[lmm]

> I'm far from a translator... but it is not "We opened a door" but "A door is open to do missions that were not possible before".

You're being overly literal. Omitting the subject is normal in Japanese; translating that to a passive-voiced sentence in English is usually misleading.

[mathrawka]

Yes, but... 新しい扉が開き vs 新しい扉を開き

[lmm]

Again, not a distinction that carries the same nuance that it would in English. The whole animate/inanimate distinction just isn't there in the same way in non-indo-european languages.

[mathrawka]

新しい扉が開き

が makes the subject the door, not JAXA. Plus it would be very uncharacteristic of a Japanese person in that position making such a bold claim. It goes against Japanese society norms.