Next-Generation GRACE Satellites Arrive at Launch Site

A pair of advanced U.S./German Earth research satellites
with
some very big shoes to fill is now at California’s Vandenberg
Air Force
Base to begin final preparations for launch next
spring.

Following a
year-long test campaign by satellite manufacturer
Airbus Defence and Space at
IABG in Ottobrunn, near Munich,
Germany, the twin Gravity Recovery and Climate
Experiment
Follow-On (GRACE-FO) satellites were loaded aboard an air
freighter
at Munich airport Dec. 11 and arrived at the launch
site on California’s
central coast Tuesday, Dec. 12. GRACE-FO
will provide continuity to the Earth
climate data record of
the extremely successful predecessor GRACE, which completed
its science mission in October after more than 15 years in
orbit.

GRACE-FO will
extend GRACE’s legacy of scientific
achievements, which range from tracking
mass changes of
Earth’s polar ice sheets and estimating global groundwater
changes,
to measuring the mass changes of large earthquakes
and inferring changes in
deep ocean currents, a driving force
in climate. To date, GRACE observations
have been used in more
than 4,300 research publications. Its measurements
provide a
unique view of the Earth system and have far-reaching benefits
to
society, such as providing insights into where global
groundwater resources may
be shrinking or growing and where
dry soils are contributing to drought.
GRACE-FO is planned to
fly at least five years.

The GRACE-FO spacecraft
will undergo final tests before being
integrated atop a SpaceX Falcon 9 rocket,
where they will
share a ride to space with five Iridium NEXT communications
satellites.

“With this milestone, we are now in position to launch GRACE
Follow-On and restart the valuable observations and science
that ceased in
mid-2017 with the end of the GRACE science
mission,” said Michael Watkins,
director of NASA’s Jet
Propulsion Laboratory in Pasadena, California, and GRACE
Follow-On science team lead.

After a few
months of in-orbit checkout, GRACE-FO will track
changes in
the distribution of liquid water, ice and land
masses by measuring changes in
Earth’s gravity field every 30
days. GRACE-FO
will essentially measure how much mass is
gained or lost each month on the
continents, in the oceans,
and in the ice sheets. These data will improve
scientific
understanding of Earth system processes and the accuracy of
environmental monitoring and forecasts.

The continuous
movement of masses of water, ice, air and the
solid Earth that GRACE-FO will
track is driven by Earth system
processes such as:

  • Terrestrial
    water cycle processes, such as precipitation,
    droughts, floods, changes in ice
    sheets and land glaciers,
    evaporation from the oceans, and groundwater use and
    storage.
  • Tectonic
    processes, such as earthquakes and variations in
    Earth’s lithosphere (the rigid
    outer layer of our planet that
    includes the crust and upper mantle) and mantle
    density.

The GRACE-FO satellites will be launched into a polar orbit
at
an altitude of about 311 miles (500 kilometers). Flying 137
miles (220
kilometers) apart, the satellites will use a
JPL-built microwave ranging system
to take continuous, very
precise measurements of the variations in the distance
between
each other. These variations are caused by minute changes in
the
gravitational pull on the satellites from local changes in
Earth’s mass below them.
The microwave ranging data are
combined with
GPS tracking for timing, star trackers for
attitude information, and an
accelerometer built at ONERA in
France to account for non-gravitational
effects, such as
atmospheric drag and solar radiation. From these data,
scientists will calculate how mass is redistributed each month
and monitor its
changes over time.

Each satellite
will also carry an instrument called an
atmospheric limb sounder that will
provide an innovative and
cost-effective technique to measure how much signals
from GPS
satellites are distorted by the atmosphere. The sounders will
provide up
to 200 profiles of atmospheric temperature and
water vapor content each day to
aid weather forecasting.

While similar
to their predecessor GRACE satellites, GRACE-FO
incorporates design upgrades
gleaned from 15 years of GRACE
operations that will improve satellite
performance,
reliability and mission operations. GRACE-FO will also fly a
new,
more precise inter-satellite laser ranging instrument,
developed by a
German/American joint venture, which will be
tested for use in future generations
of GRACE-like missions.

GRACE-FO is a partnership
between JPL and the German Research
Centre for Geosciences (GFZ) in Potsdam,
with participation by
Deutsches Zentrum für Luft- und Raumfahrt (DLR), the
German
Aerospace Center.

For more
information on GRACE-FO, visit:

https://gracefo.jpl.nasa.gov/

News Media Contact

Alan Buis
Jet Propulsion Laboratory, Pasadena, California
818-354-0474
Alan.Buis@jpl.nasa.gov

2017-320