It is simpler if the port and starboard solar arrays use the same design but it is not necessary. Keeping the ISS in orbit until 2020 would allow a 6 - 7 year soak test of rival designs.From the above figures20 metres per day for 7 years = 20 * 365.25 * 7 = 51,135 metresA 15 minute VASIMR burn uses 0.085 kg of propellant and 3.4 hours per day are needed. 15 minutes = 0.25 hoursTotal propellant = (0.085/0.25) * 3.4 * 365.25 * 7 = 2,956 kgAssume solar array is 150 W per kg UltraFlex BOL and 300 kW is needed300,000/150 = 2,000 kgAllocate mass of VASIMR thrusters, power converters, cables and cooling system to the experiment. Extra mass is 2,956 kg + 2,000 kg = 4,956 kg.With 10% mass reserve 5.5 mT.It will be interesting to know the mass and cost difference of using chemical fuel for the station keeping.
Quote from: A_M_Swallow on 12/04/2009 08:50 pmIt is simpler if the port and starboard solar arrays use the same design but it is not necessary. Keeping the ISS in orbit until 2020 would allow a 6 - 7 year soak test of rival designs.From the above figures20 metres per day for 7 years = 20 * 365.25 * 7 = 51,135 metresA 15 minute VASIMR burn uses 0.085 kg of propellant and 3.4 hours per day are needed. 15 minutes = 0.25 hoursTotal propellant = (0.085/0.25) * 3.4 * 365.25 * 7 = 2,956 kgAssume solar array is 150 W per kg UltraFlex BOL and 300 kW is needed300,000/150 = 2,000 kgAllocate mass of VASIMR thrusters, power converters, cables and cooling system to the experiment. Extra mass is 2,956 kg + 2,000 kg = 4,956 kg.With 10% mass reserve 5.5 mT.It will be interesting to know the mass and cost difference of using chemical fuel for the station keeping.I'd like to see what the fuel requirements are to change the orbital inclination from 56 degrees to 23 degrees to be in line with lunar orbital plane, using VF-200.
I'd like to see what the fuel requirements are to change the orbital inclination from 56 degrees to 23 degrees to be in line with lunar orbital plane, using VF-200.
Quote from: mlorrey on 12/04/2009 10:23 pmI'd like to see what the fuel requirements are to change the orbital inclination from 56 degrees to 23 degrees to be in line with lunar orbital plane, using VF-200.I don't think it would be useful, because nodal regression will rotate your orbit plane out of moon plane.
Quote from: Stephan on 12/05/2009 08:20 amQuote from: mlorrey on 12/04/2009 10:23 pmI'd like to see what the fuel requirements are to change the orbital inclination from 56 degrees to 23 degrees to be in line with lunar orbital plane, using VF-200.I don't think it would be useful, because nodal regression will rotate your orbit plane out of moon plane.It will be useful at least once per day even with regression.
Quote from: mlorrey on 12/05/2009 10:02 amQuote from: Stephan on 12/05/2009 08:20 amQuote from: mlorrey on 12/04/2009 10:23 pmI'd like to see what the fuel requirements are to change the orbital inclination from 56 degrees to 23 degrees to be in line with lunar orbital plane, using VF-200.I don't think it would be useful, because nodal regression will rotate your orbit plane out of moon plane.It will be useful at least once per day even with regression.An alternative to launching 29 metric tons of propellant to move the ISS to 23 degrees is to launch a Bigelow Transhab space station.Call it the Earth Tropical Inter-planetary Space Station.Facilities4 docking ports (Earth, inter-planetary, emergency return and spare).Sleeping quarters for crew and passengers.Robot arm to transfer cargo.Control room.Station keeping thrusters.Propellant depot.
For changing the inclination of the ISS orbit an electrodynamic tether with energy store is far and way the most effective method. Virtually no additional energy is required (just battery and system losses) as the final orbit has similar energy to the initial orbit.I can't find the study but I think the time frame was of the order of a year. The battery needs to charge/discharge every orbit so about 6,000 cylces, with high Power / Energy rates. This suits some of the new Li-ion automotive batteries.
Quote from: alexterrell on 12/06/2009 01:10 pmFor changing the inclination of the ISS orbit an electrodynamic tether with energy store is far and way the most effective method. Virtually no additional energy is required (just battery and system losses) as the final orbit has similar energy to the initial orbit.I can't find the study but I think the time frame was of the order of a year. The battery needs to charge/discharge every orbit so about 6,000 cylces, with high Power / Energy rates. This suits some of the new Li-ion automotive batteries. Although they currently have lower energy density, supercapacitors have much higher specific power and lower recharge/discharge losses as any kind of battery, besides having longer lifetimes. It's quite likely they would be preferable to lithium ion batteries for this application.
How hot can a liquid sodium heat pump get? If you could get the radiators up to 1200 K, you could do more than 400 MW with a couple of square radiator panels 30 metres on a side.Just make sure the rest of the spacecraft is real shiny....and, of course, you have to have a reactor hot-side temperature pushing 2800°F to get 200 MW of useful power out of it with a cold side that hot...You'd have to do a tradeoff between radiator compactness and combined power cycle efficiency, maybe with practical considerations thrown in just for the heck of it. I don't have actual experience in this area (and I'm super busy right now), so I'll bow out for the moment...Really, just build the VASIMR engine with a cooling loop. There's nothing 35% of 200 MWe will do to your radiator problems that 67% of 600 MWth won't.
What makes VASIMR superior to other forms of electric propulsion, for example MPD-Thrusters?
Quote from: DLR on 08/16/2009 09:34 amWhat makes VASIMR superior to other forms of electric propulsion, for example MPD-Thrusters?I searched through all the pages on this topic and didn't see one of the other major selling points for VASIMR beside variability: no cathode, arrays, or grids to degrade since it uses a helicon to heat the plasma (major drawback of MPD). I believe the only other thruster that compares to VASIMR is the HDLT being developed at ANU.
Quote from: mlorrey on 12/04/2009 10:23 pmI'd like to see what the fuel requirements are to change the orbital inclination from 56 degrees to 23 degrees to be in line with lunar orbital plane, using VF-200. AssumingISS mass = 350 mTAverage velocity = 27,743 km/h = 7,706.6 m/sVASIMR VF-200 force is 5 newtons at Isp 5000 secondsPropellant = 0.085 kg per quarter hour = 0.340 kg/hourInclination change (Delta-I) is 56 degrees to 23 degreesStart and finish orbits are circularDelta_V = 2 v sin( delta_I / 2)* = 2 * 7706 * sin( (56-23) / 2) = 4377 m/sa = F/mt = Delta_V / a = Delta_V * m / F* = 7706 * 350000 / 5 = 306,390,000 seconds or 85,108 hoursReal time. A SEP does not work when in the Earth's shadow and 4.3 hours a day are needed to handle drag. So burn hours per day is 24/2 - 4.3 = 7.7 hours per day (controversial)Time to change orbit is 85,108 / 7.7 = 11,053 days or 30.26 yearsMass of propellant is 85,108 * 0.34 = 28,937 kgSo using a single VF-200 to move the ISS to 23 degree orbit will take over 30 years and 29 mT of propellant.
And what about the Pulsed inductive thrusters such as in this nasa study http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930023164_1993023164.pdf , which also offers multi-mw thrusters (without the cathode erosion problem like vasimr).
Quote from: isa_guy on 02/09/2010 05:14 pmAnd what about the Pulsed inductive thrusters such as in this nasa study http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930023164_1993023164.pdf , which also offers multi-mw thrusters (without the cathode erosion problem like vasimr).What cathode in the VASIMR are you referring to? Last time I looked, the propellant ionization process was accomplished by the contactless first stage helicon antenna.
And what about the Pulsed inductive thrusters such as in this nasa study http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930023164_1993023164.pdf , which also offers multi-mw thrusters (without the cathode erosion problem like vasimr) .
...So I can assume you can use other fuels than hydrogen? Why not an O2 rocket? O2 is more plentiful, and a large byproduct of Lunar mining.