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The Planetary Society BlogBy Emily LakdawallaA slight reprieve for DawnMar. 8, 2006 | 12:34 PST | 20:34 UTC
They are reporting over at NASA Watch that "the impending cancellation of the Dawn asteroid exploration mission has been put on hold pending a review by NASA Administrator Michael Griffin." If true, this is clearly not un-cancellation, just a reprieve, but just about any news would be good news for Dawn at this point.
JPL has been doing some trajectory simulations and we have learned that if Dawn is cancelled, it will be something like a decade and a half before Vesta and Ceres can be done again by a single mission. These are high-priority targets. Vesta is the smallest terrestrial planet, formed 'dry', has an iron core, has had volcanism covering its surface in basalt, and is the source of about 4% of meteorite falls on the Earth (information hugely leveraged by going there). Ceres is the largest surviving protoplanet between Mars and Jupiter, has differentiated with a rocky core and ice-rich mantle, and may have a subsurface ocean -- which could make it rival Europa in importance for astrobiology (and would be a lot easier to get to and offer a less harsh operational environment). The bottom line is that we will doubtlessly be sending separate spacecraft to these objects if Dawn is cancelled, but at a price probably exceeding $1 billion rather than the additional tens of millions of overrun faced by Dawn. In fact, since Ceres' potential subsurface ocean was modeled long after the Dawn proposal was approved, I was [hoping to? intending to?] add an additional few million dollars to Dawn to restore a magnetometer for an additional means of determining the existence of the ocean beyond surface morphology and gravity modeling!The bottom line is that the Dawn team clearly hasn't lost hope. There has been a lot of discussion in the Members Forum and elsewhere about the cancellation of Dawn and its significance. A lot of people seem to think (without having any inside information to confirm this) that Dawn is mostly a victim of bad timing. The budget is very, very tight, and NASA has been getting increasingly irritated by cost overruns and descoping (which means cutting instruments or mission goals) on Discovery missions. These are some of NASA's cheapest missions, but they are competitively selected, so it's quite predictable that their proposers might downplay technical challenges or otherwise end up over-promising what they can do for the amount of money available to a Discovery mission, in order to be competetive in the selection process. As a result, it's become traditional now for Discovery missions to run over budget. (Not that it's not common in other programs, it's just particularly noticeable in Discovery because they are supposed to be cheap and quick.) As Mark pointed out in his earlier comments to me, Dawn's no different from other Discovery missions in this. What's different is this year's budget climate, and that NASA may finally have decided to "get tough" on Discovery missions by making an example out of Dawn. Which would be too bad, if it's true (again, I repeat this is just Internet speculation and has no basis in any reliable source). Whether or not this message is truly NASA's intent, the message has gotten across; I've seen "Controlling under-costing / cost-overruns of missions" as an agenda item on future planning meetings!
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