[amsat-bb] LongJiang and Doppler correction

[Nico Janssen]

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 at 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.
>
> 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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>
> _______________________________________________
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