New planets are a popular idea for Astroneer, but continuously adding more and more planets can become a pain, as more gateways and cores would need to be added, and all of the core activating would become too time-consuming and redundant. A possible way to fix this is not directly adding planets to the main solar system, but rather, add planets to other solar systems, perhaps with different core activation requirements or completely new system altogether, to keep the player interested.
How to get to a new solar system
To keep players from speeding ahead from the main storyline, there should be a requirement needed, such as using geometric triptyches or activating all cores. Once this requirement is reached, there are several different possibilities:
Semi-Conventional Spacecraft: A new spacecraft (likely an Extra Large Shuttle, ELS) would work in the context of the game. The ELS would function like any other spacecraft, but instead of being limited to the bounds of the system, it could be able to launch into interstellar space, requiring more fuel than interplanetary travel.
Warp Drives: In reality, massive distances are in between systems. For example, Proxima Centauri is about 265613 AU (4.2 light years) away from our solar system. For reference: 1 AU is the average separation in between the Earth and the Sun. This makes using conventional fuels very inconvenient. Although Astroneer is not completely based on reality, using a non-conventional mean of traveling would be better, as it would require more of a challenge. Warp drives would be large (tier 3) objects that require energy, lots of energy. Electric current values typically experienced while activating the chambers of difficult planets would make sense. Since the ELS will likely have 2 tier 4 slots, enough energy can easily be placed inside of it and still have plenty of room for other storage. When an ELS has a warp drive, it has the option to jump to another system (perhaps with the "V" button on PC's, instead of it being used for interplanetary travel).
Some lore-based element: The Astroneer lands in a world filled with unusual technologies. On these planets exist large chambers that utilize teleportation, massive, carved out cores with technology far beyond our current understanding, and an unusual artificial satellite that exhibits strange properties. It would make sense that the creators of these would also have the power of interstellar travel. Perhaps this is how one can obtain a warp drive, or maybe, a player on a spaceship gets flung into another system if the player activates something. These are some of the limitless possibilities.
Planets and other objects in these systems:
There are so many unique ideas of planets, these are only my ideas:
A planet predominantly covered in mountains. Gray in color, this planet could have below average gravity (which helps create mountains), and have many natural resources, such as Hematite and Titanite, among others. Using rovers on these planets would be very impractical, as sheer cliffs and many holes would halt transportation to a standstill. Some type of hovercraft could be used instead. This planet will also enjoy high solar and moderate to high wind.
A planet covered in a storm, similar to what Calidor used to be, but a bit different. Dust storms or other types of storms (rainstorm, thunderstorm, high wind?) would be present here. This planet would certainly be a challenge, but many of the rarer materials (or perhaps new ones) should be found to make going to this planet worthwhile. Patches of "calm" should also exist, where there are no storms. Solar power would be almost useless, while wind power would be dominant.
An asteroid belt or ice belt would be an unusual addition to this game. Almost no gravity would exist on the belt, nor will wind. Solar power would be the likely choice for these planets. Using a hovercraft would likely be one of the only ways around on this area. These areas would host a variety of materials, and thus, can be a great spot for mining colonies. Asteroid belts and Ice belts would be very similar, apart from different appearance and maybe materials.
Thank you for reading through all of this, it is really appreciated! I spent too much time on this so any type of feedback and criticism is not only welcomed, but also encouraged. I may be able to update this as time progresses.