Community > Forum > Technology & Science > Getting the water of comets?

Getting the water of comets?

Posted by: Ekkehard Augustin - Wed Aug 02, 2006 11:57 am
Post new topic Reply to topic
 [ 14 posts ] 
Getting the water of comets? 
Author Message
Moderator
Moderator
avatar
Joined: Thu Jun 03, 2004 11:23 am
Posts: 3745
Location: Hamburg, Germany
Post Getting the water of comets?   Posted on: Wed Aug 02, 2006 11:57 am
I remember several recent german articles saying that the observation of Temple showed that coments lose millions of tons of water when they appraoch the sun.

What about gathering this water? Which way could it be done and how much of it could be got?

For example the could be a group of tank-like vehicles that follow the comet closely - a portion of the water would be captured. But what amount? Another idea might be to keep them very very close to the comet - then more water per unit of volume of space could be caught.

Might it be possible to apply thin films that are cooled down? ...



Dipl.-Volkswirt (bdvb) Augustin (Political Economist)


Back to top
Profile
Moon Mission Member
Moon Mission Member
User avatar
Joined: Tue Oct 05, 2004 5:38 pm
Posts: 1361
Location: Austin, Texas
Post    Posted on: Wed Aug 02, 2006 12:42 pm
The problem is that comets are very hard to reach. Most of them have orbits that go out past Jupiter, which means the space craft going to comets would have to expend enough propellant to go out past Jupiter too. The fact that comets occasionally pass near Earth makes no difference at all, because it is not only the position, but also the velocity that must be matched to rendezvous with them.


Back to top
Profile WWW
Moderator
Moderator
avatar
Joined: Thu Jun 03, 2004 11:23 am
Posts: 3745
Location: Hamburg, Germany
Post    Posted on: Wed Aug 02, 2006 12:56 pm
Recent science missions to comets have shown that it is practicable. There was the impactor shot into Temple from a probe flying before Temple.

It isn't required really that the comet the collectors are to fly behind are close to Earth - they simply must manage to reach the comet and start to collect the water. They might do that for a decade or longer and then return to Earth while another group of collectors or samplers arrive at the comet.

In principle a portion of the water could be consumed by the collectors - it could be broken inot Oxygen and Hydrogen, both colled down later and then used to launch tem away from the comet. The gravity of the comet will be not that large and the initial collectors could even use gravity assists to return to the Earth-Moon-system.



Dipl.,-Volkswirt (bdvb) Augustin (Political Economist)


Back to top
Profile
Moon Mission Member
Moon Mission Member
User avatar
Joined: Tue Oct 05, 2004 5:38 pm
Posts: 1361
Location: Austin, Texas
Post    Posted on: Wed Aug 02, 2006 3:22 pm
Missions that fly past comets, such as the Deep Impact mission to comet Temple 1, do not stay near the comet. They simply fly by at thousands of kilometers per hour. To stay near the comet would require the space craft to match the comet's velocity. The DeltaV (change in velocity) needed to match velocities is found in a way similar to what the game I described here shows:
http://www.spacefellowship.com/Forum/vi ... aking+game
That DeltaV is the same as the v in the rocket equation v = ve*ln(Mv/Ml). The propellant required to do that would be excessive and it has never been done by any space craft.


Back to top
Profile WWW
Spaceflight Participant
Spaceflight Participant
User avatar
Joined: Fri Nov 11, 2005 10:12 pm
Posts: 63
Location: Bremen, Germany
Post Re: Getting the water of comets?   Posted on: Wed Aug 02, 2006 4:50 pm
Ekkehard Augustin wrote:
What about gathering this water? Which way could it be done and how much of it could be got?

For example the could be a group of tank-like vehicles that follow the comet closely - a portion of the water would be captured. But what amount?


Have you been to the Alps recently?

Imagine Montblanc is evaporating - or rather, that whole part of the Alps - say a metre or so is blown away, dust and water mixed, during a hot summer. Now you come with your spacecraft that's maybe as big as Rosetta - 3 tons, and launched on an Ariane 5 - to gather that water. How much would you get? :o

Simply forget about it, man!

Without actually having done the calculation (it'd take like five minutes if you have the data, but I don't) it'd probably be cheaper in terms of energy just to lift that water off the Earth. Now, if you really want to get water off a comet for some reason, just rendezvous with it, land on it, and dig. :idea: You'd have years and years out in the cold to work while it's far away from the Sun, rather than having to face flying debris during Sun approach.

But finally, what do you want comet water for? To use on a spacecraft? Forget it, it's dirty. To water Mars? Rather wait another 60 years and then send a whole comet to be captured by its gravity. Or just as a scientific trick?

No harm intended, but this kind of idea is why I have serious doubts about letting people with a political background decide scientific goals.

Three cheers for inventivity, anyway! :D

Max

_________________
There's space for all of us, if each will leave some space for the next one :)

The ideas expressed above are my own, not necessarily those of my employer.


Back to top
Profile
Moon Mission Member
Moon Mission Member
User avatar
Joined: Tue Oct 05, 2004 5:38 pm
Posts: 1361
Location: Austin, Texas
Post    Posted on: Wed Aug 02, 2006 6:19 pm
Ah, I forgot about Rosetta. That space craft will rendezvous with the comet in 2014, but it will take 4 gravity assist maneuvers and 10 years travel time to do it with the propellant available. With that much DeltaV it could go to Jupiter. In fact the Rosetta will actually go past the orbit of Jupiter, because once it rendezvous with the comet it is in the same orbit as the comet, which crosses the orbit of Jupiter. And if you can get to Jupiter, you get a nice gravity assist that can send you on to Saturn or even out of the solar system. There is plenty of ice on Saturn's moons, and on some of Jupiter's moons too. A nuclear powered lander could just melt the icy surface and make tons of LH2 and LOX.


Back to top
Profile WWW
Spaceflight Participant
Spaceflight Participant
User avatar
Joined: Fri Nov 11, 2005 10:12 pm
Posts: 63
Location: Bremen, Germany
Post    Posted on: Wed Aug 02, 2006 9:52 pm
campbelp2002 wrote:
(...) Rosetta. That space craft will rendezvous with the comet in 2014, but it will take 4 gravity assist maneuvers and 10 years travel time to do it with the propellant available. (...)


I totally agree. Rosetta is the prime example of the enormous delta-V necessary to acually interface with a comet... and that's a low-period comet, which is even relatively "slow".

Your outer-planets idea might have some potential, but I'm still waiting for our esteemed E.A. to explain what he wants that water for, and by that, what sort of quantity.

Regards
Max


Back to top
Profile
Moderator
Moderator
avatar
Joined: Thu Jun 03, 2004 11:23 am
Posts: 3745
Location: Hamburg, Germany
Post    Posted on: Thu Aug 03, 2006 7:17 am
Hello, Max Lange,

I posted concrete thoughts as catalysts merely - I've experienced often that that causes good and practicable ideas, solutions and concepts.

Regarding Temple I and at least one other mission I seem to remeber that probes have been flying along the course of the comet.

Thinking about it it seems that courses of probes crossing orbits of comets have to do with the requirement to fly to the comet merely than with impossibility to fly behind or before the comet constantly - in principle it is possible to insert a probe into the orbit of a comet so that it orbits the sun right in that orbit.



Dipl.-Volkswirt (bdvb) Augustin (Political Economist)


Back to top
Profile
Spaceflight Participant
Spaceflight Participant
User avatar
Joined: Fri Nov 11, 2005 10:12 pm
Posts: 63
Location: Bremen, Germany
Post    Posted on: Fri Aug 04, 2006 7:39 pm
Ekkehard Augustin wrote:
I posted concrete thoughts as catalysts merely - I've experienced often that that causes good and practicable ideas, solutions and concepts.


This is very laudable indeed. I'm sorry for maybe trashing your concrete idea with a bit too much spirit; your interest in tickling our grey matter is highly appreciated.

Quote:
Regarding Temple I and at least one other mission I seem to remeber that probes have been flying along the course of the comet.

Thinking about it it seems that courses of probes crossing orbits of comets have to do with the requirement to fly to the comet merely than with impossibility to fly behind or before the comet constantly - in principle it is possible to insert a probe into the orbit of a comet so that it orbits the sun right in that orbit.


Yes, of course that's possible. That's the idea in a so-called comet rendezvous, as Rosetta will perform. The reason why myself and Campbell don't think it's of much use to your idea, is that it consumes a fabulous amount of energy to perform. If the challenge is just to get at some extraterrestrial water, there are easier ways to do that. And thinking practically, a comet nucleus is fairly large (as I hinted in my post about Mt Blanc) and any gas or water vapour emitted from it forms a very large cloud - typically over 100000km wide and millions long - of extremely low-pressure gas. It's not like you could go there and expect your spacecraft to get all dewy. The only chance would be to go very, very close, find a fissure in the nucleus where water evaporates, and catch it there, if you want more than a microscopic quantity. And in this case, it really would be more interesting to fetch that water either from another place (like a Saturnian moon) or during another period in the comet's life, when the water is frozen and easy to collect (though even then you'd first have to travel well beyond Pluto).

I hope this helps to clear matters up.

Regards
Max

_________________
There's space for all of us, if each will leave some space for the next one :)

The ideas expressed above are my own, not necessarily those of my employer.


Back to top
Profile
Moderator
Moderator
avatar
Joined: Thu Jun 03, 2004 11:23 am
Posts: 3745
Location: Hamburg, Germany
Post    Posted on: Sat Aug 05, 2006 9:05 am
Hello, Max Lange,

I had no problem with your post, it's okay and alright.

There are two advantages of comets - the low gravity and the evidence that Temple contains water. I can't remember having read of such an evidence regarding asteroids.

You are right regarding the moons of gas giants - but those moons ahve the disadvantage that the gravity of the gas giants has to be handled. This might require much more propellant than to levae from a comet to Earth or Moon..

The problems of catching the water of a comet might be outweighed by long mission-times - I have in mind the threads of the Financial Barriers section this moment.

If I remember correct it was SpaceDev who consider to mine the water of asteroids to get cheap fuel for lunar and interplanetary flights. Because of the low gravity at, near and around comets they should be considered too - with question marks of course. May be that SpaceDev have been speaking of them too.



Dipl.-Volkswirt (bdvb) Augustin (Political Economist)


Back to top
Profile
Moon Mission Member
Moon Mission Member
User avatar
Joined: Tue Oct 05, 2004 5:38 pm
Posts: 1361
Location: Austin, Texas
Post    Posted on: Sun Aug 06, 2006 1:00 am
The low gravity of the comets combined with their proven water deposits is not enough to overcome the fact that it takes more DeltaV to rendezvous with those comets and return with a load of water than it does to launch the same load of water from the surface of the Earth!


Back to top
Profile WWW
Moderator
Moderator
avatar
Joined: Thu Jun 03, 2004 11:23 am
Posts: 3745
Location: Hamburg, Germany
Post    Posted on: Sun Aug 06, 2006 7:54 am
Like I said -
Quote:
The problems of catching the water of a comet might be outweighed by long mission-times - I have in mind the threads of the Financial Barriers section this moment.
.

Long mission times can outweigh the Delta-V also - this depends on the duration of such a mission. To get to a comet the Delta-V is required only once - and the Delta-V to return to the Earth-Monn-system alos is required only once

And it isn't required that the water-collector lands on Earth later. Since SpaceDev's thought is to use this water as propellant of vehicles the water will be delivered into LEO, a lunar orbit or a martian orbit. This means that begiining at the second water-collecting mission to a comet the required Delty-V will be less than that required for the first such mission because the first mission will have to be launched from the earthian surface.

If the water-collecting missions are launched out of a lunar orbit the required Delta-V will be reduced the more.

One idea regarding the probblem to collect the water of a comet. Of course normal tanks or huge bottels aren't sufficient by far. But there might be other methods. What about the equipments similar to light sails and ballutes for example? the materials are micrometers thick only and there are NIAC-studies considering light sails of diameters of 400 m and several km also.

I hab´ve no idea what the maximum diameter or area of such a sail is. But it would collect much m,ore water than the normal and usual tanks. Such a sail might be connected to a vehicle of sufficeint mass to prevent the water-collector from being blown away from the comet.

The surface of the sail might have micro- or nano-scale chanells guiding the water-molecules to a tank attached to the huge sail.

At this point tghe idea comes to my mind that the sail might be kept at the comet all the time and only the tank to be attached to the huge sail needs to travel between the comet and Earth, Moon or Mars or another planet.

May be that the sail can be made of nanocarbontubes which - as their name tells - are much thinner than the light sails NIAC studied. There seems to be carbon in abundance in space - so such carbontube.sails might be made in space perhaps.



Dipl.-Volkswirt (bdvb) Augustin (Political Economist)


Back to top
Profile
Moon Mission Member
Moon Mission Member
User avatar
Joined: Tue Oct 05, 2004 5:38 pm
Posts: 1361
Location: Austin, Texas
Post    Posted on: Wed Aug 09, 2006 3:38 pm
The DeltaV from LEO to a comet is about the same as the DeltaV from the Earth's surface to LEO. Since it takes that DeltaV to go to the comet and that same DeltaV again to come back, it takes twice as much DeltaV per trip to deliver water from a comet to LEO as it does to deliver it from the surface of the Earth to LEO. Delivery of water to Mars orbit from the surface of Mars, which does have water, would be even easier due to Mars' lower gravity, while reaching a comet from Mars orbit is about as hard as it is from Earth orbit. Delivery of water from the surface of the Moon to lunar orbit would be easier still, if there is water on the Moon.


Back to top
Profile WWW
Moderator
Moderator
avatar
Joined: Thu Jun 03, 2004 11:23 am
Posts: 3745
Location: Hamburg, Germany
Post    Posted on: Thu Aug 10, 2006 7:38 am
The DeltaV is no scale or criterion that can tell if it is advantageous to fly to a comet and gather its water ressources over years or decades.

Such a scale or criterion can be only propellants to be consumed, propellants and their amounts required and so on - all these are topics of Economics: propellant costs, transportation costs, revenues and the like. These I don't have in mind here and don't want to discuss here.

The focus is on the ways and methods to get the water of comets - thoughts very similar to something SpaceDev explicitly have said. Regarding transporation there are several trajectories even regarding the Moon - t/Space for example have in mind a three-months-trajectory for deliveries of propellant by their tanker. This trajectory saves propellant. Something like this may be possibel in the case of comets also - so this shouldn't be discussed here but is worth a particular thread. (...)



Dipl.-Volkswirt (bdvb) Augustin (Political Economist)


Back to top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 14 posts ] 
 

Who is online 

Users browsing this forum: No registered users and 16 guests


© 2014 The International Space Fellowship, developed by Gabitasoft Interactive. All Rights Reserved.  Privacy Policy | Terms of Use