Thruster keel for an interplanetary solar sail.

[holmec]

I have been playing around with ideas on how an interplanetary solar sail ship would navigate say from the Earth to Mars. I ended up doing vector calculations to see how much thrust would a "keel" require to keep the ship going accross the Sun's rays. I came up with some fairly positive numbers (sail angle to the sun 67.5 degrees, you get about 140% of the amount of "keel" thrust in solar thrust across Sun's rays ) but I realized that a thruster "keel" needed to operate for months.<br /><br />For a manned solar sail ship technology for a "keel" seems to be futuristic. Is there any way or technique a chem thruster could provide thrust over months? <br /><br />Clarification: I'm using the idea of keel from a sail boat. The keel translates the power the sails receive to a specific direction. In this case the keel would be thruster or booster. As opposed to the rudder which would equate to the rotation control thrusters.<br /><br />**NOTE this is not an intersellar excersise. So take you little intersellar ideas to another post. This in just Earth to Mars and maybe back.*** <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[fingle]

How about ion thrusters like those used by Deep Space 1 ??<br /><br />fgl<br /><img src="/images/icons/smile.gif" /><br /> <div class="Discussion_UserSignature"> </div>

 

[holmec]

Good question. Unfotunately they currently do not provide enough thrust for such a manned space craft.<br /><br />Now if they can be made bigger and more efficient then that could certainly be an option given their long term use.<br /><br />I don't have numbers, but previously due to this forum I did calculate how much thrust in terms of Gs they did provide, and it was not much. Remember Smart-1 took 3 years to get to the moon on one. <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[willpittenger]

How do you intend to get solar energy between star systems? By the time you reach Pluto's orbit, you would loose thrust from our sun even with a sail 20 km across. <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>

 

[qso1]

Not only that, how fast would this ship be capable of going if it went interstellar? <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[alokmohan]

It may take paultry million years.

 

[holmec]

>How do you intend to get solar energy between star systems? By the time you reach Pluto's orbit, you would loose thrust from our sun even with a sail 20 km across.<<br /><br />Let's see Mars.....Interstellar....."Does not compute...Does not compute". I'm just talking about going to Mars. Not Jupiter, not Venus, not to Kuiper belt, and defenitaly no interstellar. <br /><br />Interstellar is a whole different problem. Where a sail might help in a sling shot around the sun but not much else.<br /><br />No, I am talking about going to Mars. In fact I was hoping that maybe someday we can build a interplantary bus that roams around the inner solar system. But this excersise was to understand how a solar sail would work going from Earth to Mars as opposed to just Earth orbit which was explained to me by the Planetary Society when they were about to launch Cosmos1 as solar sailing craft which blew up with the russian rocket that launched it. <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[holmec]

>Not only that, how fast would this ship be capable of going if it went interstellar?<<br /><br />Not even considering it. <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[willpittenger]

Sorry. I saw "interplanetary" and for some reason read "interstellar". <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>

 

[jamie_young]

Shame, as interstellar would be huge.

 

[halman]

holmec,<br /><br />You have to learn to think in a different way. A solar sail will gain velocity from the solar wind, while it is in orbit around the Sun. The sail is kept at 90 degrees to the solar wind, which imparts velocity continuously. The payload must be kept between the sail and the sun to prevent the shrouds from fouling. The velocity gained will raise the orbit of the payload, but very slowly. To rendezvous with a planet will require some form of impulse, unless you are very lucky. <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

 

[holmec]

>You have to learn to think in a different way. A solar sail will gain velocity from the solar wind, while it is in orbit around the Sun. The sail is kept at 90 degrees to the solar wind, which imparts velocity continuously. The payload must be kept between the sail and the sun to prevent the shrouds from fouling. The velocity gained will raise the orbit of the payload, but very slowly. To rendezvous with a planet will require some form of impulse, unless you are very lucky. <br /><<br /><br />Actually this will provide no acceleration since the sail will not catch any solar light at all. I'm kinda assuming I am using sun light here and not neccesarily solar winds. I know there are two type of sails available. Solar wind sailing seems to be more complex than I can fathom at this point.<br /><br />That's why I chose 67.5 degrees to the sun light. Doesn't solar wind particles just blow from the surface of the sun and outward from there? It seems you need to consantly attapt your angle to get max propulsion depending on your position relative to the wind.<br /><br />You defenately want you acceleration in the 90 degree angle, to accomplish this a keel is negate the 0 degree vector the sun light will try to send you so you end up with an acceleration in the 90 degree direction. <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[holmec]

>I am no sailer but I think you mean more like 180 degrees. <br /><<br /><br />The assumption is that light is coming directly form the sun. In sailing you want to deal with 0 to 90 degrees angles 180 does nothing for sailing, its the same as 0 degrees in effect. This is because the sail is flat on four faces and full on two faces (if you enclose the sail in a hypothedical cube). <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[willpittenger]

I just remembered that I had my own concept for a solar sail craft.<br /><br /><br /><br />Several important aspects:<br /><br />*I assumed that the craft would never approach Earth closer than about 1.3 times the lunar orbit diameter. This would allow the craft to enter and leave orbit with just the solar sails, but avoid the orbital debris and minimize the amount of time that would be required to enter and leave orbit.<br /><br />*I assumed a huge sail -- 20-30 miles across (which would be a very good reason not to get too close to Earth's orbital debris field).<br /><br />*The sail could be furled or partially furled. It would partially furl the sail when less thrust is needed or it could be damaged.<br /><br />*I used gravity rather than a keel to navigate. This meant that the only fuel needed was for orientation.<br /><br />*The vehicle was unmanned and automated (like Deep Space 1).<br /><br /><br /><br />The concept was for a trip to Pluto (which might be too far out even for that size sail). The craft would take an orbiter there from Earth and then return having left the orbit behind.<br /><br />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. <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>

 

[halman]

holmec,<br /><br />I have used the same poetic license that Arthur C. Clarke used in his story "The Wind From The Sun" to describe the sunlight that powers a solar sail. The charged particles that make up what we now call the 'solar wind' would have some effect on its velocity, I imagine, but it is the light that is true driving force. To capture that light most effectively, you must have your sail perpendicular to it. I am not enough of a mathematician to be able to calculate the orbit, but the sail will continue to orbit the sun while it accelerates, just as if a rocket ship wer to point straight out from the sun and burn its fuel. Because the rate of acceleration is very slow, the effect is somewhat different than that of a rocket, for the rocket will only change the perehilion of its orbit. The solar sail will gradually raise its orbit, increasing both perihelion and aphelion, because the solar wind pushes the sail away from the sun, not around it.<br /><br />Clarke has stated that a sail with a surfare area of one square mile will experience a pressure totaling about 5 pounds. Tilting the sail away from the sun will reduce that value.<br /><br /> <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

 

[willpittenger]

Tilting it away would also change the direction. If you only want to change the thrust, you have to partially furl 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>

 

[holmec]

>Clarke has stated that a sail with a surfare area of one square mile will experience a pressure totaling about 5 pounds. Tilting the sail away from the sun will reduce that value. <<br /><br />Good info. Thanks.<br />5 pounds per square mile.. eh. <br /><br />Yes this has been stated that to capture as much light from the sun as possible you have the sail perpendicular to the sun's rays. But a sail boat's sail does not function like that. A sail on a boat functions like a wing or an air foil. It also does not function alone but with a keel and a rudder to provide the desired direction.<br /><br />I endevered to figure out how to wield the sun's light not let it wield a ship. So a keel and a rudder was needed. The keel had to be either a thruster and/or the G forces by the Sun itself. And the rudder had to be RCS thrusters.<br /><br />I figured out that it might be plausible to wield the sun's rays for solar orbital maneuvrs. Thus getting from earth to Mars and back.<br /><br />My calcuation says that if you angle the sail at 67.5 degrees then you need about 14% of the captured thrust by the sail (in a parallel direction to the sun's rays) from the keel thruster for an extended period of time. This will provide about 34% (if memory serves) of total thrust in an orbital direction (perpendicular to the sun's rays) .<br /><br />Seemingly inefficient, yet it does state that you can save fuel because you are using less than half thruster fuel than if you did the same acceleration just on a thruster alone without a sail.<br /><br />So my conclusion is if in the future we have materials lightweight enough strong enough we could possible make such a craft for human travel. Wether it be for missions, ferrying passengers, or regatta races to Mars. LOL.<br /><br />Anyway navigation with solar sail may be in the future and it seems elegant and challenging, even comparable to the best sailing stories.<br /><br />I think Ahab would be excited. <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[holmec]

>Tilting it away would also change the direction. If you only want to change the thrust, you have to partially furl the sail.<br /><<br /><br />Correct. You also note that unlike boats, the sail provides acceleration and not just velocity.....of course you all knew that. <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[rocketman5000]

Perhaps a second sail? By varying the s sizes and angles relative to the sun you should be able to get a steady state force rather than a moment from the angle. <br /><br />By balancing the force of the sails around the COM of the ship you could balance out the forces making the "ship" want to rotate. I'll try to create a sketch and post

 

[willpittenger]

<blockquote><font class="small">In reply to:</font><hr /><p>But a sail boat's sail does not function like that. A sail on a boat functions like a wing or an air foil. It also does not function alone but with a keel and a rudder to provide the desired direction.<br /><br />I endevered to figure out how to wield the sun's light not let it wield a ship. So a keel and a rudder was needed. The keel had to be either a thruster and/or the G forces by the Sun itself. And the rudder had to be RCS thrusters.<p><hr /></p></p></blockquote><br />I should point out that as you turn the sail, even with thrusters, there is one additional difference between your system and a sailboat: The Venturi Effect. One of the reasons why Jib sails are so efficient is the vacuum created.<br /><br />This is why in the older post, I used the angle of the sail only for steering. My thrusters would be much smaller than yours with less fuel and on the periphery of the sail's support structure. <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]

>I should point out that as you turn the sail, even with thrusters, there is one additional difference between your system and a sailboat: The Venturi Effect. One of the reasons why Jib sails are so efficient is the vacuum created.<br /><br />This is why in the older post, I used the angle of the sail only for steering. My thrusters would be much smaller than yours with less fuel and on the periphery of the sail's support structure. <<br /><br />Interesting. Is this for solar orbital sailing? <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[holmec]

>Perhaps a second sail? By varying the s sizes and angles relative to the sun you should be able to get a steady state force rather than a moment from the angle.<br /><br />By balancing the force of the sails around the COM of the ship you could balance out the forces making the "ship" want to rotate. I'll try to create a sketch and post<<br /><br />Sure you should be able to control rotation with a second sail or even a segmented sail like in Cosmos 1 of the Planetary Society.<br /><br />But if we are talking about solar orbit. I think there is little recourse but to rely on thrusters or reduce your orbital speed with the sun to provide a gravitational pull from the sun to take effect as to help in a keel effect.<br /><br />Ideally you want to navigate to a higher orbit like Mars is from Earth. Then you need little or no keel thrust, but just let the sun rays take you to Mars. <br /><br />I suppose you could use no thruster at all for a keel but to open and furl the sail at intervals so you have a zig zag or tacking effect. And have a segmented sail like Cosmos1 (A design I really like http://www.planetary.org/programs/projects/solar_sailing/)<br /> so you can control one way of rotation, and also furl without furling to a degree. <br /><br />I think I'm starting to get the idea of what your saying.<br /><br />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. Because I think with the sail (if its big enough) you could "fly" away from the sun.<br /><br />Its sounds so elegant. <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[holmec]

>Perhaps a second sail? By varying the s sizes and angles relative to the sun you should be able to get a steady state force rather than a moment from the angle.<<br /><br />Ok you can possibly use a second sail, or you can do what planes, or I should say hanggliders do, and that is to shift the weight relative to the sail. If your ship module is attached to the center of the sail via a boom then you can shift it in relation to the sail. That would be cool. Then you can also have a segmented sail and control direction with the sails. When you wand to furl them, just set the sails on their sides and you should fall to a stable orbit (depending on your orbital velocity). <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[rocketman5000]

At 90 degrees to the sun you'd get a thrust vector radial from the sun. Assuming a counter clockwise orbit a positive rotation of the sail from the 90 degree would create a force vector on the sail that would increase orbital velocity.<br /><br />conversly a negative rotation from the 90 degree position would create a force vector that would slow orbital velocity.<br /><br />Without 2 sail a change from positive to negative would probably end in line foul as the spacecraft flew by the sail. With 2 sails you could close the leading sail then open the trailing sail thus avoiding flying by or thru your lines. <br /><br />I had a skydiving friend who got a canopy wrap when another jumper flew through his lines. He had to cutaway to his reserve. Therefore I'd want to avoid line fouling at all cost.

 

[green_meklar]

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 />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... <div class="Discussion_UserSignature"> <p>________________</p><p>Repent! Repent! The technological singularity is coming!</p> </div>