3:30 PM - 5:00 PM
[PPS01-P05] The Ganymede Laser Altimeter (GALA) for the Jupiter Icy Moons Explorer (JUICE): The Backend Optics (BEO) mocule and the Focal Plane Assembly (FPA) module
Keywords:JUICE, GALA, Jupiter, Ganymede, BEO, FPA
The Jupiter Icy Moons Explorer (JUICE) is a science mission led by the European Space Agency, being developed for launch in 2023. The Ganymede Laser Altimeter (GALA) is an instrument onboard JUICE. The development of GALA has proceeded through an international collaboration between Germany (the lead), Japan, Switzerland, and Spain. The Backend Optics (BEO) and the Focal Plane Assembly (FPA) are GALA's hardware modules developed in Japan (as well as the Analogue Electronics Module, AEM).
BEO receives the return plus from the receiver telescope, and performs spatial filtering using a pinhole entrance and wavelength filtering using a bandpass filter to achieve a high signal-noise-ratio. The entrance aperture of BEO is a pinhole with a diameter of 700 micron. The mechanical interface between the German-made side (the receiving telescope side) and BEO was set so that the pinhole aperture was located at the focal point of the receiving telescope. The number of lenses (made of quartz) was minimized to two and both sides of each lens were treated with an anti-reflection coating to realize the required efficiency of the optical system. The bandpass filter achieved a good transmissivity of 96% on average (the required value was 90%) through the entire required transmission wavelength range (1064.53+/-1.5 nm). The BEO housing is made of stainless steel with surface treatment applied, which also has role of radiation shield. To meet the requirements of the mechanical interface with the receiving telescope, the BEO housing was manufactured by high precision machining from a single piece material. The lens optics and the bandpass filter are housed in the housing without the use of adhesives.
FPA houses the avalanche photodiode (APD) sensor module. FPA receives the return pulse from BEO, and converts it from an optical signal into an analog electrical signal using the APD detector (for more detail about the APD detector, see presentation by Kobayashi et al. in this meeting). As well as the BEO housing, the FPA housing is made of stainless steel with surface treatment applied, which also has role of radiation shield. Two optical fibers (for redundancy) feed a small fraction of the start pulse into FPA. The fed start pulse is concentrated by small ball lens, and introduced onto the APD detector by tiny mirror optics. The mirror optics is realized by machining structure parts inside FPA and applying gold coating. Thanks to this configuration, the start pulse and the return pulse are detected using one APD detector, which provides an advantage for determining the time difference of the start and the return pulse. Removing the heat generated by the APD is sometimes a problem in development of a laser altimeter. For FPA for GALA, we developed thermal path removing the heat form the APD module, which is compact and has high thermal conductivity and low stiffness.
Individual, and then integrated testing was conducted for BEO and FPA in Japan, as well as AEM. Hardware simulators were developed and utilized, for international development of GALA. In July 2020, the Proto-Flight Models of BEO, FPA, and AEM were delivered from Japan to Germany.
In this presentation, we show development of the BEO and the FPA.
BEO receives the return plus from the receiver telescope, and performs spatial filtering using a pinhole entrance and wavelength filtering using a bandpass filter to achieve a high signal-noise-ratio. The entrance aperture of BEO is a pinhole with a diameter of 700 micron. The mechanical interface between the German-made side (the receiving telescope side) and BEO was set so that the pinhole aperture was located at the focal point of the receiving telescope. The number of lenses (made of quartz) was minimized to two and both sides of each lens were treated with an anti-reflection coating to realize the required efficiency of the optical system. The bandpass filter achieved a good transmissivity of 96% on average (the required value was 90%) through the entire required transmission wavelength range (1064.53+/-1.5 nm). The BEO housing is made of stainless steel with surface treatment applied, which also has role of radiation shield. To meet the requirements of the mechanical interface with the receiving telescope, the BEO housing was manufactured by high precision machining from a single piece material. The lens optics and the bandpass filter are housed in the housing without the use of adhesives.
FPA houses the avalanche photodiode (APD) sensor module. FPA receives the return pulse from BEO, and converts it from an optical signal into an analog electrical signal using the APD detector (for more detail about the APD detector, see presentation by Kobayashi et al. in this meeting). As well as the BEO housing, the FPA housing is made of stainless steel with surface treatment applied, which also has role of radiation shield. Two optical fibers (for redundancy) feed a small fraction of the start pulse into FPA. The fed start pulse is concentrated by small ball lens, and introduced onto the APD detector by tiny mirror optics. The mirror optics is realized by machining structure parts inside FPA and applying gold coating. Thanks to this configuration, the start pulse and the return pulse are detected using one APD detector, which provides an advantage for determining the time difference of the start and the return pulse. Removing the heat generated by the APD is sometimes a problem in development of a laser altimeter. For FPA for GALA, we developed thermal path removing the heat form the APD module, which is compact and has high thermal conductivity and low stiffness.
Individual, and then integrated testing was conducted for BEO and FPA in Japan, as well as AEM. Hardware simulators were developed and utilized, for international development of GALA. In July 2020, the Proto-Flight Models of BEO, FPA, and AEM were delivered from Japan to Germany.
In this presentation, we show development of the BEO and the FPA.