Given how much difficulty they've had with welds and materials to date, is it really feasible to conduct in-situ repairs without a ton of advanced equipment?

It probably depends on what needs repairs. Repairs around the fuel tanks will be difficult as they would not readily have the equipment to purge the tanks of the fuel/oxidizer. Anything that is bulk structural is likely to be repairable to some extent.

I would not be surprised if part of the reason for building these in a tent is so they can gain experience for building/repairing these rockets with as little infrastructure as possible.

I feel the same way. Likely not to start but over time I think they would build up capability. I wonder how lesser gravity on Mars would help/hurt their efforts. Easier to heft heavy gear up high?

I'm also thinking on the flip side, say a Starship somehow gets irreparably damaged getting to Mars (but successfully gets there). With some basic gear they should be able to part it out and re-use the steel.

Like for a new door on all the Cybertrucks rollin' around up there. /s

The idea of using parts of the landing unit for materials to build local structures and machines is not new. Probably, with proper planning and construction of the lander unit parts, it can be facilitated.

But you have to plan for another mission to pick up the crew, unless you're on the Moon where you could use an electromagnetic catapult to achieve orbit, and then slowly ascend to the rocket that would take you home.

I didn't know that. Sure, it doesn't sound like a revolutionary idea, and I'm not surprised at all its been thought of. I was basing it on the assumption there are people there already who aren't leaving. With a colony on Mars/Moon it surely becomes more useful to have a vast amount of steel to reuse than some crazy alloy.

Electromagnetic catapult, huh. Sounds fun as hell.

The difficulty is making it light and strong. If you're doing an emergency patch repair on a small area you could sacrifice some cargo and use much thicker material and more welds to be sure it will hold. It wouldn't be easy but is much easier than the initial build.

The difficulty is making a weld that doesn't weaken or anneal the parent metal through heat induced material changes.

Welding thick to thin is nontrivial because of the different heat input required in each substrate. You tend to burn through the thin part.

Patching may be possible but thick patches don't make things any easier.

Most importantly, you mostly need it light to escape Earth's atmosphere. (And somewhat to have enough fuel.)

On Mars, Moon or in space this constraint is reduced.

That's what I was thinking. At the very least, they'll either have to come up with some very fancy welding rod matrials, or train their welders in some interesting techniques. Reminds me of the difficulties in welding aluminum.

Still it's much easier to work with, compared to titamium, to say nothing of carbon fiber composites or silica-fiber tiles like the Space Shuttles used.

That is, something you can have a fair chance of fixing while in orbit or on Moon or Mars.