Space Probes & MERs History Recap
Pioneer 10 & its twin probe Pioneer 11 reference
Courtesy of Uwe's response on my question :-
- Pioneer 10 was planned for 21 months of operation. It did work 31 years, that is 16 times longer. We should be very happy about such a reliable space probe.
Voyager 2 & its twin probe Voyager 1 reference
- Voyager 1 and 2 were designed for 5 years of operation: They work 41 years now, about 8 times longer. So Pioneer 10 did work 16 times longer than planned, much longer than the Voyagers. If the Voyagers work till 2025, it will be only about 10 times longer than planned.
MER-A known as Spirit
- The rover completed its planned 90-sol mission. Aided by cleaning events that resulted in more energy from its solar panels, Spirit went on to function effectively over twenty times longer than NASA planners expected. Spirit also logged 7.73 km (4.8 mi) of driving instead of the planned 600 m (0.4 mi), allowing more extensive geological analysis of Martian rocks and planetary surface features.
MER-B known as Opportunity
- With a planned 90 sol duration of activity (slightly more than 90 earth days), Spirit functioned until getting stuck in 2009 and ceased communications in 2010, while Opportunity was active as of June 10, 2018 when a dust storm forced it to hibernation. It has operated 5275 sols since landing, having exceeded its operating plan by 14 years, 215 days (in Earth time). Opportunity has operated for over 55 times its designed lifespan. As of June 10, 2018 when contact was lost, the rover had traveled a distance of 45.16 kilometers (28.06 miles).
Nonetheless, with so many references showed that the Pioneer program, Voyager program and two relevant MERs Spirit & Opportunity were so successful and already operated for over dozen times longer than initially expected. It is undeniable that NASA is indeed a great and professional national space agency. But presumably those space probes & MERs were actually designed to operate that long in the first place, why wouldn't NASA just announces their expected lifespan slightly off than their actual lifespan instead; those expected and actual numbers recorded in the history were so distant? Or should I say it is essentially unpredictable?
Maybe we can assume NASA didn't want to take unnecessary risks plus considered other external factors that would concerns the mission (e.g. decay of the RTG over time be more of an absolute limiting factor) so in a nutshell they'd rather purposely give a smaller number on expected lifespan. What's up with all these?