Quote from: Impaler on 03/04/2015 05:15 pmHere is the solar array, it's from the Airforce and is called RAPDAR (Roll-out And Passively Deployed Array).It appears to be is a thin-film solar membrane on a memory shape material that unrolls in the warmth of the sun.It's not rigid? How will you keep the surface perpendicular to the sun's rays?...
Here is the solar array, it's from the Airforce and is called RAPDAR (Roll-out And Passively Deployed Array).It appears to be is a thin-film solar membrane on a memory shape material that unrolls in the warmth of the sun.
Here is the solar array, it's from the Airforce and is called RAPDAR (Roll-out And Passively Deployed Array).It appears to be is a thin-film solar membrane on a memory shape material that unrolls in the warmth of the sun.http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CCoQFjAA&url=http%3A%2F%2Fwww.dtic.mil%2Fcgi-bin%2FGetTRDoc%3FAD%3Dada444956&ei=E0b3VLmZAoapogSclYGYDw&usg=AFQjCNGIl9ZWrPlnvVDUGJO1T3-RcwZOOg&sig2=NOHULiIg5knnM_pVDUIBNAhttp://www.nsti.org/Nanotech2009/abs.html?i=1497
Why would you characterize IKAROS as speculative? It already flew.A fairer suggestion would be that it is an unorthodox space structure due to its very low stiffness, and thus would require more care than usual for designing your spacecraft correctly, but I don't believe "speculative" makes sense, there....and I'm sorry for jumping on that word (when in all likelihood we're in violent agreement), I just think it's an important distinction to make.People have been testing (and preparing for launch) solar sail craft for a while, now. An IKAROS-esque solar array would be no more speculative than that sort of structure. Clearly wouldn't be characterized as fantasy.
As far as I'm aware, the rapdar stuff is rolable. I'd be interested in some figures for the power to area as well. I'm thinking of doing a 3D model of one of these things. I was thinking that you could unfurl the solars in petals from the central core. You could even put a gentle spin on the ship to stabilize them.On that subject, how much fuel would you need for an X3 hall thruster vehicle if you were to try to get to Mars in 40 days? It might be wasteful, but how does it compare to having to carry all the extra consumables for a crew for the extra months? Also, if you were an astronaut, and they told you you could get to Mars in 40 days, or you would have to spend an extra 6 months living in a balloon the size of a school bus, what would your reaction be?
I think a good proposal for a small-sat tech demo would be a "solar power sail" type craft with extremely good alpha.IKAROS-style high voltage solar array (make it very long and skinny so that it demonstrates scalability) hooked directly up to a very high specific power thruster (built for high operating temperature so that extra heat rejection using a complicated radiator system is not required) using, say, solid-state relays. I bet you could demonstrate 1-2kW/kg OVERALL specific power (but with a system mass of, say, 100-200kg). It'd be a challenge, but should definitely be possible and would seriously change the whole calculus of SEP....then again, we're still waiting for even modest SEP propulsion tech on cubesats...
Quote from: tea monster on 03/04/2015 07:47 pmAs far as I'm aware, the rapdar stuff is rolable. I'd be interested in some figures for the power to area as well. I'm thinking of doing a 3D model of one of these things. I was thinking that you could unfurl the solars in petals from the central core. You could even put a gentle spin on the ship to stabilize them.On that subject, how much fuel would you need for an X3 hall thruster vehicle if you were to try to get to Mars in 40 days? It might be wasteful, but how does it compare to having to carry all the extra consumables for a crew for the extra months? Also, if you were an astronaut, and they told you you could get to Mars in 40 days, or you would have to spend an extra 6 months living in a balloon the size of a school bus, what would your reaction be?It's not that you'd need much propellant for Hall thrusters, it's that you'd need lots and lots of them. The mass of the thrusters themselves would dominate if you wanted enough thrust to get to Mars in 40 days. Hence the idea for VASIMR -- better thrust-to-weight, at the cost of worse Isp (so more prop needed).
Quote from: ChrisWilson68 on 03/05/2015 05:39 amQuote from: tea monster on 03/04/2015 07:47 pmAs far as I'm aware, the rapdar stuff is rolable. I'd be interested in some figures for the power to area as well. I'm thinking of doing a 3D model of one of these things. I was thinking that you could unfurl the solars in petals from the central core. You could even put a gentle spin on the ship to stabilize them.On that subject, how much fuel would you need for an X3 hall thruster vehicle if you were to try to get to Mars in 40 days? It might be wasteful, but how does it compare to having to carry all the extra consumables for a crew for the extra months? Also, if you were an astronaut, and they told you you could get to Mars in 40 days, or you would have to spend an extra 6 months living in a balloon the size of a school bus, what would your reaction be?It's not that you'd need much propellant for Hall thrusters, it's that you'd need lots and lots of them. The mass of the thrusters themselves would dominate if you wanted enough thrust to get to Mars in 40 days. Hence the idea for VASIMR -- better thrust-to-weight, at the cost of worse Isp (so more prop needed).That's backwards, Halls have higher power to mass then VASIMR. VASIMR has higher ISP range but in the area where the ISP ranges overlap (the low end of VASIMR, the High end of Hall) the Hall has better thrust to mass ratio. VASIMR would be the choice for a very slow trajectory with minimal propellent usage by utilizing it at near the maximum ISP it's capable of.
Maybe a bit off-topic question, but.. cout a VASIMIR engine be used to take the ISS to Mars? Not necessarily as a spacecraft.., but maybe as a support station in Mars orbit. Even if it takes 5-6 yrs to get there.. better than being decommissioned.
No your still completely backwards, ISP and thrust are inversely proportional, the high ISP range is thus the low thrust range. HALL is low to medium ISP, VASMIR is medium to high ISP.At the medium ISP where an apples to apples comparison can be made HALL has better thrust to mass, this has been pointed out by multiple people already in this thread and in the electric propulsion thread, VASIMR is a very massive system with an impressive ISP range and high maximum ISP, but at the low end it's not competitive with a modern HALL.
I had been trying to find the numbers on the MegaROSA and how it compared with original ROSA, I had thought the power density was much lower around 150W/kg for ROSA and couldn't find a number for MegaROSA, your link doesn't seem to have a reference to power density though, do you have one that dose?
I was thinking that this would be an excellent case for a Lagrange point 'Gateway Station'. You could set up a station there with a propellent depot and a manipulator telerobot. If the Telerobot was good enough, you may not even have to have the station permanently manned.
No your still completely backwards, ISP and thrust are inversely proportional, the high ISP range is thus the low thrust range. HALL is low to medium ISP, VASMIR is medium to high ISP.