If your logs from outerspace use atomic clock that is programmed to represent the current UTC, taking into account the effects of Einstein's generalrelativity (curvature of spacetime), then there shouldn't be any problem.
The problem you will have to deal with is the delay in _indextime . See, your log's _time is the information your search timepicker will look after.
Say your spaceship has a log at 2020-03-01T00:00:00 about a malfunction of one of its thingamagjiggies. Your search head that is on Earth has an alert that looks after "malfunctions on one of the thingamajiggies" every 5 minutes. It will cause an issue if the log arrives on your Earth-bound indexer 6 minutes late. Because at 2020-03-01T00:00:00 and at 2020-03-01T00:00:05 , the alert wouldn't be able to detect the log (because it's not ingested yet). And at 2020-03-01T00:00:10 , the alert would've already missed it. There are however tweaks that can solve these types of issues.
In short, having a Splunk forwarder from outerspace wouldn't cause much headache as long as the network is alright (heck, I've seen NASA livestreams from low-orbit space, forwarding logs wouldn't be that hard).
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