Virgin Galactic på farten igjen - AW&ST

Next Two Virgin Galactic Spaceships Assembled As Powered Flights Resume Guy Norris  As SpaceShipTwo VSS Unity coasted to a new record apogee of more than 84,200 ft. over California on its first powered flight on April 5, the moment signified new heights not only for Virgin Galactic but also for the vehicle’s builder, The Spaceship Co. (TSC). Far beneath the arrow-straight exhaust plume that marked the first successful airborne ignition of a TSC-built hybrid rocket in a TSC-made suborbital spacecraft, employees of both Virgin companies stood on the flight line at the Mojave Air and Space Port and cheered the completion of a huge step on the path toward final development of a Mach 3 vehicle for the fare-paying public. While both organizations acknowledge the road has been far tougher and longer than anyone could have guessed, the prolonged gestation of Virgin Galactic—now marking its 14th year—has had a more enduring effect. Almost four years after the fatal 2014 flight-test loss of prototype SpaceShipTwo (SS2) “Enterprise,” the venture finally is on the verge of reaching space with a more robust, safer vehicle. Powered flight of Unity was first for all-TSC-assembled vehicle and hybrid rocket motors Automation techniques eyed for large-scale production of hybrid rocket motors TSC incorporating design changes for SS2-3 and SS2-4 TSC, which was developed from the ground up as the vertically integrated production arm of sister company Virgin Galactic, is meanwhile deep into the assembly of two more spaceships and has, by necessity, matured into a sophisticated design, test and manufacturing organization. As a result, Virgin sees a broader role for TSC beyond spaceships, which ultimately could lead to development of high-speed, intercontinental passenger aircraft and other air and ground transport concepts. To reflect this potential role, TSC has been rebranded with a stylized “maker’s mark” logo based on the thumbprint of founder Richard Branson which Virgin says, underscores a shift from specialist space work under its original iris-based logo to a company with broader aerospace and transport engineering and design capabilities. TSC is “coming of age,” says the company’s president, Enrico Palermo. “We have greater street credibility now that we have flown a powered flight. Our new logo articulates the new sophistication of the company as we continue to build spaceships and start to work on future projects that are not space-related but [have] to do with transportation.”

Virgin Galactic pilots Mark “Forger” Stucky and David Mackay reported a smooth ignition and initial acceleration during the first powered flight, VP-01. Credit: The Spaceship Co./Virgin Galactic

Palermo, who was the first employee at TSC, whose workforce now numbers 478, says the expansion has come with experience. “We were set up as a sort of cost center to start with, and our job was to build spaceships and Virgin would launch them,” he explains. “But having done the last few spaceships, we have developed end-to-end capabilities, from preliminary vehicle design to post-flight servicing, and it would be a mighty shame not to leverage that capability and do other things which we know we can do. No one else, as far as we know, is working on building and testing a fleet of rocket-powered spaceplanes. We’re it. And we are doing it not just for research and development but for commercial operations.”  For now, TSC’s priority is completing assembly of SS2’s Nos. 3 and 4 this year to support the long-awaited beginning of commercial flights from Virgin Galactic’s initial operational spaceline base at Spaceport America in New Mexico. First to enter service will be VSS Unity, the second SS2 built, and the first to be assembled by TSC. The first SS2, Enterprise, was built in the late 2000s by Scaled Composites, along with the WK2 carrier aircraft before Virgin acquired the specialist development company’s 30% stake in TSC in 2012. While VSS Unity was produced and assembled in 2015 in much the same manner as Enterprise, the process has been altered radically for the first pair of “production-standard” spaceships. “Our big focus on these next two spaceships has been design for manufacturability, assembly, maintainability and performance,” says Palermo. “It is important we make them efficient to build, so we’ve made a lot of design changes. It’s not that on VSS Unity or Enterprise that the design is inadequate; it is more about making them easier to manufacture. “As can be expected on a first build, many lessons were learned on the build of VSS Unity that we are rolling into the next spaceships’ design,” Palermo notes. “Through these design improvements, we expect to save several hundred pounds compared to VSS Unity, and we expect some of this weight optimization to flush back into the VSS Unity design eventually.”  As the program’s experimental flight-test vehicle, VSS Unity incorporates additional mass for items such as test instrumentation, which will not be needed on the next two spaceships. Informally named after Branson’s twin grandchildren, SS2-3 “Etta” and SS2-4 “Artie,” the two vehicles are in different stages of assembly in TSC’s two main Mojave facilities: Building 79 and the newer final assembly, integration and test hangar (FAITH). The cabin of SS2-4 was bonded in Building 79 in March while other subassemblies and parts continue to come together around it. Parts such as the crew station have been reengineered to become more integral with the forward cabin structure, eliminating several weeks of build time. Assembly of SS2-3, which will be the second spaceship to enter service, is more advanced in FAITH, where TSC has invested “a lot of money,” it says, in two large fuselage assembly fixtures. “Unity and Enterprise were both built in one spot whereas with the next two, we are building them much more like you’d see an airliner come together,” says Palermo. Eight major subassemblies—including the fuselage, wings and feathering tail system—will be brought into FAITH, where “we snap it all together.”

The exhaust plume from the rocket in the vertical test rig fires down a U-shaped  14-ft.-dia. flame tube that tunnels 60 ft. beneath the desert surface. Credit: The Spaceship Co./Virgin Galactic

Besides the almost complete basic cabin assembly for SS2-3, the lower and upper wing skins are being prepared for attachment to the spars. The closed-out cabin already incorporates much of the vehicle’s wiring, brake systems and pneumatics. “At this point, Unity’s systems weren’t installed,” Palermo says. “We did those afterward, whereas here the systems are also being assembled modularly with the wiring and black boxes being made here in our avionics lab.” TSC also is building a “copper bird” ground-test rig for all SS2 systems and electronic components. “We will build a replica on the ground before we integrate them into the vehicle because we are making some changes to the actuation system for weight and performance improvements,” Palermo says. In another work cell in Building 79, work is underway to complete the torque tube at the heart of the spaceship. The 23-ft.-long composite structure runs transversely and forms the pivot point for the movable tail booms that deploy into a 60-deg. upward position for the vehicle’s “feathered” reentry configuration. The single-piece unit, which also supports the flaps, was 46 days into a targeted 125-day build cycle when Aviation Week visited TSC in mid-April. Although the torque-tube design reflects design changes to ease production, the pneumatically actuated feathering system itself remains unaltered. Changes have, however, been made to the control system to prevent inadvertent or premature unlocking of the type that led to the loss of the Enterprise. New safety features include a mechanical inhibit system consisting of a locking pin with a solenoid switch controlled by the flight-control computer, as well as an override device. TSC also is building the second of three new aft spars, following a redesign. Two will be flight articles, while the third will be used as a structural test piece to verify changes, which, like the other components, are being made for ease of production.  “It was not the greatest experience building the first ones, from a tooling integrity perspective,” Palermo says. “It took us a few tries to get the one we used ready for flight, so as part of making it more manufacturable and enabling us to make the vehicle quicker, we’ve had to make design changes.” Another redesigned element is the lower nose section, which, in the first SS2s, had to be cut open for installation of the landing skid and its housing. “We re-tooled and made it a single-part piece, which took 13 lb. out of the structure, eliminated a lot of structural bonds and saved several hundred hours of assembly work,” Palermo explains. The machine shop area in the east end of Building 79 is dedicated to production of the hybrid rocket motor; assembly is currently running at two per month based on a single shift. “We are starting to work on how we productionize the rocket motor because, when we have three spaceships flying, we will need a lot of them,” he says.  Perfecting the rocket system, which is the only non-reusable element of the vehicle, has been the most challenging aspect of the suborbital spaceplane project. Developed originally with Sierra Nevada, the engine is a scaled-up, 65,000-lb.-thrust version of the same rubber-based hydroxyl-terminated polybutadiene-fueled (HTPB) hybrid motor used in the original XPrize-winning SpaceShipOne. Despite briefly evaluating an alternate polyamide-based grain to boost thrust and propulsion consistency amid continuing development issues in 2014, Virgin reverted to the original fuel and brought all development in-house in May of that year.

Design improvements for manufacturing, including the use of fuselage jigs, are featured in the next pair of spaceships. The cabin for the first, SS2-3 Etta, is being assembled in the FAITH. Credit: The Spaceship Co./Virgin Galactic

The motor “is qualified to get us to space now,” Palermo reports. “We’ve fired it on the ground longer now that we anticipate flying, just to give us margin from a safety perspective. The minimum mission to which we have committed is the NASA definition of space [50 mi./81 km], and we have a motor that will get us there. The important thing is until we fly the full profile, we won’t know the exact performance, though we have very high confidence of hitting the NASA milestone.” HTPB is poured from a central mixer into filament-wound cylinders in one of two core stands. The flow rates and grain mixture are controlled precisely and allowed to cure. However, with the prospect of producing hundreds of hybrid motors, TSC also sees the rocket line as providing an early opportunity to introduce automation. The company has acquired a KUKA  robot as part of studies to automate trimming and pressing materials for making the filament-wound motor casings. “Automation could be used for the rocket motor but also eventually apply to other programs that will be done by TSC,” Palermo says. Development, test and qualification of the hybrid motor has been accomplished using a recently constructed vertical test stand that sits over a 60-ft.-deep U-shaped flame tunnel. The rig augments the original horizontal test stand but better replicates the attitude of the motor when it is powering SS2 in its near-vertical climb. “With the horizontal stand, we couldn’t mimic all the characteristics and phases of flight, so to get a fair shot at it, we wanted to test downward,” says Dave Raibeck, TSC propulsion test supervisor. Use of the vertical rig precludes needing a snorkel to scavenge the nitrous oxidizer that settles at the base of the motor in the horizontal position, affecting the rocket’s overall performance.  Motor improvements appear to be verified by results from the first powered flight, VP-01, during which pilots Mark “Forger” Stucky and David Mackay reported a smooth ignition and initial acceleration. “Initial data review results show that the TSC hybrid motor performed very well and to specification,” Palermo says.  However, while the 30-sec. rocket burn—which powered VSS Unity to Mach 1.87 and 84,271 ft.—expanded the flight envelope more than any other step in terms of motor-burn duration, Mach speed, apogee and loads, TSC says “a tremendous amount of data” still needs to be analyzed before the next procedures are determined. “We are not going to go full duration on the next one, and it might even be a repeat of this one,” cautions Virgin Galactic CEO George Whitesides. “We are going to spend time testing the basic parameters of the vehicle, then get into envelope expansion and exploring different scenarios. In parallel, more to the later side, we also will do interiors testing to make sure the customer experience and the hardware associated with that does what we want it to do.” The main test priorities are focused on structures, rocket engine burn time and handling qualities, Virgin Galactic President Mike Moses says. “As long as everything is going well, we just have to verify things with the structure, and it is the same thing with the burn time. So handling qualities [are] what we are down to and all the potential unknowns.” Envelope expansion will continue with various weight and center-of-gravity positions, many of which will be used to validate the model-based test program.  Virgin originally hoped to start powered flight tests in late 2017, but peer reviews of loads analysis on the structure of VSS Unity, which was beefed up in the redesign following the loss of the first SS2, took longer than expected. Although glide flights provided some insight into the airframe loads, these imposed less than 60% of the stresses imparted during powered flights. The highest structural loads occur as the rocket ignites and the vehicle begins its climbing, or gamma-turn, maneuver. Future testing is planned to include deployment of the feathering reentry system at supersonic speed, which will require a rocket burn of 45-50 sec. Full-endurance flights, in which the hybrid motor will fire for up to 62 sec., will follow, with tests of handling qualities at rocket burnout as well as those of the thermal environment in suborbit.