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Ed Lu letter from space #4

20 June 2003

Progress

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. 

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. 

-Ed Lu -

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