Hundreds of students from grades 3-12 are now engaged in solving
the "Where in the World Are These P.E.T. Mystery Sites?" -- an
enrichment activity developed as a fun and challenging follow-up to
the LFM Planet Explorer Toolkit activity.

The Mystery Site activity models the "Launch Phase" data collection
by presenting data and images from five mystery sites found
somewhere in the world. The goal is for students to analyze the data
and images, compare what is known about the sites in terms of
weather, flora, fauna, soil, rock, water, etc., and decide the specific
location of each of the five sites. Students are also using the
Planetary Data Input shared online by participating P.E.T. classes
(who analyzed their own unique sites) as a base for comparative
data analysis to help narrow the possible mystery site locations.

Different levels of difficulty provide an ever-challenging task for
upper grade levels.  Students of the elementary grades receive a
multiple-choice answer form allowing them to select the mystery
site location from three known locales. Middle-school students
select from a possible five known locales and high-school students
receive a range of latitude and longitude within which the sites are
located. High-school students must identify the sites by latitude and
longitude based on their analysis of data.

The mystery site activity is open to all students, regardless of past
participation in the Planet Explorer Toolkit activity. Prizes will be
awarded to winners from each grade level. Classes must register for
participation by sending email to: jwee@mail.arc.nasa.gov. Please
include the following information:

- name of sponsoring educator
- location of school/homeschool, etc. (Give full mailing address)
- number of students participating, age and grade level
- email address of sponsoring educator

NOTE: If you are the coordinator registering for several classes, you
may send one email with a list of the classes, grade level/age,
number of students, and sponsoring educator.

A full overview of the Mystery Site Activity is online at:
http://passporttoknowledge.com/lfm/teachers/mystery.html
This activity is open for participation through May 20, 1997.

MARS TEAM JOURNAL #1: Burning the Midnight Oil


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 22, 1997

Working graveyard shifts this week, going in to work around 9 p.m.,
and coming home with the dawn. Strange to be driving home under
rosy skies, pulling the pillow over my head to shut out the morning
light. Stranger still to hear meetings called for midnight or 2 a.m.
and having to ask, honestly, whether something scheduled for 6 is
a.m. or p.m. Oddly enough, what I learned of myself and my own
tolerances, at science fiction conventions (when I tried to
stay up all night, for fear that I would miss something) has actually
helped me in these tests. I know, for instance, that I can either go
without sleep, or go without food for an extended period of time, but
things get real surreal if I try to do both. Snacking all night keeps
my blood sugar up, helps me concentrate. Small things are important:
I brought in slippers so that my feet are comfy and so I can sit
Indian-style in my chair more easily. And I find that the hardest
time is between 2 and 4 a.m.--my mind starts to wander and follows
odd routes to the strangest places. I have to keep reminding myself
of the immediate task at hand. I take copious notes, both to keep
from forgetting something (my memory goes as the hours advance)
and as a focus to stay on track, or return to the track when I've
taken a mental stroll.

This test hasn't gone well. Many mistakes on all sides have added up
to some major concerns. I think it will all sort itself out; from my
own experience, early rehearsals are often disastrous. I think the
telling point will be how much and how fast we learn from this, and
whether we can keep making new mistakes, rather than repeating old
ones.

Seventy-two days and counting...



MARS TEAM JOURNAL #2: "Hey Navigator... Wheres the Spacecraft?"


by Pete Kallemeyn

[Editor's note: Pete is the navigation team leader for the Mars
Pathfinder spacecraft. he is responsible for determining where
Pathfinder is, predicting where it will go in the near future, and
determining the means to correct the path in order for us to reach
the surface of Mars on July 4!]

April 29, 1997

This is the first in a series of four journal entries that details the
steps the NAV team and others go through to plan, design, test and
execute a trajectory correction maneuver (TCM), which is a major
activity for a spacecraft in cruise.

Today the NAV team is to perform orbit determination and maneuver
computation for the third mid-course maneuver. The design of the
maneuver, a critical event during interplanetary cruise, is a process
that takes a few days to complete. I hope to step you through the
whole process in four journal articles. This first one is a bit long
because it deals with orbit determination, my specialty, so forgive
me if I talk a bit too long...

The first step in designing a maneuver is to determine where the
spacecraft currently is and accurately predict its motion until
arrival. That process is referred to as orbit determination, which is
a complicated process, but I'll try to explain it as best I can.
Basically, we start with a computerized model of the spacecraft's
trajectory that our navigation software can process. The numbers
from the computer model should closely represent the actual
trajectory that the spacecraft is flying, but it's not perfect. In order
to make it as perfect as possible, we use tracking data to measure
the real trajectory and adjust the computer model accordingly.

Tracking data for Mars Pathfinder consists of two types, Doppler (a
measure of how fast the spacecraft is receding from Earth) and
range (a measure of the distance from the station to the spacecraft).
There are other types of possible tracking data types, but on Mars
Pathfinder we prefer to use only Doppler and range to reduce
operational complexity and spacecraft resources. The Deep Space
Network measures the range and Doppler from the stations to the
spacecraft at regular intervals, and the results make their way to
the NAV team in the form of a "Tracking Data File." The NAV team
reads the file and compares the actual tracking data values with
values we would expect from our model. Any error in our trajectory
model will show up in the tracking data, and our programs know
how to adjust the model to match the data correctly.

This may sound straightforward, but it's really not, for a number of
reasons. First, there are a lot of physical effects that affect the
spacecraft's flight path through space. Gravity of the Sun and the
planets is the most obvious, but there is also a small but continuous
acceleration due to the photons from the Sun hitting the spacecraft.
Solar radiation pressure is what this is called, and it has been a
difficult effect to model for us until just recently. There are also
small changes in velocity that occur whenever the spacecraft's
thrusters are fired to change the attitude, and we can't forget the
results from past TCMs.

Secondly, since we use tracking data to help determine our
trajectory, we need to know what phenomena will affect the
measuring and collecting of that data. This includes the locations of
the stations on the surface of the Earth, the orientation of the Earth
at the time the measurement is made, the effect of the atmosphere
and the ionosphere on the signal from the spacecraft to the station,
and finally the electronic delays in both the spacecraft hardware and
the station components that collect the data. That's quite a lot of
stuff to keep track of, but is necessary in order to obtain the best
possible trajectory solution.

Finally, we have to be careful to check the tracking data before
using it, because sometimes we get bad data that could mess up our
solution process. So the art of orbit determination sometimes
involves editing out bad data, adjusting slightly flawed data, and
reporting these errors to the Deep Space Network, who needs to
know how they are doing. Orbit determination is also experimental in
nature. The NAV team will try different strategies in orbit
determination, always looking for the right one. Sometimes we'll use
only Doppler data and ignore the range, or maybe we'll try the
opposite. Sometimes we'll try estimating a particular effect and see
what the result is, or we might choose to leave it unmodelled. A lot
of comparisons between solutions are done, and this is where the
human element of "judgment" comes into play, something you can't
really program into software without a lot of effort. Experience
with orbit determination is very important to know if you've got a
good solution, an okay solution, or a bad solution.

After a number of experiments have been tried, we'll select a few of
the better experiment results for consideration in selecting the
'right' solution. Today, for example, we had four possible solutions
to pick from. All of these solutions were within 10 kilometers of
each other, so we really could have picked one at random and had a
good solution virtually guaranteed. Yet we prefer to discuss briefly
any advantages or disadvantages a given solution might have, and
narrow down the field to one solution. This we did in a meeting
around 11:15 today. After discussing the various aspects of each
solution and the implications of each for maneuver design, we
selected one that Robin Vaughan had done. Its 'code number' was
970429rv104630, which identifies it among the many solutions
we've done to date. I figure, I have done over 500 solutions since
launch, so you can see that we need some method to keeping track of
all these solutions.

Now we know where we are... The next step is to determine where
we want to go, which is the subject of the next entry.

WHAT TO EXPECT AT THE LANDING

Really, truly, "live" from Mars

This July 4 and in the weeks thereafter, expect to see extensive
coverage of Pathfinder's landing on TV newscasts, in print and on the
Internet. NASA-TV plans minute-by-minute coverage on landing day,
with actual footage intermixed with press briefings. Several
networks are planning special coverage. The LFM Web site will
provide updates as we learn more. And remember, the LFM Teacher's
Guide provides suggestions for Activities you can undertake before
school ends to "set" students up to appreciate the events of this
summer. Let us know how this works! (And if you're district has
summer school, by all means participate from class.)


Coming soon to a science center near you...

In addition to headline reports in the mass media, Live From Mars
and its partners from the American Museum of Natural History in
New York, Mississippi State University and The Planetary Society
(TPS), plan special live, interactive TV programs to be offered via
satellite on July 6 and 9, from 2-4 p.m. Eastern (11 a.m.-1 p.m.
Pacific.)

July 6 will not only feature the events of the first two days on Mars,
the best color enhancements of the first pictures returned and a
chance to hear NASA scientists' first reactions, but also the TPSs
"Planetfest" -- a combination Star Trek convention and celebration
of space exploration and scientific discovery, promising a good time
for all! To be held in Pasadena, Calif., just a few miles from the Jet
Propulsion Laboratory on July 4-6, we plan to link "Planetfest" in via
video to JPL, New York, and many other live locations around the
nation. It's hoped that CU-SeeMe, real audio and other Internet
technologies will also share "Planetfest" and the events of "Landing
Week" with those unable to access satellite TV.

Though primarily designed for participation by youngsters, families
and camp groups in science museums and planetariums (since school
is out for the summer in most places), anyone with access to a
movable satellite dish can obtain the programming. Many science
centers are already planning events around Pathfinder's landing. We
expect many will integrate Live From Mars into this, but we can't
promise or predict. Please check locally and if your local museum
doesn't yet know about what's going on, share what you know with
them, and direct them to our Web site, which will have increasingly
detailed information.

Stay tuned and use Live From Mars to link directly to the very
latest from the Red Planet!

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

Friday, May 2,1997

No major activities took place this week. For the past three weeks,
few activities have occurred because the Surveyor spacecraft has
been configured in a quiet state for a search campaign to detect
gravity waves. According to theoretical physics, these waves are
gravitational disturbances emitted by all objects in the universe.
However, because gravity is a relatively weak force, detection of
these waves is almost impossible unless they are generated by
massive objects such as black holes and matter at the center of the
Milky Way Galaxy.

To date, nobody has ever detected a gravity wave. If Surveyor
encountered these waves, the spacecraft would experience an
extremely small jolt. This tiny bumping motion would cause a tiny
shift in the frequency of the spacecraft's radio signal transmitted to
Earth. Analysis of the data generated by this experiment will take
six months or more.

After a mission-elapsed time of 176 days from launch, Surveyor is
92.74 million kilometers from the Earth, 37.03 million kilometers
from Mars, and is moving in an orbit around the Sun with a velocity
of 23.89 kilometers per second. This orbit will intercept Mars 132
days from now, slightly after 6:00 p.m. PDT on September 11 (01:00
UTC, September 12). The spacecraft is currently executing the C7
command sequence, and all systems continue to be in excellent
condition.

[Editors note: NASA Press Release #97-85]

NASA's Mars Global Surveyor spacecraft can safely and successfully
aerobrake into its final orbit around Mars this fall with its one
partially deployed solar panel in a modified configuration, mission
managers have decided.

No special maneuvers will be conducted to attempt to force the
array to latch, and the focus of the Surveyor engineering team now
will turn to minor modifications to the critical aerobraking phase
that will circularize the spacecraft's orbit for the beginning of two
years of science operations.

"After careful analysis of the situation, we've determined that the
solar panel on Mars Global Surveyor that is not fully deployed
presents very little risk to the mission," said Glenn E. Cunningham,
Mars Global Surveyor project manager at NASA's Jet Propulsion
Laboratory (JPL), Pasadena, CA.

The decision by NASA's flight team at JPL and its partners at
Lockheed Martin Astronautics, Denver, CO, was reached after several
months of extensive analysis of spacecraft data, ground-based
computer simulations and a series of very slight spacecraft
maneuvers that were carried out in January and February to
characterize the situation.

"Thanks to an early launch that gave us an advantageous trajectory,
we will not have to aerobrake into the Martian atmosphere as fast as
we had originally planned to reach the mapping orbit, and that will
reduce the amount of heating that the solar panels undergo during
this gradual descent," Cunningham explained.

"We will rotate the solar-cell side of the panel that is not fully
deployed by 180 degrees, so that it faces into the direction of the
air flow that exerts drag force on the spacecraft as it dips
repeatedly into the atmosphere," he said. "This way, the unlatched
panel will not be in danger of folding up onto the spacecraft's main
structure, nor will the panel be at any greater risk of heating up too
much."

The solar panel in question is one of two 11-foot wings that were
unfolded shortly after Surveyor's Nov. 7, 1996, launch from Cape
Canaveral Air Station, FL. Data suggest that a piece of metal called
the "damper arm," which is part of the solar array deployment
mechanism located at the "elbow" joint where the entire panel is
attached to the spacecraft body, probably was sheared off during
deployment in the first day of flight. The lever that turns the shaft
became wedged in a two-inch space between the shoulder joint and
the edge of the solar panel, leaving the panel tilted at 20.5 degrees
from its fully deployed and latched position.

Although the situation was never considered a serious threat to
accomplishing the science objectives of the mission, the tilted
array caused the JPL/Lockheed Martin flight team to re-evaluate the
aerobraking phase, in which the spacecraft must rely almost solely
on its solar panels for the drag needed to lower it into a nearly
circular mapping orbit over the poles of the planet. This phase of the
mission will begin a week after Mars Global Surveyor is captured in
orbit around Mars on Sept. 11, and will last approximately four
months.

Aerobraking was first tested in the final days of the Magellan
mission to Venus in October 1994. The technique is an innovative
method of braking which allows a spacecraft to carry less fuel to a
planet and take advantage of the planet's atmospheric drag to
descend into a low-altitude orbit.

Mars Global Surveyor will use an aerobraking phase much like that
used to circularize Magellan's orbit. The solar wings -- which
feature a Kapton flap at the tip of each wing for added drag --
supply most of the surface area that will slow the spacecraft by a
total of more than 2,684 miles per hour during the four-month phase.
Surveyor's orbit around Mars will shrink during this phase from an
initial, highly elliptical orbit of 45 hours to a nearly circular orbit
taking less than two hours to complete.

Engineers determined that the deployment springs currently holding
the tilted solar panel in its nearly deployed position will not be
strong enough to withstand the forces of aerobraking. To solve that
problem, they designed a new configuration in which the tilted solar
panel, along with the deployment springs, will be rotated 180
degrees, using a motor-driven inner gimbal actuator, and held in
position with force applied by an outer gimbal actuator. Sequencing
software will be modified to turn the gimbal actuators on before
each closest approach to the planet and off at the conclusion of each
drag pass.

As a consequence of the new aerobraking configuration, the more
sensitive cell-side of the unlatched wing will be exposed directly to
the wind flow of atmospheric entry, requiring that aerobraking be
done in a more gradual, gentle manner. Ground tests have
demonstrated that the unlatched solar panel will have more than
adequate thermal margin to withstand additional heating as the
spacecraft circularizes its orbit for the beginning of science
mapping in March 1998.

Meanwhile, Mars Global Surveyor continues to perform very well on
its arcing flight path toward the red planet and its arrival in orbit. A
third, very minor trajectory correction maneuver, planned for April
21, was deemed unnecessary and canceled. In addition, science
instrument calibrations continue to go well, and plans are being
prepared to take an approach image of Mars a few days before the
July 4 landing of Mars Pathfinder, which passed Mars Global
Surveyor en route to Mars on March 14, 1997.

Mars Global Surveyor is the first mission in a sustained program of
robotic exploration of Mars, managed by JPL for NASA's Office of
Space Science, Washington, DC.

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