[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Live From Mars - Update #42
L I V E F R O M M A R S - A Passport to Knowledge Project
UPDATE # 42 - July 2, 1997
SPECIAL REPORT: BEHIND THE SCENES FOR PATHFINDER'S LANDING ON MARS
PART 1: A mile-a-minute day
PART 2: A long road nearing the end
PART 2: Subscribing/unsubscribing: how to do it
______________________________________________________
A MILE-A-MINUTE DAY
Rob Manning
July 2, 1997: 6:30pm Pacific
This has been a mile-a-minute type of day. I'll tell you, the
excitement and drama of what's going on is up to a high pitch.
Everyone's fingers are clammy!
I slept pretty well last night, though I did wake up at 4 a.m. to do
some work. I sat in my bathrobe at my dining room table going
through all these numbers, looking at the times and getting the
idea that yes, this IS going to work!
When we run through the software in our testbed we actually can
watch all the events that happen. We have support equipment that
listens in to what the computer and the hardware are doing,
including opening the airbags and rockets (even though there are no
real rockets opening). We can make sure that all the events that are
supposed to happen, happen and that they are happening at the right
instant. We're actually trying to make sure that everything happens
to within a fraction of a second of accuracy. When we do one of
these tests, it produces a whole ream of paper that unfortunately
we have to go through by hand to really understand what's going on.
However, every time we run these tests the software causes the
rockets to fire within a few thousandths of a second of when they're
supposed to fire. This is better than we need, by a lot! It's so much
fun to confirm that over and over again!
I spent the rest of today answering a lot of fast questions from the
media. Our science team did a press conference and all of us were
eagerly listening to see how they would handle the bombardment of
questions. We're interested to know what kind of questions people
have, so we can tune our answers to match the questions. One of the
problems we have is that we're so familiar with this mission, we
know all the details, that it's hard to really know how much other
people know about it. So we basically try to listen to other people's
questions and who's doing the asking and then try to judge how to
explain all of this. There are a lot of complicated series of events.
It's especially hard talking with television reporters because we
have to explain things very succinctly and quickly, most importantly
very quickly, without using any acronyms and trying to use words
that people can see very visually. It takes practice and we're
practicing.
Tonight, in my free time (which I have very little of!) I'm working on
a script that I'm going to read during the landing. I'm trying to
synchronize my talking with what I think should be going on at each
given moment. I know there's going to be a lot of people listening, all
over the world, and I have to make sure I say the right thing and that
I don't misplace my tongue. Most importantly, I have to keep my
concentration up because I have to get up at 1 a.m. to spend the
early morning hours as mission manager for that phase of the
descent and landing.
Just a few moments ago, we may have sent (we don't know yet for
sure) the very last command to the spacecraft until after it lands.
We do the best job we can aiming for Mars, but Mars moves! Mars'
position is being influenced by Jupiter and the asteroids. Just today
we started to see a tug of Mars. Right now Mars looks like the Moon
from Earth; that's how big it is if you were on the spacecraft. We are
less than a million miles from Mars. And at that distance Mars is
starting to pull a little bit and the spacecraft is starting to very
slowly accelerate toward Mars, as if it's falling into Mars. Hopefully
it falls just the right way so it skims the atmosphere to slow down.
It looks like we are a little bit off target, but not too much. We're
not going to do to much to change the direction of travel but we
want to tell the software onboard exactly where it's going so the
spacecraft will open the parachute at just the right height. Even
though the software onboard Pathfinder is running and the clocks
are ticking, anytime between now and 8:30 a.m., Pacific, Friday, we
can send commands to the spacecraft to update these key
parameters that control how the parachute gets opened. We have
the ability to very quickly generate these commands based on the
latest knowledge of where we're going. and that's based on
information gathered by our navigators.
The Navigation team works together to take our best estimate of
where we think we're going and figure out exactly how to take that
information and propagate it to the ground. They can actually
simulate the spacecraft flying through a computer-generated
atmosphere and figure out how the lift and drag work. Pathfinder
looks like a funny-shaped glider and we can actually go through the
process of simulating that whole lift, drag and acceleration due to
gravity (the tug of Mars) all the way down until that point where the
parachute opens up and beyond. We do this over and over again with
the new information we get.
The parachute will open up anywhere from about 5 km above the
ground to as high as 11 km or more. In fact it looks like, from where
we're coming right now, we're going to open the parachute a little on
the high side, which means it'll take a longer time to soar to the
ground. The spacecraft is soaring to the ground at a very, very high
speed and once the parachute opens it has got a lot to do: get rid of
the heat shields, repel down a 20-meter bridle, turn on the radar and
start looking for the ground and begin the processing. On top of all of
this, Pathfinder has to have enough time to figure out how high it is
above the ground and how fast it's going in order to open the airbags.
The airbags open about 1000 feet above the ground and once they
open, the lander can no longer see the ground through the airbags.
That's the reason that we do these updates-to get a better sense
of where we're going and to get the parameters just right.
The command we sent about 15 minutes ago is still flying through
space at this minute. It only takes about 1000 bits of information,
which we send from the Deep Space Network in Goldstone, CA. These
1000 bits are shipped up one bit at a time, back-to-back. But even
though it takes awhile to get all those bits out the antenna, by the
time the last bit is out, the first bit is still flying through space.
All those thousand bits are like little soldiers marching in series
until they get to Mars, at which time they'll be received one at a
time by the spacecraft.
My day isn't over yet. Now I must prepare for tomorrow's press
conference...
______________________________________________________
A LONG ROAD NEARING AN END
Linda Robeck-Fuhrman, Deputy Mechanical Engineering Manager for
Pathfinder Assembly, Test, and Launch Operations
July 2
For Linda, Pathfinder's July 4th landing is the end of a long road begun
just over two years ago, when she joined the Pathfinder team for the
Assembly Test and Launch Operations phase of the Pathfinder mission. ATLO,
as they call it, is where a spacecraft makes its last stop on Planet
Earth, first at JPL's Spacecraft Assembly Facility (SAF), and finally at
the test and launch facilities at Kennedy Space Center. At KSC,
affectionately referred to as "the Cape", the spacecraft goes through
final test and assembly, is mated to the launch vehicle for yet another
round of testing, and then ultimately lifts off for the trip to Mars. It
was just over a year ago that Linda helped pack up Pathfinder to begin
its long road to Mars, starting with a four-month intensive effort at
the Cape. But even before launch, the events of this hectic week of July 4
1997 were very much in the minds of the entire Pathfinder team.
"We were there from June through mid-December, and it was round-the-clock
action the entire time." Linda was in charge of the group which assembled
and tested the Pathfinder lander. It was a challenging time, since when
the inevitable problems came up, Linda's team had to improvise tests and
solutions on the spot, far from the support of the main JPL facility in
California.
"One serious issue that came up was in how the spacecraft would respond to
the venting of cooling fluid, which happens right before final approach to
the planet on July 4. The concern was that the venting fluid would act as
a thruster, either spinning the spacecraft or pushing it off-course. My
team had to devise a way to measure the mechanical characteristics of the
spacecraft there on-site at the Cape, to prove to ourselves and those back
at JPL that the venting could be done without disrupting the spacecraft's
motion or attitude."
"Another situation we faced, which seems kind of funny now, is when we were
doing the final closing of the lander. This lander structure consists of
"petals" which fold up around the rover, electronics, and science
instruments, and will be opened up again when the lander is safely on Mars.
Anyway, this event turned out to be a big public spectacle; Dan Goldin
(NASA Administrator) was giving a speech on the same day, and there was a
huge crowd of media people and cameras around to witness our buttoning-up
of the spacecraft. Well, the petals didn't close all the way. We were
horrified! We could see that there was a tiny space between each of the
petals, when they were supposed to be sealed tightly. None of the visiting
guests could tell, because the gap was small and unless you really knew
what to look for you couldn't see it. But we knew that it was supposed to
fit perfectly and that something had to be wrong. We had to call off the
live video feed into the press conference and send all the press home.
Then began the frantic scrambling to find the problem. It turned out that
we had never put the whole lander together before with everything on it at
one time, and it was now much heavier than it used to be; parts of the
lander were sagging under their own weight. The sagging made the parts not
quite fit right, which forced us to really look closely at the parts, called
"latches" , that held the petals together. It turned out to be serendipitous,
because when we really looked at it, we realized we needed some modifications
to the latches to make darned sure the thing would work on Mars, even
though Mars gravity is much lower than that on Earth. To fix the problem,
we actually had people back at JPL pull parts off of an engineering model
of the spacecraft, modify them slightly, and then hand-carry them out to
the Cape to replace the identical parts we removed from the real spacecraft.
It worked out just fine, but it was a desperate few days."
Back at JPL, Linda has taught the Pathfinder operations team everything she
knows about the lander and how it was put together. She won't be actually
involved in the landing activities -- unless something unexpected happens,
which means the operations team might be calling her for her expert
opinion.
"I'm wearing a beeper, and they know they can call me any hour of the day
or night. I'll be on pins and needles the whole time, hoping they don't
need to."
Linda's beeper may also go off this week for an entirely different sort of
crisis -- a TV or newspaper crew needs someone to interview, right away!
"I'm on the 'Interview List', which means I'll be available at any time to
give a commentary on what's going on or to explain something in the mission
or spacecraft. Over the last few weeks, they've given us training on how
to deal with the media, the kinds of angles that reporters would like to
know about, and even what to wear for TV! What's funny is that I've
actually heard from a few high school friends of mine, who are now in the
news business and are calling me to use the personal touch to get the
inside story."
"I'm planning to be at JPL for the whole series of events this week -- no, no
Fourth of July vacation, but we'll still be celebrating. I'm going to
watch the launch events with the rest of my crew from ATLO. These people
include guys from the machine shop, technicians, and engineers. We've got
a little conference room at the Lab with a TV monitor, a microwave -- we're
even getting a fire permit for a BBQ pit right outside! The first
spacecraft activity I'll be watching for closely will be that coolant
venting event we worried about way back during ATLO. This will happen
about 9 in the morning of the 4th. Pretty soon after that, data coming
back from the spacecraft will let us know whether things worked out OK.
Since it was something I was personally involved in, I'll be anxious to see
the results. After that, we won't be able to see much during the descent
to the planet surface, so we won't know for sure everything worked until
sometime later in the afternoon. We'll be biting our fingernails until
then. I just know that it will be successful, though, and I'm especially
excited about seeing that first picture.
You see, I first got interested in space as a teen-ager, when I saw the
pictures sent back from Mars by the Viking lander. Now, just like the
first picture from Viking on Mars was of its very own foot -- you could
even see a footprint in the dust where the lander had apparently bounced
once! -- these first pictures from Pathfinder will be of its own open side
petals. For me, it will be like coming full-circle; years after
marveling at those first pictures from Mars, I'll be seeing Mars
again -- but through the eye of a spacecraft that I helped build with
my own hands. I can't wait."
______________________________________________________