It's not a secret that NASA uses Nikon cameras and lenses (http://www.nikon.com/news/2009/1221_NASA-D3S_01.htm) after using Hasselblad cameras during the Apollo mission.
Could we reveal the reason?
very, very simple reason:
Hassy has a bigger camera body ( more easy to manipulate the settings in a space suit)
Nikon sensors have better DR than Canon.... and in space this performance is crucial.
Yes it must be the DR. NASA has been awaiting that for years up until last year when Nikon introduced the D800...
Do you believe yourself what you're writing?
You.... again 
Well, factually speaking, DR is NOT the most important thing in space. NASA bought into Nikon a few years back because at the time Nikon was the king of HIGH ISO. You don't shoot the dark side of the Earth from space at ISO 100...you shoot it at ISO 6400, 12800 and at high shutter speeds to freeze the motion of 17,500mph! At High ISO, DR is physically limited. You lose about 1 stop DR per stop of ISO increase...you have only 7 or 8 stops at those high ISO, so the most important thing is the total electrons per pixel at maximum saturation. The higher the charge, the lower the noise.
Today, Canon rules the high ISO/SNR realm. By a relatively small margin compared to how much Nikon rules the low ISO/DR realm, but enough to give them an edge now. I believe the only reason NASA currently uses Nikon and has not changed to Canon is there really isn't any reason to. They are invested. They have the gear, have the lenses. Why change? They don't need the compelling features of the 1D X...it was built for sports, so it has an AF system and frame rate to match. I'd figure the most compelling Canon camera for NASA would be a 40-50mp FF monster with good ISO 25600 performance...which doesn't exist quite yet.
