Limits to accelerate a spacecraft by spinning it in a circle

In summary, the concept involves using spinning objects in space to preserve momentum and accelerate nanocrafts in the desired direction. This idea has been inspired by the Breakthrough Starshot initiative. The main limitations are the speed at which spinning disks can be used (1-2 km/s) and the high accelerations required (up to 2 million g's). Using a tether for momentum exchange may be a more feasible option. Further research is needed to determine the practicality and limitations of this concept.
  • #1
PicnicDoctor
5
0
The basic concept is to have your space probe(s) - likely nanocraft [1] on a spinning object in space which allows you to preserve the momentum you give it while accelerating it faster. Then once you are at a speed you can simply release the nanocraft in the direction you want it to go in.

More specific example:
Spin a 10m wheel at 30m/s^2 until it reaches say 10,000 m/s on the outside of the wheel. On the edge of the wheel are 4 nanocraft that are released when it reaches that speed.

If there are limits with having a full object spin we could have a series of tracks possibly accelerating the next one via maglev, then stabilizing the previous ones to be able to accelerate the outer one again.

I'm trying to better understand the feasibility of these ideas, and I am guessing some one has already thought of them and evaluated them. Would love if anyone can point me in the direction of more information if this has already been evaluated.

If not, I'd like to start learning the limits so I can evaluate it, my questions so far:
1. How fast can you spin something in space? The only obvious limit I've gotten so far would be if it's a single mass object spinning you don't want the middle to get to the speed of light - I'm guessing there is another limit somewhere?
2. How fast can we practically spin something in space using a motor (flywheel in space*)?
3. What kind of problems do we need to watch out for on our nanocraft so they will keep working and be able to release at the correct time?

Maglev/track idea introduces new questions like:
4. Will the tracks stay stable enough accelerating in opposite directions to not require power to keep them close together (I don't see a remotely practical way to power the outside track)
5. At what velocity would maglev acceleration no longer be effective at? Can we get to Project starshot speeds? At what rate does it decrease?
6. My estimate of the acceleration I can get from maglev was 30m/s^2 from reading that many trains could cause several G forces of acceleration - need a better number here.

I also might not even know the right question to ask, so feedback very appreciated! Happy to break this up into subforums, but figured it made sense to start here.
Thanks!

[1] This entire concept was inspired from their idea described here: http://breakthroughinitiatives.org/initiative/3
* I've found a few papers about flywheels which seem to be the closest thing, but I've never found them describing the speed on the outside of the wheel (or the size for that matter). Maybe I'm just looking for the wrong terms?
 
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  • #2
Spinning disks are limited to about 1-2 km/s with current materials, if you try to spin them faster they break. Carbon nanotubes might get a bit more speed. This does not depend on the disk radius and tapered disks don't reach much more either.

Accelerating something on a maglev track doesn't have this limit, but very high accelerations are still problematic with it. The acceleration to stay on the track can be significantly higher than realistic accelerations to increase the speed.
 
  • #3
Bear in mind conservation of momentum applies. How do you propose to spin the arm? You could use solar panels and contra rotating arms but that still means if you fling one nanocraft directly away from Earth you push the launcher in the other direction (eg towards earth). If you want to keep reusing the launcher you need to keep pushing it back to its original orbit.

The cost of a launch usually depends on the mass. You want to minimise the amount of "wasted mass" needed to get the "wanted mass" to the destination.
 
  • #4
PicnicDoctor said:
Spin a 10m wheel at 30m/s^2 until it reaches say 10,000 m/s on the outside of the wheel. On the edge of the wheel are 4 nanocraft that are released when it reaches that speed.

In this example, the acceleration at the outside of the disc would be about 20,000,000 m/s^2, or about 2 million g's. This is easily the biggest limitation, you'd have to increase the diameter of the disc by several orders of magnitude to make it feasible for orbital speeds.
 
  • #5
CWatters said:
Bear in mind conservation of momentum applies. How do you propose to spin the arm? You could use solar panels and contra rotating arms but that still means if you fling one nanocraft directly away from Earth you push the launcher in the other direction (eg towards earth). If you want to keep reusing the launcher you need to keep pushing it back to its original orbit.

The cost of a launch usually depends on the mass. You want to minimise the amount of "wasted mass" needed to get the "wanted mass" to the destination.

Would it make sense to launch pairs of nanocraft in opposite directions, to address these concerns?
 
  • #6
etudiant said:
Would it make sense to launch pairs of nanocraft in opposite directions, to address these concerns?
That's what I was thinking. I was also not planning to try this anywhere near a planetary body.
 
  • #7
Might work but which is more useful in orbit... 1kg of fuel or 1 kg of mass you only sent up so you have something to throw in the wrong direction (which might be downwards)?
 
  • #8
Seems like this is better handled by a tether then the ring I was proposing. Nice video on that:

Thanks all for your responses.
 
  • #9
PicnicDoctor said:
Seems like this is better handled by a tether then the ring I was proposing. Nice video on that:
Thanks all for your responses.
Proper words for technology you are investigating is
Momentum exchange tether
 

Related to Limits to accelerate a spacecraft by spinning it in a circle

1. What is the concept of spinning a spacecraft to accelerate it?

The idea is to use the centrifugal force generated by the spinning motion to provide additional acceleration to the spacecraft.

2. How does spinning a spacecraft affect its speed?

When the spacecraft is spinning, the centrifugal force generated is directed perpendicular to the direction of motion, thus adding to the forward speed of the spacecraft.

3. What are the limitations of using this method to accelerate a spacecraft?

The main limitation is that the amount of acceleration achieved is limited by the strength of the materials used to construct the spacecraft. Excessive spinning can also cause structural damage or affect the stability of the spacecraft.

4. Can a spacecraft be slowed down by spinning it in the opposite direction?

Yes, by spinning the spacecraft in the opposite direction, the centrifugal force will act in the opposite direction, slowing down the spacecraft.

5. Are there any real-life examples of spacecraft being accelerated by spinning?

Yes, NASA's New Horizons spacecraft used this technique to increase its speed during its journey to Pluto. The spacecraft's spin was increased from 5 to 10 revolutions per minute, resulting in a speed boost of 4 meters per second.

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