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Flying In Space For Low Cost


Apr 20, 2003

Scaled Composites unveiled its privately funded manned space program here on Apr. 18, displaying largely completed hardware designed to take three people in a suborbital trajectory to 100 km. (62 mi.) altitude. It is in essence a version of the 1960s NASA/USAF X-15 rocket plane program but with less severe aerodynamic and thermal stresses.

Scaled President Burt Rutan said the main goal of the program, called "Tier One" internally, is to show that people can fly to space for very low cost. "All decisions in design focus on the absolute minimum recurring cost," he said. "We use the lowest technology possible, not the highest."

The spaceship should have enough performance to meet the X-Prize, a privately funded competition requiring that three people be taken to 100 km. and that the ship repeat the flight within two weeks (www.xprize.org). But Rutan is focused beyond the X-Prize. "The big message is not to reach the X-Prize, but to show that space tourism is affordable."

An undisclosed customer is funding the program, and this includes multiple flights to 100 km. A rough estimate by Aviation Week & Space Technology is that the program will cost $20-30 million. The customer may be revealed when the craft reaches space, Rutan said. Captive carry of the spaceship will occur "very soon," signifying it is ready for gliding flight. "I would like to do a manned spaceflight before the Wright Brothers' anniversary," he said.

The overall system includes:

A turbojet-powered carrier aircraft called the "White Knight," designed to drop the spaceship from about 50,000 ft. This unusual configuration was first revealed with a spy photo in this magazine shortly after its first flight on Aug. 1 last year (AW&ST Sept. 2, 2002, p. 18).

The winged spaceship, powered by a hybrid rocket engine and featuring huge pop-up "feather" surfaces for a high angle-of-attack entry at supersonic speeds. It is called SpaceShipOne.

A cockpit-replica fixed-base simulator and a training program. This editor had an opportunity to fly the simulator (see www.AviationNow.com/space).

Ground service equipment.

One of the clever features of the system is that the carrier aircraft and spaceship have almost identical cockpits and share system components. This means that the White Knight can serve to train some elements of the SpaceShipOne profile, and that spaceship components have their reliability tested on every flight of the carrier aircraft in the near-space environment of 50,000 ft.

Scaled is building the rocket engine case and the tank for the nitrous oxide oxidizer, and two companies are competing to provide the solid fuel and oxidizer injector and plumbing. Both have made full-performance, partial-duration runs at an outside test facility here.

The craft is air-launched and hand-flown like the X-15. The mission profile starts with the White Knight dropping SpaceShipOne from level flight at 50,000 ft. The SpaceShipOne pilot zooms the gliding spaceship up into a slight climb and lights the rocket. This pushes his back into the seat with 3-4gs of force. Using manual controls and electric trim, he continues rotating to a nearly vertical climb for the 65-sec. burn, reaching about Mach 3.5 but only about 240 kt. equivalent airspeed. Shortly after burnout, the atmosphere drops to nil, and the spaceship continues in a zero-g coasting climb, peaking at about 100 km. (328,000 ft.), followed by free fall.

In this period, the pilot deploys the feather mechanism, readying the configuration for entry. The crew has about 3.5 min. to enjoy zero-g and play with the attitude via thrusters, then the pilot commands the proper entry attitude. SpaceShipOne goes through peak heating and G forces with essentially no input from the pilot. The peak loads are a little over 5gs down into the seat and are above 4gs for more than 20 sec., with the Mach number reaching 3.3 but equivalent airspeed staying below 160 KEAS. When the high entry stresses are over, the configuration is returned from feather to a normal glider, and the pilot makes a conventional landing at an airport with an approach speed around 110 kt.

SpaceShipOne is registered as a glider, and its tail number is N328KF, representing 328,000 ft.--N100KM was already taken. It is Scaled Model 316, and the White Knight is Model 318.

Conceptual design started around 1997 and went for four years, including computational fluid dynamics (CFD) studies and tests of the thermal protection coating, heat-resistant windows and drop models of the entry configuration. A lot changed. The original scheme involved parachute recovery of a capsule with deployable high-drag "feathers." Rutan wanted to avoid the careful control of entry angles needed for survival by winged vehicles like the X-15 and space shuttle. One fatal X-15 breakup involved improper entry angles. "I wanted to be able to throw it sideways at the atmosphere," he said.

Nevertheless, a winged vehicle had appeal. However, he also wanted a manual flight control system--it is cheaper, simpler and more reliable than a powered, fly-by-wire system. But Rutan could not find a configuration that had enough relaxed stability to trim at a high angle of attack for supersonic entry, yet be stable when the center of pressure moved forward in subsonic flight, while using manual controls.

The solution is a variation of an old free-flight model airplane trick--pop the entire tail up to force a high angle-of-attack steep descent. In this case, the aft part of the wing pops up along with the tail booms, driven by pneumatic actuators. The feathered shape gives shuttlecock stability for carefree reentry, yet handling is acceptable as a glider. "This gave me the courage for a horizontal lander instead of a 'chute landing," Rutan said.

Serious development of the Tier One system started after the customer contract was received in April 2001. With full funding, work has been rapid since there is no need to pause for another round of financing, Rutan said. But it is behind the original schedule, which would have had the craft in space by now, he said.

SpaceShipOne has monocoque structure with fuselage skin made mostly of carbon fiber/epoxy honeycomb with a Nomex core. The skin aft of the horizontal stabilizer pivot is fiberglass for radio transparency to the antennas there. The wing is built-up construction with several ribs and honeycomb carbon fiber/epoxy skin. In a few high-temperature areas a phenolic resin is used instead of epoxy on the outer face sheet for 50-70F more heat tolerance. Wingspan is 16.4 ft. and wing area is 160 sq. ft. Weights remain undisclosed.

The spaceship will reach at least Mach 3.5, yet Scaled's experience has been on Mach 0.6 airplanes. The supersonic design skill is largely borrowed from reading the "Datacom" Air Force compendium of aerodynamic information, from experienced consultants, and from CFD programs. The control surfaces have thick trailing edges reminiscent of the X-15, which used 10-deg. wedge tail surfaces for good effectiveness at hypersonic speed. As is typical, Rutan plans no wind tunnel tests. They cost money, and real data will be collected during flight test buildup.

There are no control surfaces on the wing. Roll and pitch are controlled by elevons on the tail booms driven manually by the control stick. At the end of the tail booms are upper rudders that deflect outward only, manually driven by pedals that have no crossbar--both rudders can deflect outward at the same time. They are faired to neutral by a strong spring with an overcenter lock to prevent flutter. Lower rudders are electrically moved by a cockpit knob and are used for trim and control at supersonic speed.

At high speed, the stick becomes ineffective--engineers estimate 300 lb. of pull will be required to produce 1g, because of both the high dynamic pressure and the drop in elevator effectiveness at supersonic speed. The full-flying stabilizers are electrically moved in pitch and roll for control in this region, as well as trim. The never-exceed speed is designed to be 260 KEAS.

Outside the atmosphere, attitude is controlled with a redundant set of pitch, roll and yaw thrusters powered by 6,000 psi. bottles of dry air in the cabin. Full throw of the stick and pedals electrically valves the gas either full-on or full-off. For simplicity, there is no stability augmentation in any of the control systems.

The feather motion is powered by a pair of pneumatic actuators. The elevons are mechanically locked out in the shuttlecock configuration, but the rudders and electric stab trim still work. The feather can be activated after equivalent airspeed drops below 10 KEAS during ascent, and is retracted when speed has dropped to subsonic on entry and load factor is under 1.2g, which occurs at about 80,000 ft. The shuttlecock angle of attack is 53 deg. at Mach 3 and 65 deg. subsonic. Even though the shuttlecock lift-to-drag ratio is 0.7, the downward velocity is generally so high that the descent remains essentially vertical, with only 2-3 mi. of offset, Rutan said.

The shuttlecock mode has a draggy terminal velocity of 60 KEAS, equivalent to a ballistic coefficient of 12 psf. This means that entry deceleration will start early and high, spreading out the G and thermal loads over a greater period and making SpaceShipOne design easier. The Mercury capsule had a ballistic coefficient of about 60 psf., creating more intense loads.

There is no hydraulic system in SpaceShipOne other than the wheel brakes. There is a set of 6,000 psi. dry air bottles for the feather actuator, attitude jets, window defogging, and to maintain cabin pressure. Springs extend the landing gear and are manually released. Independent wheel brakes activate at full extension of the rudder pedals. The nose has a skid with a maple tip. Electrical power comes from lithium batteries. The time from leaving the carrier aircraft until landing is under 30 min.

The cabin is sealed, with a pressure relief valve. Rutan expects it will be maintained at about 6,000 ft. with a little flow from the air bottles to offset about 100-fpm. leakage. This is done by hand, watching a cabin altimeter. A "Sodasorb" carbon dioxide scrubber is used, though it may not be necessary for short flights, and no makeup oxygen is required. A three-man crew has done a 3-hr. test in the sealed cabin.

The crew will not wear pressure suits--Rutan believes the overbuilt structure of the cabin provides the same safety backup as a spacesuit. There are oxygen bottles and masks for emergency use. While carried under the White Knight, cabin heat comes from engine bleed air directed at the outside of the aft pressure bulkhead. Otherwise temperature is free to vary--the sidewalls are insulated and engineers expect it will remain within 20-30F of room temperature.

There are 4-in. hole plugs on the left and right walls that can be removed at lower altitudes to let in fresh air. Otherwise, the cabin quickly gets hot below 10,000 ft. in summer. The plugs will pop in if outside pressure becomes greater than inside during descent. One plan may be to keep them out until 10,000 ft. during climb, then use the air bottles to pressurize the cabin to 6,000 ft.

The nosecone is a big keyed hatch that comes off after a 7.5-deg. turn, leaving a 36-in.-dia. opening. An internal ring gear gives the leverage to turn and lock it. The rudder pedals and many of the instruments come off with the hatch, and the crew crawls in and out the front. There also is a 26-in. plug door on the left side, which is usually left open during taxi for cooling.

The 16 9-in. windows are double-paned with a 1/4-in. gap. The outer panes are 5/16-in. Lexan polycarbonate to withstand heat, and the inner panes are 5/16-in. Plexiglas. The outer panes have several small holes, putting all the pressurization on the cooler-running Plexiglas, which deflects 0.2 in. under load.

The biggest environmental problem seen on White Knight's similar cabin has been humidity that fogs the windows, coming from the crew's breath and sweat. Ice forms on cold parts like the front hatch ring. While most of the mission can be flown on instruments, landing requires a good view out the windows. Attempts to combat fog include running air through a "13X" desiccant, flowing bottled dry air through the window pane gap and overboard via the outer holes, directing electric heat at them, using peel-off films of plastic and wiping with a cloth. The problem still isn't completely solved, said Douglas B. Shane, Tier One director of flight operations. It may be that reentry heating will automatically defog the SpaceShipOne windows. Some windows were moved back from the nose to avoid high heat.

The stagnation temperature at peak heating is about 1,100F, with heat loads roughly similar during ascent and entry. About 25% of the surface is covered with a proprietary ablative material about 0.035-in. thick that can be recoated between flights. The rest of the skin will be white paint. The lip of the feathered surface will have thermal protection and is partially protected by the cove at the hingeline. If there were no ablative, calculations and tests show only the outer two plies of structural composite would be damaged and the thicker inner face of the honeycomb would be intact, keeping the craft safe, Rutan said.

The White Knight's gull wing provides room underneath for SpaceShipOne, and the outboard tail booms give aft clearance for the drop. Wing area is about 468 sq. ft. at the current 82-ft. span. It was originally 79 ft. with flat wingtips but flying showed there wasn't enough dihedral to bank the plane with rudder alone, and when tip dihedral was added, the span grew to 82 ft. Further extension to 92.5 ft. is possible if more ceiling is required, at the cost of some G capability.

The aircraft is powered by a pair of afterburning General Electric J85-GE-5 turbojets taken from a Northrop T-38 supersonic trainer, rated at 3,850 lbf. static thrust each. The White Knight never-exceed speed is 160 KEAS and Mach 0.6, making it perhaps the slowest aircraft equipped with afterburners. "It is the only aircraft with a panted nosewheel and twin afterburners," Rutan said. All this thrust is to achieve a ceiling above 53,000 ft. at light weight. The used engines can run a little erratically there. If more thrust is required, the 5,000-lbf. J85-GE-21 engine from the Northrop F-5 fighter could be installed. Or a small hybrid rocket could be placed in the fuselage tailcone, Rutan said.

Internal fuel capacity is up to 6,400 lb., carried in the wing leading edge bay and boom tanks above the main landing gear. The White Knight can carry and drop payloads up to 8,000-9,000 lb. Scaled doesn't want to disclose other weights, but when the spaceship drops, the carrier aircraft will pull almost 2gs due to the instantaneous loss of weight, Rutan said, meaning that the carrier weighs slightly more than the fueled spaceship.

Primary flight controls are all manual. The ailerons are outboard of the tail booms, and the rudders and elevators are on the T-tails, with a trimmable horizontal stabilizer. Pneumatically powered "spoil flaps" inboard of the booms can be activated separately in inboard and outboard pairs for steep descent. Shane said the aircraft has a big center-of-gravity range and "flies remarkably well. Without a yaw damper it has good Dutch roll at 50,000 ft."

The main landing gear are pneumatically retracted and have a rubber biscuit strut for springing and damping, since experience with the company's Proteus aircraft at high, cold altitude showed the oleo struts were prone to leakage. The panted nosewheels at the tip of each boom don't retract. The left one is free-castoring and the right one is steered, which already has proven useful when a main wheel brake failed.

The White Knight has a sealed cabin and environmental systems similar to SpaceShipOne. Construction is almost completely of composite materials, primarily carbon fiber/epoxy. It has a dual pitot-static system. One probe is on the removable nosecone and supplies backup instruments that are mounted there. The second probe is just aft of the nosecone joint and feeds the avionics system.

The aircraft has made about 20 flights as of Apr. 14 and accumulated 40-50 hr.

The spaceship is suspended from a fore-aft pair of hooks and is stabilized by cone fittings in line with the hooks, and sway bars pressing on the wings. Following electrical arming by both the White Knight and SpaceShipOne crews, a manual pull in White Knight activates a big spring to retract the hooks toward one another, releasing the craft. The spaceship is above its stall speed so the trim is carefully set to not fly back into the carrier. No wind tunnel modeling of separation has been done, but CFD shows there should be little interference. Mounted, there is only 1-ft. clearance between the two craft.

The White Knight and SpaceShipOne cabins are nearly identical. Both have the same 60-in. maximum outside diameter. Where there are throttles in White Knight, there is the feather actuator and lock controls in SpaceShipOne, and turbojet instruments are replaced with rocket instruments. Otherwise they are very similar, letting spaceship pilots get training time in the carrier aircraft. At light weight, the White Knight has a thrust-to-weight ratio greater than 1, so pilots can practice flying near-vertical profiles. It can give 20 sec. of zero-g, and windup turns can simulate the G-loading of entry. Activating the spoil flaps gets the lift-to-drag ratio down to about 5 to practice the spaceship's gliding approaches.

The White Knight also tests the spaceship's systems. The avionics and environmental system are the same, as are the stabilizer and rudder trim actuators. The actuators that retract the landing gear are the same as those that feather the spaceship.

The first flight was plagued with banging spoilers that were a test of the spaceship's attitude control jet system. The pressure bottle and valve were remotely located in the wing and electrically signaled, as was the plan for the spaceship roll jets at the time. Instead of a jet, the valve drove an actuator that raised an outboard spoiler. The actuator had an intentional leak so a spring could retract the spoiler. But the aerodynamic loads were misestimated and larger than the spring force, causing the spoiler to flap up and down and shake the airframe. The spoilers were then bolted shut and later removed, and the spaceship roll control system was modified so the pressure bottle and valve are in the warmed cabin, and only the nozzle and a feed tube are in the wing.

The White Knight will also be used as a flying wind tunnel with the spaceship in captive carry, to measure control surface hinge moments. And spaceship systems can be tested inflight using umbilical power from the carrier.

The first spaceship flight is to be a glide from 46,000 ft. The first rocket-powered flight will have just a brief burn, probably accelerating to Mach 1.2. Several more powered climbing flights will expand the Mach envelope before going for an altitude flight. The advantage of an air launch is that if the motor hiccups it can be shut off and there are 15 minutes to dump oxidizer while gliding to base, Rutan said. The equivalent airspeed envelope is to be expanded by diving in glides. There will be ground vibration tests to search for flutter.

Rutan believes flight test will pose little threat to the test range. The rocket motor can be shut off, and the kinetic energy in a terminal dive is about half that of a light twin like the Beech Baron, and about 2% that of the X-15.

Spaceship launch and entry are to occur in the Edwards AFB, Calif., restricted areas, but takeoffs and landings will be at Scaled's home base at Mojave, 5 mi. outside the Edwards airspace. "It will be the first time a commercial airport is used for space flight," Rutan said.

The first flight to 100 km. is to be with one person, but there are plans for several flights with two or three people. The cockpit is high-workload and the second person can run the environmental system, read the checklist, and be a backup set of eyes. A mobile van is fitted to be mission control.

There are no ejection seats, these being judged too heavy, complex and expensive. To bail out, the front hatch is cranked open to fall away and the crew climbs out, Rutan said.

The four pilots that will be testing the Tier One system are Shane, Brian Binnie, Michael W. Melvill and Peter Siebold.

Rutan pointed out that there was no government involvement in this project. "I believe the government is the reason it's unaffordable to fly into space. We didn't want them to know; their 'help' causes cost problems." Two weeks ago he briefed his congressman, the FAA Commercial Space Transportation office and USAF space officials at the Pentagon and Edwards AFB about Tier One.

After the end of the funded program, Rutan would like to fly once a week to 100 km. for five months to discover operational issues and gauge recurring costs. He doesn't know if this will happen. His current guess is that costs would be under $80,000 per flight. But he can't charge for rides because the aircraft are not FAA-certified. Rutan guesses certification would cost $100-300 million--"How can you amortize that?" he asks. "I'm not interested in certifying it, but I'd supply parts to someone who is." Marketing studies show there would be thousands of people who would pay $100,000 for a suborbital ride, but a tourist craft would need at least 6-8 seats and more windows to be economical.

"I want to do something different and fun, and show it can be cheap," Rutan said. "The next step is unknown now. Going to orbit has been done before. Maybe go to the Moon or planets. Maybe a figure eight around the Moon."

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