The SLIM lander (Smart Lander for Investigating Moon) is a small-scale lunar lander developed by the Japan Aerospace Exploration Agency (JAXA). Its mission goal was to demonstrate precise landing technology on the Moon’s surface. SLIM successfully landed on the Moon on January 20, 2024. However, due to its solar panels not facing the intended direction, the spacecraft ran on battery power for only a few hours. Controllers then shut it down, hoping sunlight might later recharge its batteries. On January 28, 2024, JAXA confirmed that communication with the SLIM lander was successfully re-established, allowing mission operations to resume. On the same day, we captured its radio signal from the Moon using our INTREPID 500-20 5.0m ground station for S/X/Ku/Ka-band!
SLIM lander radio signal in S-band
On January 28 at 22:30 UT, our INTREPID 500-20 ground station, installed in Italy, detected the SLIM lander radio signal in S-band.
- Ground station: INTREPID 500-20, 5-meter diameter, S/X-band.
- Waterfall plot: processed with a 131k channel FFT over a 2.5 MHz bandwidth.
- Spectral resolution: 19 Hz/channel.
- Main carrier frequency: ~2212 MHz with SNR of 15 dB.
- Subcarriers: Two subcarriers clearly visible, located ~680 kHz from the main carrier, about 10 dB weaker.
- Modulation: No modulation detected in this observation.
This analysis confirms a stable carrier signal transmitted from the lunar surface.
Doppler analysis of SLIM lander
We also performed a Doppler analysis on the SLIM lander signal acquired on January 28, from 21:39 to 21:52 UT (907s) in the S-band.
- Carrier frequency: ~2212 MHz.
- Resolution: 0.08 Hz/channel.
- Result: The signal’s Doppler curve matches that of a fixed object on the Moon’s surface.
Interestingly, the observed Doppler shift differs slightly from the model predicted by Horizon software. This variation is consistent with the “double Doppler” effect, which occurs when a ground station tracks a stationary lunar object.
Conclusion
The successful detection of the SLIM lander signal by the INTREPID 500-20 ground station highlights both the spacecraft’s resilience and the capabilities of our ground system. Capturing radio signals from the Moon in the S/X/Ku/Ka bands not only supports lunar exploration but also demonstrates the importance of advanced space communication technologies in future missions.
