Stephen Coonts - Combat

“Endeavour, Houston, Confirm orders.”

Diane shook her head as she said, “I want it on the record that I disagree with the orders, but I will execute them. I will secure all objects in preparation for the OMS burn.”

“Roger, Houston out.”

Slowly, Diane turned around, only to be welcomed by Colonel Frank Ward wearing a headset. The plastic oxygen mask floated under his square chin. The UNSC colonel had been listening to the conversation. McGregor stood in the back, flanked by two of Ward’s men. The short F-16 pilot looked quite helpless next to the large and muscular soldiers in all-black uniforms.

“All set?” Ward asked.

Diane Williams nodded and turned back to her instruments. “We’re about to start an orbital-change maneuver. Everyone take your seats.”

Ward floated toward the back of the flight deck and disappeared through one of the interdeck hatches. The two soldiers followed him.

McGregor approached Diane as she strapped herself to her seat and put the headgear back on.

“Diane, are you—”

“Is the airlock secured, Gary?”

“Ye — yes. It’s secured.”

“Good. Strap in. We’ve got work to do.”

Diane refused to let her emotions surface more than they already had. She was a professional. She was Endeavour’ s commander. She would behave as such for as long as the mission lasted.

Before starting the final approach to the ISS, Diane had to realign the Inertial Measurement Units — three all-attitude, four-gimbal, inertially stabilized platforms that provided critical inertial attitude and velocity data to Endeavour’ s General Purpose Computers — to maintain an accurate estimate of orbiter position and velocity during the orbital flight.

She did a quick radio check inside the orbiter to make sure all was secured. Satisfied, she reached for an overhead panel and enabled the Star Tracker system. Talk-back lights on the same panel told her both Star Tracker doors just forward and to the left of the front windowpanes had fully opened, exposing the two sophisticated bright object sensors to the cosmos. In addition to the nose attitude-control rockets, the Star Tracker system was another reason why the segmented mirror could not cover the orbiter’s nose section.

The Star Tracker system measured the line-of-sight vectors to the two brightest stars within the system’s field of view. The data was fed to the GPCs, which calculated the orientation between the selected stars and Endeavour to define the orbiter’s attitude and relative velocity. A comparison between the calculated attitude and the attitude measured by the Inertial Measuring Unit provided Diane with the correction factor necessary to null the IMU error.

The newly adjusted position and velocity vectors, or “state” vectors, were then compared to the International Space Station’s state vectors fed to Endeavour’ s GPCs via S-band telemetry communications relayed from Houston. Both sets of state vectors, updated once every millisecond as both Endeavour and the ISS orbited the Earth, were fed to the Guidance, Navigation, and Control software running in the GPCs, which in turn fired the Orbital Maneuvering System thrusters.

Diane’s eyes drifted to the OMS helium pressure and hydrazine propellant indicators as the engines came to life, unleashing twenty-six thousand pounds of thrust for fifteen seconds, directing a tail-first Endeavour toward its planned delivery orbit, nicknamed Delta. The mild deceleration force pressed her against the back of her flight seat as the southern portion of South America flashed across the top of the front windowpanes before disappearing behind the edge of the segmented mirror frame. In her mind, however, flashed the armed charges shifting inside their containers.

Focus!

A scan of control panel F7, where three five-inch-by-seven-inch green-on-green CRTs displayed the status of Endeavour’ s vital systems, showed nominal. The array of talk-back indicator lights between CRT#1 and CRT#2, and directly above CRT#3 also showed no warnings. The OMS helium pressure indicator to the left of CRT#3 marked 3,700 pounds per square inch, matching the digital readouts on CRT#1 directly above.

“ETA to Delta Orbit, fifteen minutes,” said McGregor, typing a few commands on the right keypad of the center console beneath control panel F7, while checking the readouts of the rendezvous radar measurement, which provided range and range rate to the station. Unlike the late nineties rendezvous radar systems, which could not be used until the orbiter got within fifteen miles of the target, the new system gave them ranging information from as far away as nine hundred miles.

Diane barely acknowledged it, her eyes switching back and forth between the mission event timer and CRT#1. At Delta Orbit, Endeavour would have achieved the necessary translational velocity to maintain an orbit six miles behind the ISS.

The GPCs stopped the OMS engines. “Burn complete,” she said as the software programmed the aft and forward Reaction Control System verniers to turn the orbiter without disturbing its translational velocity, positioning the mirror toward the ISS. The moment the inertial system detected that the orbiter achieved the desired attitude, the GPCs fired the RCS thrusters in the opposite direction to counter the rotation.

She briefly glanced at McGregor before using a secured S-band radio frequency and speaking into her voice-activated headset. “Houston, Endeavour.”

“ Go ahead, Endeavour.” She heard Jake’s voice coming through very clear. Audio and video communications, as well as telemetry-data transfer, were established through the S-band frequency. Information from Endeavour traveled to one of three Tracking and Data Relay Satellites (TDRS) in geosynchronous orbit, where the signal was amplified and relayed to White Sands Tracking Station in New Mexico, before arriving in Houston. Although the link had been established nearly thirty years before, it still remained the best and most reliable way to establish clean, secured, and uninterrupted communications during a mission.

“Houston, OMS burn complete. ETA to Delta thirteen minutes, twenty seconds, over.”

“Endeavour, you’re confirmed .”

“Will be within firing range in one minute,” Diane said while checking the leftover pressure on the OMS helium and propellant tanks, which told her that Endeavour now had enough fuel left for two more orbital maneuvers besides the deorbit burn at the end of the mission.

Diane glanced at McGregor, who brushed his mustache with a finger while frowning slightly, obviously feeling as nervous about this whole ordeal as she did.

“We’re in range,” McGregor said, while releasing his restraining harness and heading to the aft station, where he could make adjustments to the RMS arms if necessary.

Diane turned around and gave McGregor a glance. The Mission Pilot already had planted himself in front of the aft station, his right hand on the RMS hand controller, which was currently set to control the starboard mechanical arm.

As the orbiter quickly reached its orbital position behind the ISS, Diane prayed that the mirror would hold in place and that the soldiers kept the HEP safe.

His feet secured to Velcro attachments in front of the crew support station of the Habitation Module, Sergei Viktor Dudayev heard the proximity alarms disturb the peaceful whir of the air-revitalization system inside the International Space Station.

He checked the timer on the support station before pulling free of his Velcro anchor and propelling himself across the twenty feet that separated him from the Unity module, which connected to the aft section of the cylindrical module.