Is it possible to have a satellite that bounces data back from sattelites farther out in the solar system?

Question

Say we put a satellite in orbit around Neptune or Uranus that simply stores and sends data back to earth? Like as a big range extender for missions like New Horizons that work so far out that communications are an issue?

I know there would be issues with orbits lining up and data storage, but is that sort of thing feasible?

Answer 1

No, this is a bad idea for several reasons. It might be a good idea if there ever becomes a lot of spacecraft out there, but otherwise...

1. The relative positions changes over time. One would need a number of these to work reliably, otherwise there's a good chance it just wouldn't work.
2. Solar power doesn't work that far our. The current method to power spacecraft is radioactive decay. It looses efficiency over time, so the mission would be limited.
3. Orbiting that far out is really difficult, and hasn't been done yet.
4. The pointing of the antenna correctly would be more difficult. Basically pointing at the Sun points at the Earth when you are that far out, pointing at the nearest satellite is more difficult.
5. If one of the satellites failed, you'd potentially lose the mission. Not really an option.
6. If you are really far out there, it doesn't matter that much. Voyager's are both over 100 AU. Uranus is only 19. Hardly a scratch. Most spacecraft going out that far for the foreseeable future aren't going to stop, they will be at a solar escape velocity, and thus keep moving further with time.

Basically I think it'd only work if there was a lot of spacecraft out there. Maybe around 100, but no fewer than 30. That means you aren't quite as reliant, which should improve things somewhat. I can't see that happening for a long time.

Where this does work is if you have a number of spacecraft close together. Where does that happen? Mars. A Mars communication satellite has been discussed for a number of years, and in fact most Martian satellites double as communication relays after their primary mission is over, and to a lesser extent before their primary mission is over. It complicates the operations somewhat, but it does work.

Answer 2

Because the planets don't line up, there's not much point in putting relays in orbit around a particular planet. For a general solution, you'd need to put a bunch of them out there in circular orbits at various distances from the sun, at great expense.

You could also send one or more relays after each specific probe mission you launched, at progressively slower speeds.

But why bother? The only problem with New Horizons' faint signal is that the transmitted data rate is very slow; when it takes nine and a half years to get to your destination, what does it matter if it takes a day or a week or a month to get the pictures back?

Answer 3

In addition to the points already mentioned: on Earth, we can build dish antennas with a diameter of 70 m. Even the 300 m Arecibo antenna has been used on special occasions. In space, the largest antenna ever deployed is 10 m (the Spektr-R radio astronomy mission). Weight goes up with the square of the antenna radius, so a large antenna gets very expensive to launch.
You also run into space limitations: the largest single piece that can be launched is in the region of 20 m long and 5 m wide, so a large antenna must be folded and/or assembled in space.