Spaceshipone needs to stabilize

Date: Sep 30, 2004

Spaceshipone needs to stabilize

Date: Oct 1, 2004

I think Spaceship One already has a reaction control thruster system. It uses compressed air in several Scuba tanks (simplicity itself!) I can't seem to find the information about the scuba tanks, but there is a good picture from Scale Composites at:

http://www.scaled.com/projects/tierone/data_sheets/html/space_ship_one.htm

There are two sets of two thrusters each, one on top and one on bottom near the tip of the leading edge of each wing. They are the small "Cyan" colored objects.

They only appear to be 'roll control thrusters.' There doesn't appear to be any yaw or pitch thrusters--this may be why Burt Rutan chose the 'shuttlecock' flight profile. It allows for an almost perfect reentry, and is intrinsically stable (notice that Spaceship One's spin did not continue once it reentered the atmosphere. But I'll bet Mr. Melvill was probably a little dizzy from the spin!) The guess about a failed actuator could have caused the spin. Had it happened lower in the atmosphere, the turning moment would have been greater owing to the denser air--so my guess is that Michael Melvill would have had to abort his flight and come back. You don't want to spin so fast that you lose consciousness.!

Date: Oct 1, 2004

Thanks for the explanation, I think the spaceshipone crew has a good system. I see no problem with paying passengers supporting companies that offer service-finally private business got into space, better late than never!

Date: Oct 7, 2004

That should be the essence of Space Commerce: paying passengers. I think Space Ship One has the potential to eventualy turn a tidy proffit for Scaled Composites as well as the prestige of offering the first regular space tourism service. Whether this is the plan or not--I don't know. I think Burt Rutan realizes this is still pretty experimental--however, I believe that he and the Scaled Composites Team are on the right track!

Congrats to Scaled Composites--Mission Accomplished and a Job Well Done!

Date: Oct 19, 2004

http://www.aviationnow.com/awin/awin_awst/awin_awst_story.jsp?issueDate=2004-10-18&story=xml/awst_xml/2004/10/18/AW_10_18_2004_p36-41-01.xml

World News & Analysis

Pilots Reflect on SpaceShipOne Development

Aviation Week & Space Technology, 10/18/2004, page 36

Michael A. Dornheim, Los Angeles and Mojave, Calif.

Winning the X Prize took courage. Next craft will have electronic assist.

Trials of SS1

Rocket motors that either wouldn't ignite or stop burning, sticky dampers that gummed up the controls and bleak choices after being dropped from the mother ship--these are some of the trials that faced designers and pilots of SpaceShipOne on its way to being the first private spaceship and claiming the $10-million Ansari X Prize on Oct. 4.

Scaled Composites test pilots Peter Siebold, Michael Melvill and Brian Binnie gave their colleagues first-hand insight into SpaceShipOne (SS1) development at the recent 48th annual Society of Experimental Test Pilots (SETP) symposium held in Los Angeles. A Discovery Channel/Vulcan Productions television documentary that aired this month also added fresh information.

THERE WERE SEVERAL test failures in the competition between SpaceDev and Environmental Aerosciences (eAc) to design and build parts of the hybrid rocket engine. SpaceDev's first 15-sec. run resulted in a post-shutdown fire that destroyed part of the test stand. The oxidizer valve wouldn't fully close and kept feeding the fire. Later, the eAc configuration failed to ignite four times in a row.

The two companies came up with significantly different thrust profiles. Scaled was looking for a slow ramp-up to give the pilot time to pull the nose to a vertical ascent before full thrust started, so that impulse was not wasted in the horizontal direction (see chart). They wanted a high level of maximum thrust to get acceleration done quickly while still in the atmosphere so aerodynamic controls would be effective to counter thrust asymmetries. Scaled also wanted a tailoff of thrust that matched the craft slipping out of the atmosphere, to get the last bit of impulse with thrust low enough to be countered by declining aerodynamics. With the ideal profile, this tailoff would start at 140,000 ft. at 80 kt. equivalent airspeed (KEAS).

Neither SpaceDev or eAc met Scaled's wishes. The SpaceDev design, which has four longitudinal ports in the rubber fuel for enough burning area for high thrust, comes on with a bang, producing maximum thrust at the start--not the smooth ramp-up envisioned to turn the corner. The peak thrust is only about 85% of the desired plateau, and declines steadily from there, according to the Sept. 18 SETP presentation. Despite the early start, this still means that to get enough total impulse to loft SpaceShipOne above 100 km., the motor has to run longer than desired, in the very thin atmosphere where control is tenuous.

The eAc motor didn't ignite until five sec. after the switch was thrown, and then also came on with a bang, but the initial combustion instabilities were less. It has a single port and compensates for the lower burning area with fuel additives to increase burning rate. But not enough, because it only made about 65% of the desired thrust. That required the burn time to be even longer for sufficient total impulse, extending the engine run farther out of the atmosphere.

Longer burn time of the eAc motor was considered the more serious problem, and the contract went to SpaceDev. Engineers decided they could run the engine down to 40 KEAS at about 180,000 ft. in tailoff thrust.

http://www.aviationnow.com/media/images/awst_images/large/AW_10_18_2004_1549_L.jpg

The webs of rubber between the four SpaceDev ports thin out and come apart toward the end of the run. The chunks extrude through the nozzle, causing frightening shaking and explosion noises in the cockpit. It happened at least three times on one flight and Melvill thought the tail had blown off. After minutes by himself in zero-g and entry, he was relieved when chase aircraft said the spaceship appeared alright.

SpaceShipOne may be the highest performance aircraft without stability augmentation. A lot was learned from the first 15-sec. powered flight on Dec. 17, 2003. The jolt at ignition pushed Binnie 6 in. back into the seat, taking the stick with him. This increased the angle of attack (AOA) beyond the angle for maximum lift for the first 10 sec., making the roll and yaw handling poor and causing roll and Dutch roll on the way up. Also, the partial load of oxidizer went to the back of the tank, shifting the center of gravity aft, further compromising handling.

Melvill added, "It's really difficult to handle in the first 10-15 sec. We jacked up the early oxidizer flow for more thrust but it gives unstable flow--in the video you can see your head jerk back and forth. You need instruments to round the corner, it's too disorienting."

Binnie found that after initially flying with the sensitive manual stick and rudder, it was hard to transition to using the electric trim as primary flight control in the supersonic part of boost. That was considered necessary because manual controls become very stiff at high speed.

He reports his situational awareness was narrow due to the high workload. Melvill echoed that comment. "On my first powered flight there wasn't enough mental bandwidth," he says. "I didn't hear or feel anything, I just focused on the display. By the third time I noticed a lot more. The rocket made a weird howling noise at high altitude; I didn't notice that on the first flight."

A control surface damper was added for the first powered flight but became so stiff at cold temperatures it caused the heavy landing that collapsed the left landing gear. This was first reported by Aviation Week & Space Technology, but now Scaled has added that the damper raised the control stick breakout force to 12 lb.--a large amount that made the sensitive, lightly damped SpaceShipOne difficult to control (AW&ST Dec. 22, 2003, p. 37).

After the Dec. 17 flight, a heater was added to the damper to eliminate the cold stiffness, making pilot Binnie the only one to have experienced the high breakout forces. "It was our fault to not put a heater on it," Rutan says. Binnie said of the first powered flight to Rutan: "Just when you think you've got it under control, something different would happen." Binnie's well-executed flight on Oct. 4 was his first on the spaceship since the hard landing. "I'm happy to get it behind me," he says.

SCALED'S FIXED-BASE simulator became a comfortable training tool due to the low flight rates, but it's "hard to remember that the sim doesn't fly exactly like the real aircraft," Siebold says. "It's harder when the sim teaches you techniques that just don't work in the aircraft."

On the Apr. 8 second powered flight, flown by Siebold, the oxidizer slosh was addressed by completely filling the tank. Even though it was going to be a half-duration 40-sec. firing, the rocket also got a full rubber fuel load to prevent case burnthrough if the oxidizer valve didn't shut, as happened on the ground test. This made it the heaviest launch yet.

The flight became tense immediately after drop when Siebold sensed "lots of main wing [flow] separation" as well as poor lateral-directional control, and discussed with the control room whether the craft might go out of control if the rocket were lit. This drama was revealed in the Oct. 3 TV documentary. The alternative of landing with a heavy propellant load was poor, as was the idea of dumping the liquid oxidizer, which would move the center of gravity aft due to unburned fuel. Melvill explained that would make the aircraft so tail-heavy it would be landing with the stick full forward and going 150-160 kt.--about 50% faster than normal. The team decided it was better to ignite the rocket. The craft was gliding toward Earth for about 2 min. during this time and the motor was ignited at the lowest altitude yet, 38,300 ft.

http://www.aviationnow.com/media/images/awst_images/large/AW_10_18_2004_1531_L.jpg

The joined White Knight and SpaceShipOne go through dawn preflight for the first Ansari X Prize flight on Sept. 29.Credit: DAVID M. MOORE

Changes to reduce pilot motion in the seat included a ratcheting seatbelt, stiffer cushions and an elbow restraint to prevent jerking the stick back. The rudders were canted out 3 deg. to get them out of an aerodynamic deadband.

Controllability seemed acceptable during boost, with two roll excursions of about 45 deg. "Due to high wind shear the Dutch roll was still excited, but Pete showed that with patience it would damp out by itself, so little would be gained by trying to get in the loop with conventional controls," Melvill told the SETP audience. There was only about 8 deg. of pitch overshoot on the 90-deg. vertical climb target, and it took Siebold less than 4 sec. to roll 180 deg. so he could correct in a positive pitch direction.

Roll oscillations during the feather descent were within about ±20 deg. Large side forces moved the pilot's hand on the stick and drove roll oscillations, but "Pete showed he could damp with aggressive closed-loop lateral stick inputs," Melvill said.

On Melvill's first powered flight on May 13, he was able to counter his own misleading simulator training. "The workload during pullup after ignition is very high," he said. "When it goes transonic the Dutch roll mode kicks in and was exacerbated by wind shear on all powered flights. I found myself working hard to control roll oscillations, using yaw trim as trained in the sim. But my DNA instincts took over and I resorted to using the rudder pedals. It worked for me. Instincts won over the simulator."

Melvill found the May 13 first supersonic feathered entry to be smooth but the loud airflow noise to be "very scary." When it went subsonic the ride became "very rough," with large amplitude vibrations in the tail booms.

The June 21 flight was the first to use a higher expansion ratio nozzle and it produced more thrust asymmetry than before. "The 0.4 deg. of thrust asymmetry is a big deal, it caused me to fly southwest of the course," Melvill says. "Because I was concentrating on the height predictor, I failed to put in enough right yaw to maintain the trajectory and found myself 20 mi. south of Mojave. We can glide 50 mi. even in adverse wind so there was no danger, but once defeathered I headed back to the airport as soon as possible."

IN THE DESIGN PHASE, the pilots wanted stability augmentation, but Rutan wanted simple, reliable manual cable controls. SpaceShipOne has achieved its goal of being the first private spaceship (AW&ST Oct. 11, p. 34), but only through a high level of pilot skill, courage, and training.

It will be a different matter for a Virgin Galactic craft carrying paying passengers (AW&ST Oct. 4, p. 30). "It has to be very straightforward to handle," said Alex Tai, a senior Virgin Galactic official who is rated to fly airliners and business jets. And the Scaled pilots are sure that means the next craft will have stability augmentation.

Date: Oct 19, 2004

Good post.

I think this just serves to illustrate that space launches will never really be routine nor completely safe. Sounds like Scaled Composites got lucky. Good engineering and a good team---with a healthy dollip of luck can get things done.