my eyes!
I've enjoyed this thread: it's always interesting to see how different people interpret the same rules in often very different ways. Or, in this case, the lack of a specific rule (until the later supplement came out). I always played the 'if it goes up then it must be able to come back down' version of the air/raft, with the assumptions previously stated about grav drives. I can see the other viewpoint, and I'd accept that if someone else were reffing besides me and accept that.
Thats always the thing that keeps me coming back to Traveller. I've played a lot of RPG's in my time, but CT has always been a perfect mix of open-endedness balanced with a good consistent rules framework. Your imagination can fill in all the blanks easily and logically, but it isn't limited by endless rules. An excellent result of that has always been the ease of getting new players into the game - a lot of the people I've played with never even bought the rules, they understood them through play easily enough that they never felt the need to study them at home. It's that good.
On a side note I'm amazed by the discussion started by a pun I started earlier involving drop tanks. One guy gets the joke, I expand on it a little and it's off to the races.
So for my 2-Credits, and just to take my pun seriously - if you can't just figure on entering atmo slowly enough to avoid atmospheric friction because you don't want to burn the tanks off the Free Trader, then land from a geostationary orbit on the other side of the planet from the target, then accelerate to the target at nap of earth. The troopers in battlesuits can crawl out of the ship and hang on to the sides of the tanks at the line of departure.
If on the other hand you want to land ASAP then why not just mount the tanks on top of the Free Trader, since you would be using the angle of attack to slow the descent like the shuttle does?
And finally, my air/rafts can reach orbit on their own power, but to land from orbit they need to be purpose built for it. I treat air/rafts like cars: the family wagon isn't made to survive off-road, and the off-road jeep isn't as comfortable as the family mini-van. Landing-capable (in atmo) air/raft is sealed, built heavier, and is a wee larger and more expensive than the standard job. At this point it's like a smaller version of the Book 2 grav-carrier. They weigh 6 tons and carry 6 people (or 4 and 1 ton cargo).
The gunships referenced in Mercenary are what I think the grav tanks are described to be in later games and supplements. Remember that Mercenary came out right after the initial CT release and they were still working out the details of the OTU so gunships later became grav tanks. There is no mention of in-atmo gunships in later supplements and games.