It MUST be risky if they already stay up so long and now maybe for six months!
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I heard that it was because Boeing did NOT load the software that would allow the capsule to return automatically (without humans). As I understand it (and may be wrong) but it requires someone to be inside the capsule to disconnect from the space station.
The capsule has so many problem it may not return to earth safely so it would be suicide for someone to attempt to return in it.
This is a major obstacle to the Mars trek estimated to be six months total minimum at this time.