Bearing test for mirror support mechanism of space infrared telescope - design and evaluation of rigid spacer for hybrid ball bearing in cryogenic environment -

Paper number

IAC-06-C2.2.07

Author

Mr. Masaki Haruna, Mitsubishi Electric Corporation, Japan

Coauthor

Mr. Masaki Tabata, Mitsubishi Electric Corporation, Japan

Coauthor

Mr. Naoya Tanaka, Mitsubishi Electric Corporation, Japan

Coauthor

Mr. Takeharu Oshima, Mitsubishi Electric Corporation, Japan

Coauthor

Prof. Takashi Onaka, Japan Aerospace Exploration Agency (JAXA)/ISAS, Japan

Coauthor

Dr. Keigo Enya, Japan Aerospace Exploration Agency (JAXA)/ISAS, Japan

Coauthor

Mr. Hidehiro Kaneda, Japan Aerospace Exploration Agency (JAXA)/ISAS, Japan

Coauthor

Prof. Takao Nakagawa, Japan Aerospace Exploration Agency (JAXA)/ISAS, Japan

Year

2006

Abstract

In order to observe deep space, SPICA(Space Infrared telescope for Cosmology and Astrophysics) project is planned by a working group on JAXA (originally, ISAS). The SPICA satellite will be launched by an H-IIA rocket to Solar-Earth L2 Halo orbit. The SPICA telescope is a Ritchey-Chretien optics with 3.5m diameter primary mirror, and cooled down to 4.5K in orbit by radiation cooling and mechanical cryo-coolers. Main wavelengths of the SPICA observation are 5 - 200 micron. According to precedential satellites, many highly technical development would be needed to realize the SPICA mission.
 
One of the key components is a mirror support mechanism to connect the large primary mirror to the optical bench. A usage of ball bearings for the mechanism is suggested. It is required the ball bearings not only to meet some special requirements to space (ultra high vacuum, high reliance, tolerance for launch vibration load, and etc.), but also to restrain force transmitting to the mirror generated by a relative difference of thermal deformations between the mirror and the optical bench under an extreme temperature change from 300K to 4.5K.

In our previous research, as a first step, a bearing test equipment was developed in order to take an accurate measurement of friction torque in cryogenic environment and it was confirmed that a hybrid ball bearing constructed of Silicon Nitride balls (Si3N4) and stainless steel inner and outer rings was useful to suppress cold welding in ultra high vacuum environment. As a next step, it is needed to reduce an increase of friction torque caused by a difference of thermal deformations between Si3N4 balls and stainless steel rings of a hybrid ball bearing preloaded with rigid spacer under cooling down to cryogenic temperature.

 In this paper, in the first, it is mentioned that a rigid spacer for a hybrid ball bearing is designed in order to compensate the thermal deformations in cryogenic environment, and it is confirmed that the increased friction torque caused by the deformations under the extreme temperature change is able to be suppressed by the usage of the designed rigid spacer. In the secondly, it is indicated that the tolerance of the hybrid-bearing and the rigid spacer for launch vibration load is verified by the fact that the difference between the friction torque in cryogenic environment before and after the vibration test is within the accuracy of the developed test equipment.

Abstract document

IAC-06-C2.2.07.pdf