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NASA Studying Solar Powered "Space Tugboat"

samzenpus posted more than 2 years ago | from the Teddy-the-space-tugboat dept.

NASA 86

Zothecula writes "Last year, NASA announced it was seeking proposals for mission concept studies of a high-power solar electric propulsion (SEP) system that could be used in a 'space tugboat.' Such a ship would be used to ferry payloads in low Earth orbit (LEO) into higher energy orbits, including geosynchronous Earth orbit (GEO) and Lagrange point one (L1) — saving on fuel and the use of expensive secondary boosters. NASA also anticipates an SEP system could be used to propel spacecraft into deep space for science missions and for the placement, service, resupply, repositioning and salvaging of space assets by commercial operators."

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86 comments

Sigh (5, Insightful)

ShooterNeo (555040) | more than 2 years ago | (#38895929)

Welcome to the 1970s? Solar panels + some kind of high ISP, extremely low thrust engine (used to be ion engines but apparently casamir effect thrusters are much better) have been planned ever since.

The problem is really simple. It's cheap to study a potential space travel mechanism on paper. But you cannot make any real progress unless real hardware is built and tested in space. And that costs a fortune, because a kilogram in space costs about $10,000 to get it there. Not to mention costs other than money, such as time and launch windows and delays and so forth.

SO...a rational person at NASA, if the organization was not at the mercy of Congress for every project, would dedicate ALL of their budget to getting that $10k/kilogram cost down to something affordable. Even if this took a large up-front investment to solve this problem.

Re:Sigh (3, Funny)

Anonymous Coward | more than 2 years ago | (#38896011)

Obviously Gingrich had this in mind when he proposed setting up a permanent base on the moon by 2020 and making it the 51st state. The guys a frickin' genius. I propose calling this type of propulsion a Newt drive.

Re:Sigh (-1)

Anonymous Coward | more than 2 years ago | (#38896091)

Also, newt has a HUGE penis. Seriously, it's big.

Re:Sigh (0)

Anonymous Coward | more than 2 years ago | (#38898593)

Yeah, and if he wins the election it's going to be shoved up all of our asses. Without lube.

Re:Sigh (1)

Hentes (2461350) | more than 2 years ago | (#38896037)

SO...a rational person at NASA, if the organization was not at the mercy of Congress for every project, would dedicate ALL of their budget to getting that $10k/kilogram cost down to something affordable. Even if this took a large up-front investment to solve this problem.

But...but what about the moonbase they were supposed to build?

Re:Sigh (1)

vlm (69642) | more than 2 years ago | (#38896127)

Welcome to the 1970s? Solar panels + some kind of high ISP, extremely low thrust engine (used to be ion engines but apparently casamir effect thrusters are much better) have been planned ever since.

The problem is really simple. It's cheap to study a potential space travel mechanism on paper. But you cannot make any real progress unless real hardware is built and tested in space.

That stuff is like, old, man.

http://en.wikipedia.org/wiki/Ion_thruster#Operational_missions [wikipedia.org]

I know for a fact the wikipedia list is only NOTEWORTHY unusual historical missions involving ion electric engines, not every boring little comsat that has yet another station keeping system.

Re:Sigh (4, Interesting)

rtb61 (674572) | more than 2 years ago | (#38896301)

Might be smarter to attempt to 'surf' the planet's electromagnetic field.

Re:Sigh (1)

K. S. Kyosuke (729550) | more than 2 years ago | (#38896139)

SO...a rational person at NASA, if the organization was not at the mercy of Congress for every project, would dedicate ALL of their budget to getting that $10k/kilogram cost down to something affordable.

Which translates to "more power (and money) to SpaceX and co.", I assume. I just wonder how much money has been spent on that Constellation nonsense.

Re:Sigh (4, Insightful)

ShooterNeo (555040) | more than 2 years ago | (#38896421)

SpaceX has spent less money to get actual rockets to orbit than NASA spent to build a launchpad. Perhaps privatization isn't always better, but apparently in some cases it works incredibly well. Privatizing something is a bad thing, I think, when you are essentially having government give a private entity a natural monopoly. Hence, privatizing the power grid, etc.

Re:Sigh (0)

Grishnakh (216268) | more than 2 years ago | (#38897297)

Yep, it's all about competition. If the government can foster competition between multiple companies, then it usually works out quite well. If it just hands a monopoly to some corporation, it usually turns out to be a disaster because the company isn't answerable to the taxpayer the way the government is, and having a monopoly doesn't care about keeping customers happy. So if something needs to be a monopoly, it's really better to just have the government do it directly, preferably through an autonomously-run government-owned corporation like the USPS or MTA.

Unfortunately, the teabagger types seem to think that "government = bad, corporation = good", so they want to privatize everything regardless if there's any competition at all.

Re:Sigh (2, Interesting)

khallow (566160) | more than 2 years ago | (#38898619)

Unfortunately, the teabagger types seem to think that "government = bad, corporation = good"

Careful, your insipid bigotry is showing.

so they want to privatize everything regardless if there's any competition at all.

If only there were evidence for this assertion. Demonizing political opposition is a favorite past time on Slashdot, but it rarely hits the mark. But as it turns out, there are a lot of perils in privatization.

Failures of privatization can sometimes be traced to a market that naturally lacks competition, such as the electricity grid, but more common causes of failure are forced actions, artificial scarcity and abundance, or rent seeking.

For example, California attempted to deregulate its electricity industry, but the three main providers had the option to deregulate or not (that means here that they had a choice between fixed rate and a floating rate for consumers which started lower, but actually exposed them to the cost of the electricity they were buying). Only one of them had made the switch by the time that the California electricity crisis [wikipedia.org] happened and the other two were prevented from doing so.

The three primary negative effects were: rolling blackouts which had a modest effect on California residents and industry, a huge distortion in generator-provided electricity prices in and around California which resulted in regional energy intensive businesses such as aluminum smelters in Washington state and copper mines in New Mexico shutting down, and the depletion of capital of the three big Californian electricity providers which resulted in one bankruptcy and another coming very close to bankruptcy.

This all got fixed by first, allowing electricity providers to set up long term contracts for peak electricity rather than forcing them to buy all that power on the spot market, and second, by exposing electricity consumers to the actual cost of their electricity. Thus, we have here both forced actions (required to buy peak electricity on spot market) and artificial abundance (consumers not paying the cost of their electricity). It's also worth noting that California had blocked virtually all new power plant construction for about a decade (artificial scarcity of power generation capability) which contributed to the problem greatly.

The Russian attempt to privatize its oil industry (a policy which it has done much to reverse, I gather) provides an excellent example of rent-seeking. The "oligarchs", a collection of well-positioned businessmen, politicians, and/or crime lords bought assets for a fraction of their cost and made vast amounts of wealth almost instantly. If those assets had been sold by open auction, Russia would have gotten a lot more money for them, the local industry would have been more competitive and probably vigorous, and there wouldn't be subsequent moves to seize and redistribute these assets to a new set of cronies.

So in summary, it's worth noting that privatization at any cost routinely results in remarkable failures. I think in general it's a good idea to privatize most government functions, but it's worth remembering that such a process is very easy to break and/or corrupt.

Re:Sigh (4, Insightful)

AnotherBlackHat (265897) | more than 2 years ago | (#38896479)

Ion thrusters have a distinct advantage over Casimir effect thrusters in that the former actually exist.

For LEO to HEO I think tether propulsion [wikipedia.org] is a far better candidate.

Re:Sigh (2)

Intrepid imaginaut (1970940) | more than 2 years ago | (#38896717)

Have we not actually found a material that enables the construction of a space elevator in graphene though, which would reduce the costs to orbit to a tiny fraction of what they were previously? Yes spinning it out to the correct length is a serious engineering challenge, but its not physically impossible. And for the record, I was one of the greatest sceptics of space elevators until I heard about graphene.

Re:Sigh (1)

Jeng (926980) | more than 2 years ago | (#38896869)

How about a tension-leg platform that is made to be lighter than air by large rigid balloons that contain a vacuum?

That way no unobtainium is needed. Just have to figure out how to deal with the very high winds in the upper atmosphere.

Doesn't go far enough (1)

stevelinton (4044) | more than 2 years ago | (#38896961)

Doesn't go nearly far enough. Just getting up through the atmosphere is not really the point. Balloons do that pretty well. The trick is to build a tower so high that
it reaches geostationary orbit, so the top of the tower is in orbit, not just in space. That's about 36000 km up.

Re:Doesn't go far enough (1)

CrimsonAvenger (580665) | more than 2 years ago | (#38897069)

The trick is to build a tower so high that it reaches geostationary orbit, so the top of the tower is in orbit, not just in space. That's about 36000 km up.

The top of the tower needs to be higher than that. With something large and heavy up there.

You want a counterweight above GEO so that the station at GEO isn't dragged down into a spectacular crash.

Re:Sigh (2)

Jeremi (14640) | more than 2 years ago | (#38899805)

How about a tension-leg platform that is made to be lighter than air by large rigid balloons that contain a vacuum?

That way no unobtainium is needed

Except for the unobtanium that you'll be constructing the balloons out of.

Re:Sigh (1)

Jeng (926980) | more than 2 years ago | (#38902363)

Except for the unobtanium that you'll be constructing the balloons out of.

I was thinking about something like this.

http://www.liquidmetal.com/ [liquidmetal.com]

Twice the strength of titanium and is able to be molded like plastic. I thought I remember them saying that they were able to produce finished products that are accurate down to the micron, but I don't see that on their site anymore.

Re:Sigh (1)

Jeremi (14640) | more than 2 years ago | (#38918489)

Twice the strength of titanium and is able to be molded like plastic.

Do you really think that that material will be both (a) strong enough to keep from collapsing/imploding due to the air-pressure differential and (b) light enough to stay aloft, i.e. lighter than the equivalent volume of air?

It would be cool if it was, but I'll believe that when I see it.

Re:Sigh (2)

khallow (566160) | more than 2 years ago | (#38899987)

large rigid balloons that contain a vacuum

This is a very hard design requirement. You'd be better off with hydrogen filled balloons that have a lot less structure to them. And even with perfect unobtainium balloons, you'll only float to about 100-150km, the limits of the buoyant part of the atmosphere. As another poster noted, you need to get past 36,000 km. That's not going to happen even with magic balloons.

Re:Sigh (1)

TheRaven64 (641858) | more than 2 years ago | (#38900817)

It's not quite that simple. The problem isn't really height, it's speed. Ideally, you want to do most of your acceleration in the upper atmosphere, where air resistance is low but there is still enough air available to use it as reaction mass (so you don't have to lift it with you) and you can burn some of it with your fuel. The most energy efficient launch would probably involve taking a balloon up a hundred km or so, then accelerating hard horizontally with a scramjet. You'd then be in a wildly elliptical orbit, and you'd need some mechanism to correct it, but there are a few relatively cheap ways of doing this if time isn't your highest priority.

Re:Sigh (1)

khallow (566160) | more than 2 years ago | (#38907971)

The problem isn't really height, it's speed.

With a space elevator you get up to speed over a few days as you move up the elevator. At geosynchronous orbit (which I find from Wikipedia is actually 42k km), you are traveling exactly the speed you need to go to stay in that orbit. And somewhat lower altitudes, you can enter lower orbits though you might want to circularize it somewhat.

The most energy efficient launch would probably involve taking a balloon up a hundred km or so, then accelerating hard horizontally with a scramjet.

No, it wouldn't be. You have energy loss due to air resistance and work done in accelerating the mass of the remaining propellant in the scramjet. The most energy efficient system is one where "downmass" (that is, mass that is being taken from space to the surface of Earth) exchanges energy with "upmass" (mass being put into space).

I point that out as a theoretical absolute. In practice, the energy cost of putting things in space is negligible compared to the other costs.

Re:Sigh (1)

NalosLayor (958307) | more than 2 years ago | (#38897657)

Yes and no. We would need to build a single walled carbon nanotubes that run the whole length of the elevator, but we can currently build them a few centimeters long at most, and we need something like 25,000 Kilometers.

Re:Sigh (1)

Anonymous Coward | more than 2 years ago | (#38898333)

Yes, we have a material that barely meets the required strength to be self-supporting with reasonable taper.

  • We do not have a way to manufacture 1m strips of it, much less the 40 Mm we need. (We're making good progress here, but it's not apparent we'll ever get to 40Mm continuous, so we're gonna have to figure out how to join smaller pieces with no loss of strength.)
  • It doesn't have a great surplus of strength to keep it intact when a micrometeoroid hits it.
  • We don't have a way to repair it after such an impact, or a particularly good scheme for joining multiple ribbons to redistribute the load if one is severed entirely by a larger impact, though both those will likely become more clear once we figure out splicing.
  • We don't have a real good scheme for deploying it -- best guess so far seems to be a graphene production facility in GEO, paying out tether in both directions, and AFAIK we have no vehicle, real or planned, capable of launching well over 100t (facility plus feedstock) to GEO (for comparison, the Saturn V could get about 100t to LEO).

While I don't deny that a terrestrial space elevator does seem possible, eventually, it seems that a launch loop [wikipedia.org] is far more feasible from where we're at today, and likely required as a stepping-stone to the space elevator (as a means of launching stuff to GTO). And once you have a launch loop, what's the benefit of a space elevator? It's no good for human spaceflight (not even for LEO -- the point where "letting go" drops you in an elliptical orbit for aerobraking to LEO is ~23 Mm altitude) because of the slow trip through the Van Allen belts, and it's only a little better than launch loop for GEO launches -- about the only thing it really excels at is Earth escape launches, and I'm not sure that justifies the cost.

Re:Sigh (1)

TheRaven64 (641858) | more than 2 years ago | (#38900829)

To your last point, the plan is usually to put a carboniferous asteroid in approximately the right orbit and use it for the raw materials. You still need to get the production facility into orbit though, and that's not exactly cheap. Neither is moving several-hundred ton lumps of rock around, even in orbit...

Re:Sigh (0)

Anonymous Coward | more than 2 years ago | (#38905983)

Yes, but IMO dragging a NEO into GEO*, despite possibly requiring less delta-v, is even farther from current capabilities than lifting a couple hundred tons of coal from Earth.

*(insert jokes about handheld gaming consoles here)

Casamir effect thrusters? (4, Informative)

buback (144189) | more than 2 years ago | (#38896979)

Do you mean VaSIMR?
http://en.wikipedia.org/wiki/Variable_Specific_Impulse_Magnetoplasma_Rocket [wikipedia.org]
Or Hall Effect Thrusters?
http://en.wikipedia.org/wiki/Hall_effect_thruster [wikipedia.org]

And Ion Thrusters of various types have been used as primary propulsion n space successfully ever since Deep Space 1. They've been used for satellite orientation and station keeping for decades. They are vastly more efficient than chemical thrusters, reducing the amount of propellant you need to carry, and therefore reducing launch costs.

Re:Sigh (3, Insightful)

Grishnakh (216268) | more than 2 years ago | (#38897255)

The problem with reducing launch costs is there's only a couple ways to really do that. One is to improve existing rocket tech and costs, the way SpaceX and others are doing with privatization. That might help some, but you're not going to get order-of-magnitude or better improvements out of that approach, because the laws of physics and the cost of fuel put big limits on just how cheap you can make launching that way.

The second way is to build a space elevator. Of course, we're still in the phase where people are laughing about it instead of doing it, because the idea seems too far-fetched for morons^H^H^H^H^Hlaypeople, and also because it relies on a material that's extremely new and not yet proven in industrial applications. Even with graphene or carbon nanotubes or whatever, the initial cost will still be extremely high, and you know how short-sighted humans are with economics (they'd rather pay much more over a long term than pay a big up-front cost and spend less over a long term; that's why they get loans for everything and buy subsidized cellphones).

Another way is to follow Newt's idea and build a moon base. (I can't believe I'm defending Newt here; the guy is a scumbag, but just like a stopped clock is correct twice a day, he's right about the moonbase, though I have no idea how he proposes to pay for it since he, like every other non-Paul Republican, wants to maintain giant military expenditures and start a war with Iran to boot.) With a moon base in place that has manufacturing facilities, researchers on Earth would be able to send stuff to their colleagues on the moon base to be manufactured and tested either on-site or in space. The launch cost for anything from the lunar surface would be dirt cheap compared to here, because of 1/6g gravity. Of course, that's only once you have the base in place and fully stocked with equipment, and able to mine and refine materials and energy or fuel from the lunar surface. Getting to that point will probably cost a lot more than building the space elevator (just guessing), but it can be done with present technology mostly, and would have some other additional benefits as far as providing us experience in sustaining human life off-world.

Re:Sigh (1)

icebike (68054) | more than 2 years ago | (#38897745)

Launch from altitude make more sense than any of those.

Substituting fairly cheap fuels and reusable lift vehicles [wikipedia.org] to bring your space craft [wikipedia.org] to 50-70,000 feet reduces costs and risks substantially.

Expensive space fuel requirements are drastically reduced, as you are burning Jet A to get to launch altitude.

Lets face it, space elevator is not happening any time soon, and moon base is loony-tunes until we have better lift capability. We can barely keep the ISS manned at this point. Getting any amount of building materials or modules to the moon and landing them safely is simply off the drawing board until this problem is solved.

Re:Sigh (0)

Anonymous Coward | more than 2 years ago | (#38904887)

Actually SpaceX is already close to an order-of-magnitude reduction in launch costs. Once they get the Falcon Heavy flying, they will break the $1000/lb threshold (a little over a year from now). However, they're also working to achieve the goal of "completely and rapidly reusable" rockets. [youtube.com] If they can do that, then the cost of a launch drops from fuel+rocket to just fuel (plus the cost of the rocket amortized over 10s or 100s or 1000s of flights) like an airplane.

For reference, a Falcon-9 rocket sells for about $50M. The fuel needed to launch it costs about $150~$200K. You can do your own math... but by any reckoning, that's at least a two-orders-of-magnitude reduction in price.

If you want a more realistic view of future development, check out this speech by Jeff Greason [youtube.com] at the 2011 ISDC conference. In a nutshell, it's a "ladder" of progressively more distant places for in-situ resource utilization (ISRU). (Send robots to the moon to mine propellant, and deliver it to orbit... then use that fuel to send robots to Phobos to mine fuel there, and use that to get down to the surface of Mars and mine fuel there too... and use that to get off of Mars, etc...)

[taiwanjohn: posting as AC because I already modded in this thread.]

Re:Sigh (1)

DarthVain (724186) | more than 2 years ago | (#38907291)

Getting the infrastructure in a "moon base" to build and launch anything significant will be difficult and far off to say the least.

Really the only option that has been put forward that even has some realism is the space elevator, and even that is pretty fantastic.

When it comes down to it, the reason it is so impractical is A) it is so big and would require X amount of resources to physically build, and B) the dimensions being so big that no current material would be able to withstand the stresses required for construction. You mention nano-tubes and graphene (and I recall something called buckyballs, which might just be something about carbon nano-tubes), but the problem with those right now, is to make the amount required for even a hairs strand is very hard to do and expensive.

Seems to me, if anyone is really interested in space travel we should really be intensifying our research into engineering materials, and getting the construction costs of that and the elevator down.

Unless of course some magic wand technology is invented in the meantime of course.

Re:Sigh (1)

Grishnakh (216268) | more than 2 years ago | (#38908751)

When it comes down to it, the reason it is so impractical is A) it is so big and would require X amount of resources to physically build, and B) the dimensions being so big that no current material would be able to withstand the stresses required for construction. You mention nano-tubes and graphene (and I recall something called buckyballs, which might just be something about carbon nano-tubes), but the problem with those right now, is to make the amount required for even a hairs strand is very hard to do and expensive.

Seems to me, if anyone is really interested in space travel we should really be intensifying our research into engineering materials, and getting the construction costs of that and the elevator down.

Yes, exactly. Carbon nanotube composites have been determined to have more than the strength needed, but manufacturing those in sufficient quantities is still not developed; that needs funding to do. But of course, we don't like to invest in forward-thinking stuff like that if there isn't going to be an ROI within 3 years...

Re:Sigh (1)

icebike (68054) | more than 2 years ago | (#38897567)

The problem is really simple. It's cheap to study a potential space travel mechanism on paper. But you cannot make any real progress unless real hardware is built and tested in space. And that costs a fortune, because a kilogram in space costs about $10,000 to get it there. Not to mention costs other than money, such as time and launch windows and delays and so forth.

Cheap to study indeed. From the announcement:

Following the announcement, NASA awarded five companies four-month study contracts totaling approximately US$3 million, with a maximum individual contract award of $600,000. The selected companies were Analytical Mechanics Associates, Ball Aerospace & Technologies, Boeing, Lockheed Martin, and Northrop Grumman. Each company is tasked with providing a final report that will help identify technology gaps and look at possible solutions using SEP systems.

$3 million spread among 6 companies is not serious money. It actually sounds like "lets keep Joe on the payroll" money. Money to keep a company interested and a few scientists (maybe 5 or 6 per company) employed till there is something "real" to do. (Not that I think that is a bad idea in general, scientists have to eat between big projects, especially if you want them to stick around and not wander off to some other industry.).

But I don't think this is serious money. Its barely brain-storm money.

In fact its so suspiciously small it could actually be a cover for something else, with one guy writing a summation of all existing SEP science, while the rest work on something cool for the future.

Re:Sigh (3, Insightful)

hairyfeet (841228) | more than 2 years ago | (#38897733)

I thought the Russians solved this problem with their Hall Effect Thrusters [wikipedia.org] which they have been using in space since the early 70s? So there you have it, its proven mature tech that has been used in space and i'm sure the Russians have most if not all the bugs worked out. hell we buy many of our rocket engines from them anyway, not to mention hitch rides with them, i'm sure we can buy some HETs that will be suitable for purpose.

The really great thing about this idea IMHO is how much money we could save if we turned the ISS into basically a "space fixit shop" so that the next time Hubble or some majorly expensive sat starts malfunctioning we could have the space tug pull it up to the ISS where they could work on it instead of trying to go out to where it is and work on it there. Hell when not pulling sats maybe we can tie some sort of net or sticky material to try to clean up the massive amount of floating debris we have out there right now, making it better all around for our sats and ships.

. I'd just like to say if any NASA guys are reading this I really like the new direction you've taken. Instead of wasting tons of money on meatbags in space between the probes and ideas like this it looks like you guys are back to being the goto guys for hard science and that's just great. We probably learn more real facts from a single one of your probes than a dozen LEO trips at a hell of a lot less cost and ideas like this just shows you can still come up with some really cool ideas without them involving meatbags in space. I just hope you guys get the funding for this because the amount we could save long term if we could repair sats easily from the ISS would make this worth every penny IMHO.

Re:Sigh (2)

LifesABeach (234436) | more than 2 years ago | (#38897769)

Well, it sure beats what NASA is doing now, which is watching re-runs of what NASA use to do. The side benefit is that it might be possible to push a spent satellite that's still useable into an location where it can be repaired, and sent back to work. How about space junk retrieval? Spare parts from the space junk might not be pretty, but if they're working, why not use them?

Re:Sigh (1)

FleaPlus (6935) | more than 2 years ago | (#38899043)

SO...a rational person at NASA, if the organization was not at the mercy of Congress for every project, would dedicate ALL of their budget to getting that $10k/kilogram cost down to something affordable.

Quick correction: It's actually down to a price of ~$2k/kilogram with the SpaceX Falcon Heavy [wikipedia.org] . That's still a fair bit of cash, but somewhat reasonable compared to the cost of developing a payload.

Re:Sigh (1)

TheRaven64 (641858) | more than 2 years ago | (#38900839)

$2/kg, for certain values of 'in space'. That's $2/kg to LEO, which just about qualifies. When you want to get into a higher orbit, things get a lot more expensive (although that's something this project is aimed at addressing). $10/kg to, for example, geosynchronous orbit, is still pretty good.

Re:Sigh (2)

Zorpheus (857617) | more than 2 years ago | (#38900769)

Why are you so negative about reducing the cost of transfers to GEO?
The same Atlas V can transport about 5 times as much to LEO as it can transport to GEO. [wikipedia.org] A space tug could transport a satellite from LEO to GEO. The cost for this is mostly in bringing the tugboat into space. Since the ion drive needs only small amounts of propellant the running cost is pretty low.
The tugboat reduces the cost of a transport to GEO to the cost for LEO (which is just 1/5th) plus the cost for the tug. This can save a lot of money, no matter what launch system is used.

Re:Sigh (0)

Anonymous Coward | more than 2 years ago | (#38901687)

Launch loop ftw!

Electricity source (1)

K. S. Kyosuke (729550) | more than 2 years ago | (#38896043)

Perhaps it's time for NASA to finally push forward its Stirling engine projects... They've been talking about it for at least a decade.

Re:Electricity source (4, Informative)

Darth Snowshoe (1434515) | more than 2 years ago | (#38896347)

The sterling engine work that NASA is doing is to make the RTGs more efficient - this is not for propulsion but for providing power to other systems on the spacecraft (avionics, transceiver, instruments). Part of the motivation is to reduce weight, or to get more power for the same amount of weight. The other issue is that the isotopes which are commonly used for RTGs were byproducts of nuclear weapon production, hence, have not been produced (in America, at least) for decades.

Re:Electricity source (1)

K. S. Kyosuke (729550) | more than 2 years ago | (#38897093)

The sterling engine work that NASA is doing is to make the RTGs more efficient - this is not for propulsion but for providing power to other systems on the spacecraft (avionics, transceiver, instruments). Part of the motivation is to reduce weight, or to get more power for the same amount of weight. The other issue is that the isotopes which are commonly used for RTGs were byproducts of nuclear weapon production, hence, have not been produced (in America, at least) for decades.

The thing is that the Stirling engine does not care where the heat comes from, and its efficiency is higher than the efficiency of even good solar cells. I just wonder how well would a solar-heared Stirling fare - mass-wise, compared to solar cells - for power output in the 100KW-1MW range.

Re:Electricity source (0)

Anonymous Coward | more than 2 years ago | (#38897505)

Well, the hard part is not _getting_ heat, but _dumping_ heat -- radiation over a delta of 300K or so sucks. Of course, that's an issue with PV arrays as well -- so I suspect the systems will come out pretty similar in weight for a given heat input (which is pretty much proportional to collecting area, whether it's a parabolic dish concentrating radiation to a heat engine, or a PV array).

A tugboat (1, Insightful)

Osgeld (1900440) | more than 2 years ago | (#38896115)

with nothing to tug?

one would have to get shit into space for a reasonable cost before shuffling it around would be an issue

Re:A tugboat (1)

ArsonSmith (13997) | more than 2 years ago | (#38896485)

just put a winch on it and drop a hook down to earth.

Re:A tugboat (1)

Aryden (1872756) | more than 2 years ago | (#38896693)

You know, when I read "tug" that's the exact image that popped into my head...

Re:A tugboat (2)

Glonoinha (587375) | more than 2 years ago | (#38898613)

It'd be a good place to listen to Rasta dub music, mon. Not to mention the occasional need to move stuff around Freeside.

In Another Newsflash (2, Funny)

NEDHead (1651195) | more than 2 years ago | (#38896241)

Dr. Einstein - a german patent clerk - has declared a galactic speed limit. It is estimated that this limit will extend our whale oil supplies well into the next decade.

Re:In Another Newsflash (1)

sconeu (64226) | more than 2 years ago | (#38896965)

299792458 m/s. It's not just a good idea... IT'S THE LAW!!!

Technical Question (5, Funny)

NEDHead (1651195) | more than 2 years ago | (#38896259)

How will this work at night?

Re:Technical Question (1)

OzPeter (195038) | more than 2 years ago | (#38896383)

How will this work at night?

You'd simply have to line the spaceways with construction lights like they use on freeway work. Just make sure to put them out the day before they are needed. Otherwise its lights all the way down.

Re:Technical Question (1)

NEDHead (1651195) | more than 2 years ago | (#38896511)

Ahh! Makes sense. They might need some kind of electric tug to put them in place. Has anyone suggested this to NASA?

maybe invent a (4, Interesting)

FudRucker (866063) | more than 2 years ago | (#38896415)

solar powered sanitation satellite that just robotically collects debris in orbit, and when its payload is full it commits suicide by diving in to the atmosphere over the pacific ocean so what does not burn up on entry falls harmlessly in to the sea

Re:maybe invent a (3, Insightful)

Detritusher (1031752) | more than 2 years ago | (#38896509)

No need to commit suicide, just tow junk down into an unstable low orbit, leave the junk there, and then it's thrusters to boost back into a higher orbit and collect more.

Re:maybe invent a (1)

Aryden (1872756) | more than 2 years ago | (#38896593)

or just compress the junk into a block and fire it at the sun.

Re:maybe invent a (1)

Detritusher (1031752) | more than 2 years ago | (#38896683)

Or we could stick with reasonable engineering and physics.

Re:maybe invent a (0)

Anonymous Coward | more than 2 years ago | (#38896873)

LHC creating mini black holes in specific orbits, designed to suck in space junk then collapse?

Right on, man.

Re:maybe invent a (1)

Aryden (1872756) | more than 2 years ago | (#38896991)

reasonable engineering and physics make it entirely possible for a construction in orbit to be able to capture low orbit junk, compress it and then jettison in a trajectory that would take it to the sun if provided enough energy to escape the Earth's gravity and get picked up by the sun's.

Re:maybe invent a (1)

Anonymous Coward | more than 2 years ago | (#38897637)

reasonable engineering and physics make it entirely possible for a construction in orbit to be able to capture low orbit junk, compress it and then jettison in a trajectory that would take it to the sun if provided enough energy to escape the Earth's gravity and get picked up by the sun's.

You say that as if it were a trivial problem, it isn't.

Re:maybe invent a (2)

jpmorgan (517966) | more than 2 years ago | (#38898633)

Reasonable engineering certainly does not.

Re:maybe invent a (1)

Aryden (1872756) | more than 2 years ago | (#38900263)

I think reasonable is where our debate is.

Re:maybe invent a (1)

Glonoinha (587375) | more than 2 years ago | (#38898663)

Silly question, but assuming that the minuscule mass of objects in low Earth orbit still contribute to the Earth's overall mass with respect to the inertia and centripetal acceleration that keeps us in orbit around the sun. If we were to start ejecting tons of crap from LEO and sending it towards the sun, however minute the volume, couldn't we potentially alter the balance slightly and possibly even impact our orbit (duration / trajectory / stability) ?

I'm guessing no, but that assumes everything in moderation.

Re:maybe invent a (1)

jcwayne (995747) | more than 2 years ago | (#38899297)

I haven't done the math, but I think you'd have to eject something roughly the size of Australia for the effect on Earth's orbit to even be measurable.

Re:maybe invent a (1)

Anonymous Coward | more than 2 years ago | (#38899729)

Silly question, but assuming that the minuscule mass of objects in low Earth orbit still contribute to the Earth's overall mass with respect to the inertia and centripetal acceleration that keeps us in orbit around the sun. If we were to start ejecting tons of crap from LEO and sending it towards the sun, however minute the volume, couldn't we potentially alter the balance slightly and possibly even impact our orbit (duration / trajectory / stability) ?

I'm guessing no, but that assumes everything in moderation.

No, because the centripetal acceleration is due to gravity, and is therefore independent of the Earth's mass. The gravitational force on an object is proportional to the object's mass, and therefore the resulting acceleration due to gravity is independent of its mass. Thus "inertial mass" and "gravitational mass" are equivalent, and moreover, the effects of being in a gravitational field are completely equivalent to being subject to acceleration. It is this realization that Einstein described as the "happiest thought in his life", and which lead to his development of General Relativity.

(Effects of the recoil attendant with ejecting tons of crap from LEO are a separate issue of course.)

Re:maybe invent a (1)

Aryden (1872756) | more than 2 years ago | (#38900299)

recoil could be dealt with using thrusters. Similar to how A-10's go full throttle when using their cannons.

Re:maybe invent a (0)

Anonymous Coward | more than 2 years ago | (#38900841)

recoil could be dealt with using thrusters. Similar to how A-10's go full throttle when using their cannons.

Sure, I just meant "these arguments do not account for recoil", not necessarily "recoil remains a problem"

Re:maybe invent a (2)

TheTurtlesMoves (1442727) | more than 2 years ago | (#38900729)

It is easier to send it into interstellar space. Which is *not* easy.

Re:maybe invent a (2)

Sinn3d (1594333) | more than 2 years ago | (#38900947)

Nah, fire it at the moon, so when Newt gets there he can use it to build a shelter ;)

Re:maybe invent a (1)

trevelyon (892253) | more than 2 years ago | (#38899341)

Or just haul those things back to L1 and contain them in the start of a scrapyard. For $10k/lbs you'd think they want to keep everything up there they spent the money to get up there. If containing it safely at L1 is not feasible then depositing it on the moon would likely be better than sending it back to earth (lower gravity well). Even though we don't have the recycling capacity up there now that doesn't mean we won't have it there or on the moon later. It just might save some mission gone awry to have some spare material around to try and jerry-rig something up. Why waste all the fuel to get it up there only to throw it away.

Re:maybe invent a (0)

Anonymous Coward | more than 2 years ago | (#38899675)

A scrapyard at L1 wouldn't be stable. L4 and L5 are much better options for that and for permanent space stations.
see http://hyperphysics.phy-astr.gsu.edu/hbase/mechanics/lagpt.html [gsu.edu]

L1 is really only useful as a transfer point to the moon.

As for naming the fist space tug - I vote they call it the Toybox.

Yes! (4, Interesting)

Intrepid imaginaut (1970940) | more than 2 years ago | (#38896691)

This is exactly the kind of basic space infrastructure NASA should be working on. Space tugboats, construction vehicles, mining drones and assayers, cargo haulers, all the simple stuff that makes a civilisation run smoothly. We need to walk before we run, and that means mastering the basic techniques of constructing and operating these types of vehicles long before any thought is given to colonising the moon or Mars.

Re:Yes! (0)

Anonymous Coward | more than 2 years ago | (#38897837)

If they build a combined space tug boat and orbital death canon they can get some DoD funding!

Re:Yes! (1)

TheRaven64 (641858) | more than 2 years ago | (#38900863)

Mod up. This is the first space story I've seen recently which talks about doing something both sensible and achievable. Of course, that probably means that it won't get enough funding...

Re:Yes! (1)

Chris Burke (6130) | more than 2 years ago | (#38902143)

Absolutely. As commercial ventures start to make the trip to LEO cheaper, what NASA should be doing is working on basic technology to enhance what we can do once we get there. Like use LEO (halfway to Mars in terms of delta-v) as a staging point for a mission beyond.

This is the kind of thing that makes me feel good about NASA's future.

Loony-Tunes Flashback (1)

snspdaarf (1314399) | more than 2 years ago | (#38896743)

Oh, the tugboat goes, "toot-toot-toot",
Some toot high, and some toot low,
But the toot-toot-toot don't mean a hoot,
It's the chuga-chuga-chuga that makes 'em go!

we need a STUDY? (0)

Anonymous Coward | more than 2 years ago | (#38896803)

We need a STUDY?

A real quick estimate shows this is not terribly practical-- a square meter of solar panel is going to collect about 200 watts, under a quarter horsepower. That's going to be able to lift 100 pounds one foot per second. And that's ignoring the weight of the panel and of the reaction engine and of the reaction mass, and the energy needed to undo the orbiting speed. GEO orbit would take, oh, a whole lot more than 3.7 years to get to. The interest expense on a GEO satellite is so high you can't afford to have it loitering around for almost 4 years.

Re:we need a STUDY? (1)

Grishnakh (216268) | more than 2 years ago | (#38897353)

I question your numbers. I believe 200W/m^2 is reasonably accurate on Earth's surface, but conditions are entirely different in orbit, where you don't have an atmosphere, cloud cover, etc. reducing your solar efficiency.

Re:we need a STUDY? (1)

mcswell (1102107) | more than 2 years ago | (#38909621)

Very little difference, I think.

SEP (0)

Anonymous Coward | more than 2 years ago | (#38896845)

If it's going to be tendered out, doesn't that make it a 'Somebody Else's Problem' field'? (Hope they remember to use metric though).

Re:SEP (1)

MichaelSmith (789609) | more than 2 years ago | (#38900315)

It will run on a single torch battery. My indifference has paid off, as usual.

All for the idea but not for the approach (1)

trevelyon (892253) | more than 2 years ago | (#38899421)

Basically this is a way to give money to companies for really not much. If you want to fund research you should fund it and publish the results or at least share them with other prospective developers. Nasa is paying 5 different companies to develop different concepts for the same thing. After which these companies will own their work and it won't be shared which results in Nasa basically getting a fraction of what they paid for. This is a very inefficient way to operate and probably one of the primary reasons we see little results from the massive amounts of money Nasa spends. I'm all for space exploration but this kind of wasteful spending is why Nasa's budget gets cut and more and more people feel a government funded space agency is a waste of money. If you want more value make it so that all the results are freely published and then we can build off it. That way the next contractor Nasa pays won't have to reinvent the wheel. Private company - government partnerships are IMO a very bad thing.

will-be was (0)

Anonymous Coward | more than 2 years ago | (#38899485)

You can't have a space tug without a will-be was engine - sorry, just not possible.

Re:will-be was (1)

Krazy Kanuck (1612777) | more than 2 years ago | (#38899649)

I was wondering when the obligatory Mission Earth/Tug One reference would surface.

Asteroid Mining (1)

rally2xs (1093023) | more than 2 years ago | (#38899991)

What we need to do is to move the Eros asteroid o where we can smelt all those metals (including a lot of gold) into pure form, then get them all back on earth (without accidentally killing ourselves or the planet.) There's probably enough precious metals in it to literally pay off the national debt.

Re:Asteroid Mining (1)

MichaelSmith (789609) | more than 2 years ago | (#38900325)

Smelt them on Eros, or build an induction catapult on Eros to process the metals somewhere else. But my bet is on building the processing plant in low earth orbit, flying it to a near earth asteriod and producing metal products on site.

Tubgoat? (1)

CyberDruid (201684) | more than 2 years ago | (#38900801)

I read the title as "Tubgoat" and thought, as any normal person would, that it was about something like Tubgirl, but.. worse.

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