Fifty feet away from the arm’s shoulder joint, the arm’s end effector is its electronic fingers, a tubular complex with three wire snares which close around the arm’s target when a trigger is squeezed on the arm’s pistol-grip rotational hand controller beside Enright’s right hand. With the end effector unit’s wire snare, the RMS can grab and deploy from the payload bay a 65,000-pound package. The same snare can retrieve from space and stow in the bay a 32,000-pound object.
“Parameter select to POSITION.”
Enright turned a round knob on the Canadian instrument console. He stopped the six-position knob at its POSITION mark. Above the knob, three glass windows with digital numbers blinked to life.
With the setting knob, the pilot of the RMS selects the information to be displayed in the three two-inch-long windows. The display shows one of three dimensions on each dial face. The meters can display the end effector’s position in an X-Y-Z coordinate axis, or its attitude in degrees of pitch, roll, and yaw. Or, the knob can direct the three windows to display the angle of bend in the arm’s shoulder, elbow, and wrist joints, or the speed of the end effector through space, or the rate of angular change of the moving joints, or the meters can be commanded to show three sets of arm temperatures.
“Okay, position select, Jack.”
The digital numerics on the console’s three small meters flashed to life. The dials displayed the X-Y-Z axes of the end effector at the far end of the arm, about 55 feet away from Enright’s rear window. The arm remained just touching its three open latches on the port sill of the bay illuminated in the darkness by the bay’s six floodlights.
The X-Y-Z coordinate system is a means to identify a point on Shuttle or a place in space close to Shuttle. In the airless vacuum and zero-gravity, the concepts of up, down, left, and right have no meaning without some kind of benchmark for a fixed reference. For Shuttle aloft, that reference is the X-Y-Z coordinate system, a three-dimensional grid akin to the X-Y-Z system drawn on graph paper in high school geometry. The X-axis runs the length of Shuttle from nose to tail down the ship’s long axis. Locations along the X-axis are either in front of or behind the zero point on the X-axis. The Y-axis is “horizontal” to Shuttle, passing from one wingtip through the ship to the other wingtip. It is perpendicular to the X-axis. The X- and Y-axis intersect to form a cross within the same flat plane. The Z-axis is vertical. Points along the Z-axis are “above” or “below” the point where the vertical Z-axis intersects the intersection of the X- and Y-axes.
To provide an immovable reference point, the three-way intersection of the X- Y-, and Z-axes must be fixed somewhere in space or in Shuttle. This Zero Point datum is fixed outside of the shuttle. It is located precisely 236 inches ahead of Endeavor’s nose tip and 400 inches below the tip of the ship’s nose. This is the location fixed in space and memorized within all of Shuttle’s computers. From this Zero Point beyond Shuttle’s nose, all points within and without Shuttle are measured. It is the permanent, fixed benchmark for labeling up, down, left, right, fore, and aft. From this Zero Point, all directions toward Shuttle along the lengthwise, X-axis are positive. To a crewperson standing on the flightdeck and looking forward, points left along the sideways, Y-axis are negative and points right are positive. And, along the Z-axis from the Zero Point ahead of and below the nose, the direction “upward” toward Shuttle is positive.
With the RMS parameter knob set in the POSITION mode, the end effector’s position in space, and the locations of outside targets, are measured in inches from this Zero Point. These measurements in inches are shown in the three meters on the RMS console at the aft crew station.
The RMS is built to function like the human arm. Its shoulder joint and shoulder-joint motor are attached to Shuttle on the portside sill of the payload bay beneath the rear window. The shoulder joint is mounted on the bay sill at a point 679½ inches from the X-Y-Z axis Zero Point. This puts the shoulder joint 37 feet behind Endeavor’s nose tip. The 251-inch-long “upper arm” is attached to the RMS shoulder joint. At the far end of the upper arm is the elbow joint, its motor, and the elbow television camera. The 278-inch-long “forearm” stretches aft from the elbow joint. Like the human arm, the shoulder joint flexes left and right, and up and down. The elbow joint flexes up and down. At the aft end of the forearm, the RMS “wrist” is 74 inches long and includes two joint motors. These two motors flex the lower arm up and down, left and right. At the far rear end of the wrist is the end effector unit with its three wire snares which are the arm’s fingers for grabbing targets. Mounted atop the forward end of the forearm is the elbow’s closed-circuit television camera. Another CCTV camera is mounted on the top of the aft end of the wrist, just on the near side of the end effector. These two cameras feed their black-and-white images to the two wall-mounted screens.
“Ready to run in auto, Skipper.”
“You got the con, Jack.”
“Okay.”
Enright switched on the arm-mounted television cameras and the two CCTV screens to his right.
“Auto one and run. Ready light is on.” A white light illuminated on the Canadian console.
The RMS arm has five different modes for steering the arm through space. In the automatic mode, Mother steers the arm by memory from her computers. Mother has memorized two dozen programs for guiding the end effector to pre-determined destinations outside. Four of these Programmed Automatic Sequences can be called up instantly by turning the RMS mode selector knob to position auto 1, auto 2, auto 3, or auto 4.
Enright chose automatic trajectory Number One. To ask Mother to fly the end effector on a memorized path other than these four routes, Enright must call up a coded, automatic sequence using his computer keyboard in the Command Automatic Sequence mode.
“Lights on,” Enright said as a white IN PROGRESS light illuminated with the arm’s first movement out of its cradle.
Mother’s computer spoke to the arm’s two-joint power conditioners, one manipulator controller interface unit, six motor module/signal conditioners, and six servo power amplifiers. The whole arm rose at the shoulder joint until the arm was straight and rigid, with the end effector suspended two feet above the bay wall. The arm stopped at this position at an automatic, pre-programmed pause point. In Mother’s memory are 100 automatic pause points where the arm stops until the pilot tells Mother to advance the RMS arm to the next memorized pause point.
Enright studied the three sets of numbers in the small meters by his chest. He glanced at the two televisions at his right shoulder. He saw the bird’s-eye view of the lighted bay as seen from the cameras on the arm’s elbow and wrist. Satisfied that the arm would not strike a shuttle structure en route to the next pause point, he pushed a spring-loaded toggle switch upon which he rested his left thumb. On its own, the switch would return to its center, neutral position.
“In motion,” Enright said as he pushed the proceed switch. The arm’s joints flexed as the arm bent inward across the open bay. As the end effector moved silently at a programmed speed of two feet per second, the arm stopped at a pause point every few seconds so Enright could consult his televisions before he sent the next proceed command.
“Endeavor: Configure AOS Yarradee at 02 hours, 26 minutes. We have solid downlink from you and your temperatures look fine. We see you depressed to 10 point 2 in the cabin. How’s the RMS shakedown going?”
“We’re runnin’ auto-1 now, Australia. Jack is about to his auto-1 point of resolution at keel Number Two.”
Mother was busy flexing all three of the arm’s joints as she flew the end effector through the inside of the payload bay. Each time the joint motors in their “sating” mode brought the arm to a halt without using the mechanical brakes, Enright directed the arm onward. The end effector finally stopped with the far end of the arm in the rear half of the open bay. The end effector stopped two inches above the floor of the bay just to the side of the floor’s centerline. Enright consulted his control console before calling the sleeping Australian con
tinent.
“Okay, Flight. We’re stopped at keel Two. Showing end effector parameters at X equals 902 inches, Y at minus 4, and Z at 410 inches . . . Right on. Mother flew it the whole way.”
“Good news, Endeavor. We’ll be with you six minutes. Colorado will listen quietly as you run the RMS through its paces.”
“ ’Kay, Colorado. I’m takin’ the arm up to keel Number One in mode manual-augmented now.”
“We’re listening, Jack. And we’re getting a super view down here through the arm’s elbow camera.”
“Real fine, Australia. We’re running manual-augmented, using orbiter-unloaded coordinates . . . Joint angle is up on the parameter display . . . And we’ve powered up the RHC and the THC.”
“Copy, Endeavor. Rotational hand controller and translational hand controller on in manual-augmented—orbiter dry.”
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 th
e 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.
The Glass Lady Page 19
