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“Right ADP inhibited,” Enright confirmed as his left hand touched the center console between himself and Parker.

Karpov intently watched the two serious pilots cover page after page of pre-descent checklists. Depending upon which pilot was closest to the switches and circuit breakers being checked off, one airman challenged the item while the other read back and touched the switch. The two armed air data probes were stowed within the cabin walls. They would deploy into the slipstream outside after Endeavor was well within the atmosphere.

Endeavor flew upside down over the north Pacific 1,436 statute miles due west of San Diego. The mission clock ticked up through 09 hours 18 minutes and the event timer ticked down past 37 minutes to de-orbit ignition of the right orbital maneuvering system rocket.

Inside Mother’s four primary General Purpose Computers, re-entry program OPS-3 was running. The fifth backup computer rode shotgun on the four main computers. Computer program Major Mode 301 supervised the de-orbit preparations.

“TACAN, Jack.”

The crew flipped to the checklist page for warming up the three navigation beacon receivers which would listen for the Okinawa instrument landing signals. The TACAN receivers would give the pilots range-to-go vectors when Endeavor acquired Kadena Air Base’s beacon 500 miles from Runway 23 about 19 minutes after hitting the atmosphere.

“Breaker AC-1, Panel Left-4, Row P,” Enright read aloud.

The AC touched the round black circuit breaker at his left elbow.

“Closed, Jack.”

“MDM, Flight Forward One, Overhead Panel-6, on.”

“On.”

“Channel select flight control system, set.”

The AC turned four thumb-wheels to bring a four-digit code into tiny windows.

“Flight control system channel set, set, set, and set.”

“TACAN Number One, mode select, Overhead Panel-7, to GPC.”

“Number One to General Purpose Computer.”

“Antenna select, Overhead Panel-7, auto.”

“Automatic.”

“Overhead Panel-7, tone ident off.”

“Identifier off… TACAN Number One ready.”

The crew repeated the TACAN receiver protocol for receivers Number Two and Three.

“Endeavor, Endeavor: Configure AOS by Goldstone at 09 Hours 20 Minutes.”

“With you, Flight.”

“Copy, Will. We remind you of sunset in 10 minutes. We want you to shoot a final P-52 alignment after sundown. And you can dump the 0I data now. We’ll update your state vectors in 2 minutes. For data dump, use high bit rate, please.”

“Rogo, California. Operational Instrumentation comin’ atcha. We’ll get the balls aligned at about 9½.”

As Parker spoke, he could see the inverted Pacific outside as Shuttle cruised a thousand miles west of Baja California. The AC could not see land on the hazy western horizon. The ship flew heads-down, tailfirst, ready for the OMS burn. Enright double checked his side of the cockpit to confirm that Shuttle’s three main engines remained slightly retracted within the square tail section for protection from reentry’s searing fury.

“Okay, Jack. MLS Number One: Breaker Main A, Panel Overhead-14, Row E, closed.”

“Closed.”

“MLS One to off, Overhead-8.”

“Off.”

“Channel select, Overhead-8.”

“Set, set, set, and set.”

The three receivers for the Microwave Landing System were checked. These instrument landing beacons guide the 100-ton glider’s final approach when the ground’s beacons are picked up by Mother 12 miles from the runway at an altitude of 18,000 feet. The crew checked out MLS receivers Two and Three.

“Next, radar altimeter, Number One: Breaker, Main A, Overhead-14, Row E, closed.”

“Closed, Skipper.”

“MDM, Flight Forward One, on, Overhead-6.”

“On.”

“Radar altimeter One, off.”

“Number One, off.”

The routine was repeated for radar altimeter Number Two. These two ground-sensing beacons come on when Endeavor descends below 5,000 feet. These C-Band radio signals are vital to the last 100 feet of the final approach to landing.

“Endeavor: Your data dump is in. Your state vectors are now coming up. Colorado standing by through GDX.”

“Rogo, Goldstone… Aerosurface amplifiers, Jack. Number One ASA.”

The aerosurface electronics receive and generate computer commands to guide Shuttle’s aerodynamic control surfaces: the elevon-ailerons on the back edges of each wing for roll control and pitch control, the tail’s vertical rudder for side-to-side, yaw control and turn coordination, and the tail’s speed brakes. ASA black boxes also work the body flap under the tail for center-of-gravity, trim control during descent. Four separate flight control system channels work the four aerosurface activation loops.

“FCS, Number One, channel select, lever-locked auto, Panel Center-3.”

“Auto,” Parker replied as he touched the center console under his right arm.

“MDM, Flight Forward One, Overhead-6, on.”

“On.”

“MDM, Flight Forward Two, Overhead-6, on.”

“On.”

“Flight Forward Three, Overhead-6, on.”

“On.”

“ASA, Loop One, on.”

“Overhead-14, Main bus Alpha, ASA Number One is on.”

Aerosurface loops Two, Three, and Four were readied for coming home.

“Coming up on the edge by California, Endeavor. With you after de-orbit burn by Botswana in 36 minutes. Keep your feet dry and keep your airspeed up, guys.”

The starship’s final Stateside pass ended in static as Shuttle left the range limits of the Goldstone, California, antenna. The mission clock showed 09 hours 25 minutes and the event timer began the last 30 minutes of counting down to de-orbit ignition command. Endeavor’s ground track never touched the continental United States, home. She would not make a major landfall until Peru in 3,300 miles. The winged spacecraft arced down the North American western coastline, barely visible on the far purple horizon to the east of the inverted ship.

“Landing gear brakes, Jack. Main bus A, Overhead-14, on.”

“Main Alpha, on, Will.”

“Main bus Bravo, Overhead Panel-15, on.”

“Main B, on.”

“And, Main Charlie, Overhead-16, on.”

“Main C, on.”

“Your side, Jack, Panel Right-4, brake heater hydraulics A, on.”

“Alpha, on.”

“Brake heater hydraulics B, to on.”

“Bravo, on.” Enright touched the cluttered panel at his right elbow.

“And, heater C, on.”

“Charlie hot, Skipper.”

“ ’Kay… Nose wheel steering: Circuit breaker, Overhead Panel-14, Row E, Main bus A.”

“Bus Alpha, closed.”

“And my side, Panel Left-2: Nose wheel steering, mode select to GPC.”

“My side, Will, Right-4: Landing gear hydraulics isolated valve Number One to GPC; Number Two to GPC; and, Number Three also to General Purpose Computer.”

“Check, check and check.”

“Your side, Will, Panel Forward-6: Landing gear PBI to armed. And my side, Panel Forward-8, gear pushbutton indicator also armed.”

“Armed, Jack. My side, Left-4, Row P: Circuit breaker, landing gear sensors One and Two, closed and closed.”

At 09 hours 27 minutes, Mission Elapsed Time, Shuttle darted headsdown over the small speck of Isle de Revillagigedo, 730 nautical miles west of Mexico City. Only Alexi Karpov aft saw the little brown island through his window above his head. The sea 150 statute miles below was in deepening twilight although Endeavor had a broiling white sun low in the west out the front windows.

The AC turned up the forward flightdeck lights and he pulled off the tinted sunshades from his one front and two side windows. Enright did likewise.

“Horizontal Situation Indicator, Jack, my side and yours, select entry mode.”