If/When Mars or the moon are colonized, transport will be needed between bases. Over long distances, rovers would be too slow and traditional aircraft would not work well in thin to non existent atmosphere. Obviously due to low gravity the rocket could be quite small with a non traditional design. Perhaps similar to the apollo lunar module?
$\begingroup$ Mass accelerators would be great for launching suborbital payloads. Catching them at the other end is problematic. Maybe a big Bouncy Castle? $\endgroup$– WoodyNov 13, 2021 at 15:55
$\begingroup$ Related post about maximum lift for helicopters on Mars: space.stackexchange.com/questions/55644/… $\endgroup$– WoodyNov 13, 2021 at 15:58
$\begingroup$ related blogpost: hopsblog-hop.blogspot.com/2014/06/travel-on-airless-worlds.html a comment on this post suggests a dragon would have enough deltav to work $\endgroup$– Small-JaguarNov 13, 2021 at 16:08
1$\begingroup$ What distances are you planning to service? Do you want to transport crew or material only? Do you want to limit the question to rocket based solutions only? We all love rockets, but their EPA fuel economy isn't great. $\endgroup$– WoodyNov 13, 2021 at 18:39
1$\begingroup$ "Over long distances, rovers would be too slow" – There's a simple solution to that: don't build your bases long distances apart. By the way: the only one who is really serious about colonizing Mars is Elon Musk. Now, what does his other company do again … $\endgroup$– Jörg W MittagNov 13, 2021 at 21:33
The energy, material and safety costs of rocket flight on the moon probably mean most bulk cargo will travel by some form of surface transport.
For those cases where use of a rocket is justified some work has been down on exploiting in situ Aluminum, reacting with Oxygen or Water. The water option appears more stable and easier to handle than cryogenic oxygen, but involves water which may be more useful as life support and has a performance loss due to the energy involve in liberating the hydrogen.
The suggested performance for oxygen/aluminum seems to have an ISP of around 200, giving fuel loads of between 50% and 70% depend on how 'orbital' your planned route is, so in terms of what the craft looks like, it is going to be at least half tankage, exact nature of that tank will depend on how the Aluminum is stored and handled noting that getting the predicted performance seems to be complicated where the aluminum is in solid or powder form- the logistics of fueling and servicing a craft with one tank of liquid oxygen and the other liquid aluminum seems excessively exciting.
One note with any aluminum based rocket is that it will tend to produce solid particulate as exhaust at very high velocities, which probably cannot be allowed to routinely impact solar panels or similar habitat structures, suggesting that any launch facility will need to be carefully positioned.