Around the Block
Michael Lopez-Alegria's Mission Log
On ISS, we have a three-car garage, and as of now we only have two cars. One car is Soyuz TMA-9, which we drove here three weeks ago. The other is Progress 22. We can’t drive the Progress; it has no seats, no life support system and no steering wheel. It’s an unmanned cargo vehicle that is basically like a U-haul trailer with an autopilot. The Progresses are launched full of supplies – water, fuel, clothes, groceries, spare parts, special tools, and sometimes special goodies – and two days later they automatically dock to the ISS on one of the three docking ports (spaces in our garage). They stay docked for a few months; long enough for us to slowly
empty their contents, then refill them with trash. After undocking they re-enter the Earth’s atmosphere where the intense heat of reentry destroys them, as well as their contents; nothing makes it to the ground. From the outside, Progress looks just like Soyuz. Luckily from the inside they look quite different, so there’s no danger of climbing into the wrong one when it’s time to come home.
Image to right: The docked Progress 22 spacecraft is featured in this image photographed by an Expedition 13 crew member from a window on the International Space Station. Image credit: NASA
Another important function of the Progress is to perform periodic re-boosts of the ISS. Very little in – or out of – this world is absolute, and that goes for the vacuum that surrounds us. The negligible density of particles at our orbital altitude of about 220 miles is enough to very gradually slow us down. This resistance is akin to what one feels when putting their hand out of the open car window while traveling down the highway, but much, much milder. Although we’re going a lot faster, no matter how fast you drive (about 17,500 miles per hour), the air is much, much less dense. Nonetheless, this friction results in minute deceleration, which in turn leads to a lowering of our altitude. If we did nothing about it, we would eventually reenter the Earth’s atmosphere, something that, due not only to pollution concerns, we want to avoid. So periodically the Progress’ main engine is used to gently push the station, much like a tug on a barge, forward. Though the Progress’ engine is plenty big for the Progress, it’s awfully small for the ISS. Still, every little bit helps.
Of our docking ports, two are on the nadir (lower) side of the station, facing the Earth, and the third is on the aft side of the station. In order to maximize the effect of the Progress’ engine during reboost, it makes sense to park it on the aft docking port so its thrust vector can push along the long axis of the station. A picture would be helpful, but I don’t have one handy. When Misha, Anousheh and I arrived a few weeks ago in our Soyuz, the aft port was the only space left in the garage. When Pavel, Jeff and Anousheh returned to Earth in Soyuz TMA-8, they left one of the nadir ports open. Yesterday’s task was to move from the aft port to the forward-most nadir port to make room for a Progress that will launch in a couple of weeks.
Moving your car from one spot in your garage to another is a simple task. If for some reason you can’t get back in the garage once you left it, you could always just park in the driveway. Not so here in space, so we must prepare the station for the possibility that once we undock, due to a technical problem that might develop, we might not be able to re-dock. It’s somewhat analogous to preparing your house to go on vacation, including securing the utilities, setting timers to control the lights, holding the mail and hiding everything valuable, just to move your car. For us, that means we close most of the internal hatches in the station (ten of them); in case one module should develop a leak we would lose only that module and not the whole station. We also power down most of the Russian segment (Mission Control in Houston does most of that via ground-controlled commands on the U.S. segment) and make some cooling system (plumbing) changes on the U.S. segment. Finally, we closed the final hatch behind us and settled in to our cramped Soyuz. Back to the womb.
Image to left: The Soyuz TMA-9 spacecraft, piloted by Mikhail Tyurin, maneuvers near the International Space Station. Image credit: NASA TV
After six hours of preparation, the actual undocking, flyaround and redocking took less than half an hour. Misha flew the vehicle manually, using a rotational hand controller in his right hand and translational hand controller in his left. There is nothing sophisticated about the Soyuz. Just like during the rendezvous, the maneuvering jets that fire to control our attitude and our translation sound like distant cannons, and there is no doubting their effectiveness. The effect of the jets makes the ride feel like the Autopia cars at Disneyland/World that you thought you were driving when you were a kid, but which were actually bouncing from one side of the guide rail to the other. Likewise, the Soyuz holds attitude a little like a drunk who is just sufficiently sober enough to stay on his feet. We backed away from the aft port, flew behind and below the station (all the while keeping our “nose” pointed at it so that Misha could observe it through a forward-looking periscope), then slowly but surely advanced toward our docking port. Misha aimed the periscope at a cross-shaped target that stands above a background target with a similar cross painted on it. This combination gives both attitude and translational errors to the pilot. His job was to make the standoff cross overlay the background target cross. We gradually slowed as we approached contact to a closure speed of 0.1 meters per second (about a quarter of a mile per hour). Upon contact of our docking probe with the receiving cone of ISS, all of the Soyuz’s forward firing thrusters push us to complete the mechanical mate. From that point we performed some leak checks, equalized pressure with the station, opened the transfer hatches, and said hello to our home once again. Luckily, no one broke in while we were gone.
Finally, we retraced our steps to make the station like it was when we got up that morning, about eighteen hours beforehand. There’s nothing like sleeping – or floating – in your own bed.