“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 continent.
“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.”