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Rosetta: Down, But Not Out
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By A.J.S. Rayl
The Planetary Society
23 January 2003

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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