[inquest]

However it requires more energy to initiate than Deut+Deut fusion.

And we have to find the He-3. Not quite as abundant as H-2, is it?

[Crazieman]

Correct.

Except on the moon. Thats why people like to point to it for He3 mining. However its uneconomical since we have no way of producing a fusion effect without putting more energy into it - yet.

[IonImplantGuru]

He3+He3 fusion results in no free neutrons (Seen as the holy-holy grail of fusion) However it requires more energy to initiate than Deut+Deut fusion.

And we have to find the He-3. Not quite as abundant as H-2, is it?

He-3 is rarer than hen's teeth! He itself is not that abundant, but He-3 constitutes only 0.00013% of all He.

H, of course is very abundant and H2, though rare, amounts to 0.015% of all H. That makes its relative isotopic fraction 3 orders of magnitude greater than He-3.

Above info is from my old (40+ years) chart of the nuclides, but I doubt the data have changed significantly.