A close encounter with comet Hartley 2 on Nov. 4th will provide NASA with its best view yet of a comet.

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Title: Epoxi: Mission to Comet Hartley 2 The Deep Impact mission was a mission to comet Tempel 1 to deliver an impactor in 2005. The instruments on the Deep Impact spacecraft were designed to be diagnostic in a flyby of a comet.

We got some fascinating results from comet Tempel 1. But once we got past Tempel 1 we had plenty of fuel left, the spacecraft was healthy, then immediately everybody set to work on figuring out what new bodies we could get to. That's what led to the proposal to go to comet Hartley 2.

It's really a good deal for NASA and the American public, to send a spacecraft to a whole new mission for a small fraction of what the new mission costs. We were able to retarget the spacecraft using a few flybys of Earth, take advantage of the gravity assist from Earth to retarget ourselves, change our trajectory just enough so that now we're able to get to comet Hartley 2 in November. Because this wasn't what the spacecraft was planned for, there's challenges and there's inevitably going to be surprises.

The geometry of the Tempel 1 flyby was such that we could look at the comet, and take images at the same time that our high gain antenna was pointed at Earth. Because of the geometry of the Hartley 2 flyby, when we're pointed at the comet on approach, our high gain antenna can not see the Earth.

So we cannot downlink data in real time. So we have to design everything, for one thing, to protect that imaging sequence to make sure that no matter what happens, we're able to recover and keep taking images. The things we will be looking for will be how different is the nucleus compared to the other comets that we've been to. What does the nucleus look like that makes it so active?

Can we see which parts of the comet are emitting so much gas, and what's the nature of the chemicals, the compounds that are coming out of the comet? The excitement about studying comets is really driven by getting a better understanding of the early phases and early formation of our solar system.

Comets essentially have been in the refrigerator since the beginning of the solar system and so when we explore these objects, we find out what they're made of, we get to look back to the beginning of the formation of the solar system. This mission is very economical and we're going to get science from this flyby opportunity.

NASA's Jet Propulsion Laboratory, California Institute of Technology
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