A Valentine's Date With a Comet

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Platt: A sweetheart of a comet flyby.
I'm Jane Platt with NASA's Jet Propulsion Laboratory in Pasadena, Calif.
Make sure to mark February 14 on your calendar-that's when NASA's StardustNext spacecraft has a Valentine's Day rendezvous with a comet. A familiar spacecraft, a familiar comet. Stardust, as it was originally called, collected samples of comet Wild 2 in 2004 and returned them to Earth in 2006. It's now low on fuel but still orbiting, and now called StardustNext, and the craft is zooming toward comet Tempel 1. That is the same comet that successfully collided with NASA's Deep Impact spacecraft in 2005.
Joining us today-Stardust-NExT Project Manager Tim Larson of JPL.
What's the main goal of Stardust-NExT and what do we hope to learn by visiting comet Tempel 1 again?

Larson: The main goal of Stardust-NExT is to revisit a comet. In this case, the comet that we had the opportunity to go to is comet Tempel 1. We were there in 2005 with the Deep Impact spacecraft, and this is a golden opportunity, the first time we've ever been able to revisit a comet on a second pass near the sun. So this will give us important information about how the surface of the comets change with each passage near the sun, whether the changes in the comet are global or just specific to certain areas on the surface. So this is the very first time we've been able to do something like this.

Platt: And refresh everybody's memory-what do we know already about comet Tempel 1.

Larson: We know that comet Tempel 1 has a huge variety of features on its surface. We have found smooth areas that look like material flows, there are rough, pitted areas, there are craters on the surface, which we don't know if they're impact craters or if they're caused by material coming out from the inside of the comet. So this is a very interesting comet in terms of variety of terrain.

Platt: And why are comets so interesting in general to scientists, and to all of us?

Larson: The comets are of interest to the science community because they're considered to contain the pristine record of the materials that were around the solar system when it was first forming 4-1/2 billion years ago. So it gives us a unique insight into the beginnings of the solar system.

Platt: Where is Stardust-NExT right now?
Stardust-NExT is right now several million kilometers away from comet Tempel 1, approaching at the rate of 10 kilometers per second. And the spacecraft and the comet are both on the opposite side of the solar system from Earth, so we're about two astronomical units away from Earth right now.

Platt: And how many miles per hour is it zooming?
Larson: 10 kilometers per second is roughly equivalent to about 24, 000 miles per hour.

Platt: How close will it be during closest approach, which is about 8:30 p.m. Pacific time, in the U.S. time zones, on February 14th?

Larson: Right, on the Pacific Coast, the closest approach will occur around 8:30 pm. At that point we'll be about 200 kilometers away from the surface of the comet, that's our aim point. That's about 124, 128 miles from the comet. So this is a very close approach, the closest we've ever been to the surface of a comet.

Platt: Basically StardustNext is a recycled spacecraft, it was originally Stardust, flew past comet Wild 2, brought back samples. What kind of engineering tricks had to happen to make it into what it is now and what it's doing?

Larson: The primary challenge with reusing a spacecraft like Stardust is, first of all, designing a new mission that it can accomplish with the fuel that it has left. And through some clever mission design using some carefully timed trajectory correction maneuvers and taking advantage of some Earth gravity assists, we were able to modify the trajectory of the spacecraft to get it out close to Tempel 1. So that's been the primary challenge, and along with that is conserving and watching the fuel that we have on board and making sure that we have enough fuel left to finish off this mission. Beyond that, there have been a few challenges in terms of aging equipment on board the spacecraft, the spacecraft will be 12 years old in early February, and it's well beyond it's design life. And although everything is generally healthy on board, we have had a couple of pieces of equipment that were starting to age, and starting to degrade slightly. So we switched over to backup equipment so we were on fresh, healthy equipment, and we still have functioning equipment as backups.

Platt: So how do you prepare yourselves and the spacecraft in the next couple of weeks?

Larson: The preparations in terms of all the design of the flyby sequences and software, those are almost complete. Those sequences have been built, we're just finishing up the testing program right now to validate that they work, that they do what we want them to do. So from now on, most of our work is going to be watching our daily optical navigation images, we're tracking where the comet is relative to the spacecraft, and that will feed into our trajectory correction maneuvers, we have three more of those left before we arrive at the comet. And those will be used to target the spacecraft to the desired flyby point.

Platt: Off the top of your head, do you have the dates?

Larson: Yes, these TCMs will occur on January 31, February 7, and then the last fully designed TCM will occur on February 12, two days before we arrive.

Platt: And what are the possibilities image-wise, what might we see with the spacecraft at Tempel 1?

Larson: As we fly by Tempel 1, we have a limit of 72 images that we can take with the spacecraft and store on board. So those will be carefully timed to center them around the closest approach to the comet, so we can get the best possible resolution. We should be able to get around three dozen images that are at better than 80 meters per pixel resolution and our closest approach images should be down below 20 meters per pixel resolution. That will be good enough to resolve a lot of the key features on the surface of the comet and start that process of comparison.

Platt: Anything else you want people to know about the spacecraft, the mission?

Larson: The stardust spacecraft, this will be the culminating event of its career. This spacecraft is about 12 years old now, we're low on fuel, and so after we finish this flyby, we will have capped off an incredibly successful career for this spacecraft, with a very successful primary mission, sample return, two flybys of an asteroid and a comet, now a third flyby with Tempel 1. I think its good to note that NASA does everything that it can to get as much as it can out of these spacecraft, and this becomes a very cost-effective way to keep getting new science for the science community to work on over the years.

Platt: All right, thanks a lot, Tim, and course, best of luck for the flyby.

Larson: Well, thank you Jane. All of us are very excited about this flyby and we're looking forward to February 14.

Platt: Okay, More information on Stardust Next is online at http://stardustnext.jpl.nasa.gov . Thanks for joining us. You've been listening to a podcast from NASA's Jet Propulsion Laboratory.

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