Telescopes Planned for Far Side of the Moon Preliminary plans are underway for an array of new radio telescopes that would cover an area of up to two square km. The Lunar Array for Radio Cosmology (LARC) is planned as an array of hundreds of telescope modules designed to pick up very-low-frequency radio emissions.
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Telescopes Planned for Far Side of the Moon

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Telescopes Planned for Far Side of the Moon

Telescopes Planned for Far Side of the Moon

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JOE PALCA, host:

This is TALK OF THE NATION: SCIENCE FRIDAY from NPR News. I'm Joe Palca sitting in for Ira Flatow.

Later in the hour, we'll be talking about using math to restore old recordings and mapping genetic diversity. But first, NASA said this week that it's interested in putting telescopes on the moon. To see if such a plan is really feasible, the space agency picked a team of scientists to come up with a detailed plan. Basically, the idea is to set up an array of radio telescopes on the far side of the moon, away from interfering radio waves coming from Earth. Such a vantage point would be a good place to study the early universe - the time after the Big Bang, but before stars and planets.

Joining me now to talk about the Lunar Array for Radio Cosmology, as the project is known, is Jackie Hewitt. She's a professor of physics and the director of the MIT Kavli Institute for Astrophysics and Space Research at the Massachusetts Institute of Technology in Cambridge.

Welcome to the program, Dr. Hewitt.

Dr. JACKIE HEWITT (Professor of Physics; Director, MIT Kavli Institute for Astrophysics and Space Research): Thank you very much, Joe. I'm glad to be here.

PALCA: Well, it's good to have you. And then, I'd like to invite our listeners to join the discussion if they wish. Our number is 800-989-8255, that's 800-989-TALK. You can also find us on "Second Life" on the SCIENCE FRIDAY Island. And if you want to know more about what we're talking about this hour, you can go to our Web site at, where you'll find links to our topic.

So, I mean, is this practical? I mean, you know, we don't have anything on the moon, but we have some - our hardware we sent up a long time ago. But this is pretty ambitious. Are you - is this just fun to participate in or do you really think you'll be around to watch it constructed?

Dr. HEWITT: Well, to tell you the truth, I think it's one of the science opportunities that actually make a lot of sense to do from the moon, and so we should try to do it if we can. And I don't think it's impossible or I wouldn't be spending the next year or two of my life studying this. But it definitely is something we have to work out. There are a lot of engineering challenges and it's also going to be quite expensive if you want to do something like this. And that's exactly what the study is for - it's to figure out if it really makes sense to do this.

PALCA: So what are - I mean, engineering challenges - I mean, apart from actually getting there, is there - and getting stuff up there, what are the things that you're most concerned about?

Dr. HEWITT: Well, the first thing you worry about - well, it's just the total mass. Okay? Because we want to put about two square kilometers of collecting area of the antennas on the moon, that's a lot. But you can actually sit down and work out, you know, how thick a wire is, how the mass of the metal you like to make it out of the area you need. And it actually comes out to, you know, just that kind of calculation that the total mass is less than what NASA is planning for the capability of the launch vehicles to the moon. So that's good, we passed that test.

And if you work out the power requirements, those are also quite high, and that's something that's actually quite uncertain at this time. We're going to have to work out, you know, what the requirements actually are and find out from NASA what the plans are for power in the moon and whether solar rays could handle it, that sort of thing. And if we use solar rays, the sun only shines two weeks, and then it doesn't shine for two weeks, we have to store the energy. So there are all these considerations.

And, finally, I think it's going to be difficult to land the antennas on the moon. There's no atmosphere - you can't use parachutes, you can't use air braking. So that, you know, how much energy it will take to slow things down enough so they can land on the moon without breaking apart. That's another consideration.

But it'll be, you know, very interesting to work these things out, and we'll see what the answer is in a couple of years.

PALCA: Would you need - I mean, I suppose - I mean, would it be necessary to build really big telescopes or can you take advantage of the fact that the noise is smaller to build smaller telescopes?

Dr. HEWITT: Well, we've actually done - worked that out. And that was part of our proposal to NASA. We figured out all - there's the total collecting area that you need.

PALCA: Right.

Dr. HEWITT: And you can make it out of big telescopes or small telescopes. And at that point, you - it becomes an optimization problem and, you know, it tends to cost a lot more to make a big telescope per square meter of area.

PALCA: Right.

Dr. HEWITT: So it turns out there's an optimum size which comes out to be about 10 meters on the side - roughly.

PALCA: Uh-huh. So that's 30 feet on the side.

Dr. HEWITT: Right. Exactly. And then we need several thousand of those - I mean, many of those to actually make up the collecting area.

PALCA: Right. Right. So they become - the size becomes a virtual giant thing by linking them together electronically.

Dr. HEWITT: Exactly. And what we'd like to do, actually, we think if we try to lay, you know, many miles of cable on the moon that that's not going to be practical. So we actually think we like to connect them by laser. Have them send the data back and forth using laser beams. So it, actually, should work very well on the moon.

PALCA: Right.

Dr. HEWITT: And, you know, details need to be worked out, but that's the basic idea.

PALCA: Right. Because you don't lose signal over long distances quite as much, I guess.

Dr. HEWITT: That's right.

PALCA: All right. Interesting. And what - okay. So why - you know, I - we've implicitly stated that there's advantages to working on the far side of the moon. Could you be explicit about what some of the advantages are?

Dr. HEWITT: Yes, definitely. And we've thought about this quite a lot because we're trying to do this from the ground right now. We're - actually a group of us at MIT and some Australian universities and Harvard - we're actually building one of these arrays in Australia, in Western Australia. And the reason we're going to Western Australia is because we're trying to get away from things - radios, TV. The radio frequencies where we need to do this measurement are down in the radio and TV band, and so we can't do this anywhere in the United States. There are just too many radio shows like this one that get in the way.

PALCA: Right.


PALCA: But I'm sure that, you know, it would be much more interesting to listen to this show than discover life on another planet or something like that.

Dr. HEWITT: Well, I know. But…

PALCA: Okay. Now…

Dr. HEWITT: Okay. So we went to Western Australia, but we still get some interference there and we actually would like to push even down to lower frequencies where the interference gets even worse. And we actually don't think it'll work to do the, you know, the real low frequency measurements in Australia. And the other thing is the atmosphere. The Earth is surrounded by a blanket of charged particles - the ionosphere - and that really interferes with radio propagation. So the radio waves that come from, you know, the very early universe, come to us all scrambled because they have to go through the Earth's ionosphere.

So you want to get above the Earth's ionosphere; so somewhere in space. And we want to get away from the Earth's interference and so by going in the far side of the moon where we're shadowed from the Earth's interference, it was a good place for that. And also, it turns out, we believe that it's useful to have the platform of the moon, the surface of the moon to lay all these antennas down rather than having them swarming around in orbit, and eventually crashing into each other - that sort of thing. And so for those three reasons, we really would like to be on the far side of the moon.

PALCA: All right. Well, I'm for it. I do think it's - as you say, a technological hurdle. But let's hear what some of our listeners have to say about this.

Dr. HEWITT: Sure.

PALCA: And go to Audrey(ph) in Fort Myers, Florida. Audrey, welcome to SCIENCE FRIDAY.

AUDREY (Caller): Hi. Thanks for having me.

PALCA: Sure.

AUDREY: I'm so glad you guys are discussing this topic.

PALCA: Uh-huh.

AUDREY: I'm in an online astronomy class right now. And I actually have a paper due Monday…

(Soundbite of laughter)

AUDREY: …on this Big Bang theory and how we are using radio waves to discover more information about Earth.

PALCA: Right. And so…

AUDREY: And my question was, is this - if they can land this on the moon, will this give scientists into the first few milliseconds of the Big Bang? Is that the goal?

Dr. HEWITT: Well, actually, a couple of goals. The first measurement, which is a little bit easier than what you just described, is actually look how the first galaxies formed, and that happens much later in the history of the universe, okay, about 500 million years after the Big Bang. So that's one thing. But then if we even push down, go to lower frequencies, you know - and that's why the moon was really important to get to those lower frequencies - we can look at the very details of how the initial matter distribution was set up in the Big Bang, in the period of inflation, right? I don't know if you study about inflation, but there's a period right after the Big Bang where we believe the universe expanded very quickly. And also, the initial fluctuations and the density were set out. And we - if things go well, we should be able to measure that and really understand the basic physics of that very early time of the universe that you're interested in. So, yes, that is one of the goals of this…

PALCA: Excellent. Excellent. Let's hear from another caller now. And how about if we go to Michael(ph) in Mokelmne, California maybe.

MICHAEL (Caller): Hi.

PALCA: Did I get it right?

MICHAEL: Yeah - close. It's Mokelmne Hill Township.

PALCA: Oh, okay.

MICHAEL: And 774 souls.

PALCA: All right. Well, you're one. Go ahead.

MICHAEL: Yeah. I mean, how are they going to deal with the moon dust? It's everywhere, and it's sticky.

PALCA: Yeah.

Dr. HEWITT: Hey, for us it's not a problem. If you're trying to build a big optical telescope, the last thing you want is dust coating your lenses, right?


Dr. HEWITT: Radio waves won't affect us. So that's actually, you know, aside from the reasons we want to do this for the science, it's also one of the instruments which are much more feasible to be built on the moon than others because of things like this. It doesn't really matter exactly where we place the antennas, we can just lay them out approximately, they'll work okay. And similarly, if there's a layer - if dust gets on the instrument, it won't significantly affect the performance. So we're actually not worried about that. We don't plan on having any moving parts.

These antennas won't tilt to point. It's an array like a radar array - what we're planning. So it's just a lot of antennas on the ground, and you point them by actually steering them electronically. So there's no mechanical steering. So don't have to worry about dust getting into the gears or anything like that. So, like I said, we're not worried about dust.

PALCA: Well, you got enough other things to worry about. I'm glad the dust is not one of them. Let's take one more quick call and go to Andrew(ph) in Alexandria, Virginia. Andrew, welcome to the program.

ANDREW (Caller): Hi. I'm wondering why 30-by-30 feet is the optimal size for these antennas. I mean, why wouldn't you use hundreds of much smaller antennas that would be autonomous and could be corralled once they get to the site.

Dr. HEWITT: That's a very good question. And we've actually - that's something we're studying very carefully. But the problem when you go to too small, okay, is you have to attach a receiver and a little laser communicator on each one of those elements, okay? And so that costs money. And so while a large aperture costs a lot to build, small apertures cost a lot to instrument, to get all those receivers and lasers on. And furthermore, it turns out when you want to process the signals to produce the measurements you want, the computation load goes as a square of the number of the elements. That really is - makes you not want to built a lot of small ones.

And so you balance those two things, and there's an optimum antenna size which depends on the cost of these lasers, you know, and that's exactly what the study will do, is figure out exactly what that size is. So we think it's something around tens of meters.

PALCA: So politics aside, I mean, let's say somebody decides they do want to do this, do you have a date where you're just hoping to get this thing up?

Dr. HEWITT: Actually, we - you know, we need to have a target date for some of our planning. And so we've picked the number, the year 2025, that's when we're going to build it if all goes well.

PALCA: 2025, okay. Well, Jackie Hewitt, I throw down this challenge. In 2025, I want you to come back on this program and tell us how it went, okay?

Dr. HEWITT: All right. I'll be glad to.

PALCA: All right. Well, thanks very much for taking the time to describe this project to us. Sounds fascinating.

Dr. HEWITT: Sure. Thank you.

PALCA: Jackie Hewitt is professor of physics and director at the MIT Kavli Institute for Astrophysics and Space Research at the Massachusetts Institute of Technology in Cambridge, Massachusetts. And when we come back, we're going to talk about the Grammy Awards. SCIENCE FRIDAY goes to Grammys, you can't miss that. Stay with us.

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