NASA probes approaching the moon

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  • #2
D H
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This satellite pair will give a much better picture of the Moon's gravity field, especially the field on the far side. Uncertainty of the gravity field on the far side of the Moon is about 100 mGal, 10 times greater than the 10 mGal uncertainty on the near side. The goal is a uniform 0.1 mGal, or 10-6 m/s2, uncertainty gravity model. (1 Gal, or 1 galileo, is an acceleration of 1 cm/s2.)
 
  • #3
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Latest news is that both are in initial elliptical polar orbits. They've got to get down to ~35 mile high circular orbits before the 'science' can begin...

linky
 
  • #4
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I was surprised to see any NASA activity in space: I thought President Obama pretty
much shut them down...but maybe that was only manned spaceflight?
 
  • #5
D H
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I was surprised to see any NASA activity in space: I thought President Obama pretty
much shut them down...but maybe that was only manned spaceflight?
Credit goes to Bush, not Obama, for the end of the Shuttle program. Credit Obama for canceling the Constellation project. However, development of the Orion Multi-Purpose Crew Vehicle is ongoing. (Without a rocket on which to put it. Different story.) For now, the US is outsourcing human launch services to Russia. At $62.7 million a pop.
 
  • #6
BobG
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For now, the US is outsourcing human launch services to Russia. At $62.7 million a pop.
Which is significantly cheaper than the $450 million for each Shuttle mission.

There's a lot of depressing things about the idea of the US having no manned space capability of its own, but the cost isn't one of them (at least if the Shuttle is the US's only manned space program).
 
  • #7
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This voyage to the moon was "fuel saving", though it took longer. How does this work? You still have to escape Earth, still have to slow down (brake) into moon orbit -- how do you manage to save fuel? And about how much fuel (%-wise) is saved?
 
  • #8
D H
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This voyage to the moon was "fuel saving", though it took longer. How does this work? You still have to escape Earth, still have to slow down (brake) into moon orbit -- how do you manage to save fuel? And about how much fuel (%-wise) is saved?
The missions took advantage of some features of the restricted four body problem. Here the four bodies are the Earth, the Moon, the Sun, and the spacecraft (the "restricted" body, meaning an object with negligible mass). A vehicle that goes into the vicinity of the Moon by going through the space in the vicinity of the Earth-Moon L1 or L2 point with the right energy will automatically enter lunar orbit without need for any burn. It will be captured ballistically. So how to get this "right" energy? One way is to have the vehicle slowly inch its way there. That's what was done with Hiten.

These missions did something different. They instead took advantage of a weak coupling between the Sun-Earth and Earth-Moon systems. The name for the underlying theory is weak stability boundary theory. Taking advantage of this apparently saved about 150 m/s Δv, but at the cost of increasing the flight to the Moon from the 3 to 4 day mission for a direct transfer to 60 or more days.
 
  • #9
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Thanks for the reply! Space.com says there was a 40-minute burn of the main engine to insert one of the Grail spacecraft into lunar orbit, so I'm still a bit confused about this. See http://www.space.com/14102-nasa-grail-spacecraft-moon-orbit-2012.html. My best guess, from what you say, is that this burn actually did not use very much fuel, or at least not as much as would be needed to brake from a "direct" approach to the moon.
 
  • #10
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I was surprised to see any NASA activity in space: I thought President Obama pretty
much shut them down...but maybe that was only manned spaceflight?
The New Horizons probe is en route to Pluto, just beyond the orbit of Uranus.

Cassini is still orbiting in the Saturn system returning excellent data.

Juno is en route to Jupiter for detailed studies of the planet, rather than its satellites. (It is due a final sling shot gravity boost past Earth next year, though it is currently out beyond Mars.)

Oddysey is still functioning, I think, in Martian orbit and the Opportunity rover is wintering at Endeavour crater.

Mars Science Laboratory, a one ton lander, is due to arrive in August.

Messenger continues its program in orbit around Mercury and NASA has extended funding for a further year of data collection.

Dawn is in orbit around the asteroid Vesta, but will leave in a year or two for the dwarf planet Ceres.

There are also a plethora of probes in orbit around the Earth returning science information, plus space telescopes, sun observatories, etc. And don't forget NASA still receive data from both Voyager spacecraft, launched in 1977. They are 114 and 94 AU from the sun, nearing the edge of the solar system.
 

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