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Recent Progress on Solar Sails

‘Leave the propellant at home’ is a key maxim of deep space exploration. If we can find ways to substantially reduce or even eliminate the need for on-board fuel tanks, we maximize the payload and enable missions that would otherwise be impossible. In the near term, solar sails are the ideal way to realize this goal. Driven by the momentum transfer of solar photons, sails can achieve high speeds and, by tacking methods that are in ways analogous to conventional ocean sailing, can move to and fro in the Solar System on their free photon ride.

Laser and microwave beaming to sails is another thing entirely. We’ll one day use those technologies for extended missions into the Kuiper Belt and the Oort Cloud and, if the dreams of some theorists come true, perhaps for interstellar missions at ten percent of light speed. But all that depends upon learning how sails work, and on that score, it’s useful to know of the continuing NASA work on sail technologies. A recent paper by Les Johnson, Roy Young and Edward Montgomery (Marshall Space Flight Center) apprises us of developments in the last few years that should pay off down the road.

L'Garde sail demonstrator

For although the press is fixated on the Space Shuttle and the International Space Station, NASA’s quiet but continuing work on sails offers promise of new technologies. In 2005, two different 20-meter solar sail systems were developed, deployed and tested in NASA’s Glenn Research Center’s Power Facility at Plum Brook Station in Ohio. The companies involved in the research were ATK Space Systems (formerly Able Engineering, Goleta CA) and L’Garde (Tustin CA). In both cases, their sails included four deployable booms and are scalable to larger, 150-meter sails (first-generation sails will doubtless be in this larger size range).

Image: L’Garde’s 20-meter ground system demonstrator, a glimpse of early solar sail technology. Credit: L’Garde/MSFC.

Operational sails will consist of their ultralightweight supporting trusses, a central hub, and a flat, smooth material covered with a reflective coating. The first sails we should see on actual missions will probably use aluminized Mylar or CP-1, materials that have been tested in space and are now being scrutinized for their behavior during long-duration exposure to space environments. Future sails would doubtless use a more robust (and considerably lighter) network of meshed carbon fibers.

This work has proceeded through NASA’s In-Space Propulsion Technology program, whose vision is outlined in the paper:

Early in the project, In-Space Propulsion funded the development of a prototype solar sail system for ground testing that would be used to validate design concepts for: sail manufacturing, packaging, launch to space and deployment; attitude control subsystem function; and to characterize the structural mechanics and dynamics of the deployed sail in a simulated space environment. A square sail configuration consisting of a reflective sail membrane, a deployable sail support structure, an attitude control subsystem, and all hardware needed to stow the sail for launch were developed.

The paper on this work takes the research from its six-month concept refinement phase (completed in 2003), a hardware development phase beginning in June of 2003, and a twelve month system verification phase. The latter included testing fully integrated 20-meter solar sail demonstrator systems including their launch packaging containers and operational subsystems, with exposure to high vacuum conditions at the Plum Brook facility as well as launch vibration and ascent vent tests.

But new spacecraft design isn’t solely about hardware. The solar sail research has included the development of simulation tools to predict sail behavior during representative flights, the ultimate goal being to develop an optical diagnostic system that can observe and monitor the health and integrity of the sail after deployment. The paper discusses the other aspects of this research, including developing new modeling techniques, testing solar sail materials, analyzing sail behavior in charged particle environments and examining long-term environmental effects.

None of this makes the evening news, but you build great things incrementally, one carefully defined step at a time. What we’re seeing here is the necessary groundwork that takes the solar sail concept through ground testing and the development of its subsystems, operational tools and computational models. That’s a foundation that will one day be put to work — just when depends as always on funding levels — in the form of space-based testing and, one day, operational missions. The benefits in terms of Solar System exploration should be immense, particulary as we look at increasing the scientific payloads available.

And for truly speculative endeavors? If we can make a sail robust enough, and light enough, and send it on a Sun-diver trajectory with a close solar pass followed by rapid sail deployments, speeds of hundreds of kilometers per second are theoretically possible. That makes Kuiper Belt missions practical and gives us options for pushing out toward the Oort Cloud. And needless to say, the more we learn about solar sailing, the more we will understand the sail technologies that may one day be perfected for beamed propulsion missions to nearby stars.

Les Johnson’s name should be a familiar one to Centauri Dreams readers, particularly in light of his recent book (co-authored with Gregory Matloff and C. Bangs) Living Off the Land in Space (Springer, 2007). We’ll have much to say about this title in coming weeks. The paper is Johnson et al., “Recent advances in solar sail propulsion systems at NASA,” Acta Astronautica 61, pp. 376–382 (2007).

Comments on this entry are closed.

  • Darnell Clayton September 5, 2007, 13:50

    Its ironic how we once sailed our oceans using wind sails, and now we will sail the celestial heavens with solar sails.

    Hopefully we can work out the kinks with solar sails, as warp (star trek style) may be a few centuries away at best.

  • ljk September 5, 2007, 16:08

    NASA MSFC Solicitation: P-POD Microsatellite Launcher With
    Supporting Technical Assistance

    http://www.spaceref.com/news/viewsr.nl.html?pid=25310

    “NASA/MSFC has a requirement for spacecraft deployment and
    launch vehicle integration support. NASA’s Marshall Space Flight
    Center is proposing to purchase a Poly Picosatellite Orbital
    Deployer (P-POD).

    In order to accomplish CubeSail Mission level activities, NASA’s
    Marshall Space Flight Center intends to build and fly a 3U CubeSat
    called the CubeSail, on a USAF-STP Minotaur IV launch that is
    tentatively schedule for the third quarter of FY09.”

  • Adam September 6, 2007, 4:30

    Hi All

    Tsiolkovsky was the first modern to correctly describe solar sails, though Kepler himself wondered if there couldn’t be ships to sail between the planets. It’s such an elegant idea, but damnably tricky to achieve in actual practice. Ultra-low areal densities and proper deployment of such gossamer sails challenges our best space know-how. The ultimate solar-sail would be a star-sail dragging a WorldShip on a multi-millennial voyage, though we’re not the right species to travel in such a slow fashion. Yet given motivation we might try.

  • Paul Dietz September 6, 2007, 11:57

    Laser beamed sails may end up looking very different from solar sails. Laser light is highly monochromatic, which enables one to play interesting games, such as scattering the light off ions trapped in magnetic fields (resonance scattering cross sections can be enormous), and also exploiting various optical refrigeration techniques so that the laser beam actually cools, rather than heats, the sail.

    Both this approaches would enable much higher power density on the sail than a broad spectrum solar sail could support.

  • Adam September 6, 2007, 18:15

    Hi Paul

    There was a design for a microwave pushed electron-resonance mirror spacecraft in the JBIS a few years ago. Absolutely massive – 200 metre diameter ring to provide spin-gravity during the trip to Mars at 100 kps. Basically the designer was arguing for a mass-transit infrastructure to support large-scale colonisation. The multi-terawatt beam would have needed gigantic fly-wheels or huge super-conducting rings to store the power needed, which would be slowly repowered over a few days.

    Would have some advantages for launching low-mass probes if the beam focusing issues can be addressed.

  • Administrator September 6, 2007, 20:35

    That’s a new one on me, Adam. If you have the reference nearby, please post. I’d like to track the paper down.

  • Adam September 7, 2007, 1:38

    Hi Paul

    I’ll have to dig for it. I turned off the idea when I realised how much power it needed – pushing things with photons needs a lot of juice.

  • Paul Dietz September 7, 2007, 9:31

    Laser propulsion by light pressure really only makes sense at very high speed, since the energy efficiency increases nearly linearly with vehicle speed.

  • Adam September 7, 2007, 23:53

    Hi Paul

    The references are:

    Minovitch, Michael A. (1997) “A Propulsion Method for Achieving Commercial Space Travel Part 1”, JBIS, v.50, pp 137-148.

    Minovitch, Michael A. (1997) “A Propulsion Method for Achieving Commercial Space Travel Part 2”, JBIS, v.50, pp 451-462.

    …he also proposed using the system for sub-orbital flight.

  • Gordon R. Vaughan September 20, 2007, 0:43

    That’s interesting, but what we REALLY need is a bona fide demonstration flight. Is one actually part of these plans?

    I volunteered with the World Space Foundation way back in the early 80s, and helped build a sail, though it was not intended for flight. WSF first demonstrated a sail deployment, of about the same size as that shown above, back in 1981.

  • Administrator September 20, 2007, 8:29

    Agreed re the demonstration flight, Gordon. To my knowledge, plans for in-space testing keep getting pushed back because of continuing funding issues. So we watch and wait.

  • ljk November 14, 2007, 16:04

    Article on Solar Sailing by Louis Friedman in the June issue of
    Professional Pilot:

    http://planetary.org/programs/projects/solar_sailing/pro_pilot_0607.pdf