My brother and I have recently been addicted to Space Agency on iOS. It was on sale for free when we got it, but I'm not sure if it still is.
Basically, you are creating space missions. It starts out with a few rocket parts available and you perform simple tasks, such as putting a satellite in orbit or orbiting in a crew capsule and splashing back down on Earth. In later missions you complete a moon landing and return home. Each mission has a goal with difficulty rankings based on cost of your rocket and the time to complete the mission. Each rocket part costs money and has different attributes. You can find more powerful/quicker ways to reach your target destination, but if you don't have the proper parts you may find yourself unable to correct minor course adjustments so you can accurately arrive at your target. The problem is you may have less fuel. Once you are on a mission you are controlling the spacecraft. You have to perform the roll program during launch, dock with a space station, match the rotational speed of the moon as you land, and keep your heat shields down when entering an atmosphere. And because this is space and science, the tiniest error can mean you have to start from scratch.
It is strategy game with timed mission with resource management, and physics-based puzzles. Definitely a nerd game. It does simplify things for the average gamer, by using generic speed and distance units and having orbital velocity for every moon, planet, and the sun be the same, which is indicated by green on your gauge. And distances are shrunk down a lot. I got Voyager to take a picture of all the exterior planets in under 20 minutes. You don't need to be a rocket scientist to play, but it is definitely targeted at those interested in space. And once you unlock a lot of rocket parts there is a free mission where you can go do whatever you want. It all exists within the same timeline as your campaign missions. Currently I am building a space station around another planet to use as a staging point for a manned landing.