The tandem mission
ensures that Jason-1 will continue seamlessly adding to
the nine years of TOPEX/Poseidon data, and for a time--for as long
as TOPEX/Poseidon remains in good health--increasing our global coverage
of data twofold by doubling the science, and bringing us that much
closer to solving the global climate
puzzle.
Launched December 7, 2001, Jason-1 entered its
orbit 10 km (6 miles) below and leading TOPEX/Poseidon
by 1 to 10 minutes in very nearly the same orbit. Soon after launch,
Jason-1 deployed its solar array,
powered-up the instruments, and oriented the altimeter
to point down to geodetic nadir,
the shortest path to the ocean.
Jason-1 then raised its orbital altitude to a position as
close as 60 seconds away from TOPEX/Poseidon. Though at orbital
speeds of 8 km/sec, this may be 500 km (300 miles) away. Jason-1
will be positioned to move along the same groundtrack,
in front of TOPEX/Poseidon's path. These delicate maneuvers
should take between 20 and 40 days.
In position in front of TOPEX/Poseidon, Jason-1 and its predecessor will
cross-calibrate
their instruments. This period lasts up to six months. The near
simultaneous measurements from the same altitude of the same sea
surface locations by the Jason-1 and TOPEX/Poseidon altimeters will
enable a rigorous comparison and correlation of the Jason-1 and
TOPEX/Poseidon altimetry results.
Triple-tracking of the satellite's location by three onboard instruments:
the Laser Retroreflector Array,
the Blackjack
GPS
receiver, and the DORIS instrument
provides a means to very accurately locate Jason-1 relative to the
ocean's surface.
At the end of the calibration phase, TOPEX/Poseidon maneuvers to change its orbital position relative
to Jason-1. This is very tricky! The older spacecraft is commanded to move onto a parallel groundtrack
so that it will be mid-way between two adjacent Jason-1 groundtracks. Now the data stream will be doubled,
and, until TOPEX/Poseidon succumbs to the radiation-induced failures of spacecraft old age, the
investigators on earth will feast on a genuine banquet of scientific information.
For additional information on the tandem mission, watch the
tandem mission animation (1 MB Flash animation), or go to
The Tandem Mission page in the Science section.
