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: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...

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 ;)

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.