Health concerns
 
Shooting down a satellite is particularly sensitive because of controversy over China's anti-satellite test last year, when Beijing shot down one of its own defunct weather satellites.
 
The move led to criticism from the US and other countries because of the amount of debris created from the explosion.
 
About half of the 5,000lb spacecraft is expected to survive its descent through the atmosphere. The debris could then scatter across several hundred miles.
 
The satellite also includes about 1,000lb of a highly toxic propellant called hydrazine, which can be harmful to the human central nervous system and can even be fatal in large doses.
 
Additionally, there are concerns that some of the satellite's equipment may fall into the wrong hands.
 
"We are worried about something showing up on eBay,'' defence and intelligence expert John Pike told AP.
 
The decision over how and when to shoot the satellite down will involve several agencies, including the National Security Agency, the department of homeland defence and the US state department.