another general question....

 

if you have an object in space (ie. a spaceship) and you want it to orbit nearby planets, can you do it by taking the centre of mass of the 2 planets.

 

Cheers guys (i hope this thread is in the right place )

 

Sarah

or what kind of physics (sections of classical mechanics) would be useful to solve these kinds of problems?

Not sure if I understand the question.

 

The rocket is going to orbit the center of mass of the system, the mechanical energy of the system has to be negative, and the orbit is going to be elliptical (following Kepler's laws for orbits)

k thanks

i was thinkning about doing this problem using a computer, ie. making a program to do it. but i have limited skills in this area. is there anyone here who could help me with this?

 

Cheers

 

Sarah

That's not particularly easy due to the nature of the problem (elliptic orbits are a bit nasty to deal with). You might want to take a look at Orbiter, which is a space simulator (free). It's rather good - perhaps qiute a way off what you were thinking - but it gives you an idea about how complex these things can become.

k thanks

If you want to use some math to model it for you, you can write a fairly simple program using OpenGL and C. But if you knew enough programming to succesfully do that, then you wouldn't have asked. However, you can download a mathematics program such as Livemath (not too good but it will suffice for your purposes) to model elliptical orbits.

 

To do so just use the polar formula for an ellipse, a/(1+b*sin(theta)) and model it for whichever a and b you desire in order to model the orbit you want. If you want to add even more realism, you can program this orbit in relationship to the velocity of the orbiting body, and this velocity is going to be determined by amount initially given and the acceleration of the body due to gravity (-Gm_1m_2/r^2). Anyway, all you really need is 1/(1+bsin(theta)) and you should be able to get what you want.

yeah the problem is to do with a small object orbiting 2 much larger objects, so do you think it would work for something like that? ie. have to work out the time it takes and so on...

yes you can do it using the animation variable. For some use 2*a to make it move faster, 1/2*a to move slower, tec.

k thanks then