Xinhua reported today that Chang’e 4 entered lunar orbit at about 08:39 UTC on Dec 12th. No amateur observers reported observing the event; however, three highly competent amateur observers in Europe shared observations hours after the lunar orbit insertion burn was executed. No evidence of a signal from Chang’e 4 has been noted since my loss of signal earlier on Dec 12th. I later conducted similar observations and searched around the Moon for the signal and found nothing we can relate to Chang’e 4. Only signals from Chang’e 5T-1 and Queqiao where noted.
[UPDATED – Dec 13th, 2018]
Closing in on the Moon
As the Moon set into the trees here on the evening of Dec 11th (my local time) the obvious effects of lunar gravity had Chang’e 4 in its grips as the trajectory was more and more deviating from the Earth based orbit we where using to compare our data to and track the spacecraft.
Meanwhile in lunar orbit Chang’e 5T1 made itself very present as the tracking antenna’s beam-width was clearly within the Moon’s presences as well.
As Chang’e 5T-1 shares the same radio channel as Chang’e 4 it was deemed important to obtain Doppler and time data from Chang’e 5T-1. This was to anticipate the need to potentially differentiate between the spacecraft without resorting to exhaustive long term analysis if the orbit of Chang’e 4 resembled Chang’e 5T-1’s.
Lunar Orbit Injection
Within minutes of the posted LOI burn timing China Lunar Exploration Project (CLEP) communicated on Chinese social media that Chang’e 4 had been successfully inserted into a 100km x 400km orbit.
With the perilune and apilune published I was only a napkin or two away from calculating the other basic parameters of the orbit based on a very basic lunar model:
- Eccentricity = 0.075490689
- Period = 7948 seconds
- Semi-major axis = 1987km
Interestingly, the period of the orbit appeared close to Chang’e 5T-1’s. But we knew from previous missions and public statements from Chinese officials Chang’e 4 would be first put into a polar orbit and Chang’e 5T-1 is clearly in a non-polar orbit.
A Surprise at Moonrise in Europe
As far as I know, there where no amateur observations of the LOI burn made while the Moon was over eastern Asia on Dec 12th. However, in Europe three well equipped observers where listening a couple of hours later as the Moon rose over Europe.
Credit: @uhf-satcom / www.uhf-satcom.com
All three made excellent observations of the a signal on 2210.81MHz. But as we will see the characteristics of this signal match the characteristics of Chang’e 5T-1 so well that it leaves little doubt about its identify. In the plot below we analyzed the timing information obtained the day before from Chang’e 5T-1 and extrapolated that in a crude manner by simply predicting where the next frequency reversals in the Doppler curve would occur.
I then took the data from Paul Marsh, M0EYT and plotted that and made note of the expected timings of the frequency reversals and the observed and considering the inaccuracies of the method and data the timings correlate well. Edgar DF2MZ also provided timing data for the frequency reversals and those also correlate well.
But the timings do not seem to match perfectly. This is most likely due to error in my crude methods but should not be overlooked if a trend develops.
A few notes about the plot above:
- I, VE7TIL obtained Doppler frequency and time data from Dec 11th and determined the period of the orbit of CE5T1 before CE4 arrived, orange marks.
- Using that period I created a table that should show when to expect each frequency peak, the yellow marks on the plot.
- M0EYT’s data has IQ reversed (upside down) but this does not effect timings which is what we are studying here. It correlates strongly with my extrapolated peaks in Doppler frequency timings blue Doppler data with peaks marked in red.
- DF2MZ’s data is provided as rough timing estimates from waterfall charts but correlates very well with M0EYT’s recorded data, marked in green.
A third set of observations was provided in a format that has lead to some challenges reducing into quantified data. We’re working on that and will update the blog once that is complete. A qualitative look at his data reveals it correlates with the results above.
Finally the Moon rose over North America and I took a look. Scanning near and far from the Moon but hearing nothing other than Chang’e 5T-1 and Queqiao on S-band.
What about Queqiao!
Wait didn’t China expend a lot of effort on putting a special communications satellite at behind the Moon at the Earth-Moon L2 point? Indeed, they did.
Meanwhile up on 2234.52MHz Queqiao emits it’s TT&C beacon and every fortnight it apparently transitions to 2245.01MHz. Paul Marsh monitored this beacon for some time as well as other frequencies, China has co-ordinated with the ITU, on S-band and X-band for communication with Chang’e 4 and presumably other missions. No signals where detected that would indicate Chang’e 4 activity via the Queqiao.
So what has Queqiao been up to since launch in the summer? It has taken up position at the Earth-Moon L2 point and appears to have completed commissioning successfully as the Chinese would certainly not have launched Chang’e 4 without it working.
As you can see from the plot below the satellite is busy even over North America. You can see numerous locks to other stations by the marked difference from the expected Doppler behaviour. Implying someone or thing was interacting with Queqiao even over North America.
I have also seen ground locking on Chang’e 5T-1’s signal in the past over North America. This strongly implies the Chinese have an Earth station of substance in the Americas. This ground locking behaviour seen by Chang’e 5T-1 could also explain changes in the observed amplitude of the Doppler curve seen recently by other amateur observers.
[UPDATE] – Readers have feedback the probable location of the ground station in North America.
How do you know where to Listen?
Anyone including a country needs to co-ordinate their use of radio ultimately with the International Telecommunication Union (ITU). This ensures that all users of our shared radio spectrum resource do so in a manner that avoids interference to each others activities and an orderly and productive use of the radio spectrum is maintained around the world and even in space. Radio for a spacecraft is it’s only means of communication with Earth.
The ITU maintains a number of records related the the Chinese Moon exploration program:
- CE-1 (Chang’e 1, 2 and 5T-1 Lunar Orbiters)
- LUNAR ORBITER-A (unknown, no observed use of frequencies)
- LUNAR LANDER (Chang’e 3 and Chang’e 4)
- LUNAR CTDRS-1 (Queqiao)
- LUNAR S-SAT (Amateur Radio satellite DSLWP-A and B)
Note that a ITU coordination does not appear to refer to a specific mission but rather a specific use of radio spectrum in a certain place and at certain frequencies. So you could for example replace Queqiao with a new identical satellite without a lot of effective change to the co-ordination posting.
It should be noted China as far as I can tell strongly adheres to ITU commitments.
What is Chang’e 4’s fate?
Without any relay activity and without activity from the onboard TT&C beacon there doesn’t seem to be a way of tracking and communicating with the spacecraft. One would expect the Chinese to be highly interested in monitoring the trajectory and health of the spacecraft after LOI and as it is clear they have overseas assets to monitor and control these missions it is unclear why the beacon has not been detected once in orbit around the Moon.
Amateur observation of the Chinese Moon program have produced a lot of observations about the program’s use of its radio communication equipment and not transmitting particularity after a critical maneuver provides no means of verifying the trajectory or health of the spacecraft. Previous missions have run their beacons constantly so this is unexpected.
What could be going on?
- Nothing, the mission is proceeding normally and they just decided to turn the beacon off and/or have changed their standard operating procedures.
- Chang’e 4 is emitting signals on a frequency that is not co-ordinated with the ITU.
- Something happened during or after the LOI that now prevents the beacon from operating or effectively radiating toward Earth and China is figuring out how to resolve the issue before reacting publicly.
So what next?
We sit back and keep monitoring. At some point Chang’e 4 needs to emit radio signals either toward Queqiao or Earth for the mission to advance and one way or another we will notice them. Activity particularly on X-band would be a clear sign of Chang’e 4 moving forward with its mission.
Finger’s crossed we get some (independent) sign of life soon!
Remember there’s a bunch of silk worms on this mission that have their lives depending on this.