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Vince
2005-Mar-02, 09:46 AM
Why do we send rubish from the space station back to earth, to burn up
in the atmosphere, why not give it a push and send it in to the sun? B)

eburacum45
2005-Mar-02, 12:03 PM
To get something to burn up in the Earth's atmosphere only needs a small orbital adjustment- you only need to ensure that the object intercepts the very top of the atmosphere for a short time and it will be slowed down. This slowing means the object will intercept even more of the atmosphere next time- slowing down the object- rubbish, what have you- very cheaply.
This is called aerobraking, and is the cheapest way to change obit sufficiently to re-enter. Most re-entering satellites burn up causing almost exactly zero environmental impact.

On the other hand it is very difficult to get to the Sun; an object has to escape the Earth's gravity, then slow down from the Earth's orbital speed to almost zero before it can reach the Sun. In fact the Sun is one of the most difficult places in the solar system to reach- to demonstrate this, consider the Mercury Messenger mission;
this probe will flyby the Earth once, Venus twice, and Mercury itself (at speed) before it finally gets to the inner planet. This shows just how difficult it is to plot a mission to the vicinity of the Sun.