Ion Thrusters: HDLT vs DS4G

Still, where's the power source going to come from? The ESA SMART-1
probe that went to the moon was solar-powered, if I'm not mistaken. So
if the tenfold improvement claim is correct, then that could mean that
a SMART-1 probe using DS4G could go to Mars, which is almost ten times
farther than the moon. But I guess solar energy drops off significantly
as you go out towards Mars, so that would be a problem.

And do solar panels really offer good power-to-mass ratio?

Gee, if only there were some good power source that fit the bill,
without the hazards of nuclear energy.