Solar Super-Sail Could Reach Mars in a Month

ti-coune sent us a story running on newscientist describing solar super sails and how they could one day get us to Mars in a month. The key is a special new paint. The cast of Trading Spaces is unavailable for comment.

Comments

Re:Cast? What cast?

[MyLongNickName]

The grandparent was meant as a joke (almost as fast as dihydrogen monoxide is the tip off).

I put 2 jokes in there.

[numbski]

TWO JOKES!

I should be modded funny. Not interesting, and not troll. :P

That was supposed to be funny. You're in a vaccuum. I almost mentioned something about Paige Davis and sex tapes, and STAYED ON TOPIC!!!!

Come on mods, live a little. :P

Re:Then what?

[merlin_jim]

So you're going faster than any interplanetary craft to date, and your only propulsion system requires you to be moving away from the sun (or the Earth, if they're using a laser to push you)

As I've previously discussed on slashdot, you do not need to be moving outward from your energy source in a solar sail, you can achieve thrust vectors in any direction from full away to orthogonal (perpendicular for the 2D vector peeps)

And orbital mechanics isn't of the form of "thrust straight at where you want to go" it's more like "thrust in the direction of orbit to move away from primary, thrust against the direction of orbit to move towards primary"

The only time a solar sail would even find it efficient to thrust directly away from the inner solar system is if it was an interstellar sail, after it reached escape velocity... before then thrust away from the primary doesn't change the mean orbit distance, it changes the eccentricity of the orbit.

Re:Holes in the sail?

[merlin_jim]

I wonder how susceptible this sail would be to space dust, meteorites and space junk?

Not that susceptible. You design it to tear on impact, leaving an impact hole only marginally larger than the impact object.

This sail isn't like a wind sail; wind sails work off of a pressurized fluid, which will tend to flow through holes and tears, meaning even a small tear can greatly effect efficiency.

This sail works off of photon pressure, which does not flow like a fluid, so a small hole means you only lose thrust in proportion to the area of the hole...

Airobreaking

[essreenim]

1. Airobreaking.

This is where a craft uses the planets atmosphere to dramatically reduce speed using friction. Its actually been used for decade but never on this large a scale..!! Later on

2. Slowing down sufficiently with a Mars based system similar to the one on earth.

OR

3. A series of mirors which are swung into position at the right time to begin deceleration which reflect the light onto a surface pointing the opposite direction from source of beams..

Re:Cast? What cast?

[Jonathan_S]

"The feat would require a 60-megawatt microwave beam with a similar diameter to the sail. It would also have to be capable of tracking the craft as it accelerated away. But this power level could not be delivered by any existing microwave transmission system. The deep-space communications network that NASA uses to communicate with Mars rovers and the Cassini probe now orbiting Saturn can only manage half a megawatt. The Benfords say the power could be ramped up in future and hope to persuade NASA to consider doing this as part of a future upgrade to the network.

So basically NASA's currently-used equipment is 1/120th of the power needed to get this sail to Mars. I would say this idea is not in our near future for sure.

Um, NASA's current communications system puts out 1/120th of the power needed for this sail.

That's like saying since your cell phone can only put out 1/2 a watt it's impossible to heat things in your microwave.

A couple of points of reference, the radar mounted on US Aegis cruisers can put out 4 MWs and the stationary Cobra Dane early warning radar that went online in 1977 puts out 15.4 MW.

I don't think we are that far away from building a 60 MW transmitter now that we have a reason to.

Re:Cast? What cast?

[GileadGreene]

The sail emits carbon monoxide to get its speed boost. You know, the stuff the kills humans almost as fast as dihydrogen monoxide.

Actually, if you RTFA you'll see that they discovered the effect as a result of inadvertently boiling off carbon monoxide, but the paint that the article is about would actually use something like hydrogen (or perhaps methane).

You know, the stuff that burns much faster than dihydrogen monoxide ;)

Orbital velocity

[willCode4Beer.com]

Remeber, both Mars and Earth are going around the sun. You aren't sending it in a straight line. You are actually pushing it out to a "higher" orbit to intercept with Mars. To bring it back, simply change the angle (vector of force) and push it to a "lower" orbit. Plain 'ol high school physics here.

- higher means further from the sun and lower means closer.

Re:Cast? What cast?

[Tassach]

A couple of points of reference, the radar mounted on US Aegis cruisers can put out 4 MWs and the stationary Cobra Dane early warning radar that went online in 1977 puts out 15.4 MW.

I don't think we are that far away from building a 60 MW transmitter now that we have a reason to.

Unfortunately, RADAR, like all other forms of non-coherent EM radiation, spreads out over distance. In order for this to work, you need to have the power actually hitting the sail, which basically means you're going to need a battery of MASERS which will still be sufficiently focused at 35 million miles to deliver most of their power to the sail.

Re:Why pipe microwaves from the surface?

[Tim C]

The amount of solar radiation incident on the surface of a sphere at the distance of the Earth's orbit is approx 1370W/m^2.

I'm not an EE, but I used to be a physicist :-)

Re:Why this is not helpful; other useful technolog

[Dr. Zowie]

That's correct -- the energy isn't coming directly from chemical bonds -- but it's still difficult to make the molecules leave with more energy than is contained in the bonds holding them in place. The issue is that, once they obtain sufficient energy to escape, they do so. In order to put any more energy on onto the propellant, you have to somehow keep interacting with it after it already has obtained the escape energy.

Ion rockets do this by putting an electrical potential on the propellant mass. Then when a freshly ionized propellant molecule leaves the engine, it is electrostatically repulsed from the back of the engine (and perhaps attracted by the exit grid). That repulsion is what imparts the final "kick" to it. It's the same technology that makes old-style television sets and other particle accelerators work.

But this paint scheme has no such macroscopic design -- from the article, it sounds like they're just trying to heat it fast with microwaves.

Re:Cast? What cast?

[JJ]

Yes, but you could anchor the corners, like we do here with a mast. Does a sailboat sail only provide momentum to the portion of the boat that is behind it? A mast erected at the stern of a sailboat still pushes the whole of the boat forward.

Re:Cast? What cast?

[Tomfrh]

Slender members buckle under compression regardless of whether they are space or not. Gravity has little to do with a members compression buckling load.

Members which 'hold things apart' as you put it, cannot be thin, because thin members buckle. Have you never pushed on the ends of a ruler and seen what happens? This buckling behavior happens in space too. Based on what you are saying, astronauts could not push on the ends of a ruler and make it buckle. The simply fact is that thin elements, or more specifically members with a very low section modulus, are not rigid in bending, and are thus not suitable as compression members.