Slinky® in space!

Slinky® in space!

Photo of metal Slinky A Slinky® is a simple, old-fashioned toy. Slinkies have been around since your grandparents were kids. Perhaps you've seen one. It is a springy coil made of plastic or metal. When it is coiled up, or closed, it is only a few inches thick. But uncoil its 89 loops, and it stretches out to over 19 meters (63 feet)!

Slinkies are floppy. But, what if you had a "magic wand" kind of Slinky—coiled up small one minute, then—Presto!—long, straight, and stiff the next minute?

Now that would be useful! For example, you could use this straightened out Slinky as a mast to support solar sails on a spacecraft. (See sidebar.)

But how would you make a Slinky so that it would be stiff once straightened out? How could you make a Slinky work as a mast for a solar sail?

Here's one way:

First, make the Slinky of a special kind of material that "remembers" its original shape. Then coil it up like a spring. When you let go of the coil, it will straighten itself out because it "remembers" that it is supposed to be straight.

Drawing of Slinky partly uncoiled

Second, make the Slinky stiff when it is straight, so that it could support something like a solar sail. How about using three strands of Slinky material instead of just one? Let's call these three long strands "longerons." Wouldn't having three longerons make it stiffer? Yes, but still not stiff enough.

Drawing of three wavy longerons.

Third, we try tying short pieces of the Slinky material between the long strands to hold them apart in a triangular shape. Let's call these shorter pieces "battens." Do the battens make it stiffer? Maybe, but there's still something wrong. It still needs to be stiffer.

Drawing showing three longerons held in triangular shape by three short battens placed at regular intervals.

So, fourth, tie the longerons and battens together diagonally with strong, flexible threads. Let's call these thread "diagonals." Tie the diagonals tightly so that the battens are bent a little. This way, the battens will push out on the longerons and make them very stiff. But stiff enough?

Drawing with longerons and battens, plus diagonal wires pulling everything tight and rigid.


Now, the only thing left is how to coil and uncoil the mast. You want it tightly coiled for launch into space. Then you want it to uncoil slowly so it doesn't just go "spro-innng" and shake, rattle, and roll the rest of the spacecraft!

So, fifth, put a cap on each end of the mast. Now, connect the two caps with a long cord (call it a "lanyard" ). Shorten the lanyard to coil the mast and make it small. Let the lanyard out slowly to uncoil the mast and let it grow to its full length.

Photo on left shows mast partly uncoiled.  Photo on right is mast coiled up.

Space engineers have figured all this out! It's a new design called SAILMAST. It was developed and tested as part of NASA's Space Technology 8 mission. SAILMAST is less than half a meter (19 inches) thick when coiled up, but 40 meters (about 130 feet) long when straightened out—more than twice as long as our uncoiled Slinky!

A similar design, but quite a bit heavier, was flown on the Shuttle Radar Topography Mission.

Artwork of the Shuttle Radar Topography Mission in Earth orbit.  A long mast holds one of two radar antennas far from the Shuttle.

The SAILMAST experiment team on Space Technology 8 is testing how well it works. Using special methods to copy the weighlessness of space in a laboratory, they will carefully measure SAILMAST's stiffness and its effect it might have on the spacecraft as it uncoils.

Space Technology 8 is part of NASA's New Millennium Program. This program's job is to test new technologies to make sure they will work for future missions of discovery.

Here's a movie of SAILMAST being uncoiled in the laboratory at ATK Space Systems, where it was developed.

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