MMRTG- thermal and electrical output

Question

I haven’t been able to find a definitive number for the thermal output (in watts) of the MMRTG used aboard the Perseverance rover. The numbers I’ve seen range from 1950 watts to over 2000. I also haven’t found a reliable number for the electrical output either. Some sources say 110 watts, some 145 and others 120.

A lot of sources contradict each other and even some NASA documents can’t seem to agree on a number. The only reliable number I’ve seen is that it has a minimum life time of 14 years.

Some of the articles I looked at -

This NASA document

This article from the Office of nuclear energy

Answer 1

Wikipedia has some facts about Plutonium:

each gram of ²³⁸Pu spontaneously generates 0.568 W of heat.

There is 3,478 g of ²³⁸Pu at the start of the mission. The product of both numbers is 1975.5 W. That fits well to the 1,975 W in the document.

Some sources you found simply rounded 1975.5 W to either 1950 or 2000 W.

There was an early design goal for the MMRTG of 125 W electrical power. For the rovers Curiosity and Perseverance both :

approximately 110 watts at launch with little decrease over the mission time are specified.

The electric power of the thermocouples depends on cooling influenced by the environment. On a cold day on Mars it may be 120 W, on a warm day only 110 W. (At the beginning of mission).

The Perseverance rover will need about half a year to Mars. The half-life of ²³⁸Pu is 87.75 years. After 0.5 years 99.606 % of ²³⁸Pu will remain, the heat power will drop from 1975 to 1967 W. 13.7 g of the ²³⁸Pu will be decayed during the flight.

But the decay of ²³⁸Pu does not start at launch, ²³⁸Pu starts to decay when it is synthesized. If it waits 5 years for launch, 3.87 % of it is decayed. Thermal power will be reduced from 1,975 W to 1,898 W during this time.