Okay, I’m an idiot. Just to preface this. But let’s say I’m in space. There’s no wind resistance right? If I accelerate, I’ll maintain that speed. Why can’t I just burn more fuel and go faster?
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Motion of such large vessels is… difficult… logistically speaking in space.
Lets say, you’re in orbit over Earth, completely writing off the effort already undergone to get there in the first place, and you want to fly to Uranus as you’ve heard it’s particularly phat this time of year.
Well, you get there by burning fuel. Your thrusters overcome the weight of your vessel + the gravity well of Earth and your orbit expands ever outwards until you break free of Earths gravity and you’re sling-shot toward your destination… But, wait. Fuel is a heavy as shit. More fuel means more weight. So Earths gravity is stronger than ever, pulling on your heavy ass fuel tank. So now you need more fuel to overcome the weight of your fuel. *ah…*
That is the major problem. Mass in space is more fundamental than it probably first appears. Anything heavy needs a proportionate amount of energy to propel it. You need to precisely ration fuel, as you’re fighting against the various gravity wells you encounter on your journey, so the weight of said fuel needs to be the perfect ratio for the distance it will actually get you. You need to know when to burn to speed up, and to slow down to take advantage of gravity slingshots. It’s complicated stuff, and not just a “bee-line” to your destination.
So let’s say you figure that out. And you see Uranus on the… erm… “horizon”, and it is indeed as phat as they said. Say you wanted to orbit it. Well, uh oh… How do you do that? As you said, there is no wind resistance, no friction.
Your thrusters have gotten you up to the speed of a few thousand, maybe tens of thousands of meters per second. And it’s gotten you to Uranus… But what now? There are no brakes in space. To slow down, The only option is to burn the opposite direction to cancel out your momentum, which (you guessed it) requires more fuel. Which again increases your mass.
So in short, you need to make sure you have just enough fuel to get you to where you’re going, enough fuel to slow down enough to get captured in the gravity well of Uranus to circularize your orbit. And presumably enough fuel to escape orbit, and return home. Assuming no mistakes of course.
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