[amsat-bb] LongJiang and Doppler correction

[Scott]

Hi Jean Marc.

I have tried to follow the news of these lunar satellites.  While several of 
the guys with DSN capability have received the S-Band downlinks, I'm not 
aware of anyone hearing anything on 70cm past the first day as the sats left 
Earth.

In fact, even though I am listening every night for the 70cm telemetry 
(using the team's GNU Radio flowgraphs), I have not heard any confirmation 
that the 70cm transmitter is even on (telemetry -or- JT4).

-Scott,  K4KDR


=======================================================

-----Original Message----- 
From: Jean Marc Momple
Sent: Tuesday, May 29, 2018 12:37 PM
To: AMSAT BB
Subject: Re: [amsat-bb] LongJiang and Doppler correction

Dear All,

May be a stupid question for the experts, but genuine from me.

Has anyone received any FT4G beacon signal from the Longiang Sats so far?

I have being trying to do so for the past week without success.

73


Jean Marc (3B8DU)




> On May 26, 2018, at 8:54 PM, Nico Janssen <hamsat at xs4all.nl> wrote:
>
>
> 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