# eli5: When probes are released into space they start to spin. What gives every object in space this momentum to rotate? Would it be possible to send something to space and release it very cautiously so it won’t get any energy from the releasing spacecraft and the object hence wouldn’t rotate?

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eli5: When probes are released into space they start to spin. What gives every object in space this momentum to rotate? Would it be possible to send something to space and release it very cautiously so it won’t get any energy from the releasing spacecraft and the object hence wouldn’t rotate?

In: Physics

They have a small engine that push the object to spin. since there isnt anything in space Newton’s law doesnt apply, there is no force acting upon the probe to suspend its movement. I hope I explained it good enough.

Are you talking about spinning around is own axis or “spinning” (orbiting) around the earth, the sun, or some other body in the solar system?

Spinning around its axis has been a way to stabilize some rockets and even some probes but it is not a requirement to do that. Most satellites are stabilized so they point on the same side toward earth. That is technically spinning one around its own axis per obit.

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When you launch a satellite to orbit the earth it does that because you accelerate it you 7.5km/s parallel to the surface of the earth for low earth orbit, The majority of the rocket is used do this.
If you just go straight you will fall back down. The energy to go up to the altitude of the low orbit is a lot lower than is required for an orbit. The needed acceleration is around 2km/s compared to the total of around 9.5km/s for low earth orbit.

You can launch straight up and if it sends you far enough you will be out of earth’s gravitation influence and orbit the sun. Earth orbit the sun at 29km/s the acceleration you have done is added or subtracted from that. It is not that different than if you throw a ball in an aircraft the ball will move at the speed of you + the speed you throw the ball.

You need to accelerate so you move at 29km/s in the opposite direction of Earth’s orbit to have an orbit around the sun. That acceleration is higher than needed to get out of the solar system if you do it in the other direction- So it is harder to get the sun compared to Pluto and beyond because you start with the motion of the earth.

You could, but it would be bad.

Even if it started with no spin in any axis, the first atom of gas or microscopic piece of something it came in contact with would start a rotation.

By establishing a specific, planned, controlled spin, you can use gyroscopic effects to offset other issues.

The alternative, like say the Hubble space telescope, is to have internal motor driven inertia wheels. This allows you to compensate for rotations the spacecraft picks up and turn it as desired. These systems are complex, and these gyros are the life-limiting factor in Hubble.

It is totally possible to release an object into space without spinning it. We purposefully spin them. It helps them remain on planned trajectory. Same principle behind the spin on a football.

As for where the momentum comes from, most manmade craft will have jets angled to provide spin , but also the larger releasing object has more inertia than the released object.

Planets rotate because when they form the clouds of matter have a momentum of their own that is maintained when they coalesce into a single body.

As far as small bodies tending to rotate, physically speaking there is nothing preventing you to have a body moving with no spin It is however extremely *unlikely,* just like there is no physical law preventing you to balance a pen on its tip.

Just imagine having a rod perfectly still in space. It will still be subjected to gravitational forces from distant planets or winds of photons coming from distant stars, the likelihood of these forces being balanced, i.e. generating no momentum, is vanishingly small.

For the same token, an astronaut jumping of the ISS may appear to move with no spin at the beginning but if left to drift, poor man, any imbalance in the forces expressed by his/her feet will result in a rotation.

This line of reasoning does not apply only in space but also in robotics. You could ask the best engineers to build you a robot moving in a perfectly straight line but, sooner or later, it will start to drift left or right, possibly due to a tire being more inflated or any other reason.

Active guidance is required to have anything in a stable trajectory, be it on land, water, or space.