There are basically 3 means of tracking satellites:
- Radar- Can hide from this, see anything about stealth aircraft out there (Same principals)
- Visible- To hide from visible, it would basically be necessary to absorb any light for anything that might be pointed to the ground. This would heat the satellite up, and might make it less useful. In theory one could dissipate the heat upward, but this would make it easy to spot by IR searching satellites.
- Infrared- The ideal way of achieving this is to make it as cool as possible. This is challenging, to say the least, but tends to work best by reflecting most light.
As a result, it is very difficult to hide from both Visible and IR.
The truth is, it's very difficult to hide a satellite. But to use any of these detection methods, it helps to have at least a rough idea of where it is. The best thing you can do to hide a satellite is to not let it be known where it is, and make it as stealthy as you can.
This was done previously with the Misty satellites. Of course, these were identified by amateurs eventually, but it did take some time.