4M has transmitted its last message at 0135UTC on the 11th of November. The last messages have been received by Rein, W6SZ,
>01:25 LX0OHB 4M5256
>01:35 084V381A -16C
Some transmissions yet occurred but were not demodulated and the cells were at the lowest limit of discharge.
After more than 438 Hours, 4M has largely exceeded its design lifetime and by all accounts is a huge success as it fulfilled all its goals.
Serendipity was even there and brought us unexpected learnings.
The most wonderful thing that happened is the amount of participation of the radio amateurs. They were (and we were also at LuxSpace) the central piece of the success. We hoped for 10, more than 60 participated! … And we were overwhelmed by the return, the mails, and the participant number to the contest.
It is amazing to see to which great lengths some went in order to receive even few messages and could say: ‘I did it’. From Eggbeater antenna with Funcube dongle or small hand pointed Yagi set on wooden ladders and to large arrays for EME, all the taxonomy of amateur station was represented.
Each one will receive a dedicated and printed certificate that will be shipped by postal mail using special stamps. Those not yet having sent their postal address, please quickly do so at firstname.lastname@example.org
The most gratifying thing was all the positive comments we received, save only one.
“When is the next one?” could not be more rewarding and encouraging.
Not only did we receive all data from the radiation dosimeter experiment, but it also allowed a pretty accurate orbit determination after the flyby.
Thanks to Anatoly, UA9UIZ for pointing out that many talks took place in Russia.
The result of the contest is the following. Thanks to LSE Space, who setup the automated data collection, it was pretty easy to summarize all the results. Half of the logs were received by mail and had to be manually processed. We sincerely hope to have not messed up too much. Congratulations to Lucien Serrano F1TE
We have one regret: no intercontinental team registered.
We sincerely apologize if some errors still remain in the counting and ranking. We shall rectify upon request.
All recorded messages were received. All those who entered a greeting message will receive a certificate of reception including who received their message and when.
There were some long sentences cut into 13 characters chunks.
The first message was simply a copy of the memorial page to Pr Fuchs
We also had:
REMEMBER THE SPACE PIONEER MANFRED FUCHS.
REST IN PEACE MANFRED FUCHS.
DAMIT ALLE MENSCHEN AUF DERWELT IN FRIEDEN ZUSAMMEN LEBEN.
LA LI LU NUR DER MANN IM MOND SCHAUTZU WENN DIE KLEINEN KINDER SCHLAFEN UND SO SCHLAF AUCH DU. (A traditional German lullaby)
DO NOT GO WHERE THE PATH MAY LEAD GO INSTEAD WHERE THERE IS NO PATH AND LEAVE
ALL LIFE IS AN EXPERIMENT. THE MORE EXPERIMENTS YOU MAKE THE BETTER.
We understand that some have been a little bit frustrated by not having accurate pointing elements. Therefore, some explanations are required.
4M was attached on the last stage of the LM-3C launcher. There were reasons for that. The main mission was limited in time, it was on the funds of the company, and we had planned to 6 days minimum lifetime in the expenditures plan. The team needed also to rest after 5 very dense months.
Being attached to the last stage also meant that the injection vector was not very accurate. We worked on the best estimates to generate the first two lines elements.
After the flyby, it soon appeared that the best estimates were quite off the mark. The first indication was being given by an unexpectedly high Doppler. However, as the Local Oscillator of 4M was not precisely stable (+/-5ppm), we initially thought that the temperature drop was in cause. It was soon found out that it was not the case and 4M was received in Europe (on the back lobes of the antenna) much sooner than expected.
The process to determine the new orbit began. For those not familiar with this kind of exercise, suffice it to say that is no simple game, especially when you have no real information on the frequency accuracy nor of the time stamping accuracy of the receiving stations (and of 4M neither). Very small variation of the vector at flyby injection led to widely dispersed trajectories.
We managed to have a first rough estimate that allowed a course pointing to get enough Doppler information.
Finally, a special group endeavoured to determine the orbit using the Doppler information, and we thereafter worked together to refine the solution, which finally happened around the 6th November although we had already rough and useable estimates as soon as the 1st of November.
It is also recalled that TLE’s are not really meant for this kind of orbit. In addition some amateur softwares are really picky on the input format. This made for some days of apparently random publications as I had to figure out what was wrong in some softwares that would not accept the parameters.
Given the severe constraints on the launcher, the antenna was all but optimal, and I had to cope with that. I did not succeed in transforming the last stage into an isotropic antenna. We made EM simulations to have an estimate of the radiation pattern, but the incomplete data (and limited amount of resources/time) rendered this estimate closer to a wild guess.
The average gain was initially estimated to -6dBi, with a lot of uncertainty, therefore a huge margin ( from a telecom engineer point of view) was introduced so as to make sure the signals would be received at 400Mm, albeit not with a single medium gain Yagi.
It turned out that the average EIRP was in the order of 50mW, rather than 250mW.
Despite this inconvenience, 100% of the messages were received up to the flyby, and 50% after the flyby, which, I recall, sent the 4M up to 420Mm. Quite a DX for 50 mW EIRP !!
There was lot of fading (QSB) due to the mounting. No way was practicable to solve the problem in the design and within constraints, and this was also a justification for the huge margin.
Unfortunately, this huge margin was detrimental to the lifetime. As the illumination was not guaranteed, and that we wanted the mission (i.e. going round the Moon) to succeed, it was required to provide for enough internal energy. This was achieved by putting 28 cells LSH20HTS from SAFT. (The same as on board Philae). In the worst case of low temperature (-40°C), the cells were able to give enough energy for a 4W payload during 100 hours. (Adding that their small internal dissipation would keep them above -40°C due to the thermal insulation)
A secondary source of power was a solar panel and rechargeable batteries (that we both had at hand from a previous project). They clearly contributed to extend the lifetime.
JT65B link proved to be extremely robust in these conditions. Additional ‘analog information’ was provided at the end of the sequence, mainly as to allow pattern recognition and setting the dSec of WSJT demodulating software.
Reason is that the OBC clock (that we also had at hand from a previous project, and that proved to be highly reliable) was known not to be accurate and thus could widely drift during the mission.
The OBC clock was set at integration in such a way that the known drift would make 4M start to within 1sec of the UTC minute at activation therefore allowing an easy tracking of the drift during the mission. (4M started at the exact planned minute after launch i.e. 1918UTC)
The PL architecture was rather simple. An OBC, an interface control board, an IQ modulator, a RF PA (provided by RFPA.com, their 6th PA we successfully put in orbit), a radiation dosimeter (from IC-Malaga), some bits and pieces to couple all the cells, batteries and solar panel. I’d add that a severe counter EMI design was adopted as we were located 50cm away from a 1kW EIRP S band transmitter.
The OBC’s internal DAC’s were generating I&Q signals for the IQ modulator (MiniCircuit, followed by MMIC driver from Avago and filter from TemWell). My colleague Klaus wrote an heroic piece of software to fit the JT65B encoding, the IQ generation and all the PL housekeeping in the flash memory of the OBC, in addition of the messages.
This experiment was designed and setup by IC Malaga, and worked as long as expected, providing very useful data. The results have been published, and brought in the nice result of coming very close to the simulations provided by HOMER.
IC Malaga designed and manufactured the dosimeter in 3 weeks. It used their entirely new chip, which possesses a very high potential and nothing could have barred us to test it in real life, avoiding months of difficult qualification tests.
The curves are self-speaking (you can find them in the radiation experiment section of this website). The most impressive part is to see the steep increase in dose when crossing the van Allen belts soon after the launch and during the first hours.
There is strictly nothing new, but seeing this curve is dramatically spectacular if you are not convinced by the abstraction of the simulations. (And even more if you think that RadHard and RadTol components or architectures are just excessive)
The reason why DRALUX (the intimate name of this experiment) stopped working after 215 hours is not yet clear.
TDOA and FOA
A totally unexpected result and success is the orbit determination using the Doppler. Again, there is nothing new in it, but that it worked well in such conditions is much of a finding. Serendipity happens.
Thanks to the special group and my colleague Jean-Baptiste who came up with a complete algorithm in two days during his free time.
TDOA did provide what was expected: not much. Reason is not linked to the 4M, but on the limitations of WSJT and the lack of accuracy and precision of the time stamping process.
There are lot of improvements to be made in the radio amateur stations regarding this aspect. A separate article will be published, based on the findings of the 4M mission and the requirements to achieve this.
It is not an academic or wishful thinking, 4M is for sure the first mission of its kind and can be inscribed in the amateur historical record, but it certainly will not be the last. Navigation of interplanetary probes is a critical item, and I cannot imagine that future amateur or commercial small probes could rely on DSN or very few big dishes. (May be to Mars, but to the Moon, this would be an overkill, would work up to Lagrange point L1 with reasonable means).
To Roland PY4ZBZ, who relieved me just after the launch by providing the first reports.
To Cees Bassa, Scott Tilley
To Wayne, VK5APN, for keeping me awake and aware that all was going well. (no joke)
The Moon.net list and all very active and most interesting comments the participants provided.
To all those who provided comments, expressed thanks and above all: enjoyed this mission.
Will there be another one ?
The Japanese are going to launch a probe in December. They have included a JT65B link on 435MHz. this will be an exciting experiment and a bigger DX for sure.
As for us, if we can, we surely will do it again.