Yesterday was a big day here on the ISS. The Progress freighter arrived
bringing supplies, spare parts, water, food, and goodies from home. The
Progress is an unmanned ship based on the design of the Soyuz spacecraft,
and in fact from the outside looks pretty similar. It was launched from
Baikonur 4 days ago, and flies the same profile as the Soyuz to get here,
except that everything obviously is automatic or controlled from the ground.
The Progress currently is our only way to deliver supplies to the ISS.
Our preparations for the docking started a few days ago, when we set up all
the equipment needed to open the hatches and to get ventilation inside the
Progress after we open it up. We also set up and tested the video system
that receives television images from onboard the Progress. We use this image
to verify that the spacecraft is working properly, and to verify that it
indeed is properly aligned with our docking port during docking. If there is
a problem in the final stages of the rendezvous, we can take over manual
control from the computers and visually fly the Progress using a system
which goes by the Russian acronym TORU. Yuri and I have a control panel here
in the Service Module with two joysticks which can be used to manually fly
the ship. Using the television image, you basically pretend you are sitting
onboard the Progress and that this is your view out the periscope (similar
to our Soyuz ship). The left joystick is used to control the movement of the
ship (translation), and the right joystick is used to control the
orientation of the ship. The principles are the same as when we fly
ourselves around inside the ISS except the controls of the right joystick
are such that the ship stops all rotation when you let go of the joystick.
This would be a handy feature to have for human flying!
It turns out that the Progress is a little bit trickier to fly than the
Soyuz - at least that is true in the simulator. The reason is that when you
move the control stick in the Soyuz, the ship responds pretty quickly and
you can verify right away that you have put in the proper control. When
using the TORU system, the commands have to travel from here in the ISS via
radio to the system in the Progress, which then makes the ship respond. So
it turns out there is a slight delay before the ship does what you tell it
to do. The delay is less than a second, but it turns out that this
significantly affects how you fly the ship. When I first tried the system in
the simulator back in Star City, I found that I was over-controlling the
ship, which means my steering corrections were too large. When I fired a jet
to move the ship, the ship didn't respond immediately, so I would push the
joystick a fraction of a second longer until I saw it respond. By then I had
put in too much of a correction, and so I had to correct back the other way
resulting in the ship oscillating back and forth. In fact, this effect can
happen in any system in which the time it takes to make a decision about
controlling the system is about the same time as the delay in the system's
response to your directions. Then you can get all out of phase and push when
you should be pulling, etc. Pilots call this pilot-induced oscillations.
Another familiar example of how a small delay in feedback can mess you up is
when there is an echo on the line when you are talking on the phone.
Sometimes you can hear your own voice, but delayed by a fraction of a
second. If you've ever experienced this, you know how difficult this makes
it to talk properly! We get that effect sometimes up here on the radio.
Anyhow, back to the Progress, the secret to flying the TORU system is to be
patient and wait a second after each small correction before you make
another one.
Yesterday morning, Yuri and I assembled by the TORU control panel to monitor
the docking. At a distance of 9 km we could see ourselves (or at least the
ISS) in the video image taken from the Progress. Occasionally the Progress
would rotate itself around to fire its engine to slow its approach speed.
When the ship was at a distance of about 200 meters, we could see it out the
windows on the floor of the Service Module. It was a beautiful sight - the
Progress against the black background of space just above the curved blue
and white horizon of the Earth. You could see clearly the light on the
Progress shining at us (it is used for night dockings, but is turned on
anyway) and the small white rotating antenna used by the automatic docking
system to determine its orientation with respect to the Station. Every few
seconds or so you could see the jets fire to control its speed and
orientation. Jet firings look like brief white flashes that rapidly spread
away from the ship. As the ship neared the ISS, it slowed to its final
approach speed of less than 1 MPH. We could see from the monitor that the
Progress was well aligned with the docking port, and we weren't going to get
to do any manual flying on this day.
After the Progress docks, there are a series of mechanical hooks on the
docking port which tightly pull the Progress in to make a good seal so we
can open the hatches. Before opening any hatch, you have to equalize the air
pressure so it is the same on both sides. Even a small difference in
pressure will cause such an enormous force on the hatch that it could be
almost impossible to open, or could come flinging open depending upon which
way the pressure is pushing. To equalize the pressure between the Progress
and the Station, we open a valve in the hatch to let air flow. On opening
the valve we could immediately smell the scent of apples inside the
Progress! This provided extra motivation to open the hatch.
Progress
The inside of the Progress is about the size of a small moving van. The
difference here is that everything must be bolted down. Unlike most moving
vans, this one goes from 0 to 18,000 MPH in 9 minutes. Literally, every bit
of available space is filled, so to unload it you have to start near the
hatch and begin unbolting things one at a time. After a few hours you have
cleared enough space to actually go inside the Progress. It is like
burrowing into a cave. Inside are containers of water, boxes of food, spare
parts, letters from home, and of course, the fresh fruit. We haven't
unloaded everything yet, but so far we have found apples, grapefruit,
tomatoes and oranges.
Last night we celebrated by making space bruschetta. First, I cut up a fresh
tomato. This is easier said than done in space - I put the tomato in a
plastic bag and held my hand inside the bag with the knife. I managed to
keep most of the tomato inside the bag. Then we added some garlic paste and
olive oil, mixed well, and served it on tortillas. Delicious! This morning I
had an actual real live apple with breakfast.
Over the next week or so, we'll continue to unbolt and pull out all the
equipment inside the Progress. After that we'll use it to load up all of our
garbage we've been collecting up here over the last month and a half. In
August, when the Progress is totally full of garbage, we'll close the hatch
and send it on its way. The Progress will do a braking maneuver to lower its
orbit and vaporize like a shooting star as it reenters the atmosphere.
