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Thermal Vacuum Test of Kibo's Manipulator Main Arm

A Thermal Vacuum Test of Japanese Experiment Module Kibo's Manipulator Main Arm was conducted at the Tsukuba Space Center from June 29 to August 27, 1999.


Kibo's Manipulator
Main arm and Small fine arm
Kibo's manipulator is a robot arm. It consists of three components, the main arm, small fine arm, and manipulator console. The main arm will be used to manipulate large objects. The small fine arm will be attached to the end of the main arm and will be used to conduct fine manipulations. The manipulator console will be used to control both the main arm and the small fine arm. This manipulator will be used for exchanging experiment payloads or onboard equipment, and for supporting experiments or maintenance tasks.


Thermal vacuum test
Temperatures in space range from 120C (248F) in the sun to -150C (-238F) in the shade, a difference of 270C (486F). Also, in space, heat is transferred only by conduction and radiation; there is no convection. As a result, things heat up and cool down very quickly. Since the ISS circles the Earth in about 90 minutes, the ISS will heat up and cool down every 45 minutes.

Kibo's manipulator is thermally protected by thermal insulator and by heaters. The manipulator will be able to continue working for the 10-year ISS operational life, in spite of such great temperature swings because it is covered by thermal insulation. Furthermore, heater power will be turned on and off to keep its temperature within the required range.

This proof test is conducted to confirm that temperatures of the main arm's parts can be kept within the required range. The test results will be compared with the simulation output from the thermal model developed during the design phase. If a significant difference is found between them, the thermal math model will be revised.


Test Procedure
Placing the main arm in the 13m diameter space chamber.
A 13m diameter space chamber is used for this test. It can simulate the space vacuum and thermal environments. With the main arm inside, the air is removed to create a vacuum, and the wall is cooled by liquid nitrogen. Temperatures in about 180 locations on the main arm are then measured while applying simulated solar light to simulate the sunny and shaded environment. Xenon arc lamps, which have an optical spectrum similar to that of the sun, are used to simulate the solar light.

This test was conducted in the following two cases.

1)Launch configuration
Retracted position for launch
Kibo's manipulator will be launched in the cargo bay of the Space Shuttle. It will be attached to the Pressurized Module of Kibo with its arm bent in the retracted position and power turned off. The manipulator is covered by multilayer insulator (MLI). The MLI covering the joints will be removed by astronauts during extravehicular activity when Kibo is attached to the International Space Station (ISS) and its power is turned on.
2)Initial position in orbit
Initial position in orbit
The initial position is the position taken first when the manipulator is used in orbit. When the manipulator grasps or manipulates an object, it will take this initial position first then proceed to the next action. Power will be turned on beforehand.
Since the manipulator was designed to operate in a zero-gravity environment, the manipulator is turned 90 degrees and supporting poles are inserted under the joints to minimize gravitational effects.


Thermal math model
A thermal math model is a mathematical equations which represents manipulator temperature conditions in a space environment. Items that are impossible to test on the Earth are evaluated by simulation using this thermal math model. For instance, the manipulator temperature will be affected by thermal sources other than solar radiation, such as radiation from Kibo's exposed facility, or the heat generated by the actions of the manipulator itself.

It would be convenient to conduct these tests on the ground systematically and consequently proved the manipulator's thermal design to be reasonable. However, since the manipulator was designed to be operated only in a zero-gravity environment, manipulator movement tests cannot be conducted in the direction of gravitational force. Also, since we have no test facility capable of accommodating the total Kibo system, it is impossible to test all of the cases. The thermal math model is utilized to cover these cases.


Comments from the key person
It takes up to one and a half days to remove the air in the space chamber to create a vacuum. Furthermore, the test scale is quite large, so we have to be very careful in preparing for the test. During this test period, we attached the manipulator to the thermal dummy of Kibo's pressurized module, and set the manipulator in its initial position in orbit. This is the first and the last opportunity for Kibo's manipulator to take this position on Earth, so the picture here is precious.
Manipulator is attached to Kibo's thermal dummy and is set to its initial position.Mr. Shinnji Ueno
JEM Project Team
Office of Space Utilization Systems
NASDA


Last Updated : November 25, 1999

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