Make the planets visible from space somehow.
Perhaps use an image of the planet below, and it increases in size depending on how close you are to the planet. Would be very very useful for landings, and it would give a bunch more situational awareness in space, and make the game look better. Also, make the camera automatically point down to the ground. Landing upside down is disorienting.
Gregory Brannon commented
In real life, you can see the world beneath you, and this is super-duper important for landing spacecraft. In Simple Rockets, often times you can't see the surface until it's too late. Additionally, there's no context for where you are, what planet you're orbiting, etc. So to fix this, you could have a picture of the planet take up a certain portion of the screen, but it would zoom in and get pushed down (essentially flattening it) more and more as you approach it. It would be like seeing the land in the background as you descend. And it would make the game much prettier.