Quote from: Hop_David on 03/04/2015 11:14 pmQuote 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?...It doesn't HAVE to be perfectly rigid. If you're off by a few degrees, there's only incredibly slight reduction in power. And it is deployed, so launch harmonics isn't a concern.This is different from a traditional antenna or a concentrating solar array which DO have to be rigid because of their high pointing requirements (phased array antenna can compensate for this).
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.
Big welcome to the site's forum to Mr. Greason, two posts back!Quote from: tea monster on 03/05/2015 02:40 pmI 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. Gateway you say? http://www.nasaspaceflight.com/tag/gateway/
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.
Quote from: Robotbeat on 03/05/2015 03:35 amWhy 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.I think we are generally in agreement, while IKAROS has flown the power system your extrapolating at 1 kw/kg is 'derived' from it and has some significant engineering challenges when being scaled up to the size (multiple MW) that would be the kind of total power needs that would be desired, demonstrating scale is a big part of making the specific power number relevant for SEP. So I'm simply calling any specific power density goal which is not the design goal to a current development program a 'speculative' one. Essentially I assume all current development programs that are just refining current tech will meat their goals (admittedly optimistic) but anything outside of a program has some chance of not being delivered upon and thus is a 'speculation'. Naturally their are huge ranges between very likely to be delivered upon and very unlikely to be delivered upon speculative systems. When the speculation exceeds what even the best known materials or some very obvious thermodynamic or practicality limits then I'd call it fantasy, and I'd say that when it comes to solar power density the >2kw/kg can be called fantasy, 250W-2kw can be called speculative, and <250W/kg can be taken to the bank.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?
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.
Quote from: Robotbeat on 03/05/2015 02:42 amQuote from: Hop_David on 03/04/2015 11:14 pmQuote 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?...It doesn't HAVE to be perfectly rigid. If you're off by a few degrees, there's only incredibly slight reduction in power. And it is deployed, so launch harmonics isn't a concern.This is different from a traditional antenna or a concentrating solar array which DO have to be rigid because of their high pointing requirements (phased array antenna can compensate for this).I would think the concern would be thermally induced occilation. Parts of the array that are a few degrees off would be cooler than those that aren't. Might this not result in disaster if there is no means such as actuators to keep harmonic flexing from increasing like the Hubble arrays demonstrated? The inference seems to be that concentrators need so much greater rigidity that their more than an order of magnitude advantage (as demonstrated by the L'Garde prototype) would somehow be eaten up by added structure. This makes no sense to me.
This second cuts propellant usage substantially, but has departure windows that are orbital+synodic instead of monthly+synodic, and does not offer an orbital location that is reusable across synods, as far as I can tell: One departure mission, one station.
Quote from: Burninate on 03/05/2015 10:49 pmThis second cuts propellant usage substantially, but has departure windows that are orbital+synodic instead of monthly+synodic, and does not offer an orbital location that is reusable across synods, as far as I can tell: One departure mission, one station.While I am skeptical that SEP would remotely benefit from a periapsis drop and kick-stage burn (better to use the propellent mass in the SEP system normally). This departure timing dose not seem too hard to overcome, the low DeltaV window for transit for a conventional rocket is nearly a month long so we should be able to consistently get a departure, though admittedly it is an instantaneous window which can be dicy. Also depending on which side of the Earth we go around we have two possible exit trajectories which are rotating around so one should be passing any desired direction every 15 days if they are equally spaced (no clue if they are).
A rough approximate figure from the phase I ROSA winglets is ~3 square meter per kW.
Why would you characterize IKAROS as speculative? It already flew.
Quote from: Robotbeat on 03/05/2015 03:35 amWhy would you characterize IKAROS as speculative? It already flew.Sunlight's power density at Venus is more than double than at 1 A.U.And at 1.52 A.U. Mars distance, it's less than half, more like 2/5.So I don't know how applicable Ikaros' 1 kWe/kg is to solar arrays on an MTV.Also at perihelion from an earth to Venus Hohmann, the mast need only move at 2 degrees per day to stay aligned with the sun. In LEO a mast would need to move 4 degrees per minute.
I.e. this sort of thing, but with very thin solar cells operating at high voltage:(The mass of that thing is just 20kg for 1000 m^2 of area... solar cells would add to the weight as would the thruster, but that can be calculated in a relatively straightforward manner.)
Nah, the 1kWe/kg was calculated (by me, just so we're clear...) assuming 1 AU, not Venus' orbit.
Plans to test VASIMR on ISS apparently cancelled. Paywalled source: http://sen.com/blogs/irene-klotz/nasa-nixes-ad-astra-rocket-test-on-the-space-station
Quote from: cdleonard on 03/11/2015 12:31 pmPlans to test VASIMR on ISS apparently cancelled. Paywalled source: http://sen.com/blogs/irene-klotz/nasa-nixes-ad-astra-rocket-test-on-the-space-stationEither kill the VASIMR or find a way to attach it and solar panes to a spacecraft. Since they have navigation and RCS a Dragon or Cygnus would do nicely.