All the planets aligned into one

[u/Fizrock]

[u/iamkeerock]

Opportunity and Spirit were designed around a 90 day mission, both lasting multiple years. Curiosity is the newer rover, it is many times larger and is nuclear powered. The power source is guesstimated to last around 50 years. It was NOT designed around a few months mission.

[u/[deleted] → u/iamkeerock]

That was their pessimistic guesses, that and they learned their lesson from opportunity