Photos: Asteroid Vesta from NASA's Dawn Spacecraft

[weakmagneto]

Vesta is one of the largest known asteroids in the solar system. NASA's Dawn spacecraft has been documenting Vesta's features while orbiting it. Here's a link to the photos:

http://www.space.com/11540-photos-aster ... -dawn.html

Here is another link to a BBC News article, dated March 23, about Vesta:

http://www.bbc.co.uk/news/science-environment-17481911

[Marshall]

The Dawn mission to Vesta and Ceres (an icy dwarf planet in the asteroid belt) is certainly one of the most interesting exploration missions so far.

Vesta, the largest asteroid, is already interesting and Dawn has sent back fascinating pictures.

In about 3 months, in July 2012, Dawn is scheduled to fire up ion drive (a kind of solar powered electric rocket thruster), depart from Vesta, and head out to Ceres.

Ceres is actually a prospect for manned base, for several reasons:
1) cheaper and safer to land on than either Moon or Mars because of very gentle gravity. Easier to get off of if you need to return to Earth.
2) possibility to tunnel down into the ice for shelter
3) large amount of water ice
Pros and Cons of colonizing Ceres are discussed here:
http://en.wikipedia.org/wiki/Colonization_of_Ceres

General information about Ceres:
http://en.wikipedia.org/wiki/Ceres_(dwarf_planet)

Basically it is the nearest dwarf planet to us. Nearest icy body. Diameter about 1000 kilometers.

[Marshall]

article on ion propulsion for spacecraft
http://en.wikipedia.org/wiki/Ion_thruster
Interesting that Dawn is not using the most powerful state-of-art ion drives. they actually used 3 modest SURPLUS thrusters left over from an earlier project

they are a type called NSTAR, 92 millinewton force. the oldest model listed in the article. Here are some comparisons:
http://en.wikipedia.org/wiki/Ion_thruster#Comparisons
Despite this, Dawn has been very successful so far. Gone a long way and gathered a lot of information/pictures just with those out-of-date surplus thrusters.

[Watson]

Wouldn't the gentle gravity be a problem in itself. Looking at the relative sizes of Ceres, moon and earth how gentle is gravity on Ceres. Moving to fast could mean a problem stopping. Digging down could be a problem if you don't have the weight to put on the shovel or drill.

[weakmagneto]

Wow! Love the links, Marshall! Very informative and this is the first I have learned about Ceres and the potential to colonize.

[Marshall]

Magneto,
Definitely a fascinating place. Glad you are interested too!

Watson,
About not moving too fast, escape velocity is 500 meters per second. So you don't have to be afraid of drifting off into space. You still need a substantial kick to launch something into orbit.
But sure there are a lot of technical problems. Like stopping, as you mentioned, in surface transportation. If you are an ice-skater who weighs only 6 pounds. Or even getting started in the first place. What shoving off force can a skater get if they weigh only 1/30 as much? What source of power would a base use? Solar panels, nuclear reactor? If you wanted to tunnel, what kind of driill would you use? How would you anchor the drill.

The surface gravity is about 1/30 of normal earth gravity, or 3%. You are right that you would have to anchor stuff. I weigh 190 pounds in normal gravity, so roughly 6 pounds on Ceres. In an ice cavern with normal earth pressure atmosphere I could probably fly, weighing only 6 pounds. How would I do that?
You can design the gear, if you are curious and want to think about it.

[Watson]

Ok then I'll handle the drill, cause I'd be 7-8 pounds. First we'd need a small drill to anchor the larger equipment. Would 8 pounds pressure on a half inch bit going into ice and rock be enough? Then how strong is the anchor going to be against the bigger drill. I think you would need to step up the drilling for ever larger anchors. I'm glad I wasn't totally offside with my suggestions. So sneezing could be a potential problem as well?

[Marshall]

There is also melting a hole into the ice. Rather than drilling. You can tunnel into ice without exerting much of a force.

BTW your thoughts about MOORING a lander in low gravity were considered by the designers of a craft which is scheduled to land on a COMET soon. As I recall, it is designed to fire little harpoon barbs into the comet ice and use them to secure it at the landing site.

It will then ride the comet in towards the sun and around the sun, observing what happens to the comet, the chemistry of the evaporating plume, and so on.

Another icy, low gravity environment, with interesting challenges calling for imagination. I may be able to find a link. If you recall the name of the mission please mention it. I've forgotten.

Oh yes! The main spacecraft is called ROSETTA and the lander it carries to the comet is dubbed PHILAE

[Marshall]

http://www.esa.int/esaSC/SEMJUZS1VED_index_0.html

Rosetta was launched in 2004. It used several flyby's of Earth and Mars in order to pick up speed (a free boost from their gravity). I don't know when it is scheduled to meet the comet.
http://www.esa.int/esaSC/120389_index_0_m.html

The comet is called "Comet 67P" plus it has a hard-to-remember Russian name like "Churyumerov--Gerasimenko"

Here is info about the lander:
http://sci.esa.int/science-e/www/object ... ctid=31445

This page has a time-table. Rosetta is slowly closing on 67P and will rendezvous in May 2014.
http://sci.esa.int/science-e/www/object ... ctid=31397

There is a little animation showing the ORBITS of the planets, the craft, and the comet. It looks to me that the spacecraft is on an ellipse very similar to the comet's orbit and both are still far out from the sun (about the same distance as Jupiter). The animation lets you fast forward, so I can see them gradually converge over the course of 2012 and 2013.

[Watson]

There is also melting a hole into the ice. Rather than drilling. You can tunnel into ice without exerting much of a force.

It would not be practical in this case, I think. You would need a lot of heat directed to melt it in such a cold environment. Then you have a hole full of water and rock to bail out. Then people or equipment is getting wet and freezing up. This is not to say other options are more practical.

[Marshall]

There is also melting a hole into the ice. Rather than drilling. You can tunnel into ice without exerting much of a force.

It would not be practical in this case, I think. You would need a lot of heat directed to melt it in such a cold environment. Then you have a hole full of water and rock to bail out. Then people or equipment is getting wet and freezing up. This is not to say other options are more practical.

Good for you for imagining! Imagining a physically different environment is a way of honing your understanding of physics.

But is your scenario realistic? Could liquid water exist at Ceres surface conditions?

To get quantitative, a "Bar" is a pressure unit about equal to earth normal atmospheric pressure. The pressure on Ceres, in a hole open to the surface (not a capped pressurized cave) is LESS THAN A MILLIBAR.
At that pressure, any liquid water lying around immediately boils away.


In fact you cannot even properly "melt" water in the strict sense of making a stable liquid phase.

If you heat ice up to -20 Centigrade, it just GOES AWAY. It turn directly into vapor and dissipates into the vacuum. Technically one says that ice "sublimes" at -20 C. It does not even wait to form a liquid.

AFAICS -20 C is a hot temperature, on Ceres, relative to standard surface conditions (deeper in the ice, at some depth below surface, standard conditions could be different)

[Watson]

In fact you cannot even properly "melt" water in the strict sense of making a stable liquid phase.

If you heat ice up to -20 Centigrade, it just GOES AWAY. It turn directly into vapor and dissipates into the vacuum. Technically one says that ice "sublimes" at -20 C. It does not even wait to form a liquid.

Give this, how likely is any kind manned landing or base? I can see a lander of some sort relying data.

Ceres is actually a prospect for manned base, for several reasons:
1) cheaper and safer to land on than either Moon or Mars because of very gentle gravity. Easier to get off of if you need to return to Earth.
2) possibility to tunnel down into the ice for shelter.
3) large amount of water ice.

The problems I see are:
1-recruting the travel team, using the words "if you need to return to earth."
2-possible but extremely difficult to tunnel to a shelter, not to mention the need for shelter.
3-lots of ice, that vaporizes before it ever gets to be water.

Seems like a manned mission is not practical, but the movie would be worth a look.

[Marshall]

In fact you cannot even properly "melt" water in the strict sense of making a stable liquid phase.

If you heat ice up to -20 Centigrade, it just GOES AWAY. It turn directly into vapor and dissipates into the vacuum. Technically one says that ice "sublimes" at -20 C. It does not even wait to form a liquid.

Given this, how likely is any kind manned landing or base? I can see a lander of some sort relaying data.

The fact that ice vaporizes when heated to some such temperature would be common to both Moon and Mars. Not particular to Ceres. Any place with low atmospheric pressure. Liquid water would exist mainly in pressurized shelters (e.g. caves).

Good for you for being able to picture a lander relaying data. How about picturing a robotic lander which studies the ice layer on Ceres by boring a tunnel down into the ice? Call it "drilling" if you want but it really just amounts to little more than lowering an electric heater element down into the ice on a cable.

Taking samples down a hole in the ice would be part of studying the history of the dwarf planet, and by extension understanding the history of the solar system. (Ceres is one of the most primitive objects, other planets formed by clumping of smaller units like that---it just happens to be in apparently pristine condition, like before the earth existed.)

Ice layer could be more than a kilometer thick. Probably thicker than that, from the planet density estimates I have seen.

Ceres is actually a prospect for manned base, for several reasons:
1) cheaper and safer to land on than either Moon or Mars because of very gentle gravity. Easier to get off of if you need to return to Earth.
2) possibility to tunnel down into the ice for shelter.
3) large amount of water ice.

The first stages of exploration, including probes into the ice, would be robotic of course. I would expect that a robotic mission could actually hollow out a pressurizable chamber several tens of meters below the surface. I don't see robotic preparation of something of that sort as especially difficult. But perhaps you do.

[Watson]

Well, I'll be off line for a few days but i hope to get back to this line of thought, as it is of interest.