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g99
2003-Mar-08, 05:56 AM
The newest APOD has a picture of a proposed NASA solar sail.

http://antwrp.gsfc.nasa.gov/apod/ap030308.html

From above site: Continuous pressure from sunlight would ultimately accelerate the craft to speeds about five times higher than possible with conventional rockets -- without requiring any fuel! If launched in 2010 such a probe could overtake Voyager 1, the most distant spacecraft bound for interstellar space, in 2018 going as far in eight years as the Voyager will have journeyed in 41 years.

How would you construct a craft like that economically?

Would it be constructed in space or on the earth?

Is it a feasible robotic spacecraft for exploring planets?

Can you steer it?

_________________
"Watch out for falling coconuts!".
"It takes Thousands to fight a battle for a mile, Millions to hold an election for a nation, but it only takes One to change the world." - Dan Sandler 2002

<font size=-1>[ This Message was edited by: g99 on 2003-03-08 00:57 ]</font>

Colt
2003-Mar-08, 07:02 AM
On 2003-03-08 00:56, g99 wrote:
The newest APOD has a picture of a proposed NASA solar sail.

http://antwrp.gsfc.nasa.gov/apod/ap030308.html

From above site: Continuous pressure from sunlight would ultimately accelerate the craft to speeds about five times higher than possible with conventional rockets -- without requiring any fuel! If launched in 2010 such a probe could overtake Voyager 1, the most distant spacecraft bound for interstellar space, in 2018 going as far in eight years as the Voyager will have journeyed in 41 years.

How would you construct a craft like that economically?

Would it be constructed in space or on the earth?

Is it a feasible robotic spacecraft for exploring planets?

Can you steer it?

_________________
"Watch out for falling coconuts!".
"It takes Thousands to fight a battle for a mile, Millions to hold an election for a nation, but it only takes One to change the world." - Dan Sandler 2002

<font size=-1>[ This Message was edited by: g99 on 2003-03-08 00:57 ]</font>


You could use plastics coated with a thin reflective material, this is pure speculation on my part though.

Orbit would probably be the best place since it would not have to be under the strain of gravity and the damage that might be incurred once it was launched.

I think that it would be feasible for a manned mission, perhaps to Mars and back. This of course would require a much larger sail as it would have to tow along not only sensors and the transmitter but also the life support systems for the crew. A robotic mission is of course more feasible, but probably not as useful.

It might be possible to steer by tacking bits of the sail like you would on an ocean-going vessel. Otherwise you could use rocket thrusters at the edge of the sail to orient it.

Let me lay out a simple, robotic, mission to Mars. 1. The SSP (Solar Sail Probe) is boosted from Earth orbit and set on its way to the red planet. 2 The probe gradually accelerates along its course. 3. The SSP reaches Mars orbit where the probe whips around the planet collecting data and orients itself so that the probe is pointing toward the Sun. 4. The SSP leaves Mars orbit on its way back to Earth orbit still retaining a good deal of velocity. 5. The probe's sail acts as a brake as it moves back toward the Earth. 6. The probe reaches Earth orbit where it nabbed by the Orbiter.

This is of course if you wanted the probe to return and capture it for some reason. Otherwise you just send the probe there and let it be captured by Mars. There are probably several errors in the above sequence but I am tired so you can't blame me.

Oh yes, glad someone (g99) finally started a thread about Solar Sails so I can rant. -Colt

g99
2003-Mar-08, 07:40 AM
How can you send a sail into the suns path?

A sail boat can go into the wind using the same principles that a plane can stay in the air. Basically.

But there are no real pressure differences in space. So how would the sail work going towards mars?

P.S. Colt. I am sure i wasn't the first to bring this up. Just to most recent. I am just a very humble person with a napoleonic complex. /phpBB/images/smiles/icon_smile.gif

_________________
"Watch out for falling coconuts!".
"It takes Thousands to fight a battle for a mile, Millions to hold an election for a nation, but it only takes One to change the world." - Dan Sandler 2002

<font size=-1>[ This Message was edited by: g99 on 2003-03-08 02:41 ]</font>

tvelocity
2003-Mar-08, 10:41 AM
It's actually been tried. It failed due to technical problems not related to the technology itself.

http://www.cnn.com/2001/TECH/space/07/21/solar.sail/index.html

Lexx_Luthor
2003-Mar-08, 01:54 PM
CNN:: Woah wait a minute. Protons?

I thought solar sails did the photon thing.

Regards sailing the solar system. Depending on which way you slant the mirror relative to the sun, you can change tangential velocity and thus your orbit about the sun. I think this is the primary way of thinking about solar sailing.

Also...rather than using small thrusters to orient the mirror, fold up or black out parts of the mirror edge, thus causing more photons to hit one side than the other and so causing a slow spin. Half way through the spin, reverse the process to slow the spin and the mirror will be oriented the way you want it.

----------------

By the way, solar sailers should be mirrors and reflect as many wavelengths as possible. This doubles the momentum transferred from photon to mirror surface. The worst performer is a "black" surface that does not reflect. This worst case gets only half the "thrust" available to a perfectly reflecting mirror. The EM persons/personettes here should know more about this.

russ_watters
2003-Mar-08, 03:44 PM
G99, solar wind works like regular wind, except much less dense and much higher velocity. Ther IS a pressure difference and the sails work the same way sails on a boat work, with one exception: In a boat you can go 45 degrees from directly upwind because you have a stabilizer (centerboard/daggerboard) to keep you from sliding sideways. Without this, I don't think you'd ever be able to go upwind at all with a solar sail - at best 90 degrees off.


Woah wait a minute. Protons?

I thought solar sails did the photon thing. No, I think (not entirely sure) that the solar wind is actual particles thrown off by the sun at a high fraction (.75?) of the speed of light. Since the sun is mostly hydrogen and hot hydrogen has no electrons, you get protons. It really is a physical wind and though not all that strong, it is strong enough to shape the tail of a comet.

<font size=-1>[ This Message was edited by: russ_watters on 2003-03-08 10:47 ]</font>

russ_watters
2003-Mar-08, 03:55 PM
On 2003-03-08 08:54, Lexx_Luthor wrote:
CNN:: Woah wait a minute. Protons?

I thought solar sails did the photon thing.

Regards sailing the solar system. Depending on which way you slant the mirror relative to the sun, you can change tangential velocity and thus your orbit about the sun. I think this is the primary way of thinking about solar sailing.

Also...rather than using small thrusters to orient the mirror, fold up or black out parts of the mirror edge, thus causing more photons to hit one side than the other and so causing a slow spin. Half way through the spin, reverse the process to slow the spin and the mirror will be oriented the way you want it.

----------------

By the way, solar sailers should be mirrors and reflect as many wavelengths as possible. This doubles the momentum transferred from photon to mirror surface. The worst performer is a "black" surface that does not reflect. This worst case gets only half the "thrust" available to a perfectly reflecting mirror. The EM persons/personettes here should know more about this.

edit: thinking about the directional control, I relize with no centerboard, you would have no control over your direction at all once you have accelerated to the speed of the solar wind. It is only during acceleration that you would have limited (and reducing) directional control.

Lexx_Luthor
2003-Mar-08, 06:49 PM
edit: thinking about the directional control, I relize with no centerboard, you would have no control over your direction at all once you have accelerated to the speed of the solar wind. It is only during acceleration that you would have limited (and reducing) directional control.

I always heard solar sails are supposed to be pushed by light rays (Photons--fotons) not Protons. Light travels at the speed of light. Wozop with the protons? Wozop with CNN?

--------------

Going "upwind" here means moving straight toward the sun. This not an issue here because the sail will always be in a solar orbit. To get closer to the sun, you slant the sail so the sail gets accelerated opposite its current velocity (deceleration). This slows the sail and it enters an elliptical orbit that carries it sunward. At bottom of orbit (perhelion) slant the sail to accelerate (actually decelerate again) so it matches the orbital velocity of your target planet.

Similarly, "downwind" would mean climbing straight away from the sun with no tangential velocity component. Not an issue with solar system orbits.

Again, solar sailing is a way to (slowly) change your velocity so that you achieve a new solar orbit around the sun, probably (just guessing here) with the target planet near the aphelion or perhelion of your new orbit--which is only very slowly achieved so even this is like a continous range of an infinite number of differing orbits.

You probably need a computer to chew on all the differing orbits you will be moving through given the *very* slow acceleration so you know how to continously vary the slant of the sail.

g99
2003-Mar-08, 07:22 PM
On 2003-03-08 10:44, russ_watters wrote:
G99, solar wind works like regular wind, except much less dense and much higher velocity. Ther IS a pressure difference and the sails work the same way sails on a boat work, with one exception: In a boat you can go 45 degrees from directly upwind because you have a stabilizer (centerboard/daggerboard) to keep you from sliding sideways. Without this, I don't think you'd ever be able to go upwind at all with a solar sail - at best 90 degrees off.



How do pressure differences work in space?

Colt
2003-Mar-08, 08:58 PM
On 2003-03-08 08:54, Lexx_Luthor wrote:
CNN:: Woah wait a minute. Protons?

I thought solar sails did the photon thing.

Regards sailing the solar system. Depending on which way you slant the mirror relative to the sun, you can change tangential velocity and thus your orbit about the sun. I think this is the primary way of thinking about solar sailing.

Also...rather than using small thrusters to orient the mirror, fold up or black out parts of the mirror edge, thus causing more photons to hit one side than the other and so causing a slow spin. Half way through the spin, reverse the process to slow the spin and the mirror will be oriented the way you want it.

----------------

By the way, solar sailers should be mirrors and reflect as many wavelengths as possible. This doubles the momentum transferred from photon to mirror surface. The worst performer is a "black" surface that does not reflect. This worst case gets only half the "thrust" available to a perfectly reflecting mirror. The EM persons/personettes here should know more about this.



This is more of what I was referring to when I said "tacking". Here is a fairly good page on solar sails and it mentions the use of differen't pressures to steer: Solar Sails (http://www.ugcs.caltech.edu/~diedrich/solarsails/). -Colt

g99
2003-Mar-08, 10:12 PM
So bascially it is the lazy man's way to get around the solar system. Slowing down and speeding up around the sun untill your orbit matches the planets. Yes a rocket does the same thing, but on a much more rapid rate.

Now i am wondering. The APOD article said that it can travel to Voyager in only 8 years. If it changes orbits so slowly, how can it catch up so fast?

What are the aceleration rates of a chemical rocket Vs. a solar sail?

Thanks everyone.

Colt
2003-Mar-08, 10:39 PM
I don't think you would be able to beat a rocket.. Simply because the force used in a rocket is so powerful compared to the Sun's gentle pressure. More later. -Colt

Nightfall
2003-Mar-08, 11:14 PM
On 2003-03-08 17:39, Colt wrote:
I don't think you would be able to beat a rocket.. Simply because the force used in a rocket is so powerful compared to the Sun's gentle pressure. More later. -Colt


*Don't take out a calculator, or use a calculator program*

Would you take a job that only lasted one month and on the first day they paid you $0.01? Then for the next day's work they paid you $0.02? Each day you work there, you get twice as much as the day before. So would you take it? (note: You'll be working seven days a week.)





*spoiler for the above problem*
On the last day of that job, assuming that it was for only February, you would get paid $1,342,177.38 just for that day's work. You'll have the wages for the other twenty-seven days. This is the idea behind solar sails&sup1;. They start out slow, but once they get moving they can go increadibly fast. Rockets are only good for short trips, but for longer trips they are impractical because they give you a quick bang and then their gone. Rockets biggest draw back is their need for fuel, and lots of it. In order to travel great distances you'll need to take enormous amounts of fuel, but this fuel also weighs the spaceship down, at least on earth, so you'll need more fuel to get it moving. Solar sail's only drawback is that they need time to get moving. From what I've seen, I think the best method would be some sort of hybrid. Rockets, or some type of engines, to get the ship moving at a decent velocity, and the solar sails to get it to cruising speed.

Edited for typos.

&sup1;Edited again to add: I just realized that if you take the analogy too far, it breaks down. The analogy should stop at the idea that little by little can you create a bigger item. Solar sails, unfortunatly, do not work exactly like the above situation of doubling money.

<font size=-1>[ This Message was edited by: Nightfall on 2003-03-08 18:18 ]</font>

<font size=-1>[ This Message was edited by: Nightfall on 2003-03-08 19:24 ]</font>

RafaelAustin
2003-Mar-09, 12:31 AM
My question about solar sailing always has been: Does anybody know the effective range of the solar wind? Surely at some point it becomes insignificant. Would this be at the boundary of the Oort cloud? At that point, it seems it would be safer for the craft to jettison it's sail and continue coasting on its momentum.

Lexx_Luthor
2003-Mar-09, 12:44 AM
Xample:: You could use a low Earth orbiting solar sail to spiral out until you reached near the moon's orbit and change your sail slant and fall into orbit around the moon. The goal is speed (kinetic energy) that you trade for altitude (potential energy) above the Earth. Same with sailing away from the sun. Of course, the sail must rotate along with its orbital period about the Earth so that the sun will *not* push it slower as it moves toward the sun in its orbit. Just now thinking of this stuff. Alot to think about really and I do not have a handle on it. But it is fun.


I think the best method would be some sort of hybrid. Rockets, or some type of engines, to get the ship moving at a decent velocity, and the solar sails to get it to cruising speed.This is the neat thing:: as long as the sun is shining, you benefit from the sunlight's push. There is no "cruising speed." You don't try to go "faster" in the long run, but try to gradually change orbits. Today's rockets thrust for very short time, thus we think of them as starting out in one orbit (say Earth's orbit about the sun), blasting away and changing to another orbit to get to the destination (and hopefully the target is there when we get there), and lastly the rocket fires a burst to change it's orbit to match the target's orbit about the sun.

Solar sails "blast away" the whole trip, continously, but very slowly, changing orbits along the way.


Solar sail's only drawback is that they need time to get moving. /phpBB/images/smiles/icon_biggrin.gif A bigger draw back than the "only" one is that they are less useful in the outer solar system, much like electric solar panels don't work well way out there. Not enough light.

Fortunately, the "only" problem of rockets is engine specific impulse (here I go again). Unfortunately, this will be the most sticky problem that will ever face space travel. This is what needs the most work.

If solar sails are needed it will be because of failure to vastly increase rocket engine specific impulse. Don't always celebrate failure.

Also, I was holding back, cowering in a cryopod, earlier about slanting the sail so it accelerates (+ or -) in a direction parellel to its current orbital velocity. To catch sunlight, you must accept a slant that also contains a radial acceleration toward or away from the sun. There are some here who are working through (I think) the USAF Fundamentals of AstroDynamics and they would know more about this. When I get arbitrary thrusting into my spacecraft sim, I can check this out.


-----------------


Anyway, solar sails are worthless if the ship goes behind the dark side of the sun. /phpBB/images/smiles/icon_biggrin.gif

ToSeek
2003-Mar-09, 01:22 AM
On 2003-03-08 19:31, RafaelAustin wrote:
My question about solar sailing always has been: Does anybody know the effective range of the solar wind? Surely at some point it becomes insignificant. Would this be at the boundary of the Oort cloud? At that point, it seems it would be safer for the craft to jettison its sail and continue coasting on its momentum.


Solar sails do not use the solar wind. They use the light pressure from the Sun. Still, that also diminishes (at an inverse square rate), so it would cease to be useful beyond a certain distance. Plans I've seen to use solar sails for interstellar missions involve first getting the probe in close to the Sun in order to maximize the thrust generated by the sail.

roidspop
2003-Mar-09, 03:07 AM
I think Robert Forward re-invented solar sails with his story "Rocheworld"; an interstellar expedition is launched with a two-stage solar sail. Instead of relying on feeble sunlight alone, we build a giant laser complex near Mercury, capable of sending a manned mission off at a substantial fraction of the speed of light. The second stage comes into play at the destination system; the sail comes apart into a huge outer ring and a much smaller inner disk to which the payload is attached. The laser beam is reflected from the ring onto the 'braking' sail and the effect is to slow the payload and drop it into orbit around the target star. We are certainly capable of building some big lasers now...somebody might think seriously about interstellar probes based on Forward's ideas...just as soon as we get that space elevator built!

g99
2003-Mar-09, 03:17 AM
We could also attach a laser to some of the larger asteroids or moons of other planets to slow down the ship faster or allow for faster return trip. We would just have to get out there to build the laser in the first place.

Erekose
2003-Mar-09, 03:34 AM
On 2003-03-08 22:07, roidspop wrote:
I think Robert Forward re-invented solar sails with his story "Rocheworld"; an interstellar expedition is launched with a two-stage solar sail. Instead of relying on feeble sunlight alone, we build a giant laser complex near Mercury, capable of sending a manned mission off at a substantial fraction of the speed of light. The second stage comes into play at the destination system; the sail comes apart into a huge outer ring and a much smaller inner disk to which the payload is attached. The laser beam is reflected from the ring onto the 'braking' sail and the effect is to slow the payload and drop it into orbit around the target star. We are certainly capable of building some big lasers now...somebody might think seriously about interstellar probes based on Forward's ideas...just as soon as we get that space elevator built!


But you would be using "the feeble light of the sun", the reason you put the laser on mercury is because you can build a more efficient solar power plant that close to the sun, this would be used to power the laser

<font size=-1>[ This Message was edited by: Erekose on 2003-03-08 22:35 ]</font>

russ_watters
2003-Mar-09, 04:06 AM
How do pressure differences work in space? Same way they do everywhere else - except a LOT weaker.

People are saying though, that solar sails work off of light, not solar wind - and after a quick google, I find I'm wrong...

Chuck
2003-Mar-09, 04:22 AM
Maybe a Daedalus type of mechanism could be used to slow the ship when it gets far from the sun. The nuclear bombs would be sent out in advance of the crewed mission, using solar wind only with no laser assistance. That would keep the cost down. The laser assisted crewed mission would catch up to the bombs and use them for slowing.

g99
2003-Mar-09, 04:31 AM
How about use a combination of a ion engine and a solar sail? Use both at the same time and then onece the sun's contribution is near nill then roll in or let loose the sail and use the ion engine the rest of the way.

Colt
2003-Mar-09, 06:30 AM
^ Both gradual and gentle. /phpBB/images/smiles/icon_biggrin.gif I was going to post now and explain more of what I was thinking but other people got in front of me. *goes off to pout* -Colt

tvelocity
2003-Mar-09, 10:50 AM
There seems to be some confusion on this thread between solar radiation and solar wind. A solar sail would be propelled by radiation, most likely in the visible spectrum. Solar wind, on the other hand, is composed of charged particles, like protons and helium nuclei. CNN seems to be experiencing this confusion as well. I don't know if solar wind can be used this way, but it seems to me that solar wind would be somewhat unpredicatble, especially near a strong magnetic source like Earth or Jupiter. Light, on the other hand, always has a vector pointing directly away from the sun.

Nightfall
2003-Mar-09, 09:06 PM
On 2003-03-08 19:44, Lexx_Luthor wrote:

Fortunately, the "only" problem of rockets is engine specific impulse (here I go again). Unfortunately, this will be the most sticky problem that will ever face space travel. This is what needs the most work.

If solar sails are needed it will be because of failure to vastly increase rocket engine specific impulse. Don't always celebrate failure.


Or solar sails could be needed because they are a simpler and more practical approach to space travel, atleast within the solar system. The problem is that we haven't tested solar sails enough to know which is better. Don't always assume something will fail before you test it.

Nanoda
2003-Mar-10, 12:07 AM
I seem to recall that there was an international solar sail competition planned, but cancelled, which is how Mir ended up with one of those giant mirrors they tested a while back. Google isn't helping me; am I confuzled?

FYI - One of the "sponsored links" searching for solar sails is this place: www.teamencounter.com (http://www.teamencounter.com/) They seem to have some genuine NASA contacts and some real science, but it's mixed with a huge dose of almost star-registry class fund raising. Plus they don't say when they're launching their sail. :-/

Lexx_Luthor
2003-Mar-10, 12:48 AM
Or solar sails could be needed because they are a simpler and more practical approach to space travel, at least within the solar system.Actually, inner solar system. Agreed:: Wind sails are simpler and more practical for sailing the Earth's oceans when there are ~no~ mechanical engines. /phpBB/images/smiles/icon_biggrin.gif The trick here is the development of engines that can replace sail vessels. Granted, the specific impulse of today's rocket engines is the same as saying ~no~ engines are available, so sailing the solar system is the way to go. Until when (or even if ever) such engines are made, we can agree solar sails are our best bet.

As this is a solar sail thread, it must be mentioned that failure to develop sufficiently efficient rocket engines means total failure to move beyond solar sails. I am not anti~solar sail. Like Babylon 5 creator JMS, I just tell the story like it is. Of course, JMS got attacked by Christians and Athiests alike for not choosing one side over the other. The universe is far more fascinating than one person's/personette's message.

Do we still have a stereotype of a "rocket" from the old Buck Rogers movies?

Even with fantastic engines available, solar sails may be more cost effective (hence practical) at un-manned interplanetary cargo shipping. Once you fill up a route with sailing cargo, the goods will arrive at the destination with sufficient frequency to be useful. Remember, these cargo solar sailers have no crew.

Beware interplanetary pirates using high specific impulse rockets. /phpBB/images/smiles/icon_biggrin.gif

Colt
2003-Mar-10, 06:09 AM
Looking at the picture on APOD I thought up some specs for it.

- Partial cable-tension and rigid rigging.
- Maybe solar power to supplement onboard power (guessing at what those rectangles are).
- Perhaps a RCS system, no other idea what those tanks might hold.

- Main communications disc similar to those used on earlier probes, maybe fixed so the RCS is used to orient it.

I actually do not see a "sensor pod" on it. Where would this be located at? On the front of the sail or behind it?

Found this (http://www1.msfc.nasa.gov/NEWSROOM/news/video/2000/2000movies/00-150/Animation.mov) by going through the "explored by NASA" link on the APOD page. Wouldn't the satellite in orbit also be pushed too? Or would the Earth's (or other object's) gravity well be sufficient to hold it in place?

A satellite of this sort would raise some serious questions.. It could possibly used as a weapons platform. -Colt

g99
2003-Mar-10, 06:49 AM
Yikes! I would not want that satelite to be turned around. No matter how much power it puts out. If it can propell the sail so it accelerates that fast it must be powerful.

But then again it will make the family B-B-Q really cheap. /phpBB/images/smiles/icon_smile.gif

daver
2003-Mar-10, 06:31 PM
There are two types of solar sails. The older type uses photons, and a mirrored sail. A. C. Clarke wrote a short story involving a solar sail race to the moon (Sunjammer, i think).

The newer type of solar sail uses the solar wind and a magnetic sail. This is sometimes called a magsail.

Neither one has been demonstrated outside of a lab; the one in the article is of the first type--maybe we should call it a lightsail.

Robert Forward has proposed similar sails using beamed microwaves.

logicboy
2003-Mar-10, 07:35 PM
I didn't read every post so excuse me if this has been covered in an earlier post.

Can you use light from other stars?
If you cant, how do they propose using solar sails for interstellar travel?
If you can is it possible to make the sail so that it can only be pushed in one direction therefore allowing you to go in any direction using light from other stars.

daver
2003-Mar-10, 08:05 PM
On 2003-03-10 14:35, logicboy wrote:
I didn't read every post so excuse me if this has been covered in an earlier post.

Can you use light from other stars?
If you cant, how do they propose using solar sails for interstellar travel?
If you can is it possible to make the sail so that it can only be pushed in one direction therefore allowing you to go in any direction using light from other stars.



Inverse r-square.

Some proposals have been made for solar sails for interplanetary travel. You can use the solar sail by itself to accelerate to some small percentage of light speed and, when you get close enough to your target, use the light from that star to brake you into stellar orbit.

You can use a laser launcher to boost your solar sail to a somewhat larger percentage of light speed; you'll need some method of slowing down again at the far side. Maybe magsail or a staged solar sail (the staged solar sail assumes that by the time your probe gets to the target star that a really huge laser array has been built around ours).

Colt
2003-Mar-11, 05:42 AM
"..secret, secret, I've got a secret!"
Bah, I can not get it out of my head. I will post later, I have some ideas. -Colt

David Hall
2003-Mar-11, 05:35 PM
On 2003-03-10 13:31, daver wrote:
There are two types of solar sails. The older type uses photons, and a mirrored sail. A. C. Clarke wrote a short story involving a solar sail race to the moon (Sunjammer, i think).


The Wind From the Sun, 1964. Printed in the short story collection of the same name, but it was titled Sunjammer when it was first published in Boy's Life. It's about a solar sail yacht race. They start in geosynchronous Earth orbit, circle the Earth twice to pick up speed, then race outwards. The first ship to cross lunar orbit was the winner.

Logicboy, other stars put out photons too, so the light could be used except for the fact that they are too far away. But if we were to use solar sails to travel to another star, we could accelerate using our own Sun, then turn around and use the other sun to slow us down again. But it would be a pretty slow way to go about it. You'd be decelerating for half the distance there (varying depending on the photon output of the other sun). Niven and Pournelle had a solar sail ship do this at the beginning of A Mote in God's Eye, for example.

daver
2003-Mar-11, 07:47 PM
On 2003-03-11 12:35, David Hall wrote:
But if we were to use solar sails to travel to another star, we could accelerate using our own Sun, then turn around and use the other sun to slow us down again. But it would be a pretty slow way to go about it. You'd be decelerating for half the distance there (varying depending on the photon output of the other sun). Niven and Pournelle had a solar sail ship do this at the beginning of A Mote in God's Eye, for example.



You aren't going to get much acceleration unless you're quite close to the sun. After Saturn, it might be best to furl your sail to protect it from damage during the voyage (this assumes you have a decent mechanism for furling and unfurling it. a sail repair mechanism might be less complicated).

If you're boosted with laser light you're presumably going to need something other than starlight at the other end to slow you down. It's been a long time since i read the book--did the Motie capsule have a fusion drive for deceleration?

Donnie B.
2003-Mar-11, 08:17 PM
As I recall it...

The Moties knew that there were intelligent beings at Murcheson's Planet (the goal of their sailing mission). They assumed that the humans would recognize the meaning of the coherent light from their launching laser and build one of their own to decelerate them.

The humans didn't, so when the Moties arrived they basically flew into the star, unable to decelerate enough to make planetfall and unwilling to allow the humans to pursue and capture them.

Colt
2003-Mar-12, 03:42 AM
Yeah, just give away the entire plot, why don't you.. /phpBB/images/smiles/icon_biggrin.gif I need to go raid my local bookstore again for Niven Novels. /phpBB/images/smiles/icon_smile.gif

Would someone link me to a page about the book "Rocheworld" or tell me a bit about it? Thanks.

If we ever did invent some sort of cold-sleep/hibernation/stasis technology would we be able to mount a manned mission to the nearest stars? Would it even be the best choice? -Colt

roidspop
2003-Mar-12, 05:56 AM
Would someone link me to a page about the book "Rocheworld" or tell me a bit about it? Thanks.


This is what I found; http://www.goldkeys.com/ScienceFiction/reviews/0671499394.html

Chip
2003-Mar-12, 05:37 PM
The Planetary Society, working with the Russian Space Agency, is moving toward an important solar sail (http://www.planetary.org/solarsail/) test.

We discussed an interesting article about solar sail interstellar flight applications, written for the layperson here (http://www.badastronomy.com/phpBB/viewtopic.php?topic=4032&forum=1&29), and the thread is also interesting despite an inevitable drift into nonsense.

daver
2003-Mar-12, 05:40 PM
On 2003-03-11 22:42, Colt wrote:

If we ever did invent some sort of cold-sleep/hibernation/stasis technology would we be able to mount a manned mission to the nearest stars? Would it even be the best choice? -Colt



For interstellar voyages we'd probably need stasis rather than cold sleep. Voyage time is going to be on the order of centuries.

I don't know if it would be your best choice. O'Neill colonies would likely be less expensive--colonize our system before going to others. If you could get a colony that could survive for millenia without outside resources, someone is going to launch their's towards another star.

So, sleeper ships or generation ships or something else? I see no reason to believe that a stasis field will be discovered, and cold sleep probably won't work for more than a few decades. So, most likely something else, least likely sleeper ships. IMO, of course.

Colt
2003-Mar-13, 12:24 AM
On 2003-03-12 12:37, Chip wrote:
The Planetary Society, working with the Russian Space Agency, is moving toward an important solar sail (http://www.planetary.org/solarsail/) test.

We discussed an interesting article about solar sail interstellar flight applications, written for the layperson here (http://www.badastronomy.com/phpBB/viewtopic.php?topic=4032&forum=1&29), and the thread is also interesting despite an inevitable drift into nonsense.


Don't you mean "working with the Russian Black Hole"? /phpBB/images/smiles/icon_biggrin.gif

I thought that that experiment ended when the Russian's piece of junk rocket failed and the entire thing smashed into a penninsula somewhere? -Colt

Chip
2003-Mar-13, 12:39 AM
On 2003-03-12 19:24, Colt wrote:
"I thought that that experiment ended when the Russian's piece of junk rocket failed and the entire thing smashed into a peninsula somewhere?" -Colt

Well...yes and no. Yes, the test last year failed. The Planetary Society is going to try again. (Their WebPage is old.) The rocket by the way was fired from a submarine. Kind of unusual. And no, despite the perception that Russian technology is cruder than Western technology, this isn't always true. The rocket they used was pretty advanced and well built, but as you know, space is dangerous and glitches can arise within anyone's space program. /phpBB/images/smiles/icon_wink.gif

Colt
2003-Mar-13, 02:29 AM
Tell that to the owners of that commsat that got stuck in LEO a while back. /phpBB/images/smiles/icon_wink.gif -Colt

Chip
2003-Mar-13, 08:35 AM
On 2003-03-12 21:29, Colt wrote:
Tell that to the owners of that commsat that got stuck in LEO a while back. /phpBB/images/smiles/icon_wink.gif -Colt

Again, I would say generally speaking, Western aerospace technology is more refined than Russian technology - historically. I've been around early MiGs up close (MiG 15,) and they are very well made, though harken back to WWII technology in terms of riveting and finish. Newer MiGs are on par with U.S. designs in quality. Rockets can develop all sorts of problems, and American and Russian designs have had more than their share of launch-pad mishaps and explosions. Both are generally much more reliable today, but nobody's perfect.

My point is, space is dangerous (to humans and robots) and that's accepted. Some Russian spacecraft are outstandingly well built. The American Mars Polar Lander (built for NASA) was also an excellent design. It crashed too. I don't think that was because it was badly made. The fault was a glitch in the programing. Same thing happened with the trajectory of the Russian rocket intended to deploy the solar sail.

tvelocity
2003-Mar-13, 09:09 AM
The Russian approach to engineering vs. American can be seen in priorities. American engineering tends to include a lot of gee-whiz gadgets and gizmos, using very high-tech and very expensive technology. The Russians, lacking somewhat in all of this tend to refine what they have, which ingenious results. The best assembly language programmers in the world are Russian, mainly because they still use 386-486/DOS based machines, and have to wring every bit of performance that they can out of them. The Russians are very good engineers with nothing to engineer. We should be hiring them and using their practical methods and expertise to keep our own space program within budget and our solutions realistic.

ToSeek
2003-Apr-28, 04:23 PM
Commercial effort toward a solar sail-propelled spacecraft (http://www.space.com/spacenews/spacenews_businessmonday_030428.html)