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UPDATE # 54 - October 12, l998 PART 1: Plans for STS-9 PLANS FOR STS-95
Sorry this is late! Things are beginning to pile up quickly now that I've
returned to the home base, but I want to be sure to share with you news of
upcoming plans surrounding the next Shuttle flight:
It may seem that the Challenge Project is winding down since we completed
the mission in the Scott Carpenter Space Analog Station, successful
despite Hurricane Georges interruption. Nothing could be further from the
truth. The Challenge Mission focused on participants selected because
their lives spotlight the themes of lifelong learning and fitness. This
was meant to serve as an "anticipatory set" for John Glenn to return to
space after 36 years, to help us focus interest in STS-95.
On October 29, the planned date of launch of STS-95, Quest's Learning
Technologies Channel joins the Space Team Online and Challenge Projects to
celebrate this historic event live from the Kennedy Space Center. For two
hours prior to launch (scheduled for 2:00 KSC time {11:00 Pacific}),
participants may join a live webcast coming to you from the Press
Viewing site at the Kennedy Space Center where the air will be electric
with the preparations for launch.
During the first hour, the NASA Life Sciences will bring you Challenge
Project participants addressing the themes including space-based research
on aging of which Sen. Glenn will be a part. During the second hour, Mike
Ciannilli, a test project engineer at the Kennedy Space Center, will
describe the preparation of Shuttle Discovery and will let you know what
to anticipate during liftoff. During all of this, you will be able to
interact with questions fed to the online experts through a QuestChat
room.
At the appropriate time, we will switch to NASA TV, and you will be able
to watch the "real thing" from your computer desktop. Within the next day
or two you will find a link on the top page of the STO and Challenge
websites taking you to the site for this exciting event. Do mark your
calendars for this two-hour extravaganza!
I hope you'll plan to join us,
Linda
UPCOMING CHATS
->Thursday, October 15, 1998, 10 AM Pacific Time (1 PM Eastern Time):
Liz Bauer, hardware engineer at Johnson Space Center supporting the
International Space Station effort. Read Liz Bauer's profile at
http://quest.arc.nasa.gov/space/team/bauer
->Tuesday, October 20, 1998, 11 AM Pacific Time (2 PM Eastern Time):
Sebastian O'Kelly, aide to Senator John Glenn, and a part of the Challenge
Project can discuss Sen. Glenn's preparations for STS-95. Read Sebastian
O'Kelly's profile at:
http://quest.arc.nasa.gov/space/challenge/team/okelly.html
->Tuesday, October 20, 1998, Noon Pacific Time (3 PM Eastern Time):
John-Henry Williams, president, Hitter Communications as part of the
Challenge Project, can share the ways dad, Ted Williams, communicates the
themes of lifelong fitness and learning. Read John-Henry's profile at:
http://quest.arc.nasa.gov/space/challenge/team/williams.html
[Editor's note: Bill is an engineer involved in "rocket science." He works with a group that helps design, build, and test many of the rocket engines, valves, and propellant tanks on the Space Shuttle Orbiter vehicles.] WORKING WITH FIRECRACKERS IN THE PYROTECHNIC TESTS September 24, l998 Interviewer: Lori Keith We will always work on and perform pyrotechnic tests. These are done because this is how the shuttle and its various parts separate after liftoff. Pyrotechnic devices are explosives, like firecrackers, used inside the nuts or bolts that connect the solid rocket boosters to the external tank. When these explosives go off, or are detonated, the nuts break allowing the bolts to slip out, and the boosters fall off. The same thing happens when the shuttle separates from the external tank. The bolts and nuts are very large. This is all very controlled. This explosive material is raised in temperature electrically, using electric contacts. (See the diagram below.) When electrical current passes through these contacts, it heats it, causing the explosive material to ignite. This causes the explosion which breaks, or shears, the nuts in half. Explosive charges are also used to break metal, like to open a sealed valve separating two fluids. The explosion occurs when it is time for the two fluids to mix. These are also used on fluid flow paths for fluid systems, where no leakage can be tolerated. These are called pyro-valves. These are sometimes used when a payload is being carried in the shuttle that is to be deployed in space. The payload will have these types of valves to connect its engine system to its fuel system after the payload is deployed and a safe distance away from the shuttle. The charges are ignited and the payload, satellite or whatever, can then propel itself. When we enter the building where we do the pyrotechnic tests, we leave our badges on a board at the front of the building and use a special badge. The reason for this is so we know who is in the building at all times. This is a safety precaution used because of the nature of the work done in this building. We are currently testing 2 1/2" and 3 1/2" nuts for the shuttle. They are rather large and weigh about 15 pounds apiece. (See the pictures below.) Besides using pyrotechnics for separating nuts and bolts from each other and for opening and closing valves, they can be used for other different applications. Maybe we'll explore some of these other applications in the future. [Editor's note: Rick is an associate staff scientist/Research Engineer for the National Center for Microgravity Research at NASA Lewis Research Center. In this journal he helps to describe what he does - it's the first of two parts, this one focuses on Microgravity and how it enhances the study of combustion] WE'RE "UNDER PRESSURE" TO "PLAY WITH FIRE" ON THE SHUTTLE
September 21, l998
I work as a research engineer/scientist on micro-gravity combustion
research, and I'm going to tell you a few things about what I do. But
before I do that, I'll take a little time to explain a few things, like
what microgravity is and how it applies to combustion research. So bear
with me...to have a good picture of what a researcher does, you need to
know a little about what he's studying.
Microgravity combustion research is the study of how things burn when you
take away the influences of gravity. NASA is interested in this for
several reasons. The obvious reason is spacecraft fire safety. Since
it is well known that flames behave differently in reduced gravity, it
makes sense that you need to understand flame behavior if you want to
fight or (hopefully) prevent a fire in a spacecraft.
But that's not the ONLY reason we study "micro-gravity
combustion." We're also interested in this from a fundamental science
standpoint. Fire is an extremely complicated process, involving chemistry,
fluid dynamics, heat transfer and thermodynamics. Although fire is one of
man's oldest technologies, it is still understood in only a broad sense.
So by sorting out some of the fundamental details, we can learn enough
about the process to help us do all kinds of applied things.
Why do we study this in reduced (or "micro") gravity? The answer is one
word: buoyancy. This is something that everyone's familiar with (whether
they realize it or not); it is the tendency for hot gasses to rise...it is
exactly the reason that hot-air balloons can fly! This is also illustrated
by striking a match; the teardrop shape of the flame is due to the hot,
expanded gasses rising and being replaced by cool fresh gasses. The hot
gas rises because it is less dense than the cooler gas. Therefore the hot
gas weighs less (for those of you who have had a chemistry or physics
class, think about the ideal gas law: pv=NRT. Since density is 1/v {where
v is the specific volume}, as Temperature goes up, density goes down).
Buoyancy is an effect caused by gravity; if you take gravity away, there
are no buoyancy effects! Now, you might think, "Don't hot gasses expand
and get less dense whether there's gravity or not?" Sure they do . . . but
without gravity, the "heavy" (i.e., cooler) gasses don't get pulled down,
which means that the "lighter" (hot) gasses don't get pushed up.
Okay...so why do we study flames in reduced gravity? Why not just study
them in normal gravity? Well, we do study flames in normal gravity, so
that we can compare them to those in reduced gravity. But the reason we go
to all the trouble of removing (or minimizing) the effects of gravity is
that in normal gravity there is an airflow velocity that is induced by
the buoyant effects. To look at flow speeds that are less than that
produced by buoyancy, you have to take buoyancy away! Flow speed is a very
important factor in how flames burn. If you think back to our example of a
burning match, how do you put out a match? You blow on it! This is a case
where the flow speed is so high that the flame goes out, which goes to
show that flow velocity is important to how a flame burns! It turns out
that very low speed flows can have just as important of an effect on the
flame as a high-speed flow. So when you come right down to it, we study
how flames burn in the presence of very low speed air (oxidizer) flows.
Since the flow speed has such a big effect on how the flame works,
high-speed flows have a tendency to mask some of the other physics that
are happening in the flame. By reducing the flow velocity, we can also
gain some insight into what else is happening in the flame!
The next obvious question would seem to be, "So how do you take gravity
away? Isn't gravity EVERYWHERE?" The answer to that is, YES it is, but
we can, if we're clever, remove its effect on an experiment for some
(usually short) time. To see how we do that, think about standing on a
scale, on a diving board over a swimming pool. While you're still on the
board, the scale shows your weight, which is equal to the mass of your
body times the acceleration of gravity (F=ma, for those of you who've had
a physics class). Now imagine that you dive off the board into the pool
with the scale 'glued' to the bottom of your feet. While you're in the
air, you are in a state of freefall (mostly, at least; wind resistance is
pretty small for this example). Guess what the scale NOW measures?
NOTHING!! This is because the scale is falling at the same rate that your
body is. So there is no local acceleration (the 'a' term in the F=ma
equation) between your feet and the scale. (Another way of thinking about
that is that the ground {or diving board} is no longer there to push 'up'
against the back of the scale). So this tells us that an object in
freefall doesn't experience any local acceleration (of course, it's going
to experience some negative acceleration when it hits the bottom). The
freefalling body "feels" like it is in a state of "zero-gravity." We
researchers take advantage of that fact to do our experiments!
So you might ask, "What about the astronauts? They float around, and
they're in orbit, not falling!" Actually, yes they are! Many people think
they float because they are so far away from the Earth that they no longer
are affected by gravity. But the truth is that the acceleration from
gravity is almost as strong on them at that altitude as it is on us here
on Earth (not quite, but it's close). What's happening is that although
they are falling towards the ground constantly, they are moving forward so
fast that they are always 'falling over the horizon!'
This is easier to understand if you think about a "thought experiment"
that Isaac Newton invented. Think about a cannon placed on the top of a
VERY high mountain, aimed parallel to the ground. If you fire the cannon,
the ball will go a long way but will eventually fall to the ground. If
you fire the ball faster, it will travel farther but will still
eventually fall to the ground. However, if you fire it fast enough (and if
it doesn't slow down from air resistance), it will circle all the way
around the world and come back to where it started -- it will be in orbit!
That is exactly what is happening with an orbiting spacecraft!
Because of this, a spacecraft can stay in a period of freefall (and
therefore, "reduced gravity") for a long time. So this is a GREAT place to
do microgravity experiments, and, in fact, we do quite a lot of
experiments
on the Space Shuttle (and other spacecraft). But this is VERY expensive,
so we have to do a lot of our work in other ways...
So far, we've talked about two ways of putting an experiment in a
reduced-gravity environment. One way is to drop it and another is to put
it in a spacecraft in orbit. But space flight is expensive, and there are
clearly limits to how far you can drop something (in practical terms, you
can drop things hundreds of feet, which takes up to about 5-10 seconds
depending on the exact distance). So there needs to be other ways of
"creating" a reduced gravity environment, and there is. It turns out that
if you fly an airplane on a parabolic flight path (which is like the path
that a ball takes when you throw it a long way), during a portion of that
path, the airplane is in a kind of freefall. If you were to trace out the
path of the plane in the sky, it would look a lot like a really big roller
coaster hill. If the airplane is moving fast, it can trace out a very
large parabola (or "arc" because that's what it looks like), which then
gives about 20-30 seconds of low gravity time.
So that's a quick overview of why gravity is important to combustion, and
how you can take away the effects of gravity. But you might be wondering,
"What does a microgravity combustion research scientist actually DO?"
That's a good question . . .
[Read Part 2
<http://quest.arc.nasa.gov/space/team/journals/pettegrew/fireplay092198b.html>
to find out "the answer."]
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