A Finnish design making the news recently is hardly the only concept for near-term space sailing, but the possibility of testing it in space for a relatively small sum of money is attractive. This is especially true at a time when strapped budgets like NASA’s are focused on ratcheting up conventional propulsion techniques to get us back to the Moon and on to Mars. Yes, let’s keep pushing outward into nearby space with what we’ve got, but we need next-generation thinking, too, and the Finnish sail, the work of Pekka Janhunen and Arto Sandroos, points in that direction.
Unlike magnetic sails that create an artificial magnetosphere around the spacecraft, the Finnish concept is to use long, thin conductive wires that are kept at a positive potential through the use of an onboard electron gun. The two researchers considered how the charged particles of the solar wind would interact with a single charged wire in a 2007 paper that we looked at in this Centauri Dreams article just over a year ago. A full-scale mission would use fifty to one hundred 20-kilometer long charged tethers. Supercomputer simulations come up with potential speeds of 100 kilometers per second, which is about five times what New Horizons is doing on its way to Pluto/Charon.
That’s also a speed that gets you into the nearby interstellar medium in about fifteen years, a time frame that should quicken the heart of many a deep space scientist. When he looked at some of the potential mission concepts in Next Big Future, Brian Wang mentioned the possibility of transporting raw materials from the asteroids for use in making fuel at high Earth orbit. I see that Janhunen noted the asteroid idea in a recent interview, tying it to a broader human future: “Starting the long-awaited asteroid resource utilization could be significant for the longer-term well-being and survival of our civilization on this planet.”
That article, published in Space.com (and thanks to John Hunt for the link), notes the nature of the sail’s first prototype, seen as a smaller sail using 8-kilometer long tethers in an elliptical Earth orbit, a scenario that would allow tests on the force of the solar wind on the spacecraft. The team would also investigate using radio waves to excite solar wind particles in an attempt to boost the possible thrust.
So many good concepts, so many budgetary constraints. Long an admirer of Robert Winglee’s Mini-Magnetospheric Plasma Propulsion concept, I watched with growing enthusiasm as it sailed through Phase I and Phase II rounds at NASA’s Institute for Advanced Concepts and went on to further scrutiny, but getting some kind of solar, magsail or electric sail concept into actual space testing now seems a remote possibility. The Finnish team’s sail awaits the resolution of its own funding issues, a quick fix being the infusion of somewhere around 5 million Euros.
One thing is for sure: Propulsion concepts that let us leave the fuel on Earth have a huge future in opening up the outer planets and the interesting places beyond. Solar sails can do this by using the momentum provided by photons from the Sun, but these effects drop dramatically as we move beyond Jupiter. The solar wind, streaming outward from the Sun at speeds approaching 1.5 million kilometers per hour, may offer a way to boost sail performance through magsail and electric concepts, but we have much to learn about how sails might interact with it. In both cases, we need sail deployment in space to take the necessary next steps.
A good way to keep up with the Finnish sail studies is to track the latest papers and press releases here. You’ll also find the latest paper I know about, which is Mengali et al., “Electric sail performance analysis,” Journal of Spacecraft and Rockets Volume 45, Issue 1 (Jan-Feb, 2008), pp. 122-129, available as an abstract with included figures on the site. It’s interesting as well to see that a workshop on electric sailing will be held at the European Space Research and Technology Centre in the Netherlands on Monday, May 19.