Space Travel for Writers

Five basic rules for space travel in science fiction. Sci-fi writers probably know these already, but I'm still surprised how often they're ignored.

(The NRI, or Nerd Rage Indicator, is an estimate of how likely you are to get flak for breaking a given rule. 1 is the least likely (e.g. that guy who runs your local comic shop cares, and only that guy). 5 is the most likely (e.g. Wil Wheaton and John Scalzi publicly destroy your sci-fi cred)).

RULE #1: There is no sound in space. Sound means fluid (air, water, etc.) vibrating against your ear drum. No air, no vibrations, no sound. This happens more in movies than novels, but you should still be aware of it before describing that "bone-shaking explosion that ripped the skies."
NRI: 1 (as important as it is, most people don't notice until it's brought to their attention, especially in prose).

RULE #2: Astral objects are really, really, really far away from each other. The moon is 384 megameters (it's a thing!) away. At our very fastest, it takes us 10 hours to get there. Not so bad? Try Mars. At the same speed, it would take 2 months to get there at best. Jupiter? Almost 2 years. The nearest star system (which may not even have planets)? More than a century. Mostly this means your spaceships either need fuel and provisions for the whole trip, or they have to go really, really fast. The latter, though, raises other considerations (see Rules #3 and #4).
NRI: 5.

RULE #3: Spaceships can't travel faster than the speed of light, no matter how much we want them to. Unless science is wrong, it would take an infinite amount of energy to accelerate an object to the speed of light. There are ways you can mess with this (see Rule #5), but you should at least give a nod to the rule before doing away with it.
NRI: 4 (I figure Wil Wheaton can't complain too much since the biggest violation of this rule is Star Trek's "warp speed").

RULE #4: If you travel fast enough, you have to deal with the weirder effects of special relativity. In particular: time dilation. Effectively, the closer you get to light speed, the slower time moves for you. So if you fly to Jupiter so fast it only takes you 2 days, then decades will have passed back on Earth (and probably faster spaceships will have been built, which is pretty interesting in itself).
NRI: 3 (Star Trek totally ignored it, and most people have a hard time getting their heads around it. I'd say you're 50/50 for getting flak on it).

RULE #5: You can bend the rules, even make them up, but you must be consistent. Wormholes, hyperspace, jumpgates, folding space--these are all viable (and mostly-scientific) methods of faster-than-light travel. The details are entirely up to you, but once you make up the rules, don't break them. If you use a jump gate to get from Earth to Epsilon Eridani in five minutes, you can't say later, "It'll only take three hours for the Eridanis fleet to come through that gate and destroy us all!"
NRI: 5.

A lot has been done already in science fiction, which actually makes things easier for you. You don't have to explain jumpgates or wormholes much to include them. But even if you don't explain them to the reader, you need to know what's behind them. Not the science, necessarily, but the rules that govern it.

Are there any rules I missed? To the comments!