Transcript of Webcast

Hello from the NASA Ames Research Center. This is Brian Day with th LCROSS mission. With me is Linda Conrad and coming in from the East Coast, we have famed space historian, author and educator Andy Chaikin, who is joining us today, and who, incidentally, has a new book out.

Today, we have a working webcast . This is with regards to our navigation challenge where you are coming up with how we’re going to get from the Earth to the Moon.

This is, again, a working webcast today where we’re going to work with you in refining your designs, getting ready for your final design submission. So a really good idea, if you’ve got some questions, please get them into our chat room early so that we make sure that we can get to you.

You’ve met Andy during the first webcast, and we’ve been really enjoying looking at your designs, we’ve got some very, very interesting ideas here.

Linda, can you tell us a bit about who has been joining in on this activity?

OK, we have special mention to 3 students from Esther Karpf home school. These are 7th and 8th graders and this is a picture of their great LGALROs I believe,

And we have the AFTF, Great NASA acronym type thing here. That what they do at NASA a lot! This is Allyn’s Full Throttle Fliers from Mrs. Purrells class.

Next, OK, her we have the SNMM crew, also from Mrs. Purrell’s class. I think this is the Solinshki Group, I’m not quite sure, but their SNMM stands for Solinski Nerdy Moon Missioners.

Charting a course to the moon: by PWS: Purrell’s Water-Seekers, a good title for the LCROSS challenge. These are also 6th grade science students.

Here’s an orbit drawn by our folks in Romania who I see are on line now – Ms. Stoica’s class. This is the 9th grade and I believe it’s an I class.

And here’s the F class, 9th grade from the National College of Computer Science in Bucharest.

7th graders from the same school with Ms. Stoica in Bucharest.

Here we have the 5th grade from Orleans Elementary.  Ms. Currier is their teacher and this is their orbit drawing.

And Julian did a nice descriptive text remarks – we have no picture to put up, but hopefully he’ll be drawing his orbits for the final web submission – Ms. Rogers class in Oregon.

Ms. Florio’s class has put together a nice power point, this one is by the 8th grade. Great!

Is that it? It must be! There’s one that came in after the wire, and it’s from Ms.  Jamison’s class, and it is online. I think everyone should take a look at everybody else’s designs – good for getting help with it.

And now we’ll get some comments from our experts. 

Do you want to start off Andy, or shall I?

I just want to say that I’m really impressed with all the teams and the work they’re putting into this and they’re really thinking things through. It’ll be neat to see what else they do as the challenge goes on. I will say though that I think that we have one misconception, which is that some of the teams are designing this as if there is going to be people aboard and, of course Brian, that’s not the way it’s going to work.

That’s very true. Right now with the LCROSS mission we’re starting out with a robotic mission. This is a robotic mission to the Moon that will pave the way for later missions that will be crewed by actual human beings, but we’re going to start out with robotics. Especially since the plan for LCROSS is to crash it into the moon – it would be highly unfortunate  if we did have people onboard.  

Yeah, I don’t think we’d get any volunteers for that one, so that means that, students, you do not , you should not include spacesuits, oxygen supply, radiation protection, rescue devices and so forth, because if there’s no people onboard, you don’t need those things.

You also don’t need a very large vehicle like the shuttle. You only need a vehicle that is powerful enough to launch LCROSS and LRO.

That’s an excellent point Andy. While the space shuttle itself is a nice vehicle because it is tried and tested and we always like to use things that are tried and tested, I would encourage you to take a look at:  What is the furthest that the space shuttle has ever been from the Earth? Has the space shuttle ever gone to the Moon? And if not, Why?

That may help you to determine if the space shuttle might not be an optimal choice.

Also, one thing I would like to bring up, is I’m very impressed with the fact that people are realizing that you start out with a pretty big launch vehicle, and as you make your way along your journey, we’re shedding parts. You know, you leave stages behind and that’s very, very good. That’s actually what we do!  

But give some real serious thought to how you dispose of those parts, fuel tanks, rocket boosters, whatever that you’re leaving behind. How are you going to get rid of them in a responsible way? Now blowing them up in space is certainly one of the more spectacular ways to get rid of it, but, please keep in mind that we have a lot of really important and very expensive satellites in orbit about the Earth up there. And, you may have read in the news recently, about how two satellite collided and there was a whole bunch of debris, and that debris is actually kind of dangerous to other satellites and people on the Space Station are keeping a big eye out for any of that debris.

So, one of the things we have to do when we have a space mission, is we have to look at any debris hazards we might cause, because even a little tiny gravel-sized piece of  material, if it hits a satellite that is going really, really fast, could cause a great deal of damage. So give a little more thought to how you’re going to dispose of those parts of your space vehicle that you don’t need anymore. 

I’m getting a message that I just want to get to our control room – I’m getting a message that our transcriber is not getting audio at this time. So maybe we can get that fixed up, but in the meantime we’ll go on here – Sorry to interrupt.

Again, one of the things I am very pleased to see is that a number of people are making use of some really great concepts here, looking at triangulation from large antennae here the Earth, looking at celestial navigation, looking at types of orbits we might use: I’ve seen mention of transit orbits, I’ve seen mentions of LGALRO: There are some people out there who are doing some real research, so I want to compliment you very much on the level of thought and work that is going in to these designs. It’s really very gratifying to see!

Linda, do we want to maybe take questions from our teams at this time do you think?

That’s really good. I do have four new questions this morning, and again I want to encourage those of you who are watching, to please get your questions into the chatroom so that we can get them taken care of  during the webcast.

I have, and I’m going to ask your pardon if I mispronounce it, but Kaiserslautern Middle School, I believe it is: Wants to know how many days with LCROSS Mission last before impact? I think this may have something to do hoping --I think they’re hoping to set up the design properly.

>> That's actually a very good question.

And I wish I had a very good answer for you.
But quite frankly there is q big question mark there.
Because we're designing a lot of flexibility into the mission.

So right now what we have going on is, even before we launch, we have some probes that a number of countries have put up around the Moon right now.

And they are scouting out the area. It's quite possible that they may find something really, really interesting.

So we want to make sure that we are able to time all -- we can tailor the mission by how many of these big orbits we make and it will help us determine just where on the Moon and when we're going to hit.

I just lost something.
>> I think we've just had a technical problem.
>> I think we're going out okay, yeah.
>> We lost Andy.

Fortunately we have a telephone backup so he'll be with us momentarily again.
So again, we're saying somewhere in the three to five month range.

>> Brian, I was going to say that you can sort of think of this in terms of how long does it take to make one orbit in that orbit and you have to have a complete multiple of orbits.

So if you know the number of days that it takes you to go around once, right?

You just -- you know, assume a certain number of those orbits and it gives you the total number of days.

>> Yeah, actually in addition to having a whole number of orbits, we can also do some solutions where we have a half number of orbits.

So it might be 3 1/2 orbit solution and there you would have the Moon 180 degrees, essentially, around the other side of its orbit around the Earth.

>> Yeah.

>> Okay.

Another one from Kaiserslautern Middle School Middle School.
The question is, how much frozen water do you need to survive for long periods of time on the Moon?

>> Well, we're actually going to get to that.

I don't want to tip our hand here because we're going to get to that in some upcoming challenge questions.0

>> Okay.

>> I'm going to kind of keep us mum on that subject.

>> Good to see you're thinking along the same lines that we are, though.

>> Yes, right.

Keep those thinking caps on.

>> Great, great.

Okay.

Do you think there are any life forms in the frozen water on the Moon?

>> Well, that's an interesting question.

The water in what we hope to find in those permanently shadowed craters, the original source of that water is from comets. And so what happened is that over billions of years in the early history of the solar system, comets hit the Moon and they contain ice as well as dust.

And so the question would be, if you had some living things, even if they were just bacteria in that ice, which by the way I think is probably most people would say is not very likely for something as small as a comet which has no internal heat source, but let's say by some chance you did have some bacteria, then this comet hits the Moon, okay, it goes splattering all over the surface, at which point all that ice is evaporates in the intense solar radiation of the Moon.

Those water molecules are then what bounce across the Moon in sort of a random fashion until they end up in these permanently shadowed craters.

So by the time that ice has reached the place where LCROSS is going to hit, it would have no hope of having anything alive in it because it would have been destroyed at the time of the impact and the immediate aftermath of it.

As we know, the Moon contains almost very, very minute amounts of water deep in its interior but no water anywhere near the surface.

>> Sometimes when we send spacecraft to other planets, we do special procedures to sterileize them because we might not want to take any of our microbes to say the surface of Mars and let's look at what we do to a spacecraft to sterilize it.

We submit it to extreme temperatures, really, really hot or really, really cold.

We can put it in a vacuum and do all kinds of things to do our best to make sure that we get rid of any kind of bacteria that might be on it.

And you know something?
Just those kinds of conditions are exactly what the Moon does naturally.
The Moon is probably an excellent way to sterilize any source of material.
So I think a lot of people would be really surprised to see any kind of life anywhere on the Moon.

>> Okay.

I'm going to do a follow-up on that one just because we're on the topic.

But if there's a life form on the Moon, What life forms do you think would be in the water?
Again if there were...
Would the life forms be helpful or harmful to the water supply?

>> Well, again, you would have to think about what kind of life form could possibly survive on the Moon.

And you basically need three things to have life. You need water in liquid form, you need organic material and you need a source of energy. And so again, on the surface of the Moon liquid water--

>> Oh oh. We lost Andy.

>> It's also exposed to deadly radiation from the Sun and the other stars on the surface. So nothing can survive on the surface of the Moon. The only hope for there to be any kind of life on the Moon would be under the ground. If there were some sort of underground spring or aquifer on the Moon you might have a hope of life existing there.

Now, we think that's the case for Mars but nobody thinks that that's true for the Moon.

>> And I think some of the emphasis here on the water on the Moon is, don't place too much emphasis on just thinking of the water being there for drinking. Long before anyone takes a drink of that water, that water is going to be very, very, very carefully analyzed.

But some of the things we will be able to use that water for is in a building material, mixing it with lunar soil to make Moon concrete.

Think of using it to make fuel.

Using it to make oxygen.

So -- yeah, the water, well before anyone drinks it, is going to be very carefully analyzed and purified.

It is not just bacteria that we would be worried about.

We also want to look at -- think that this ice is going to be mixed in with the lunar soil.

And so there are things that we want to look at in terms of possible chemical contaminants that would be in the water.

So well before we consume any of this water, we're going to be looking at it very carefully.

Think of the other uses we put that water to.

>> Okay.

Back to the challenge here.

ANDRA asks what happens if a solar storm takes place while the spacecraft is on its way to the Moon?

>> Hopefully it won't knock out the electronics on the spacecraft.

>> That's a very good point and it makes a big difference, much more of a difference for the -- for a mission with human beings on it than a robotic mission, fortunately.

Our spacecraft can go into what's called safe mode.

If something happens, if there is a big blast of radiation that might cause the electronics to reset, and in that case it will just kind of shut down in a very graceful manner and wait for us to essentially press a reset button here on Earth.

>> Okay.

We have a couple questions from Ms. Courier's class.

How long do you think it will take to find out if there is water on the Moon?

>> Well, if it's there in the spot where LCROSS impacts it will just be a matter of minutes, I think, right, Brian?

>> Yes, if we uncover ice we could have an idea very, very quickly.
But let's keep in mind that if -- when LCROSS hits we don't see any water ice, does that necessarily mean there is no water ice anywhere on the Moon?

No.

It means there is no water ice where we have looked.

Now, fortunately we have some really smart people who are targeting what they think are the really most likely places for water ice to be.

But I've heard some of our chief scientists talking about the nature of water ice on the Moon, if it's there.

And they talk about it in terms of peanut butter.

Is the peanut butter smooth or chunky?

So do we have a nice, smooth distribution of water ice in the soil or maybe is it chunks here and there?

We don't know.

So we're starting to find out now.

This is a mission that is going to just begin our exploration of the Moon all over again.

>> I'll put my money on chunky.

>> Very good.

>> Okay.

Another question from Sylviana.

She says do we have to submit with our final design a drawing of the spacecraft and the rocket propulsion with it?

>> The more you can add the better.

I think wherever your research takes you and whatever you're working with in the classroom, that's great! What you're doing is learning and that's the real point.

>> And also I would say, you know, just speaking from the standpoint of us who are going to be looking at your proposals, you can get an idea --

>> You might be able to get an idea across better with a drawing and a few words to accompany a drawing.

If that's the case, by all means do a drawing.

>> I can talk right now a little bit about the proposal processes here.

And when you are proposing a space mission, as thorough and as detailed as you can be, the better.

>> Great.

Okay.

This is one I'm glad I don't have to answer.

I will leave it to you folks.

Also from Syviana.

Is the trajectory of the spacecraft concave or convex in relation to the imaginary line uniting the Moon and the Earth?

In parentheses, the major axis of the ellipse which the trajectory of the spacecraft is a part.

>> You just answered your own question, I would say, right, Brian?

>> So let's think about this.

Part of the mission design here is you coming up with a course. And you coming up with a path for here to the Moon.

And, you know, there is some basic geometry involved, but take a look at some of the images from, say, the Apollo missions, and they are taking a very different path to the Moon than LCROSS is because they want to do something very different.

But there are some differences in those shapes.

But once again, the fact that you're using an ellipse is a really good clue, but please keep in mind you're telling us the nature of the path you're going to take and how you're going to navigate that.

>> All right.

Another question from Miss Courier's class.

How fast do you normally go to get to the Moon?

>> Well, if you look in the -- I don't think we should give them that answer but I think that's probably -- number one, it's something they can easily find out by doing a little research.
And number two, if I'm not mistaken, that information is in the exploration nav challenge information.

>> But you could do a back of the envelope calculation.

You can get on the web and look at how long it has taken missions to get from the Earth to the Moon.

Look at the Apollo missions, look at Lunar Prospector, look at Surveyor, look at Clementine and so knowing how long it took to go from the Earth to the Moon for them and knowing how far the Moon is from the Earth, you should be able to make a calculation.

>> That will give you an average speed.

But, of course, your speed is changing moment to moment because you are climbing up the side of a hill -- so to speak. It is not literally a physical hill.

It is a good way of thinking about flying to the Moon is to think of the spacecraft climbing up a hill of the Earth's gravitational pull and that hill, you know, as we say in the nav challenge information is steeper the closer you get to the Earth and flatter the farther you are away.

So when you start your flight to the Moon, you are going the fastest that you'll be going.
And you're also being pulled back the most that you'll be pulled back.
Your speed is decreasing at the highest rate, the closer you are to the Earth.
As you get farther away yes, you're slowing down but your speed is changing less rapidly as well.
So it's a little bit complicated.

You kind of have to -- the way I think about it is you know those games where you have a -- like a steel ball and a spring, and the spring is at the bottom of a puddle and you have to pull back hard enough on that spring that when you release it the ball will coast up the side of the funnel.

That's exactly what is going on here.

You can think of the spring in this case as the rocket firing that gets you out of Earth's orbit and sends you on to the upper path to the Moon.

Once you shut down that engine you're basically coasting.

And so you've got to know how much force you need, how much speed you need to make it all the way to the Moon.

>> Okay.

Speaking of which, I want people at home to be -- at school to still be entering their questions into the chatroom.

But I think this is a good time, speaking of the proper speed and angle and all that good stuff, to introduce a little problem.

Andy.

>> That's right, Linda, we have a little extra twist that--

>> Oh, oh

>> Can you hear me okay?

I must be having trouble with my software.

We have a little twist that we would like to introduce to the problem.

And this twist is sort of an emergency situation that we are going to give to the students to let them sort of get a sense of what it's like to be on a real space mission where problems come up all the time.

So the name of this problem is called off course.

Let me read this information to you and you follow along.

Here is the setup.

You are the navigation officer on the LCROSS Mission Control team.

You have just received new tracking data that says that the spacecraft is off course and will miss its target crater by 10 kilometers.

The spacecraft is currently ten hours away from its impact on the Moon and there is a final opportunity to perform a correction maneuver two hours from now.

If the spacecraft weighs 7,275 pounds, then here is the question.

How long must be fire the on board thrusters to get back on target and save the mission.

Everybody got that?

All right.

So now let's look at some additional concepts and information that you need to know to solve that problem.

One of the key concepts as the great English scientist stated moving objects have a property that causes them to continue moving until -- unless acted on by a force.

Same property causes an object at rest if no force acts upon it.

That is called inertia.

Let's go to the next slide.

Another important thing to keep in mind on Earth, one of the forces acting on a moving object to slow it down is friction.

Yet in the vacuum of space there is no friction.

It is as if everything were moving on a perfectly smooth three dimensional ice skating rink.

So if you fire the spacecraft's thruster even for a brief moment it will cause an increase or decrease in the spacecraft's velocity that will remain in effect indefinitely until the spacecraft is acted upon by another force.

Therefore, one way to counteract a burst from a thruster in one direction is to fire a burst in the opposite direction.

And I think we have one last slide, right?

Now, you'll need to know this.

LCROSS has two on board thrusters that are used for trajectory correction maneuvers.

Each produces five pounds of thrust.

Both thrusters always fire together.

So to change L-cross's end.on the Moon you must fire its thrusters in a direction parallel to the direction you want to shift the aim point.

Let's look at a picture that represents this situation.

So on the left you see a kind of blowup of the target area.

And the red X represents the place where LCROSS is currently going to hit if you do nothing.

And notice that it is 10 kilometers away from the green X, which is inside the permanently shadowed crater and is the spot where you want to hit.

So you need to fire the thrusters to a setting point 10 kilometers over the amount of time between the time you fire the thrusters and the time you impact the Moon.

And on the right you see a representation of the spacecraft firing its thrusters in a direction parallel to the direction you want to shift the aim toward.

So you can review this information.

This information will be available to you, and this is how we want you to attack this problem.

We have a video to show you that will get across this concept of inertia, so if we can roll that video.

This is a video -- a computer graphic showing the Apollo mission and this is the spacecraft separating from its booster getting ready to go to the Moon.

Look at those panels that we're throwing away.

Once they get separated they're spinning.

They have no ability to control their own path so they keep going the way they were originally going.

The spacecraft, on the other hand, has its own little thrusters.

You can't see the flame from those thrusters but it can control its path and it turns around and docks with the lander.

Meanwhile, the panels, which have no thrusters on them, continue to spin and continue to move away with the same velocity, the same direction that they had when the force of separation was applied to them.

So this illustrates in a way the concepts that we're trying to get you to understand about inertia and about the lack of friction and this idea that you're moving on essentially a three dimensional skating rink like you were an ice skater but in three dimensions.

So Linda and Brian, do you have anything to add to that?

>> The only thing I would add is in case there are teachers out there that are panicking because of testing and spring break and all the rest of that, this is an optional glitch that we're throwing your way and however, I want you to rest assured that the additional information we now have up on the web, or will have within the hour, will be very helpful.

It will help you temper this to the age of your students, and Brian, if you could hold that up we've put up a document by itself taking care of this, ten pages, and also added it to the educator guide so it's part of the new educator guide that's online now.

>> Again, this is an optional activity if you have gotten to a point where you feel you're comfortable with the design that you've come up with for getting to the Moon and you want to go deeper into the subject, this is a way for you to do so.

It's a very, very interesting exercise and it is the kind of thing that the spacecraft operators here at NASA actually have to think about.

So you're assuming a very realistic role here.

>> Great.

Okay.

We'll go ahead and handle some more questions especially if they have to do with this new glitch.

I have one here from Andra.

What if the spacecraft on its way to a a Moon hits a meteorite or another celestial body.

>> That would be unfortunate.

And again, because a meteor in the sky, that object can be moving somewhere even in the vicinity of 60,000 miles-an-hour.

If something even very small hits your spacecraft at that speed, that can present a real problem.

Now, fortunately space really is mostly empty.

And so we really haven't had much of a problem that way.

But there are certain times of year and there are certain times when basically we pass through the orbital paths of comets that have left a lot of debris behind and there have been some instances where you really start thinking about what do you want to do in terms of the timing of a mission?

And those times of year when we might be passing through a cloud of debris.

And see, would you like to elaborate on this?

>> Well, it just brings to mind every summer here in Vermont we like to go outside in August, around August 10 and 11 to see one meteor shower.

Those are actually -- those are particles of dust that are shed by I believe it's comet temple, I can never remember.

We know the comet that that dust comes from.

And when we look up at the sky during a meteor shower, we see a beautiful display of meteors going across the sky.

But those meteors, as Brian says, are moving at many thousands of miles an hour and even though they're very small, something that is moving that fast can punch right through the spacecraft.

So that would be bad.

And so, you know, it's something to worry about, for sure.

That's the only kind of celestial object we're really in danger of hitting.

We know that, for example, we're really not likely to hit anything bigger than a grain of sand.

But even in something the size of a grain of sand could do tremendous damage.

>> Now that applies to the majority of our flight.

But with LCROSS, remember the very end of its mission it is going to be flying down through a plume of debris that was created when the big centaur upper stage hits the surface of the Moon.

So there is some question as to whether or not the LCROSS spacecraft itself will continue transmitting all of the way down to the surface of the Moon or if it might get damaged as it descends through that plume of debris.

We feel very confident that it will make it through enough of that plume of debris to give us the scientific data that we need.

But keep in mind, we're going to be flying through this cloud of material that we have created ourselves near the surface of the Moon.

>> Okay, great.

I have to comment, however, Andy, I'm really impressed how you bop out and handle the phone and mute the right things while you're talking, reconnect with us.

It's really very impressive.

>> Do I get extra points for that?

>> Absolutely.

>> All right.

>> We have a question here from Ms. couriers' class.

What's the best type of fuel for a rocket.

?

>> That depends on what you're trying to accomplish.

Let's take liquid fuel versus solid fuel, okay?

So there is a big difference between those two.

If you look at the space shuttle, for example, the shuttle itself, the shuttle orbiter has three liquid fuel rocket engines which help it get into orbit.

It has liquid fuel rocket engines inside.

Back at the launch are two enormous solid fuels.

Literally the fuel is inside.

The big difference between liquid fuel and solid fuel rocket you can turn a liquid fuel rocket on and off as you like.

A solid fuel rocket is on and it will stay on until it runs out of fuel.

So those big solid rocket boosters that are attached to the shuttle burn for 2 1/2 minutes and then they fall away.

You couldn't turn them off even if you wanted to.

So I guess the question is, what are you trying to accomplish?

There are some situations where you don't care if you can turn the rocket off before it runs out of fuel and other situations where you really do care.

Now, let's say you decide that you want a rocket that you can turn on and off.

Then the question is, how much force do you need from that rocket?

And there are some combinations of fuels that are more effective than others.

But there are also some fuels that are easier to handle than others.

And so you have to look at all these factors.

The shuttle and the centaur, for example, both use a combination of liquid hydrogen as the fuel and liquid oxygen as the oxygen because there is no oxygen in space, you have to carry along your own oxygen and get the fuel to burn and so liquid oxygen and liquid hydrogen are a tried and true very reliable combination.

Other rockets, the thing about liquid hydrogen and oxygen is they have to be kept very cold.

And so you can't store them forever.

You have to have them in kind of a thermos bottle on board the vehicle.

Eventually that is impossible to keep cold.

But there are other fouls that can exist at room temperature.

Those are call hypergolic fuels that ignite on contact so these are all factors to consider when you're -- You can tell it gets kind of complicated.

>> Absolutely.

Okay.

I -- we have a very appropriate question here.

We're getting near the end here so I want to pick the most poignant questions.

This one is very interesting.

What if due to the weather conditions the launch of the spacecraft is delayed?

Funny thing about that.

Do we need to include a plan B for this eventual situation?

>> Very good.

Excellent, excellent question.

And this gets into the whole concept of what we call launch windows.

So times of opportunity when you will launch from the Earth and that timing is right to get you to your planned destination.

It's not kind of like just getting in your car and you can leave any time you want.

Okay?

So what we do is we look specifically at oftentimes a block of days.

So we can have the launch pad for some number of days and then what time on each of those days would be the appropriate time for you to be able to launch.

And it's basically a question of geometry.

When is the geometry going to be right for your launch from that pad to get to the place that you need to go.

And you ask a very relevant question, because I have seen this happen time and time again down there.

Sometimes if we're launching from Florida, one thing Florida does have a lot of is thunderstorms.

And you don't get to launch your mission through a thunderstorm.

But even on days that are perfectly clear, I've gone out and said look at this, we couldn't have asked for a better day.

There is not a cloud in the sky.

It's gorgeous.

And the conditions right there on the ground are wonderful.

But then someone will say hey, there are some really fast upper level winds at 60,000 feet.

The winds are blowing really, really strong.

And that can be enough for launch control to say no, we're not going up today.

Then you have to start looking at the next days in your launch block and say okay, so what time on each of these following days do things line up so we would launch.

>> Let's get real personal here.

Ms. courier's asked when is the LCROSS mission scheduled to launch?

>> Well, we currently have a scheduled launch date of may 21st.

However, there -- we're not the only spacecraft that is scheduled to use that launch pad.

Right now there is another spacecraft sitting on the launch pad and it has met up with some challenges and they have some technical difficulties that they're working through.

And as a result, its launch has been delayed.

It was supposed to launch at the end of March, and here we are now at the beginning of April.

And so right now you have people trying to figure out just what is that going to mean for the launch of lunar LCROSS.

We're still trying to figure that out.

We will have a much better idea when we see this next -- this earlier spacecraft called WGS2, when it actually launches and clears the pad, then we'll have a much better idea of what our schedule is going to look like.

Right now we're just not sure how this may or may not impact our actual launch day.

>> Okay, great.

I have one last question we're going to handle here from Rebecca.

And she asks, how will the crater that is impacted be selected?

>> That is an outstanding question.

And there are several things that will go into this calculation.

First of all, as we mentioned, we have spacecraft right now orbiting the Moon, that are looking at the potential impact craters.

Also, something that enters into the calculation is when exactly we launch.

And how long we decide to fly.

Keep in mind that the Moon tilts back and forth so sometimes during its orbit its north pole is tilted toward us and sometimes its south pole is more tilted toward us.

And we would prefer to impact on a pole that is tilted toward us rather than away from us because that gives us a better view.

But one of the prime considerations is going to be looking at the information that comes from the spacecraft we have in orbit now and keep in mind LRO is going to get to the Moon well before LCROSS does its impact.

So we'll get a lot of good data that will help our scientists decide of the possible target craters at the lunar poles, which ones do we really want to zero in on.

>> Okay, great.

Thank you very much, students, for your excellent questions.

And thank you, Andy and Brian, for your answers.

I'm going to go ahead and let you start to wrap up, Brian, with some reminders.

>> Okay.

So please make sure that you get us your final designs and if you decide you want to include our added twist, please get them in to us.

We'll post them online in the order that we receive them.

Those that we receive by the deadline will be reviewed during the final webcast.

So you'll be able to see your review online.

Please make sure that you also submit a drawing or image or map of your navigation route.

Remember, this is more of a navigation challenge than a spacecraft design challenge.

So we really want to see how you're going to be plotting that course to the Moon.

The problem situation that Andy presented today is -- will be available online.

So please go online and take a look at that.

It is a really fun and interesting problem.

Your final plans and answers are due to us on April 27th.

That's our deadline.

And keep that in mind.

We're going to get back to that.

That's an important date.

Join us for the webcast, our final culminating webcast, on may 7th.

You'll receive feedback on your design and we'll get some final announcements.

The weekly questions will resume next week on April 6th.

Get ready for that.

Keep an eye on our event calendar for weekly challenge questions and more information as it happens.

We'll also post any updates with regard to the LCROSS mission.

We'll make sure you're kept up to date as to what's happening.

Now, one of the things that we've decided to do is to add a little bit of motivation for you to submit your final challenge design.

And so what we're going to do is we're going to have a drawing at the end of this challenge.

Any team that submits a final design will be entered into a raffle.

What we'll raffle.

Greg, can you show us what it is we'll be raffling off?

A small piece of rock.

Wow, isn't that exciting?

Actually, it is.

It's a very thin slice -- it's a small piece.

It is definitely less than an inch across.

This is not the actual one we'll be be raffling off but it is something similar.

This is a piece of actually a meteorite.

But this is a very, very special meteorite.

This is actually a piece of the Moon that got blasted off the surface of the Moon by one of those big crater-forming impacts and this piece of the Moon flew through space and Labor Dayed -- landed here on Earth.

Basically as a reward for participating in this challenge your classroom will get the chance to have your very own small piece of the Moon.

I have to tell you, I think that's pretty cool.

So remember, get your final designs in to us by April 27th.

We look forward to seeing them.

>> I do want to add that for the raffle one of the teasers is that we do need the teachers to do the post-challenge survey as well.

The drawing will be after that.

We'll announce it on the web and let you know.

Andy, thank you for joining us.

You have some parting words?

>> I just want to say good luck to everybody and we'll look forward to seeing what you come up.

>> I have a quick question for Andy.

Andy, can you tell us the name of any new books that people should be looking for?

>> Why, yes, Brian.

>> Shameless.

>> If you go to my website andrewchaikin.com, that has information on my books but I have a book on Mars exploration that came out last fall called "a passion for Mars" and I have two books coming out in May about Apollo, the Apollo missions to the Moon, one is for young readers called "Mission Control, this is Apollo."

The other is called "voices from the Moon" that contains descriptions by the astronauts what it was like to go to the Moon.

I hope you get a chance to see those.

>> Great.

>> Well, thank you very much.

Andy, thank you, Linda, thank you, Greg in our studio and thank all of you for participating in our navigation challenge.

We look forward to seeing your designs.