[meteorite-list] Dawn Spacecraft May Visit Third Asteroid After Ceres and Vesta

[Ron Baalke]

https://www.newscientist.com/article/2085288-nasas-dawn-probe-may-visit-third-asteroid-after-ceres-and-vesta/

NASA's Dawn probe may visit third asteroid after Ceres and Vesta
By Govert Schilling
New Scientist
April 20, 2016

Some spacecraft just can't sit still. After exploring asteroids Vesta 
and Ceres, NASA's Dawn probe may fly off to a third destination.

Dawn was launched in September 2007, orbited Vesta for 14 months in 2011 
and 2012, and then flew on to orbit Ceres in March 2015, where it remains 
today.

It is the first ever spacecraft to visit two different asteroids, a hop-on, 
hop-off tour made possible thanks to Dawn's low-thrust ion drive, which 
uses electricity to spit out xenon ions rather than conventional rocket 
fuel.

This summer, Dawn's Ceres mission will officially end. But earlier this 
week, principal investigator Chris Russell of the University of California 
at Los Angeles and his team sent a proposal to NASA for an extension.

Secret destination

Spacecraft at the end of their life are normally parked in an out-of-the-way 
orbit, or crash land on the body they have been studying. That's the 
plan for the Rosetta probe, which will touch down on comet 67P/Churyumov-Gerasimenko 
later this year, but that fate won't be possible for Dawn.

"The spacecraft has not been sterilised, so we aren't allowed to touch 
down on the surface of Ceres," says Russell. Strict planetary protection 
rules forbid us sending Earth microbes to other worlds. "Instead, we 
want to go the other way, away from Ceres, to visit yet another target."

Given the small amount of xenon fuel remaining, the list of potential 
destinations is probably not too long, but Russell is keeping it a secret 
for now. "As long as the mission extension has not been approved by 
NASA, I'm not going to tell you which asteroid we plan to visit," 
he says. "I hope a decision won't take months."