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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."
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
One of our competitors trademarked the term "hypothesis". From now on, we will call them "boneheaded ideas".
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.
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.
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.
Real Daleks don't climb stairs - they level the building.
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.
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.