With just six hours of satellite
coverage for high-speed data
transmission, researchers at the
South Pole have had a limited window of
opportunity for transmitting their data.
With more advanced technologies comes
a need for increased functionality and
more data capacity. During the past two
years, Raytheon Polar Services and its
partners have been building a new South
Pole satellite communications system to
meet this need.
With the enormous data sets created by
ongoing expansion of the IceCube neutrino
detector and increasing data from the South
Pole Telescope, the current intercontinental
satellite communications pipeline is full. The
new system's science data link transmission
rate was increased to 150 megabits per
second or about 100 times faster than most
home high-speed Internet connections. The
South Pole also has greater flexibility in
using NASA's Tracking Data and Relay
Satellite (TDRS) system. The station can now
schedule time on any TDRS satellite simultaneously
visible at the South Pole and NASA's
White Sands Complex in New Mexico. The
aggregate daily connect time through all
satellites will vary daily and may be more or
less than the fixed six hours currently provided
by NASA's TDRS Flight 1 (TDRS F1).
The daily pass schedule depends on many
things, including: queued data volume,
TDRS mission taskings such as the space
shuttle or Hubble Space Telescope, satellite
visibility at the Pole, and equipment status.
The Current State
Most communications satellites are in geosynchronous
orbits (GEO) parked in a fixed
location over the equator. Their position and
the Earth's curvature hide them from the
North and South Poles. Low earth orbiting
(LEO) satellites can cover the Poles, but only
for brief periods of time, and they require
more satellites (like the Iridium constellation,
which has 66 satellites). Currently, there is
no LEO satellite constellation with the
bandwidth that the South Pole needs for
off-continent science data transmissions.
In 24 hours, a GEO satellite traverses a
ground trace that looks like a big Figure 8.
When the bottom of the Figure 8 has an
angle greater than 8.5 degrees below the
equatorial plane, the satellite becomes
visible at the South Pole for several hours of
its orbit. This orbital characteristic provides
the station access to communication systems
that support Internet and telephone
service access for the few hours a day that
the satellite can be "seen."
When satellites get old, they begin to
stray outside of their normal orbit patterns,
moving farther north and south. Since
1999, the South Pole has used NASA's
TDRS F1, which is now nearing the end of
its life. It could fail tomorrow or last a few
more years; no one knows for sure.
However, everyone seems to agree that
it is operating well beyond its design life.
The original South Pole TDRS Relay satellite
ground station (SPTR-1, pronounced
spitter-one) uses TDRS F1, fixed pointing
antennae, and an electronics suite incompatible
with the rest of NASA's TDRS satellite
constellation and ground station
network. The fixed pointing antennae limit
the number of hours during which data
can be transmitted off station. When TDRS
F1 reaches end-of-service life, SPTR-1 will
become obsolete.
Enter SPTR-2
A team comprising managers, engineers
and technicians from the National Science
Foundation (NSF); Raytheon Polar Services;
Space and Naval Warfare Systems Center
Charleston, S.C.; LJT & Associates; NASA
White Sands, N.M.; Goddard Space Flight
Center, Md.; and L-3 Datron designed,
engineered, installed and now operate a
new South Pole satellite communications
system called South Pole TDRS Relay-2
(SPTR-2). The system encompasses new
electronics at White Sands and the South
Pole as well as a new tracking 4-meter diameter
antenna that permits expanded
communications over NASA's Space
Network. The new antenna is currently
being used with SPTR-1 electronics while
TDRS F1 is still operational, providing the
station complete TDRS F1 pass coverage
and the maximum data rate possible.
Operating in this configuration also provides
valuable data and experience that will be
useful when full SPTR-2 operations turn to
using the TDRS F4, F5 and F6 satellites.
SPTR is not just a satellite communications
system. It also incorporates a science data
store-and-forward system; interfaces with
station communications infrastructure for
Internet service, telephone service and
video teleconferencing; and White Sands-to-Denver network upgrades. Raytheon
Polar Services designed and implemented
these critical data communications and
network components during a SPTR-1 upgrade
at the South Pole, White Sands and
Denver during the last two years. These
subsystems will continue operating in the
SPTR-2 architecture.
Raytheon Polar Services' role in the SPTR-2
project was full-circle: from planning, design, management, engineering, procurement
and transportation, through actual
construction of the site, antenna
platform, equipment shelter, radome, data
networks and utility tie-ins at the South
Pole. It also played a key role in upgrading
the NSF data network at White Sands to
enhance performance, redundancy and security.
It will continue to provide the glue
to keep the technical and operational aspects
working together for the unique
Antarctic environment.
While SPTR-2 will give the station access to
more TDRS satellites, its use will be different
than that of TDRS F1. The South Pole
will not have exclusive access to the satellites
when they are above the local horizon.
Instead, the South Pole will submit
scheduling requests to NASA every week.
NASA will then assess all requests and
develop a daily contact time schedule for
all users, including the South Pole, based
on system status, operations needs and
mission priorities.
Change comes to all things, including the
South Pole. SPTR-2, like many aspects of
the new station, represents a change for
the South Pole community. However, it will
provide a reliable path for science data and
station communications between the continent
and outside world well into the 21st
century. Also, SPTR-2 has application beyond
South Pole communications. Raytheon is
using the project's engineering and operations
lessons learned in its efforts to field
National Polar-orbiting Operational
Satellite System (NPOESS) ground stations
that use similar equipment.
Raytheon Polar Services' role in the SPTR-2
project was full-circle: from planning, design, management, engineering, procurement
and transportation, through actual
construction of the site, antenna
platform, equipment shelter, radome, data
networks and utility tie-ins at the South
Pole. It also played a key role in upgrading
the NSF data network at White Sands to
enhance performance, redundancy and security.
It will continue to provide the glue
to keep the technical and operational aspects
working together for the unique
Antarctic environment.
