More ideas on that invisible asteroid.
Research item: "Alien Staging Area" or "Alien Refuelling Station".
Prerequisites: all typical UFO types (no Envoy and other special types):
- STR_SMALL_SCOUT
- STR_MEDIUM_SCOUT
- STR_LARGE_SCOUT
- STR_HARVESTER
- STR_ABDUCTOR
- STR_TERROR_SHIP
- STR_BATTLESHIP
- STR_SUPPLY_SHIP
- STR_SENTRY_SHIP
- STR_FIGHTER_SHIP
- STR_LAB_SHIP
- STR_EXCAVATOR
Ufopaedia text: All UFOs we've downed had their elerium reserves filled to the brim. Our research indicates they all uses some artificial or natural satellite of Earth as a refuelling station and rendezvous point. To reliably triangulate this invisible satellite we need Hyperwave Decoders at 8 bases.
There's also a chance that some space agency has already discovered this satellite, but is covering it up. If only we knew where to look...
The number of required decoders may be lower than 8, but triangulation requires at least 3
Maybe conventional radars can be employed too.
The following item is either unlocked by having 8 decoders after having researched "Alien Refuelling Station" or is given randomly for researching a decoded cartridge:
Research item: Pelops
Ufopaedia text: Pelops is an asteroid orbiting Sun in 1:1 resonance with Earth, making it a quasi-satellite. Due to its unusual black colour it is virtually undetectable by optic telescopes. Aliens have placed a fuel depot there, which they occasionally resupply. It can be raided by any of our elerium-powered ships, but we expect it to be heavily guarded by robots and booby-trapped.
Size: 100 x 100 x 200 m
Distance to Earth: <2.5 million km
There may be a random event "Pelops fuel depot restocked" after which any ship can be sent to raid it for a while, or it can be available at any time.
I envision the mission itself as something similar to the surface part of Cydonia mission, only without the "sphinx", with black terrain (does it need a new set of tiles, or would changing the texture suffice?) and with no underground entrance. Protected by holodrones, cyberdisks and sectopods. The containers that hold eleruium detonate randomly, destroying their contents. The player may break containers with plasma(?) fire and pick elerium or kill all guards and get elerium from all unexploded containers. Only space-capable weapons are allowed.
Mission name: "Asteroid Raid"
Mission Briefing: Our approach has triggered the self-destruct sequence of elerium containers. Some of them will explode every turn until none is left. Eliminate all guard robots and you will be able to disarm the remaining containers. To abort the mission return X-Com operatives to the vehicle and click on the 'Abort Mission' icon.