Thruster keel for an interplanetary solar sail.

[j05h]

> Please excuse my ignorance, but I still don't understand how you can tack against the sunlight. <br /><br />The solution is to angle the solar sail so that it slows down in it's orbit. It's as simple as pointing the sail. You can "tack" essentially and it doesn't require a medium to push against. It relies on momentum transfer from photons striking the sail: light has mass. <br /><br />Solar sails work best outbound, for sure, but can be used to get back to Earth from Mars or the Main Belt.<br /><br /> /> Also, on the subject of solar sails, I was just thinking of another interesting idea. If you were to have several sails arranged radially and angled them like a pinwheel, you should be able to get your ship spinning. And a spinning ship could have some possible benefits...<br /><br />That is a solar heliostat. A university group was trying to build a demonstrator a few years ago. The Cosmos I solar sail also would have been able to spin up.<br /><br />For the thread header: what kind of keel are you talking about? The attach point for cargo or a steering "keel"? Sorry I'm so late in this thread.<br /><br />Josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[willpittenger]

<blockquote><font class="small">In reply to:</font><hr /><p>Have a solar sailer control itself entirely of sails. And using its weight but furling and unfurling the sail to increase speed and drop back to orbit.<p><hr /></p></p></blockquote><br />That is what I proposed. I was using thrusters only to orient the sail. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>

 

[willpittenger]

Not sure what you mean by that. My craft would <b>leave</b> orbit completely and take a direct vertical (away from the sun) route. To decelerate while going away from the Sun or accelerate while moving towards it, you furl the sail completely and let gravity take over. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>

 

[holmec]

>Not sure what you mean by that. My craft would leave orbit completely and take a direct vertical (away from the sun) route. To decelerate while going away from the Sun or accelerate while moving towards it, you furl the sail completely and let gravity take over.<<br /><br />I mean solar orbit. Since Earth and Mars are in solar orbit, that is where you have to operate in to get from Earth to Mars and back. I don't intent to use this outside the solarsystem. Anyway I think no matter how fast you go you are always in orbit around something. <br /><br />So what is the scope of operation for your craft? <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[holmec]

>Please excuse my ignorance, but I still don't understand how you can tack against the sunlight. As far as I can tell, tacking in a sailing ship depends on the fact that you're going through water which is not moving while the wind is moving. In space, you have nothing you can use the way a ship uses water. So how do you ever turn that energy into a force going in the other direction, even on a zig-zag path like the ones ships take? It seems to me that the only way you could get back in towards the Sun using a solar sail would be to go away from the sun towards a planet, close up the sail and then get a gravity boost back towards the Sun. <<br /><br />Your quite correct. I was only using an analogy, not a very good one, to describe how to correct your trajectory without thrusters. If you have your sail at 67.5 degrees to the solar rays, that is basically the direction your sail will take you as you acceerate (I'm assuming that is so), then you can "furl" the sails so they have no "lift" so the weight of the ship and the Sun's gravity will bring the ship closer to the sun automatically obeying the natural orbital mechanics. Then you can "raise" the sail and get more acceeration in the 67.5 degree direction, and continue this process. I called this "tacking" but it has little to do with real tacking that sail boats do. Because sail boats do this to travel contrary to the wind and they use the keel extenstensivly in such an operation. <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[holmec]

>For the thread header: what kind of keel are you talking about? The attach point for cargo or a steering "keel"? Sorry I'm so late in this thread. <<br /><br />This thread is a "think tank" of sorts on solar sailing. I origionally thought that a solar sail ship needed some kind of a keel to control its tragectory as it is in Solar orbit. The origional keel I thought of was a some kind of long term thruster (that perhaps really doen't exist yet, but something like the ion drive on DS1 and Smart1).<br /><br />But the other possible keel could be the weight of the ship itself and the effect the solar gravity has on it. Thus using orbital mechanics and sails alone.<br /><br />I have to say the sail should be big enough to lift the whole ship away from the Sun with orbital velocity of 0. It should also be able to slow the ship in its orbital speed and accererate the ship in its orbital speed. So then you have the mechanics to be able to go from Earth to Mars and back. <br /><br />The idea seems so elegant as opposed to just rocketing yourself to Mars and back with all the fuel it requires.<br /><br />The problem seems now that at 5 lbs per square mile (as someone suggested that Athur C. Clarke said) of sail is quite low. So for humand sail flight (sounds like a hybrid statement) the sail has to be very large and very light. <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[holmec]

>1. Start be leaving Terran orbit.<br /><br />2. Angle the sail off to the side at 45° such that the sail provides just enough thrust to keep it at 1 AU while slowing its orbital motion.<br /><br />3. As the craft loses orbital energy, unfurl the sail more to keep it from falling towards the Sun.<br /><br />4. As the last bit of orbital energy is lost, completely unfurl the sail and change the angle to 90°.<br /><br />5. The craft begins to move radially through the solar system rather than along a tranfer orbit. Due to the size of the sail and the possibility damage from even dust, I suggest going "above" or "below" the asteroid field.<br /><br />6. As you reach Pluto's orbit, furl the sail to slow down.<br /><br />7. As the speed drops, unfurl the sail and orient it to the side at 45° to cause the Sun's energy to accelerate the craft into a orbit. Use the same system to enter Pluto's orbit.<br /><br />8. To return, simply repeat the process, except you furl the sail after deorbiting and unfurl it to deccelerate. <<br /><br />Sound good. But I see you seem to be decerating your solar obital velocity, couldn't you accelerate it and have more energy to get to Pluto?<br /><br />Also why 45 degrees? At least by my calculations 45 degrees is not the optimat angle for solar orbital acceleration and deceleration, but 67.5 degrees is.<br /><br />Also what if you used your craft for going to Mars? How would that play out? <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[green_meklar]

<blockquote><font class="small">In reply to:</font><hr /><p>The solution is to angle the solar sail so that it slows down in it's orbit.<p><hr /></p></p></blockquote><br />Ah, I see now. *hits self for not getting it before* Thanks! <div class="Discussion_UserSignature"> <p>________________</p><p>Repent! Repent! The technological singularity is coming!</p> </div>

 

[willpittenger]

Actually, at 67.5 degrees, you will apply thrust in that direction. You will not travel in that direction due to inertia (which is worse if you are in an orbit). <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>

 

[willpittenger]

<blockquote><font class="small">In reply to:</font><hr /><p>I mean solar orbit. Since Earth and Mars are in solar orbit, that is where you have to operate in to get from Earth to Mars and back. I don't intent to use this outside the solarsystem.<p><hr /></p></p></blockquote><br />I know that. I was talking about leaving solar orbit to go the the outer planets via a more direct route without transfer orbits. You would move radially along the solar system. Since you talked about having a sail large enough to support the ship's weight, I assume you and I are talking about something similar.<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>Anyway I think no matter how fast you go you are always in orbit around something.<p><hr /></p></p></blockquote><br />Sort of. If you deorbit from the Sun, but remain suspended, you are orbiting the Milky Way with the Sun. However, as far as all Solar System objects are concerned, including the Sun, you have left orbit.<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>So what is the scope of operation for your craft?<p><hr /></p></p></blockquote><br />Deep interplanetary delivery of orbiters to remote planets. The orbiter would save its own fuel for one it has arrived. It would be on its own once in the outer edges of that system. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>

 

[willpittenger]

<blockquote><font class="small">In reply to:</font><hr /><p>Sound good. But I see you seem to be decerating your solar obital velocity, couldn't you accelerate it and have more energy to get to Pluto?<p><hr /></p></p></blockquote><br />The idea was to <b><i>leave</i></b> solar orbit and rely entirely on the Sun. We are talking about a solar sail that can operate in a unique manner compared to other propulsion systems. The route is very direct. You would be moving radially along the Solar System rather than around it.<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>Also why 45 degrees? At least by my calculations 45 degrees is not the optimat angle for solar orbital acceleration and deceleration, but 67.5 degrees is.<p><hr /></p></p></blockquote><br />The objective, as stated above, is to leave solar orbit completely. It is undesirable. As you leave the orbit, you would change the angle to 90 degrees for maximum speed.<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>Also what if you used your craft for going to Mars? How would that play out?<p><hr /></p></p></blockquote><br />The same type of trajectory could be used. However, I would suggest using a craft with a smaller sail. What I specified was optimized for conditions in the outer solar system. Near Earth, it would probably normally partially furl its sail.<br /><br />Notice the window for a radial trajectory is different than the conventional one. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>