Stephen Coonts - Combat

“Coming up on the one-minute point on the countdown, everything is going smoothly. The firing system for the ground suppression water is armed.”

Diane battled her rocketing heartbeat. Just like in the Marines, Diane. she told herself. Relax and do what you do best!

“T minus thirty-seven seconds and counting; switching control of the launch to the computer sequence.”

Launch countdown control switched from KSC’s Launch Processing System to Endeavour’ s five General Purpose Computers, four working in parallel, the fifth checking the output from the other four.

“T minus twenty seconds: SRB hydraulic power unit started, the SRB nozzles have been moved to the start position. Coming up on fifteen. Switching to redundant start sequence. T minus twelve … eleven … ten … nine.”

Diane closed her eyes and visualized the sound-suppression water system nozzles popping up from the Mobile Launch Platform base, like lawn sprinklers, and beginning to spray water onto the base of the MLP at the rate of 900,000 gallons per minute in anticipation of main engine start.

“Seven … six … we’re going for main engine start!”

The GPCs ordered the opening of the liquid-hydrogen and liquid-oxygen feed valves of the huge External Tank, channeling both propellant and oxidizer to the Space Shuttle Main Engines through seventeen-inch-diameter feed lines, at the rate of 47,365 and 17,592 gallons per minute respectively. The highly cooled chemicals reached each of the SSMEs, where two sets of turbopumps boosted the chemicals to pressures of 6,500 PSI for the propellant and 7,400 PSI for the oxidizer. The chemicals reached the combustion chambers at fulminating speeds before exploding in a hypergolic reaction that created a colossal outburst of highly pressurized steam.

The soul-numbing rumble that followed reverberated through the entire orbiter as each of the three SSMEs, capable of unleashing 375,000 pounds of thrust, kicked into life at 120-millisecond intervals, and automatically throttled up to the ninety percent level.

“We’ve got main engine start … three … two!”

The GPCs verified that all three engines had maintained the required thrust level before firing the pyrotechnic device in each of the two Solid Rocket Boosters, and the resulting blast echoed through Diane’s soul as the astounding uproar of 7.5 million pounds of thrust thundered against the cushion of water above the Mobile Launch Platform. The acoustic shock wave pounded the ground on this warm and humid dawn as the brightness from Endeavour’ s engines illuminated the indigo sky, casting a yellowish glow for miles around.

The GPCs verified proper SRB ignition and, a fraction of a second later, initiated the eight explosive hold-down bolts — twenty — eight inches long and 3.5 inches thick — anchoring the shuttle to the Mobile Launch Platform. All three SSMEs throttled up to 104 percent, and the computers started the mission timer. Diane sensed upward motion.

“Liftoff! We have achieved liftoff!”

The 4.5-million-pound shuttle rose vertically in attitude hold until the SRBs’ nozzles cleared the tower by forty feet.

“Houston, Endeavour . Starting roll maneuver,” commented Diane in a monotone and controlled voice, shoving away all of her fears.

Endeavour began a combined roll, pitch, and yaw maneuver to position it head down, with the wings leveled and aligned with the launchpad.

“Roll maneuver completed.”

“Endeavour, Houston. Got a visual from the ground. You’re looking good. Mark twenty seconds, ” Jake Cohen said from JSC.

“Roger, Houston,” responded Diane.

Diane glanced at CRT#1, where an ascent-trajectory graph showed the desired ascent route and Endeavour’ s current position as the GPCs issued millions of commands every second to the gimbal-mounted SSMEs and the SRBs to keep the orbiter on track. With this part of the mission totally automated, Diane and McGregor limited themselves to monitoring equipment and instruments as the shuttle rose higher and higher, leaving behind a billowing trail of steam and smoke.

“Houston, Endeavour . Mark thirty seconds. Throttling down for Max Q.”

“Roger , Endeavour. Throttling down.”

Endeavour’s main engines throttled down to reduce the aerodynamic stress on the 21,000 thermal protection tiles glued to the orbiter’s all-aluminum skin as the vehicle approached the speed of sound.

“Passed Max Q. Engines back up to 104 percent,” reported Diane, as ice broke off from the External Tank and crashed against the front windowpanes. Diane saw their minute explosions before they disintegrated and washed away in the slipstream. One point three Mach. They had gone supersonic.

“Houston, Endeavour . Mark one minute ten seconds,” reported McGregor. “Five nautical miles high, three nautical miles downrange, velocity reads at 2,300 feet per second.”

Diane’s eyes drifted to CRT#1. Right on track , she thought. The GPCs and their complex ascent phase algorithms performed beautifully. Right next to CRT#1 were the master alarm warning lights. All looked normal. Below it she saw the mission timer.

“Mark one minute twenty seconds, Houston,” Diane read out. “Nine nautical miles high, six nautical miles downrange. Three thousand feet per second. Mark one minute thirty-five seconds.”

“Roger , Endeavour. We copy you at one minute forty-five seconds. You are now negative seats. Repeat. Negative seats.”

“Roger, negative seats,” responded Diane as Endeavour soared above the maximum altitude for safe use of ejection seats.

Diane checked the chamber pressure of both Solid Rocket Boosters. It had dropped to 55 PSI down from 400 PSI at liftoff. At 50 PSI both SRBs automatically shut off and the GPCs’ SRB separation sequence software automatically fired the bolts holding the SRBs to the External Tank.

Diane watched the pyrotechnic display as Endeavour , still mated to the ET, rocketed at nearly five thousand feet per second while both SRBs arced down toward the Atlantic almost ten miles below.

“Endeavour, Houston. Confirm SRB sep.”

“Smooth, Houston. Very smooth,” responded Diane. “Mark two minutes twenty-five seconds.”

“ Roger , Endeavour.”

Diane and McGregor monitored the readings from the CRTs for the next five minutes as Endeavour gathered speed and altitude while depleting the propellant and heavy oxidizer in the External Tank. This made the shuttle progressively lighter without a change in upward thrust, allowing Endeavour to accelerate to 24,000 feet per second — the speed necessary to break away from the Earth’s gravitational pull and achieve an orbital flight.

“Houston, Endeavour. Mark eight minutes twenty seconds, altitude sixty-three nautical miles, 645 nautical miles downrange. Standing by for MECO.”

“ Roger. Endeavour.”

Diane watched the GPCs initiating the Main Engine Cut Off sequence. All three SSMEs shut off the moment the feed-line valves connected to the umbilical cords coming out of the External Tank were closed. Eighteen seconds later, the computers jettisoned the ET by firing the explosive bolts anchoring it to the orbiter. Suddenly engulfed by the silence of space, Diane watched the ET separating with a velocity of four feet per second. The tank would continue on a suborbital trajectory, which would take whatever survived the reentry breakup to an impact location in the Indian Ocean.

“Houston, Endeavour . We have ET sep,” said McGregor.

“Roger , Endeavour. Eight minutes fifty-eight seconds, confirmed External Tank separation.”