# Q & A: orbital power

Q:
Hi, I am a Master of Science student in Sweden. I would be grateful if you might help me with a difficult problem in mechanics that I have tried to solve for a long time without success. The problem is a part of a bigger problem that I am trying to solve and is therefore important to me. Here is the problem: How much power P [W] is needed to force a satellite (modeled as a point particle) to move in a perfect circular orbit with radius r [m]? The mass of the satellite is m [kg] and its tangential speed v [m/s] is constant. Important conditions: - It is assumed that NO GRAVITY affects the satellite! - The mass loss due to fuel consumption is neglected. - The power is assumed to act under ideal conditions, i.e. there is no energy loss due to friction or the choice of engine. - It is also assumed that v
- Oscar Carlsson (age 20)
Sweden
A:
Fv = 0.

Mike W.

(published on 01/29/2012)

## Follow-Up #1: gravity-free orbit

Q:
If there's no gravity influencing the satellite, then there's no orbit! Orbit = moving "straight" in a curvated spacetime. No curvature, i.e. no gravity = moving in a straight line. By the way, power = energy consumption over time. The only thing need is acceleration which is a = F / m. Also, there's nowhere in our universe where there is no gravitationnal influence! The main problem with theories is, they always work perfectly in an perfect universe...
- Anonymous
A:
Maybe this orbit is supposed to be maintained by a long string. The original question didn't specify, except to ask us to neglect gravity.

Mike W.

(published on 01/29/2012)