In the coming days the doppler shift on the 70 cm downlink of LongJiang 2 will vary between +2000 and -2200 Hz (for my QTH). This can easily be calculated with GMAT using the script I published a couple of hours ago (see my earlier post).
73, Nico PA0DLO
On 26-05-18 17:44, charlie@sucklingfamily.free-online.co.uk wrote:
Michael
I think that there are three main components to the Doppler shift for a satellite orbiting the moon.
- Earth rotation moving the observer toward the moon at moonrise (+ve
Doppler) and moonset (-ve).
- Earth-moon distance variation (smaller than 1, and very slowly
changing in comparison).
- Orbital velocity of the satellite itself.
1 and 2 are easy to work out using EME software, eg WSJT-X or Moonsked. I can't help with 3.
Taking today as an example, total of 1 and 2 for the moon vary from ~ +3 to -4.5kHz at S-Band.
With DSN satellites many of us use(d) JPL Horizons to calculate Doppler shift for Deep Space missions. Observing the Doppler shift change when probes were captured by the target planet was quite interesting (a slowly changing shift to a cyclic one).
73
Charlie G3WDG
I find that an interesting question. One would think that since the moon orbits the earth at a much much slower rate than a satellite that there would be almost no Doppler correction required. If you compensate for the speed of the orbit around the moon that is also at a much lower speed than a Earth satellite would be traveling at. Earth satellites are in the 17,000 mph range and moon satellites are in the 2000 mile an hour range orbiting speed. Also the chance that the satellite orbiting the moon could be at such an axis where it is in full visibility the earth the whole time, at that point there would not be a Doppler correction based upon satellite velocity only the moon's velocity. Will be interesting to hear the experts chime in on this.
Michael Vivona Sent from my iPad
On May 25, 2018, at 5:49 PM, Stefan Wagener wageners@gmail.com wrote:
The problem will not be the pointing (you could just point to the moon :-) Pending distance, speed and orbit around the moon and position to earth, you might have a difficult time adjusting for doppler. I let more knowledgable folks chip in on this one.
Stefan, VE4NSA
On Fri, May 25, 2018 at 2:40 PM Jordan Trewitt jmtrewitt@gmail.com wrote:
If it was the 70 cm downlink, you might be able to schedule something with someone else's SATNOGS station (idk how that'd work with getting a rotator to work though), if they have a large enough yagi that is. -Jordan KF5COQ
On Fri, May 25, 2018, 12:46 PM Zach Metzinger zmetzing@pobox.com wrote:
On 05/25/18 11:25, Nico Janssen wrote:
It is confirmed from China that LongJiang 2 has performed a successful braking maneuver, so that it is now in lunar orbit. No further details yet.
Nico,
Do you know of any WebSDRs which are pointed and tuned to the downlink signals?
73,
--- Zach N0ZGO
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