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star girl
2003-Nov-14, 02:07 AM
Last assignment in science for this trimester. Who better to turn to than the Bad Astronomers themselves? So, I have to plan a mission to go to a planet/moon.

BACKGROUND:
1)where I am going. Already know this one, Europa.
2)whyI chose this place . Because..... why not?
3)already know. I know it is a moon of Jupiter, covered in ice, and possibly life.
4)problems with sending a mission there. A little help here please.
5)mission purpose. To see if there is life there.


OBJECTIVES:
1)type of mission. Robotic, landing on moon
2)what data to collect. water/ice
3)target site/ specific area of moon. help!
4)equipment. I'm thinking of a large ball that lands and opens up, lowers a drill, drills to water, collects water, comes up, and sends pictures/other info to Earth.
5)images/maps. O.K. I can do this part. I'm not that helpless


I would love any suggestions and/or ideas. THANKS!!!!!! :D

ToSeek
2003-Nov-14, 02:18 AM
The two main problems that occur to me are:

1. Getting there. You've got to get a probe from the Earth to Jupiter, and then slow it down enough for it to survive the landing.
2. Surviving the radiation environment.

This site (http://irsps.sci.unich.it/research/projects/icy_satellites/eu_mission/europa_mission.html) has some stuff about an Europa mission.

If you google on "Europa mission" and ignore the links referring to Galileo, it appears that there are more such sites.

kenneth rodman
2003-Nov-14, 12:03 PM
Getting there. You've got to get a probe from the Earth to Jupiter, and then slow it down enough for it to survive the landing.


well we know we can get one there we have done so already. Perhaps we could use the gravitational force of jupiter to slow down the probe.

eburacum45
2003-Nov-14, 12:47 PM
The Venus flyby trajectory saves a lot of fuel; however the mission shown in To Seek's link starts on 13/6/08 and arrives at Jupiter 24/11/11.
So your ship will be on route more than three years on this flightplan (note the fly-by of Earth; this will happen at a fairly large velocity).

Some of the experiments you might want to pack on board;
you will have to google them and choose which

Hi res Panoramic/stereoscopic cameras with multiple filter options
Near-and Thermal-infrared imager
laser altimeter
Gamma ray spectrometer
Microscopic imager
Ice abrasion tool
APXS alpha particle X-ray spectrometer
imaging spectrometer/spectrographs for UV, visual, IR, and thermal IR
mass spectrometer
gas chromatograph
Descent Accelerometer
Impact Accelerometer
magnetometer, coils and electrodes for electromagnetic sounding
gravitometer
Seismic probes and penetrators/seismic net


And you want to include a drill as well? Perhaps this drill should be left for the second mission, after the seismic probes have determined the thickness of the ice.

Tau
2003-Nov-14, 02:03 PM
The ice crust is definitely a major concern here. We should consider if it even necessary to drill all the way through to the liquid ocean, since at least some lifeforms (if there are any) may be present in the ice as well.

Luckily, we already have efficient and compact drill technology thanks to the level of refinement needed in studies of Antarctic ice.
You will likely use the Antarctic cryobot (http://robotics.jpl.nasa.gov/~behar/JPLAntIceProbe.html) as some sort of template for this Europan explorer.

ToSeek
2003-Nov-14, 03:11 PM
Getting there. You've got to get a probe from the Earth to Jupiter, and then slow it down enough for it to survive the landing.


well we know we can get one there we have done so already. Perhaps we could use the gravitational force of jupiter to slow down the probe.

It's doable, but it's not easy. Galileo needed three gravity assists (one from Venus and two from Earth) in order to get flung out to Jupiter, and even then it wasn't trying to land anywhere at the other end.

Jack Higgins
2003-Nov-14, 04:56 PM
It's doable, but it's not easy. Galileo needed three gravity assists (one from Venus and two from Earth) in order to get flung out to Jupiter, and even then it wasn't trying to land anywhere at the other end.
Why not use a JIMO- style propulsion system? Lots more thrust for amount of fuel, and no gravity assists needed. Also has much more power for science instruments!

daver
2003-Nov-14, 05:45 PM
The straight-line mission (blast off from Earth, direct insertion into Earth-Jupiter Hohmann, decelerate into Europa orbit) requires about 3.2 km/sec more delta V than a launch into GTO to put it into the Hohmann transfer, and 5.5 km/sec to brake into a low Europa orbit. You might be able to save a bit of fuel by using Jupiter's atmosphere to aerobrake, but that's a pretty dicey maneuver (if you go too deep you crash and burn, if you're too shallow you don't lose enough velocity to remain in the system. Aerobraking also implies a relatively compact craft (no high gain antenna until after the maneuver, no RTGs or instruments out on booms).

You might be able to do something funky with close flybys of the other moons to reduce the Europa insertion problem. I'm too lazy to write a program to do these calculations.

The Earth/Jupiter insertion burn could be done by a high energy propellant like LH2/LO2. This implies a mass ratio of about 2.2. The Europa burn probably needs to be done with storable propellants, which brings the overall mass ratio up to about 15.

Ariane 5 can throw perhaps 10 tons into GTO, so if you use the Ariane you're talking a final probe mass of perhaps 600 kg.

Oops, i see you want a lander. Again assuming an Ariane launch, that puts your lander mass at perhaps 300 kg.

I'd be tempted to launch two missions, one a Europa orbiter and radio relay, the other the actual lander. The relay could possibly do some radar maps of Europa while it's there. So, you launch it, wait 33 months until it takes up orbit around Europa to get the maps, wait another 6 months for a suitable alignment, and launch your lander. Wait 33 months for it to enter the system and touch down on Europa.

Problems. Weight. Delta V (I'm assuming UDMH/NTO; i think most probes now are launched with MMH as a monopropellant. Higher energy storable propellants would help immensely). Communications. Power. Radiation environment. Autonomous landing.

I don't believe Europa has enough of an atmosphere to be useful as an aerobrake, and your probe is going to have to shed an awful lot of speed before it sets down; i imagined the lander as boring in directly (aim directly for Europa, impact speed about 6.5 km/sec, fire your engines at the last minute). I don't know if the bouncy ball or landing legs would be best--for such a light probe air bags might have an edge.

space cadet
2003-Nov-14, 07:17 PM
As Star Girl's older sister, I feel compelled to point out that this is just a ninth grade science project. She's not trying to write her college thesis or anything, and she has never taken a physics class. Anyway, I told her that she might be able to find help on the BA boards, but I think this might be a little bit over her head.

Do you think you could simplify a little?

ToSeek
2003-Nov-14, 07:23 PM
Another website: Europa geology (http://www.psrd.hawaii.edu/Feb01/EuropaGeology.html)

I'd vote for landing on the banded terrain while avoiding the chaotic terrain.

Nineplanets page for Europa (http://seds.lpl.arizona.edu/nineplanets/nineplanets/europa.html)

Edit: just reread your initial post about drilling through the ice. In that case, you want to land somewhere the ice is thin. Perhaps you have an orbiter with radar first that can figure that out, then the lander is targetted to a suitable site afterwards.

daver
2003-Nov-14, 08:54 PM
As Star Girl's older sister, I feel compelled to point out that this is just a ninth grade science project. She's not trying to write her college thesis or anything, and she has never taken a physics class. Anyway, I told her that she might be able to find help on the BA boards, but I think this might be a little bit over her head.

Do you think you could simplify a little?

Well, the conclusions still stand, even if you leave out the math (the math wasn't accurate enough for more than ballpark estimates anyway). Weight is a definite problem--it takes a lot of fuel to land on Europa. You can deal with the weight problem in a few ways--you can launch on the biggest rocket available, you can be tricky in your choice of orbits (gravity assists on the way there, gravity assists off of other moons once you get there), you can use high energy fuels, and you can limit the weight of your probe. One way to limit the probe weight is to have multiple probes--an orbiter that does data relay and a lander that gathers the really useful stuff.

Jupiter's radiation environment is intense. This problem has been more or less solved, but it will contribute to the probe's mass.

Power will almost certainly be from RTG's--there's not enough sunlight for solar cells to be useful. The problem with RTG's is that they don't produce all that much power--your power budget is going to be nearly as tight as your weight budget.

Communications is mainly a solved problem. High gain antennae with as much power behind it as you can get. If you have a relay satellite in orbit the lander doesn't need anywhere near as strong of a transmitter. The relay satellite can also be used for other, later landers.

The lander is going to barrel right in to Europa. I don't know if you've played lunar lander or its variants, but the cheapest way to land on a moon is to wait until the last possible moment to light your engine and then burn as hard as you can. The communications lag with earth means that the landing will have to be performed by the probe with no help from earth. This means that it's going to have to be reasonably intelligent about finding its landing spot and homing in on it.

Another problem is going to be deciding what NOT to put on your probes. Your weight budget is very limited, and everyone is going to want to put their pet instrument on board.

mike alexander
2003-Nov-14, 09:26 PM
My son's a 9th grader, too. so...

Without getting into the awesome comments earlier, how about some kind of more or less passive melter probe? A container with a heat source (radiothermal generator?) that could roll out of a bouncer/lander and then start to slowly melt its way in. Put on a couple of spectrometers (ultraviolet, infrared, for example) to look at the melted water as it flows by. Easy, pretty rugged tests for organic materials dissolved in the water.

cyswxman
2003-Nov-14, 10:01 PM
Just a little technicality here, but does it have to be a manned (or "womaned" if you will) mission.

daver
2003-Nov-14, 10:14 PM
Just a little technicality here, but does it have to be a manned (or "womaned" if you will) mission.
Umm, i hope not. We're a long ways from the technology required for that.

dgavin
2003-Nov-14, 11:29 PM
Actually since DS1 gravity assist's are not needed for probes, even ones that land.

For the probes main engine use a Solar Eectric Ion drive similar to the used on the Deep Space 1 Probe. Nasa is currently testing a sooped up version of that drive, that can achieve 4 times the speed of DS1.

Ion drives have a very slow acceleration curve, about the equivelent thrust of the weight peice of paper resting on someone's hand in gravity. The Ions move at 10% the speed of light though so with continuous use it's the fastest engine possible. Using both Gavitational Sling Shots and the Ion drive could possibly reduce trip times to a year and a half. Acceleerate half the time, and decelerate the other half of the time.

Four the landing of it carry a small amount of chemical fuel with it's own engine that will be used for the final deceleration for landing. (Similar to how the Moon Lander did it).

The real issue is not so much in getting there, but is in not contaminating Europa with earth based bactiria on a probe. Because of the suspected subice-terraign ocean, even -one- bactiria from earth could change Europa's entire suspected Eco-system, or start a Eco-system where none was before. That's where the real challange is, is how to -completely- decontaminate the probe.

And if you try for a return sample it gets doubly difficult, as you also can't contaminate the Earth with any Europa based Bactiria's.

This is the delemia thats been facing and delaying a Europa mission at NASA for years.

ToSeek
2003-Nov-15, 01:40 AM
This is the delemia thats been facing and delaying a Europa mission at NASA for years.

I don't think that's the only thing or even the primary thing. Doing an Europa lander under current budget constraints is really tough, even before you start considering the biocontamination issues.

star girl
2003-Nov-16, 06:13 AM
Thanks guys. That is really helpful.

:wink:

daver
2003-Nov-16, 08:28 AM
Actually since DS1 gravity assist's are not needed for probes, even ones that land.

For the probes main engine use a Solar Eectric Ion drive similar to the used on the Deep Space 1 Probe. Nasa is currently testing a sooped up version of that drive, that can achieve 4 times the speed of DS1.

Do you have any stats on that one?



Ion drives have a very slow acceleration curve, about the equivelent thrust of the weight peice of paper resting on someone's hand in gravity. The Ions move at 10% the speed of light though so with continuous use it's the fastest engine possible. Using both Gavitational Sling Shots and the Ion drive could possibly reduce trip times to a year and a half. Acceleerate half the time, and decelerate the other half of the time.

That's off by a few orders of magnitude. The Isp of the DS1 ion engine is 3100--that puts its exhaust velocity at about 31 km/sec--0.01% c. Maybe you got your 10 from 10x the Isp of chemical propellants.



Four the landing of it carry a small amount of chemical fuel with it's own engine that will be used for the final deceleration for landing. (Similar to how the Moon Lander did it).

The real issue is not so much in getting there, but is in not contaminating Europa with earth based bactiria on a probe. Because of the suspected subice-terraign ocean, even -one- bactiria from earth could change Europa's entire suspected Eco-system, or start a Eco-system where none was before. That's where the real challange is, is how to -completely- decontaminate the probe.

And if you try for a return sample it gets doubly difficult, as you also can't contaminate the Earth with any Europa based Bactiria's.

This is the delemia thats been facing and delaying a Europa mission at NASA for years.
That might be part of it, but i think the cost and the low performance of chemical rockets might also have something to do with it.

daver
2003-Nov-16, 09:09 AM
I thought I'd work out some stats on an ion mission as well. DS1 has been quoted as an example--DS1's ion engine has an Isp of 3100 secs, a power consumption of 2.5 kW, and a thrust of 92 mN. The ion engine masses about 8 kg.

I'm going to assume for now a 10 ton launch mass for the probe. I think you're going to need around 40x the thrust of the DS1 ion engine, which will need on the order of 100 kW of electricity. Because it's hard to gather that much solar energy (particularly at Jupiter) I'm going to assume a nuclear reactor. You might scope out how much a solar electric array capable of delivering that much power would weigh. I don't know how much a nuclear reactor of that output would weigh either, I'm guessing about 1 ton. Your probe can't accelerate as efficiently as a chemical rocket can (there's a line about this in Robert Heinlein's juvenile "The Rolling Stones"--i didn't understand what he meant until a long time later); anyway, i figure your ion engine, because it has such low thrust, will need to provide a bit over 20 km/sec delta V (if you don't understand what that is, never mind. I'm trying to show enough of my work that people can point out my mistakes). Anyway, i figure the probe will have to be just about half fuel--5 tons. That leaves 4 tons for payload (compare that to 600 kg for the chemical mission).

I don't know how to figure the trip time; i'm guessing around four years.

This trip takes longer than the chemical trip (blame the low-thrust ion engines and the heavy reactor), but not appreciably longer. The probe you get at the far end is MUCH more capable. For one thing, it has a 100 kW electric power supply--that's more power than any probe that I know of, i expect it's more than the shuttle is capable of delivering, and probably more than ISS will ever be capable of generating. It's certainly more than Magellan used during its radar mapping of Venus.

You have enough leftover mass (4 tons) to include both a lander and an orbiter. Your lander will be about half fuel; if your total lander mass was 1 ton, you'd have about 500 kg left for instruments once it got on the ground (your lander wouldn't have the luxury of its own nuclear reactor--it'd probably have to rely on RTGs (although maybe you could figure out some way the orbiter could beam it power via microwaves).

The reactor causes some additional problems. Firstly, there's the political problem of launching a reactor into space. This can be ameliorated (where's that dictionary when i need it) slightly by saying that you won't start up the reactor until the probe has achieved more than escape velocity. Secondly, a nuclear reactor is likely to disrupt some of your more sensitive instruments. You can put the reactor out on a boom, and put your fuel between your reactor and some of your instruments. Jupiter's a pretty nasty environment anyway, so maybe it's not that big a deal.