[Wikipedia](http://en.wikipedia.org/wiki/Space_debris) writes to say 

> 
> As of 2009, about 19,000 pieces of debris larger than 5 cm (2.0 in) are tracked,[1] with another 300,000 pieces smaller than 1 cm below 200 km altitude
> 
> 
> 

Control collision avoidance attempt to maintain a clear 2KM cube around the ISS. Whenever an object is expected the pass through this virtual cube, ISS has to manoeuvre. 2KM might sound a lot, but we're talking of a velocity of 7km/s - so it's not even a half-a-second away!

The orbit around Mars is probably not quite as crowded. On the other hand, there are 3 live spacecraft in orbit

* MO
* ME
* MRO

There may also be other craft from older missions in Martian orbit.

With the imminent arrival of NASA MAVEN, and ISRO MOM, the number will increase this week.

**Given the signal lag**, is there any active collision avoidance system aboard any of these craft ? Is such a system needed at present?