“P-52 completed, Jack. We have our REFSMAT.”
“Okay. Crankin’ reference stable member matrix into IMU Number Two. So, Skipper, which way is up?”
Will Parker raised a thumbs-up above the center console between their seats. He smiled and deep creases cracked around his eyes. “That way, Jack.”
“Pretty technical stuff,” Enright laughed 100 nautical miles above the black sea 48 minutes from home and 1,500 nautical miles west of Australia.
The crew’s momentary respite from work ended abruptly when a square light labeled SM ALERT lighted with a warning tone beneath the left CRT screen above the center console.
“Systems management!” the AC called as he pushed the alert-light pushbutton to kill the audio alarm. Above the center television, on the 40-light annunciator unit, the rectangular warning light labeled FUEL CELL REAC glowed ominously red.
“Running it down,” Enright said as he tapped out a sequence of numbers on his small keyboard on the center console by his left thigh. A fuel cell malfunction checklist blinked onto the right CRT screen.
Endeavor carries three independent electrical systems, each fed by the super-cold liquid oxygen and liquid hydrogen tanks nestled beneath the floor of the still-closed, payload bay. Each fuel cell contains 64 stacks, or chambers, where preheated liquid oxygen and hydrogen meet to form electricity and waste water. The water overflow is filtered and decontaminated with iodine for crew drinking. Each fuel cell generates direct-current electricity for one of three DC circuits: Main A, Main B, and Main C. Each DC bus is routed to three inverters which convert the direct current power into alternating current used by Shuttle’s systems. Fuel cell Number One feeds DC circuit Main A, which is converted to AC line AC-1. Fuel Cell Two feeds DC Main B and AC-2, while fuel cell Three powers DC Main C and AC-3.
“Looks like Main B, Skipper. Running it down…”
The electricity output meters and all electrical distribution controls are the domain of the copilot in the right seat. Enright followed the video checklist as he managed the bulky fuel cell by the switches and meters located in front of his face and next to his right arm on Panel Right-One on the cabin wall.
Enright first checked the temperatures in fuel cell Two’s twin stacks of electricity-generating cells.
“A hundred ninety degrees and two hundred ten degrees. Stack temps okay.”
The copilot examined the three round meters above his right knee on the forward panel. He turned a large, round knob until it pointed to Cell Two.
“Two kilowatts at 31 point 5 volts DC; 60 amps. Looks okay, Will.”
Then Enright asked the green CRT about cell Two’s water output.
“Damn. There it is, Skipper. Six pounds per hour water production. That’s two pounds too high. Got room? She’s barfin’ water.”
“Let’s see,” the Colonel drawled. “Plenty of room in potable water Tank B. Tune her down if you can and we can manage the damn thing later… I hope.”
Shuttle carries five potable water tanks for collecting water generated by the three fuel cells.
“Crankin’ her down, Skip. Okay. Lights out.”
The red Caution and Warning light flickered and winked out.
“We’ll let Mother in systems management mode keep an eye on that baby, Number One. Meanwhile, let’s go on down the routine.”
As the crew interrogated the computers, Mother put her finger on the fuel cell Two vitals, like any mother laying her face against a feverish brow. Enright followed his bloated baby out loud.
“Power controller assembly, check… load controller assembly, check… mid-power controller, check… forward load controller, check… aft load controller, check. Looks stable, Skipper. Three essential bus lines—1BC, 2CA, and 3AB — all look healthy. Strange glitch in there some’eres.”
“Fine, Jack. At least we won’t have to light the candles. Don’t want to repeat STS-2!”
Both fliers had thought of Shuttle Two in November 1981, which was brought home early after only half a mission when a whole fuel cell threw up and drowned in its own water.
The headphones crackled in the south sea night.
“Endeavor, Endeavor. Yarradee has downlink at fifty-one minutes. Be with you for six. We’re looking at a fuel-cell saturation C-and-W.”
“Mornin’, Australia. Rogo on the caution and warning,” the command pilot called to Australia’s western coastline, which Shuttle would not cross this pass as she coasted heads-up past and under Australia’s southern shore. “Number Two fuel cell burped up but Jack got a blue bag on her in time. Keepin’ an eye on it. We’ve aligned the platforms and everything is right and tight. How do we look by PM downlink?”
“Real fine, Will. Telemetry is coming in crisp and clean. You are in plane and closing on your target now fifteen miles ahead of you and ten above you. R and R-dot are right on. You have a Go for closed loop rendezvous.”
“Roger, buddy. Understand we can run with on-board range and range-rate digitals. How’s Brother Ivan?”
“Ah, we show Soyuz now in daylight just south of Norfolk Island, about 170 degrees east by 30 south. They’re radio silent within two miles of the target. They should be braking very soon. No comm with them at all so far.”
“Copy, Yarradee. We’re ready for Terminal Phase Initiate up here. Jack’s called up our MCC-3 digitals which you should be lookin’ at now.”
“We see it, Will. Mid-course correction three looks fine, well within your propellant budget. After you lose contact with Orrora, we want you to roll minus-Z well before sunrise which will be at seventy-six minutes, MET.”
“Got it, Flight.”
“Endeavor: Let’s see PCMMU Number Two for a while, please. Your downlink data still looks a bit noisy.”
“You got it, Flight.”
Endeavor’s Pulse Code Modulation Master Unit controls the flow of on-board operational instrumentation data from Shuttle’s systems by way of 13 signal conditioners. The signal conditioners convert Shuttle’s vital signs to computer talk which one of two PCMMU black boxes routes to a Frequency Division Multiplexer for telemetry broadcasting to the ground through the Network Signal Processor.
“And your TM data now looks real clean. Much better, Endeavor.”
“Fine, Flight,” the pilot in command radioed.
“Yeah, Will. We were afraid you had a quad glitch.”
Endeavor speaks to the ground over seven, S-band antennae: Four “quad” antennae surround the rear cockpit bulkhead; there is one “hemispheric” antenna in the cockpit ceiling and another on the underside of Shuttle’s nose behind the nose wheel well; and, the seventh antenna is located on Endeavor’s back just ahead of the closed payload bay doors. Mother chooses which antenna is the best for a direct shot to the ground stations. The crew can also pick the best antenna combination should the computers get lazy. In all, Shuttle carries 19 different antennae built by Watkins-Johnson in San Jose, California.