Hapax Legomenon wrote:

1. If something - say, a cargo ship moving between habitats in relatively low Martian orbit - were to fall from Mars orbit to the surface, how long would it take? Are we talking on the order of 30 seconds, five minutes, 10 minutes, what? Seems to me that guy who jumped from the edge of the atmosphere spent like five minutes in free fall. 1a. How much would it change above timeframe if said ship was actively doing a kamikaze dive and powering into the planet?

As zombiekat pointed out, you can't really compare a skydive from the edge of space to a ship in orbit. Objects in orbit stay in orbit through a very different mechanism than a balloon flying to the edge of space. Objects in orbit are continually being pulled towards the planet, but they're going fast enough sideways that they miss the planet - and that's obviously really fast as planets are big. You can't just "lose" bouyancy or power and then you fall from the sky. To fall from the sky, you need to reduce speed. If you just reduce speed a little bit, you'll just miss the planet by a little less for each orbit. To actually do a kamikaze dive would require shedding all your speed relative to the ground, and that will take almost as much fuel as it took you to get into orbit (since most of the fuel is used to get you up to orbital speed), or you have to shed speed by aerobraking. I googled the space shuttle descent: http://www.nasa.gov/mission_pages/shuttle/launch/landing101.html Rough numbers: 3 minute engine burn to begin descent 25 minute until it hits upper atmosphere 12 minutes of hot aerobraking surrounded by plasma that makes radio comms impossible 12 minutes of flying in S-shapes to shed even more speed and get below supersonic 5 minutes of final approach flight On Mars you're going slower but there is less dense atmosphere so braking will be less effective, even with the terraforming. I'd cut the descent to upper atmosphere in half but leave the rest as is and you probably have something that works for a controlled descent. If you want a kamikaze drop, you probably can't do the hot aerobraking any faster without burning up, but after that you could do a nosedive instead of slowing down. A big question though is: can the cargo ship survive reentry heat? Does it have the aerodynamic shape and structural strength for atmospheric flight? Does it have aerodynamic control surfaces? For your purposes, if you really need to have an orbital cargo ship drop, you need to have it (or its cargo) sturdy enough to handle the reentry but other than that it is hard to see it doing any sort of maneuvering. Also, cargo ship between habitats that has to go in the direction the habs are travelling would need to speed up to catch the leading habitat - if it lost power it would move into higher and higher orbits rather than fall to the ground. So it needs to be flying in the opposite direction from what the habs are moving in.

Dam didn’t realise the shuttle got down so fast, only a little over an hour from ‘leaving now’ to ‘on the ground’ probably feels like longer if your there. Its worth noting however that the shuttles flight path is designed to shed speed. I am thinking that whoever hacked this freighter isn’t interested in a controlled landing. Try a 10 minute burn 1 min to touch atmosphere and a 5 minute uncontrolled descent. Although they won’t know the TQZ is the target until just before it hits the atmosphere. You could justify descent times up to 20 min with a shorter initial burn Because freighters are not designed for re-entry the shill will take damage during the descent, bits will fall off from the leading edge, and insane super AI or an expert pilot, who is insane, could use the aft maneuvering thrusters to keep the ship from tumbling and breaking up entirely, the insanity is necessary because you ego has to be on the ship to do it. This is however when somebody wanting to make a ‘covert’ entry to marse would jump of the ship in a high dive suit and be mistaken for debris from the ship. Once it hits the ground most of the ship will be destroyed. Major structural beams bent or snapped most cargo badly damaged. The only things I could see being recoverable are raw materials (maybe it was carrying feed stock not readily available locally) or micro objects (viruses, bacteria, nanobots, exurgant samples) while many individual microbs would be damaged there would be enough surviving to keep a viable culture. Only the most durable containers for them would survive (you know the containers made by paranoid people for holding exurgant virus that are made from 3 inches of high strength composite materials.

Hapax Legomenon wrote:

Thanks for the help. I had the idea that a cargo ship might have been hacked or otherwise taken over and kamikaze'd into Mars near the border of the TQZ. The engines would pretty much be burning at full blast with no intention of that ship ever being useful again.

In my opinion you have a lot of leeway about what "burning at full blast means". The cargo ship could carry only enough fuel for the delta v needed to dock with the destination hab and be on a slow flight to conserve fuel, which would mean a very long descend time from orbit to upper atmosphere. Or it could be on a fast route and also have enough fuel to return home or to an alternate destination in case of an emergency, giving it many more options. Maybe it's even TRANSPORTING fuel, that it could route into the engines for lots of burn time :D