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Rosetta Retasked For 10 Year Trip To Comet Churyumov-Gerasimenko

If the February 2004 launch window is also missed there is yet another opportunity to launch to Churyumov a year later, with its arrival at the originally planned date -- although this would require that the more powerful Ariane 5-ECA be ready for use by then to avoid the need for an extra Earth gravity-assist flyby.
by Bruce Moomaw
Sacramento - Jun 11, 2003
The European Space Agency's ambitious Rosetta mission to rendezvous with and orbit a comet nucleus for the first time -- and then dispatch a small lander onto its surface -- has just survived the most bizarre crisis imaginable.

Rosetta's planned launch last January to the comet Wirtanen had to be cancelled because the first test flight of an improved version of its Ariane 5 booster failed disastrously the month before.

Although it was believed (correctly) that this failure was due to the new features of the improved "Ariane 5- ECA", the failure investigation board nonetheless concluded that there were still enough serious questions about quality control in the manufacture of the original Ariane 5 (which had failed on three of its 13 flights) that the ESA should not risk flying even the regular version for several months, until the questions could be answered.

Ironically, the regular Ariane 5 passed its reexamination, and has since made a successful flight in April -- but by the time the study was complete, Rosetta had missed its launch window, and the mission had to be redesigned for launch to another comet.

Rosetta's engineers found another target -- Churyumov-Gerasimenko -- and a flight plan to reach it with a launch in Feb. 2004, although this involved some redesign of the mission. But the 13-month launch delay in itself produced a strange new crisis: financing.

The need to redesign the mission, and to store the craft on the ground for another 13 months before launch, inevitably added another 70 million Euros (82 million US dollars) to mission costs.

But, simultaneously, several of the other missions in the ESA's Space Science Programme underwent a rash of problems forcing their short-term expenditures to rise as well.

Europe's first Moon probe, SMART-1, also had its launch delayed until Aug. 22 by the Ariane 5 problems. The Mars Express mission successfully launched on June 2 also had some mission cost increases, and the sophisticated Herschel and Planck space telescopes scheduled for simultaneous launch on the same booster in 2007 have had a whole series of serious cost overruns.

ESA Science Director David Southwood and his committee had engaged in some downright remarkable mission redesign and schedule-juggling efforts last year in response to earlier cost overrun problems --allowing the ESA's ambitious space science program for the next decade to be not only preserved with just a few minor delays, but to actually have two new missions (Venus Express and Eddington) added to it.

But this year's new wave of problems left him confronting the fiscal equivalent of the perfect storm. The Space Science Programme, with a budget of 430 million US dollars for this year, suddenly found itself fully $230 million in the red.

The ESA's rules did not allow him to borrow funds for this year from the program's planned funding through the next few years. And, even after juggling launch schedules for further delays to the maximum possible extent, he found that there was simply no way to reshuffle this year's funds to cover the deficit without canceling Rosetta's 2004 launch.

Moreover, the loss of its original target Wirtanen leaves Rosetta with very few options for a replacement mission. Virtually no alternate targets were available other than the 2004 launch to Churyumov without a radical mission redesign and launch delays of several years, which would in turn foul up the financing of Rosetta and the entire Space Science Programme enough to force total cancellation of the mission.

Thus the ESA -- thanks to its overconfidence in the reliability of Ariane 5 -- found itself in the grotesque position of having an already-built, perfectly good spacecraft whose scientifically crucial $1 billion mission might have to be totally cancelled.

The only way out for Rosetta was for the ministers responsible for space affairs in ESA's 15 member nations -- already scheduled to meet in May to deal with Ariane 5's continuing financial woes -- to allow a one-time break in the long-standing prohibition against an ESA division borrowing from its future-year budgets to cover a current-year deficit. And such a resolution would have to be passed unanimously.

Fortunately, on May 27 the ESA Ministerial Council came through, allowing Southwood to reshuffle all of the funding scheduled for the Space Science Programme through 2006 to cover the 2003 funding crisis.

At the same time, they passed a series of major measures intended to deal with Ariane 5's serious financial problems -- including approving two more test flights of the improved Ariane 5-ECA in 2004.

The first of these may have to be flown with a dummy satellite, although the ESA is still frantically looking for a commercial comsat manufacturer willing to risk putting its payload on this flight.

The second test flight in fall 2004 -- which will actually be just another test of Ariane 5-ECA's new second stage, mounted on the first stage of a regular Ariane 5 to reduce risk -- will launch the first of the ESA's new "Automated Transfer Vehicles" to carry supplies to the International Space Station, thus reducing the burden on the Shuttle and the Russian Progress vehicle to resupply the Station.

Southwood tells "SpaceDaily" that he is very far from deciding how to reshuffle funds among all of ESA's space science missions over the next four years to cover the current funding problems, and indeed that the final decision on this will likely not be made until November.

However, the immediate and crucial consequence is that Rosetta's February 2004 launch to Churyumov has been officially approved. All the missions scheduled for later this decade (except for the 2005 Venus Express) have considerable elasticity in their launch schedules and can tolerate various degrees of delay.

Southwood also tells SpaceDaily that another important decision regarding the ESA's next major Solar System exploration mission -- the two "BepiColombo" Mercury orbiters, currently set for 2011-12 -- will probably be made earlier.

The ESA earlier had to provisionally cancel its plans to add a small Mercury soft lander to one of the two orbiter missions, but Russia's Babakin Space Agency has indicated that it may be willing to provide at least some of the components of such a lander.

Southwood says that the final analysis of the different options for design and scheduling of the BepiColombo mission is not due until the end of June, "and I am not hurrying things unnecessarily."

As for the redesign of the Rosetta mission: it will, in one respect, be more difficult than its originally planned mission to Wirtanen. Because Churyumov's nucleus is considerably larger (it's thought to have a diameter of about 9 km), Rosetta will have to drop its lander onto the surface from a distance of less than a kilometer -- and will have to use its thrusters to briefly slow down its own forward movement during the drop, and then immediately fire them after releasing the Lander in order to resume moving forward.

However, the team is increasingly confident that this can be done successfully, and that no actual hardware changes to the spacecraft will be needed at all.

Project chief scientist Gerhard Schwehm tells SpaceDaily that the official May 28 ESA press release announcing the mission go-ahead actually contains one big error.

It says that Rosetta will not rendezvous with Churyumov until Nov. 2014 -- only 9 months before the comet reaches perihelion -- which, if true, would seriously shorten the time during which the craft could study the comet before the increasing amount of dust boiled off the nucleus by the sun's increasing warmth would seriously interfere with its instruments.

But Schwehm says that the plan is still for Rosetta to rendezvous with Churyumov in May or June 2014, when it is still fully 580-600 million km from the Sun -- and that the November date actually refers to the time at which the Lander will be released to touch down on the nucleus (at which time the comet will be about 450 million km from the Sun).

Schwehm also says that the science return from the redesigned Rosetta mission may actually be considerably larger, because the distance from the comet to Earth during the mission will be a good deal less than would have been the case with Wirtanen, allowing the spacecraft's data rate to be greatly increased.

The delay in arrival also means that the ESA will have one, and maybe two, additional DSN receiving dishes operating by then than would have been the case with the Wirtanen mission.

At any rate, it appears that the ESA's space science program has yet again managed to escape from a seemingly deadly scheduling crisis. Of course, all this depends on whether Rosetta actually is successfully launched at the end of Feb. 2004.

If this new launch window is also missed, however, there is yet another opportunity to launch the craft to Churyumov a year later, with its arrival at the originally planned date -- although this would require that the more powerful Ariane 5-ECA be ready for use by then, as a substitute for the boost the craft would receive from an extra Earth gravity-assist flyby that is scheduled for a year after the Feb. 2004 launch.

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Rosetta To Play Orbital Mechanics To Reach Churyumov-Gerasimenko
Sacramento - Mar 23, 2003
Although a delayed launch to comet Wirtanen next January cannot be completely ruled out, the most probable replacement mission for Europe's Rosetta comet exploration mission is a launch next February that will see Rosetta weave its way across the solar system to reach comet Churyumov-Gerasimenko after several planetary and asteroid flybys sometime in 2014.



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