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Z1 truss


Z1 truss
Z1truss
The Z1 truss is an early exterior framework to allow first U.S. solar arrays on flight 4A to be temporarily installed on Unity for early power. It weighs 8.3t and is 4 to 5m in length and width. It is made of aluminum alloy and will be attached to the Unity module during mission STS-92.
It includes four control moment gyros (CMGs) that perform attitude control, S-band and K-band antennas for communicating with ground stations, and DC-to-DC converter Units(DDCUs) .
The CMGs and communications antennas will be launched mounted on the Z1 truss; the DDCUs and EVA Tool Stowage Devices(ETSD) will be attached to the Z1 truss by EVAs.

Structure of the Z1 truss
The P6 truss (with solar arrays)
will be installed in this direction.
Zarya and Zvezda are to
be oriented in this direction.
  The shuttle docking port (PMA-2)
is to face this direction.

View from opposite side of MBM

MBM(Manual Berthing Mechanism)
ETSD(EVA Tool Stowage Device)
RPCM(Remote Power Controller Module
SGANT(Space-to-Ground Antenna)


Common Berthing Mechanism (CBM)
A common berthing mechanism (CBM) will be used for the first time to connect Unity and the Z1 truss.
The CBM is a commonly used mechanism to connect non-Russian pressurized modules. Two pressurized modules will be brought to the connection position using a robot arm, and the each modules latch mechanisms will be connected by driving a motor which includes active CBM(ACBM). Once the connection is established, the CBM will Provide the resource connection such as, electrical power, communication signals, and fluid between the connected modules. It also serves as a path for the crew. A total of six CBMs will be mounted on each nodes. At present, only Unity (node-1) has been launched. A CBM will also be used to connect the Japanese Experiment module "Kibo" to the ISS.
Connecting modules using the CBM is an extremely difficult operation that requires fine robot arm manipulations. Cooperation between crew members is also important. The Passive CBM(PCBM) that takes the passive position will be launched attached to the Z1 truss.

PCBM
(passive CBM, Z1 truss side)
ACBM
(Active CBM, Unity side)


Control moment gyro (CMG)

Control moment gyro (CMG)
A CMG generates torque to control large spacecraft. It can generate larger angular momentum and torque than the reaction wheels (*1) used for satellite attitude control.
In a CMG, a flywheel(*2) attached to the gimbal(*3) is rotated at a constant speed (6,600rpm for ISS), generating a large angular momentum. Since the gimbal containing the flywheel tries to maintain a constant direction, any action by another motor to tilt this gimbal generates a large torque. This is the same gyro effect you can experience when spinning a toy top.
The magnitude of this force is the product of the angular momentum of the flywheel and the rotation speed of the gimbal. This method can generate dozens of times greater torque than a reaction wheel. CMGs have been used in the US Skylab and in the Russian space station Mir.
CMGs will be launched attached to the Z1 truss, and activated on flight 5A.


*1. Reaction wheel: Used to change a satellite attitude by the reaction of acceleration or deceleration torque generated by changing the rotation speed of the flywheel.
*2. Gimbal: A device that allows an attached system to take any desired attitude. Installed in stands of ship compasses and airborne cameras.
*3. Flywheel: A device used to maintain a stable attitude; stores angular momentum by rotating a wheel with a mass.

S-band communication system
The S-band communication system will transmit and receive ISS operation data and voice data to and from Earth.

Ku-band communication system
The Ku-band communication system will transmit large amount of various data to Earth obtained from experiments on ISS as well as image, voice and other data.



Last Updated : September 28, 2000

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