Is there any way to set things up so that it can be active or inactive, and when it is running all other OXPs are disabled?
Your question has been answered, but for those curious about how this works:
Exploration.oxp is set to not load in the basic core scenario. You can install it and it will do absolutely nothing in the normal game: it won't even be read or show up in the Latest.log OXP list.
The Loader.oxp only contains a scenario file. So it is always running and loaded even in a normal game, but all it does is give you a new "start new game" option, so that's perfectly safe.
The scenario file itself has scenario definition attributes in it which tell Oolite that save games based on it can load the Exploration.oxp, and also tell it to suppress loading of a number of core game plists (so the core game ships, trade goods, and world scripts are overridden rather than added to as a conventional OXP would) - essentially it makes Exploration.oxp plus some but not all of the Oolite core files into a new base game.
@cim: yellow text against a sun is nigh-on impossible to read, and I seem to have a problem getting moving after certain scans.
I do mean to put a proper cockpit on at some point, once I'm sure all the HUD dials are in the right place.
Sounds like you didn't turn off the gravity scanner fully. If you could have read the console messages, it would probably have been easier to switch to the "power" mode of the scanner to turn it off. Easy mistake to make: I've not yet overheated from it, but I have taken far longer than necessary to get clear of quite a few stars doing exactly this.
If you're in the same situation again and not mass-locked, then hit 'h' twice: so long as you cancel it before the drive is fully charged, you won't take damage, but it will disable the grav scanner. If you are mass-locked by the star as well, just hit 'b' followed by 'n' until you can move - the worst that will happen is you overwrite your mass measurement for the star and need to do it again once you've cooled down.