type
  PSolarSystem = ^TSolarSystem;

  TUniverse = class(TObject)
  public
   Width, Height : Int64;
   SolarSystems : array of PSolarSystem;
   SolarSystemCount : integer;
   constructor Create;
   procedure addSolarSystem(Fx, Fy: Int64; planetCount: integer);
  end;

  TEntity = class(TObject);
  TSolarSystem = class(TEntity)
  public
    X, Y : Int64;
    constructor Create;
    procedure init(Fx, Fy: Int64; planetsTotal: integer);
  end;


implementation

constructor TUniverse.Create;
begin
  inherited;
  Width := 10000;
  Height := 10000;
  SetLength(SolarSystems, 10);
  SolarSystemCount := 0;
end;

procedure TUniverse.addSolarSystem(Fx, Fy: Int64; planetCount: integer);
begin
  SolarSystems[SolarSystemCount] := @TSolarSystem.Create;
  SolarSystems[SolarSystemCount].init(Fx, Fy, planetCount);
  inc(SolarSystemCount);
end;


constructor TSolarSystem.Create;
begin
  inherited;
end;

procedure TSolarSystem.init(Fx, Fy: Int64; planetsTotal: integer);
begin
  X := Fx; <----- HIER DIE ZURGIFFSVERLETZUNG !!!
  Y := Fy;
  SetLength(Planets, planetsTotal);
  planetCount := 0;
end;

end.

procedure TForm1.Button1Click(Sender: TObject);
var u : TUniverse;
begin
  u := TUniverse.Create;
  u.addSolarSystem(0, 0, 5);
end;