Re: Chang'e 5 moon mission Navigational Warnings

From: Scott Tilley via Seesat-l <>
Date: Thu, 19 Nov 2020 16:15:49 -0800
Hi All

I've used the launch timings to complete an analysis for a search orbit 
for Chang'e 5 after launch.  The goal is to acquire it's TT&C radio 
beacon and further refine the orbit to maybe even allow suitably 
equipped observers to image it.

I have noted over the years that China prefers to plan their lunar and 
deep space missions such that significant mission evens occur will the 
space craft is high over China as their deep space radio network is 
concentrated there.  Using this knowledge greatly limits the possible 
cases of where Chang'e 5 will enter lunar orbit, thus allowing us to 
constrain a transfer orbit. Historically Chang'e 3 and 4 both used 
essentially direct trans-lunar injections well before the first orbit 
was completed. Interestingly LRO also used a similar method to get to 
the Moon. So looking at the coast times that these three missions took 
to get to the Moon revealed something interesting:

LRO - 4.57986 days

CE3 - 4.68261 days

CE4 - 4.59861 days

Earlier this week rumors abounded that CE5 will launch on November 
24th.  Using that knowledge I looked for the time the Moon would be 
overhead of the longitude of Beijing and found that was 
2020-11-28T14:45:00 UTC.  Looking back ~4.6 days revealed a launch 
window centered around 2020-11-24T00:00:00 UTC.

Marco's observation of the NOTAM and a launch window centered on 
2020-11-23T21:00:00 appears to agree with my guess that CE5 could arrive 
and the Moon for a LOI at approximately 2020-11-28T14:45:00 UTC.

To create a search orbit, I then created two synthetic observations at 
the perigee (instantaneous TLI time) and at the guessed arrive at the 
moon for LOI.  I then took the transfer orbit Bill Gray created for CE4 
and I corrected with Doppler observations and fit those two points to it 
to correct the RAAN, MA, AoP and ECC.  The orbit agrees reasonably well 
with where the Moon is at and the s/c in the parking orbit at the 
timings noted above.

CHANG'E 5 radio search orbit
1 70001U          20329.87500000  .00000000  00000-0  00000-0 0 07
2 70001  29.4496  17.0072 9572599 213.4938  32.8278  0.08563329 03
# 20201123.86-20201128.54, 2 measurements, 1.214 deg rms

I've created a visualization of the orbit and it can be found here:

Chang'e 5 will most likely emit on 2210.81 and/or 2257.68MHz. The ITU 
list these for the lander and orbiter respectively.  CE4 and CE5T1 used 
2210.81MHz.  My guess is 2257.68MHz may be the TT&C for the returning 
sample return capsule.

Scott Tilley

8049 ST 49.4348 -123.6685 40. Scott Tilley
8048 ST 49.4175 -123.6420 1. Scott Tilley

Keep tabs on COSPAR 8049 on Twitter:

On 2020-11-19 7:13 a.m., Marco Langbroek via Seesat-l wrote:
> CHANG'E 5 parking orbit
> 1 70000U 20999A   20328.83333333  .00000000  00000-0  00000-0 0    03
> 2 70000 023.5000 350.8367 0037296 133.1289 324.0771 15.81924308    00
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Received on Thu Nov 19 2020 - 18:16:58 UTC

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