The remote arm’s manual-augmented mode for flying the RMS is a semi-automatic routine. Although Mother flies the entire arm system in the automatic mode, Mother and the arm’s pilot work together in manual-augmented.
In the manual-augmented mode, the arm pilot steers only the arm’s far end, the end effector unit. The astronaut standing behind the command pilot’s empty seat steers the end effector with a gearshift-style stick protruding from its box housing between the two aft windows facing into the payload bay. This is the translational hand controller, THC. The THC directs the end effector in motion through space. Pushing the THC’s knobby handle forward toward the rear wall moves the end effector unit, EEU, toward Shuttle’s tail. Pulling on the THC directs the EEU backward toward the flightdeck. Pushing the THC left or right, up or down, moves the EEU in the same direction. Where Enright stood at Parker’s right, the copilot’s right hand can squeeze the pistol grip of the rotational hand controller, RHC. Located in the port corner of the aft flightdeck station, the RHC beneath the two CCTV screens directs the rotation of the EEU about the arm’s wrist joint. As the RHC handle is rocked, the end effector moves in the corresponding direction at its stationary position.
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.”