Looking for the James Webb Space Telescope

January 6th, 2022

Artist conception of the James Webb Space Telescope. (Credit: NASA GSFC/CIL/Adriana Manrique Gutierrez)

As the long-awaited launch of JWST happened recently at Christmas and it is on the 1.5 million km journey to Lagrange Point L2, I found some time to collect information about the communication system. I was very pleased to see a frequency in the satellite band next to the 13 cm amateur radio band. It is being used for a telemetry downlink with 6 W into a pair of omni-directional antennas. Feed and LNA are not really designed for this part of the band, but still usable with some loss. Later the scientific traffic will happen in the 26 GHz Ka-band.

When looking for tracking data, I found a two line element data set at NORAD dating back to December 28, 2021 for JWSTs NORAD number 50463.

1 50463U 21130A   21362.00000000  .00000000  00000-0  00000-0 0  9999
2 50463   4.6198  89.0659 9884983 192.3200  17.4027  0.01958082    27

My tracking software accepted it and the calculated information looked very plausible, as the distance to the object was very close to the one published on the official JWST website and azimuth and elevation pointed roughly to L2. I am aware, that JWST must not fly on the direct line, as it will be in a wide orbit around.

Five Lagrange points in the Sun-Earth-System (not to scale). (Credit: NASA)

As in the past, when I received signals from exotic sources like ISEE-3 and Longjiang-2, I used my 3 m dish with the ring feed and LNA for 2320 MHz. I tried to use one of my PLUTO SDRs instead of the 13 cm transverter, but these are far too deaf and the LNAs gain of 16 dB is not enough to show any change in the noise, when switching it on and off. So I used a similar configuration, as before and mounted the 13 cm band ATV converter, I used to receive TV signals from the ISS, to get a sufficient signal level on the IF for the PLUTO.

Trace of the JWST signal, it is not audible. (DJ5AR)

Last, but not least, I saw a trace in the waterfall diagram, a little below the operating frequency. I calculated the doppler of the moving probe to about -2 kHz, which has to be combined with the doppler effect resulting of the Earth rotation. I found the signal 1 kHz too low in the reading, but the PLUTO is stabilized just by an OCXO only and the converter is not locked at all, so I didn´t worry about the difference. Turning the dish away and back to JWST resulted in disappearing and reappearing of the signal. The observed doppler drift over 1.5 hours matched quite well the calculated drift caused by Earth rotation. The shift at the rise is about -400mHz and at the set -2900 Hz, -200 Hz per hour.

Well, I am pretty sure, I have received the signal of the James Webb Space Telescope in a distance of nearly one million kilometres!