NASA Launches Mission to Gravity Map the Moon

This week's "current" event comes from NASA, which launched its GRAIL mission on September 10. Here's a video of the launch. It's awesome to watch, and I love the sound of the rocket engines. (Frankly, that's my favorite part of being in the Air Force, too; living on or near a base and hearing the jet engines. Air Power--rrroawr!)




GRAIL stands for Gravity Recovery and Interior Laboratory, and really what NASA hopes to do is make a gravity map of the moon. GRAIL consists of two satellites that will fly the exact same orbits, one following the other. As the composition of the moon changes, whether because they are overflying a mountain or something beneath the surface is more massive than the stuff around it, one satellite's orbit will be affected slightly. By recording the differences, they'll be able to better figure out the composition of the moon.


Scientists believe this can also help us understand other planets as well; sadly, the video doesn't really say what or how. However, the key lies in the fact that the moon has no atmosphere, so it holds an accurate history of the past 4.5 million years of our universe. If we know what's inside the moon, we know what's been around, when and what it did. For example, did you know the moon isn't round? It actually has a bump on the far side. In fact, there's one theory that earth had two moons once upon a time and that one hit the other. A gravity map might shed some light on this and other questions.

My friend Virginia (and that's her actual name this time) asks, "Why are they taking months to get there? Are they driving?" Those who remember the Apollo missions know that we got to the moon in a matter of days, but the GRAIL probes will take three and a half months.

Are we there yet?

Not driving, but they are trying to save on fuel. Unlike when you drive on earth, the direct route from A to B isn't always the most fuel-efficient. That's partly because as the satellites are moving, so is their target, but mostly because you want to be able to slow down and get into orbit. Slowing down takes a lot of fuel, and the spacecraft don't have it. So they make use of a nifty astronomical feature called a LaGrange point.

The LaGrange point is a kind of null space, gravitationally. If you put something there, it will stay there. So NASA is using that to help slow the satellites down. I couldn't find a good explanation for how this works, but my guess is that it gives the ships time to coast, and they can make fewer course changes and don't have to use as much power to slow down to get into lunar orbit. Also, it takes a less powerful rocket to send something up to the LaGrange point than it does to get to the moon.

The other thing it does is give the satellites time to "out-gas." Gas gets caught in the spacecrafts, even on the molecular level, and will sublimate in vacuum. They need the satellites to do this first to make sure they get accurate readings when mapping the moon. You can find fuller details here: http://www.spaceflightnow.com/delta/d356/preview.html.

For further reading:
http://science.nasa.gov/missions/grail/
http://moon.mit.edu/objectives.html
http://www.spaceflight101.com/grail-mission-design-timeline.html