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Hale_Bopp
2002-Feb-08, 02:23 AM
Guess he wants to wait another 200 years or so to go.

http://www.astronomy.com/Content/Dynamic/Articles/000/000/000/746tljzz.asp

Here's hoping Congress has more sense than shrub.

Rob

Simon
2002-Feb-08, 04:11 PM
Well, it does mention that instead they're developing a nuclear-electric drive that might get to Pluto faster, without the Jupiter gravity-assist.

Still seems like a dumb way to do things. Send one in 2004, or spend a bunch of time and money to develop new technology so you might send one later.

The Bad Astronomer
2002-Feb-08, 05:18 PM
The Division of Planetary Sciences, a division of the American Astronomical Society, has weighed in, asking Congress to support the new budget, though they are unhappy with the New Horizons program being cancelled. Here is their statement I just received.





Contact:
Dr. Wesley T. Huntress, Jr.
DPS Chair
202-478-8910
huntress@gl.ciw.edu

DPS Comments on the proposed FY2003 budget for NASA

The Administration released its proposed FY2003 budget for NASA today.
This is the first budget developed by the Bush Administration and the
new NASA Administrator, Mr. Sean O'Keefe. The Division of Planetary
Science (DPS) of the American Astronomical Society commends the support
this budget provides for planetary exploration, which includes a new
initiative for nuclear power and propulsion, and a second new initiative
for a "New Frontier" line of competitively procured planetary space
flight missions. Funding has been increased in real dollars for
Research and Analysis programs, which provide a fundamental knowledge
base allowing for the design of focused, efficient missions.

The Administration gave high ratings to the Discovery program of
low-cost planetary missions and as a result has introduced a new line of
moderately priced missions modeled on the Discovery program. The "New
Frontier" missions would be about twice the cost of Discovery missions.
The budget proposal would provide for about one Frontier mission every
three years, bringing a new level of flight opportunity to the science
community with competitively procured missions of higher capability.

The DPS is concerned about the cancellation of the outer planets
program, which included the New Horizons mission to Pluto and the Europa
Orbiter. The cost-capped New Horizons mission was recently selected
after an open competition in which scientists and their industry
partners spent millions of dollars and months of time in good faith
response to a NASA call for proposals. This precedent discourages
community participation in NASA's efforts to produce cost-effective
missions through competition. Whether New Horizons may be resurrected in
the New Frontier program will depend on its ultimate prioritization in
the Planetary Decadal Survey.

The surprise in this budget is the proposal to revive development of
nuclear technology for in-space propulsion and power. Development of
this technology was terminated in the 1970s and planetary exploration
has been limited ever since to long, complex flight missions using
conventional propulsion and to spacecraft barely capable of powering a
single light bulb. Nuclear propulsion will increase accessibility of
Solar System objects and decrease the flight time for some missions.
On-board nuclear power will provide a power-rich environment for science
investigations at the planets and increase the lifetime of these systems
to years instead of a few weeks or months.

The planetary Research and Analysis program was given a 3% increase
above inflation, and a new program was funded at $10M to develop
planetary instruments for biological investigations on other planets.
Mars exploration will continue as planned through this decade, but the
large rover planned for 2007 is delayed until 2009 in order to
substitute nuclear for solar power and increase its lifetime from months
to years. A fully competed Discovery-class Mars Scout mission will be
flown in 2007.

The DPS calls upon Congress to support the President's proposed FY03
NASA budget. It builds on the strengths and successes of our planetary
program. New nuclear technology for both power and propulsion will
extend our reach and capabilities to the outermost regions of our Solar
System while increasing our capabilities in the inner Solar System.
The "New Frontier" program offers exciting opportunities, including
restoration of missions to the outer solar system.

The DPS is the world's largest professional organization dedicated to
the exploration of the Solar System.

Azpod
2002-Feb-10, 09:05 PM
Ok, as much as it annoys me to ditch the Pluto/Kupier Belt Express, I can understand balking at the cost for the mission, given how much science we can expect from it. Simply put, we could theoretically fund several smaller missions and get more science, but leave the extreme outer solar system for more advanced probes decades down the road.

But the Europa Orbiter?! Europa is as important, if not more important of a destination as Mars is! While we may land people on Mars someday and thus want to explore it as a possible site for our first permanent off-world colony, Europa has an excellent chance of proving once and for all if we are truly alone in the universe. If we go there and find extraterrestrial life (which is not unlikely), and if that life is different enough to prove that it and the life on Earth developed independantly (i.e. no interplanetary cross-seeding), then we have great evidence that we will likely find life commonplace throughout the universe.

That significant of a find would seriously affect how we construct experiments for decades to come. We could look for chemical signitures that are common between life on Earth and life on Europa. If they find that Europa is in fact a sterile world, then it would beg the question: why? The answer to that question would save us billions of US dollars on science missions, because we know what to look for, or what not to look for.

In short, it is irresponsible not to go to Europa, first with an orbiter to map the surface and ice depth as well as doing detailed analysis of the surface and its scant atmosphere. Then use that data to send a lander to either take surface samples or (preferred) punch through the ice somehow and see what's down there.

I understand the need to cut the fat at NASA and to get the most amount of science data that we can for our money, but killing something like the Europa Orbiter is not the way to do it!

lpetrich
2002-Feb-11, 05:01 AM
Although I agree that it was a bad idea to cancel the Pluto-Kuiper Express and the Europa Orbiter, I don't agree with some of Azpod's claims.

He seems to think that if Europa is lifeless, then the rest of the Universe is therefore lifeless. An idea which reminds me of something curious in the introduction to Sagan and Shklovskii's Intelligent Life in the Universe -- there used to be in Alma Ata, Kazakhstan an Institute of Astrobotany, some of whose members claimed that Dialectical Materialism, the official Soviet philosophy, implies that there is life on every planet -- strongly implying that there being no life on Mars or Jupiter would falsify DM. S&S noted that an agonized official rebuttal soon appeared, arguing that Mars or Jupiter being lifeless would not falsify DM.

Furthermore, there is the whole question of where to look. One reasonably expects Europan life to require liquid water, but liquid water there will be at least a few kilometers beneath its visible surface, which is ice that is at a temperature of 110 K.

Furthermore, surviving in the darkness underneath the ice will require some chemical disequilibrium, and that will require living near some hydrothermal vents (hot springs). Which will, of course, be at the bottom of that ocean.

Europa's ocean depth, like its crustal thickness, is unknown, but it could be a few hundred km.

Thus, one would need to sink a mineshaft through its crust, and then send a submarine down further. However, Europa's surface gravity is 0.14 (1/7) that of Earth, meaning that pressures will not rise as fast as they do on Earth. The pressure at the bottom of Earth's oceans will be reached at 35 km on Europa.

As an example of the amount of material that will have to be sent to Europa, I will consider something simple: equipping a tunnel through Europa's crust with cables for supplying electricity and providing communications. Imagine that they have a density of 1 g/cm^3 (about right for insulator; low for metals) and a total cross section of 1 cm^2 (optimistically low, judging from cables I'm acquainted with). As a result, 1 meter of cable weights 100 g, 1 km of cable weighs 100 kg, and 10 km (possible Europan crust thickness) of cable weighs 1 metric ton. And that is with optimistic assumptions.

I'll try to estimate how much rocket will be needed to send the necessary combination of mining equipment and submarines to Europa. I will use the Cassini spacecraft as a reference; it did a flyby of Jupiter, but it will go into orbit around Saturn.

Cassini was launched with a Titan 4B (http://www.astronautix.com/lvs/titan4b.htm) rocket, which has a total mass of 943 metric tons.

Cassini itself (http://www.jpl.nasa.gov/missions/current/cassini.html) has a total mass of 5.7 metric tons, of which 3.1 metric tons are propellant. This leaves a dry weight of 2.6 metric tons, which is less than 1/360 the mass of its booster rocket.

So one ought to either have a lot of Titan-4B equivalents available or a manufacture-from-asteroids capability. The cabling alone would require nearly one Titan 4B to lift from the Earth.


<font size=-1>[ This Message was edited by: lpetrich on 2002-02-11 08:06 ]</font>

ToSeek
2002-Feb-11, 02:21 PM
I'd love to see a Europa mission as well, but it's liable to be the toughest unmanned mission NASA has ever done. In addition to the severe radiation problems, the delta-v (change in velocity) required to get a spacecraft into orbit (or to land) on Europa is unprecedented. I wouldn't be surprised if it takes them a number of years to figure out how to do it.

ToSeek
2002-Feb-11, 02:56 PM
Still hope for Pluto mission? (http://www.spacedaily.com/news/outerplanets-02a.html)

lpetrich
2002-Feb-11, 03:55 PM
The velocities necessary are not difficult to compute; I searched with Google for "Europa orbital velocity" and similar parameters.

Europa has an escape velocity of 2.02 km/s, a little less than that of the Earth's Moon.

Europa's average orbital velocity is 14 km/s, yielding an orbital escape velocity of 20 km/s. Thus, an incoming spacecraft going from zero velocity at infinity will be traveling at least 6 km/s relative to Europa when it arrives; the best case is for Europa being at the orbit's periapsis.

However, the spacecraft will have a nonzero velocity "at infinity" relative to Jupiter on account of its traveling there. The best case for a relative arrival velocity comes from a Hohmann Transfer Orbit, which has its periapsis at Earth and its apoapsis at Jupiter. This works out to be v_J*(1 - sqrt(2*a_E/(a_E+a_J)))

and with Jupiter's orbit velocity being 13 km/s and its orbit being 5.203 times bigger than Earth's, the best-case approach velocity becomes 6 km/s. However, that requires a departure velocity from Earth of 8.8 km/s, which is 14.2 km/s lifting off from the Earth's surface (the combined velocity here is sqrt(escape_velocity^2 + long-distance_velocity^2) -- the Earth's escape velocity is 11.2 km/s).

Shaving off a few km/s to save rocket fuel means a much slower departure velocity from the Earth, meaning that it's necessary to do flybys of Venus and Earth to gain velocity for traveling to Jupiter. But that's a side issue.

A Hohmann Transfer Orbit means a travel time of 2.7 (Earth) years; with a faster velocity at Earth, one will arrive sooner.

Applying the same sqrt(sum of squares) rule for arrival at Jupiter, one gets a little over 20 km/s at Europa's orbit unless the arrival velocity is more than 20 km/s, which is unlikely; using an arrival velocity of 6 km/s yields 21 km/s at Europa's orbit (10 km/s yields 22 km/s at that orbit)..

If the orbit's periapsis is at Europa's orbit, then the Europa-relative velocity becomes around 8 km/s, which is a formidable challenge.

A hydrogen-oxygen rocket can achieve an exhaust velocity of 4 km/s; however, neither hydrogen nor oxygen are easily storable at Earth orbit. Checking out fuels with higher boiling points, we find kerosene/oxygen is 3 km/s, UDMH/N2O4 is 3 km/s (that's unsymmetrical dimethylhydrazine / nitrogen tetroxide),decomposing hydrazine is 2.25 km/s, etc.

Using the standard rocket equation: v = v_exhaust*log(full_mass/empty_mass) and referring to 8 km/s, we find full/empty ratios of 7 for hydrogen/oxygen, 14 for kerosene/oxygen and UDMH/N2O4, and 35 for hydrazine. So if you want to land a 1-ton spacecraft on Europa, you'll need 6 tons of hydrogen/oxygen, 13 tons of kerosene/oxygen or UDMH/N2O4, or 34 tons of hydrazine!

An alternate way of landing is to do a hard landing -- to crash into Europa. But not many spacecraft are designed to survive impacts of 8 km/s into ice; the Ranger missions of the 1960's, which got closeups by crashing into the Moon, were essentially kamikaze missions.

However, there are some crash-landing missions in the works.

The Deep Impact (http://deepimpact.jpl.nasa.gov) mission will feature an impact onto a comet, but the impactor is not expected to survive its impact velocity of 10 km/s. This is not stated explicitly, but the site's pages have nothing on what the impactor will do after the impact.

And the Ice Pick (http://klx.com/europa/) committee is exploring missions to Europa, though it does not have anything definite at this point, such as how Europa will be landed on. The page's text suggests a penetrator, but that's about all.

lpetrich
2002-Feb-11, 05:43 PM
Sorry if that last message seemed long-winded, but I think that it's a useful exercise in spacecraft-mission planning. If you wish to have a career sending spacecraft to elsewhere in the Solar System, you'll end up doing something like what I had done.

Now for the ionizing radiation from Jupiter's magnetosphere. Here's a good page on outer-space radiation exposures (http://zimmer.csufresno.edu/~fringwal/w08a.jup.txt).

The Jovian satellites have these exposures:

Callisto: 0.01 rem/day
Ganymede: 8 rem/day
Europa: 540 rem/day
Io: 3600 rem/day
Inner satellites: 18,000 rem/day


Earth's sea-level dose is 0.14 rems/day; 3-6 rems/day causes noticeable radiation poisoning, and a quick dose of 500 rems is lethal.

So human missions to Europa are unlikely in the near future; however, the radiation hardening necessary for surviving a big solar flare (2000 rems/hr) will be sufficient for an automated Europa mission.

Another Phobos
2002-Feb-11, 08:31 PM
No mission to Europa because finding life elsewhere in the universe would seriously crimp Bush's conservative Christian world-view and political agendas.

Oops! Did I say that?!?

lpetrich
2002-Feb-12, 12:53 AM
It is certainly true that some Fundies think that the Earth is the only inhabited planet; some dislike speculation about extraterrestrials and some even consider UFO's to be demonic phenomena rather than extraterrestrial spaceships.

However, I don't think that that seedling of a President has the intellectual capacity to think much about stuff like that.

I think that a more plausible hypothesis is that there isn't a big lobby behind it; having such lobbies keeps lots of dubious things going.

AstroMike
2002-Feb-12, 02:06 AM
Human exploration to Europa seems highly unlikely, but Ganymede and Callisto could be possible. Based on your data lpetrich, Ganymede and Callisto is far enough from the major radiation belts. However, if the spacecraft is travelling at 40,000 km/h, it would still take about 2 years to get there, which means virtually no chance of avoiding a major solar event.

_________________
"The contemplation of celestial things will make man both speak and think more sublimely and magnificently when he descends to human affairs." -Marcus Cicero

<font size=-1>[ This Message was edited by: AstroMike on 2002-02-11 21:46 ]</font>

Another Phobos
2002-Feb-13, 07:56 PM
Why would we even consider a human mission to Europa at this stage when a robotic mission could do so much...and much cheaper?

Maybe in a couple hundered years...

Bob S.
2002-Feb-13, 07:58 PM
Thus, one would need to sink a mineshaft through its crust, and then send a submarine down further.
:
I'll try to estimate how much rocket will be needed to send the necessary combination of mining equipment and submarines to Europa.

Another idea, if you wanted to send an unmanned probe (I'm pretty sure this is not an original idea, but I can't remember where I heard it), don't drill through the ice, melt through it.

You would have a probe in 2 parts. 1 would be the relay becon with dish. The second part would be your probe, heated by some radio-isotope (which could also drive a thermovoltaic generator) to heat it, melting the ice beneath and slowly sinking down. It could unravel a cable connected to the relay dish to send back readings. The cable would become buried in the ice as the water re-froze. It doesn't even have to be that heavy, just thick enough for a simple signal (how thick of copper wire would you need for a signal to transmit over 20 miles?). Once the probe melted through the bottom of the ice, the wire may act as a tether to keep it from getting swept away by currents. The probe would then suck up however much water it needs to run its tests. Admitted you may not be able to swim around searching for geothermal vents unless you had an exceptionally long wire. But you could still do a lot with this simpler probe that is a bit more feasable.

Chief Engineer Scott
2002-Feb-15, 11:23 AM
There was a BBC programme recently (may have been one of the Horizon series, but unfortunately I can't confirm that) which suggested that a robotic probe with an independant heat source could be used to melt through the Europan ice mantle, this device could leave tranmission relays at the top and bottom of the "shaft", then proceed on a completely independant mission, within the "line of sight" limits imposed by the location of the transmitter. This would seem to be much more "weight" effective than running a tethered probe.

Bob S.
2002-Feb-15, 07:35 PM
...a robotic probe with an independant heat source could be used to melt through the Europan ice mantle, this device could leave tranmission relays at the top and bottom of the "shaft",...This would seem to be much more "weight" effective than running a tethered probe.

Not bad. So it would ultimately come down to an engineering problem. Which is less weight: a spool of 20 to 40 km long insulated transmission cable, or a relay with a power source and transmitter strong enough to broadcast through 20 to 40 km's of ice (since the shaft would re-freeze).
The more I think about it, the more the latter does sound more feasable since a solitary probe wouldn't know how thick the ice is at any random landing point so you wouldn't know how much cable to send (unless you sent precursor probes with geologic sounding equipment).

Hale_Bopp
2002-Feb-15, 07:56 PM
Okay, since we are talking about melting our way through several miles of ice, does anyone know what the farthest down we have managed to get in the Anarctic ice sheet? I don't think it compares to Europa, but if we can't get down at least a few thousand feet there, we shouldn't start planning the Europa dig too soon.

Any Antarctic experts out there to answer that one?

Rob

Kaptain K
2002-Feb-15, 08:58 PM
Project AMANDA (Antarctic Muon And Neutrino Detector Array) went 2 kilometers (1.2 miles) into the ice.
See here:
http://amanda.berkeley.edu/amanda/amanda.html

Espritch
2002-Feb-15, 11:06 PM
I don't know much about the technical side of probing Europa, but I have an idea of how to get funding. Just tell President Bush that there's oil there. /phpBB/images/smiles/icon_smile.gif

Phobos
2002-Feb-16, 01:37 AM
I wonder if we could use more extreme measure to "punch" through the ice. If a large solar object (asteroid ?) were defected at distance, would it not be possible that such an object impacting on Europa could do the work for us ?

Perhaps such an extreme solution has been considered and found to be totally impractical, but I can't help wondering if it could be made to work.

There would still be enormous technical issues to resolve, but the idea of a deflected body being followed at some "appropriate" distance by a hardened spacecraft still fires my imagination.

Jeff

<font size=-1>[ This Message was edited by: Phobos on 2002-02-15 20:38 ]</font>

johnwitts
2002-Feb-16, 01:52 AM
And if there is life there, do you think they'd appreciate us dropping a small moon into their ocean? We'd run the risk of destroying the very life we were trying to find.

Simon
2002-Feb-16, 01:03 PM
Not to mention that it would probably be pretty dangerous to land a spacecraft in the kind of crater that would cause. Probably wouldn't look good to get your probe creamed by an iceberg or stuck in re-freezing ice.

Phobos
2002-Feb-16, 05:15 PM
On 2002-02-15 20:52, johnwitts wrote:
And if there is life there, do you think they'd appreciate us dropping a small moon into their ocean? We'd run the risk of destroying the very life we were trying to find.


A casual observation of the surface of Europa will show that the moon has not only received numerous small hits, but that it is still receiving impacts.

What I had in mind was not exceeding the type of impacts that the moon is already subjected to. The question remains would it be possible to make a window of possibilty for a following spacecraft to take advantage of.

Needless to say I understand the reasoning behind the critisism of the concept, I was just curious as to if it could be done.

As to the impact on the life that we intend studying, provided that our impact was no different than those that are already taking place then I would have thought there would be no problem there.

What I believe may be more of a problem, is if we find that the impacts which are happening now are not sufficient to break through to the believed liquid sub-surface. That being the case then obviously there would be no point in further discussing the possible merits of this proposal.

Jeff

Phobos
2002-Feb-16, 05:22 PM
On 2002-02-16 08:03, Simon wrote:
Not to mention that it would probably be pretty dangerous to land a spacecraft in the kind of crater that would cause. Probably wouldn't look good to get your probe creamed by an iceberg or stuck in re-freezing ice.


What I had in mind was timing the arrival of the spacecraft which follows the meteor/asteroid so that rather than trying to land on a frozen surface, it struck a liquid surface. Given the temperatures involved we would expect any exposed surface to rapidly start to refreeze, but the possiblilty still seems present.

Phobos

NottyImp
2002-Feb-20, 11:48 AM
OK, maybe I'm being dumb, but if you melt your way down trailing a cable, won't the column of water just freeze above you locking the cale in place, and thus preventing the probe going much deeper than about a few metres?

Kaptain K
2002-Feb-20, 05:20 PM
The cable is spooled out from the probe, so the limit equals the length of cable carried on the probe.

_________________
When all is said and done - sit down and shut up!

<font size=-1>[ This Message was edited by: Kaptain K on 2002-02-20 12:23 ]</font>

Ilya
2002-Feb-20, 06:51 PM
lpetrich:



If the orbit's periapsis is at Europa's orbit, then the Europa-relative velocity becomes around 8 km/s, which is a formidable challenge.

A hydrogen-oxygen rocket can achieve an exhaust velocity of 4 km/s; however, neither hydrogen nor oxygen are easily storable at Earth orbit. Checking out fuels with higher boiling points, we find kerosene/oxygen is 3 km/s, UDMH/N2O4 is 3 km/s (that's unsymmetrical dimethylhydrazine / nitrogen tetroxide),decomposing hydrazine is 2.25 km/s, etc.

Using the standard rocket equation: v = v_exhaust*log(full_mass/empty_mass) and referring to 8 km/s, we find full/empty ratios of 7 for hydrogen/oxygen, 14 for kerosene/oxygen and UDMH/N2O4, and 35 for hydrazine. So if you want to land a 1-ton spacecraft on Europa, you'll need 6 tons of hydrogen/oxygen, 13 tons of kerosene/oxygen or UDMH/N2O4, or 34 tons of hydrazine!


Your calculations are correct, as far as I can tell, but no one proposes a direct Earth-to-Europa mission. Every orbiter or lander plan involves a Jupiter orbit insertion with Io (or Europa) gravity assist, followed by many moon flybys to lower the probe's apojove and eventually to match orbits with Europa. Fuel requirements for such mission are much lower than the ones you listed, yet still greater than Galileo's. Galileo had one big burn - to enter Jupiter's orbit (1.4 km/sec IIARC). Europa probe will have two - JOI and Europa orbit insertion (or landing). Barely within engineering ability, but possible.

The tradeoff is that mission-total radiation exposure becomes enormous. BEYOND current engineering ability.

ToSeek
2002-Oct-10, 07:46 PM
House subcommittee approves Pluto mission (http://spacedaily.com/news/outerplanets-02m.html)

We're getting there!

Jim
2002-Oct-11, 12:24 PM
Good news! Here's a little more info, including a petition you can sign:

http://www.planetary.org/html/UPDATES/Pluto/pluto_europa_action.html

Meanwhile, Congressman Nick Lampson has introduced the Space Exploration Act of 2002, which sets some pretty sweeping but definitive goals for NASA... and provides the funding to meet them.

The "Space Exploration Act of 2002" requires the NASA Administrator to set the following goals for the future activities of NASA's human spaceflight program by the development and flight demonstration of reusable space vehicles capable of carrying humans from low earth orbit . . .

*to the L 1 and L 2 Earth-Sun libration points and back, to the Earth-Moon libration points and back, and to lunar orbit and back within 8 years;

*to and from an Earth-orbit crossing asteroid and rendezvousing with it within 10 years;

*to the surface of the Moon and back, as well as the deployment of a human-tended habitation and research facility on the lunar surface within 15 years;

*and to and from Martian orbit, the deployment of a human tended habitation and research facility on the surface of a Martian moon, and to the surface of Mars and back within 20 years.

The bill establishes an Office of Exploration within NASA, headed by an Associate Administrator, which will be responsible for planning, budgeting, and managing activities undertaken to accomplish the above goals.

For more:

http://www.house.gov/lampson/infocus.htm

Argos
2002-Oct-11, 12:36 PM
Going to Pluto costs peanuts. For a very small fraction of the military budget the programs could be implemented. It is a real shame, and shows the lack of vision of the current Am administration.

Nanoda
2002-Oct-11, 06:04 PM
As engineering challenges go, you could solve this by teflon coated cable, heated cable...
but if you just put the spool on the submersible I think you'll see that problem disappears. /phpBB/images/smiles/icon_wink.gif

Back on topic, I'm very sad to see the funding to this mission cut. I was about to say that it was one of my favourites coming up, but actually, there seem to be so few probes sent that each one is amazing.

BTW, does anyone know how much (if at all) other countries contribute to such missions? I know the ESA has a few of their own missions, and Canada makes instruments for some, but it always seems that NASA is mostly alone in these endeavours. Is this true, or do they just have more publicity?
Basically I feel Canada is on the sidelines here. Is there anything I could do to help missions like this?

Kaptain K
2002-Oct-11, 09:22 PM
...but if you just put the spool on the submersible I think you'll see that problem disappears.
See my post above. You're still limited by the length of cable carried on the probe. /phpBB/images/smiles/icon_smile.gif

Nanoda
2002-Oct-12, 11:25 PM
Doh. I swear the thread was only 1 page long before I posted.
You're right too... apparently my info on Europa is very old, because this (http://news.bbc.co.uk/1/hi/sci/tech/2002218.stm) says that the ice is up to 25km thick, or an order of magnitude more than previously thought.
Perhaps at the cracks it's shallower, as I seem to recall that the lighter colour indicated water ice...
Cable doesn't seem so great now. Perhaps VLF, though I guess you'd lose pretty pictures. :-/

That petition sounds nice, but I have enough trouble getting elected representatives of my own country to give a d@mn about me. /phpBB/images/smiles/icon_wink.gif

Rodina
2002-Oct-13, 04:32 PM
Why do you -have- to have a cable? I don't know the limits of radio here, but upping the broadcast capacity of the radio would certainly take less mass than a 100km cable, regardless of how thin it is.

Kaptain K
2002-Oct-13, 06:36 PM
Water is opaque to most radio frequencies. Only VLF radio waves can penetrate water to any distance, but they have their own drawbacks, such as low data transmission rates and the need for huge antennas.
The antennas used for communication with on-station submarines are laid out over tens of square kilometers of arctic ice.

xriso
2002-Oct-14, 07:23 PM
Prediction: When we get around to looking on Europa, there will be no signs of life. As a result, more and more missions will be sent there to dig deeper in hopes of finding the life. Eventually there will be consensus that Europa is lifeless. This of course won't prove anything. Titan and Mars will be explored exhaustively (probably at the same time as Europa) and with similar results -- though Mars might have some Earth-derived life on it.

At some point along the road, it will be recognised that Earth life is the only life in the solar system. But by then, there will be Mars/Earth/Venus-like planets discovered in other planetary systems, and we'll make missions for those places. There will always be somewhere else where life just might be.

That's how I think it's gonna be, at least. I'm not what you might call a Saganite.

<font size=-1>[ This Message was edited by: xriso on 2002-10-14 15:26 ]</font>

Doodler
2002-Oct-16, 03:04 PM
Nanoda, about using an international consortium to fund the missions, have you consider the kluge that has become the ISS because of international "cooperation"? Better one country bites the bullet and just gets the job done. God help any probe done by committee.