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UPDATE # 40 - June 27, 1997

PART 1: July WebChat Schedule
PART 2: Journal Update #1: How to Write a Pathfinder Sequence
PART 3: Journal Update #2: Thanks to Everyone!
PART 4: Journal Update #3: Making a List, Checking it Twice...
PART 5: Journal Update #4: Getting Ready for the Big Day!
PART 6: Mars Pathfinder Mission Status Report
PART 7: Subscribing & Unsubscribing: How to do it!


Tuesday, July 1, 2 p.m., Pacific, Bridget Landry
Bridget is the deputy uplink systems engineer, which means she teaches
computers on the ground to speak the same language as the Pathfinder
spacecraft. In other words, she takes very complex, but general computer
programs and makes them understand all the commands that the Mars
Pathfinder knows. Bridget will bring us up to date on all the pre-landing
activities the spacecraft is going through. 

Tuesday, July 8, 9 a.m., Pacific, Jeff Plescia
Jeff is a Mars research scientist whose primary interest is planetary
geology. He was an investigator on the Viking mission to Mars in the 1970s
and is anxious to compare past Viking images of the surface of Mars with
new images from Pathfinder. Jeff will answer all of your questions about
touchdown on the surface of Mars and the daily routines of the lander and

Tuesday, July 15, 7 a.m., Pacific, Peter Thomas
Peter, a research scientist at Cornell University, studies pictures of
other planets and satellites sent back by spacecraft. His particular
interest is in Mars and how the wind shapes the surface by moving sand and
dust, sometimes in global storms, and how the polar caps have affected
Mars' geology and climate. Peter will fill us in on the current climate on

Tuesday, July 22, 9 a.m., Pacific, Jack Farmer
Jack is an exopaleontologist--a searcher for fossils on other worlds. His
most important contribution to the Pathfinder mission to date was to
recommend the landing site at the mouth of Ares Vallis (a large outflow
channel). While it is unlikely that Pathfinder will discover fossil
remains of ancient life forms, it may allow us to determine if the right
kinds of rocks are present, that is, rocks of sedimentary origin that
could harbor a microfossil record.

Due to the large number of anticipated participants, it is necessary for
you to register for WebChats in order to participate. All you need to do
is RSVP to sandy@quest.arc.nasa.gov no less than 24 hours in advance in
order to reserve a space for yourself. You will receive confirmation of
your registration and a password to enter the chat room.


How to Write a Pathfinder Sequence

[Editors note: David Mittman wears three hats: one as a flight engineer
where he is responsible for the day-to-day operations of the Mars
Pathfinder lander and the rover. As a mission planner, he tries to balance
the requests of the various scientists and engineers who want the lander
and rover to perform specific tasks. As a flight controller, David talks
with the people in California, Spain and Australia who operate the Jet
Propulsion Laboratory's Deep Space Net.]

David Mittman
June 23, 1997

3:15 AM -- Argh. Isn't Monday bad enough without getting up at three
o'clock in the morning? I showered in the dark so as not to wake up the
kids, got dressed and went off to work. (By shaving the previous night I
figure that I got about 10 extra minutes of sleep!)

Today I am a flight controller instead of a mission planner (see my
previous journal entry). And while it's early morning here at the Jet
Propulsion Laboratory in Pasadena, California, it's mid-morning in Madrid,
Spain, where Deep Space Station 65 is located. Lucky Spaniards...eating
lunch while I attempt to drink my first cup of coffee of the day. 

And what a day! Today's activities are likely to be worth getting up early
for! Today we collect together all the work we've been doing over the last
several months and send it all to the Mars Pathfinder flight computer. All
the flight engineers have been developing "sequences" -- collection of
commands executed in order by the spacecraft -- in preparation for
landing. Our sequences have been tested using a test spacecraft located in
our lab and during the many Operational Readiness Tests (ORTs) we've had
over the last few months. These sequences have gone through many reviews
and revisions (some sequences have been changed as many as 20 times as
we've learned more about how to operate Mars Pathfinder).

If you were a flight engineer, this is what you would see if you were
writing a Mars Pathfinder sequence:

1997-186T10:02:51 IMP_CCD_HEATER("OFF")
1997-186T10:03:21 STORE_IMP()
1997-186T10:08:35 IMP_CAMERA_POWER("OFF") 

There, you've just turned off the Mars Pathfinder camera for the night.
Thanks! Of course, the Mars Pathfinder flight computer can't read English,
so we have computer programs translate these sequences of commands into
something like this:

C5A0 A572 0870 0000 A5C0 77A0 7003 A5C0 AB7A 7801 0000 

Once the sequences are in a form that the Mars Pathfinder flight computer
can understand, they need to be stored onboard in the spacecraft's memory.
To get them to the spacecraft, we transmit them through space from Earth
to the spacecraft. That's my job today, transmitting almost 300 different
sequences to the spacecraft using the Deep Space Network's 34-meter
antenna in Madrid, Spain. Traveling at the speed of light, each sequence
takes 9 minutes and 40 seconds to arrive at the spacecraft. If you'd like
to see where I work, take a look. I'm located just out of the picture off
the bottom of the image. I'll let you know how it goes. I'm on duty until
2:30 PM today...

2:30 PM -- I'm about to go home for the day after a day of sending
sequences to the spacecraft. A communications equipment failure here at
JPL left us without spacecraft data for about 40
minutes but overall the sequence loading went well. Hopefully, technical
glitches won't create these lengthy data outages on Landing Day!


Thanks to Everyone!

[Editors note: Bridget Landry is the Pathfinder deputy uplink systems
engineer. She takes very complex, but general computer programs and makes
them understand all the commands that the Mars Pathfinder knows.]

Bridget Landry
June 23, 1997

Walking around the floor today, rereading all the good wishes we have
posted everywhere, I'm struck again by the support that has been offered
so freely by so many. From the sheets signed by the Mars Global Surveyor
personnel wishing us a "nominal day" for our launch, to the huge poster
from the Galileo team, everyone at JPL has been positive and upbeat.

But it doesn't stop there--letters from school children to their congress
critters asking for more support for the space program, the "Martian
Driver's License" sent to our rover drivers by one class, the enormous
rocket with students' pictures and a "piece of Mars" for it to land on,
the advice, the good luck wished to us by children, students, and people
from all over--it's been overwhelming.

I just hope that when that first picture comes down from Mars next Friday,
everyone who has written, drawn, sculpted, or otherwise conveyed their
support for our team understands that they have been a part of it; not
just in taxes paid, but in the emotional energy, the reaching out, the
curiosity, the drive to know more. Yes, spacecraft require money to be
built, but they also need people--those cheering and watching no less than
those with the wrenches and those at the keyboards. Knowing how much
everyone believes in us and is pulling for our success really brings out
the best in us. Thanks so much!


Making a List, Checking it Twice...

Bridget Landry
June 22, 1997

In reading over my last journal entry, I realize how much has changed.
We've done two more tests, both of which went quite well. Many of the
sequences we will use in the first few days on Mars are done, tested and
onboard the spacecraft.

We're now pulling a "Santa Claus"--we're making lists and checking them
twice, tweaking sequences, making sure that all the "that's a good idea;
we'll do that right after this test" things actually get done and tested.
We're putting finishing touches on procedures: lists of what a particular
job entails on a very detailed and step-by-step level.

Not everything we'd like to do is done; moreover, not everything will get
done. However, all the important things, the necessary things, the
critical things WILL get done. In all my years in the theater, there was
never a time when I didn't want *one more* rehearsal. I've only rarely had
a costume completely finished the first time I wore it. And I always mean
to go back and clean up the code I write, to make it cleaner, faster,
easier for someone to read and understand. But there is only so much time
and money and energy--you do the things that matter most, until it's "good
enough." Striving for perfection is a good and worthwhile effort.
Perfectionism, expecting to actually attain perfection, can kill you. The
trick, of course, is in determining where that distinction lies. That's
where experience--your own, and that of folks who have done it
before--comes in, helping you to prioritize.


Getting Ready for the Big Day!

[Editors note: Mark Adler is the Mars Exploration Program architect. What
this means is that he spends a lot of time talking with scientists to
understand in detail what the scientific goals of Mars exploration should
be. In addition, he talks with spacecraft engineers to understand what's
possible and with the technologists to hear what may be possible in the
future. And finally, he chats with managers to understand what these
things will cost, and what resources will be available, or what resources
may become available in the future.]

Mark Adler
June 21, 1997

During the week of July 4, I will be one of many people interfacing with
the media for the Mars Exploration Office. My job will be to help shelter
the people who are actually operating the spacecraft from having to do a
lot of media interaction so that they can continue to operate the

I'm preparing for this role by trying to get a much deeper understanding
of the Pathfinder mission, what's going to happen when and why, especially
at the times we're not getting data back to tell us what's going on. For
example, there will be a long period of time between when Pathfinder lands
on Mars and when we'll get pictures back. People will want to know what's
happening. I'll be able to tell them things like the panels should be
coming down, the airbags are being sucked under or the high-gain antenna
is setting up. Between 10 a.m., when Pathfinder lands on Mars, and 2 p.m.
when we expect to receive the lander's first signals, I'll have to
describe what operations the lander is going through because no spacecraft
data will be received during those four hours. Around 2 p.m., which is
sunrise at the landing site, if everything's working, we should get some
signal back from the lander that says, "I'm here and ready to go!" Then,
sometime after 4 p.m. the first pictures begin to arrive. Of course, this
is all assuming that everything goes as planned! It rarely does.

So, people here at the Jet Propulsion Laboratory are very busy rehearsing
post-landing procedures. There are all kinds of contingencies and
possibilities and events that are being rehearsed for possible different
failures: what the lander team would do in a certain situation, how they
would do it, what information they would get and how they would respond to
it. The team is busy planning for all possible challenges.

Team members are definitely excited but I wonder if they have had time to
really think about the significance of what's going on. There are
rehearsals 24 hours a day. A guy was in my office yesterday saying that he
had been here 16 hours and fortunately his job was over because two hours
before Pathfinder "landed" in the rehearsal. After the "test" landing his
job was finished as he was responsible for the entry analysis and the
aerodynamics of the landing.

As far as what I'll be doing to help the Pathfinder team, I'll be prepared
to assist with the media as early as July 2 until about July 5. I think I
should set up a cot in my office because I have a feeling I'm going to be
very busy. JPL is preparing to accommodate 19 microwave trucks, which will
beam data back to their satellites for transmission to where ever in the
country or the world the broadcast is destined. There will also be a lot
of media as well as the public in downtown Pasadena at PlanetFest.
Sponsored by The Planetary Society, PlanetFest is going to have a very
large, multi-TV screen panel showing what's going on all the time.

If I had to summarize the feeling here at JPL, it's a combination of
excitement, anticipation and stark terror. :-) Obviously, excitement about
landing on Mars for the first time in over 20 years. Anticipation about
what we might learn, since every time we've sent a new spacecraft to Mars
in the past, our view of the planet has changed. And lastly, stark terror
of significant failure in a very ambitious mission that is both trying a
new way to land on Mars and operating the very first wheeled robot to ever
be sent to Mars. There is always risk in sending our robot agents alone
out into the dark expanses of space and the vast uncharted surfaces of
other worlds. But if it all works, and we think it will, then all of Earth
will share with us the wonder of exploring a new world.

Mars Pathfinder Mission Status Report

[Editor's note: This press release was prepared by the Public Information
Office at the Jet Propulsion Laboratory.]

June 26, 1997

Mars Pathfinder, now eight days away from landing on the surface of Mars,
performed the last of its scheduled trajectory correction maneuvers at 10
a.m. Pacific Daylight Time on Wednesday, June 25.

The correction maneuver was performed in two phases occurring 45 minutes
apart. The first burn, lasting just 1.6 seconds, involved firing four
thruster engines on one side of the vehicle. The second burn lasted 2.2
seconds and involved firing two thrusters closest to the heat shield. The
combined effect of both burns changed Pathfinder's velocity by 0.018
meters per second (0.04 miles per hour), which places the spacecraft on
target for a July 4 landing in an ancient flood basin called Ares Vallis.
Pathfinder is scheduled to land at 10:07 a.m. PDT (in Earth-received
time). The one-way light time from Mars to Earth is 10 minutes, 35
seconds, so in actuality, Pathfinder lands at 9:57 a.m. PDT.

If necessary, a fifth trajectory correction maneuver may be performed just
before Pathfinder hits the upper atmosphere of Mars. The maneuver would be
carried out either 12 hours or six hours before Pathfinder reaches the
atmosphere at 10 a.m. PDT in Earth-received time. The flight team will
make a decision to proceed with the final correction maneuver the evening
before landing.

A final health check of the spacecraft and rover was performed on June 20.
All spacecraft systems, including science instruments and the critical
radar altimeter, remain in excellent health from the last check about six
months ago. The rover received a "wake up" call, woke up on command from
the lander, then accepted a software upgrade. Flight controllers next
loaded the 370 command sequences that will be required by Pathfinder to
carry out its surface operations mission.

The spacecraft is now ready to begin its entry, descent and landing phase.
It will be commanded into that mode at 1:42 p.m. PDT on June 30 by an
onboard sequence.

Mars Pathfinder is currently about 180 million kilometers (111 million
miles) from Earth and about 3.5 million kilometers (2.2 million miles)
from Mars. After 202 days in flight, the spacecraft is traveling at about
18,000 kilometers per hour (12,000 miles per hour) with respect to Mars.


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