There's a reason that basically every released space game uses something else (and in most cases that's "some custom in-house engine")To really save development time and cost, just use Unreal 5.
Unreal is great at what it does - and what it does covers the requirements of the vast majority of computer games. But space games have a completely different requirement set.
- for planetary landings, extreme use of dynamic terrain generation will mess up basically every optimisation it has for the usual computer game case of "someone designed the terrain and it's in this data file"
- for the average computer game, a draw distance of tens of kilometres is absolutely fine. Anything beyond that can be a pre-rendered backdrop. The average ED scene contains objects moving in real-time at distances between metres and thousands of light-seconds (sure, anything outside the current solar system is pre-rendered).
- most computer games can assume that the direction and strength of gravity is a constant.
...and so on. All sorts of things which are great optimisations for a normal computer game are actively counterproductive when making a space game
Poking around the internet it seems that there are still serious issues with getting an Unreal map to be more than about 20x20km (though 5 at least lets you try). For most games, not a problem - either the map is far smaller than that or it can be broken into smaller chunks without anyone really noticing. For space games ... not a chance.