I like this thread. Thanks for the overview. I noticed you didn't mention any space solar power concepts, I think there is a lot of overlap, and large SEP tugs/ mars transfer vehicles might be a stepping stone to conventional SSP visions.Now I do wonder about using any kind of ion thruster or centralized drive with a large deployed structure. I know the accelerations are very low, but I just think there might be a more graceful propulsion tech to match/ compliment a large deployed space structure like what we are talking about here: M2P2 propulsion. With the large structure already existing for the support of the solar power panels/ films, it might be possible to exert much better control over and couple much better momentum transfer from the plasma cloud/ sail of the M2P2 drive- especially if the structure was built with that in mind.There may be a problem of premature wear on the solar elements from the plasma, but that is an unknown, and it might not be a problem with the right plasma cloud management.-my two cents
M2P2 won't work until outside of Earth magnetic field - when all of the main work is already done.
Energia retained the electric engines of the 1969 MEK design but dropped the nuclear ractor for its 1989 Mars expedition design. This spacecraft used the same thruster arrays requiring the same power output (15 MW) as the 1986 nuclear design. But in this case two enormous panels, each 200 m x 200 m would generate a total of 15 MW of power at earth. The use of ultra-thin (less than 50 micrometer) / low mass (0.2 kg per square meter) photovoltaic cells with a high specific power value (up to 200 W per square meter) minimised the weight of these vast arrays. The total mass of the electric engines, structure, and solar panels was 40 tonnes. The power generated would be used primarily by two ion engine clusters mounted perpendicular to the living block. In high-power mode these would have a specific impulse of 3500 seconds. They would consume 165 tonnes of xenon propellant during the voyage (of 355 tonnes total spacecraft mass).
Quote from: Nathan on 02/13/2010 12:41 amM2P2 won't work until outside of Earth magnetic field - when all of the main work is already done.Good point. So how about this: when the craft is inside a planetary magnetosphere it won't waste gasses trying to sustain a plasma cloud. Inside a planetary magnetic field the craft could use the large reach of its structure and the existing magnetic field control hardware that it normally uses to shepherd its plasma cloud to instead thrust against the planetary magnetic field directly- like a glorified version of the "tether propulsion" concept..Maybe a reconfigurable structure would be valuable in this case, but either way I think this kind of craft would look really alien- a spiders web of conducting coils and loops and gas vents amid fields of solar panels.
Mhm, the last actual SEP reference mission I have heard of was Energia's updated MEK proposal (see below). They baselined a cluster of many ion thrusters, 120,000 m² of solar arrays (72 squares about 40m x 40m), the use of xenon gas and a nominal mission time of 2 1/2 years (so no VASIMR Ad Astra type claims of high-energy trajectories). The old MEK mission baselined a total mission weight of 400mt, nor sure if that is still the case for the 2005 updated MEK mission (the article below speaks of a total of 280mt xenon gas as fuel).Anyway, I think their concept shows quite well how large the solar arrays would be compared to the crew compartment. At a 100W/m² efficiency at 1AU, this assembly would provide 12MW or quite enough for the Ad Astra 85day to Mars reference mission using VASIMR based mission IF the solar panels + supporting structure aren't prohibitively heavy.http://www.ng.ru/science/2005-01-12/15_heart.html
Any data on how they dealt with the Van Allen belts? This is key to low thrust trajectories.
In order to clear the earth's radiation belts as quickly as possible, the mission profile began with a relatively 'high thrust' acceleration by the engines in a spiral from low earth orbit to 40,000 km. This altitude would be achieved in 29 days. Thereafter the engines would shift into their normal regime, with a lower thrust but higher specific impulse. The spacecraft would reach escape velocity after a total of 100 days of firing, followed by a 270 day coast to Mars. A 38 day braking manoeuvre would bring the spacecraft into Mars orbit. 30 days would be spent in Mars orbit, during one week of which the crew would descend to the surface. It would take 28 days to accelerate away from Mars, followed by a 250 day coast to earth. The crew would enter their return vehicle and re-enter the earth's atmosphere at 13.5 km/sec.
How does solar-dynamic power generation compare with photovoltaic? I'm thinking in terms of the Brayton-cycle turbine proposed for the TAAT power-beaming demo and possibly for NAUTILUS-X too. Does solar-dynamic offer superior specific power under any circumstances? Is its advantage that it is less susceptible to radiation?
What about long-term durability? If NAUTILUS-X is supposed to operate for years, is it possible that a solar-dynamic system would suffer less degradation over, say, a decade?
So what reason could there be for TAAT to propose solar dynamic?
Quote from: Proponent on 02/09/2011 03:42 amSo what reason could there be for TAAT to propose solar dynamic?A guess. Cost?
Quote from: A_M_Swallow on 02/09/2011 04:11 amQuote from: Proponent on 02/09/2011 03:42 amSo what reason could there be for TAAT to propose solar dynamic?A guess. Cost?Also mass a solar reflector for a solar dynamic generator can be a very light weight inflatable structure.
Quote from: Patchouli on 02/12/2011 03:50 amQuote from: A_M_Swallow on 02/09/2011 04:11 amQuote from: Proponent on 02/09/2011 03:42 amSo what reason could there be for TAAT to propose solar dynamic?A guess. Cost?Also mass a solar reflector for a solar dynamic generator can be a very light weight inflatable structure.The solar dynamic generator itself is very heavy. Also, no reason a thin-film photovoltaic array can't be just as light as just the reflector you posted, but without the need for the heavy generator and without the precise pointing requirements.
Okay, enough dancing around the issue. What is the capabilities, in terms of watts per kilogram, of solar dynamic? I want relatively hard figures, not stuff pulled out of one's nether regions.{snip}
In Phase I, we completed the design of a 12 kW dual-opposed free-piston Stirling convertor and controller. The convertor is shown in Figure 1. The convertor mass is calculated as 188 kg not includingthe piping shown, and the controller is projected at 68 kg for a total of 256 kg. The machine operates at 60 Hz at an operating pressure of 6.2 MPa (absolute). The convertor is approximately 0.3 m (11.9 in.) indiameter and 1.1 m (43 in.) long.
Quote from: Robotbeat on 02/14/2011 04:00 pmOkay, enough dancing around the issue. What is the capabilities, in terms of watts per kilogram, of solar dynamic? I want relatively hard figures, not stuff pulled out of one's nether regions.{snip}I have found a report on a Stirling convertor being developed for use on the Moon. A space tug would also need radiators, mirror and sun tracking hardware.12kW * 1000 / 256kg = 46.8 W/kgOr excluding the controller 12kW * 1000 / 188kg = 63.8 W/kgTitle "Free-Piston Stirling Power Conversion Unit forFission Surface Power, Phase I Final ReportNASA/CR—2010-216750"http://gltrs.grc.nasa.gov/reports/2010/CR-2010-216750.pdfQuoteIn Phase I, we completed the design of a 12 kW dual-opposed free-piston Stirling convertor and controller. The convertor is shown in Figure 1. The convertor mass is calculated as 188 kg not includingthe piping shown, and the controller is projected at 68 kg for a total of 256 kg. The machine operates at 60 Hz at an operating pressure of 6.2 MPa (absolute). The convertor is approximately 0.3 m (11.9 in.) indiameter and 1.1 m (43 in.) long.
Quote from: A_M_Swallow on 02/16/2011 02:10 amQuote from: Robotbeat on 02/14/2011 04:00 pmOkay, enough dancing around the issue. What is the capabilities, in terms of watts per kilogram, of solar dynamic? I want relatively hard figures, not stuff pulled out of one's nether regions.{snip}I have found a report on a Stirling convertor being developed for use on the Moon. A space tug would also need radiators, mirror and sun tracking hardware.12kW * 1000 / 256kg = 46.8 W/kgOr excluding the controller 12kW * 1000 / 188kg = 63.8 W/kgTitle "Free-Piston Stirling Power Conversion Unit forFission Surface Power, Phase I Final ReportNASA/CR—2010-216750"http://gltrs.grc.nasa.gov/reports/2010/CR-2010-216750.pdfQuoteIn Phase I, we completed the design of a 12 kW dual-opposed free-piston Stirling convertor and controller. The convertor is shown in Figure 1. The convertor mass is calculated as 188 kg not includingthe piping shown, and the controller is projected at 68 kg for a total of 256 kg. The machine operates at 60 Hz at an operating pressure of 6.2 MPa (absolute). The convertor is approximately 0.3 m (11.9 in.) indiameter and 1.1 m (43 in.) long.Thanks. So, it appears solar dynamic is not competitive, on a pound-for-pound basis, with photovoltaics.