ALMA high-performance nutating subreflector

Victor L. Gasho; Simon J. E. Radford; Jeffrey S. Kingsley

doi:10.1117/12.457911

4 February 2003 ALMA high performance nutating subreflector

Victor L. Gasho, Simon J. E. Radford, Jeffrey S. Kingsley

Proceedings Volume 4837, Large Ground-based Telescopes; (2003) https://doi.org/10.1117/12.457911
Event: Astronomical Telescopes and Instrumentation, 2002, Waikoloa, Hawai'i, United States

Abstract

For the international ALMA project’s prototype antennas, we have developed a high performance, reactionless nutating subreflector (chopping secondary mirror). This single axis mechanism can switch the antenna’s optical axis by ±1.5’ within 10 ms or ±5’ within 20 ms and maintains pointing stability within the antenna’s 0.6” error budget. The light weight 75 cm diameter subreflector is made of carbon fiber composite to achieve a low moment of inertia, <0.25 kg m². Its reflecting surface was formed in a compression mold. Carbon fiber is also used together with Invar in the supporting structure for thermal stability. Both the subreflector and the moving coil motors are mounted on flex pivots and the motor magnets counter rotate to absorb the nutation reaction force. Auxiliary motors provide active damping of external disturbances, such as wind gusts. Non contacting optical sensors measure the positions of the subreflector and the motor rocker. The principle mechanical resonance around 20 Hz is compensated with a digital PID servo loop that provides a closed loop bandwidth near 100 Hz. Shaped transitions are used to avoid overstressing mechanical links.

Citation Download Citation

Victor L. Gasho, Simon J. E. Radford, and Jeffrey S. Kingsley "ALMA high performance nutating subreflector", Proc. SPIE 4837, Large Ground-based Telescopes, (4 February 2003); https://doi.org/10.1117/12.457911

ACCESS THE FULL ARTICLE

INSTITUTIONAL
Select your institution to access the SPIE Digital Library.

SELECT YOUR INSTITUTION

PERSONAL
Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.

PERSONAL SIGN IN

No SPIE Account? Create one

PURCHASE THIS CONTENT

SUBSCRIBE TO DIGITAL LIBRARY

50 downloads per 1-year subscription

Members: $195

Non-members: $335 ADD TO CART

25 downloads per 1 - year subscription

Members: $145

Non-members: $250 ADD TO CART

PURCHASE SINGLE ARTICLE

Includes PDF, HTML & Video, when available