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Expedition
7 Flight Engineer and NASA ISS Science Officer Ed Lu. | | Related
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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.
Here is
Yuri and I at the TORU panel during the docking.
This
is what the Progress looks like when it is about 500 feet
from the ISS.
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