[amsat-bb] LongJiang and Doppler correction

[charlie at sucklingfamily.free-online.co.uk]

Michael

I think that there are three main components to the Doppler shift for a
satellite orbiting the moon.

1.  Earth rotation moving the observer toward the moon at moonrise (+ve
Doppler) and moonset (-ve).

2.  Earth-moon distance variation (smaller than 1, and very slowly
changing in comparison).

3.  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 at 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 at 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 at 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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