Dec 31 2007
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More on EPOXI flyby
A couple of quick notes:
The EPOXI (nee Deep Impact) spacecraft will do a flyby of the Earth tonight. You probably won’t be able to see it without a big ’scope, but it’s out there. I erroneously said in my earlier post that it was stealing some of Earth’s energy, but in fact the opposite is true: the Earth is stealing energy from the spacecraft! This will move the Earth in its orbit a teeny tiny little bit, which means in a zillion years we’ll be an inch different in our orbit than we would have been otherwise. The spacecraft has very little mass compared to the Earth, so while it loses a lot of energy relatively, the Earth gains very little.
Second, the EPOXI team has posted images of the Moon taken with its instruments.
These were taken when the spacecraft was still 1.2 million kilometers from the Moon. They’re slightly out of focus (I’m not clear why; the website doesn’t say as far as I can tell). The team compensated by using a technique called deconvolution, which sharpens up an image but can introduce artifacts (like overly bright or overly sharp features; I used this technique ad nauseum on my early Hubble images). Don’t tell Hoagland! Let’s see if he claims to see giant statues of Ozymandias in the images.
I don’t know if they will take any images of Earth; I hope so, but I have not yet heard anything. I’ll post them if I find them!
So does that mean my earlier predictions will not come true, and I must give up my claim to James’ Randi’s reward?
I think I’ll cry now….
The reason the images are out of focus because the HRI imager has a defect which was found after launch - the telescopic mirror couldn’t focus the image, a problem going back to when the instrument was built.
That’s why there weren’t spectacularly good images of Tempel 1 either, but it’s also (ironically) the blur which makes it perfect for stellar observations of EPOXI. You spread the star image over more pixels so you can gather more photons without saturating the CCD.
I know it’s wrong of me to think this on so many levels but I imagine this conversation between our national avatars (or personifications, or whatever):
Europe:Let’s send a rocket to hit the moon!
Japan: Ours is better, it goes into orbit.
China: Oh yeah, we can do that too!
India, Britain: Us too, us too!
USA: Better just swing some old probe past the moon to remind ‘em all who’s boss.
Will Hartley 2 be visible from the US when the fly-by occurs?
The Hartley 2 encounter will be in Oct 2010. I haven’t looked at the observing circumstances yet (the details that would be of interest to amateur observers)… I do know that the comet will only be about 0.14AUs from Earth though. We will post info on the EPOXI and Amateur Observers Program website eventually about the observing.
Elizabeth
Correct me if I’m wrong, but I thought that the Earth would gain the same amount of energy as the spacecraft loses. Isn’t it just the effect on the motion of the Earth that is smaller?
Great question. Here’s some discussion I found on it with a quick search:
http://www.meteorobs.org/maillist/msg06101.html
The short answer is that the guy who wrote it thinks Hartley 2 may be naked-eye visible in the 3.5-4 magnitude range.
Apologies on the timing. My post was meant to answer Baldape’s.
I was about to post the same as Paul: the probe loses as much energy as the earth gains. It’s speed where the big difference is, not energy.
[…] More on EPOXI flyby By The Bad Astronomer The team compensated by using a technique called deconvolution, which sharpens up an image but can introduce artifacts (like overly bright or overly sharp features; I used this technique ad nauseum on my early Hubble images). … Bad Astronomy Blog - http://www.badastronomy.com/bablog […]
@ Paul & Michael:
BA said: “The spacecraft has very little mass compared to the Earth, so while it loses a lot of energy relatively, the Earth gains very little [relatively].” There, I fixed it. Energy in the flyby is conserved, but the amount that the Earth receives relative to its pre-flyby energy is so small as to be a rounding error, much like if a flea were to leap off of you, you might not even feel it, but the flea definitely would. So, yes, you’re both right, and so is BA.
PS @BA: A zillion is 10^x; what is x? Does earth have that much time left? I think I’ll go outside during the flyby and pull the earth in the opposite direction so it all evens out.
Thanks Mandy, it makes sense to me now…
I wonder if I can use the effects of this flyby for not being able to walk straight or stand up? Tomorrow, when I wake up with a headache, I’ll just blame EPOXI!
“…but the amount that the Earth receives relative to its pre-flyby energy is so small as to be a rounding error, much like if a flea were to leap off of you, you might not even feel it, but the flea definitely would.”
Effectively a gigantic Mössbauer effect.
I’m a little bit surprised (to say nothing of gloating) that Phil hadn’t heard about the HRI mirror problem on Deep Impact — they discovered it right after launch, and the similarity to the Hubble mirror fiasco was positively embarrassing. It turned out that Ball Aerospace had optically tested the HRI mirror at room temperature, without considering the possible that its near-cryogenic temperature in space might warp it. Deconvolution did a lot to improve it, but its resolution is still only about 2 or 3 times better than the unaffected MRI camera (instead of 5 times better, as planned).
It is nice, though, that the problem won’t affect the EPOXI part of the mission — that is, they’ve found a way to cure EPOXI…
EPOXI : A resin used to continue flying after a Deep Impact
Sorry couldn’t resist it.
Well done NASA - & don’t forget add the sub-orbital private “space” entrepreneurs to the “you showed ‘em” listing. NASA - and national space agencues generally maty not be perfect but they - esp. NASA - have achieved a huge amount and we should never forget that or fail to be appreciative and respectful of it.
Call Deep Impact or call it EPOXI this lil’ robot wanderer has gone a long way …
Thumbs up!