Possible Clues:

• Canceled ... or a hint to answering 17-, 27-, 34-, 45- and 57-Across
• Failure for 7-Down
• Cancelled rocket launch, e.g
• Postponed flight, at NASA (2 words)
• Space scrap?
• Don¿t say yes to progress in forbidden area
• Useless
• Scrubbed, at 7 Down
• NASA launch cancellation (2 words)
• 'Ixnay'