I see this will need to be further explained...
What burns the Vampire:
Sunlight when on a habitable planet. Define habitable: A planet which contains life, both alien or human in nature. This also means that the vampire can stare into the sun while adrift in space, however, once within the atmosphere of a habitable planet, that is no longer possible without damage. This doesn't prevent you from landing the craft, rather, vampires just can't do it unless it is night.
If a planet contains no habitable life, meaning that it wasn't brought there and wasn't left behind that the vampire can walk in sunlight. Should this change in some way, they are no longer able.
The Sleep Cycle:
When on a habitable planet, the vampire is subjected to the requirements of the it. Therefore, the vampire must slumber during daylight hours and rise only when it is dark spending vitae as normal. This means that on planets that are never dark, the vampire can never rise and thus locked in torpor. This is a common practice for research and development on Vampires, as well as prisons. On planets that are in a constant night cycle, the vampire can stay awake for ages, however, vitae is spend every 24 Terran hours in order to resist the urge to slumber. However, there seems to be a unknown maximum number of times this can be done (mechanically, it is equal to your humanity score)