Doable; an example follows. The values can be tweaked to taste, but what this does is make a 1,000kt unit that can be built, then sent into orbit, where it stays. The only thing it can carry is a single Space Yard component, and in combat it looks like a space station. I haven't tested it since the demo won't allow it, but it should work.
This goes into VehicleUnitTypes.txt (note the line maximum in space- this restricts the player from building a horde of these things):
Code:
Vehicle Unit Type Name                       := Space Yard
Unit Texture Start X                         := 0.50
Unit Texture Start Y                         := 0.50
Unit Texture End X                           := 1.00
Unit Texture End Y                           := 1.00
Maximum In Space Per Player Per Sector       := 1
Number Of Unit Capabilities                  := 13
Unit Capability 1 Type                       := Can Communicate
Unit Capability 2 Type                       := Can Be Scrapped
Unit Capability 3 Type                       := Can Self-Destruct
Unit Capability 4 Type                       := Can Be Fired On And Destroyed By Owner
Unit Capability 5 Type                       := Can Be Launched Into Space
Unit Capability 6 Type                       := Has Spaceyard Capability
Unit Capability 7 Type                       := Has Facing
Unit Capability 8 Type                       := Can Obscure Sectors
Unit Capability 9 Type                       := Can Be Deconstructed And Analyzed
Unit Capability 10 Type                      := Can Be Transferred While In Cargo
Unit Capability 11 Type                      := Cannot Move And Tracks Target
Unit Capability 12 Type                      := Can Be Mothballed
Unit Capability 13 Type                      := Can Be UnMothballed
This goes into VehicleTypes.txt:
Code:
Name                                            := Space Yard
Short Name                                      := Space Yard
Description                                     := 
Code                                            := SY
Vehicle Type                                    := Space Yard
Maximum Level                                   := 10
Tonnage Space Formula                           := 1000
Tonnage Structure Formula                       := 1000
Cost Minerals Formula                           := 500
Cost Organics Formula                           := 125
Cost Radioactives Formula                       := 125
Engines Per Move                                := 0
Maximum Model Size                              := 20.0
Vehicle TopDown Picture Index                   := 10
Vehicle Portrait Primary                        := [%EmpireName%]_Portrait_Spacestation.bmp
Vehicle Portrait Alternate                      := [%EmpireName%]_Portrait_Spacestation.bmp
Vehicle Portrait Default                        := [%EmpireName%]_Portrait_Spacestation.bmp
Vehicle Large Portrait Primary                  := [%EmpireName%]_LargePortrait_Spacestation.jpg
Vehicle Large Portrait Alternate                := [%EmpireName%]_LargePortrait_Spacestation.jpg
Vehicle Large Portrait Default                  := [%EmpireName%]_LargePortrait_Spacestation.jpg
Vehicle Inv Portrait Primary                    := [%EmpireName%]_InvPortrait_Spacestation.jpg
Vehicle Inv Portrait Alternate                  := [%EmpireName%]_InvPortrait_Spacestation.jpg
Vehicle Inv Portrait Default                    := [%EmpireName%]_InvPortrait_Spacestation.jpg
Vehicle Inv Configuration Layout Primary        := [%EmpireName%] Spacestation Layout
Vehicle Inv Configuration Layout Alternate      := [%EmpireName%] Spacestation Layout
Vehicle Inv Configuration Layout Default        := [%EmpireName%] Spacestation Layout
Vehicle XFile Class Name Primary                := [%EmpireName%] Spacestation
Vehicle XFile Class Name Alternate              := [%EmpireName%] Spacestation
Vehicle XFile Class Name Default                := [%EmpireName%] Spacestation
Vehicle Texture Start X                         := 0.25
Vehicle Texture Start Y                         := 0.75
Vehicle Texture End X                           := 0.50
Vehicle Texture End Y                           := 1.00
Space Combat Maximum Speed Per Movement Point   := 0.0
Space Combat Turn Rate Base                     := 0.0008
Space Combat Turn Rate Decrease Per kT          := 0.0000005
Space Combat Turn Rate Minimum                  := 0.0001
Space Combat Acceleration Rate Base             := 0.0
Space Combat Acceleration Rate Decrease Per kT  := 0.0
Space Combat Acceleration Rate Minimum          := 0.0
Space Combat Deceleration Rate Base             := 0.0
Space Combat Deceleration Rate Decrease Per kT  := 0.0
Space Combat Deceleration Rate Minimum          := 0.0
Space Combat Banks When Changing Height         := FALSE
Ground Combat Maximum Speed Per Movement Point  := 0.0
Ground Combat Turn Rate Base                    := 0.0
Ground Combat Turn Rate Decrease Per kT         := 0.0
Ground Combat Turn Rate Minimum                 := 0.0
Ground Combat Acceleration Rate Base            := 0.0
Ground Combat Acceleration Rate Decrease Per kT := 0.0
Ground Combat Acceleration Rate Minimum         := 0.0
Ground Combat Deceleration Rate Base            := 0.0
Ground Combat Deceleration Rate Decrease Per kT := 0.0
Ground Combat Deceleration Rate Minimum         := 0.0
Ground Combat Banks When Changing Height        := FALSE
Number Of Abilities                             := 2
Ability 1 Type                                  := Combat To Hit Defense
Ability 1 Description                           := Large size makes base [%Amount1%]% easier to hit in combat.
Ability 1 Scope                                 := Space Object
Ability 1 Range Formula                         := 0
Ability 1 Amount 1 Formula                      := -20 + ([%Level%] - 1)
Ability 1 Amount 2 Formula                      := 0
Ability 2 Type                                  := Ship Maintenance Cost Modifier
Ability 2 Description                           := Reduced wear and tear allow for a decrease in maintenance cost of [%Amount1%]%.
Ability 2 Scope                                 := Space Object
Ability 2 Range Formula                         := 0
Ability 2 Amount 1 Formula                      := -50
Ability 2 Amount 2 Formula                      := 0
Number Of Requirements                          := 2
Requirements Evaluation Availability            := 1
Requirements Evaluation Allows Placement        := 2
Requirements Evaluation Allows Usage            := TRUE
Requirement 1 Description                       := Empire must have at least tech level 1 in Ship Base Construction. 
Requirement 1 Formula                           := Get_Empire_Tech_Level("Base Construction") >= (1 + ([%Level%] - 1))
Requirement 2 Description                       := This vehicle cannot have any movement.
Requirement 2 Formula                           := Get_Design_Ability_Component_Count("Movement Standard") <= 0
And this goes into Components.txt:
Code:
Name                                            := Space Yard
Description                                     := Ship construction component which can work on one ship at a time.
Picture Number                                  := 8
Maximum Level                                   := 21
Tonnage Space Taken Formula                     := 400
Tonnage Structure Formula                       := 1000
Cost Minerals Formula                           := 200 + (([%Level%] - 1) * 2)
Cost Organics Formula                           := 0
Cost Radioactives Formula                       := 500 + (([%Level%] - 1) * 5)
Supply Amount Used Formula                      := 0
Ordnance Amount Used Formula                    := 0
Can Be Placed On Vehicle Types                  := Space Yard
Can Be Placed In Ship Sections                  := Inner Hull, Outer Hull
Component Type List                             := Technological
General Group                                   := Construction
Custom Group                                    := 0
Number Of Requirements                          := 1
Requirements Evaluation Availability            := AND
Requirements Evaluation Allows Placement        := TRUE
Requirements Evaluation Allows Usage            := TRUE
Requirement 1 Description                       := Empire must have at least tech level 10 in Space Yards.
Requirement 1 Formula                           := Get_Empire_Tech_Level("Space Yards") >= (10 + ([%Level%] - 1))
Number Of Abilities                             := 6
Ability 1 Type                                  := Space Yard
Ability 1 Description                           := Can construct with [%Amount2%] minerals per turn.
Ability 1 Scope                                 := Space Object
Ability 1 Range Formula                         := 0
Ability 1 Amount 1 Formula                      := 1
Ability 1 Amount 2 Formula                      := 1000 + (([%Level%] - 1) * 100)
Ability 2 Type                                  := Space Yard
Ability 2 Description                           := Can construct with [%Amount2%] organics per turn.
Ability 2 Scope                                 := Space Object
Ability 2 Range Formula                         := 0
Ability 2 Amount 1 Formula                      := 2
Ability 2 Amount 2 Formula                      := 2000 + (([%Level%] - 1) * 100)
Ability 3 Type                                  := Space Yard
Ability 3 Description                           := Can construct with [%Amount2%] radioactives per turn.
Ability 3 Scope                                 := Space Object
Ability 3 Range Formula                         := 0
Ability 3 Amount 1 Formula                      := 3
Ability 3 Amount 2 Formula                      := 2000 + (([%Level%] - 1) * 100)
Ability 4 Type                                  := Tonnage Repair Ship
Ability 4 Description                           := Can repair [%Amount1%]kT of ship tonnage per turn.
Ability 4 Scope                                 := Space Object
Ability 4 Range Formula                         := 0
Ability 4 Amount 1 Formula                      := 200 + (([%Level%] - 1) * 20)
Ability 4 Amount 2 Formula                      := 0
Ability 5 Type                                  := Tonnage Repair Unit
Ability 5 Description                           := Can repair [%Amount1%]kT of unit tonnage per turn.
Ability 5 Scope                                 := Space Object
Ability 5 Range Formula                         := 0
Ability 5 Amount 1 Formula                      := 60 + (([%Level%] - 1) * 20)
Ability 5 Amount 2 Formula                      := 0
Ability 6 Type                                  := Tonnage Repair Facility
Ability 6 Description                           := Can repair [%Amount1%]kT of facility tonnage per turn.
Ability 6 Scope                                 := Space Object
Ability 6 Range Formula                         := 0
Ability 6 Amount 1 Formula                      := 150 + (([%Level%] - 1) * 20)
Ability 6 Amount 2 Formula                      := 0
Weapon Type                                     := None