By the way, I used something similar to sensor shadowing in my book. Here's the relevant passage:
In Miranda’s office, Barbara pointed out a green glowing signal light. “Approximately every thirty or forty minutes, that light flashes a code. Then it just glows green again for a long period, but if it ever goes for more than an hour without flashing the code, it will begin blinking red, indicating that our circuit has been discovered and eliminated.”I was watching the "Red Jacket" gun-smithing show the other day. They were making a gun-mount for a helicopter platform. One of the things they mentioned was putting in blocks to the gun traverse so that it would be impossible to shoot yourself in the tail-rotor for example.
“But how could you do that? We can’t interrogate our circuit without drawing attention to ourselves!”
“So we don’t interrogate it, but as long as it’s functioning, it puts a shadow impulse out on the navigation interrogation signal that gets beamed down to certain landmarks, including a nearby peak. I’ve set up a simple relay device to receive that shadow signal, which is only a fraction of the normal sequence, and delayed as well. The normal equipment just discriminates it out as an echo. Nobody ever knows it’s there.”
As they watched, the light blinked a bright pattern of impulses, then steadied to a pale green. “There, one of the orbiters just did a Nav interrogation sweep. Now the station will update its position data. And we get an update of our mission status as well.”
I used a similar concept. On my fictional world, orbiting laser forts are up there to protect the populace from the occasional errant meteor, but there is a danger that if you get on the wrong side of the government, you could have them aimed at you!
So I sent up a team of saboteurs, to replace the aiming equipment electronics. The new boards had some special circuitry that added several locations to the "forbidden to fire" parameter, which protected our erstwhile rebels.
The sensor shadowing took place on the navigation side, but all of the replacement equipment's functioning had to be invisible until the hour of action arrived.
Don’t know how devious the EVAlite version of Eva is, she would have had to do lots of devious things behind the scenes for near one hundred years to get that to work when she steals Sigma out from everyone’s noses.