Comments on: GRAIL closing in on Moon https://gregladen.com/blog/2011/12/29/grail-closing-in-on-moon/ Sun, 01 Jan 2012 16:05:34 +0000 hourly 1 https://wordpress.org/?v=6.4.6 By: StevoR https://gregladen.com/blog/2011/12/29/grail-closing-in-on-moon/#comment-510740 Sun, 01 Jan 2012 16:05:34 +0000 http://scienceblogs.com/gregladen/2011/12/29/grail-closing-in-on-moon/#comment-510740 Success! Well half of it anyhow. GRAIL A has successful entered lunar orbit – GRAIL-B still has to do the same at least last I’ve seen.

See :

http://www.nasa.gov/mission_pages/grail/news/grail20111231.html#

& GRAIL website here :

http://www.nasa.gov/mission_pages/grail/main/index.html

]]> By: daedalus2u https://gregladen.com/blog/2011/12/29/grail-closing-in-on-moon/#comment-510739 Sat, 31 Dec 2011 00:43:39 +0000 http://scienceblogs.com/gregladen/2011/12/29/grail-closing-in-on-moon/#comment-510739 I suspect that they are using ion drives which are low thrust but high specific impulse. Once you are in space all that matters is the total impulse, not the thrust. It takes a lot of thrust to get clear of the atmosphere and into orbit and high thrust means high fuel consumption.

They need to be able to adjust the orbits of each one, so as to keep them flying together. Using the same ion drive to get to the moon makes a lot of sense because it conserves mass for payload. They need to fly very “cleanly”, where all non-gravitational forces can be accounted for. That includes things like radiation pressure from the sun and from thermal radiation from the satellites themselves. Off gassing is important too, and that is very hard to predict, so letting them sit in vacuum for a while is a good idea.

The GRACE experiment was able to measure things like the change in mass of ice in Greenland from its gravity. Grail will be a lot closer to the moon (the moon has no significant atmosphere), and the moon has a lower gravity field so deviations should be more apparent.

I don’t think that it is expected that there are any dynamic processes on the moon to actually measure, but if there are, this might be able to see them. If it could measure voids, like empty lava tubes, that would be very interesting and important.

]]> By: Greg Laden https://gregladen.com/blog/2011/12/29/grail-closing-in-on-moon/#comment-510738 Fri, 30 Dec 2011 20:33:05 +0000 http://scienceblogs.com/gregladen/2011/12/29/grail-closing-in-on-moon/#comment-510738 Steve, good question. I’m going by what they said in the press release, though I’m not sure if they directly address that. Perhaps they are using the time well, but stuck with it for some reason having to do with propulsion.

]]> By: StevoR https://gregladen.com/blog/2011/12/29/grail-closing-in-on-moon/#comment-510737 Fri, 30 Dec 2011 13:19:58 +0000 http://scienceblogs.com/gregladen/2011/12/29/grail-closing-in-on-moon/#comment-510737

But the GRAIL mission has taken months to get there, because of the kind of orbit they wanted to achieve.

Is it that or is it more due to their weaker propulsion method and absence of a Saturn V rocket launcher?

]]> By: StevoR https://gregladen.com/blog/2011/12/29/grail-closing-in-on-moon/#comment-510736 Fri, 30 Dec 2011 13:17:51 +0000 http://scienceblogs.com/gregladen/2011/12/29/grail-closing-in-on-moon/#comment-510736 @3. Hengist McStone | December 29, 2011 6:29 PM :

This sounds like a lunar version of GRACE

It does doesn’t it? Hope both missions work smoothly and successful and wish those involved the best.

See :

http://www.csr.utexas.edu/grace/

&

http://moon.mit.edu/index.html

For comparison.

]]> By: StevoR https://gregladen.com/blog/2011/12/29/grail-closing-in-on-moon/#comment-510735 Fri, 30 Dec 2011 12:55:47 +0000 http://scienceblogs.com/gregladen/2011/12/29/grail-closing-in-on-moon/#comment-510735 @Alph | December 29, 2011 2:13 PM

“going around the planet’. Since when is the moon a planet?

Since the nuclear waste dump there exploded and threw it out into interstellar space back on the 13th of September 1999? 😉

(See : http://en.wikipedia.org/wiki/Space:_1999 for details.)

]]> By: Hengist McStone https://gregladen.com/blog/2011/12/29/grail-closing-in-on-moon/#comment-510734 Fri, 30 Dec 2011 00:29:27 +0000 http://scienceblogs.com/gregladen/2011/12/29/grail-closing-in-on-moon/#comment-510734 This sounds like a lunar version of GRACE

]]> By: MadScientist https://gregladen.com/blog/2011/12/29/grail-closing-in-on-moon/#comment-510733 Thu, 29 Dec 2011 21:55:55 +0000 http://scienceblogs.com/gregladen/2011/12/29/grail-closing-in-on-moon/#comment-510733 That’s interesting – so they’re not using a gravity sensor like the one used on that ESA satellite a year or two ago? I wonder what the expected magnitude of anomalies are.

]]> By: Alph https://gregladen.com/blog/2011/12/29/grail-closing-in-on-moon/#comment-510732 Thu, 29 Dec 2011 20:13:46 +0000 http://scienceblogs.com/gregladen/2011/12/29/grail-closing-in-on-moon/#comment-510732 “going around the planet’. Since when is the moon a planet?

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