Traveller never has been intended to be "Hard SF" as a game. (Source: Marc Miller. multiple times over the years.)
To be fair, very little SF in RPGs is anywhere close to Hard SF. G: Terradyne, G: Uplift... sure. SpaceTime (BTRC). Albedo (The comic's pretty hard SF, despite being Anthros)...
2300 AD was the "Let's try to be hard space opera" attempt. It's still less hard on the tech than any of the ones in the preceding, and on par with GT and GTIW... TNE and T4 are both in the hard space opera transition; it's soft sci-fi, but has some illusions of realism. It was worked out that HEPlaR was needing exhaust velocities in the single digit denominator fractions of C. Artificial gravity, Cold Fusion, Jump Drive... it's exceeded the old SFWA guideline of 3 breaks from known physics right there. But there are more... Gravitic shielding (otherwise the Gravitic-focused lasers would kill everyone aboard every shot), the Traveller Pi⁼ Meson, the Meson Screen, the tightly collimated plasma weapons... but more than anything, not even T4 nor TNE really give sufficient space to radiators; other editions ignore them completely.
Hell, CT-77 and CT-81 both indirectly reference the Lens in the Psionics rules. Hard SF lacks psionics.