The probe capsule would require an electrical charge (from a battery/solar panels) to function but is lighter and smaller then it's manned counterpart
Anything that makes electrical power a consideration would add a huge element to the game.
The game would really be complete with probes, New engines, and moons for each individual planet.
Joey Sparks commented
Add special parts that rely on solar panels! I have some ideas in mind:
A portal core: a wide ring about the size of a strut that needs six or more solar panels that can warp ships from the ground to the station. When on the ground, there is a button that says "mobile warp", when you activate it pulls you through a portal that places you just beside the station. Only ONE can be used per ship and needs a 10min cool down. Cool down can be sped up by time warp.
A Maglev system: a high tech crate that can control other ships within a range of 300 meters. Can easily slow down the velocity of other ships and make docking easier. Requires 10 solar panels. To use: tap on the maglev crate, the game will pause and ask you if you want to use it, press "yes" and tap on the ship that you want to want to control. Then the HUD will be replaced with a control panel similar to the RCS controls the targeted ship will immediately
be given the precise velocity and direction of your ship, and will be under your control.
Probes: EVERYONE likes probes, they only require batteries but must be charged on their station. They can build additional structures on you ship (fuel tanks made by them will be empty).
The stations must have solar panels to recharge them. The more panels, the faster they charge! Note: they can build all items in the construction bay, but take a while and the heavier the item, the longer it takes! Also, probes must attach themselves to the side of the ship in order to build,and in case the battery runs out, they can be moved back to charger by use of maglev.