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Post by the light works on Jun 7, 2014 20:57:45 GMT
The thrust you get from a solar sail is considerably smaller than what you get from a rocket. Therefore, for a solar-sail to get up to the same sort of velocity as a rocket it has to apply that thrust for longer - ie ideally be as close to the sun as you can manage for as long as possible. Sideways movement, 'leeway' of the solar variety, isn't a major issue and would be factored into your calculations - apart from anything else the orbit would increase as the speed increased anyway. The 'orbit' would therefore be a spiral one way or another, the trick is to get that spiral as tight as you can manage at least in the initial stages so the speed builds up as high as can be managed. Again, this is assuming that you are trying to head out of the solar system. If you just want to reach another planet within the solar system then you don't need - and probably wouldn't want - speeds that high. actually, they are apparently already using solar sail technology to fine tune interplanetary trajectories. but again, with a solar sail, if you want it to be efficient, it will not be a spiral - it will be either a progressive ellipse or a single pass, followed by a hyperbolic trajectory; and that will get you going as fast as you can you can enter orbit from without retro rockets. again: the only way to keep yourself close to the sun when using the sun as a source of thrust - is to reduce your the amount of thrust you are using, which kind of defeats the purpose. |
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Post by the light works on Jun 7, 2014 21:01:57 GMT
The sun "Radiates" a lot of energy, in many forms, radio waves, Light, light invisible to human eyes, and all points between. Using it to power a space craft would involve collection of energy and using that to create propulsion. Sailing on the solar winds?... I propose to do that you would perhaps need to try to orbit the sun for some time until you attain a certain speed and then use that as well as a slingshot effect to get on the move. That way, you use Gravity as well as other power sources?... if you are drawing direct thrust from solar wind, you might have a bit of trouble tacking, as a solar sail spacecraft is more a paraglider than a sailboat. - space gives you nothing for your keel to act against. to revisit the original comment you challenged. |
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Post by Cybermortis on Jun 7, 2014 21:03:41 GMT
www.nasa.gov/mission_pages/tdm/solarsail/index.html#.U5N9E3JdWtNNASA will be launching a solar sail to test the way they work, and how effectively, later this year. Note; When I mentioned above that solar sails provide considerably less thrust than conventional rockets I wasn't kidding. Turns out that the craft they will be launching will have the largest solar sail ever deployed, with a surface area of 12 or 13,000 square metres. (Unhelpfully both figures are listed for the same craft in different places). The total thrust this will provide is 0.01 newtons. Or about the same amount of thrust as a small packet of sugar.
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Post by the light works on Jun 7, 2014 21:21:44 GMT
www.nasa.gov/mission_pages/tdm/solarsail/index.html#.U5N9E3JdWtNNASA will be launching a solar sail to test the way they work, and how effectively, later this year. Note; When I mentioned above that solar sails provide considerably less thrust than conventional rockets I wasn't kidding. Turns out that the craft they will be launching will have the largest solar sail ever deployed, with a surface area of 12 or 13,000 square metres. (Unhelpfully both figures are listed for the same craft in different places). The total thrust this will provide is 0.01 newtons. Or about the same amount of thrust as a small packet of sugar. well, sugar doesn't have much thrust at all... but it appears that this measurement is based on being at Earth's orbital elevation above the sun, which means the thrust will increase significantly if it is sent closer to the sun. it does further reinforce the perception that it is technology best used for cargo drones, though - although one of the many articles I've gone through today suggested about a 2 year turnaround to the inner planets; which is pretty brisk, all things considered. |
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Post by silverdragon on Jun 8, 2014 9:45:28 GMT
That the problem with Metric, its liable to change dependant on the designers intake of caffeine.
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Post by the light works on Jun 8, 2014 13:53:33 GMT
That the problem with Metric, its liable to change dependant on the designers intake of caffeine. I would guess the smaller size it the spec for the sail area, while the larger is the size of hole it will fit through. |
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Post by Cybermortis on Jun 8, 2014 14:31:42 GMT
No, both are specifically listed as the surface area of the sail and were used in relation to it being the largest even deployed in space.
Either someone used the wrong figure for some reason, or one is the size of the original design and the second the actual size. I'd guess the most reasonable explanation is that they decided to make the sail a little smaller to save on weight, or so that it fitted more easily into the available space - the sail is from what I can tell designed so it can be deployed and possibly retracted while in flight.
It would certainly make sense to design it so you could furl the sail back in to protect it. If nothing else I would imagine that the sail might cause some problems if deployed when in orbit or during docking manoeuvres if such craft were going to be used for resupply missions.
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Post by the light works on Jun 8, 2014 14:36:44 GMT
No, both are specifically listed as the surface area of the sail and were used in relation to it being the largest even deployed in space. Either someone used the wrong figure for some reason, or one is the size of the original design and the second the actual size. I'd guess the most reasonable explanation is that they decided to make the sail a little smaller to save on weight, or so that it fitted more easily into the available space - the sail is from what I can tell designed so it can be deployed and possibly retracted while in flight. It would certainly make sense to design it so you could furl the sail back in to protect it. If nothing else I would imagine that the sail might cause some problems if deployed when in orbit or during docking manoeuvres if such craft were going to be used for resupply missions. or it was simply a rounding fault. one person truncated it for convenience, and the other padded it for impressiveness. |
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Post by ponytail61 on Jun 8, 2014 18:11:31 GMT
They also have different weights for the thing.
Yet collapsed it weighs just 70 pounds and takes up about as much space as a dishwasher...
But when collapsed, it's the size of a dishwasher and weighs just 110 pounds.
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Post by the light works on Jun 8, 2014 21:33:34 GMT
They also have different weights for the thing. Yet collapsed it weighs just 70 pounds and takes up about as much space as a dishwasher... But when collapsed, it's the size of a dishwasher and weighs just 110 pounds. that could represent a sabot used to be sure it gets safely out of the launch vehicle. |
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Post by Cybermortis on Jun 8, 2014 22:37:30 GMT
They also have different weights for the thing. Yet collapsed it weighs just 70 pounds and takes up about as much space as a dishwasher... But when collapsed, it's the size of a dishwasher and weighs just 110 pounds. that could represent a sabot used to be sure it gets safely out of the launch vehicle. 40 pounds seems a little too heavy for something that would in effect get dumped, especially considering that every extra pound of weight adds to the cost of a launch. I'm also suspecting that the intention is for the sail to be collapsed once the craft reaches its destination - I don't recall this being specifically mentioned but is the impression I'm getting. I'm thinking its more likely that they lowered the weight to lower launch costs, or so they had more options regarding the launch vehicle. This would most likely be accomplished by making the sail a little smaller. Or they might have had concerns over the structural strength of the larger sail, and decided to make it smaller to reduce the stresses placed on it. After all the primary intention is to test the way solar sails work and the control system they have developed. *Shrugs* A lot of possible reasons. But I'd say it is fairly clear that the sail they will be using is smaller than the one they originally planned. |
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Post by the light works on Jun 8, 2014 23:20:43 GMT
that could represent a sabot used to be sure it gets safely out of the launch vehicle. 40 pounds seems a little too heavy for something that would in effect get dumped, especially considering that every extra pound of weight adds to the cost of a launch. I'm also suspecting that the intention is for the sail to be collapsed once the craft reaches its destination - I don't recall this being specifically mentioned but is the impression I'm getting. I'm thinking its more likely that they lowered the weight to lower launch costs, or so they had more options regarding the launch vehicle. This would most likely be accomplished by making the sail a little smaller. Or they might have had concerns over the structural strength of the larger sail, and decided to make it smaller to reduce the stresses placed on it. After all the primary intention is to test the way solar sails work and the control system they have developed. *Shrugs* A lot of possible reasons. But I'd say it is fairly clear that the sail they will be using is smaller than the one they originally planned. yeah - original specs and what actually got built... |
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Post by chriso on Jun 9, 2014 4:37:49 GMT
I found a nice article talking about planning interplanetary travel. - again, this is designed around thrust based propulsion rather than solar sail propulsion, but it illustrates my point about when we send ships from earth to mars, there is a point they stop basing their trajectory on earth orbit, and transition to basing their trajectory on solar orbit. in the same way, when we aim for interstellar travel, there will be a point at which we stop doing solar orbit and start doing galactic orbit. www.philsrockets.org.uk/interplanetary.pdfI also found a couple papers on solar sail trajectories: www.intrance.org/paper/200408_providence_dachwald_sail.pdfand www.engr.uconn.edu/~cassenti/SpacePropulsion/OptimumSolarSail.pdfthe dachwald model looks an awful lot to me like a series of maneuvers calculated to allow the sail craft to pass as close to the sun as possible without melting it down, to get as much initial thrust as possible, and then allowing it to depart on a hyperbolic path. in those particular models, the goal is to end up in orbit around a planet that is still in orbit around the sun, but it still involves transitioning from an orbital path around the sun to a path that is significantly away from the sun. so again - to summarize - by my understanding of the papers: for interstellar travel by rocket, you would begin in earth orbit, accelerate out of earth orbit, putting you in solar orbit, and then accelerate out of solar orbit, possibly using planets for slingshot maneuvers to assist in accelerating out of solar orbit, putting you in galactic orbit. for interstellar travel by solar sail, you would begin in earth orbit, accelerate out of earth orbit, putting you in solar orbit, then DEcelerate to maximize your acceleration from the solar sail by maximizing your proximity to your power source - and at that point, you want to make your transition to thinking in terms of galactic orbit, and using the sun for your slingshot maneuver Interesting read. I see what you are getting at now, its "cheaper" to accelerate as far insystem as you can where the energy is abundant, then head out. It looks like the craft spends a number of passes going nearly perpendicular to the sun to gain energy, then moves in really close where it is easy to shift to a hyperbolic orbit. Though I am not quite sure where the energy is being stored: as far as I know, moving into the system should reduce the tangential velocity, even if it does increase the angular velocity, so how it is increasing its energy while decreasing its orbit is a bit of a mystery to me. the critical difference between the two schools of thought is that with a rocket, your thrust is equal regardless of orientation. if your motor can deliver 10G of thrust, you can deliver thrust in any direction relative to the sun's gravity. with a solar sail, your primary thrust is directly away from the sun's gravity, and while you can modify the thrust by changing your angle of sail, it also reduces your total available thrust. I.E. if you want to thrust directly towards the sun, you will essentially have zero thrust. while the falloff ratio will undoubtedly not be exactly proportional, if you want to thrust at 90 degrees to the sun, assuming your maximum acceleration is 10 Gs, you would only be able to achieve 5 Gs of acceleration. It might be a better analogy to ask how your trajectory would be different between launching a ship to mars by rocketing it from the moon, and launching it to mars using a tractor/pressor beam to push it from Earth. Bit of a nitpick: G's are not a unit of force, they are a unit of acceleration. While force is related to acceleration, they are not the same thing and should not be treated as such. The Newton [N] is the SI unit of force. Also, I absolutely agree that the solar sail is more situationally dependent then a conventional rocket. But on the other hand, a conventional rocket would have to use gravity-assists to get there in the first place, so the solar sail would still probably win... |
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Post by silverdragon on Jun 9, 2014 5:13:45 GMT
Wel what do you know, its all a matter of conversion.
The designer worked on feet and inches, the technical reporters "Converted" it by hand to decimated....
Or deckamal.... or crackpot....
A Solar Sail is best retracted when not actually getting any "Wind", as in between places.
That way less chance of damage from micro-meteors.
Space is not as empty as some would have you believe?....
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Post by the light works on Jun 9, 2014 13:57:51 GMT
I found a nice article talking about planning interplanetary travel. - again, this is designed around thrust based propulsion rather than solar sail propulsion, but it illustrates my point about when we send ships from earth to mars, there is a point they stop basing their trajectory on earth orbit, and transition to basing their trajectory on solar orbit. in the same way, when we aim for interstellar travel, there will be a point at which we stop doing solar orbit and start doing galactic orbit. www.philsrockets.org.uk/interplanetary.pdfI also found a couple papers on solar sail trajectories: www.intrance.org/paper/200408_providence_dachwald_sail.pdfand www.engr.uconn.edu/~cassenti/SpacePropulsion/OptimumSolarSail.pdfthe dachwald model looks an awful lot to me like a series of maneuvers calculated to allow the sail craft to pass as close to the sun as possible without melting it down, to get as much initial thrust as possible, and then allowing it to depart on a hyperbolic path. in those particular models, the goal is to end up in orbit around a planet that is still in orbit around the sun, but it still involves transitioning from an orbital path around the sun to a path that is significantly away from the sun. so again - to summarize - by my understanding of the papers: for interstellar travel by rocket, you would begin in earth orbit, accelerate out of earth orbit, putting you in solar orbit, and then accelerate out of solar orbit, possibly using planets for slingshot maneuvers to assist in accelerating out of solar orbit, putting you in galactic orbit. for interstellar travel by solar sail, you would begin in earth orbit, accelerate out of earth orbit, putting you in solar orbit, then DEcelerate to maximize your acceleration from the solar sail by maximizing your proximity to your power source - and at that point, you want to make your transition to thinking in terms of galactic orbit, and using the sun for your slingshot maneuver Interesting read. I see what you are getting at now, its "cheaper" to accelerate as far insystem as you can where the energy is abundant, then head out. It looks like the craft spends a number of passes going nearly perpendicular to the sun to gain energy, then moves in really close where it is easy to shift to a hyperbolic orbit. Though I am not quite sure where the energy is being stored: as far as I know, moving into the system should reduce the tangential velocity, even if it does increase the angular velocity, so how it is increasing its energy while decreasing its orbit is a bit of a mystery to me. it is not - it is simply positioning itself to get the optimum launch vector. the only time it increases energy is when it does the final dive before the hyperbolic trajectory towards its intended destination - and even that is somewhat marginal, as the craft will decelerate by gravity to the same degree it accelerated on the approach. |
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Post by chriso on Jun 9, 2014 14:29:37 GMT
Wel what do you know, its all a matter of conversion. The designer worked on feet and inches, the technical reporters "Converted" it by hand to decimated.... Or deckamal.... or crackpot.... A Solar Sail is best retracted when not actually getting any "Wind", as in between places. That way less chance of damage from micro-meteors. Space is not as empty as some would have you believe?.... You have no idea how many hours I have spent tracking down the fact that I had forgotten to change grams to kilograms. I hate converting units. |
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Post by the light works on Jun 9, 2014 14:35:29 GMT
Wel what do you know, its all a matter of conversion. The designer worked on feet and inches, the technical reporters "Converted" it by hand to decimated.... Or deckamal.... or crackpot.... A Solar Sail is best retracted when not actually getting any "Wind", as in between places. That way less chance of damage from micro-meteors. Space is not as empty as some would have you believe?.... You have no idea how many hours I have spent tracking down the fact that I had forgotten to change grams to kilograms. I hate converting units. Phrench... the adjective you are looking for is Phrench. to be specific, a meter is one ten-millionth of the length of the meridian through Paris from pole to the equator. |
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Post by silverdragon on Jun 11, 2014 6:38:02 GMT
They are upset, because someone has invented a way to do the math amd set a standard length by how long it takes light to travel a certain distance, and just to be "British" (Read: Bloody Awkward...) they did the distance in Inches.
They also measured it in GMT.
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