(CNN) Mysterious Russian satellite worries experts.

CNN doesn’t ask around enough.  It’s not hard to figure out the likely mission of the Russian satellite.  It’s most likely a  tristatic array.

The U.S. has a stealth satellite program, which aims to prevent detection of the satellite from the surface of the earth. For this limited goal, it is necessary to specially design the surface of the satellite that faces earth. The surfaces of the satellite that cannot be seen from earth may have relaxed requirements of low observability.

In all cases involving stealth targets,, there is a huge advantage in observing the target from multiple locations. Bistatic radar, where the transmitter and receiver are separately located, can detect a stealth aircraft, though not necessarily track it.

So the “Russian doll” design of the mystery satellite is intended to detect satellites that are difficult to see, but not absolutely invisible. With three dolls, the basic principle of  radar, of timing the signal echo to measure distance, becomes inessential. With pure triangulation, the relative speed of the target is immaterial.

For the Russian approach to work,  a rough idea of where the satellite is required. The satellite is launched on a trajectory that will take it a bit above the target. The biggest doll gets a whiff of the target via radio or thermal emissions and a rough orbit determination.  Then it ejects the intermediate doll into an appropriate nearby orbit. The ejection must be timed carefully, since the two dolls will drift apart. With two observations, they are on their way to a triangular solution.  Now they know where to send the third doll; the U.S. stealth satellite is triangulated, possibly via LIDAR.

The above explains why the dolls are launched as a set, to maximize the time they can stay in close proximity.

In the finale, one of the dolls places itself in the way of the U.S. satellite. Explosives are not required; when cars crash in space, there are no survivors.

Since U.S. reconnaissance satellites possess sensors of extraordinary complexity, functionality, and cost, they cannot be replaced by constellations of more survivable micro satellites. It may be necessary to host future systems on space-planes like the X-37. Since the X-37 has very high delta-V, it could escape the trap of the Russian dolls.