Finnish space boffins have been awarded €1.7m and placed in charge on an international effort to build the fastest thing ever made by the human race – namely a spacecraft propelled by the pressure of sunlight striking an enormous electrical field. The "electric solar wind sail" is not your common or garden solar sail, familiar …
what happens when you fly closer to other celestial "noisy" bodies such as juptier and saturn? How do you steer this behemoth?
ION still seems to be the way to go - even if it is fueled.
It is like sailing, angle the sail to the incoming wind and you can steer. Like the light-sail though, there's no equivalent to a keel so you still can't sail into the wind at all.
Planets act as windbreaks for this sort of sail, you coast for a while if you get behind them. Mag-sails are where the gas giants come in handy as you can get a decent kick in velocity and heading by going through their magnetic fields.
Hmmm, we need a "Yes, it's Rocket Science" icon...
Presumably you steer it as you do a helicopter:
sequentially reduce the voltage on the cables on one side of the disc, voila: vectored thrust, and without any of that messy swash-plate business to go wrong.
you could employ a sailboat-style "tacking" procedure, allowing you to travel into the wind.
Presumably you can retract the thing and just zip by on momentum when things get turbulent. Or just drop the electrical current.
Space is Big. Really Really Big.
You're assuming that it will fly close to said bodies. Unless they're specifically on the itinerary, just set your initial course to miss them. Space, even our inner solar system, is so vast that it's much much easier to avoid a given planet than it is to actually fly near it.
Consider Earth. It's a prett big planet (volume of approximately 1,097,509,500,000 cubic kilometers) but the space encompassed by just the plane of its orbit is about 900,081,000,000,000,000,000 cubic km -- over 820 million times as much space. That's just the plane of its orbit at the thickness of the earth -- a sphere the size of earth's orbit would have approximately 20 thousand times the volume of the plane.
Furthermore, using method A for propulsion does not negate using method B for steering. ION still works best when small chemical rockets are used for "quick" course corrections,and solar sails would be no different.
At a guess I'd say you wind in the wires, perform a standard gravitational sling-shot manoeuvre and then, when you're past Jupiter, extend the wires again and (possibly) get a double push. Sorted.
Do Jupiter and Saturn generate noticable amounts of ionised particles flying outwards? (Genuine question, I've never heard that they do, but I'm no expert).
I would've thought you'd just route around them if they were such a problem - there's a lot of space where Jupiter and Saturn aren't sitting.
In addition, I certainly hope we've learnt how to steer a large sail within wind. It's not like we've had sailing ships for a few thousand years.
This occurred to me, too. Surely trying for a gravity assist would make the sail fail, so it must be that the trajectory would be planned to _avoid_ outer planets. Note that this probably means this sail is not good for any target closer than Neptune, or possibly Uranus.
The ion drive is still a lot lighter than carrying tanks of rocket fuel, so use both. The electric sail would seem to have a higher efficiency in open space while the ion drive works inside the heliopause of planets. They're compatible systems since both are high-voltage electric drives. Both can be run off solar panels or a small nuke inside the asteroid belt and both would use a nuke further out, though of course any type of sail looses out when its among the outer planets unless you're blowing it along with humongous great lasers on the moon or Mercury.
No, you need a keel or centreboard to counteract the force of the wind, otherwise you'd just get pushed sideways with the wind. It's like when you squeeze a wet bar of soap between your fingers.
I don't think you can use the example of a sphere for the orbit. That only becomes relevant if the craft is going to leave the plane of the ecliptic and surely that would a Bad Thing(tm). Space is three-dimensional but pretty much everything within a solar system is on the same plane. Presumably it requires more fuel to leave the PoE than staying within it and since there's bugger all there for anyone to visit you'd be on your own. It would be like a trip from London to New York via the Moon. That might avoid issues crossing the Atlantic but if you breakdown you're a long way from help :)
As for the general idea of 'easy to miss a planet' doesn't that depend on your schedule? You might not have fuel constraints with a sail but you will presumably have time constraints. You might not have any practical choice. Sling shotting would still be a useful technique.
The only problem with ion drives and solar sails
....is that you still need a chemical booster to land and take off on anything, adding to the payload.
not a problem
Your sailing ship stays in orbit while you take a shuttle to the surface, or beam down!
I imagine you could steer by winding the cables in and out, effectively changing the centre of mass of the sail. eg. if you shorten the cables on the the 12 o'clock to 6 o'clock half of the sail you'll get less force acting on that side and the sail will gradually steer in that direction.
The sail rotates...
So shortening the cables won't work...
However... I guess you could adjust the electric field by applying voltage to one side of the field as it spins.
This only works in a resistive medium. Without an atmosphere, sea or ground friction to slow down the side that isn't receiving the force, the whole mass of the ship would be accelerated equally.
You probably have to continually adjust the field
to ensure that the sail stays pointing in the correct direction and doesn't start yawing (is that the right sailing word). If one half gets more total force than the other the direction of motion won't change but the sail will start to spin around another axis which will not be good.
If the applied force is not directly in line with the craft's center of mass, there will be a torque, and thus rotation. No friction necessary.
How do you stop it. 'cause you don't really get solar winds blowing from your target unless it's another star.
So what this really should say is "Scientists estimate this craft will reach Pluto in 5 years and crash into its surface harder than an other human built craft has before." Which would be epic if we had a non-crashing camera out there to video it and upload it to youtube for us.
In the article they refer to something called a 'plasma brake' which could come handy for that.
The concept of plasma brakes is based on electromagnetic tethers, which are being studied now for going cheaply to a higher orbits.
Throw the solar anchor over the side.
There are two forces involved
The outward pressure from the solar wind and the gravitational attraction back to the sun. To reach pluto quickly you would use the solar sail to increase your orbital velocity and hence move outward from the sun. To drop back toward the sub use the solar sail to slow your orbital velocity. This is exactly like tacking in a marine sail boat. Remember if you want to see pluto you would need to come along side in the same orbit.
Pressure Accelerating Radial Ion Sail.
Not the first...
...or the best such idea - NASA came up with M2P2 (Mini-magnetospheric plasma propulsion) back in 2000, which requires no physical sail at all:
Do it by starlight.
At night, of course :)
Orbital mechanics is your friend
Angle the sail so your angular velocity relative to the sun decreases. You will happily fall down towards the center of the solar system funnily enough accelerating in the process. A bit of ping-pong around major planets gravity fields to drop your speed and voila - you are back at earth in couple of years.
There was a repeated statement about "yeah, but you cannot tack because no keel" in half of the replies so far. You do not need any bloody keel. Sun's force of gravity can happily do the same job.
And yes it is rocket science:)
I can't see what prevents
the the wires just folding up in front of the payload. I read that the whole thing spins, so centripetal force will keep the wires extended, but unless the force is very even, surely the psudo-disk will start to precess as soon as the force becomes uneven (such as when tacking), and as the wires will not be rigid (at 25 microns, they could not be), they will just get wrapped up.
I suppose that you could say that the electric field is what is being 'struck', not the wires themselves, but I think that the small push would be transmitted back to the closest wire deforming it away from the disk.
In addition, spinning the construct would be an interesting exercise, as you would have to take into account conservation of angular momentum, and spin relatively fast when starting to deploy it and slow down as it extends outward, again, because the wires are so thin they cannot be rigid. And twisting it to tack...
The mathematics is beyond me (at least, without getting the text books out), so this is just a gut feel
The wires repel each other
"I can't see what prevents the the wires just folding up in front of the payload."
In addition to the rotation you mentioned, there is the fact that they are "tensioned" to the same high voltage, so they repel one another, and would (like electrified hair in dry air) try to stick as far from each other as possible.
>> I can't see what prevents the wires just folding up in front of the payload. <<
"The charged tethers repel solar wind protons so that the solar wind flow exerts a force on them and pushes the spacecraft in the desired direction."
Even assuming perfectly even forces, the tethers will be blown backwards into a cone. This will be resisted by their rotation, but how is the angular momentum of the tethers conserved?
I see the spacecraft body winding up a cone of tethers behind it until the tethers start snapping and it all becomes a tangled mess.
Maybe they could wind the tethers in and out periodically to even things up, but it still doesn't address the issue of maintaining spin of the whole system.
I await correction...
VASIMR, actually, because this allows you to do (relatively) high acceleration burns if required.
A VASIMR could fly to Mars and back with far less fuel and reaction mass than any chemical drive and while perhaps not as efficient as an ion drive, it allows far greater acceleration and much shorter travel times.
This may be the largest thing the human race has built (bearing in mind it doesn't exist), but it won't be the fasted. Whilst it is important to note the frame of reference (relative to the Earth, the surface of the Earth, the Sun, other planets etc.), a speed of 30km/sec would not qualify. The Helios probes approached 250,000km/hr or about 64km/sec at their closest approach to the Sun. In addition, the Gallileo probe reached 48km/sec when it was intentionally destroyed plunging into Jupiter. Even if measured against the Earth as a frame of reference, these will still beat this proposal.
It might be said that using a gravitational well is cheating, but at least these craft were built..
It will have to go it some to beat voyager 1 as well - its in the news today as it starts to head out of our solar system. It has travelled 10.8 billion miles in 33 years, which gives an AVERAGE speed of approx 17km/s. Not too shoddy for something older than most Reg readers! And if thats the average, what the hell top speed did it attain?
Forgot the brakes?
An interesting idea. But when you arrive at Pluto after only five years travel, how do you stop?
You time it to arrive at Pluto at night. No ions from the sun, so it just stops.
Pluto in 5 years
Very nice (if you're into extremely cold and dark lumps of rock), but how do you stop when you get there?
This sounds like it's one small step .... towards the real thing.
Your tax money at work
Beam me up Scotty!
Another advantage of this system is that the sail is mostly holes, so less chance of taking significant damage. Even a small rock is going to mess up a normal solar sail going 30kps.
Plus you don't have to worry about accidentally gift-wrapping an asteroid if you crash on it.
how do you keep the spokes (wires) from overlapping one another? Assuming space isn't "smooth", nor the solar wind, won't the spokes migrate about without a "wheel" to keep them in position? Or, could they use the electrical fields to control the wires?
like charges repel
Presumably a 20kv charge on the wires will keep them reasonably spaced, altho I suspect in practice it won't be quite so clean and easy. Resonance effects and such...
From what I remember of freshman astronomy, such a craft would be on an "ever increasing" orbit for the outer planets (ever decreasing for inner). The "thrust" vector from the sail would be angled to slightly speed up the orbit direction for the visit to an outer planet.
Since Jupiter's year is about a dozen earth years (and Saturn a few dozens), it would not be too difficult to plan a path to miss these behemoths (and be on the other side of the sun)
Science is cool
Read another story today on scientists on the verge of curing diabetes using cells extracted from the nads.
Now we are on the verge (in terms of the species...) of travelling to pluto on an intergalactic sailing ship.
Steady on there
<pedant> Steady on there David. I think you might be getting ahead of yourself. The spacecraft is only* going to pluto so we can only say it's an "intrasolar" or "intrastellar" sailing ship.
I can't even imagine what an intergalactic sailing ship might be like. </pedant>
*It's not every day you can use "only" in the context of going to pluto.
How do you stop it, and what about the return trip; are you supposed to tack the whole way back or will they have a trailing tow line?
If it's one way like the other trips, then no worries.
Just answered my own question
1 minute of research on their website talked about it not being a straight flight but more of a spiral.
This is a title, There are many like it but this one in mine.
Scientists create the biggest granny knot EVER.
What about impact damage?
Have they done an impact damage (micro-meteoriod and / or space debris) assessment at all?
A) This thing is going to have a big surface area (each wire at 25 micrometers* 40 km length is a square metre), and they are planning to make a disk out of these things. Sounds like hundreds of square metres.
B) Each broken wire is going to go sailing off into the distance, unless these wires are actually in some kind of net (more weight, and not as described in article).
C) A 5 micrometer thick piece of Al foil which was pointing away from the earth for about 6 years in low earth orbit got 30 micrometre holes punched in it at a rate of a 0.5 per day / sq.meter (7*10^-6 impacts / sq meter per second) (MAP experiment on LDEF, Hi to Tony et al if you're reading this)
D) If a particle could make a 30 micrometer hole in a piece of foil, it could almost certainly take out a 25micrometer wire.
So... I'd give each 40km piece of wire about a 2 days lifespan before it breaks somewhere, or maybe 4 days before at least half of it has gone off into the void.
And they want to get to Pluto?
Is it just me or will something relatively small, travelling at 30km/s, be utterly annihilated the moment it makes contact with a tiny particle of dust travelling in the opposite direction?
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