We all would like to see a large Mars Rover that could
keep going for years and years on the surface of Mars.
Solar-panels & batteries have their limitations because
you could only charge up the batteries so many times.

Plutonium RTG's?....The majority of taxpayers
get nervous everytime they're told that plutonium dust
can cause cancer.

Cesium or Strontium isotopes?
There are people old enough to remember the Strontium-90
"nuclear fallout scare".

Cobalt-60?...It's a strong source of gamma-rays, requiring
heavy lead shielding to keep certain science instruments
and electronics unaffected...Though that recently discovered
fabric/polymer that absorbs G-rays may help. Check last year's posts on HZ.

What about the isotope Nickel-63 for RTG's?
Nickel-63 has a half-life of just over 100 years, more than long enough
for it to be practical for deep-space missions, but a HL short enough
to keep anti-nuclear activists from protesting its use.

Furthermore, Nickel-63 is hardly a gamma-ray source [check the yahoo.com
isotopic chemistry webpages] and it primarily emits negative beta-particles
gradually converting Nickel-63 to the stable isotope Nickel-64.

Negative Beta-particles, I think, are ideal for RTG's 'cause they are
easily stopped by a thin metal shield or even a few centimeters of plastic,
wood or glass...and in the process of being stopped and absorbed, the kinetic-energy of a Beta-particle should be readily converted to heat energy.

Jacob

"We choose to go to the moon, and do those OTHER THINGS, not because they are easy, but because they are hard."
John F. Kennedy