Satellite Reliability
How long do hashtag#satellites last?
Vanguard 1 has been in orbit more than 65 years [1] and Voyager 1 had a mission duration of 46 years, 4 months and 11 days [2]. The most complex object in orbit, the International Space Station National Laboratory (ISS) has been operational for more than 23 years. [3] Landsat-5 holds the world record for the longest operating satellite at 29 years, 3 months and 4 days. [4]
However, most satellites have much shorter lives because they are designed to last a limited time. Design lifetimes are up to 30 years. Most satellites designed to operate between 7 and 15 years. [5]
During that lifetime, things do not always go as planned. Just like cars, TVs, and any other device, parts of satellites occasionally fail. But since they are in orbit, when one part fails, the satellite is retired rather than repaired.
A paper by Hiriart et al from 2009 looked at all satellites in orbit between 1990 and 2008 to empirically estimate the failure rate. [6] They looked at the reliability as a function of orbit. The conclusion was that the reliability varied between 92.5% and 95% at 15 years. Medium earth orbit satellites were most reliable followed by low earth orbit and then by geosynchronous satellite.
This kind of reliability rate indicates that large satellites with redundant subsystems can last very long times, much longer than 15 years.
Space based solar power (SBSP) satellites will be large. These satellites are expected to have large numbers of parallel systems that provide redundancy which can make up for individual component failures. Unlike most satellites where a single subsystem failing is fatal, the size of SBSP satellites will make it robust to any single point of failure.
For example, if each subsystem is 93% reliable at 15 years, putting 2 subsystems in parallel will be 99.5% reliable. Putting 5 subsystems in parallel will be 99.9998% reliable. SBSP satellites will have thousands of subsystems in parallel. The reliability should be very high.
Properly engineered, this redundancy will lead to graceful degradation, a gradual loss of performance, rather than failure as subsystems stop working [7]. Scaling from reliability today, this implies that a 30 year or longer life will be achievable with good engineering practice based on existing satellite capabilities.
References:
[1] https://en.wikipedia.org/wiki/Vanguard_1
[2] https://en.wikipedia.org/wiki/Voyager_1
[3] https://en.wikipedia.org/wiki/International_Space_Station
[4] https://en.wikipedia.org/wiki/Landsat_5
[5] https://www.linkedin.com/posts/edtate_solar-sbsp-power-activity-7153355357879230465-Bi6O
[6] https://ssdl.gatech.edu/sites/default/files/ssdl-files/papers/conferencePapers/IAC-2009-D1.6.1.pdf
Hiriart, T. & Castet, Jean-Francois & Lafleur, J.M. & Saleh, Joseph. (2009). Comparative reliability of geo, leo, and meo satellites. 9. 7182-7196.
[7] https://lifetime-reliability.com/tutorials/parallel-system-arrangements/
