"Asteroids in the region were accumulating mass when the formation of Jupiter disturbed their orbits," he added. "They began crossing each other at higher and higher velocities and getting catastrophically destroyed. Only Vesta and Ceres survived, and today they’re surrounded by hundreds of thousands of the fragments of their brothers and sisters who didn’t survive."
"There was a lot of drama in the early Asteroid Belt," said Sykes. "We’re going to go to these objects to understand what was going on before all the destruction began."
Dawn’s suite of instruments will measure Vesta’s and Ceres’ mass, shape, volume and spin rate; record their magnetization and composition;
It will also provide a "ground truth" for meteorites that are already in hand. "Dawn gives us something to compare meteorites to for a better understanding of where they came from and how they evolved," said Project Manager Sarah Gavit of NASA’s Jet Propulsion Laboratory, which is managing the mission.
Added Sykes, "until now, it’s been like studying the nails, hair, [and] tissue sample of a larger beast. Now we get to see the beast itself to understand where all those pieces go. We can combine all that information with the object itself and understand just how it all works."
All of these goals are to be accomplished for a projected cost of $271 million, fitting well within the Discovery Program’s cap of $299 million.
Making it possible to jump through that budgetary hoop is the availability of solar-electric propulsion, which has been proven to work with its successful use on NASA’s Deep Space 1. That mission launched in 1998 to validate a dozen technologies that had been too risky for spacecraft to rely on before.
As Sykes put it, "Deep Space 1’s validation of ion propulsion was the only reason Dawn had a chance."
Why the connection? Solar-electric propulsion (SEP), using propellant such as xenon gas, is 10 times more efficient than standard chemical propellant. That means spacecraft using SEP can launch with roughly 10 times less fuel, allowing for smaller spacecraft and, most importantly in terms of budget, smaller launch vehicles.
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