[P-PS11] Planetary Sciences

[PPS11-26] JUICE/GALA-J (1) : The Ganymede Laser Altimeter (GALA) for the JUICE mission
- Introduction, current status, and role of the Japan team

*Keigo Enya¹, Noriyuki Namiki², Masanori Kobayashi³, Jun Kimura⁴, Hiroshi Araki², Hirotomo Noda², Shoko Oshigami², Shingo Kashima², Ko Ishibashi³, Shingo Kobayashi⁵, Masanobu Ozaki¹, Takahide Mizuno¹, Shin Utsunomiya¹, Yoshifumi Saito¹, Kazuyuki Touhara¹, Shunichi Kamata⁵, Koji Matsumoto², Kiyoshi Kuramoto⁵, Sho Sasaki⁶, Satoru Iwamura⁷, Teruhito Iida⁸, Yoshiaki Matsumoto⁸, Masanori Fujii⁹, Naofumi Fujishiro¹⁰, Tomoyasu Yamamuro¹¹, Kay Lingenauber¹², Thomas Behnke¹², Juergen Oberst¹², Judit Jaenchen¹², Horst-Georg Loetzke¹², Harald Michaelis¹², Hauke Hussmann¹² (1.JAXA/ISAS, 2.NAOJ, 3.CIT, 4.Earth-Life Science Institute, Tokyo Institute of Technology, 5.Hokkaido University, 6.Osaka University, 7.MRJ, 8.PLANET, 9.FAM Science, 10.Astro-Opt, 11.OptCraft, 12.DLR)

Keywords:JUICE, GALA, Jupiter, Icy moon, Ganymede, Laser altimeter

We present an introduction, current status, and especially role of the Japan team for the Ganymede Laser Altimeter (GALA) for the Jupiter Icy Moon Explorer (JUICE) mission. JUICE is a mission of ESA to be launched in 2022, and GALA is one of the payloads of JUICE.
Major objectives of GALA are to provide topographic data of Ganymede, the largest satellite of Jupiter, and to measure its tidal amplitudes. The latter is crucially important to detect and to characterize an underground ocean on Ganymede. Furthermore, GALA support geological studies, e.g., identification of characterization of tectonic and cryo-volcanic regions, impact basins, and craters. GALA also provides information on surface roughness and the albedo.
For the laser altimetry, GALA emits and receives laser pulses at about 500 km altitude above Ganymede. Wavelength, energy, and nominal repetition frequency of the laser pulse are 1064 nm, 17 mJ, and 30 Hz, respectively. Reflected beam from the Ganymede surface is received by the receiver telescope with 25 cm diameter aperture, re-focused by the BEO including a narrow band-pass filter, and then detected by the APD detector.
Development of GALA is carried out in international collaboration from Germany, Japan, Switzerland, and Spain. GALA-Japan will develop the Backend Optics (BEO), the Focal Plane assembly (FPA) including an avalanche photo-diode (APD) detector, and the Analog Electronics module (AEM) in the receiver chain. It should be noted that responsibility of development of the receiver telescope has been moved from Japan to Germany. Based on the heritage of studies for the telescope, GALA-Japan will contribute to the receiver telescope development through the German team.