Sailing to Mars

[ToSeek]

Solar super-sail could reach Mars in a month

A LICK of paint could help a spacecraft powered by a solar sail get from Earth to Mars in just one month, seven times faster than the craft that took the rovers Spirit and Opportunity to the Red Planet.

So, how many science fiction writers are named in this article?

[skrap1r0n]

Sounds like they have quite a lot of develpment to go in order to make this viable. Plus it does absolutely nothing for a return trip.

[um3k]

I like this idea.

Of course, I like any idea that speeds up space travel.

[Romanus]

Cool idea, but I have to admit that idea of a 60 megawatt MW transmitter probably gives engineers kittens. And at 60 km/s, we'd be going way too fast to slow down economically. It would be a great concept for a KBO or interstellar mission, though--a 60 km/s spacecraft could make it to Pluto in less than 2.5 years, and the heliopause in maybe 10 years. Sweet.

The solar sail concept in general has been greatly underused, IMO.

[fossilnut]

"would be a great concept for a KBO or interstellar mission,"

???

Just don't hit a speck of space dust or KAPOW!

[Cugel]

And at 60 km/s, we'd be going way too fast to slow down economically.

Maybe not. The sail is of course flat and circular, spinning with low RPM. The middle section can be seperated from the main sail. This smaller section has a diameter of 10 to 20 percent of the main sail. Roughly halfway the trip (or at any time you want to start breaking) the small middle section of the sail is cut loose and deployed in front of the main sail. The beam that powers the sail will go through the big hole that is now at the center of the main sail. It is then reflected from the small sail and will hit the main sail at the front end. This will produce a force opposite the direction of travel. For this to work you need to make the painted sail double sided of course.

This setup seems to work for ordinary laser powered sails but it seems very effective with this 'painted' type of sail.

[Nicolas]

And at 60 km/s, we'd be going way too fast to slow down economically.

Maybe not. The sail is of course flat and circular, spinning with low RPM. The middle section can be seperated from the main sail. This smaller section has a diameter of 10 to 20 percent of the main sail. Roughly halfway the trip (or at any time you want to start breaking) the small middle section of the sail is cut loose and deployed in front of the main sail. The beam that powers the sail will go through the big hole that is now at the center of the main sail. It is then reflected from the small sail and will hit the main sail at the front end. This will produce a force opposite the direction of travel. For this to work you need to make the painted sail double sided of course.

This setup seems to work for ordinary laser powered sails but it seems very effective with this 'painted' type of sail.

That would mean you'll have to point the laser at the whole sail in the accelerating phase, and only through the hole in the decelerating phase. That requires very high accuracy if you want to do that near Mars. In theory, the concept works of course. With 10% hole, you get only 80% braking power instead of 100% accelerating power, so you'll need to brake longer. (90% usable surface, and 10% still accelerating).

[Fram]

Not necessarily. It would be a bit hard to make a middle bit that is emitting gas when you want to accelerate, but that becomes a concave mirror when you want to decelerate. And a reflected beam will never have the power of the original beam, so you lose even more power. So the calculations and the technical side are a bit more complicated than that.

Perhaps (thinkong out loud here) you could make the sail switchable? I mean: when you want to accelerate, you work as described. For decelerating, you turn the shield around, so that it still receives the beam, but the gas particles are emitted on the other side (with less efficiency probably, as you don't heat them directly but through the sail, with conduction?). Then you don't need to change the beam at all, and perhaps you can even use this system to make it there and back again, instead of only there...

[Nicolas]

Not necessarily. It would be a bit hard to make a middle bit that is emitting gas when you want to accelerate, but that becomes a concave mirror when you want to decelerate. And a reflected beam will never have the power of the original beam, so you lose even more power. So the calculations and the technical side are a bit more complicated than that.

Perhaps (thinkong out loud here) you could make the sail switchable? I mean: when you want to accelerate, you work as described. For decelerating, you turn the shield around, so that it still receives the beam, but the gas particles are emitted on the other side (with less efficiency probably, as you don't heat them directly but through the sail, with conduction?). Then you don't need to change the beam at all, and perhaps you can even use this system to make it there and back again, instead of only there...

Some thoughts:
-I thought a solar sail is made to reflect in order to produce thrust, whether it has gass emission or not (you still want the photon force as well with gas emission I thought). The reflected beam will have less energy than the original one, but it won't be much if reflection is very good. So the sail/mirror problem is not a major concern I think. How to keep good reflection when having an ablative layer is another case however.

-On your braking way, you lose the photon force part if you want to heat up your shield for gas emission on the other side (a reflective shield wouldn't heat up that much)

-I was wondering what is the advantage of having a solar sail that emits mass instead of a normal engine and a normal solar sail. Allright you leave the "LASER" (thinking Dr Evil here ) at home, which has it's equivalent in the mass propulsion system you have to carry with you (not the fuel mass itself). But if you can get substantially higher exhaust velocities with a conventional engine, where is the advantage in using the sail? Is the sail's ga emission significantly more effective?

-What is the amount of the solar thrust force, if you already have a massive laser beaming at it, hence giving a large photon thrust force, and a gas emmision force? Does it still deserves the name "solar sail"?

If anyone has info on these points, I would like to learn.

[Argos]

As the paint begins to boil the haze formed by the recoiling molecules would tend to scatter the incoming microwave radiation, diminishing efficiency. At the braking phase this would be a great problem.

[Fram]

Not in my solution! In the braking phase, the incoming microwave doesn't touch the boiling surface but the other side.
There will of course be other problems, but I guess they will be pointed out soon enough 8)

[foxd]

Cool idea, but I have to admit that idea of a 60 megawatt MW transmitter probably gives engineers kittens.

I don't see that it would be much of a problem, it would probably be built using a phased array of antennas and a bunch of smaller MW transmitters frequency locked together to get the required power.

[Kizarvexis]

And at 60 km/s, we'd be going way too fast to slow down economically.

Maybe not. The sail is of course flat and circular, spinning with low RPM. The middle section can be seperated from the main sail. This smaller section has a diameter of 10 to 20 percent of the main sail. Roughly halfway the trip (or at any time you want to start breaking) the small middle section of the sail is cut loose and deployed in front of the main sail. The beam that powers the sail will go through the big hole that is now at the center of the main sail. It is then reflected from the small sail and will hit the main sail at the front end. This will produce a force opposite the direction of travel. For this to work you need to make the painted sail double sided of course.

This setup seems to work for ordinary laser powered sails but it seems very effective with this 'painted' type of sail.

How do they get the beam only to travel through the middle of the sail? When shooting lasers at the moon the laser spreads out to a 1 mile wide beam when it gets to the moon. And that is considered good accuracy to have part of that 1 mile wide beam sweep over the reflector left on the moon by the Apollo astronauts. Hitting just the small hole in the sail at 15+ million miles ought to be fun.

The reflector made laser ranging possible. By bouncing a laser pulse off that little target, we could measure the distance within a few feet. Of course, astronomers had to hit the reflector from a quarter million miles away. It was some help that even a laser beam spreads out in such a long journey. It's a mile wide when it reaches the reflector. But that's still like using a rifle to hit a dime from a distance of two miles. Then they had to catch the reflected beam when it came back.

link

Kizarvexis

edit: Fixed my quote box

[Kizarvexis]

Here is a Wikipedia page on escape velocity that also has a list of escape velocities for various points in the solar system that I thought might be useful in this discussion.

Kizarvexis

P.S. A discussion on B5wars.net spurred me to look up this info.

[Fram]

Escape velocity only counts when you stop accelerating. If you have thrust, escape velocity becomes irrelevant. In this proposal, you have a constant power source, so you could lift off with 100 kph and still leave the earth.

[Nicolas]

I know you're making a theoretical point Fram, which is correct ideed: as long as your velocity points away from the earth, you ARE moving away from the earth. That said, I just don't WANT to know the size of a lightsail that can generate enough thrust to move a satellite at a constant 100 kph away from the earth (I know, I know, that wasn't a proposal).

[Kizarvexis]

But doesn't the escape velocity of the body count when you are trying to be captured into an orbit around that body?

Kizarvexis

[Fram]

Ah, that way. Yes, it does! I had only thought about ecaping, not about not escaping