Solar Super-Sail Could Reach Mars in a Month 499
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.
Cast? What cast? (Score:4, Funny)
BTW. The sail emits carbon monoxide to get its speed boost. You know, the stuff the kills humans almost as fast as dihydrogen monoxide.
You really want to be behind that thing for a whole month?
Re:Cast? What cast? (Score:5, Funny)
Re:Cast? What cast? (Score:3, Informative)
Re:Cast? What cast? (Score:3, Funny)
Re:Cast? What cast? (Score:4, Insightful)
Re:Cast? What cast? (Score:3, Interesting)
Re:Cast? What cast? (Score:3, Insightful)
The microwave radiation thing wouldn't be an issue to the occupants of the ship - they're going to be sitting inside a metal enclosure, and will be shielded from the radiation the same way you are if you're standing in front of your countertop microwave waiting for the water to boil. Similarly, the m
Re:Cast? What cast? (Score:3, Insightful)
Since the beam was intended to be parallel, the distance doesn't matter. You could do this I suppose if you built a 100m diameter maser, although it's not immediately apparent to me ho
Re:Cast? What cast? (Score:5, Funny)
You really want to be behind that thing for a whole month?
Right, like they're going to be flying along to Mars with the windows open.
Re:Cast? What cast? (Score:2)
Re:Cast? What cast? (Score:2)
Re:Cast? What cast? (Score:3, Funny)
I'll take that risk. I was never that good at breathing in outerspace anyways....
I put 2 jokes in there. (Score:2, Informative)
I should be modded funny. Not interesting, and not troll.
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.
Re:Cast? What cast? (Score:5, Interesting)
"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.
Re:Cast? What cast? (Score:5, Informative)
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? (Score:5, Informative)
Re:Cast? What cast? (Score:5, Insightful)
Then it coasts.
So, basically you build 20 2 MW transmitters and focus their output on a point a few hundred or thousand miles away -- I assume after an hour the craft will be moving away pretty damned quick, so a few thousand miles then.
How does this thing STOP? You make Mars, but what's slowing it down from 150 miles per second so that it'll achieve orbit? Atmospheric braking? Um, no, let that go - no airbraking, it'd vaporize. Even if it could withstand a 150 mps entry without puffing out, it'd punch out of the atmosphere in seconds, with no time to kill much speed. No rockets either -- can't carry enough fuel to kill 150 mps.
You'd need another microwave array in a high Martian orbit to fire at the solar sail as it came streaking in from Earth, if you want it to downspeed to make orbit. I'd assume the sail reverses somehow, so the craft comes in tail first.
Now. If you want a FAST vehicle, build a solar powered multi-megawatt laser at an LaGrange point, and use the nicely focused red laser on a solar sail. The craft'll be at Mars in, what, two weeks?
There's a couple of points that occur to me: the mass of the object being towed by the sail is irrelevant, mostly; you could tow the Sears Tower if you want. You'd just have to fire the lasers/microwaves for a longer time. A laser/purely reflective sail would be used for really heavy objects, and the gas-outing microwave system for smaller payloads, because the amount of paint on the sail is limited and will be exhausted, while a pure mirror-sail is static and can be used indefinitely.
Re:Cast? What cast? (Score:3, Interesting)
I should have RTFA first :-) You're right.
Good question. Off the top of my head, I'd say you'd slingshot around Mars so you're headed back twords the sun and use the sun (or, as you suggest, a laser in Earth orbit) to decellerate enough to get into orbit around Mars. I don't know how long it would take to decellerate with a
Re:Cast? What cast? (Score:3, Funny)
Re:Cast? What cast? (Score:5, Informative)
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 ;)
Monoxide Warning (Score:4, Funny)
"Yeah, they found the poor bastard in his space garage with the door closed and the solar sail running. Damn shame."
Re:New Slashdot record! (Score:3, Insightful)
Re:New Slashdot record! (Score:2)
In related news (Score:3, Funny)
Re:In related news (Score:5, Funny)
man, if you have a time machine, words like "immediately" don't really mean anything.
What is this...Fark? (Score:4, Funny)
Re: what is this...fark? (Score:4, Funny)
Fuel (Score:5, Interesting)
My question is, what kind of payload is practical with this kind of thing? I've always read that to get any kind of larger payload, you cannot use solar sails. Do they get around this by using the microwave beam they talked about (ie higher energy per square meter)? I wish there were more numbers in the article...
Re:Fuel (Score:5, Insightful)
Going at 60 kilometres per second it is going to take a good amount of fuel and time to slow that thing down.
Re:Fuel (Score:4, Insightful)
Re:Fuel (Score:5, Interesting)
Incidentally, I want to see their 60 kps calculation ... that's a huge momentum change over an hour! The average acceleration for 60000 m/s in 3600 seconds is: ~16.7 m/s2. I don't know about you, but methinks they got a decimal point wrong. Or their entire ship was made of aerogel and has very little mass...
Here's some fun math: 60 MW of (1mm/300GHz) microwaves will carry a momentum of 0.2 N; if the sail absorbs all of the photons, the force would be 0.2 N; if it reflects them completely the force would be 0.4 N. To get an acceleration of 16.7 m/s2 you need a force of 16.7 N per kilogram. All this says is that they're getting a lot of force from breaking the chemical bonds in the paint. Kind of like burning fuel.
Show my work: Energy per photon is h*f where h is plank's constant and f is the frequency. For 300 GHz microwaves, f = 3e11 Hz and h is always 6.626e-34 J.s; each photon has ~2e-22 J. 60 MW means you have ~3e29 photons per second. Momentum per photon is p = h/w, where w is the wavelength (1e-3 m), so each photon has a momentum of ~6.6e-31 N.s. 3e29 photons per second of 1 mm microwaves have a momentum flux of 0.2 N.
Re:Fuel (Score:5, Funny)
Re:Fuel (Score:2)
Re:Fuel (Score:3, Funny)
Then what? (Score:5, Interesting)
How do you slow down? Orbital insertion at that speed would be seriously difficult, if not impossible.
Re:Then what? (Score:3, Funny)
Re:Then what? (Score:3, Interesting)
Re:Then what? (Score:2)
But it is a very similar principal with very similar problems, with very similar solutions to those very similar problems.
However, Niven's approach would not work going to Mars...
Re:Then what? (Score:5, Informative)
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.
Airobreaking (Score:3, Informative)
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:Then what? (Score:3, Interesting)
There's a million comments already along these lines. Isn't it obvious? You cut the lines. Then you can use any type of propulsion system to slow down before impact. Just like they use similar ways of slowing down with probes right now.
Think of it as a reverse parachute. You cut the line and then burn through your fuel to actually slow down. You don't want to cut the line too late obviously, but you
Re:Then what? (Score:2)
Then you just switch from the one microwave beam to the other when you want to slow down.
Re:Then what? (Score:5, Funny)
Getting back (Score:2, Insightful)
But it w
Orbital velocity (Score:3, Informative)
- higher means further from the sun and lower means closer.
Wow.. cool! (Score:2, Interesting)
Although it may not be the most practical thing in the world, having people visit Mars gets me excited. It's just like something out of TV shows
And how does it slow down when its there? (Score:5, Insightful)
Re:And how does it slow down when its there? (Score:2, Interesting)
Re:And how does it slow down when its there? (Score:5, Insightful)
Coming back: Send robotic missions do deliver necessary parts and prefabricated modules, then send human heroes to put everything together. If some part fails, they at least are heroes.
Mind you, exploration never included the guarantee of a safe way back. It always took some people to take the risk of losing their lives.
Because you can now safely travel over the Pacific Ocean in 5 hours doesn't mean it always was like that.
Re:And how does it slow down when its there? (Score:3, Insightful)
If you could carry enough rocket power to stop that speed, you could carry enough rocket power to build up that speed, and we wouldn't need exotic ground-based propulsion systems.
You can't use rockets to stop. In fact, the suggestion that you could use another array at Mars to stop seems unlikely because of the unlikely possibility that you could vaporize just the paint on the back side of the sail, and not cause the heat to vaporize the bottom layer of paint on the
Re:And how does it slow down when its there? (Score:3, Insightful)
Normally you need less fuel to stop a spacecraft than to get it moving because you have burned up half the fuel getting the craft moving. Since fuel is the majority of the weight, stopping a probe is a lot easier than starting it. In reality the fuel to stop a probe is still significant enough, NASA uses aerobraking or orbital tricks when possible to save that weight.
The problem becomes enormously worse if you use ground propulsion, because you need to store enough energy in the fo
Re:And how does it slow down when its there? (Score:2)
Then use the same technique as jet engines. Those suck in air at the front, accelerate it and blast it out at the end. You want to break? Just reroute the blast to exit at the front instead of back.
Turn around the solar sail or open a new sail with the magic paint on the other side to emit the whatever-oxide particles towards the other direction.
So much for my naive ideas. Someone more educated in aerodynamics (after all, this is some sort of sailing) may jump in and tell me why they're
Re:And how does it slow down when its there? (Score:3, Insightful)
Re:And how does it slow down when its there? (Score:2)
http://science.howstuffworks.com/solar-sail.htm
Re:And how does it slow down when its there? (Score:2)
Well, it slows down with retro rockets.
In my humble opinion it would probably be better to send a couple of dozen humans to Mars on a one way trip the first time around so they can start building a colony. It's just to far to think about a short hop return mission.
This will never happen, the budget will have been cut so much by the time we get around to sending humans to mars it'll be a couple of guys spending a couple of weeks there with minimal scientific expe
Jumping to conclusions! (Score:5, Funny)
Did you even bother to ask them?
Why pipe microwaves from the surface? (Score:5, Insightful)
Why does this seem incredibly wasteful of energy?
Wouldn't it be far wiser to build solar panels in orbit, use them to power Microwaves, and avoid the attenuation in the atmosphere? This would have the added advantage of not draining power from the Earth to power the spacecraft: we would get our power from the Sun and pipe it directly to the spacecraft as Microwaves, without involving the planet at all (except, of course, as controlling entity).
Re:Why pipe microwaves from the surface? (Score:5, Interesting)
Wouldn't it be far wiser to build solar panels in orbit, use them to power Microwaves, and avoid the attenuation in the atmosphere?
Well, from TFA:
The feat would require a 60-megawatt microwave beam with a similar diameter to the sail.
Now, I'm no EE, so somebody please correct me if I'm wrong, but I'm thinking that generating that much power from solar cells would be an undertaking in and of itself. You'd be hard pressed to generate that much energy in space.
We can do it (Score:2)
We can do it in more than one way. (Score:2)
It could be done with solar power. Of course, full spectrum vacuum solar in earth orbit is about 1.3 kW/m^2; so, for 60000 kW, you need a minimum of 45000 m^2 of solar collection area. Since conversion efficiency tends to be about 30% at best, 135000 m^2 is more realistic-- ballpark a dozen football fields worth.
Using that area for reflectors to concentrate down to smaller power cell areas might reduce cos
Re:We can do it in more than one way. (Score:2)
Re:Why pipe microwaves from the surface? (Score:4, Interesting)
I am EE, but I don't know what is the value of Sun's radiation. IIRC, it is about 400W/m^2 on Earth, so it is in worst case the same in orbit. With cell's efficiency of 25%, we get about 100W/m2, so for 60,000,000W we need only 600,000m2. It is sqare with side of 775m - not something too complicated to build even on our current technological level.
Re:Why pipe microwaves from the surface? (Score:4, Informative)
I'm not an EE, but I used to be a physicist
Re:Why pipe microwaves from the surface? (Score:2)
On the other hand, if we could build a solar array +
Re:Why pipe microwaves from the surface? (Score:3, Insightful)
Basically microwaves can be transmitted through the atmosphere without too much trouble, while building stuff in orbit is incredibly expensive. It might be possible to create an orbital relay station to deal with issues like focus, assuming that's a problem.
Re:Why pipe microwaves from the surface? (Score:2)
I don't know. Why should it seem wasteful? Ground-based energy is incredibly cheap after all.
Let's see. Assuming very conservatively that only 1% of the power ends up illuminating the craft. That's 6 GW for an hour. Given 10 cents per KwH, that's a cost of $600,000.
Re:Why pipe microwaves from the surface? (Score:5, Insightful)
Wouldn't it be far wiser to build solar panels in orbit, use them to power Microwaves, and avoid the attenuation in the atmosphere?
Talk about penny wise, pound foolish. A 60 MW solar power station in orbit would be far larger than the International Space Station. It cost dozens of $Billions just to launch the space station; designing, launching and maintaining a 60MW station would probably cost hundreds of $Billions.
When you spend money on something, you're allocating a certain fraction of the economy towards a that purpose. That comes with a roughly similar fraction of the world's energy consumption. Dedicating huge teams of people designing, building and launching an orbital power platform will consume a commensurate amount of energy down here on this planet as they go about their tasks. Building the station and the massive rockets to launch it will consume vast energy resources before it even gets off the ground; vastly more energy than the station could ever produce.
For example, assume the station costs $100 Billion. That's about 1% of one year of the ~$10 Trillion US economy. The US consumes about 1e20 joules of energy per year, so if the money spent on the station is associated with a proportional amount of energy, that's 1e18 joules. That's more power than a 60MW power plant would produce in 500 years.
Re:Why pipe microwaves from the surface? (Score:2)
Now, anybody know if emitting light causes an equal and opposite force to absorbing light?
Photons have zero mass (Score:3, Insightful)
Okay, I am not a physiscist, and its been 13 years or more since my last physics course, but
The thrust which isn't is due to electromagetic radiation, i.e. photons, which have no mass. The microwave transmitter won't have any back thrust, any more than a flashlight hanging in a perfect vacuum is going to produce "thrust" opposite the direct
Then? (Score:2, Insightful)
Then what....!?
Total recall (Score:2, Funny)
Microwave Lens (Score:3, Interesting)
Wrrum-wrrum-wrrum... (Score:3, Funny)
Re:Wrrum-wrrum-wrrum... (Score:2)
I doubt very much CO would be a problem (Score:3, Funny)
Do you really think that they haven't thought about that? First of all, the astronauts would be in some sort of pressurized cabin that will take care of all their air-breathing needs. I'm pretty sure they wouldn't let the CO from outside get in. Furthermore, the pressure inside will be much greater than the pressure outside. Hence air will have a tendency to flow out, rather than the CO flowing in.
Re:I doubt very much CO would be a problem (Score:2)
Since there is no oxygen in space, no carbon monoxide is formed, so it wont work.
they are looking for a coating that emits gas when heated... lithium borohydride comes to mind.
Re:I doubt very much CO would be a problem (Score:2)
You might want to look up "sarcasm" some time. ^===^
neat (Score:2)
Holes in the sail? (Score:4, Interesting)
I wonder how susceptible this sail would be to space dust, meteorites and space junk? Also, in response to an earlier comment made by someone about CO, I believe this technology would be used to send PROBES mostly and not people to Mars. Think about it... if they sent a person out there, how would they get back? They would need to use conventional means, which would defeat the whole purpose. Unless of course, they had another sail, AND a microwave transmitter on Mars.
This technology will be good for sending probes, but not for sending people, just yet.
Re:Holes in the sail? (Score:5, Informative)
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...
Coming soon to a bookstore near you... (Score:3, Interesting)
I don't expect to see it in reality anytime, though, due to the basic problems with a one-way propulsion system. How do they decelerate when they arrive? There won't be anybody waiting for them at Mars with a laser pointed the other way, after all.
60 MW ... (Score:4, Funny)
Does this take into account slowing down? (Score:3, Insightful)
And while we're at it: how does one slow down a craft like this? Without destroying it or tugging along a rediculous amount of fuel, that is.
Hmmm ... (Score:2)
But it just might work.
Gregory Benford. (Score:2)
People like Benford who do many things well are inspiring.
Now, go check out the Galactic Center series. (Someone else can find the link to Amazon, Barnes and Noble, or your local book seller.)
-Peter
Amazing what you can do with math (Score:3, Insightful)
What about the Moon? (Score:2)
Just a thought...
Slightly off-topic, but (Score:2)
Pity they couldn't have got those rifle stocks
60 kilometres per second ... (Score:2)
New paint job, huh? (Score:3, Funny)
The "ricers" were right!
And all this time, I thought that inane changes to your vehicle to make it *look* faster wouldn't actually do anything for the performance.
Boy, was I wrong.
... It's not really ... (Score:3, Insightful)
For some reason I thought that solar sails captured photon pressure to accelerate an object by very very teeny tiny amounts over a long period of time.
As I read the article, they're still using the idea of a sail, but the acceleration comes from the release of gas. So isn't this a "gas sail"?
If it is a gas sail, then don't you have to worry about holes in the sail fabric/material? You're back to fluid pressure on a sail surface, aren't you?
It seems (admittedly, in my own uneducated, poorly-informed estimation) like the "gas sail" material would have to be more robust than with a solar sail.
Can someone clarify for me?
Re:... It's not really ... (Score:3, Funny)
pimp my spaceship (Score:3)
Let me guess - a flame job on the hood to make it go faster.
Slap a whale tail on the trunk and a chrome tailpipe out the back and you could get to Mars in a week!
Why this is not helpful; other useful technologies (Score:5, Interesting)
These guys are definitely on an interesting track, though. The problem with rocket engines in general is that they have a tradeoff between mass efficiency (you want to put as much momentum on each piece your propellant as possible, so that you get as much push from it as possible) and energy efficiency (it costs energy to push propellant, and you have to supply the energy).
Chemical rockets can't get much more efficient than the Space Shuttle Main Engines, because the amount of energy available for each molecule of exhaust gas is whatever you can get by chemically reacting your fuel to make the propellant molecule. The SSMEs use one of the most energetic-per-unit-mass chemical reactions around: hydrogen and oxygen (fuels) combining to make water (propellant).
Electric ion rockets do better because each molecule of propellant gets much more energy than would be available from chemical reactions. The problem there is that you still have to produce the energy. Nuclear electric propulsion uses plutonium to generate heat, which is converted to electricity and then used to run the ion rocket. Solar electric propulsion uses solar panels to generate electricity that runs the ion rocket. The problem is that both of those schemes are limited by the power available: it's hard to make energy rapidly with either a conventional radiothermal (noncritical) generator or solar panels, so while the rocket is extremely fuel efficient it is also quite slow.
Pure solar sails use the best/worst propellant in the Universe: photons. Best, because photons are disposable -- "use all you want, we'll make more!". Worst, because photons use the most energy per unit delivered momentum of any propellant in the universe. So a sail transduces huge amounts of power (at least in the inner solar system) but uses a very inefficient process to convert that energy to momentum.
Making the sail into a hybrid rocket is a Good thing, but using this paint scheme doesn't help, because the ejected molecules don't ever get much more energy than their own chemical binding energy into the paint -- that means they're being more or less wasted as propellant, because you want to put as much kinetic energy on the propellant as possible.
A better scheme is to use a curved solar sail as a concentrator to heat up a high power electrical generator, and then use the electricity to drive an ion rocket. In 2000 or 2001 I and a colleague worked up the numbers for such a scheme (there are technical problems with making high-power ion rockets; but we considered just energy flow). A smallish curved solar sail (say, 120m in diameter) can concentrate 10 megawatts of heat onto a heat collector. At 10% conversion efficiency to propellant power (15% for conversion to electricity, times 67% efficiency in the rocket engine) that would still be a megawatt of power, enough to provide hundreds or thousands of Newtons of thrust. In several scenarios we considered, the acceleration of the whole craft is higher than the unloaded self-acceleration of the sail, so it would be necessary to repel the sail electrostatically or something like that to keep its shape correct.
Ion rockets can be 100 to 1000 times more propellant-efficient than chemical rockets, provided that there is enough energy available.
Re:Why this is not helpful; other useful technolog (Score:4, Informative)
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.
people should read the important part. (Score:3, Insightful)
How do you make a construction like this? (Score:3, Insightful)
1/2*m*v^2=P*t.
P=60MW, t=3600s, v=60km/s.
At an efficiency of 100%(!), the maximum mass you can give this speed is 120kg.
The sail will be 100m across, this is 10,000 m2.
The maximum mass per square meter, including structural integrity (there will be quite a bit of force on the sail to make it accelerate to 60 km/s in just one hour, about 2000N!) is 12g/m2.
Then, I think, you will want to have some payload to reach Mars to do the actual experiments with... This needs to be subtracted from the mass of the sail.
OK, some of the mass of the sail will evaporate to enhance propulsion, so acceleration at the end (when the construction is lighter) will be higher than in the beginning, but a lage part of the energy will be taken away by the evaporating gas as well, so efficiency will be quite abit lower than 100%.
All in all, how do they think to make this construction?
Re:how can stopi it?? (Score:2, Interesting)
Can't do it. Bad for the environment. (Score:2)
Re:Not Possible, You Will Run Out of Carbon Monoxi (Score:2)