RS: The Solar Sail That Never Was

>> Monday, July 12, 2010

Given the success in work of Japan's IKAROS, currently eleven million miles away and accelerating using the power of photons, I thought this was a good time to resurrect this classic. For those interested, I'm more than willing to expand on the subject. After all, once in a while, we even talk about rocket science. For now, though, enjoy.

Bob Johnson of Black Holes and Astrostuff asked me a question about solar sails on my “Ask the Rocket Scientist” post . As I answered him, it kind of pushed me to reminisce about the solar sail that never was. I thought some of you (or at least one of you) might be interested in the one I helped design.

See, back a billion years ago when I was going to college (1989), I took several high level aeronautics courses for my required high level engineering courses. Since most Engineering Physics student go the Electrical Engineering Emphasis route (which I detested), it turns out I missed some prerequisite courses no one ever brought to my attention, until, of course, it was too late. Therefore, as they classes were advanced design, I was at a serious disadvantage. At the end of my senior year, we had the choice of designing a fighter aircraft or designing a solar sail for an AIAA contest. I went with solar sail for two reasons. First, my lack of aircraft designing experience wasn’t a factor; we were all starting from scratch. Secondly, I thought this was way cooler.

It was a design team and there were five of us. Since some of us were graduating before the deadline (Summer 1989), one of those who were not volunteered to be leader. We separated into five responsibilities: I would do research on solar sails, design the general overall design and do materials (I can’t remember if I was assigned the second part or if it just worked out that way), someone would do navigation, someone would design the payload, someone would design the control scheme and someone (the leader) would put it all together.

Finding out about solar sails was great fun. I loved the research, and, as soon as I’d read that the circular ones were the most efficient (but no one had figured out how to deploy them), I became convinced we needed a circular one. But how to deploy? Now, in the world of solar sails, you either spin it (circular or heliogyro) or you build a frame. So, what I thought would be best is to fold it up like an umbrella - not wrapped around a pole, but flat along radians. Then, the flat side is rolled around a kick motor (required to bump it up beyond low earth orbit and the residual atmosphere) before unfurling. But the unfurling was my brainstorm: put a rim of flexible material around the surface and inflate it.
But control of a spinning sail is not without its headaches and you need a way of controlling attitude (heliogyro ones change the pitch of the particular blades–JPL’s proposed rendezvous craft was planned as a bladed solar sail). So, since I was in charge of materials, I found a polymer that would harden when exposed to radiation (already being used for space applications). The advantage to using this was that, if the inflating gas leaked away after inflation, it wouldn’t matter after six hours. Additionally, since this provided a lightweight frame as well as a way of deploying the sail, we didn’t have to spin it. The control guy took off with that and we used the payload on four guy wires attached to the rim to control it by changing the center of gravity. I designed the sail out of 2 mil (50.8 micrometer) thick mylar with a 0.2 mil (5.08 micrometer) layer of aluminum. Kevlar cable (their thinnest filament) was used as ripstop along with the glue applied concentrically and along the radial seams. Rip-stopping was vital because Mylar tears like nothing when punctured and micrometeoroids (and, though I didn’t know it at the time, orbital debris) was a serious concern.

Our payload guy was going to wrap the payload in gold foil and we were going to call the beauty “The Heart of Gold” which was both fun and cool (and if you don’t know why, you need to read Hitchhiker’s Guide to the Galaxy). Another of the graduating team members (and, interestingly enough, the only other female) did the navigation and she and I completed extensive write ups before we graduated (out of necessity). I provided our leader with some 34 pages of tightly written text, well within the confines of the requirements and our navigator wrote in detail, very clearly with excellent graphics. And we didn’t see it again until after it had been submitted.

We didn’t win.

We shouldn’t have.

I don’t know if we had the best concept, but, if we had, we still didn’t deserve the prize. After our graduation, our “leader” changed the name to “The Golden Hind” for reasons I never understood or agreed with. Most of my text had been axed and what was left no longer made sense. He had “simplified” much of it so that it was not only unclear but, in many places, um, wrong. The navigation graphics were replaced with a cartoon that, literally, showed the Earth at the center of the solar system. *Sigh*

To this day, there are few things I hate professionally more than leaving a project (still with my name on it) halfway. It happens, but I hate it. But it’s never been as bad as that in all the years since, so at least that’s something.

Cool stuff. Gotta love space.


  • The Mother

    The kids and I have been fascinated with solar sails for a while. The idea is just so cool.

    You got something out of the project anyway. Knowledge, experience...

    Not to be sneezed at.

  • Jeff King

    Very cool stuff.

  • Anonymous

    I once worked in an office where they were proposing a solar sail to the government. I remember a lot of laughter as they were brain storming it. I thought it would work, but what did I know? Their solar sail would have been ribbons of mylar miles and miles long. Would it work? Who knows?

  • Stephanie Barr

    JPL actually proposed a spacecraft as you describe Marilynne, with long long strips of sail that could be maneuvered like the blades of a helicopter (the heliogyro above). With it, they had intended to rendezvous (not fly by) a close coming comet. It did not get funding but it was fascinating.

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