Deep Impact Comet Bash, part 7 Bill Smythe’s comet discussion

[coverage of Planetary Society’s Deep Impact Comet Bash: Part 1 | Part 2 | Part 3 | Part 4 | Part 5 | Part 6 | Part 7 | Part 8 ]


Bill Smythe, payload specialist for the mission, is talking about what’s in a mission… [this is his continuation of a presentation he was giving in Part 4]

What we may have learned tonight, can we push on a comet hard enough to get it to change its path. I suspect maybe not.

Comets slow rotators.

The Spacecraft: The adapter ring, attaches spacecraft to the rocket. Tried to get a pure copper spacecraft, but couldn’t, so other materials will show up in the spectroscopy images. 6-sided spacecraft. need panels to both cool spacecraft and have places to mount intstruments. As built, made it a 5-sided. Try to have minimum mass and maximum surface area, and pentagon was better than hexagon (or 3D forms therof). Each panel folds down to get access to wiring, etc. Made it a model out of wood to get all the wiring right. Antenna to send to earth, and an antenna to send from little spacecraft to the big spacecraft is a little flap-thing. Power system, solar panels, part of whipple shield (things that protect from impacts from comet). Two cameras. 10 feet high and about 6 feet wide. weighs less than most cars.

Bunny suits: to keep from getting hair and dead skin cells from shedding onto spacecraft-in-build process. Telescope has effective focal length of 10 meters, but it’s folded. Shots of spacecraft construction/assembly, the shaker test, scary. almost as scary as launch and as scary as tonight. You spend months and months to put delicate optics together and then they shake it up.

Solid copper mass: about 220kg, ended up with lot less mass than hoped. Copper’s bad to make spacecraft with… not strong enough. Mike Ahern from Univeristy of Maryland is PI (principle investigator)

The Mission: What are we going to do? Well, we did it. You spend about 4 years of our life putting this together, and then you put it on a firecracker. Original plan was to circle earth for a year, then head to the comet. It turns out we needed that time to calibrate the spacecraft. So we spent that time on earth. and launched and went straight to the comet. (That kinda quick 6 month flight is unusual)

[he shows] One of first pix of comets from spacecraft. Exciting to get images when you spent all that time building the camera.

I think that the impact is going to be about the size of the Rose Bowl.

Seeing the Moment of Impact. Lots of the scientists on the mission weren’t at mission control, they were all off at telescopes. Got as much telescope time in the world as we could. Thanks to someone who coordinated (didn’t catch her name). And spectrometers from earth. microwave, too.

Back when we were way out there —which was, what, a week ago?— this is image and spectroscope of substances.

That’s how we’ll figure out the composition of the comet… the spectrometers.

Sites to check out for info: University of Maryland,

Q: What atomic species in spacecraft? Copper, Aluminum, A: uh, I forgot. maybe fiberglass.

Q: question about focus on high resolution imager
A: You *would* bring that up. yeah, there was a problem with that. Hard to do, hard to calibrate. There was a change in radius… and shimmed it. Shimmed it out of focus. put back into focus with image processing, but if image processing’d be even better if it were in focus.

Q: ?
A: We’re going to learn a lot from this one. Lots of data. How to land on a comet. Put down water and freeze yourself to it. But what if dust? or put a spike out and bury that… but if the material is too loose, that might not work, either. Rosetta (the European Space Agency planned comet lander) will need to figure that out.

This impact was the same as a flea/gnat hitting a 747 (i.e., not much). A teeny tiny hundredth decimal place effect. Just not enough momentum exchange to move the comet at all. Comets when they come by the sun sometimes break apart. Those that have jets coming out of them are doing it all the time.

Q: Mass/density?
A: Can’t get that when you’re flying at 10km/second, can’t tell mass. Maybe if there are boulders emitted in impact, can maybe calculate mass from that.

2 responses to “Deep Impact Comet Bash, part 7 Bill Smythe’s comet discussion”

  1. Asa Dotzler

    heh. “this impact was the same as a flea/gnat hitting a 747 (i.e., not much)”

    Well, from a visual perspective, and certainly a historical one, this was huge.

    I hope that the press doesn’t run with that very quotable bit or try to make any kind of story out of it.

    – A

  2. Susan A. Kitchens

    Actually, best I can recall from a day+ later, that quote was used at the Planetary Society event, not from NASA TV or onsite at the lab.