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Posts Tagged ‘radiation’

Naked Astronauts, etc.

Tuesday, December 15th, 2009

 

Sometimes the best questions are facetious.

This morning I was attending the moon sessions at the American Geophysical Union conference in San Francisco. One of the talks was by Justin Kasper, who works on the cosmic ray detection experiment (CRaTER) on the Lunar Reconnaissance Orbiter. After his talk, one of the audience members (Mark Robinson of the LRO Camera team) asked what have to be the most unexpected questions of the meeting:

“So, is an astronaut’s suit dangerous? In a theoretical sense, would it be better for an astronaut to go naked?”

Before I tell you the answer, let me tell you why the question is not as crazy as it seems.

Kasper had just reported on the most unexpected finding so far by the cosmic ray experiment. It was supposed to measure how much radiation on the moon is coming from outer space (cosmic rays) and the sun (mostly protons from the solar wind). But they have found that the moon itself is a significant source of radiation.

In open space, CRaTER counted about 33 cosmic rays per second. (By the way, that’s an unusually high number. The sun is currently in one of the most quiet phases ever recorded in its magnetic cycle, which means that it is not doing as good a job as usual of blocking cosmic rays from outside the solar system.) When LRO got into lunar orbit, about 50 kilometers above the surface, the count dropped to 22 cosmic rays per second. Sounds great — you’re safer on the moon than in outer space.

But here’s the catch. If you’re on the moon, the moon ought to block half the cosmic rays coming from outer space! Even if you’re orbiting 50 kilometers above the moon, the moon should still block about 14 out of 33 cosmic rays, letting only 19 through. Because CRaTER is recording 22 per second, the remainder of the radiation (3 events per second) must be coming from the moon!

At this point, they can’t be sure why, but Kasper conjectured that this radiation is produced by cosmic rays that hit the surface, smash up an atomic nucleus, and re-radiate back into space.

What does this have to do with space suits? Well, your space suit contains lots of heavy atomic nuclei for the cosmic rays to smash into. So if you’re an astronaut, you’re going to be exposed to some radiation emanating from your space suit, for the same reason. That’s why Robinson asked his question.

Now really we don’t recommend future astronauts to do the full moon-ty. There are good reasons for wearing a space suit, such as the inconvenient fact that humans need air to breathe. However, Kasper did say that we should think carefully about what we make space suits out of. Are some materials better at absorbing cosmic rays than others? It’s also relevant for building shelters on the moon. “The results suggest that building a wall is a little more helpful than building an umbrella,” he said.

Actually, this comment was facetious too, because a flimsy umbrella isn’t going to help you much against cosmic rays. In an interview last week, Jack Burns of the University of Colorado, a science advisor for NASA, told me that one of the best defenses against cosmic rays is actually a tank of water. (That is one more reason why discovering water on the moon is important.)

Tags: AGU, cosmic rays, full monty, LRO, radiation, sun
Posted in Future exploration, Just for Fun, Meetings, NASA, Science | 1 Comment »

Moon (the Movie)

Wednesday, August 12th, 2009

 

So far I’ve stuck pretty much to science in this blog, but I have promised to write about the moon in our culture as well. I’ve been looking forward to seeing the movie Moon, starring Sam Rockwell, ever since I first read about it this spring. It has been out for two months now, and I managed to catch it at a local theater that had it for a one-week engagement.

I’m very glad that I had not read anything about the plot of the movie, so that during the movie I was as clueless about what was going on as the character(s) were. Kay, who had seen a review on TV, knew more about the basic premise. So she picked up on the clues faster but missed out on some of the surprise factor. Nevertheless, we both liked the movie.

I am very much a fan of science fiction that takes place in a future we could conceivably get to, unlike such franchises as Star Trek and Star Wars that completely bend reality to suit the purposes of the storyteller. Moon has a very gritty, realistic feel. The lunar base feels claustrophobic. The space suits are always grimy. Things are broken and don’t get fixed. A central plot point, involving exposure to radiation, is a real possibility on the moon and something that the designers of lunar bases will have to contend with. (One hopes that they will never contemplate the solution portrayed in this movie.)

There are a few small holes in the plot that don’t spoil the overall story too badly. For example, any astronauts who go to the moon will certainly know about the danger of radiation and not be taken by surprise, as they seemed to be in the movie. Also, the astronauts are supposed to be on the far side of the moon, but one of them drives what seems to be a short distance and then he can see Earth.

One extremely cool thing about the movie is the computer, Gerty. It is obviously an homage to HAL, the computer in 2001: A Space Odyssey. I read one review on IMDb (after seeing the movie) that complains about the similarity, but I think it is delightful how the director plays with that cultural reference. Anybody who has watched 2001 will have certain expectations about how Gerty is going to behave — and let me just say that you will be very surprised.

Some of the visual elements of the movie are wonderful. I would nominate this movie for an Oscar in the following categories:

  • Most Effective Use of Emoticons. A little bit reminiscent of the Jack-in-the-Box commercials, but much better!
  • Best Use of a Full-Earth Shot. You’d think that we would be jaded, after seeing the Earthrise photos from Apollo, but the director gives us one look at Earth from the moon and uses the image very, very wisely. I was especially shocked at how huge Earth was — and, of course, that’s to be expected. Earth from the moon would look quite a bit bigger than the moon from Earth.

It’s interesting that the director, Duncan Jones, is the son of rock singer David Bowie, who of course had his own SF-oriented phase (“Space Oddity,” “Ziggy Stardust and the Spiders from Mars” and all that). I admire Jones for not shying away from his famous dad’s legacy, and exploring some of the same issues in a way that is completely different from his father. Also, as you might expect from the son of a musician, the music in the movie is very effective.

According to IMDb, Moon ranks in the top 250 movies (of all time!) in user rankings, coming in at #242, just above Rocky (#243) and just below Roman Holiday (#241). It has an average user rating of 8.4 out of 10. So a lot of people liked it! It probably won’t be in movie theaters too much longer, but if you can’t find it in a theater, perhaps you can catch it when it comes out on DVD.

Tags: dystopia, earth, fathers, lunar base, radiation, science fiction
Posted in Just for Fun, Movies, Science | 4 Comments »

LRO First Picture!

Saturday, July 4th, 2009

Two days ago, on July 2, NASA released the first photograph from the new Lunar Reconnaissance Orbiter. And here it is! (Actually, this is just a small piece of it, but a very interesting piece, as I will explain below.)

LRO First Light

LRO First Light

The complete photograph is actually a very long strip, something like 500 by 50,000 pixels, taken near the edge of Mare Nubium in the moon’s southern hemisphere. The LRO website ways that the photo was taken near a crater called Hell … I’m not sure why. It doesn’t seem like the best place to start a mission!

If you want to find the location through a telescope or binoculars, it’s at about 30 degrees south latitude and 10 degrees west longitude. To the south is Tycho (one of the brightest craters on the moon), and to the north is an easily spotted trio of craters, Ptolemy, Alphonsus, and Arzachel. The best time for looking at this region was two days ago, when the picture was taken — and that is no accident. Photographers on Earth like to take pictures at sunset or sunrise, and so do lunar photographers! The lunar topography shows up most clearly near the “terminator” — the boundary between the day side and night side of the moon. The LRO spacecraft is currently in a terminator orbit, circling the moon from pole to pole and following the moon shadow around. This is the place to be if you want to take stunning photographs!

There are two very interesting things to notice in this picture. First, at the very bottom, you might notice a string of craters, like beads on a chain. Is this an accident? If not, how is a chain of craters like this formed? The answer is that they are “secondary craters” — craters formed by debris that is blasted off the moon’s surface by a meteorite impact. When the debris lands, it forms smaller craters all in a line. The first person to notice this phenomenon, I believe (perhaps some historians can correct me if I’m wrong) was Ralph Baldwin, an amateur astronomer in the 1940s. At the time, the conventional wisdom was that the moon’s craters were volcanoes. Baldwin put together many pieces of evidence, like this, to conclude that at least some of them were formed by impacts.  In this case, the amateur was right and the professionals were wrong.

Also, Baldwin noticed very large-scale linear patterns on the moon, which again seem to radiate outward from some of the great basin impacts. According to the LRO team, you can see some of the linear features in the photograph. I suspect that what they mean is the overall southwest-northeast orientation of the valleys in this photo. These furrows must have been scoured out by a vastly larger and earlier impact than the one that made the little chain of craters that I mentioned above.

As cool as the LRO pictures are, I want to mention that LRO is way, WAY more than just a camera. It has seven extremely cool instruments on it. I will list them below in no particular order of coolness. I will not translate the abbreviations into English — if you want to know what they stand for, check out the LRO website.

  1. LAMP. How cool is this? We are going to see the dark regions of the moon by starlight. The stars give off ultraviolet light, and the whole darned galaxy glows at one particular wavelength, and we can use this invisible (to human eyes) light to peer into craters that never see the sun.
  2. Diviner. We’re going to take the moon’s temperature. It’s not the same everywhere. Equatorial regions range from 150 degrees below zero (Celsius) to more than 100 degrees above zero (i.e., hotter than the boiling point of water).If you’re building a lunar base, that’s kind of tough to deal with. But near the poles, the temperature is much more even, although cold — roughly 100 to 120 degrees below zero.
  3. CRaTER. This one is interesting because it is specifically directed towards human habitation. How much radiation does the moon get from the sun and from outer space? The answer will tell us how long we can keep astronauts on the moon’s surface safely. Remember that the Apollo astronauts were there for only three days or less.
  4. LEND. Another instrument that will measure radiation — this time neutrons coming from inside the moon. This is kind of a repeat of the experiment that Lunar Prospector did to confirm the presence of hydrogen (and therefore maybe water) at the poles. An interesting point here is that it’s a Russian experiment flying on a NASA spacecraft — a nice example of international collaboration!
  5. LOLA. This laser altimeter will construct 3-D images of the moon’s surface.
  6. Mini-RF. A synthetic aperture radar that will search for ice at the lunar poles. This is similar to the Clementine experiment in 1994 that started all the excitement about water at the poles, but I assume it will be much better because it will have a lot more time to gather data and because it was designed for this purpose.
  7. LROC, the LRO camera, which by now needs no introduction.

I am by no means an expert in all of these technologies (or any of them), but I hope that over the coming months I will have a chance to interview some of the scientists involved with these projects, so that I can tell you how they work.

One thing that I find interesting about the web links is that almost all of them mention that they are “heritage” or “legacy” instruments — in other words, similar experiments have flown on other NASA missions, to Mars or to other planets. In our budget-conscious age, NASA wants equipment that is cheap and reliable. Still, one can’t help feeling a little bit nostalgic for the 1960s and the Apollo missions, when nothing was a legacy experiment — everything was being done for the first time!

Tags: craters, equator, ice, LRO, NASA, opinions, poles, radiation, technology, telescope, water
Posted in Missions, Science | 5 Comments »

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