Space Tugs

I've been daydreaming about a new market that might open itself up. I have heard of two different propositions for a kind of satellite space tug to raise the orbits of other spacecraft. One of them is the electrodynamic tether, which seems very elegant to me: just run the juice from your solar panels down the tether, and it pushes against earth's magnetic field and viola, you have propulsion with no reaction mass to bother about.

The other idea involves a collector/condenser to gather hydrogen and/or helium from the solar wind or what-have-you, and use it in some sort of electric propulsion. VASIMR sounds like a good choice, if a small, light unit can be made. It should, in theory, accept whatever gas you feed it, and you can make a trade-off between ISP(fuel efficiency) and thrust (energy efficiency), depending on how much fuel you have and how fast you need to get where you are going.

Would it make any economic sense to build+launch such a craft? I know that most satellites either don't matter enough, or already have some sort of reboost capability, but there's only so much fuel a normal satellite has. So would corporations be willing to shell out the green stuff to double the life-span of their satellites?

Another possible use, but only for the VASIMR-type tug: send it off to collect an astroid of some kind and bring it back to LEO, say. Ekkehard, this is something you might know about. We are running out of some kinds of metals here on earth, tungsten being a good example. I think we are also short on palladium, platinum, and other such rare metals. If I'm not mistaken, some asteroids have large quantities of these valuable metals.

What if, instead of trying to mind the asteroids where they are, we haul them back to earth orbit first. Perhaps they might need to be fractured into manageably-sized chunks first. But once we have them in earth orbit, there are two options: One, process them in orbit, or two, put them into some kind of re-entry capsule and process them on earth.

I know it's been said that it wouldn't be cost-effective to haul lead into space even if it came back as gold. But would it be worthwhile to launch cheap, non-man-rated, expendable re-entry capsules, if they came back full of precious metal ore? And would it be more effective to have an orbital metallurgist's shop and send down only the purified metal?

What do you think?

Hello, Solo,

I will have to think about it - at present however my thoughts are concentrated on the Financial Barriers-thread about the lunar flight of Soyuz and on equipment for martian electricity.

But there are two points I want to mention here:

SpaceDev has mentioned publicly to mine asteroids for water that is to be cracked into hydrogen and oxygen as propellnt. According to SpaceDev these are to be kept in Space to reduce the flight costs. I don't remember precisely at present if they had in mind to carry the asteroids into an earthian orbit or a lunar orbit before they are mined but perhpas they had or still have. If that is economical is unclear to me at present. To mine atseroids for metals however might turn it more economical.

What I am doing in the thread about the lunar flight of Soyuz means to get an idea about the costs of repeated flights to another planet by reusable vehicles. The formular I am posting about and the Excel spreadsheet that will use the formular(s) will allow to calculate the costs of transportation to other planets also and the costs of a real transportation infrastructure. If the formular(s) and the spreadsheet result in numbers at or close to the level of the numbers I already got earlier then this may mean that it iwould be economical to carry an asteroid or pieces of it into an earthian orbit and to mine it there - a lunar orbit seems to be better because of less gravity etc. ...



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

Welcome to the boards, Solo; and how's life at UT? I assume you're at the Space Institute? I'm here at Georgia Tech in Atlanta; we'll probably run into each other at the AIAA Regional Student Conference if you go to it (not sure where it's at this year).

You're absolutely correct, asteroids could potentially be ridiculously profitable. It's just the up-front cost that hurts the concept. http://www.permanent.com/ is a decent website on asteroid mining; there's many others out there as well. For some reason, I keep thinking that there was a paper or book published by the title of "Mining the Skies" on the subject, but I can't seem to find it; maybe somebody else will remember what I'm thinking of.

As far as Electric Propulsion goes, look for this paper in your school library: AIAA 2005-3532 "An Overview of Electric Propulsion Activities in US Industry - 2005", by D. Lichtin. It's just that; a basic overview of all the EP activites in the US to date. http://www.astronautix.com/ is always a great source, too, of course.

But in answer to your main question, yes. There's absolutely no reason that you can't send a machine out to some metallic asteroid, and come back with over ten trillion USD of platinum-group metals.

Like I said, welcome to the boards, Solo!

Thanks for the links, SpaceCowboy! The permanent.com had some good stuff, though I didn't find anything on VASIMR in astronautix (not a surprize, it's a very new concept. The most attractive thing about it to me is the magnetic containment and nozzle. Seems like the fusion ppl would have heard about this before now...)

Anyway, the question still remains, is there a practical way to condense the kind of atmosphere that exists at, say, LEO, and bottle it for use as a propellant? I imagine it's mostly H and He. Probably ionized. Probably take forever to concentrate using a pump, you'd need some kind of electric or magnetic or shockwave-based system to get it to a reasonable density to pump from.

Funny you mention it, I'm actually not at UT. I considered going there, though. I'm at a small liberal arts college right now, actually. (I get a good deal b/c my dad teaches chemistry here!) I may go to UT for grad school, though, so who knows. (And for the record, I'm actually not even new to the board! Lol. I was LukeSkywalker, but I lost my password and changed my email, so I had to make a new account! But thanks for the welcome anyway, it's been a while since I've been to the site here.)

I'm really surprised about Astronautix.com not having the VASIMR.... The concept's been kicked around for a while now (about 4 years or so, I think).

As far as condensing atmosphere goes, it'd be far easier to launch bottled gas from the ground or (less costly yet) to mine it from the Moon.

Apologize for my mistake -- but it's always good to save on tuition. And in that case, welcome back, LukeSkywalker.

No need to apologize!

I thought astronautix was mainly a "history of spaceflight" kind of thing, but I guess that's just b/c I've only ever really been there to look up info on older launchers.

Re gas collection: you are probably right. I was just curious though. But obviously if the stuff could be obtained from asteroids or the moon, that woul be a jolly sight easier.

On a related note: have you seen that business about the MXER tether? That sounds really cool, and also highly impractical. It's funny, though, that the fellow who came up with it works at Tenn Tech, which isn't all that far from where I am (in fact, I've got a friend over in the mech engineering department).

Yeah, I've heard of it; I've got a friend who's working on tether research for NIAC. On top of that, I seem to remember seeing a presentation on it at Space 2006. I tend to shy away from tethers, though. Seems an over-complicated way to do things.

I agree; tethers are pretty much asking for trouble. On the face of it, they seem elegant, allowing you to re-use the momentum from the return trip from the moon or orbit to sling another cargo up. But the complexity and the hazards probably doom it in the end.

For Electrodynamic reboost of satellites, though, I think they might be useful. But that's really a whole different concept. Do you think they will ever agree to put a tether on the ISS to keep it stable and to reboost with?

EM reboost isn't nearly as bad, if they can get one working that doesn't short itself out. I wouldn't mind seeing it done, although it can take rather large amounts of power, and since the solar panels on the ISS aren't even enough to sustain its normal power usage, I doubt an EM reboost tether would ever be implemented.

I got ahold of a PPT show on ISS tether implementation that seems to suggest that it would work. Especially since they justed doubled the solar panel capacity of the station. An added benefit, the slideshow claimed, was that the tether would allow gravity-gradient stabilization. Let me go look for that PPT later. I think it was on one of the discussions in nasaspaceflight.com. Have you ever been to that forum, and if so what do you think about it?

In principle this realy requires an engine with a tank only - nothing else.

The tank would have to be refueled from time to time...

The engine alone would consume much less propellant than the engine together with the tugged object at the same velocityaimed at.

MagBeam might be of significant meaning regarding reductions of required amounts of propelant.



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