What in your opinion is or was the hardest thing to design and how crucial was or is this to any past missions or this

Question: What in your opinion is or was the hardest thing to design and how crucial was or is this to any past missions or this one?
- Keywords:
  design,
  important,
  missions,
  opinion
Asked by Jake_Kiddell to Tom on 7 Oct 2015.
- Tom Morse answered on 7 Oct 2015:
  
  Hi Jake,
  
  I think the hardest aspect is the thermal control. Can you imagine a standard DSLR camera being moved from -270 degrees C to a few hundred degrees C every hour and a half, 16 times a day, 365 days a year and still staying in focus to view objects 1m on Earth from 250 miles away?
  
  Pulling that off requires a lot of detailed thermal design, with radiators which vent heat off to Space and heaters to warm things back up. We also use complex multi-layered thermal blankets to keep things stable. It’s a tricky balance.
  
  Good luck,
  
  Tom

Question: What in your opinion is or was the hardest thing to design and how crucial was or is this to any past missions or this one?