system
Given the following post, respond as if you're commenting on Reddit:
human
Mars rover Opportunity was built to last 90 days, and lasted 15 years. Voyager aircrafts were built for five year mission and lasted 41 years. Please explain if these crafts were over-designed or Nasa just got lucky?
gpt
Suppose they built it so that they could estimate the rover had a 1 in 1000 chance of failing by the 90th day - basically a guarantee (99.99% chance of making it 90 days). With that probability of failure, the chances of making it to the 5000th day would be something like 94.6%, so it's basically just a consequence of making that 90 day target as absolutely solid as they could.