antenna aboard the space shuttle orbiter is located in the payload
bay; thus, Ku-band can be used only when the orbiter is on orbit.
The orbiter payload bay doors are opened and the Ku-band antenna
is deployed. The Ku-band system operates in the Ku-band portion
of the radio frequency spectrum between 15,250 MHz and 17,250 MHz.
The Ku-band carrier frequencies are 13.755 GHz from the TDRS to
the orbiter and 15.003 GHz from the orbiter to the TDRS. Once the
Ku-band antenna is deployed, the Ku-band system can be used as a
communication system to transmit information to and receive information
from the ground through the TDRSS. The Ku-band antenna aboard the
orbiter can also be used as a radar system for target tracking objects
in space, but it cannot be used simultaneously for Ku-band communications
and radar operations.
When the Ku-band
antenna is deployed aboard the orbiter and handover from the S-band
system to the Ku-band system occurs, the orbiter onboard NSP operates
with the Ku-band signal processor rather than the S-band transponder.
The data stream is then directed through the K-band signal processor
and Ku-band antenna to the TDRS in view, to the TDRS system WSGT
and to MCC-H on the return link. The process is reversed for the
forward link. If the Ku-band forward link is lost, the system reverts
(fail-safe) to S-band.
system can handle higher quantities of data than the S-band systems.
It transmits three channels of data, one of which is the same
interleaved voice and telemetry processed by the S-band PM system.
Two of the seven possible sources of information sent on the other
two channels are payload analog, payload digital, payload interleaver
bent-pipe, payload recorder, operations recorders, television
and Spacelab (if flown).
channels of data are sent to the Ku-band signal processor to be
interleaved. This signal then goes to the onboard deployed electronics
assembly, which contains the transmitter, to be transmitted to
the TDRS through the Ku-band antenna. The incoming signal goes
through the onboard Ku-band antenna to the onboard receiver in
the DEA and then through an internal electronics assembly (EA
1 is for communications and EA 2 is for radar) to the Ku-band
signal processor. Voice and commands are sent to the network signal
processor. A separate output from the Ku-band signal processor
is directed to the text and graphics system. (As previously mentioned,
since TDRS-A's Ku-band forward link is not functional, TAGS cannot
operate aboard the orbiters.)
deployed assembly is mounted on the starboard sill longeron in
the payload bay of the orbiter. It is deployed and activated after
the payload bay doors are opened. The deployed assembly consists
of a two-axis, gimbal-mounted, high-gain antenna; an integral
gyro assembly; and a radio frequency electronics box. The gimbal
motors position the Ku-band antenna, and the rate sensors determine
how fast the antenna is moving.
deployed antenna assembly is 7 feet long and 1 foot wide when
stowed in the payload bay. The parabolic antenna dish is 3 feet
in diameter and is a graphite epoxy structure. The deployed antenna
assembly weighs 180 pounds. The weight of the entire system is
can be steered in several selectable modes under manual control
by the flight crew or automatically by the SM computer. It provides
the interface with the TDRS when there is a line of sight between
the orbiter and TDRS.
shuttle reaches orbit, before the Ku-band antenna is deployed,
circuit breakers on panel R15 are closed to energize thermostatically
controlled heaters for the deployed electronics assembly, gimbals
and antenna assembly. They provide electrical power to the Ku-band
electronic elements, electronics assemblies 1 and 2, the signal
processor assembly and Ku-band portions of panel A2. Actual deployment
involves the controls and associated talkback displays on panel
R13L. The antenna is locked in the stowed position to clear the
adjacent payload bay doors and radiators when they are closed
processes and routes Ku-band FL and RL data. EA 1, containing
the communication data processor and antenna control electronics,
provides data to onboard displays, meters and computers. EA 2
provides control signals to configure the system for radar operations
in addition to receiving and processing return radar data.
and stowage of the Ku-band deployed assembly is controlled by
flight crew switches at the aft flight station. Twenty seconds
are normally required to deploy or stow the DA. In the deployed
position, the DA forms a 67-degree angle with the orbiter X axis.
Activating the Ku electronics frees the antenna gimbals by removing
the locking pins.
dish is edge-mounted on a two-axis gimbal. The alpha gimbal provides
a 360-degree roll movement around the pole or axis of the gimbal.
The beta gimbal provides a 162-degree pitch movement around its
axis. The alpha gimbal has a stop at the lower part of its movement
to prevent wraparound of the beta gimbal control cable. Since
the beta gimbal has only a 162-degree movement, there is a 4-degree
non-coverage zone outboard around the pole and a 32-degree non-coverage
zone toward the payload bay.
in the S-band discussion, there are times when the Ku-band system,
in view of a TDRS, is interrupted because the orbiter blocks the
Ku-band antenna's view to the TDRS because orbiter attitude requirements
or payloads' radiation sensitivities prohibit its use. In addition,
periodically the Ku-band antenna beta cabling may require positioning
to ensure that it does not become twisted in a way that could
cause the antenna to bind.
under S-band, the Ku-band system's narrow beam makes it difficult
for TDRS antennas to lock on to the signal. Therefore, the orbiter
uses the S-band system to lock the Ku-band antenna into position
first because the S-band system has a larger beamwidth. The procedure
for acquiring TDRS Ku-band communication from the orbiter is described
in the S-band section.
system return link consists of channel 1, modes 1 and 2, plus
one channel 2, modes 1 and 2, and one channel 3. Channel 1, modes
1 and 2, consists of 192 kbps of operational data (128 kbps of
operational data telemetry and payload interleaver plus two air-to-ground
voice links at 32 kbps each) plus one of the following selections
from channel 2, modes 1 and 2: (1) payload digital data from 16
kbps to 2 Mbps, (2) payload digital data from 16 kbps to 2 Mbps,
(3) operations recorder playback from 60 kbps to 1,024 kbps, or
(4) payload recorder playback from 25.5 kbps to 1,024 kbps. It
also includes one of the following from channel 3: mode 1 attached
payload digital data (real-time or playback) from 2 Mbps to 50
Mbps, mode 2 television (color or black and white) composite video,
or mode 2 real-time attached payload digital data or payload analog
system forward link consists of a mode 1 and 2 through the TDRS
in view. Mode 1 consists of 72-kbps data (two air-to-ground voice
streams at 32 kbps each and 8 kbps of command), 128-kbps TAGS
(used in place of the teleprinter) and 16-kbps synchronization.
Mode 2 consists of 72-kbps operational data (two air-to-ground
voice streams at 32 kbps each and 8 kbps of command).
S-band system, the Ku-band antenna must be stowed before the orbiter
payload bay doors are closed in preparation for atmospheric entry.
If the DA does not respond to normal stow operations, involving
proper orientation and locking of the antenna, or to the stow
operation itself, a direct stow switch on panel R13L is used.
Setting this switch to on bypasses the normal stow control sequences
and causes the DA to be driven inside the payload bay.
the normal stow nor the direct stow can position the DA inside
the payload bay, the DA can be jettisoned. To jettison the deployed
assembly, the crew closes the circuit breakers on panel ML86B
and activates the Ku ant arm and jett switches on panel A14, which
causes a guillotine to cut the cables to the DA and releases a
clamp holding the DA to the pivot assembly. The separation point
is between the DA and deployment mechanism about 20 inches above
the sill longeron. No ejective force is imparted to the DA; it
is merely cut loose and the orbiter maneuvers away from it. The
jettison operation takes approximately four seconds.
shuttle spacecraft transmits and receives through the S-band system,
the TDRS in view and the TDRS system; thus, the WSGT and MCC-H
are in the low-data-rate mode until the communications blackout
in entry. After blackout, the space shuttle again operates in
S-band through the TDRS system in the low-data-rate mode during
descent to as low a view as possible until it reaches the S-band
landing site ground station, which then transmits and receives
in the high-data-rate mode on S-band.