Shape-Shifting Satellites??

Palomar · 2004-10-28 10:51:17

*From today's Astronotes (space.com); must copy and paste. Haven't seen this previously posted:

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Satellites Could Change Shape to Alter Orbit

A new study shows it should be possible to build a satellite that can change its orbit by reshaping itself in flight.

Imagine a dumbbell-shaped satellite about the size of a football field, with one bulbous end closer to Earth than the other, suggests physicist Michael Longo of the University of Michigan.

The mass of the inner bulb feels more gravity than the outer one. Now pull the masses together, Longo says, and the center of mass of the dumbbell can be moved toward Earth, causing its orbit to change.

Doing this would cause the football-field-sized satellite to move 1 millimeter closer to Earth on each orbit. The satellite would not need propellant but could rely on batteries and perhaps solar energy to alter its shape and course.

Longo's study, based on basic Newtonian physics, appears in the October issue of the American Journal of Physics.
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Geez...what'll they think of next?

--Cindy

SpaceNut · 2004-10-28 11:15:12

yup some of the thoughts on doing this have been discused under the tethered elevator thread. Not all is understood with regards to the atmospheric drag and other such things for this style concept. But it does beg for experimentation in the future if we only had the money in NASA's budget.

John Creighton · 2004-10-29 09:51:59

Doing this would cause the football-field-sized satellite to move 1 millimeter closer to Earth on each orbit. The satellite would not need propellant but could rely on batteries and perhaps solar energy to alter its shape and course.

Why do we want a satellite to move closer to Earth with each orbit?

Palomar · 2004-10-29 10:22:26

Doing this would cause the football-field-sized satellite to move 1 millimeter closer to Earth on each orbit. The satellite would not need propellant but could rely on batteries and perhaps solar energy to alter its shape and course.
Why do we want a satellite to move closer to Earth with each orbit?

*Maybe to promote artificially-induced orbital decay so it'll burn up faster in the atmosphere once its usefulness has expired, thereby helping to reduce orbiting space junk? ???

That'd be my guess, at least one of the purposes.

--Cindy

C M Edwards · 2004-11-01 11:16:54

Hello Cindy.

I’d have never thought something like this would work. However, I went to the library, read the article, and it appears solid. Varying the tidal force tension in a tethered satellite can be an irreversible process, and it appears the change in potential can be applied to propulsion.

(The reviewer's link posted is in error. According to the original article, this effect can be used to provide propulsion up and down. It is not just useful for de-orbiting maneuvers.)

Who knew?

I also conducted my own preliminary analysis of the technique, and have some thoughts.

First, the figures given for how much the orbital radius can be changed are very dependent on the orbital radius at which the engine is run. More acceleration is available in more intense gravitational fields, meaning that a vehicle using this propulsion method would perform best in low earth orbit. Also, the model used in the article is very simplistic. The vehicle wouldn’t necessarily get the best response when aligned pointing at the central body but rather along the local gravity vector. It can be used in interplanetary space, too.

The article doesn’t make much of it, but my analysis suggests the response is very velocity dependent as well as length dependent. The faster you spin the dumbbells, and the longer their tether, the more thrust you can get. It should be possible to easily rival or exceed the thrust of ion engines with a high enough operating speed and long enough rope. And the effect is mass independent. The mass of the spacecraft only affects the motor speeds attainable, not the thrust for a given motor speed.

Also, a spacecraft doesn’t have to use just one dumbbell. Multiple systems can be used to increase thrust. A ship could conceivably built, juggling dozens of ascending and descending motors, with enough thrust for manned missions. A solar powered system requires no fuel, and uses current technologies rated for multi-year operation and readily repaired in the field.

This could be an excellent means of propulsion for a space bus or space station.

This is just too cool! Thanks for bringing it to our attention. :up:

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#1 2004-10-28 10:51:17

Re: Shape-Shifting Satellites??

#2 2004-10-28 11:15:12

Re: Shape-Shifting Satellites??

#3 2004-10-29 09:51:59

Re: Shape-Shifting Satellites??

#4 2004-10-29 10:22:26

Re: Shape-Shifting Satellites??

#5 2004-11-01 11:16:54

Re: Shape-Shifting Satellites??

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