"Grav Belt (TL12) Cr100,000, negligible weight if on; 10 kg if turned off. Personal anti-gravity transportation using a single null-gravity module and a personal harness. Performance is similar in speed and range to the air/raft."
So what are we told about speed and range for the air/raft:
"TL8 - An air/raft (grav belt) can cruise at 100 kph (but is extremely subject to wind effects), with some capability of higher speed to about 120 kph. An air/raft (grav belt) can reach orbit in several hours (number of hours equal to planetary size digit in the UPP"
that is speed and capability taken care of, if it can reach orbit it can descend from orbit.
How about duration?
"Range in time or distance on a world is effectively unlimited, requiring refueling from a ship's power plant every ten weeks or so."
So I don't think the TL12 has any difficulty in doing what the TL8 air/raft does for performance and duration.
It's something I've always thought was interesting -
CT in the original
LBBs had grav craft immediately replace all else at TL8, and gave them great endurance (ten weeks doing anything they were capable of in 1981, 'unlimited' in 1977). Then they got chopped back constantly - '81 already cuts back endurance from 'unlimited' to 'ten weeks'.
Book 4 (1978, so shortly after the original LBBs were published) puts military replacement of ground vehicles with grav back to TL10, with limited user of air/rafts at TL8-9.
Striker further cuts endurance - at TL8 a 4 ton grav vehicle capable of 120 kph needs 0.144 Tons of fuel per hour (and 1.16 tons of grav modules and MHD plant), if it carried nothing but fuel (no chassis, no seats, just lifters, power plant, and fuel) it could fly for about 20 hours. One that could carry four people and four tons of cargo wouldn't manage more than about 6 hours. Batteries are good for about 1.4 hours at TL8, 4.55 hours at TL12. Fusion's out for air/rafts until TL13 due to minimum plant size.
MegaTraveller just goes straight to TL15, gives even air/rafts a fusion plant, and gets 60 days endurance. It's probably not doable at TL12, but TL12 batteries might get you 12-14 days duration, so not too bad (still nothing like ten weeks, though).
MT says grav belts have 4 hours power at TL12, 8 hours at TL15 (and gives them vastly higher maximum speed than an air/raft - 300 kph).
TNE has TL10 air/rafts with ~14 hours endurance, TL12 models with about the same, and TL15 models with 100 hours of thrust and a month of power (and a cheaper model with only 46 hours of propellant for thrust), but they can do up to 300 kph. Grav belts have 2 hours duration, and 300 kph maximum speed (they weigh a lot when turned off, too).
T20 says '1 week' for duration. Grav belts get 4 weeks endurance, and 120 kph maximum speed (as does the air/raft).
GURPS Traveller gives us a (Traveller)TL15 air/raft with 10 years power and 160 miles per hour top speed (~200 kph). The base book doesn't list grav belts, so I looked at
GURPS 3e Ultra-Tech. A grav belt would be available from (Traveller)TL9 onwards, but it'd require a lot of batteries to get half-decent endurance.
MgT2 doesn't give endurance, but we can work back from the given speeds and ranges. For an air/raft (TL8) this gives 7.5 hours at 200 kph, and 3.33 hours at 300 kph. A grav belt is good for 200 kph and 4 hours at TL12, 12 hours at TL15.
Overall, aside from
GT, post-
LBB versions nerf air/raft endurance a little or a lot, probably largely as a side-effect of using design sequences intended to disallow grav tanks with infinite endurance at ridiculous speeds.
