LOS ANGELES — Scaled Composites is moving closer to the start of powered flight tests of Virgin Galactic’s SpaceShipTwo with the installation of major elements of the rocket system, including the main oxidizer tank, at Mojave, Calif.

Photographs released by Virgin Galactic on Oct. 19, show the large nitrous oxide tank being lowered into position in the center of the SS2. The tank will feed the Sierra Nevada-developed RM2 hybrid rocket motor that will power the vehicle to suborbital altitudes at speeds in excess of Mach 3.

Virgin Founder Richard Branson also tweeted on Oct. 19 that “space doesn’t look too far away,” and in his blog referred to the extended build-up approach to the start of flight tests that are widely expected to begin later this quarter. “The greatest successful adventures are always built on meticulous preparation, which is why we’re leaving no stone unturned as we approach the first supersonic, rocket-powered flights of SpaceShipTwo.”

He adds, “Test flights of our vehicles have gone incredibly well so far and we want to keep it that way. Our amazing engineers and pilots are preparing right now for the first powered spaceship flight, which should be followed with a fairly quick build-up to Virgin’s first proper step across the final frontier.”

Installation of the tank, with the RM2 presumably not far behind, follows a 17th full-scale hot-fire test of the RM2 on Sept. 20. Scaled Composites says the test “continued evaluation of all systems and components, including pressurization, valve/injector, fuel formulation and geometry, nozzle, structure and performance. All objectives were completed.” The test log entry says the RM2 performed a “targeted 45-sec. hot fire as planned.” It adds the duration of the run was designed to allow examination of the motor’s “internal geometry.”

The start of RM2 installation follows the completion of aerodynamic tests of the unpowered SS2 earlier this summer. That milestone, which was achieved by late August, effectively kept the suborbital spacecraft on track for the start of rocket-powered flights by November/December.

Virgin Galactic hopes that, pending a successful powered test campaign, it will be able to start passenger flights by the end of 2013. Flight envelope clearance for airspeed, angle-of-attack, center-of-gravity and structural loads was completed during a final round of six flights from late June through mid-August.

Scaled Composites retested the glide flight envelope after modifying the tails of SS2 for additional stall margin at low angles of attack. The changes, which came in the wake of a tail stall during a flight in September 2011, included replacing a pair of smaller strakes on the inboard side of each vertical tail with a larger, one-piece, horizontal strake.