If you tripled the order for the 650kg European Robotic Arm, and launched a pair of the (somewhere between 100 and 500kg) phase 1 prototype 20kw ROSA solar array winglets that NASA has already funded construction of, and sent up an extra ton of nickel-hydrogen batteries, and a pair of 7kw NEXT ion thrusters (100kg) that have already been extensively tested & flight-qualified, and 2 tons of xenon propellant, you could reboost the ISS for around 10 years at the present altitude, for 5400kg of payload. Add on 1T of storeable propellant for the ~1 emergency debris avoidance burn per year and you've got yourself a solution in two Dragon Cargo launches.
Also, constant thrust is not a viable solution.
Quote from: Jim on 07/04/2014 07:20 pmAlso, constant thrust is not a viable solution.I won't mean an absolute solution for everything. You'd wan to do desats and DAMs. But I've been wondering if you could use SEP to exactly counteract the aero drag. Wouldn't that actually improve microgravity and solve the altitude loss problem?
Quote from: baldusi on 07/04/2014 07:48 pmQuote from: Jim on 07/04/2014 07:20 pmAlso, constant thrust is not a viable solution.I won't mean an absolute solution for everything. You'd wan to do desats and DAMs. But I've been wondering if you could use SEP to exactly counteract the aero drag. Wouldn't that actually improve microgravity and solve the altitude loss problem?But how steady is the thrust from SEP? It could easily add small vibrations and degrade the microgravity environment. Better off coasting and use the occasional burn to raise the station.
But how steady is the thrust from SEP? It could easily add small vibrations and degrade the microgravity environment.
-As long as we are imagining, I would imagine the best way to keep ISS flying past 2020 is to invite China to participate in the ISS, but perhaps it's too late if Russia and China are already making plans.-angst
Quote from: Sean Lynch on 07/04/2014 04:52 amQuote from: Burninate on 07/04/2014 03:44 amIf you tripled the order for the 650kg European Robotic Arm, and launched a pair of the (somewhere between 100 and 500kg) phase 1 prototype 20kw ROSA solar array winglets that NASA has already funded construction of, and sent up an extra ton of nickel-hydrogen batteries, and a pair of 7kw NEXT ion thrusters (100kg) that have already been extensively tested & flight-qualified, and 2 tons of xenon propellant, you could reboost the ISS for around 10 years at the present altitude, for 5400kg of payload. Add on 1T of storeable propellant for the ~1 emergency debris avoidance burn per year and you've got yourself a solution in two Dragon Cargo launches.Appreciate your solution oriented comment Burninate. I love the idea of using solar electric propulsion.I assume by "storable propellant" for collision avoidance you mean Xenon?We need to know today if the Russians are really planning on quitting the ISS and if they are planning on taking Zvezda with them, because the dynamics and harmonics of the ISS are complicated. Would the propulsion systems be attached to the Z-truss? Can Dextre climb "up" there?Perhaps someone reading this has a friend at Boeing familiar with ISS dynamics that could help us out.1 ton of hypergolic propellant at 235s Isp (this is from SuperDraco, we don't have numbers for the Draco) provides only ~5.5m/s boost, and I'm not counting on the lifetime of the thruster to be very long - just be there for an extra 1-2m/s in an emergency. 2 tons of xenon at 4100s Isp provide 191m/s, which would fight aerodynamic drag to maintain altitude.
Quote from: Burninate on 07/04/2014 03:44 amIf you tripled the order for the 650kg European Robotic Arm, and launched a pair of the (somewhere between 100 and 500kg) phase 1 prototype 20kw ROSA solar array winglets that NASA has already funded construction of, and sent up an extra ton of nickel-hydrogen batteries, and a pair of 7kw NEXT ion thrusters (100kg) that have already been extensively tested & flight-qualified, and 2 tons of xenon propellant, you could reboost the ISS for around 10 years at the present altitude, for 5400kg of payload. Add on 1T of storeable propellant for the ~1 emergency debris avoidance burn per year and you've got yourself a solution in two Dragon Cargo launches.Appreciate your solution oriented comment Burninate. I love the idea of using solar electric propulsion.I assume by "storable propellant" for collision avoidance you mean Xenon?We need to know today if the Russians are really planning on quitting the ISS and if they are planning on taking Zvezda with them, because the dynamics and harmonics of the ISS are complicated. Would the propulsion systems be attached to the Z-truss? Can Dextre climb "up" there?Perhaps someone reading this has a friend at Boeing familiar with ISS dynamics that could help us out.
Quote from: RonM on 07/04/2014 07:56 pmQuote from: baldusi on 07/04/2014 07:48 pmQuote from: Jim on 07/04/2014 07:20 pmAlso, constant thrust is not a viable solution.I won't mean an absolute solution for everything. You'd wan to do desats and DAMs. But I've been wondering if you could use SEP to exactly counteract the aero drag. Wouldn't that actually improve microgravity and solve the altitude loss problem?But how steady is the thrust from SEP? It could easily add small vibrations and degrade the microgravity environment. Better off coasting and use the occasional burn to raise the station.Are you aware that we are talking about >1N thrust for a 400 tonne station?
Quote from: RonM on 07/04/2014 07:56 pmBut how steady is the thrust from SEP? It could easily add small vibrations and degrade the microgravity environment.In principle, it can be extremely good, GOCE for example. However, that doesn't mean such an approach is viable for the ISS.
The cheapest approach would be to have US cargo vehicles provide reboost and roll control, much as Progress does today.Please advise why Progress can perform these functions, but Dragon or Cygnus cannot.
Attached is an interesting concept: ISS Electrodynamic Tether Reboost Study.It's good to use our imaginations in thinking of ways to keep ISS flying. SEP, VASIMIR, Solar Sails, or even political solutions such as PFOP (pork fueled oars and paddles). Having said that, it would be better in my opinion to keep things as simple as possible because time is not our friend.CST-100 offers a huge advantage over Dragon V2 if CST-100 can provide ISS reboost:http://forum.nasaspaceflight.com/index.php?topic=22125.msg928528#msg928528We need a near term fix, but let's encourage bright minds to imagine long term solutions that may be deployed in the future. Even if we can use visiting vehicles for reboost, ISS still requires independent means of reboost and collision avoidance in case of launch disasters, etc.Quote-As long as we are imagining, I would imagine the best way to keep ISS flying past 2020 is to invite China to participate in the ISS, but perhaps it's too late if Russia and China are already making plans.-angst
Quote from: Burninate on 07/04/2014 03:44 amIf you tripled the order for the 650kg European Robotic Arm, and launched a pair of the (somewhere between 100 and 500kg) phase 1 prototype 20kw ROSA solar array winglets that NASA has already funded construction of, and sent up an extra ton of nickel-hydrogen batteries, and a pair of 7kw NEXT ion thrusters (100kg) that have already been extensively tested & flight-qualified, and 2 tons of xenon propellant, you could reboost the ISS for around 10 years at the present altitude, for 5400kg of payload. Add on 1T of storeable propellant for the ~1 emergency debris avoidance burn per year and you've got yourself a solution in two Dragon Cargo launches.Huh?What the heck are the arms for?And what says the ISS can control more than 1?What nickel-hydrogen batteries? the ISS is moving away from them.No CMG desat.Hence this is no solution.Also, constant thrust is not a viable solution.
Answer in new thread. Arms are overkill gimbals with translation. NiH batts because I assumed that was the default. CMG desat via off-axis gimballing. Arm control is a matter of software. Constant thrust seems a perfectly viable solution.