Will Dawn head to another asteroid?


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NASA is still reviewing the proposal by the Dawn science team that they send the spacecraft to another asteroid in its last years before its fuel runs out.

The spacecraft has continued operations despite problems with its reaction wheels, used for attitude control. After suffering the loss of two of its four reaction wheels earlier in the mission, a third wheel malfunctioned in April. The spacecraft went into safe mode briefly, but controllers resumed operations with hydrazine thrusters taking over for the failed wheel. That failure will eventually lead to the end of the mission when the spacecraft runs out of hydrazine. “It does reduce our lifetime because we have to use hydrazine at a faster rate,” Raymond said at the SBAG meeting in June.

That lifetime, she said, is dependent on the spacecraft’s orbital altitude. Dawn has spiraled out to a higher orbit during its extended mission, which reduces the amount of hydrazine needed for attitude control. “The lifetime is now highly dependent on orbital altitude because we need to use the jets to fight the gravity gradient torques,” she said. In its current high orbit, Raymond said that Dawn had sufficient hydrazine, as well as xenon propellant used for the ion engine, to operate at least through the end of 2018.

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5 comments

  • Dick Eagleson

    Unless there is some significant bit of additional science “take” still to be had at Ceres, it would seem pretty much a no-brainer to send Dawn off to attempt the hat trick. Dawn is nearing the end of its nominal mission in any case. If it has enough Xenon left to go to some third interesting place, it should be sent.

    Dawn, in any case, isn’t likely to have a very long observation campaign at a third target object. Such a campaign would be longer if its sole functioning reaction wheel is still working upon arrival – shorter if not. But even needing to use hydrazine thrusters for all positioning, it could still do at least a prelim survey of a third body. I suspect that would be more scientifically valuable than whatever it will be incrementally able to accomplish at Ceres.

    I say go for it!

  • SteveC

    What is it with reaction wheels? They seem to be the most failure prone part of a research satellite. I would think that old-tech like this would be bullet-proof by now.

  • SteveC: There are engineers who comment here who can probably speak on this better than I, but reaction wheels are essentially gyroscopes spinning fast. In other words moving parts that wear out.

    The technology has improved enormously over the years. Hubble’s first set of six reaction wheels needed replacement several times. The last set they installed is doing much better and lasting much longer.

  • LocalFluff

    It’s fantastic that Dawn could orbit two asteroids. And the two largest, as if they could pick any two any time. Even a flyby of a third one would be great.

    I’d like to see a true asteroid cruiser mission. Going retrograde through the asteroid belt with an IR telescope and a powerful radar to image thousands of flyby asteroids at up to 0.1 AU distance or so. To do a stocktaking and find interesting ones for future missions.

  • ken anthony

    Imagine if the emDrive worked?

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