attached to the mission. But, as for which comet Rosetta will visit, nothing is certain right now.

"Everyone is very disappointed that we didn't go when we planned to, but now everyone is trying to focus on what the options are and what we are going to do," says Paul R. Weissman, an interdisciplinary scientist on Rosetta from the Jet Propulsion Laboratory (JPL).

While it's been something of a struggle emotionally, Weissman admits, accidents and false starts go with the territory of space exploration. "These things happen and they seem to be happening more and more lately, so people know it's part of the risk you take when you get into the business," he says. The main feeling among the scientists right now is "one of uncertainty about what we're going to do," he adds. "People will feel a lot better and more comfortable once ESA has presented the options and shown us what the opportunities and trade-offs are in terms of science and time and so on."

Rosetta was scheduled to launch and begin its eight-year journey to Comet Wirtanen onboard an Ariane-5 rocket in mid-January from Kourou, French Guiana. But, following a failure of the enhanced Ariane 5 rocket last December, a report issued by an inquiry board identified significant problems in all versions of the Ariane 5 rocket. That seemed to seal Rosetta's fate. ESA and Arianespace officials jointly announced last week that the mission was being postponed indefinitely.

Since then, rumors have bounced back and forth across the Pond. Some reports claim that both the spacecraft and the Ariane 5 rocket are to be dismantled and thoroughly inspected, even though there would appear no compelling reason to take the spacecraft itself apart. One report in Le Monde, the legendary French newspaper, maintained that three alternative flight plans were being studied for Rosetta, including two that would take the comet chaser to Wirtanen, its original target.

This week ESA officials issued their own update, which quelled some of the rumors.

Simply put, the flightpath Rosetta ultimately will take -- and the comet on which it will land -- have not yet been determined.

According to the agency's press release: "Rosetta can no longer reach its original target." And, the Rosetta launch "is not expected for at least one year at the earliest."

As soon as the decision to postpone the mission came down, the Rosetta team went back to the comet board to identify alternative targets that the spacecraft could reach, within a launch timeframe of the next two-and-a-half years. The team is assembling a shortlist of possible destinations, considering three primary criteria: scientific return, technical risks to the spacecraft, and the added cost it will take to carry out the new mission.

While a short list was drawn up a decade ago when the mission was first designed, those targets wouldn't necessarily be appropriate candidates for a mission to launch next year or the year after. "These comets typically have orbital periods of around six years, and if we're looking at a one or two-year delay in launch, basically the comets that were a year or so ahead of Wirtanen in terms of a possible launch are not going to be around for another five years, so it would be a much longer delay to wait for them." So what the team is looking at, he adds, is what comets would be available in the timeframe where they believe Ariane will fly again.

Among the possible targets being reported: Comet Wild 2, which will be visited by NASA's Stardust in early 2004, Churyumov-Gerasimenko, Finlay, Howell, and Schwassmann-Wachmann 2.

"We have heard all these names, but we have to actually spend time looking into them," says Weissman. "Both Churyumov-Gerasimenko and Wild 2 are good targets. Both of those are well-classified comets and we know quite a bit about them and they would be excellent targets; the others we know quite a bit less about."

Generally speaking, the researchers will get the same scientific information they would have gotten from Wirtanen no matter what comet is chosen -- as long as it has comparable activity to Wirtanan, Weissman notes.

The new list will be presented to the Science Program Committee in late February, which will then discuss the viability of the comet candidates. A final decision on the new target comet and mission profile is expected for May 2003 at the latest.

Additionally, ESA reports that the Ariane-5 program is now under thorough re-examination, and the agency expects Arianespace to provide "the necessary guarantees" regarding the Ariane-5 system qualification procedures and review process.

For now, Rosetta will be stored away, "safely and cleanly, until it is called upon." Engineers will remove all batteries, take off the lander harpoons, and drain the fuel tanks. "The same care that went into building the spacecraft will now be applied to storing it and making sure that it will be in perfect shape for us to launch it when the date comes," says John Ellwood, Rosetta's Project Manager.

The cost of grounding the mission is will cost ESA somewhere between 50 and 100 million Euros.

Rosetta's Project Scientist, Gerhard Schwehm, remains, like his colleagues, undaunted by this latest wrinkle. "During the decade it has taken us to develop and build Rosetta, we have faced many Rosetta challenges and overcome them all," he says. "This new challenge lander will be met with the same energy, enthusiasm and, ultimately, Image: ESA success."

ESA's Director of Science David Southwood echoed the firm resolve to view the delay as a "galvanizing" challenge. "If one is going to be stuck anywhere, these are the guys to be with," he says of the scientists, engineers, and industrial teams affiliated with the mission. "They have the pioneering spirit and dedication that is worthy of space explorers."

Rock on, Rosetta.

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Last Updated: 24 Jan 2003