Periapsis

… continued from EVA

“RCS engaged. We’re lifting away from the station.”

Anna kept a close eye on the status indicators, applying minimal reaction control bursts to increase the shuttle’s separation from the alien structure. Gradually it fell away below them, invisible in the predawn darkness save for the computer-enhanced outlining painted by the lidar pings. At a hundred meters distance, nothing else distinguished it from the dark planet below, and the planet itself remained indiscernible except for the absence of stars in the absolute black of its nightside.

“I have radar lock on Aniara. Calculating maneuvers to match our apoapsis to her orbit.”

All the indicators remained green. So far, so good. Anna took several deep breaths, willing herself to relax. At two-hundred meters of separation, she used the RCS to spin the shuttle around, facing the nose toward the oncoming dawn. Far below, the advancing terminator revealed the blue planet, waxing past a quarter full, a thin atmospheric glow outlining the limb. The previous day’s cyclone was not in evidence, having advanced westward through the night.

“Engaging OMS. Moment of truth, guys. Cross your fingers.”

In order to lift the shuttle to higher altitude, Anna needed to apply prograde thrust, advancing them in the direction of their orbit. Earlier, she had ignored the usual procedures in favor of a fast and powerful direct line toward Aniara, hoping thereby to save Takashi’s life. That ended disastrously, and the retrograde vector of their acceleration instead resulted in the shuttle’s descent once the engine was cut off. Now Anna planned a more conventional ascent, pushing the shuttle to a higher, slower orbit by accelerating in the direction of their revolution about the planet. The maneuver would not be as fast, but it would be gentler.

At Anna’s command, liquid hydrogen and oxygen flowed into the combustion chambers of the twin orbital maneuvering system engines and ignited. The rapidly expanding gases pressed against the chamber walls, finding exits through the narrow thrust nozzles and explosively exiting via the nozzle cones, pushing the shuttle forward in a classic display of Newtonian physics, an equal and opposite reaction. Twin plumes of rocket exhaust streamed behind the accelerating shuttle, dissipating quickly to invisibility in the vacuum of space.

Less than a second after ignition, the pressure of exploding gases uncovered an irregularity in the starboard combustion chamber, a weakness in the chamber wall where the alien station’s defensive shot grazed but did not puncture it. Anna’s nozzle repair held, but a new hole formed, irregular and elongated. High-pressure gases found a new exit from the chamber, and milliseconds later the chamber wall blew out sideways, exploding through fuel lines and control machinery, then punching through the aft starboard hull of the shuttle. The sideways thrust threw the shuttle into a violent descending tumble before the automatic safety cutout shut down the engines.

The wrenching spin threw Anna against the seat restraints. She watched in horror as her status indicators lit up in an angry display of flashing red. Outside the cockpit windows, the stars arced from lower right to upper left, the shuttle spinning clockwise and tumbling end over end. The station hove into view, a dark band across the field of stars, far too close for comfort, and Anna realized they had tumbled past it in a steep descent toward the planet, missing it perhaps by mere meters. A second later it passed out of her view, replaced by the growing limb of the planet’s approaching dawn.

Anna heard irregular pumping sounds, and her first thought was that something had gone wrong with the air controls before she realized they were coming through the intercom, and that it was Laxmi and Jaci, in the compartment behind her, breathing fast and heavily as they held on against the spin.

“Hold on, I’m gonna try to get this spin under control.”

“Oh, and here I thought it was just me being deliriously happy we didn’t die in a massive explosion.”

“That could still happen, but you’re not dead yet, Jaci, and let’s plan to keep it that way.”

Anna focused her eyes on the display screen, ignoring the spinning field of stars. With some effort, and a few deep breaths, she held down the urge to give up her last meal while she concentrated on the nav ball. She grasped the control yoke and applied RCS thrust, counteracting the pitch, roll, and yaw of the shuttle. Red alarms continued to flash around the ball, but gradually she managed to slow its mad spinning, and when she looked out the windows again, the stars stabilized. She paused for a moment to let her heart rate slow and catch her breath, then clicked on the intercom.

“Ok, I have good news and bad news.”

“There’s good news?”

“You’re alive, aren’t you? That’s the good news, that and it doesn’t look like we’ll die immediately. Cabin pressure is holding stable, environmental systems are green, and we managed to not crash into the station as we spun past it. Also, most of the RCS thrusters are still working.”

“Most?”

“Yeah, that leads me to the bad news. We’ve lost the starboard OMS engine completely, and the starboard aft RCS thrusters seem to be out of commission as well. I’m guessing when the engine blew, it took out most of the components around it. I don’t know yet whether the port OMS will be functional at all, but even if it is, without the starboard aft RCS it’ll be difficult to achieve a stable thrust vector. Best case, I might be able to compensate with the forward RCS, but…”

“And worst case?”

“The port OMS explodes when I fire it up and we make a spectacular meteor show across the Kepler 62f sky.”

Everyone fell silent for a few moments, then Laxmi spoke for the first time since the shuttle lifted away from the station.

“Anna, are we going to be able to get back to the ship without the OMS?”

“No.”

“So, unless we can get the port engine working, we’re going to drift out here until we run out of air?”

“No, that’s not going to happen either.”

“What do you mean?”

“When the OMS failed and sent us into the spin, it pushed us around a fair amount, but mostly it seems to have been somewhat downward and retrograde. It also changed our inclination a few degrees. So, we’ve decircularized. We’re now on an elliptical orbit with our apoapsis slightly higher than the station altitude, and our periapsis significantly lower.”

“How much lower? Are we going to crash-land on the planet?”

“I’m still calculating that, but… no. The delta-v required to change the orbit that much would have required the engines to burn for a longer period of time. Still, short at it was, it was a massively uncontrolled burn, much more powerful than we would ever intentionally use, so… yeah… It looks like periapsis might be about ten-thousand kilometers.”

Jaci interjected from just behind Anna, “So we are gonna die when we run out of air, then.”

Anna turned around, realizing that he and Laxmi had come forward to peer over her shoulder through the cockpit windows. At that moment the sun rose over the planet’s horizon, flooding the cockpit with light, illuminating Jaci’s face as he peered at the blue expanse of ocean.

“No. We’ll die sooner than that. It’ll take a few orbits, and thus a few days, but eventually we’ll impact the station when approaching apoapsis. Or one of the tethers while at a lower altitude.”

“Aren’t you just a bundle of great news? Damn, Anna…”

Laxmi interrupted, “Can we maneuver around them?”

“Yes… until the fuel runs out. I think that’ll happen before we run out of air, so it looks like we’ll go out with a bang, not a whimper.”

… continued with Deorbital


header image credit: NASA/JPL-CalTech


© Matt Fraser and mattfraserbooks.com, 2018. Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Matt Fraser and mattfraserbooks.com with appropriate and specific direction to the original content.

3 thoughts on “Periapsis

  1. Pingback: WorkInProgress: Periapsis – Matt Fraser

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