A lot of dirtsider civilians think Transatmosphiric Assault Vehicles are re-usable like civilian SSTOs. This goes back to XXth century vidfics which treat space travel as an extension of air travel. The “drop-ship” is just a fancier version of the Helicopter gunships used by the Western English empire in the Sino-French conflict.
Now it’s true, most TAAVs get used more than once, and some are even designed to refuel themselves in the field, but re-usability comes at the expense of payload, and the logistics of interplanetary war prioritize payload and flexibility over re-usability. The idea of a drop ship with an armored vehicle and squad of “Space marines”, landing (let alone landing vertically) Taking off, providing fire support for the squad, and then picking the squad plus armor and then returning to an orbiting mothership on one stage with one tank of gas is a fantasy plain and simple. I’d compare it to some other XXth century literary cliches, but I’ve actually ridden a cannon to (a) moon, and served in an alien princess’ security detail.
First of all, Infantry rarely have the pleasure of riding to the surface in a shuttle, at least not during a combat operation. Even if if fit the mass allowance, it would be putting all the eggs in one basket so to speak. Anything with a pulse drops with a heat shield and a parachute. Some old interactive novels put the hero in some sort of “drop pod” which smashes into the ground with retro rockets firing at the last moment. I’m not sure where they got this idea, because they definitely had Parachutes back then. An armored pod would be too heavy, and retro propulsion is only a good idea on an airless world, in which case a sky-crane makes more sense. And there is no way a human basic is going to survive that kind of rapid deceleration. You might as well be lithobreaking.
TAAVs either land with full tanks and empty bays for an extraction, or empty tanks and full bays for a drop off. In the latter case, the vehicle has to be refueled to get back into orbit. On some planets it is possible to compromise, but this means a smaller payload and a more dangerous ascent. In either case, once it gets back into orbit, it needs to be completely refurbished. These things are designed to be serviced in micro-gravity and hard vacuum. (Another thing XXth century vidmakers got wrong was covering everything in rust and dirt) The cargo bays are not pressurized, Aside from the possibility of xenological contamination, vacuum packing everything reduces weight. Every piece of hardware that gets shipped to the front is shrink wrapped and will likely be used only once. If that seems wasteful to you, you can’t afford to wage interstellar war.
Landing with a bay full of hard vacuum is one way to cut the weight, and this is just as important going down as it is coming back up. The lighter the craft is, the more drag it will produce in the atmosphere. More drag means it will slow down at a higher altitude and not burn up like an inverted Icarus. The offloading of cargo is accompanied by the loud pop as air rushes into the bay, and lots of crackling as human hands tear in, plastic wrap that took machines hours to apply in the factory. Most of the time this hardware will never spend the rest of it’s life dirtside, when the troops come home, it will either be donated to local security forces, or destroyed by an orbital strike. Sometimes it’s not even worth it to bring troops home. Some outfits just drop shell bodies and recover mindstate transmissions, but I won’t sign up for that. Becoming my own Jodie is above my pay grade.
Going up is the same story, no reason to bring that much air into orbit. If you don’t have or can’t wear a space suit, you sit in a pressurized coffin, and nobody unbuttons until they get to the mother-ship. The cabin depressurizes during the ascent, and as soon as you clear the atmosphere, the thermal tiles and cargo bay roof are jettisoned. If there is enough fuel, the TAAV can preform an orbital insertion all by itself, but this is not always an option. Sometimes it preforms a sub-orbital rendezvous where the mother-ship pulls it into orbit with a tether. If that sounds frightening to you, I should add that another option is to jettisons the entire airframe, leaving just the empty frame of the cargo bay, and OMS thrusters. The airframe burns up on re-entry, and the payload completes the orbital insertion using the last few drops of fuel. I’ve heard stories about times when even that wasn’t enough, and the passengers had to kick off and wait to be rescued before their orbit decayed, but I don’t know if I believe them.
If the airframe is lucky enough to make it back into orbit, It will unload it’s cargo at the mothership, before being immediately transferred to fleet logistics. There it’s frame and engines will be inspected, thermal tiles and payload bay doors, replaced, and then refueled or reloaded for the next sortie. This turn around can happen surprisingly fast, within one orbit (Depending on the orbit in question) but with 98% of it’s total mass replaced, this ship of Thesis hardly qualifies as reusable. Interplanetary logistics is a river, and no man steps into the same river twice.
– Memoirs of the bug wars.