Ask the Crew: STS-92

From: Kathy Taylor, age 25
To: Mission Specialist Bill McArthur

Question: Using the S-band video system shouldn't we be able to have uninterrupted images from the shuttle, or does it use more power than the Ku band?

McArthur: INCO can probably address the power consumption issue. The issue for the uninterrupted video, though, is in the data rate. The Ku-band system is capable of 2 megabits per second or 4 megabits per second downlink; that's up to four million bits of information per second whereas the S-band is a total of 192 kilobytes in high, and of course part of that is used for data, part of it is used for voice, leaving only 128 kilobytes per second for us to use for other downlink such as the sequential still videos. So that's the deal, it's all bandwidth. It's a whole lot like the difference between an old 2400 (baud) modem and having a DSL or high speed Internet connection.

From: Allan Garrison, Statesville, North Carolina, age 46
To: Mission Specialist Bill McArthur

Question: Will the new Pressurized Mating Adapter 3 replace or add to the space station's docking structures?

McArthur: PMA 3 is an addition to PMA 2 to which we're docked and PMA 1, which joins Unity to Zarya and PMA 2 is going to be moved later but PMA 3 is an addition.

From: Jason Trimble, Ottawa, Ontario, Canada, age 30
To: Pilot Pam Melroy

Question: When the shuttle and the ISS are docked together, does movement of the shuttle with the thrusters cause stress on station joints or the station docking port?

Melroy: Yes, as a matter of fact, it does cause stress on all of the attached points all throughout the station. And an important aspect of this is when we were bolting Z1 and PMA 3 on to the station using the Common Berthing Mechanism. While we were driving the bolts, we had to take the shuttle into free drift so none of the thrusters were firing so that we didn't add any stresses to that attach point.

From: Doug McGregor, Ottawa, Ontario, Canada, age 48
To: Mission Specialist Bill McArthur

Question: I have noticed that the EVA suits are pressurized to about 3.5 PSI -- pounds per square inch. At so low a pressure, do the astronauts not feel light-headed, or is this pressure a compromise between just keeping it high enough for the health of the space walkers and not having the pressure too high so that the EVA suits would be too stiff to work in?

McArthur: That's an excellent question. We actually pressurize nominally to about 4.3 pounds per square inch. But it's pure oxygen and so that keeps the oxygen concentration in our blood at a very normal level so we can continue to operate at a fairly high metabolic rate. In other words, doing some fairly strenuous physical work outside. But you're correct, it is a compromise between our health and our physical productivity, our ability to do work, and having pressure that's so high that the suits would be too stiff.

From: Daniel Solcher, San Antonio, Texas, U.S., age 32
To: Mission Specialist Michael Lopez-Alegria

Question: During the various EVAs outside the ISS or shuttle, was there any point when you gained a sense of your actual high speed of orbit as opposed to your relative speed of movement with the ISS? Also, what differences did you experience between your actual EVA and your training in the water tank? Finally, did you folks leave a small, surprise welcoming gift for Bill Shepherd and his team in anticipation of their arrival next month?

Lopez-Alegria: Well first, Daniel, you are right, usually when we are in the shuttle and look at the Earth we don't get a sense of very high speed. You know the 17,500 miles per hour that we are traveling, it is the same as being in a commercial airliner and looking down once you are at cruising altitude. You are going close to 600 some odd miles an hour, but looking down at the earth it looks like you are just scooting along at a normal pace. However, during EVA you get a little more sense of speed because when you are up on the robotic arm, I have found that being suspended out over the structure and with most of the world in view including my peripheral vision I did get more of a sense of the high speed that we are traveling.

In reference to your second question, the differences of course between the actual EVA and the water tank. The highlight is of course, visuals are not the same. And in the water you are fighting viscosity and buoyancy differences where as in space of course we are floating in a very good micro-g environment.

Finally, as for surprises that we may have left for Bill Shepherd and his crew, well we did leave a few things, but we don't want to talk about it; otherwise it wouldn't be a surprise.

From: D. Holland, Norfolk, Nebraska, U.S., age 44
To: Mission Specialist Koichi Wakata

Question: What is the g-force the astronauts experience during a launch?

Wakata: At launch the gravity that we experience is about 1.7 g's and by the time the solid rocket boosters are separated which is two minutes into the launch the g-force will be over 2 g's. At the separation of the solid rocket booster, the g-force will decrease to just over 1 g. During the last one minute of the ascent, which is for 8.5 minutes, when the main engines ignited the last full minute, we will experience about 3 g's, and when the main engines cut off around 8 minutes, 30 seconds, you go right into zero-g and everything starts to float around.

From: William Walsh, Cortland Manor, New York, U.S., age 38
To: Mission Specialist Michael Lopez-Alegria

Question: I've often wondered: how do the astronauts maintain their sense of balance in zero gravity? Does the absence of gravity make you disoriented all the time, or is it just a temporary setback during the first moments?

Lopez-Alegria: That is an excellent question. I guess it depends on how you define balance. The fact is once we get up here we really aren't standing any more, and I guess that defines balance as your ability to keep standing up. So in fact we do lose our sense of balance the whole time we are up here but the good news is that we don't need it. Does it make us feel disoriented? Well the only sense of orientation is visual so it is easy when you are looking at something close into your body, concentrating on something too, when you look away from [it] finally you will be in a different orientation than you were when you started and that can be... It is actually fairly pleasurable because you realize that you're in a completely different attitude but that it really doesn't matter. It is kind of a lot of fun; it is a positive aspect of being disoriented.

From: Paul, Winnipeg, Manitoba, Canada, age 9
To: Mission Specialist Jeff Wisoff

Question: What kind of exercises can you do in space?

McArthur: Paul, that is a good question. What we carry on the shuttle is something very similar to a mechanical bicycle, it bolts to the floor, it's called an ergometer and your shoes snap on to the pedals. You have a seat belt that holds you down on to the mechanical bicycle and of course in space, since you can orient yourself in any direction you want, you can pedal with your feet to exercise your legs, or you can take your shoes off the pedals and stand on the ceiling and hold the pedals in your hands to exercise your arms. So it gives you a good way to work out the body. We can change the resistance of the bicycle mechanically so that you can get whatever workload you want. That is pretty much how we exercise on the shuttle. We also carry some bungies that stretch to give you resistive exercise for your arms if you would like to do that as well.