Transterrestrial Musings

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Sam Says

....billions more by having longer lived satellites and lower insurance costs. In the mean time, we can run satellites whose batteries have gone down or whose solar panels never fully deployed for longer and with more function ($500 million/year estimated value).

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Sam

Neither of these things are the primary limiting factor for a GEO comsat. The fuel load for station keeping is the primary limiting factor. The number of birds with bad batteries (I seriously doubt the ability to keep the comsat functing at ful power in eclipse) is limited and there have been very few solar array deployment problems in the past 15 years.

I also don't really buy SPS but this makes no more sense than SPS does. I also don't buy your 8% efficiency number. I would like to see a full loss chain calculation on power loss factors. You still have to emplace solar arrays on the Moon to take advantage of the laser output.

Dennis

Posted by Dennis Wingo at August 14, 2006 09:21 PM

8% number is in the Landis cite (or a previous paper he did cited in that). Even if it's 1%, it's still pretty cheap compared to launching cells. With plentiful orbital power would tethers work for stationkeeping?

The real money comes when people stop putting so many batteries or such big solar cells on the birds (and downsize launchers or increase function). You do need cells, but if the laser is 9x as powerful as sunlight after attenuated (at least at the highly tuned frequency for the cell), you can get away with fewer of them.

Ultimately they did run the new America's cup boat forwards, but first they did a substantial redesign.

Posted by Sam Dinkin at August 14, 2006 09:41 PM

Yip, extra terrestrial solar and mineral resources just do not add up for the Earth market. People also tend to forget that Earth based energy and mining systems will continue to be developed and will continue to become cheaper. As we continue to move towards more nimble distributed energy production SSP would just be a step backwards.

The market for people moving to Mars is an interesting and I think ultimately valid one, although it seems to me the moon would be an easier first step. The first settlers are going to have to carry a lot of food with them, so carbon and hydrogen sufficient for sustainable living should be readily available on the moon. I just do not see what Mars gains. If you do need to build a centrifuge in which to live – again this would be easier on the Moon than on Mars.

Having said this, by far the best place to first settle is LEO. Safer radiation environment, immediate transport to and from Earth, better access to Earth based markets – like communications, tourism, etcetera. The real clincher though is that it takes less Earth launched mass to settle in LEO than it takes to settle on the Moon or Mars. A self sufficient habitat in LEO can be very light weight indeed.

There is an economic case for LEO supporting millions of people without even using extra terrestrial resources . Although I am sure an economic way would quickly be found to transport lunar and asteroidal materials back to initial industry in LEO – where there can be a substantial work force. From LEO the equipment could be quickly developed with which humanity could then settle the solar system. At which point I expect there will be no shortage of people with the intent and the means to set out from an LEO space base camp.

Posted by Pete Lynn at August 14, 2006 09:44 PM

What are efficiencies for space based 'steam power'? Somewhere that hopefully has (or can have) water already. You'd be able to run phase change based turbines directly. And if you're willing to step up to higher temperatures (and other fluids), you can dump an awful lot of heat with a thermal background of 3K. Not an option for a satellite - but all current space based power generation is 'lab scale' anyway.

Posted by Al at August 14, 2006 09:49 PM

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Sam 9 x 1 sun = 12,222 watts per square meter?

Dude all of your savings in battery and solar array have to go into cooling the comsat from this huge thermal input.

It is just not practical.

Pete

It is much easier to move anywhere to and from LEO than it is to come up from the Earth.

I also dispute that a truly self sufficent system in LEO would be lighter or less expensive to put into place than something on the Moon. I will caveat that no where is going to be totally self sufficient, that is why there is trade.

Dennis

Posted by Dennis Ray Wingo at August 14, 2006 10:44 PM

A good large steam turbine on Earth is a little over 40% efficient. Problem in space though is that the cold end radiator is heavier than a solar/LASER concentrating mirror and drives the design, so it does not really gain you anything in this circumstance.

The cold end radiator perhaps wants to be inflatable – it will require shielding and redundancy and will probably want to run a bit hotter than an Earth based system, which will hurt the Carnot efficiency. Radiative heat transfer is proportional to temperature to the fourth power. Black body radiation at 300K is around 459W/m^2 compared with sunlight at ~1370W/m^2, (400K is 1452W/m^2), this should give you some idea of the respective areas required. Carnot efficiency is (Th-Tc )/Th, even so there is some argument for going for an inefficient very high Tc design that just intercepts more power. I once calculated that 1kW/kg might almost be ultimately possible.

Posted by Pete Lynn at August 14, 2006 11:06 PM

Denis wrote: “I also dispute that a truly self sufficient system in LEO would be lighter or less expensive to put into place than something on the Moon. I will caveat that no where is going to be totally self sufficient, that is why there is trade.”

It will be a very long time before any space settlement is truly self sufficient. LEO will greatly benefit from continued food and equipment shipments from Earth, (ongoing mass injection), and so should not be lacking in basic recycled feed stocks. Maybe Earth’s atmosphere could also be grazed for oxygen and nitrogen. I do tend to expect near total recycling from early on and the growing of base food crops sufficient to provide say 50% of the required food, (wheat, rice, algae, etcetera). This will be needed for the Moon and Mars anyway, but I expect this will first be developed and tested in LEO.

My base argument is that it might require something like 10 ton of mass to support a person in space. If you want to do that on the moon or on mars, this will increase to say 50 ton to include the propellant to get them and their life support equipment there. Sure developing insitu resources will eventually help bring that number down, but this still has to be offset against the initial propellant mass multiplier of getting them there. Initially I expect the lowest launch mass approach to sustaining the most people in space is to put them in LEO. After that it may still be more economically viable to bring extra terrestrial resources back to LEO for some time before space settlements become developed to a level that allows them to set forth out into the solar system in a highly self sufficient manner. LEO is space base camp one.

Posted by Pete Lynn at August 15, 2006 12:05 AM

Pete

I agree, that is why, even with its flaws, I support ISS. Without it there would be no space tourism proof of principle as we have today. If properly leveraged, it could be the core of such a place in LEO, even at 51.6 degrees.

Dennis

Posted by Dennis Ray Wingo at August 15, 2006 07:31 AM

Sam's idea for beaming energy up rather than down can be used to raise the orbital energy of tether systems. MXER tether ideas propose the use of electromagnetic re-boost powered by solar panels.

Power beaming from Earth could be cheaper.

Posted by Bill White at August 15, 2006 07:56 AM

Pete writes:

If we deploy MXER tethers to LEO and beam power up to raise their orbital energy, the "cost" of going on to the Moon and Mars from LEO is the cost of beaming the energy up.

= = =

Sam Dinkin, you have found a winner. Create a company and seek X Prize funding for a LEO to Luna/Mars cargo delivery service.

Halfway to anywhere (LEO) is really no where and you have identified an inexpensive means to travel the second half of any journey.

Posted by Bill White at August 15, 2006 07:59 AM

Sorry to run on, but . . .

Is it cheaper to send nuclear reactors to the Moon to crack that polar ice or extract LOX from regolith or merely beam power form Earth?

Sam is the economist, here.

Posted by Bill White at August 15, 2006 08:03 AM

I don't think you can necessarily label all SPS as unworkable, wouldn't the military have use for a SPS system that could beam 100-200 KW to remote locations?
I'm not so sure a niche market can't be found for it somewhere.

Posted by B.Brewer at August 15, 2006 09:13 AM

Bill

The size of the rectenna that you need to beam power to a tethered system (and its pointing requiremens) make that dodgy. Also, eTether boost systems don't really work above about 2500 km because of the inverse square fall off of the Earth's magnetic field. Sorry but Physics is physics.

B.Brewer

I think that SPS does have some very nice Niche markets but it is not going to save the world. Do a google on the increase in energy demand 2006-2030. We are going to need an additional 15 TERAWATTS and we are going to have to replace a lot of the capital equipment for the 17 TERAWATTS that we use today.

It would take 15,000 1 GW SPS's to meet the increased demand that the world needs. Anyone care to estimate the launch demand for that? That is 1,000 10,000 ton SPS launches per year. For 10% of the demand increase that is 100 SPS's. For 1% of the demand INCREASE that is 10, 10,000 ton systems per year starting tomorrow.

I would posit that the amount of funds to do this would be much better spent developing the economy of the inner solar system and using the power out there.

Dennis

Posted by Dennis Ray Wingo at August 15, 2006 10:44 AM

"Is it cheaper to send nuclear reactors to the Moon to crack that polar ice or extract LOX from regolith or merely beam power form Earth?" Nuclear is a good option too.

"Sam 9 x 1 sun = 12,222 watts per square meter?

Dude all of your savings in battery and solar array have to go into cooling the comsat from this huge thermal input.

It is just not practical."

A good chunk of the comm sat is battery for the eclipse. Can get rid of most of that.

If you have 1/9 the panels, you get the same heat as before so need same radiators as before, no? 800% too much? What about 100% more energy per area? If we can save 5% of the weight, we can save $150 million a year in launch costs/or harvest gains in increased function.

Posted by Sam Dinkin at August 15, 2006 11:15 AM

Sam

Not really. The problem today with comsats is that they are reaching their thermal limits within the form factor that is used. The heat lost just in the waveguides is in the several kilowatts and it is really hard to get rid of all of that heat.

The battery size is not all that big or heavy, the Apogee propellant is 1/2 the weight of the entire bird and i seriously doubt that the total battery weight is more than 3.5% of the system dry mass.

To do what you want would require major redesign of the comsat bus and after working with these guys for a few years, it is really hard to get them to change a nut or bolt much less the radical shift that you propose. I have a few ideas myself in this area but, to me, beaming power to a comsat just does not make that much sense.

Dennis

Posted by Dennis Ray Wingo at August 15, 2006 11:32 AM

Dennis, thanks.

The size of the rectenna that you need to beam power to a tethered system (and its pointing requiremens) make that dodgy. Also, eTether boost systems don't really work above about 2500 km because of the inverse square fall off of the Earth's magnetic field. Sorry but Physics is physics.

After I posted it also dawned on me that a low LEO target will overfly the beam point at a very fast clip. Less than 30-45 seconds of beaming opportunity per orbit?

Rapid target acquisition would be very tricky as well. It would essentially be a missile defense system. :-)

Momentum exchange, tossing payloads from the Moon and catching them in LEO to raise the orbital energy of the tether is the what the tether theorists seem to like. Lunar PGM miners can sell momentum to the LEO tether operators.

= = =

As for lunar electric power what about simple passive solar and a heat engine? For example, create a "cold end" of a Sterling cycle using a field of pipes buried in shaded regolith and heat the hot end with concentrated solar power using mylar on inflatable forms.

The mirrors will be cheap and light (mylar stretched over a parabolic inflatable) and you still need some sort of electric generator even with nuclear.

Without an atmosphere, heating the working fluid to well over ~1500 F with passive solar should be easy enough.

Posted by Bill White at August 15, 2006 12:22 PM

The problem with the ISS is that it was designed within the context of very expensive launch systems. Expensive design effects everything, and I mean everything, from the operational costs to the launch vehicle that must be designed to be docking compatible with it. The ISS design priorities would corrupt any associated future space infrastructure design to an unacceptable degree and for decades to come.

The first private station probably needs to cost less than a billion dollars. Even with first generation Bigelow modules I suspect this is possible, and cheaper than using the ISS for “free”. The ISS is at least one order of magnitude to expensive. That is just too great a gap for the necessary low cost ecology to bridge.

Posted by Pete Lynn at August 15, 2006 05:17 PM

The power solution I favour for the moon is a solar thermal system. Regolith is a very good insulator and one possible approach is to bury old propellant tanks and use them to store solar heated regolith which then powers a gas or steam turbine for substantial on demand power through out the lunar cycle. The cold end radiator may initially just be other old propellant tanks exposed on the lunar surface. This approach can quickly get substantially augmented, for example a large sealed underground cavern for the heated regolith. There are also possibilities of incorporating this into a regolith roasting cycle for extraction of volatiles. This seems much better than nuclear or beamed power options to me, scalable, redundant and easily grown. Solar mirrors and regolith are cheap and you would need the same sized cold end radiator and turbine system for the nuclear option anyway.

Posted by Pete Lynn at August 15, 2006 05:32 PM

I have spent a lot of time looking at momentum exchange tether systems with regard to retrieving lunar resources. There tends to be scale limitations as each payload needs its own guidance system. This will be a serious and incremental development project and I do not see it happening for less than a few billion dollars, (the lunar landing/launch section gets complicated). I expect a substantial LEO presence before this gets into full swing – though I do consider it the next step beyond LEO, and hopefully only a few years beyond at that.

There is a great deal to be said for integrating a small rotovator into the first private stations. One capable of say ~500m/s which can replace the final orbit and de-orbit burn of a launch vehicle. This roughly doubles the payload, has easy design margins and would only take a couple of launches to get up there. After that it could be incrementally increased and used to launch stuff into higher orbits and perhaps even to graze the Earth’s atmosphere for volatiles. It seems to me that such a small tether should be integrated into the design of the first private station and low cost servicing launch vehicle from the start, the economic benefits can be that immediate.

Posted by Pete Lynn at August 15, 2006 05:46 PM

Pete

I dispute that ISS is unreasonably expensive. First of all not only do the space tourists get to fly into space for their money, they get to spend a week on ISS for a somewhat reasonable cost for their efforts.

I have the cost numbers for payloads, people, and operations, and it is actually quite reasonable, if you work with our Russian friends to use ISS.

ISS is going to be hugely more capable within the next 36 months and I intend to use some of that capability.

Dennis

Posted by Dennis Wingo at August 15, 2006 08:06 PM

Going in from the Russian end should help greatly.

I tend to see the ISS as unsustainable in the Apollo and Shuttle tradition, investing all your eggs in this dead end program without a good exit plan would be worrisome. I really do hope that you can use the ISS as a stepping stone to a more commercially sustainable future. Good luck with this.

If the cost of using the ISS is not unreasonable, this gives me great hope for what a low cost commercial approach will be able to achieve.

Posted by Pete Lynn at August 15, 2006 09:10 PM

Here's an exit plan: dump ISS in the sea when the money runs out.

Posted by Sam Dinkin at August 15, 2006 09:19 PM

I tend to see the ISS as unsustainable in the Apollo and Shuttle tradition, investing all your eggs in this dead end program without a good exit plan would be worrisome.

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Pete

I don't see that this is worrying Space Adventures one iota and their business would not exist without ISS. How many of those tourists would fly on a Soyuz as a Spam in a can for 10 days with no place to pee except in a bladder?

Of course you would transition to another, more reasonably priced system when it comes about. Guess what, that solution is not going to come about (and Bigelow and I have discussed this at length) unless there are proof of principle activities on ISS.

The whole space tourism market exists because someone (MirCorp) broke the rules with NASA and with Russian help created a market that before was nothing but idle speculation.

There are other markets out there and we look forward to addressing them.

Dennis

Posted by Dennis Ray Wingo at August 16, 2006 08:04 AM

A coal plant costs about $0.75/watt peak capacity ($1B for a 750MW plant)

Late to the party, but here's my two cents. Whatever the actual merits of any of Sam's ideas, no one should under any circumstances let him run the numbers.

Posted by Dick Eagleson at August 20, 2006 05:53 PM

$0.75, $1.33? If it's within a factor of 2 it's good for an economist. The trouble is for an astronomer it's wider error bars. Big enough for a sign error. 20 years since I aced the SAT math section. Where's my editor?!

Posted by Sam Dinkin at August 21, 2006 09:05 AM

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