PART 1: Reminder: August 5 chat with Nathan Bridges
PART 2: Mars Global Surveyor mission status
PART 3: Subscribing & Unsubscribing: How to do it

REMINDER: AUGUST 5 CHAT WITH NATHAN BRIDGES

Wednesday, August 5, 10:00 a.m. Pacific Time: Nathan Bridges, planetary
geologist: Since late September, 1997, when the Mars team stopped hearing
from Pathfinder, virtually all of Nathan's time has been spent analyzing the
large amount of images and other data collected by the Mars rover. Nathan's
primary areas of study are understanding the chemical makeup of the rocks
and soil, and the effects of wind on the surface. Nathan continues to study
Mars data, and will soon have results of his investigations published in a
scientific journal. Please read Nathan's autobiography prior to joining this
chat: http://quest.arc.nasa.gov/mars/team/bridges.html

If you haven't yet signed up, there are still spaces available! You can
register for the chat at:
http://quest.arc.nasa.gov/mars/events/interact.html

MARS GLOBAL SURVEYOR MISSION STATUS

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

July 17, 1998

As of today, the Mars Global Surveyor spacecraft has completed nearly seven
weeks of science collection operations since the end of solar conjunction in
late May. During that month, the flight team suspended science operations
because Mars passed behind the Sun as viewed from the Earth. This geometry
physically blocked radio communications with the spacecraft.

Since the end of conjunction, Surveyor has completed over 100 revolutions
around the red planet and has transmitted almost two gigabytes of scientific
information back to Earth. Some of the latest images released from this
summer's science observations include pictures of a crater that may have
contained a lake long ago in Martian history.  Other highlights include
laser topography measurements of the North Pole, and analysis of radio
signals sent from the spacecraft to aid the understanding of the gravity
field in the northern hemisphere.

Over the remainder of this summer's science operations, investigators on
Earth will receive their data in less time after transmission as the Earth
to Mars distance decreases from its June 22nd maximum of 234 million miles
(377 million kilometers). At that distance, 2.5 times greater than Earth's
distance to the Sun, radio signals from the spacecraft took 21 minutes to
reach Earth. This time delay will gradually decrease to just under five
minutes by next May.

Currently, members of the flight team are preparing for upcoming activities
in the late summer and fall months. In late August and early September,
Surveyor will pass within a thousand miles of the Martian moon Phobos. This
satellite orbits the red planet once every 7.7 hours and is a potato-shaped
rock about the size of Manhattan. During the close approaches, several of
the science instruments are scheduled to make observations of the moon.

During August, the flight team will also begin training for the next phase
of aerobraking. This phase will begin in mid-September and last until
February 1999. Over the course of those four months, Surveyor will
repeatedly fly through the upper Martian atmosphere and use air resistance
to gradually shrink the size of the orbit. The goal is to reduce the period
from its current value of 11.6 hours to just under two hours. Global mapping
operations from this two-hour orbit will begin in March or April of next
year.

After a mission elapsed time of 617 days from launch, Surveyor is 232.68
million miles (374.46 million kilometers) from the Earth and in an orbit
around Mars with a high point of 11,111 miles (17,881km), a low point of
109.6 miles (176.4 km), and a period of 11.6 hours. The spacecraft is
currently executing the P430 command sequence, and all systems continue to
perform as expected. The next status report will be released sometime in
August.

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