Finnish Electric Solar Sail Nears Implementation

eldavojohn writes "A recent meeting held by the Finnish Meteorological Institute has resulted in plans to build an electric solar sail that will circle the Earth, gaining speed to test its acceleration. The purpose? 'A flight out of the solar system to measure the gas, dust, plasma and magnetic field in the undisturbed interstellar space would perhaps be the "flagship" thing to do,' said Pekka Janhunen, a researcher developing the sail at the FMI. The details and papers of this project (over two years in the making) are also available. I certainly hope it will show more success than the launch of the similar U.S.-Russian venture and its subsequent complete failure."

Comments

Not quite the same thing really

[dreamchaser]

This isn't really using the pressure of the solar wind for propulsion; rather it generates power from it which it then uses for propulsion. Neat idea.

Re:Not quite the same thing really

[CRCulver]

Is this some kind of Bussard ramjet then? I really love Larry Niven's Known Space stories (there's a great one about a ramjet chase in Neutron Star ) where ramjets serve for interstellar journeys, or Poul Anderson's Tau Zero. I wonder why ramjets aren't a big part of science fiction anymore. Even if they might not work in interstellar space, they seem to still have value inside the solar system, and this story looks like what people say a valid design would be.

Re:Not quite the same thing really

[brunes69]

The Bussard collectors on Star Trek ships (the red lights at the end of the warp nacelles) function as pseudo ramjets. They collect the material used for the fusion generators that power the impulse engines.

http://memory-alpha.org/en/wiki/Bussard_collector

Re:Not quite the same thing really

[getto man d]

Could this lead to a reliable manned mission to Mars, or for that matter elsewhere in space? If these sails are indeed more efficient than fuel, could that displaced weight be replaced with life support (e.g. nutrition, H2O, O2)?

Re:Not quite the same thing really

[Anonymous Coward]

It does use the momentum of the solar wind like any other solar sail; the difference to the other attempts is that this one uses an electric field around wires rather than a big physical surface to "catch" the solar wind particles. It'll be less efficient per surface area than a membrane sail, but allows the surface area to be astonishingly large relative to the mass of the spacecraft (compare the weight of a mile-long wire to a square mile of plastic sail) so it may still have a huge advantage.

Re:Not quite the same thing really

[Cedric Tsui]

I agree with AC.
The tendrils are not for power generation.

The craft generates electricity using the solar panels which powers an electron gun. The electron gun gets rid of electrons allowing the entire spacecraft (solar sail tendrils included) to become positively charged and then catch the solar wind for propulsion.

The electron gun can also provide a tiny amount of thrust. A very tiny amount of thrust.

Re:Not quite the same thing really

[Thelasko]

This isn't really using the pressure of the solar wind for propulsion; rather it generates power from it which it then uses for propulsion. Neat idea. That's not how I read the article. I read it as by charging a bunch of wires it increases the effective area of the solar sail. Therefore there is no need to make an entire physical sail.

Re:Not quite the same thing really

[Anonymous Coward]

No - a Bussard ramjet is supposed to use a magnetic field as a kind of funnel to collect hydrogen from the not-quite-vacuum and then use that as fuel conventionally. The problem is that until it's moving VERY fast, the magnetic field would have to extend out a hell of a distance to collect enough fuel to power the magnetic field. This concept might work once some other means of propulsion has gotten you up to high enough speed - but I think it's a non-starter for craft that are starting off from a standing start.

The device in TFA is truly a solar sail - it works because like charges repel each other. So if you charge up the wires with the same polarity as the solar wind - you get a pressure exerted. It's cheaper than the big sheet of shiny mylar film that we normally think of for solar sails because you only need the support wires - not the sail itself. However, the conventional solar sail needs no power whatever - where this one has to use solar panels to keep the wires charged up. Hence, this one is pretty much useless for interstellar travel.

Re:Not quite the same thing really

[curmudgeous]

No, the Bussard Ramjet is supposed to use magnetic fields to channel interstellar hydrogen down to a constriction point where it is burned in a fusion reactor. The concept doesn't work at low speeds so you would have to use stored hydrogen as fuel until the speed gets high enough for the magnetic scoop to be effective.

Re:Not quite the same thing really

[Anonymous Coward]

Correction: As someone pointed out, the membrane type sails gather momentum from photons rather than ionized solar wind particles. The point still stands that the Finnish sail is a momentum-gathering device that requires no reaction mass. (Unlike a solar-electric ion drive or whatever the GP was thinking about)

The low volume and speed of solar wind particles in comparison to sunlight does limit the performance. For example, you obviously can't go any faster than the solar wind, approx 500km/s near Earth. This is still a lot faster than previous deep space probes (the record is ~15km/s) so if they can get it to approach even 10% of the theoretical limit it'll be great for outer solar system studies.

Re:Not quite the same thing really

[spazdor]

"Solar sail" would be a ridiculous name for a device which tries to harness "solar wind" for propulsion. Try and come up with something a little more descriptive, alright?

Re:Not quite the same thing really

[meringuoid]

The concept doesn't work at low speeds so you would have to use stored hydrogen as fuel until the speed gets high enough for the magnetic scoop to be effective.

In Niven's setting, starships leaving Sol used light sails to get up to ramscoop speeds. Not being patient enough just to ride sunlight, they built huge lasers in the outer solar system to give them a little extra kick. When one day the kzinti arrived to raid the defenceless, unarmed, peaceful human race, these lasers were... repurposed.

Of course Jack Brennan the sometime asteroid miner turned superintelligent extraterrestrial mutant trickster had to do it differently. Unfortunately he did not leave blueprints for the devices he used to manipulate gravity like that, and his entire artificial world in the Kuiper belt got crushed onto the surface of his pet neutronium globe as he left. So we're stuck with the lasers.

Re:Not quite the same thing really

[Chrontius]

The solar system is in the middle of something called the "local bubble" - this region was created by an ancient supernova, and is defined by low-density interstellar medium. Also, the ram field generates drag - consider that this is going to look a lot like a giant parachute of magnetic force in front of the ship, that's not very aerodynamic. The drag and the thrust for a conventional Bussard fusion ramjet limit top speed to about 12-14% of lightspeed, which is just about as doable using a conventional fusion rocket design without the ram field. Also, the minimum operating speed of a ramjet is 1-6% of c.

A proton-proton fusion drive has an exhaust velocity of 12% c, so a proton-proton fusion Bussard Ramjet would have a maximum speed of 12% c. You may remember that a spacecraft with a mass ratio that equals e (that is, 2.71828...) will have a total deltaV is exactly equal to the exhaust velocity. So if a conventional fusion rocket with a mass ratio of 3 or more has a better deltaV than a Bussard Ramjet, what's the point of using a ramjet?

Some good reading for you over at Atomic Rocket Ship.

Re:Not quite the same thing really

[Anonymous Coward]

The traditional solar sail uses the radiation pressure from the Sun. When the solar photons are absorbed by the sheet, the spacecraft gains momentum.

The electric sail uses the dynamic pressure of the solar wind (proton and electron flow from the sun). The momentum of the solar wind is mainly in the protons, since electrons are ~1800x lighter. The electric sail uses charged wires (tethers) to create electrical sheet, which deflects the protons and the craft gains momentum.

Re:Not quite the same thing really

[Nefarious Wheel]

I doubt any solar sail, no matter the design, is going to take you much further than the termination shock, let alone between stars.

Do you mean that once having achieved the velocity it can from the flux-rich area near our star, it will simply stop? I doubt that gravity at termination shock is going to be enough to slow it down much. Remember that it will have felt that very minor push for quite a few years by then. A few grams thrust isn't very much, but that much continuous per second x60x60x24x365 x however many years it takes to get there, it's likely to be travelling at quite a clip by the time it reaches that point. It will eventually get somewhere between the stars.

Re:Not quite the same thing really

[Arancaytar]

I guess it's much more efficient this way - Randall Munroe explained that a normal reflection sail only harvests a fraction of the photon's energy. The solar panel does not reflect the photon perfectly (unlike a mirror surface), so it picks up more of the photon's energy.

Meta Tag?

[clonan]

For the article I am not sure it applies...

Where is the fly-me-to-the-outer-system-to-collect-dust-and-gas tag?

Re:Meta Tag?

[eldavojohn]

For the article I am not sure it applies... Where is the fly-me-to-the-outer-system-to-collect-dust-and-gas tag? Yeah but Frank Sinatra had a hard time working out the phrasing to "Fly Me to the Outer System to Collect Dust and Gas" so he had his writers rework it slightly. Although Count Basie liked the funky 10 syllables across four beats syncopation, Old Blue Eyes wouldn't bow to nobody ...

Major problem with this

[Kentercat]

So it's a 10 mile across array in an orbit that crosses the altitude of most other satellites, and it crosses the path of the bulk of those satellites at the low point in its orbit when it's moving the fastest. Um. NOTHING COULD POSSIBLY GO WRONG, COULD IT??? They should put it at the Earth-Moon L4 or L5 liberation point instead - no traffic, ample unobstructed solar wind most of the month, and close communications with Earth. That's where a responsible group would put it.

Re:Major problem with this

[FinestLittleSpace]

You better go call up the scientists! I bet they didn't think about this!

Re:Major problem with this

[Kentercat]

True, but it won't rotate edge-on without a stablization system that can pitch a spun-out array of wires once every orbit, at a variable rate (since in a non-circular orbit the velocity will change radically depending on the position in orbit at a given moment). It's meant to be a solar sail, so it will be oriented to the sun regardless of orbital position. Even if it were edge-on, it would still be 10 miles across. And even if the array consists of thin wires, anything this size can take out satellites, and the fragments can take out other satellites. Ironically, the closer it is to edge-on, the less likely it is that a satellite or space junk component will be able to slip between the wires. Older ABM systems used arrays that unfurled like this to increase the likelihood of taking out the targeted warhead or satellite. Just because the intention of this array is different doesn't mean the result would not be the same.

They could pull it off.

[blind biker]

I have known Finland and Finns for almost 10 years - though I don't know the specifics of this project, I have a strong faith in the finnish high-tech (did you know atomic layer deposition was developed in Finland? And then there's Nokia, and a lot of nanotech research, and their contribution to the ESA and...) plus Finns are quite pedantic, and I mean this in the best possible way. Part of Nokia's success is definitely down to this scholarly approach to technological projects.

Re:They could pull it off.

[Fear the Clam]

I have known Finland and Finns for almost 10 years - though I don't know the specifics of this project, I have a strong faith in the finnish high-tech (did you know atomic layer deposition was developed in Finland? And then there's Nokia, and a lot of nanotech research, and their contribution to the ESA and...) plus Finns are quite pedantic, and I mean this in the best possible way. Part of Nokia's success is definitely down to this scholarly approach to technological projects.

In other words, look at the bowl cut on that guy in the article. With hair like that he's got to be sporting some major brainage.

Making a better solar sail

[Kim0]

This should make the solar sail about 100 times lighter,
and therefore faster:

http://kim.oyhus.no/Solar_sail.html

Kim Øyhus, the inventor.

Sounds ambitious...

[Saberwind]

...solar sail that will circle the Earth...

That's one big sail.

Re:Nearing implementation?

[kybred]

So, it's not Finnished yet??

If it's nearly Finnished, does that make it Swedish?