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.
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 …
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...
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.
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.
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.
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.
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.
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.
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.
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.
...or the best such idea - NASA came up with M2P2 (Mini-magnetospheric plasma propulsion) back in 2000, which requires no physical sail at all:
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:)
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
"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?
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)
<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.
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?
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