From: baalke@kelvin.jpl.nasa.gov (Ron Baalke)
Subject: TOPEX/Poseidon Press Kit
News-Software: VAX/VMS VNEWS 1.3-4   
Reply-To: baalke@kelvin.jpl.nasa.gov
Organization: Jet Propulsion Laboratory
Date: Fri, 31 Jul 1992 00:59:25 GMT


PUBLIC AFFAIRS CONTACTS


Brian Dunbar
Headquarters, Washington, D.C.
(Phone:  202/358-0873)


Mary Hardin
Jet Propulsion Laboratory, Pasadena, Calif.
(Phone:  818/354-5011)


CONTENTS


General Release.............................................................1

Mission Overview And Science Objectives.....................................3

Satellite Tracking..........................................................4

TOPEX/POSEIDON Satellite....................................................5

Science Instruments And Spacecraft..........................................6

Mission Phases..............................................................8

Mission Timeline............................................................9

Spacecraft Specifics.......................................................10

U.S.-French Cooperation....................................................10

Mission Management.........................................................11


RELEASE 92-126

U.S., FRANCE SATELLITE TO STUDY OCEANS AND CLIMATE

	On Aug. 10, the United States and France will undertake a mission to
help provide a new understanding of Earth's environment by determining
how the global system of the Earth's oceanic currents influence climate.

	The means to this end is the TOPEX/POSEIDON satellite, a joint
mission of NASA and France's space agency, the Centre National d'Etudes
Spatiales (CNES).

	"TOPEX/POSEIDON is an investment in our future," said NASA's
Program Scientist Dr. William Patzert.  "Without TOPEX/POSEIDON, there is
no possibility of meaningful long-term climate forecasts."

	"TOPEX/POSEIDON sets a precedent for international studies of global
change," said Patzert.  "In a future of limited resources, it is imperative
that all nations work together to study our atmosphere and oceans.  We will
have to share our understanding to develop common solutions.  Climate knows no
national boundaries."

Ocean Topography

	TOPEX/POSEIDON will use the global perspective available only from
space to develop maps of ocean topography showing the barely perceptible
hills and valleys of the sea surface.  This effort will significantly expand
the knowledge developed from shipboard research which was limited to specific
locations.

	From the TOPEX/POSEIDON data, scientists will calculate the speed
and direction of ocean currents worldwide to better understand how the
oceans transport heat from the Earth's equatorial region toward the poles,
thus regulating global climate.

	The spacecraft's six scientific instruments are designed to function
for 3 to 5 years.  The resulting data base will help scientists develop more
precise long-term climate forecasts, understand and predict the timing of
the El Nio phenomenon and better comprehend the ocean's role in
regulating overall global climate.



	TOPEX/POSEIDON will be launched from the Guiana Space Center in
Kourou, French Guiana, aboard an Ariane 42P expendable launch vehicle.
The satellite will be placed into an orbit 830 miles (1,336 km) above the
Earth, inclined 66 degrees to the Earth's equator.  Launch is scheduled for
7:08 p.m. EDT.  The launch window is 44 minutes in duration.

International Cooperation

	The TOPEX/POSEIDON launch will help commemorate 1992 as the
International Space Year.  The joint science team includes 38 principal
investigators from nine countries including the United States, France,
Australia, South Africa, Germany, Norway, Japan, the Netherlands and the
United Kingdom.  Data from TOPEX/POSEIDON eventually will be made
available to global change researchers around the world for their analysis.

	TOPEX/POSEIDON is the second major satellite in NASA's Mission to
Planet Earth, a coordinated, long-term program to study the Earth as a
complete environmental system.  Mission to Planet Earth began in
September 1991 with the launch of the Upper Atmosphere Research
Satellite and continued last March with the ATLAS-1 Space Shuttle mission.

	The next element of Mission to Planet Earth is the Italian-built
LAGEOS II satellite, scheduled for launch aboard the Space Shuttle Columbia
in October.  LAGEOS II will be used to study the dynamics of the Earth's
crust.

	The U.S. portion of the TOPEX/POSEIDON project is managed by
NASA's Jet Propulsion Laboratory, Pasadena, Calif., for the agency's Office of
Space Science and Applications.  The French portion of TOPEX/POSEIDON
is managed by CNES' Toulouse Space Center, Toulouse, France.


MISSION OVERVIEW

	TOPEX/POSEIDON will be launched by the European Ariane 42P
rocket from Kourou, French Guiana.  The spacecraft will be placed in a
nearly circular orbit with an altitude of 830 miles (1,336 kilometers),
inclined 66 degrees from the equator.  This relatively high altitude will
minimize atmospheric drag on the spacecraft, reduce the effects of gravity
field variations and simplify maneuvers needed to maintain the orbit.

	The satellite's orbital period is 112 minutes.  TOPEX/POSEIDON will
repeat the same ground track every 10 days (127 revolutions), allowing
scientists to measure changes in the sea surface topography using a
sampling technique that matches changes in the global ocean currents.

	This mission builds upon the knowledge gained from three previous
ocean-observing satellites Q GEOS-3 in 1975, Seasat in 1978 and Geosat in
1985 Q which demonstrated that altimetry could measure ocean circulation.
Like these prior missions, the primary instrument on-board the
TOPEX/POSEIDON satellite is a radar altimeter.

	The altimeter is similar to aircraft radar, but the satellite altitude
and the required height precision are many times greater.  The
TOPEX/POSEIDON altimeter bounces radar pulses off the sea surface and
measures the time it takes the signals to return to the satellite.  A
microwave radiometer will correct for any errors in the time delay that is
caused by water vapor in the path through the atmosphere.

	The adjusted round-trip travel time is used to calculate the distance
between the spacecraft and the sea surface.  When this distance is combined
with the measurements of the satellites exact location in space, scientists
will first determine the height of the sea surface relative to the Earth's
center and then calculate fluctuations in currents and tides.

SCIENCE OBJECTIVES

	The primary objective of the TOPEX/POSEIDON project is to make
precise and accurate global observations of the sea level for several years,
substantially increasing understanding of global ocean dynamics.  Members
of the TOPEX/POSEIDON science team will share their data with scientists
working with the World Ocean Circulation Experiment (WOCE).  Together
they will be able to determine the general circulation of the ocean and its
variability.

	The satellite also will increase understanding of how heat is
transported in the ocean.  The ocean absorbs the sun's heat and
redistributes it.  Active currents such as the Gulf Stream carry warm water
from the tropics to the poles where it cools and sinks into the deep ocean.

	Without this circulation, the difference in temperature between
equatorial and polar waters would be much greater than it is today.  How the
water circulates in the ocean determines the speed at which the heat is
transported and how the exchange of energy regulates the world's climate.

El Nio

	Another short-term climate change influenced by the ocean is the
phenomenon known as El Nio.  Every 3 to 7 years, usually beginning
around Christmas time, there is a dramatic rise in the sea surface
temperatures in the eastern Pacific Ocean.  At the same time, atmospheric
patterns shift, causing severe environmental consequences around the globe.

	The El Nio event of 1982-83 was the worst so far this century.
Massive flooding and landslides killed hundreds of people in Ecuador and
Peru and caused millions of dollars in damage along the Southern California
coast.  Cyclones left 25,000 people homeless in Tahiti and severe droughts
plagued the southern hemisphere, especially Australia, Indonesia, the
Philippines and South Africa.

	TOPEX/POSEIDON will improve our knowledge of upper-ocean
circulation in the tropical Pacific, which is essential for reliable
prediction of these El Nio events.

	The ocean also is influenced by gravity and the Earth's rotation.
If the Earth did not rotate, the shape of the resting ocean would conform to
the Earth's gravity, a condition scientists refer to as the geoid.  But the
Earth is not still, and ocean currents raise or lower sea level from the
geoid.  The elevation of sea level relative to the geoid is called ocean
topography.

	Sea currents contribute to the low hills and shallow valleys in the
ocean which are similar to the high and low pressure systems that occur in
the atmosphere.  Sea water flows around these hills and valleys just as winds
blow around the highs and lows of atmospheric surface pressure.
TOPEX/POSEIDON will measure these changes in ocean topography, and
scientists will calculate the speed and direction of ocean surface currents.

SATELLITE TRACKING

	TOPEX/POSEIDON is equipped with instruments that enable
scientists to accurately pinpoint the satellite's location.  Precise orbit
determination is crucial because errors in locating the spacecraft would
distort the sea level measurement calculated from the altimeter readings.

	TOPEX/POSEIDON will measure the distance from the satellite to the
sea surface within 1.2 inches (3 cm).  Three independent tracking systems
will determine the position of the spacecraft within 4 inches (10 cm).  The
first, the NASA laser retroreflector array (LRA) will reflect laser beams from
a network of 10 to 15 ground-based laser ranging stations under clear skies.
	The second, for all-weather, global tracking, will be provided by the
CNES Doppler Orbitography and Radiopositioning Integrated by Satellite
tracking system receiver (DORIS).  This device uses microwave doppler
techniques (changes in radio frequency corresponding to relative velocity)
to track the spacecraft.  DORIS consists of an on-board receiver and a global
network of 40 to 50 ground-based transmitting stations.

	The third system utilizes an on-board experimental Global Positioning
System (GPS) demonstration receiver to precisely determine the satellite's
position continously by analyzing the signals received from the U.S Air
Force's GPS constellation of Earth orbiting satellites.

	TOPEX/POSEIDON also will fly over two verification sites so that
scientists can compare data taken on the ground to the readings obtained
from the satellite.  These sites are located on the Texaco Harvest Oil
Platform off Point Conception, Calif., (the NASA site) and near Lampedusa
Island in the Mediterranean Sea (the CNES site).  Throughout the mission,
comparisons of the information collected at these sites will ensure that the
satellite's instruments are calibrated very precisely.

THE SATELLITE

	The TOPEX/POSEIDON spacecraft is based on the existing
Multimission Modular Satellite (MMS) bus, modified to meet the needs of
this mission.  Built by Fairchild Space, the satellite is comprised of the MMS
and an instrument module which houses the sensors.

	The MMS command and data handling subsystem contains the main
computer on-board TOPEX/POSEIDON.  It interprets and executes
commands and receives data from all subsystems and sensors for
transmission to the ground.  The command and data handling subsystem
houses three tape recorders used for engineering telemetry and science
data storage.  Each tape recorder will record for about four revolutions or 8
hours of data before playback.

	This subsystem also provides telecommunications using a steerable
high-gain antenna dish and two omni antennas.  During normal operations,
the satellite communicates with the ground via the Tracking and Data Relay
Satellite System (TDRSS).  This link handles all commands, science data,
engineering telemetry and the operational orbit tracking for navigation and
mission planning.

	The attitude determination and control subsystem maintains the
proper spacecraft attitude during mission operations and points and
stabilizes the satellite during all orbit adjustments.  It also will
automatically "take charge" to put the satellite into a "safing" mode if
it detects a problem with its own performance or if it does not receive
the periodic "I'm OK" signal from the on-board computer.

	The spacecraft's electrical power subsystem contains the solar array
and three batteries.  The solar array is the main power source and the first
item to be deployed, 2 minutes after separation from the launch vehicle.
After deployment, the on-board controller rotates the array so that the
panels face the sun.

	The batteries provide power from about 10 minutes before launch
until the solar array takes over.  The batteries also are used to keep the
instruments operating while the spacecraft is orbiting the night side of the
Earth.

SCIENCE INSTRUMENTS

	TOPEX/POSEIDON carries five scientific instruments.  Three are
provided by NASA and two by CNES.

The Dual-Frequency TOPEX Radar Altimeter (ALT)

	The primary instrument onboard the satellite is the dual-frequency
NASA radar altimeter (ALT).  Provided by NASA and managed by the
Goddard Spaceflight Center, the altimeter was built by the John Hopkins
University's Applied Physics Laboratory.  The instrument is designed to
measure the height of the satellite above the sea at two frequency channels,
13.6 GHz and 5.30 GHz.  This is the first altimeter to use two channels to
correct for measurement errors caused by free electrons above the Earth's
atmosphere.

The TOPEX/POSEIDON SPACECRAFT

TOPEX Microwave Radiometer (TMR)

	The companion TOPEX microwave radiometer, developed by NASA's
Jet Propulsion Laboratory, Pasadena, Calif., operates at three frequencies
(18 GHz, 21 GHz and 37 GHz)  The radiometer measures water vapor, which can
delay the return of the radar pulse to the spacecraft, along the path viewed
by the altimeter and corrects the altimeter data.  The 21 GHz channel is the
primary channel for water vapor measurement.  The 18 GHz and 37 Ghz
channels are used to remove the effects of wind speed and cloud cover,
respectively, in the water vapor measurement.

Single-Frequency Poseidon Altimeter (SSALT)

	SSALT is an experimental precision altimeter designed by CNES and
built by Alcatel Espace.  This instrument is being flown as an experiment to
validate improved solid-state technology, which results in smaller, lower-
power and lower-weight altimeters for future missions.

	SSAlt uses the same antenna as the NASA altimeter but operates at a
single frequency of 13.6 GHz.  During the first 6-month verification phase,
the SSALT will operate about 12 percent of the time to assess its
performance.  For the remainder of the mission, NASA and CNES will
determine an antenna sharing plan to optimize data collection.

Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS)

	The DORIS tracking system will provide important tracking data for
precision orbit determination using microwave Doppler techniques.  This is
a proven system manufactured by the French aerospace firms, Dassault,
CEPE and STAREC, and was first flown by CNES on the SPOT-2 satellite.

	The system is made up of an on-board receiver and a network of 40 to
50 ground transmitter stations.  Operating in all weather conditions, DORIS
receives signals at two frequencies (401.25 MHz and 2036.25 MHz) which
allows the total electron content of the ionosphere to be estimated.  This
allows the removal of SSALT altitude errors introduced by traveling through
the ionosphere.

Global Positioning System Demonstration Receiver (GPSDR)

	The GPSDR is an experimental receiver developed by JPL and
manufactured by Motorola to provide a unique tracking data type for
continuous precision orbit determination.  This new technique
simultaneously measures the satellite's position relative to the U.S. Air
Force's Global Positioning System and ground stations.  By adding the
ground stations, the exact locations of which have been precisely measured,
the new system promises to revolutionize orbit determination by providing
continuous satellite tracking with a potential accuracy of 4 inches (10 cm)
or better.  The GPS receiver operates at 1227.6 MHz and 1575.4 MHz.
MISSION PHASES

	The French-provided Ariane 42P launch vehicle, manufactured by
Arianespace, is a three-stage, liquid-propelled rocket, approximately 215
feet (60 meters) long, with two strap-on first-stage solid propellant motors.
The first two stages of the core vehicle are powered by hydrazine and
nitrogen tetroxide.  Stage three contains cryogenic liquid oxygen and
hydrogen.  The vehicle equipment bay is located between the third stage
and the payload compartment, and its inertial reference system and
computer conduct the ascent attitude control, guidance and sequencing.

	The spacecraft arrived at the Centre Spatial Guyanais in Kourou,
French Guiana, on June 23 to undergo a series of performance tests prior to
launch.  Five days before launch, the encapsulated satellite will be mated to
the launch vehicle.

	After that, the satellite will continue functional testing and battery
charging cycles in preparation for flight.  Final configuring for the launch
is achieved 90 minutes before liftoff, with the exception of the tape
recorders and transmitters.

	Transmitter A is turned on 2 hours before launch.  Two tape recorders
are commanded to record at launch minus 20 minutes.  At launch minus 10
minutes, the satellite is switched to internal battery power and the umbilical
disconnect process, which takes about 40 seconds, begins a minute later.

	After the umbilical is disconnected, real-time monitoring of the
satellite's functions will be conducted through the satellite's telemetry
transmitter.

Tracking During Launch

	Launch vehicle telemetry is coordinated primarily through the Guiana
tracking facilities at Kourou.  After injection (which occurs approximately 17
minutes after launch), real-time satellite telemetry is available through the
NASA tracking station at Bermuda.

	Telemetry also is recorded on two satellite tape recorders for later
playback.  Several critical events, including injection, the orientation
maneuver, satellite separation and solar array deployment occur while the
Bermuda station is tracking the satellite.

	Madrid is the first Deep Space Network (DSN) station to track the
satellite after launch.  This pass starts 20 minutes after launch
(approximately 1 minute after separation) and continues for 12 minutes.
The DSN 26-meter antennas are the primary method of communicating
during the first day.

	Beyond that, the DSN only will be used as an emergency method of
communicating.  For the balance of the mission, the primary method of
communicating between the satellite and the ground will be via the
Tracking and Data Relay Satellite System (TDRSS).  The first TDRSS contact
is established approximately 1 hour after launch.

MISSION TIMELINE

Mission Elapsed Time	Event
L-1 day	Launch vehicle propellant loading
L-09:30:00	Satellite functional tests
L-06:30:00	Battery cycling
L-02:00:00	Satellite Transmitter A ON
L-02:00:00	Final RF tests
L-01:30:00	Configure Satellite for Launch
L-00:20:00	Configure tape recorders/trackers
L-00:10:00	Set internal battery power
L-00:09:00	Start umbilical demate
L-00:06:00	Begin Ariane automatic launch seq.
L-00:00:09	Release Ariane inertial platform
L-00:00:00	LIFTOFF
L+00:01:28	Solid separation
L+00:03:19	Stage 1 burn out
L+00:03:48	Payload fairing jettisoned
L+00:05:30	Stage 2 burn out
L+00:17:38	Stage 3 shutdown/Orbit Injection
L+00:19:28	Separation
L+00:21:28	Solar Array Deployment
L+00:26:28	High Gain Antenna Deployment
L+00:27:28	GPS Antenna Deployment

Assessment Phase

	The assessment phase begins when the satellite separates from the
Ariane rocket.  For the first 45 days after launch, the satellite's sensors
and instruments will undergo check-out and assessment.  The first spacecraft
maneuver is scheduled for 7 days after launch to refine the satellite's
orbit.  Up to six additional maneuvers will be performed to attain the
precise observational orbit.

Initial Verification Phase

	This phase occurs after the assessment phase and gives the project
team time to calibrate the instruments against ground data they are
receiving from the two laser verification sites.  This phase lasts about 6
months.



Observational Phase

	The key objective of the observational phase is the production and
distribution of the Geophysical Data Records which contains sea surface
height, sensor corrections and geophysical information.  The science data
team is responsible for distributing and archiving these sensor and
geophysical data products.

SPACECRAFT SPECIFICS

Design lifetime:	3 years prime; 2 years extended mission
Length:	18 feet (5.5m)
Width:	9.2 feet (2.8m)
Solar panel:	28.5 feet x 10.8 feet (8.7m x 3.3m)
Power:	2,100 Watts
Mass:	5,500 pounds (2,500kg)

U.S.-FRENCH COOPERATION

	TOPEX/POSEIDON is only one area in which the U.S. and French
space programs are cooperating.  French scientists are principal
investigators or co-investigators on NASA's Galileo and Wind spacecraft and
the Upper Atmosphere Research Satellite.

	There has been substantial collaboration on several Spacelab missions,
including Space Life Sciences-1 in 1991 and the ATLAS-1 and International
Microgravity Laboratory-1 missions in 1992.

	There has been substantial collaboration on several Spacelab missions,
including Space Life Sciences-1 in 1991 and the ATLAS-1 and International
Microgravity Laboratory-1 missions in 1992.  The agencies are cooperating
in development of the Visual and Infrared Mapping Spectrometer to fly on
NASA's Cassini mission to Saturn in 1997.

	U.S.-French cooperation extends back to joint solar studies in the
1960s.  In 1978, CNES provided the ARGOS data collection system that flew
on the TIROS-N satellite and subsequent satellite search-and-rescue
equipment based on ARGOS technology.  In 1985, French payload specialist
Patrick Baudry flew on Space Shuttle mission 51-G, which deployed three
satellites.


MISSION MANAGEMENT

NASA Headquarters

Daniel Goldin	        Administrator

Aaron Cohen	        Acting Deputy Administrator

Dr. L.A. Fisk	        Associate Administrator,
	                Office of Space Science and Applications

Alphonso V. Diaz        Deputy Associate Administrator
	                Office of Space Science and Applications

Dr. Shelby G. Tilford	Director, Earth Science and Applications Division

Dr. W. Linwood Jones	Program Manager

Dr. William Patzert	Program Scientist


Centre Nationale d'Etudes Spatiales

Dr. Jean-Louis Fellous	Program Manager

Michel Dorrer	        Project Manager

Dr. Alain Ratier	Program Scientist

Dr. Michel Lefebvre	Project Scientist
	                Jet Propulsion Laboratory

Charles Yamarone Jr.	Project Manager

Dr. Lee-Lueng Fu	Project Scientist
     ___    _____     ___
    /_ /|  /____/ \  /_ /|     Ron Baalke         | baalke@kelvin.jpl.nasa.gov
    | | | |  __ \ /| | | |     Jet Propulsion Lab |
 ___| | | | |__) |/  | | |__   M/S 525-3684 Telos | Most of the things you 
/___| | | |  ___/    | |/__ /| Pasadena, CA 91109 | worry about will never
|_____|/  |_|/       |_____|/                     | happen.