Authors: Douglas Savage
Although the pilot flies the EEU with the THC in his left hand and the RHC in his right hand, the arm is actually moved by the ship's computers in manual-augmented mode. The pilot's hand controllers do not directly steer either the arm or its end effector. The hand controllers tell Mother where the pilot wants the EEU to move and the computer makes every decision about which arm joint to flex to accomplish the assignment.
To steer the EEU by the pilot's hand commands in manual-augmented operation, the RMS computer must know which coordinate axis with which to tell up from down, left from right. By selection of the orbiter-unloaded position on his control knob, Enright told Mother to fly the arm with reference to an empty payload bay using the X-Y-Z axis system. The computer can also be instructed to think in terms of the EEU's own three-axis coordiate system, or to think with an orbiter-loaded coordinate system, or to think in terms of the coordinate references of an outside payload with the arm in the payload mode of operation.
“Hand controller alive,” Enright called. His left hand touched the THC between the aft windows, and his right hand held the RHC grip. Slowly, he commanded the arm to come toward the aft windows in the forward end of the payload bay. He pulled the THC and the arm's computer flexed all of the arm's joints as he asked Mother to fly the EEU toward him. The arm responded as the EEU low inside the bay moved up the open bay's floor. The flexed arm's elbow rose 25 feet into the black sky above Endeavor which cruised eastward over nighttime Australia.
“Go in Man-Aug all the way, Colorado.”
“Copy, Jack. Looks good from here,” the voice from Australia responded.
“Rogo, Colorado. Goin' back to POSITION on the parameters.”
Enright took his left hand from the THC and the arm stopped dead. He twisted the knob by his chest to call up the inches-from-datum numerics in the three small windows on his console. Returning his left hand to the THC, he flew the EEU with Mother's help to a point 214 inches from his window facing the bay.
“All stop at keel One.” Enright checked his position indicator meters. “We're at 790 inches in X0, minus 4 in Y0, and on the floor in Z0. Real fine in manual-augmented.”
With his right hand, Enright rotated the end effector with the arm's main joints stopped.
Enright used the THC to raise the EEU to the level of the shoulder joint on the bay sill.
“EEU to ZO of 444 point 8 inches. All stop.”
“Copy, Jack. We see it from down here.”
The EEU at the end of the wrist joint hung from the arm above the open bay's centerline 83 inches from each side of the payload bay.
“Goin' now to manual single-joint drive, Colorado.”
“Take your time, Jack.”
“We'll try not to bend anything back there, Flight,” the command pilot radioed from Enright's left side.
Single-joint drive is one of three manual modes for handflying the remote arm. The RMS pilot directs each of the arm's joints one at a time. The two hand controllers are not used. Instead, the astronaut selects which of the arm's segments is to be flown and he drives that joint alone by a spring-loaded toggle switch. The switch is pressed to either its positive position or its negative direction. When released, the switch returns to its neutral stop position.
Enright turned the large circular knob at the upper left corner of the Canadian console to SINGLE. At the console's lower center, he turned the parameter selector knob to ATTITUDE so the three meters would display in degrees of pitch, roll, and yaw, the attitude of the single joint selected for movement.
The arm had stopped with the upper arm reaching upward and outward over the bay's sill at the shoulder. The forearm flexed at its elbow joint high in the black sky. And the wrist section drooped at the centerline of the bay's floor.
“Endeavor: Colorado is about to lose you via Yarradee. Acquire Orrorra in one minute. Sunup in fifteen . . .”
The two pilots floating at the rear of the flightdeck ignored the ground's transmission lost in static as the station at Yarradee went out of radio range a thousand miles behind Shuttle. The nighttime horizon over central Australia blocked the FM radio signal from the ground limited to line-of-sight range.
Rushing to test each arm mode as quickly as possible, the fliers crammed into less than an hour the RMS shakedown which took four to six hours on earlier missions.
With the arm's elbow hanging over Endeavor's port side, Enright powered up the yaw axis of the wrist, one of that joint's three axes of freedom. Flicking the command toggle switch to the spring-loaded negative direction, Enright asked Mother to raise only the vertical wrist joint just beyond the crew's aft windows.
Slowly, the computer swung the wrist joint upward until the joint was perpendicular with the level of the aft station windows. When Enright removed his thumb from the switch, the wrist stopped, pointing the wrist camera and the end effector at the lower edge of Enright's rear-facing window.
Jacob Enright turned the joint selector knob to SHOULDER-YAW. A momentary flick of the command toggle switch in the negative direction swung the upper arm further over Endeavor's port side in front of the copilot. This one-second movement of the upper arm brought the end effector to the lower corner of Enright's window. He turned the knob to ELBOW. Another brief touch of the command toggle in its positive direction flexed the elbow and raised the wrist and its camera to the center of Enright's window.
Both fliers looked into the top of the two CCTV monitors by Enright's right shoulder. In the screen was Jack Enright's helmet behind the aft window's two layers of glass.
The copilot stuffed his hand into the bulging pocket in the thigh of his deflated pressure suit. He retrieved a rumpled cloth pennant from the pocket. He carefully stretched the small, square banner across the window before his helmeted face.
Parker leaned toward Enright's shoulder so he could read the sign's lettering. The brilliant floodlights in the open bay shone through the pennant and made the letters readable from behind, although the letters were backward as seen inside the flightdeck. The two pilots consulted the wall-mounted television screen to confirm that the arm's wrist camera was focused on Enright's window and its little banner.
“Merry Christmas,” Parker read from the monitor screen over his partner's shoulder. Far below, Christmas was seven days away.
“And God bless us everyone,” the radio crackled. “Colorado with you through Orrorra at 02 hours, 33 minutes. Good morning again, Endeavor.”
“And to you, Australia. But it's afternoon up here,” the AC drawled, pressing his mike button on his chest. “How's our downlink?”
“Real crisp, Endeavor. With you four minutes this pass. The CCTV from the wrist looks super from here. Continue with the RMS tests. We'd like you to run the arm to the end of its reach envelope aft in direct-drive, please. When you reach singularity, bring it back to keel Number Two in manual-backup. You'll be on your own by then for going on to PDP deployment.”
“Gotcha, Flight,” Enright called, pressing his mike button. “Goin' to direct-drive now.”
The arm's fourth manual mode of operation is one of two fully manual systems. In direct-drive, the arm is flown one joint at a time by the joint-selector knob and the command toggle switch. But unlike the three modes already tested, the direct-drive system has no computer assistance from Mother. It is strictly an eyeball operation with the pilots' aids limited to the aft and overhead windows and the arm's own television cameras. The steering commands bypass Mother and run by hard wire from the instrument panel to each joint motor. The only usable electronic aids to the crew are the three position meters in front of Enright which were set to show the end effector's position in inches from the zero datum point.
“Runnin' in direct, Flight,” Enright called as he switched first to SHOULDER-YAW.
Enright steered the upper arm which slowly moved from its shoulder joint affixed to Shuttle in the direction of the far diagonal end of the cargo bay on the starboard side. Parker at Enright's left watched the drooping wrist move outside his aft window.
“Two feet per second, Flight.”
“We see it, Jack. Super view down here of the thermal blankets from the wrist camera.”
“EEU at X0 equals 941 inches,” Enright radioed as the parameter dial confirmed that the end effector was at the center point of the bay's length.
Switching to ELBOW, Enright flicked the toggle switch which commanded the forearm of the RMS to reach toward the bay's far end. As Endeavor sped over eastern Australia in pre-dawn darkness, the 278-inch-long forearm slowly maneuvered toward the aft bay area outside Parker's window.
When a tail thruster automatically thumped once to hold Shuttle's attitude, the arm oscillated very slightly. The joint motors in their safing mode momentarily locked the arm in place until the vibration through the arm stopped.
With the upper arm and forearm nearly horizontal, Enright switched to WRIST-PITCH and the toggle switch sent the EEU reaching for the bay's far corner.
A yellow SINGULARITY caution light flashed on the control panel. The arm could reach no further.
“Okay, Flight,” Enright radioed. “We're at reach envelope. The EEU is stopped at X
0
equals plus 1,159 inches, Y
0
at plus 82 point 5, and Z
0
is at plus 444 inches. Good clearance around the OSS pallet back there.”
“We see it, Jack. We're looking via the wrist camera right into the eye of the aft bulkhead TV camera. Get on to approaching the PDP package. Forget about keel Two. We're only with you another minute.”
“Rog. Goin' to manual backup.”
The fifth and final RMS steering mode is the totally manual, eyeballs-only mechanism. The arm is flown by an entirely separate hard wire system isolated from all other arm circuits. There is no computer help, not even from the digital position meters. It is a pilot's job.
“Backup engaged,” Enright advised as he used his left hand to control the joint-selector knob and the command toggle switch. Although the other semi-manual modes all use the same joint-selector knob and command toggle switch, manual backup operation has its own of both, totally separate from any other RMS circuitry. The isolated controls are at the lower left corner of the chest-high Canadian console.
Steering the arm one joint at a time, Enright guided it toward the payload package in the rear third of the bay. He steered the arm toward the Office of Space Science (OSS) pallet bolted to the bay's floor as Parker spotted for him out his starboard window. “Up . . . Up . . . Easy, Jack . . . Wrist left . . . Elbow down . . . Easy.” As the command pilot called out the steering commands, Enright's busy hands complied. His eyes darted from window to television to window.
“You're about over the edge, guys, at 02 plus 37. Next contact in 18 minutes via Hawaii. Sunrise in 10. Good . . .”
“Copy, Australia” the taller airman drawled. “Peace and quiet at last, Number One,” he sighed into the voice-activated intercom.
“With you on that one, Skipper. Goin' to manual-augmented . . . Let Mother help.”
“Okay, Jack.”
Endeavor, Soyuz ever silent, and LACE rolling peacefully in the glare of the lights from Soyuz, all crossed the Australian eastern coastline at Brisbane for the dark South Pacific. “Looky there, Skip,” Enright called with excitement as he pointed out his window toward Endeavor's tail. “Think I saw the glow. Let's kill the bay floods, just for a second.”
“Think so? Okay, Jack.”
Enright's left hand threw the six switches which extinguished the bay's floodlights. The payload bay went black, the perfect moist blackness of the nighttime South Pacific. The RMS arm was parked a foot above the OSS pallet.
“Gawd,” Parker breathed. “Good eye, Jack. Incredible.”
The fliers were transfixed at their aft windows.
Outside, Endeavor's tail and the bulbous protrusions of the OMS pods glowed orange. A fluorescent orange glow, like a neon sign flashing “eat” bathed Shuttle's back end. The strange glow was first reported by Shuttle Three in April 1982. On Shuttle's body, high altitude atoms of oxygen struck the ship in the nearly perfect vacuum of near-Earth space. At Shuttle's velocity of 17,500 miles per hour, the occasional stray atoms of oxygen 130 nautical miles aloft hit the vehicle so hard that their energy caused the ionic orange glow visible only in darkness. The tail shimmered in the eerie and ghostly glow. A crusty old sailor before the mast would have called it St. Elmo's Fire.
“Amazing, Number One. But let's hit the floods and get the PDP out. Wanna see what LACE is sweating out.”
Enright nodded and revived the bay's arc lights one at a time. The arm still hung motionless where it had been parked.
As Endeavor sped over the dark South Pacific toward the New Hebrides Islands 1,200 miles and four flying minutes away, Colonel Parker floated at Enright's left side. The AC's left boot was anchored to a foot restraint on the flightdeck floor. His right foot was cocked behind his left ankle. With his weightless legs flexed at the knees, Parker had assumed the resting position of horses. Without thought, Parker stroked his painful and throbbing right leg. The knee pain radiated upward into his thigh across his groin and into his right hip. His sigh of anguish rode sufficient breath to trigger his voice-activated microphone at his lips.
“You okay, Will?” Enright queried with both of his hands full of RMS controls.
“Huh? . . . Right and tight, Number One . . . While you fly the arm to the plasma package, I'm goin' to visit the biffy.”
“Don't fall in, Will. It's a long way down! . . . And don't flush until the train leaves the station.” Enright grinned behind his closed visor toward the tall pilot's back. The AC had already pulled his plugs and floated toward the forward cockpit.