Accurate pointing on space object is the base of many spaceflight missions. It is hard for a single detector to obtain high acquisition probability of high speed object in various space backgrounds. A method is brought forward that forecasts the motion track by using land-based radar

and then makes the space-base detector possible work in a high degree of confidence

with the aiming of infrared

laser and visible detection. It is guaranteed to obtain high acquisition probability by using information fusion. Considering the devices available and basic demand of space payload

this paper analyses the relation between detect range and probability

and obtains its joint detection probability in various backgrounds

which provides a solution for space-based pointing.