What is the procedure if communication with the ISS is lost for an extended period?

Question

Between ground control and the ISS there is the occasional short communications loss which they are obviously able to deal with, but is there a procedure to follow if the communication is lost for extended periods of time?

I know that ground control does relay information such as impending debris in the path of the ISS so that the orbit can be changed slightly, this is obviously important enough for the safety of the crew alone to warrant a procedure for downed communications.

e.g If communications went down for 24 hours or more what actions would ground control and the astronauts in the ISS take?

To be more specific this isn't just about procedure to regain communications, but all procedure, including what must be done to ensure the continued health and safety of the crew of the ISS.

Answer 1

I did some searching, and I'm going to say that there does not exist a specific procedure for continued operations during some extraordinarily long communications outage, and here's why.

First, communications possibilities with the ISS are varied and robust. There are nine TDRSS satellites on orbit. There are a large number of NASA ground stations, which are geographically varied (i.e. one big hurricane won't take them all out). As user943 pointed out, there are redundant and dissimilar systems provided by the Russian segment that provides further robustness.

The most likely scenario, I think, would be a problem on-board, such as what happened earlier this year. The ISS suffered a 3-hour communications loss due to a software problem - they couldn't point their antennas correctly to talk to TDRSS. As the article notes, however, they were able to contact Mission Control during a pass over Russian ground stations. They went on to essentially reboot the necessary systems, and restored comms.

Theoretically, the ISS could operate in some "emergency" mode indefinitely while just maintaining comms via direct passes over ground stations while the problems with TDRSS were sorted out. Low-rate antennas typically don't require pointing, and while ground passes are short, the communications could be restricted to absolutely necessary commands, etc. (including planned debris avoidance maneuvers, although I think it might be considered too high-risk to perform one of these maneuvers during a comms blackout).

In the unlikely event that all communications were lost, the astronauts would just follow their normal procedures to regain communications, just like they did during the 3 hour outage. Basically, communications are so vital to operations, there would not be anything to do besides trying to regain them.

Answer 2

One of the advantages of the design of the International Space Station is that the Russian and US segments offer dissimilar, redundant systems. In the event that there is a failure of the communication link between NASA mission control and the US segment, the ISS can be safely operated (and communicated with) via the Russian systems and mission control center.