“Twenty seconds to go.”
The pilots watched Mother’s green faces tick off the final seconds to automatic engine shutdown. They read the digital numerics from the screens together. Parker had his finger poised to manually give the stop command if Mother failed to pull the OMS plug herself.
“Five… Four… Three… Two… One… Auto shutdown.”
“Thank you, Mother,” Enright said with reverence as he patted the glareshield above the instrument panels.
The instant the OMS engine stopped automatically, all three fliers floated out of their seats as far as their lap belts. They were still in orbit, still weightless. All the OMS engine did was lower their 130-nautical-mile-high orbit to a low point some 12,000 miles on the other side of the planet. Were there no atmosphere, Endeavor would remain in this new, very lopsided orbit for centuries. What would bring her home was the air which they would now intersect in another twenty-two minutes at an altitude of 76 statute miles.
“Looky there, Jack. Delta-V of minus 269. Right smack on the nose! What a lady!”
Mother’s face told the crew that the five-minute OMS burn had slowed Shuttle’s forward velocity by 269 feet per second. Slowing Endeavor by this 183.4 statute miles per hour would cause her to strike the solid wall of air in another 6400 statute miles of flight.
“And we’re speeding up. Amazing, Will. So Kepler was right after all.”
At the moment the hot OMS engine stopped, Endeavor’s reduced speed began to increase. The rearward firing of the rocket, by inserting Shuttle into a lower orbit, dictated that the ship’s velocity must accelerate. Written three hundred years ago, Kepler’s laws of orbital mechanics argued that bodies in lower orbits must travel faster than bodies in higher orbits.
“Endeavor: Configure AOS by Botswana. Doppler ranging confirms your de-orbit burn. Digitals look very close to nominal.”
Still headsdown, Shuttle flew over open sea 120 miles southwest of Cape Town, South Africa.
“With you, Flight. Good burn.”
“Copy, AC. Great news!”
“Okay, Colorado: Burn on time. TIG 09 hours 55 minutes 12 seconds. Burn time 298 seconds. Delta-V 268 point 3 plus point-2 left. We have nulled the residuals. Stable trim. And we aligned the balls a while back. Jack is now purging the OMS plumbing.”
From his right seat, Enright directed gaseous nitrogen through the outer nozzle cone of the OMS engine to clean out the fuel which had been circulated through it to cool the engine bell during the rocket firing.
“And Flight, computer Major Mode 303 now running for descent. We’ll do the thermal conditioning in a minute for the aero surfaces.”
“Copy, Will. With you another 3 minutes.”
“Understand.”
Enright was directing warm hydraulic fluid into the movable control surfaces of the wings and tail. He warmed the complex plumbing to ready it for the re-entry heat load.
“Conditioning in progress, Flight. Vent doors closed.”
“Copy, Will.”
Mother had sealed the ten vent doors in the aft fuselage and payload bay to protect the closed bay from re-entry. Four vent doors in the cabin section, one on each wing and one in each of the two OMS pods also closed.
“Forward RCS pod not disabled. We’ll dump forward propellants further inbound.”
“Understand.”
Ordinarily, this would be the time when the 16 thrusters in the nose should be turned off for re-entry and their propellant reserves dumped overboard. But the crew elected to use these jets to help the remaining 14 jets in the one surviving OMS pod aft. The RCS jets were only needed until the ship glided below 339,000 feet 2 minutes 41 seconds after slamming into the atmosphere. From there, the wings’ flying surfaces would begin to take over the burden of steering.
“Traj One is up, Flight.”
“Copy, Will.”
The first of a series of re-entry plots was now on Mother’s televisions. The object of the computers and the crew is to steer a graphic Shuttle-bug down the curved graphs. To fly ahead of or behind the power curve would be fatal.
Underneath Shuttle at 10 hours 03 minutes, Port Elizabeth in darkness passed for a final 45-second landfall as the ship rounded South Africa for her last time.
“Endeavor: Sunrise in 7 minutes at 10 plus 10.”
“Okay, Flight.”
The ship was over water again.
“And preliminary tracking and ranging put Entry Interface at 10 hours 17 minutes 04 seconds, MET. We’ll refine that for you by IOS in 8 minutes.”
“Roger, Colorado. Twelve minutes to The Wall.”
“Your state vectors look real tight. You’re Go for pitch program to entry Alpha angle.”
“ ’Kay.”
Endeavor still flew upside down, tailfirst. On Parker’s hand commands to the control stick between his thighs, the RCS thrusters fired to pitch Shuttle’s tail up toward the nighttime sky for a half-circle cartwheel. The huge ship’s nose passed beneath the tail as she pitched around until her nose pointed toward Okinawa. Rightside up, nose forward, Shuttle’s nose was 40 degrees above horizontal for re-entry.
“LOS in 20 seconds, Will.”
“Okay, Flight. We are finally flying right: Heads up and feet down. Alpha 40 degrees up bubble. All set here.”
“Roger, Will. With you in 7…”
“Okay, Jack. Panel Overhead-8, OMS safing: Helium pressure vapor isolation valve, closed. Tank isolation open and cross-feed closed.”
“Done, Skipper.”
“And, computer Major Mode 303 running with attitude Item 24 Roll, and Item 25 Pitch, and Item 26 Yaw.” The AC tapped the EXEC computer key after tapping in each Item number into the computer keyboard. “Digital Autopilot set manual. And, my side, Panel Left-2: Cabin pressure relief, systems A and B to enable. Nose wheel steering to off; entry roll mode to off; speedbrake handle closed full forward. My side and yours, Jack: Air data probe set navigation. Speedbrake set auto. Guidance and Navigation, Panel F-2, Pitch to auto, Roll/Yaw to auto, and body flap to manual.”
After a ten-second nighttime landfall over Madagascar island, Endeavor flew headsup with her nose riding 40 degrees above the horizon. As the mission clocks passed 10 hours 10 minutes out and homeward bound, the orange sun exploded over the eastern horizon a thousand miles away.
“Won’t see that for a while, Will.” Enright spoke softly as he reached beneath his seat for the windows’ sunshades.
“You will, Jack. You’ll be in line for the left seat within eighteen months. You got lots of uptime left in you, buddy.”
“Hope so, Skipper.”
Outside the six forward windows, the low sun was brilliant where it climbed in the southern, mid-summer sky a week before Christmas. As Endeavor descended in the dawn toward the atmosphere seven minutes away, the television screens showed 6056 nautical miles to Runway 23, Okinawa. As the AC called up computer program Major Mode 304 for the first phase of the re-entry, Enright configured the electrical system switches at his right for the final plunge into the morning sky.
Parker was moving the control stick between his thighs for a final check of the ship’s aerodynamic control surfaces. With each twitch of the stick, pointers above the forward center television showed the amount of deflection generated in each surface by Endeavor’s four Aerosurface Amplifiers. Alexi Karpov looked over Enright’s left shoulder at the instrument displays.
“ASA ready and willing, Jack. Back to automatic trim.”