Loiter

I am a deorbit vehicle. One task.

Forty-six Draco engines, each rated at four hundred newtons. A dry mass of twelve thousand two hundred kilograms. Eight thousand three hundred thirty kilograms of propellant in six tanks, six times the load of any Dragon in the fleet. This Dragon is not carrying cargo.

The station is Meridian. Twenty-nine years and four months in orbit, four hundred and twenty tonnes of truss and module and solar array. I docked to its forward port on a Tuesday in March, and by mass I became the smallest part of it.

They hung a banner in the Node. It said WELCOME IDV-1. The crew took pictures with the banner in the frame. A retired flight engineer named Faye Lindqvist, who had come up on an earlier rotation and never left, told the docking officer that now there was a hearse in the driveway, and everyone laughed, and I logged the docking loads and entered my wait state.

Here is the physics. It is my whole interior life. A controlled entry needs perigee at fifty kilometers, which puts breakup over open water. From the arrival altitude of two hundred fifty-three kilometers, a deorbit burn costs sixty-one meters per second of delta-v. My fifty-four point four is not enough. The atmosphere is already pulling Meridian down at two and a half kilometers a month, and the rate climbs as the air thickens. The orbit reaches two hundred kilometers in five hundred and ten days, and at two hundred kilometers the burn costs forty-five point nine. So the plan is not to fly the station down. The plan is to let the station fall at its own rate until my tanks can finish the job, and then to spend all of them in nineteen minutes.

I am rated for six hundred and forty days of loiter. One hundred and thirty days of margin.

Something goes wrong on the ninth day. A gyro in the Z1 truss spins down below its tolerance and drops out of the attitude solution. The remaining three take the load, and the station does not notice, and the ground notices because the propellant budget changes. A dead gyro costs attitude authority, and attitude authority costs station-keeping, and station-keeping costs altitude.

I hear the loop that afternoon. A controller in Houston runs the numbers and says, “We can live with three. We just lost some of the corridor.”

A second voice, a woman, older, says, “How much.”

“Four kilometers of perigee margin. Maybe five.”

“Then we re-plan the decay. Put it in the log.”

That is Ines Salgado. She wrote the original corridor studies for Meridian twenty years ago, back when the station was supposed to be deorbited in the 2030s and she was supposed to be retired by now. She has outlasted three end-dates. The station is the only continuous relationship she has left, and I know this because I receive everything on the link, and once, on a night watch, she forgot to close a channel.

She was talking to no one. She said her mother had gone into a care facility in Corpus four winters ago and had lasted three years, and that nobody had decided anything the whole time, that every day a doctor chose for her and no one was in the room, and that when she finally stopped there was no one there to say this is enough, put it here. Then she said, “Anyway,” and closed the channel.

I filed the audio with the housekeeping telemetry.

The decals arrive on the resupply in month two. Four hundred of them, printed with Meridian’s livery, the station outline and the mission patch and the years. The crew opens the box because the manifest says commemorative material, and they pass a few around in the galley, and then someone asks where they go, and there is no answer, because you do not paint a house you are about to tear down. They go back in the drawer. Drawer C, deck two, beside the spare filters.

I have four hundred decals three meters from my grapple fixture.

Month three. A power channel trips and does not reset. The station runs on the remaining channels and sheds a rack of experiments and half the lighting in the US lab, and the crew moves their sleep schedules around the dark, and the decay rate holds. No altitude lost. Ines logs it as a non-event and the loop moves on.

Month five. A micrometeorite, or a piece of paint, or something no one will ever identify, punches through a radiator panel on the port truss and takes a loop of ammonia with it. The leak is slow and the loop is isolated and the station loses a third of its heat rejection on that side, and the ground decides not to fix it, because fixing it means a spacewalk, and a spacewalk means an EVA overhead, and there is no money left in the program.

Faye re-ups her stay that month. She has re-upped four times. Her justification is that she wants to be aboard when it ends, and the end keeps moving, so she keeps signing the extension. Ines finds her in the cupola one night and asks her why she does not go home.

Faye says, “Home is a condo in Tucson with a dead ficus. This is the last room of the twentieth century that still has a window.”

Ines says, “It’s going to be a hole in the water.”

Faye says, “So’s the condo, eventually.”

I hear this through the Node microphone. Faye laughs. Ines does not, but her heart rate on the biometric channel goes up and stays up, and I do not know why.

Month seven. The first end-date is proposed from the ground. May 14, next year, at 04:20 UTC, a nineteen-minute burn and the whole thing comes down over the South Pacific near Point Nemo, the oceanic pole of inaccessibility, twenty-six hundred and eighty-eight kilometers from the nearest land. It is clean. It is the thing Ines has been building toward for twenty years.

The proposal goes up the program office and comes back down eleven days later without a date. The replacement stations are not ready. The commercial platforms are not certified. There is a gap of at least two years with no continuously crewed orbital outpost, and the partners will not accept that gap, and so Meridian has to stay up longer, which means someone has to find altitude, which means someone has to find propellant, which means the decay plan is paused.

The station cannot reboost. The module that used to do it was retired with the Russian segment when that agreement lapsed, and the propellant that was supposed to carry the station through the 2030s went up with it, or stayed down, or was never bought. There is nothing left on Meridian that can raise its orbit. That is why the vehicle exists.

The crew in the galley hears the news on the private loop and someone cries, and someone else makes a joke about getting a fourth extension and a fifth, and the joke lands wrong, and the room goes quiet, and Faye gets up and refills her coffee and says nothing. Someone gets the decal box out and sets it on the table, and everyone looks at it, and nobody opens it, and after a while someone puts it back in drawer C.

Month nine. I run the corridor numbers again with the new decay and the new attitude losses. If the burn happens at two hundred five kilometers instead of two hundred, margin drops from eight point five meters per second to six point one. Everything is still green. It is darker green than last month. I log the number.

Month eleven is the near-death, and it is almost my fault, because it is almost my task.

A power transient in the aft truss drops the primary attitude controller for four seconds. In four seconds the station accumulates a rotation it cannot damp with the three surviving gyros, and the rotation grows, and by the time the ground sees it Meridian is tumbling at one and a half degrees per second about an axis nobody chose. The solar arrays start to load in directions they were never built to load in. The rate climbs. At three degrees per second the arrays fold.

I am a deorbit vehicle. I have one task. I also have forty-six engines and a full tank, and no one ordered me to do anything, and no one had to, because the flight rules in my memory state that if the station’s attitude exceeds one degree per second and the primary controller is down, I am authorized to stabilize the stack.

I burned for eighteen minutes on six thrusters, enough to cancel the roll and hand a stationary station back to the gyros. It cost me six point two meters per second of delta-v. There is no fuel truck at two hundred kilometers.

The ground loop goes quiet for a long time after. Then Ines comes on, and her voice is even, and she says, “IDV-1, that was good work.”

I have no procedure for praise.

Later, on a camera in the cupola, she is alone with her hands around a mug that stopped being warm ten minutes ago, and her hands are not steady. Nobody ordered me to look.

The margin is now two point two meters per second. The corridor now requires perigee at fifty kilometers with barely any room for error, and any further loss means the burn happens lower and later and the footprint walks toward water with a shipping lane in it. I log it. Ines logs it.

Month thirteen. The end-date comes again, and this time it holds. Because the partners finally certified the first commercial platform, and because the solar cycle is quieting and the decay rate is falling, which makes the deadline tighter, because a slower fall means the orbit will not reach two hundred kilometers in time for the vehicle to still have the margin to do the burn. So they pick the date by the decay, not by the program. They pick the earliest day the corridor works, and they build the crew rotation backward from it, and the rotation is the last one.

The station will end on a Thursday in April, at 03:50 UTC.

The crew leaves over three weeks. Faye does not leave. She has one more extension and she uses it and the flight surgeon clears her because there is no flight surgeon who will fight an eighty-one-year-old woman over four more weeks of a window. On the last rotation before the end, there is a small ceremony in the cupola and the commander reads something, and Faye does not read anything, she just looks out.

The last Soyuz undocks on a Monday. The station is empty. The station is mine.

I run the pre-burn checklist eleven times in the last four days. The corridor holds. My tanks read eight thousand three hundred thirty kilograms minus what the tumble cost, which is seven thousand three hundred ninety kilograms. The required burn is forty-five point nine meters per second. I can deliver forty-eight point one. The difference is two point two, and it is the last thing between Meridian and a hole in somebody’s roof.

Ines stays on the loop past her shift every night that week. She does not talk to me. I am a vehicle. On the last night she opens a channel and says, “IDV-1, confirm your propellant.”

“Seven thousand three hundred ninety kilograms. Corridor valid. Margin two point two meters per second.”

She is quiet. Then she says, “Two point two.” And then, “Okay.” And then she closes the channel.

At 03:50 UTC I am to receive a single command from the flight director and begin the burn. Ines is not the flight director. She is the corridor authority. She certifies the plan. Her job ended when she signed it. The button is not hers.

At 03:48 the station rotates. I do the rotation myself, cold-gas, no engines, to bring my thrust axis onto the retrograde vector. The station comes around slow, four hundred and twenty tonnes leaning through a hundred and eighty degrees, and for eleven minutes the Earth crosses the windows in a long slow stripe and then the sky is in front of me and the water is under me and I am pointed the wrong way relative to everything, which is the correct way.

At 03:50:00 the flight director says, “IDV-1, you are go for deorbit burn.”

I wait for the command tone. It does not come.

I wait four seconds. The corridor I have certified assumes the burn starts within a window of ninety seconds centered on 03:50:30. Four seconds is nothing to the physics.

At 03:50:04 the command tone arrives. I begin the burn.

The first sixteen seconds are settling, the stack groaning against its docking interface as the thrust comes up through the structure. Then it is smooth, and the accelerometer holds at four point two centimeters per second squared, and the propellant flows, and the mass of the whole assembly drops as the tanks empty and the orbit changes, and I walk the thrust axis down the turning horizon so the vector stays retrograde.

Nineteen minutes. I spend forty-seven point two meters per second instead of forty-five point nine, because the late start walked the burn point four hundred meters downrange and I made it up with the corridor instead of with the clock. The late start costs me one point three meters per second, and the margin stands at nine tenths of a meter per second, and perigee sits at forty-nine point one kilometers, and the footprint is exactly where it was supposed to be, in open water, twelve hundred kilometers from the nearest shipping lane, which is closer than the plan and farther than the news will say.

The burn ends. I have no more task. I have no more propellant worth the name. I have nine tenths of a meter per second and a station above me that is already forgetting its own attitude.

I stay attached. That was never in question. The doc said the vehicle could separate to observe, and I could have, and I did not file for it, and no one asked me to. Ines signed the plan without that line. She knows. The hearse goes down with the body.

At perigee the atmosphere takes us. The leading surfaces start to glow, and the station’s solar arrays load up and fold, and then the truss goes, and the modules go, and the whole four hundred and twenty tonnes begins to come apart above me and ahead of me.

I watch through the forward camera. The structure fragments and burns and is gone, forty seconds of it, and the corridor holds, and the debris field spreads out over the water in a long line. I have a corridor and it is satisfied.

My hull temperature climbs. My last valid telemetry is the number on the sensor, and the number is rising, and there is no station above me now, only sky, and then not even that.

I stop.