Sunday, 21 June 2009

A little more on LRO and LCROSS


Regulars will know I got my name emblazoned across the LRO on a CD (or a DVD whatever) riding piggy-back on the Lunar Reconnaissance Orbiter (LRO). It's no big deal, but it is good fun (or what passes for fun chez Holroyd, at least it was free).


So here's a quick look at what the mission is about.

NASA has resolved to return to the Moon. With manned peopled crewed missions. The ultimate aim being to establish a permanent colony there. This is a good thing. Should we ever plan a trip to Mars or beyond, the experience of building and maintaining a lunar colony will be crucial.

It's also a very challenging thing. Where to land, where to build a colony? With no protective atmosphere, the Moon receives the full force of the Sun's radiation across the entire spectrum. Long term excursions out in the sunlight are very hazardous, but move into shadow and the Sun is gone. However the Moon rotates once a month, so shadows change as the Sun crosses the sky. In many areas you would have to find a cave (unlikely), or dig a hole to live in, to avoid the Sun.

So the search is on! Where on the Moon is there permanent shadow? By analogy with the Earth, we know that at the poles the amount of sunlight hitting the surface is reduced (or stretched over a bigger area) and shadows are long.

Enter the LRO. With a one year primary mission and a suite of instruments, including a high-res camera and a useless disc with names on it, LRO will enter a low polar orbit and map the surface. From 50km! That's low, the best image resolution will be about 1m which is enough to detect previous landing sites. Google Moon will need a makeover.

But just pause for thought. What does the surface of the Moon have in abundance? Craters! Could a crater near the North or South pole be deep enough to provide permanent shade. The answer is definitely yes, lots of them. The real question is which one to choose. Find a good one for instance, and you are in permanent shadow on the crater floor but raising your solar panels 20m or so, they could catch (just about) permanent sunshine (and then your iPod works 24/7).

What else is missing from this picture? There is a long cherished dream valid scientific hypothesis that comets may have carried water to both the fledgling Earth and Moon billions of years ago. Somewhere, under the floor of some craters, there could be ice on the Moon. Sitting buried for aeons till some enterprising ape comes to tap it.

Given the transport costs of supplies to a lunar colony, having a local water reserve is priceless. A liter of water is a kilogram mass, and even if you recycle sweat and urine there will be losses. Better still, if you have water and your iPod's still working, you can use electricity to split good old H2O into oxygen and hydrogen. You can then use the hydrogen as a fuel by burning it in oxygen to make water! Bingo, transportable fuel. Otherwise I suppose you could just breathe the oxygen, again reducing the transport cost from Earth.

Enter LCROSS, the Lunar CRater Observation and Sensing Satellite. Forget looking from a distance like LRO, LCROSS will plant a great big smackeroo on the Moon. Whilst the LRO detached from the upper stage of the rocket ~45mins after launch (and is now on it's way to the Moon) LCROSS remains attached and the two are now in a wide Earth orbit. The spent rocket stage is called Centaur, remember this.

LCROSS and Centaur will spend a few weeks in a strange, Earth/Moon looping, orbit, picking up some momentum and making sure Centaur's fuel tanks are fully vented (so as not to confuse future observations). The craft will re-orientate itself so that Centaur is leading (unlike the picture: the little black cube on the left is LCROSS, the brown and white thing is Centaur) and LCROSS will give the push to send them both Moonwards irrevocably. Not to caress but to hit. The ultimate guided missile.

Shortly before impact LCROSS will separate from Centaur. The target (I believe, I'm writing from memory) is a crater near the southern pole, who's floor is in permanent shadow. Centaur will hit the crater floor throwing up a plume of ejected material, some of which will be the original Moon, some may be from whatever formed the crater, and some scum from the vapourised Centaur. 4mins later LCROSS will follow Centaur down, instruments blazing, into the dust plume and right down to the surface. Like a sperm whale and a bowl of petunias they wont get much time to think about it.

Telescopes worldwide will be watching, as will the LRO. Will there be evidence of water? Let's see...

And that's why I get so hyper about space missions.

1 comment:

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