Abstract
The Ganymede Laser Altimeter (GALA) is one of the ten scientific instruments selected for the Jupiter Icy Moons Explorer (JUICE) mission currently implemented under responsibility of the European Space Agency (ESA). JUICE is scheduled for launch in mid 2022; arrival at Jupiter will be by end of 2029 with the nominal science mission—including close flybys at Ganymede, Europa, and Callisto and a Ganymede orbit phase—ending by mid 2033. GALA’s main objective is to obtain topographic data of the icy satellites of Jupiter: Europa, Ganymede, and Callisto. By measuring the diurnal tidal deformation of Ganymede, which crucially depends on the decoupling of the surface ice layer from the deep interior by a liquid water ocean, GALA will obtain evidence for (or against) a subsurface ocean in a 500 km orbit around the satellite and will provide constraints on Ganymede’s ice shell thickness. In combination with other instruments, it will characterize the morphology of surface units on Ganymede, Europa, and Callisto providing not only topography but also surface roughness and albedo (at 1064 nm) measurements. GALA is a single-beam laser altimeter operating with up to 50 Hz (nominal 30 Hz) shot frequency at a wavelength of 1064 nm and pulse lengths of \(5.5\pm 2.5\) ns using a Nd:YAG laser. The return pulse is detected by an Avalanche Photo Diode (APD) with 100 MHz bandwidth and is digitized at a sampling rate of 200 MHz providing range measurements with a subsample resolution of 0.1 m and surface roughness measurements from pulse-shape analysis on the scale of the footprint size of about 50 m at 500 km altitude. The instrument is developed in collaboration of institutes and industry from Germany, Japan, Switzerland, and Spain.
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Abbreviations
- ADC:
-
Analog-to-digital converter
- AEM:
-
Analog electronics module
- APD:
-
Avalanche photo diode
- BELA:
-
BepiColombo laser altimeter
- BEO:
-
Back-end optics
- CDR:
-
Critical design review
- DC:
-
Direct current
- DPM:
-
Digital processing module
- ELU:
-
Electronics unit
- EM:
-
Engineering model
- EMC:
-
Electro-magnetic compatibility
- EMI:
-
Electro-magnetic interference
- EQM:
-
Engineering qualification model
- ESA:
-
European space agency
- FPA:
-
Focal-plane assembly
- FPGA:
-
Field programmable gate array
- GALA:
-
Ganymede laser altimeter
- JUICE:
-
Jupiter icy moons explorer
- LEU:
-
Laser electronics unit
- LHM:
-
Laser head module
- MLI:
-
Multilayer insulation
- M1:
-
Main mirror
- M2:
-
Secondary mirror
- MOS:
-
Metal-oxide semiconductor
- Nd:YAG:
-
neodymium-doped yttrium aluminum garnet, \(\hbox {Nd:Y}_3\hbox {Al}_5\hbox {O}_{12}\)
- PCM:
-
Power converter module
- PFM:
-
Proto flight model
- RFM:
-
Range finder module
- RX:
-
Receiver
- RXM:
-
Receiver module
- STM:
-
Structural and thermal model
- TEL:
-
Receiver telescope
- TID:
-
Total ionizing dose
- TRU:
-
Transceiver unit
- TX:
-
Transmitter
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Acknowledgements
The authors would like to thank two anonymous reviewers for their helpful comments on a first version of the manuscript. Financial support was provided under grant 50 QJ 1401 on behalf of the DLR Space Administration by the German Bundesministerium für Wirtschaft und Energie. This research has been supported by the Spanish Ministerio de Economía y Competitividad under Contract ESP 2016–76076–R.
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Hussmann, H., Lingenauber, K., Kallenbach, R. et al. The Ganymede laser altimeter (GALA): key objectives, instrument design, and performance. CEAS Space J 11, 381–390 (2019). https://doi.org/10.1007/s12567-019-00282-8
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DOI: https://doi.org/10.1007/s12567-019-00282-8