thanks for playing! i'm not against a grid system on principle, but i have a few things pushing me away from one:
1) real rovers have a number of different instruments that operate at different ranges, so in my paper prototype i have 3 instruments that operate at far, middle and near distances. the near distance one depends on results from the far and middle distance instruments, which models how rovers select targets in reality - they do several passes to determine if it's worth getting up close and personal or carrying on to pursue strategic goals. cameras can investigate stuff nearby but also take pictures of the horizon, atmosphere, and other celestial bodies, while drills and microscopes are a bit more local in operation. so at this stage in the design i want to keep my options as open as possible.
2) i do actually really like 3d, and i would like to replace (or add to) the current 2d map with a 3d rendering of the rover in its environment, with some kind of LOD effect to show that stuff further away is unknown. a big inspiration of mine is also extrasolar: https://www.extrasolar.com/, which would render outputs of your rover on an alien planet. i'd definitely like to explore doing that, at least, which necessitates _some_ kind of 3d rendering.
at present there isn't really anything to help you plan, but high on my todo list is communicating the route planning to the player, so i think it's doable without a grid.
as for making the interruptions fair, i have designed 3 so far: cosmic rays will corrupt data in storage, solar flares will corrupt data in downlink and also your wheels can get stuck, negating movement until you get unstuck. the former two can be balanced by letting the player make backups of their observations, trading off storage space for security, and the latter i think will be a bit of a terrain hazard that can be mitigated by spending time up-front doing route planning. i came up with the backup idea after spending the rover's entire lifetime going after a high-value observation and getting hit by a solar flare, which felt very mean but would have been extremely gratifying had i backed it up, since the rest of my storage was full of low-value observations that i cared less about.
what i really admire about mars rovers is how they succeed as a result of careful, methodical planning and strategising, so i want that to be how the player succeeds in the game too!