If a Kardashev Type III alien civilization wanted to monitor the earth (and its inhabitants' progress) via a satellite/orbiting object, how would they realistically transmit data from this object?
Some notes:
Simple put... for all we know they already are, using much the same methods we use to monitor ourselves. Place mundane satellites into suitable orbits, with the appropriate selection of observational tools.
Anything less that a few metres across is not going to be seen for a very long time even in quite close orbit, especially if intentionally limiting its profile and visibility.
The biggest limitation is how they broadcast any collected data back home. For example on Mars the rovers transmit to the orbiter, which in turn calls home.
They would likely want to have some constellation of small observation satellites which transmit to a larger, more powerful and maybe slightly more remote transmission station, especially as it is likely going to need some form of handwavium FTL communication technology at this stage.
As far as I know, yes.
A friend of mine helps build sattelites, and she told me about the option for micro-sattelites. If you put a few hundred to thousand away from any planet or space debris and have them a few thousand kilometers apart you could capture the light from say Alpha Centauri, combine the images and have the ability to create a Google earth (or Alpha-Centauri might be a better name). So if these Aliens place these micro-sattelites somewhere in deep space relatively close to us, we would never pick up on the tiny buggers and they would have very good vision of our planet, but with a delay ofcourse as the light needs to travel there first. Place another field of sattelites on the other side, both at an angle compared to the planet's rotational field so that the other planets don't block the view and you are set!
Then perhaps just try to get a few tiny drones into our communication sattelites or our internet centers and you can look at the information we send and what kind of tech we have.
Before, say, the mid 20th century they could just put satellites in orbit. They'd want them to be unobservable, so small, as non-reflective as possible. On-board power supplies or beamed power from someplace else, say relayed from the far side of the Moon.
For ground observation, drones. Big ones flying high, small micro-drones that could hang around in building, the whole shebang.
Once Earth high-tech gets going and astronomy gets more detailed, you have to start being more careful, but, then you can use human tech itself by intercepting our own obervational tech. Stick microsats with the more sensitive alien sensors on our own satellites: unless humans have reason to visit the satellite, they'd never know the Landsat bird has a passenger of non-human origin hitchhiking on it.
Put your observation devices on the moon. Cover everything but the actual sensors (which are small - think the size of a smart phone camera) with rock. Use laser beams to communicate with distant repeater stations (perhaps on asteroids), and make sure no Earth spacecraft are in the path of the beam when it's used.
The only way this could realistically be detected is to build a moon base, and just happen to dig up one of the sensor networks in the process.
This seems precisely what Arthur C. Clarke's Sentinel was for. A simple device, undetectable by earthbound humans, that transmitted pertinent facts to it's masters.
In this case, only one fact was important, so it was a binary signal. After all, we don't want to be bothered with the details of every dance of every protozoa, either. The Sentinel's masters cared only about species that developed space travel.
If you wish for a more complex model, the Sentinel evolved into 2001's Monolith with many more useful features.
We are currently able to distinguish 'weird' stuff outside of our planet by the wavelengths it emits/reflects back to earth. If the satellite was small, accepted passive input from something/somethings on the ground instead of actively sending radiation/waves to the Earth, and did a tight-beam sendoff of its information in the direction of space, it would be damn hard to spot.
