how do i know how many radiators are enough?

[king of nowhere]

i am about to launch a satellite to moho, and i suppose it will need some cooling, but i have no idea how much. I'd rely on my tried-and-true strategy of using debug console to transfer the whole craft in moho orbit, see if it works properly, before reloading the game and launching it for real. well, i did just that, and i accelerated time, but i got no heating problems. without any radiators. which i have a hard time believing.

so, is it true that i can send a satellite around moho without any need for radiators? or is there some reason why the test did not work properly? how can i estimate how many radiators i may need without testing by random?

[bewing]

Your craft can operate just fine while permanently glowing red. So no, you don't need radiators at Moho. You really don't need them until you are getting into a fairly low orbit around the Sun, or until you start mining.

As far as testing goes for dealing with overheating in flight -- yeah, doing a SetOrbit to check is about the only way.

 

[Streetwind]

There are two separate heat systems in KSP. One is just general part heat - and for that, bewing already explained everything relevant. You can mount a radiator to lower part heat, but it's optional in most cases. Maybe see if you can incorporate a small panel or two in a visually pleasing manner? Remember that radiators only work correctly if the Sun is not shining on them.

The other system is Core Heat. It is used for machines that require active cooling: mining drills, ISRU converters, and such. For that purpose, each such part has a "cooling required" stat, and each radiator has a "core transfer" stat. The sum of the former must be matched by the sum of the latter.

[Linkageless]

A bit off-topic now, but I might add to @Streetwind's explanation by saying the cooling required is what the part needs when operating at full capacity.  I've observed that some parts, such as ISRU, are able to run under capacity, for example if the supply of ore isn't sufficient to keep it at 100% output (or indeed 125%).  In this case, I've found cooling requirements are proportionally lower.

I've not scientifically tested this, as I generally will over-engineer cooling.  There's so many variables involved and my attention is usually elsewhere.  I do have a craft in progress that might benefit from a cooling weight reduction along these lines, however, so perhaps I'll test.