Andy Thomas - "Rendezvous and Docking"

During his stay on the space station Mir, U.S. astronaut Andy Thomas published several "Letter from the Outpost," to family and friends on Earth. Here is one of them.

"Rendezvous and Docking with Space Station Mir," by Andy Thomas, March 1998.

Following launch of STS-89 and its configuration for on-orbit operations as a spacecraft, the process of synchronizing our flight path to that of the Mir space station began. This is not as easy a process as one might first think, and you cannot just point towards Mir and fly over to it.

The reason has to do with the fact that both vehicles are in Earth orbit, and constrained by the laws of orbital mechanics. For example, imagine you want to catch up to another spacecraft ahead of you. If you just accelerate toward it, you will increase your speed around the Earth slightly. But this makes you spin a bit faster around the Earth, which throws you outward to a slightly higher altitude. Here the orbit is you will actually slow down and recede from the craft you are trying to catch up to. And the converse happens if you are trying to separate from another orbiting spacecraft. The consequence of this seemingly paradoxical behavior is basically that you have to slow down to catch up to a spacecraft ahead of you, and vice versa.

The shuttle crew used a carefully controlled sequence of jet firings to account for these effects and provide the right relative motion to bring the shuttle close in to the station. Then they manually flew the remaining distance using visual cues from targets located on the Mir docking module.

We could see the station out the overhead windows, first as a point of light off in the distance that slowly grew brighter as we approached. Soon the characteristic shape of Mir could be made out with its cruciform layout of modules and their protruding solar arrays. These panels are very wing like in their shape, and indeed Mir has often been likened to a giant insect in its appearance. We slowly approached Mir from below toward the Kristall module that carries the docking fixture.

Mounted on our Spacehab tunnel was a similar docking fixture, and these latched together when the vehicles made contact in the final moments of the rendezvous. Locking latches were then activated and screws pulled the craft together to seal the attachment. We were now one large orbiting complex.

After checking the integrity of the pressure seals, we were finally able to open the hatch and meet up with the Mir-24 crew, Anatoly Solovyev and Pavel Vinogradov, as well as David Wolf, the US astronaut I was to replace. We proceeded into the Mir and joined them in the Base Block, or central core module of the station for exchange of gifts, as well as a meal.

I have to admit, my first views of the station were a little daunting, and it was very confining as we floated down the Kristall module to the Base Block. There was a lot of equipment stowed on all the panels and in every available location. But it did open out at the Base Block which is more spacious by comparison.

The second docked day was the day I officially became a Mir crew member. This took place with the change out of David Wolf's seat in the Soyuz capsule for mine, as well as checking the Russian pressure suit used during landing. At this time its fit and pressure integrity are checked, and these are significant events, because the Soyuz is the return vehicle that is used in the event of an emergency evacuation of the station. The suit fit is particularly important, and to put it on you have to be able to pull it over your head. But the Mir commander and I were unable to get me into my suit. In zero-g your spine expands a little making you taller and this, as well as the original very tight fit of the suit prevented me from donning it. The commander and I agreed, with concurrence from specialists in Moscow to let out some of the adjustment built into the suit so that I could get it on. The suit then fit properly, and I became the NASA-7 Mir crew member.

The next few days were spent in transferring all the supplies to the Mir, as well as bringing back all the instrumentation, equipment and experimental results from David Wolf's tenure onboard. We also carried water over to the station and used the shuttle oxygen supply to boost the oxygen level in the station.

On the fourth docked day, after quite busy STS-89 pulling away work by the STS-89 crew, it was time to say from Mir farewell, close the hatch and undock. This was a moment of mixed emotions for me. On the one hand I was sorry to see my colleagues leave, but on the other, it meant that I was now able to get on with the mission and work assigned to me. The shuttle was a breathtaking sight as it pulled away and flew around the station. During the daylight phase of the orbit the brilliant white of its tiled insulation system was caught in the sunlight. In the night passes the plumes of flame coming from the jet control system would light up the surrounding elements of the station.

It was not long before they were out of sight and I was now totally committed to my stay on Mir for the next four months.

As soon as the shuttle had left, I then had to prepare my living area and also prepare for the arrival of the next Mir crew coming to assume the operations of the station. I will continue with this in the next letter.