Space Forum / Space Science / September 2005

I can't find much hard data (though the pictures have a two degree
field, which should tell me enough !) but according to
<http://www.isas.jaxa.jp/e/enterp/missions/hayabusa/about.shtml>
Itokawa's diameter is about 500 meters. So Hayabusa is keeping a safe
distance for the moment.
NEAR-Shoemaker orbited Eros (20 miles in longest dimension) at a height
of about 20 miles for about a year.

-> I can't find much hard data (though the pictures have a two degree  
-> field, which should tell me enough !) but according to  
-> <http://www.isas.jaxa.jp/e/enterp/missions/hayabusa/about.shtml>  
-> Itokawa's diameter is about 500 meters. So Hayabusa is keeping a safe  
-> distance for the moment.
-> NEAR-Shoemaker orbited Eros (20 miles in longest dimension) at a height  
-> of about 20 miles for about a year.
 
As seen from the moon, Earth has an angular diameter of about two
degrees. So it is probably fairly accurate to say that the asteroid and
spacecraft are roughly a scale model of the Earth and moon. If the
spacecraft were to orbit the asteroid at its present distance, the
orbital period would be something like a month. Alternatively, if the
spacecraft were to be absolutely stationary relative to the asteroid at
its present distance, and were then to fall toward the asteroid under
the asteroid's gravity, it would strike the asteroid after three or
four days, just as the moon would strike Earth after three or four days
if its orbital motion were suddently to be stopped.
 
As you say, NEAR-Showmaker *orbited* Eros for a while. I suspect this
Japanese spacecraft must be orbiting the asteroid too.
 
                       dow