Duna and back on a damaged rocket... But in all seriousness, I would think that it would be a lot harder to repair the rocket than it would be to repair a solar panel. I would go with there is a set amount of repair points in the main command module, no matter the size of the aircraft. Or repair points for each kerbal on board. but, the solar panels and rockets would have damage percentages, and each point could repair it around 1% for a large rocket, 5% for a smaller rocket, 10% for a solar panel. They perform worse than they do normally when damaged, but still work. But at 0% it won't work and requires more points than it normally would to repair it. starting off with 100 repair points. Docking with a space station can replenish repair points, but only up to 75 repair points. As for the space stations, They would have a huge amount of repair points, around 1500, but they could only be used to repair the station and give to ships. However, repair points need to be replenished at the station too. So flights to rendezvous with the station to resupply its repair points are needed. And why not put repairing as an EVA activity.