The Farnborough air show has seen plenty of “firsts” over the decades, but the appearance this year of the first passenger-carrying suborbital commercial spacecraft takes this prestigious event into new territory.

The show debut of Virgin Galactic's SpaceShipTwo (SS2), albeit in full-scale replica form, follows a tradition of inaugurals ranging from the 1949 display of the world's first jet airliner, the de Havilland Comet 1, to the initial international appearance of the largely composite-built Boeing 787 in 2010. Although the Farnborough show is not best known for its space-related coverage, the display of the SS2 mock-up follows the 2010 establishment of a special Space Zone exhibit which organizers say will be doubled in area this year.

Richard Branson's Virgin Group is no stranger to the event, either. In 2002, Virgin Atlantic and Airbus used Farnborough to showcase the formal delivery of the first A340-600. This time, Virgin Galactic says it is displaying SS2 at Farnborough to take advantage of the additional global focus on the U.K. now, as the country is hosting a series of events ranging from the Summer Olympics to the Diamond Jubilee celebrations of Queen Elizabeth II.

But while the SS2 replica hogs the PR limelight at the show, the hard development work continues across the Atlantic at sites in the Western U.S., where flight testing is expected to culminate at year-end with the long-anticipated first rocket-powered flight. Plans to begin powered atmospheric flight tests were boosted last month when the vehicle's developer, Scaled Composites, was granted an experimental launch permit by the FAA. “It was a big step, and there are a lot of big steps in this process,” says Virgin Galactic President and CEO George Whitesides.

The permit comes as the pace of flight tests picks up at Scaled Composites' facility in Mojave, Calif., following a hiatus for modification work on both the SS2 and the WhiteKnightTwo (WK2) carrier aircraft that is used to air-launch the spacecraft. “The vehicles are now flying again,” says Whitesides. With glide tests of SS2 having resumed June 26, he adds, “our hope is to have a high flight tempo over the next few months. The basic plan is to get through the majority of the unpowered flight envelope over the course of the summer, and we hope to be in a position at that point to integrate the remaining components of the rocket motor over the fall. We should then be in a position to conduct our first powered-flight by the end of the year.”

Throughout 2013, these flights will be progressively longer, with the aim of culminating with the first truly suborbital flights. Assuming testing goes as planned, and certification authorities sign off on the work, the first passenger-carrying flights could be taking place by the end of 2013, says Whitesides. Despite the slowdown in testing caused by the discovery of an unexpected tail stall during a flight last September, the resumption of flights is encouraging to the development team, he adds. “We're still reasonably happy with where we are on the schedule. We don't have an excess amount of margin, but that's OK. We are moving as fast as possible, and as fast as is safe,” Whitesides says.

Modifications to the SS2 include replacing a pair of smaller strakes on the inboard side of each vertical tail with a larger, one-piece, horizontal strake. These have been added “to provide more margin for tail stall at low angles of attack,” says Scaled President Doug Shane. The tail stall, which occurred almost immediately after release from the WK2 during a post-maintenance check flight, was overcome by the crew deploying the feathering mechanism. This is designed to increase drag during reentry from suborbit, but in this instance helped recover full control of the vehicle in the descent.

The stall occurred as the crew was diving at a steep angle to set up for a specific test point, and it happened “because of a specific maneuver we would not normally encounter during operations,” says Scaled test pilot Pete Siebold. The change is designed to provide greater pitch authority and better longitudinal control at negative angles of attack. It will not only help during tests at unusual dive angles but “will provide added margin in regular operations,” says Siebold. “The basic aircraft has been performing very well,” he adds.

The upgrade, although relatively minor, is the second notable aerodynamic modification following the addition of nose strakes last year. These were initially tested in late May 2011 to “make the ride a little less oscillatory” in feather mode, says Shane, noting that “we're happy with that so far.”

With the resumption of glide flights, Scaled plans to go back to reexplore parts of the envelope expansion phase which originally began with the first glide flight in October 2010. “We've got to reclear the envelope and make sure the modifications we made are what is required,” says Shane. These will build up in terms of weight and varying center-of-gravity positions to gradually clear the unpowered flight envelope.

“We don't expect many differences. We shall reevaluate longitudinal stability and show that it matches predictions. We will only go and reinvestigate areas of the envelope where the strake change might impact,” adds Siebold.

With the envelope recleared, the first components of the Sierra Nevada Corp. -developed MR2 rocket motor will be installed and the buildup process to suborbital testing will begin, says Shane. Initially, glide flights will clear as much of the low-speed envelope as is practical with the aircraft ballasted with weight to represent the rocket after the fuel has been spent.

The remainder of the envelope expansion requires rocket power. “The program team has put together a plan for differing burn durations to achieve various Mach-number and altitude conditions,” he adds. The test plan will follow the example set with Scaled's SS1, the pioneering vehicle that in 2004 won the original $10 million Ansari X Prize by becoming the first private manned spacecraft to exceed 328,000 ft. twice within 14 days. Initial flights will see shorter-duration burns rocket SS2 to speeds likely in excess of Mach 1, while the feathering system will be tested later, with longer-duration rocket burns at higher speeds and altitudes above 200,000 ft. “For the first five flights, we don't need a full-duration motor,” Shane says.

“The plan is still being finalized, and although we know it will begin with short-duration burns, the exact times will be based on how we proceed in ground testing and how the rocket motor is performing. We still haven't finalized the specific goals of airspeed and altitude for each of the flights,” says Siebold. Unlike SS1, where the rocket-burn duration for the first powered flight was limited to 10 sec. to avoid going through the FAA licensing process, no such barrier exists for the already approved SS2. Previously, Scaled has indicated a target minimum burn of around 15 sec.

Testing of RM2, a hydroxyl-terminated polybutadiene and nitrous oxide-burning hybrid motor, is also accelerating with 13 full-scale, full-duration, rocket firings completed on June 26. During the five tests conducted so far this year, the motor has run over durations of 40-55 sec. Full-duration firings of 55 and 58 sec. were also accomplished in the second half of 2011. The latest test checked out pressurization, the valve/injector design, fuel formulation and geometry, nozzle, overall structure and performance.

The RM2's job is to propel SS2 and its two crew and six passengers or mission payload to altitudes over 100 km (62 mi.) with margin to spare. SS2 tests recommenced with a series of taxi tests at Mojave on June 1. Since ground and flight tests began, however, the propulsion system has become heavier than expected, resulting in an increase in operating empty weight over early assumptions. “For flight tests, this warranted looking at the overall capability of the landing gear,” says Siebold.

Unlike SS1, which was aimed at grabbing the X Prize, SS2 is designed to be a fully reusable transport. “We want a system that's robust,” Siebold stresses. “We therefore made changes to the wheels and brakes to get it closer to a production configuration.” On June 1, the spacecraft was towed behind a truck down the runway to conduct four tests of newer, higher-capacity brakes at 30-65 mph with four different pilots: Virgin Galactic chief pilot Dave MacKay and Scaled test pilots Siebold, Mike Alsbury and Clint Nichols.

Testing of the WK2 carrier aircraft has also accelerated since the aircraft resumed flights in April after a four-month spell on the ground. Much of the work so far this year has focused on the performance of a redesigned fuel inlet cooler and cycling of the gear at high altitudes after prolonged “cold-soaking.” “We've made some updates to the aircraft, and done some of those on the main landing gear,” says Shane.

Deployment of the gear at altitude is required to increase drag for faster descent. Issues with the gear have included sluggish deployment at high altitude and a partial collapse of the left main leg in August 2010. Overall, however, Shane classes the WK2 as being at a “high level of development.”

Flight-test lessons will be incorporated into production WK2s and SS2s, the first of which have now entered manufacturing at The Spaceship Company (TSC), the Mojave-based joint venture set up by Scaled and Virgin Galactic. Cabin halves, lower-wing skins and window surrounds for the next SS2 are built, while wing-skin panels for WK2 No. 2 have been laid in the 140-ft.-long wing jig in TSC's new $8 million final assembly, integration and test hangar site. Officially opened in September 2011, the 68,000-sq.-ft. facility is starting to fill up with structures and tooling. “This year is about parts fabrication and next year is for major assembly,” says TSC's vice president of operations, Enrico Palermo.

In the buildup to operations, Virgin Galactic's primary focus remains on passenger flights, despite a growing list of other applications including science, research and a potential small satellite launch. Although since its founding in 2004, the company has deliberately remained vague about the exact schedule for the start of services, the plan was believed to have aimed at beginning suborbital flights by or before 2011.

The extended schedule notwithstanding, the company continues to collect bookings for its flights at $200,000 per ticket. Virgin Galactic is expected to reveal a new tally at Farnborough this week with well in excess of 500 would-be space adventurers, and more than the total number of people ever to have traveled into space.

Preparations also continue for the start of commercial spaceflights from the purpose-developed Spaceport America facility near Las Cruces, N.M. As anchor tenant, Virgin Galactic is working with the FAA and local military airspace operators at White Sands Missile Range and Holloman AFB to “make sure we are a good neighbor,” says Whitesides. Virgin also recently held a team meeting with state authorities over ongoing work to extend the Spaceport's 10,000-ft. runway by a further 2,000 ft. “That's in the works and will be complete in time for our commercial schedule,” he adds.

The base of the highly unusual building is also nearing completion and should be finished over the summer. “The next phase will be Virgin Galactic coming in with contractors to do the requisite finish we think is required for our customers. In 2013, we will be outfitting the facility with equipment for ground support and more.”

Whitesides also says “serious effort” is going into plans for a second spaceport in Abu Dhabi, United Arab Emirates, which became a focus for future development efforts in July 2009 when the Aabar investment group based in the country committed to buying a 32% stake in Virgin Galactic for $280 million. The deal included a commitment of another $100 million to develop a satellite launch capability for the system and the creation of a spaceport. In 2011, this was subsequently raised to $110 million, giving the group a 37.8% stake in the venture.

The march to begin science flights is also underway, following the teaming in February of Virgin Galactic and Texas-based microgravity research company NanoRacks to develop a rack system for research payloads as large as 1,300 lb. to fly aboard SS2. The deal came after a busy 2011 in which the company clinched a contract from NASA to provide flight opportunities for engineers and researchers to take technology payloads into suborbit, marking the first time the agency has contracted with a commercial partner to provide flights in this way. Payload integration and flight service partners for the NASA program will include Southwest Research Institute, SatWest of New Mexico and Washington-based Spaceflight Service.

One development revealing, perhaps more than any other, a glimpse of possible things to come was Virgin Galactic's win, alongside heavyweights Boeing and Lockheed Martin, of U.S. Defense Advanced Research Projects Agency contracts to design air-launch systems. Few details have emerged of the Airborne Launch Assist Space Access (Alasa) program, announced in June, but goals include a system capable of orbiting payloads lighter than 100 lb. for $1 million, including range costs. It must also be able to perform with just 24 hr. from call-up to integration and payload launch, as well as have the ability to replan the launch in flight and relocate to a different airport at short notice.