PART 1: Answering the Challenge
PART 2: New Challenge for the Week
PART 3: April WebChat Schedule
PART 4: Mars Team Journal: A Snake Swallowing a Gopher
PART 5: Another Interesting Mars Site
PART 6: Global Surveyor Flight Status
PART 7: Subscribing & Unsubscribing: How to do it!

Last week, in CQ #5: BRUSH UP ON YOUR GREEK, we asked:
There's a letter in the Greek alphabet that's very important both to
launching NASA's current Mars missions and to getting to Mars.
What's that letter and explain how it is used.

ANSWER:
Both Mars Pathfinder and Mars Global Surveyor were launched aboard
Delta II rockets from Cape Canaveral, as seen during LFM program
101. "Delta V" is what rocket scientists (including the Navigation
teams who were featured during program 102) call the "change in
velocity" that keeps a spacecraft on course for a distant planet.
Trajectory correction maneuvers fine tune the route by a
combination of precise timing, and carefully controlled "burns"
providing additional velocity in specific direction.

CQ #6: COMPARATIVE ANALYSIS
Teachers have been telling us (referring back to the vocabulary of CQ
#1) that they think it's very useful for students to compare Earth's
"geology" and Mars' "areology." Now, a more open-ended  question,
which will require and receive some subjective, but fair,
judgments from our PTK/Live From Mars CQ staff!

What five features make Mars most like Earth? And, what
five features make Mars most unlike Earth?

We hope students will come up with some geologically correct
answers, but also with some clever, provocative and tongue-in-
cheek comparisons!

You are invited to send original student answers to:
jwee@mail.arc.nasa.gov. Please include the words CHALLENGE
QUESTION in the subject line of your email. The kids' names will be
listed online and token prizes will be given to those will the best
answers.

Answers are due within seven full days of Challenge Question
posting. (e.g. If a CQ is posted on April 24, answers are due by
midnight PDT on May 1.)

A list of answers from all students who submitted them will be
posted on the Live From Mars Web site soon.

An apology: Due to a scheduling error, the April 23 WebChat with Guy
Beutelschies, test director for the Mars Pathfinder spacecraft, was
canceled. Guy will reschedule for sometime in May. The May chat
schedule will be posted next week.

Tues. April 29, 10 a.m., PST: Bridget Landry, deputy uplink systems
engineer, Mars Pathfinder, Jet Propulsion Laboratory, Pasadena,
Calif. Bridget teaches computers on the ground to speak the same
language as the Mars Pathfinder.

by Bridget Landry

[Editor's note: Bridget is a deputy uplink systems engineer on the
Mars Pathfinder team. She takes complex, but general computer
programs and makes them understand all the commands that the
Pathfinder knows.]

April 18, 1997

In virtually every project (costuming or scientific) that I have been
involved in, the work doesn't come in a steady stream. There is a
long period where there isn't much actual work being done, because
you're waiting for people "upstream" from you to do their thing, or
you haven't been able to define the questions you want to ask. And
then, suddenly, something crystallizes and this HUGE amount of work
surges through the pipeline. I refer to this as "a snake swallowing a
gopher": it is an enormous amount of data/work/whatever and it can
almost be tracked visibly as the lump makes its way through the
system.

This was one of those weeks.

We have a five-day test coming up next week, which will simulate
the first five sols on Mars. On the basis of previous tests, there
were a lot of changes to be made to the existing imaging sequences,
and these had to be ready, not only for the test, but in time to be run
through our testing system BEFORE the test. This made it an
incredibly long week for many of us, but I feel good about the work
we've done. I think we're well on our way to having at least the first
few days fleshed out. There are always a few things that we want to
tweak, but, in the main, I think we're in pretty good shape for our
test.

And now I'm going home to sleep!

If you're interested in following the Pathfinder and Surveyor
spacecraft as they make their way toward Mars, go to:

[Editor's note: This status report was prepared by the Office of the
Flight Operations Manager, Mars Surveyor Operations Project, NASA
Jet Propulsion Laboratory.]

Friday, April, 18 1997

No major mission activities occurred this week onboard the Mars
Global Surveyor spacecraft. Back at the Jet Propulsion Laboratory in
Pasadena, California, the project management has made a decision
not to attempt any more efforts to free debris that is currently
keeping the -Y-side solar array slightly out of position. This solar
panel is currently deployed and fully functional, but is 20.5 degrees
from its proper position.

The flight team believes that the position discrepancy was caused
when a damper shaft in the array's deployment mechanism broke
shortly after launch. This damper is a device that was installed to
minimize the mechanical shock of deployment by slowing the motion
of the array during deployment. The flight team theorizes that the
broken shaft caused the damper arm to wedge into the hinge joint
connecting the solar panel to the spacecraft.

An important aspect of this position discrepancy is that the solar
panels will be used at Mars not only to produce electrical power, but
also to help the spacecraft attain its final mapping orbit. Over the
course of a four-month period following Mars orbit insertion,
Surveyor will be dipped into the upper Martian atmosphere on every
orbit. During these atmospheric passes, air resistance generated by
the solar panels will slow the spacecraft and gradually lower its
orbit. Surveyor will use this "aerobraking" technique to lower the
high point of its orbit from an initial 56,000 kilometer altitude to
just under 400 kilometers.

For the last few months, the flight team has been considering
several options to free the debris and allow the panel to latch and
lock into its proper position. One idea involved a short firing of
Surveyor's main rocket engine to provide a small force to dislodge
the damper arm. However, such efforts will not be necessary
because an extensive analysis has indicated that aerobraking with
the -Y solar panel slightly out of position is feasible with a few
minor modifications to the original plan.

One of the minor changes involves rotating the panel into a position
where the front side will face into the air flow instead of the back
side. This orientation will keep the unlatched panel from folding up
on itself when it encounters the air flow during aerobraking.
Because the front side contains the silicon cells that produce
electricity, it is more fragile than the back side and cannot tolerate
as much heating from the air flow. As a result, the flight plan will
be modified so that Surveyor aerobrakes at a slightly slow pace than
previously planned.

After a mission elapsed time of 162 days from launch, Surveyor is
76.20 million kilometers from the Earth, 44.32 million kilometers
from Mars, and is moving in an orbit around the Sun with a velocity
of 24.59 kilometers per second. This orbit will intercept Mars 146
days from now, slightly after 6:00 p.m. PDT on September 11 (01:00
UTC, September 12). The spacecraft is currently executing the C6
command sequence, and all systems continue to be in excellent
condition.

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