Article is capped at 18 views/day so can’t see numbers.

But theoretical cap of energy would be something like E_kin = (\gamma -1)mc². Without knowing anything about the mission or engine, a 50 kg probe at a velocity of .9 c means an energy requirement of about 1,0e19 J.

Fusion of H2 to H3 yields about 340e9 J/g meaning we need about 3 million kg of fuel at 100% conversion rate, or a third if we manage He3 reaction.

Realistically heating, engine efficiency, deceleration, vibrational damping and such would probably lower efficiency to at most 40% and we end up at 8 million kg of fuel to propel a 50 kg payload (not counting the fuel mass).

Seems unfeasible.

Edit as @i_have_no_enemies@lemmy.world kindly provided an alternative link.

Article only says doubly efficient, and H2 to He3 reaction.

To get to .9c we still need a couple million kg of fuel.

Even .1c needs about 40 000 kg of fuel, which is doable, but probably unfeasible.

0,05c should be in kgs range, and is probably plenty (100 km/s).