The frequency is 8465 MHz and for the moment don’t have ephemeris from the JPL/Horizons or spice kernels. For the moment using the ephems from GBOT getting a aprox RA and DEC and using my own tools for full tracking.
Integrating the Yutu using baudline the signals recorded during the seperation from the Chang’e 3 you can see two signal variations. At the 20:27:31 UTC during two minutes aprox the signal was more weak and scince the 20:35:40 UTC the signal was boosted. Then the separation was before of the 20:40 UTC ?
Yesterday the Chang’e3 spacecraft andt the Yutu rover was landing successfuly. I was start to track the moon since the 18:30 to the 22:30 UTC. And I was listen Yutu from the start of my window and the signal was over 15dB of SN at 1Hz of BW. The frequency of the rover is 8462.08000MHz with the moon doppler of -0.6Hz/s of aprox. The signal was easy to listen in the earphones, and sounds like a some kind of morse.
The command line to use rtlsdr with baudline was:
rtl_fm -g 44 -d0 -f$1 -s 250000 -F -U | ./baudline.static -stdin -samplerate 250000 -channels 1 -session rtlsdr1chUSB0 -basefrequency $1
Now you can listen how sounds the data stream from Yutu. A short audio record of the signal demodulated:
Another full orbit of Chang’e 3 centered ar 8470MHz with a 100KHz span. This time with locking to ground station included:
Zoom of one of the frequency lock to some tracking Ground Station:
Yesterday the Chang’e3 spacecraft finished the orbital insertion into polar orbit around the moon. The signal is strong and easy to listen in the receiver speaker. Today I get a full orbit of the probe. Every pixel are 10secs and the receiver was tuned at 8479.749200MHz
More info of Chang’e3 in Spaceflight101.
When the spaceprobes are very near to the Earth to do a flyby, the low gain (LGA)and medium gain (MGA) antennas are used. As this antennas not are in the central axis of the probe and it is rotating continuosly, you can see the rotational movement in the screenshoot:
The next images, I’m comparing the data using my ephemeris in the upper side and Horizons ephemeris in the lower side. Remember that Horizons dont give data for planetary probes, and are using the data of the planet that is orbiting the planet.
As you can apreciate, in the upper side, the range calculated using SPICE and the mission kernels is smaller than the range of the MARS calculated by Horizons. Then the MEX space probe not is eclipsed by the planet and then detectatble for our stations in the earth! Check the difference of 60 KHz in the predicted frecuency and doppler too.
Now the inverse case, the MRO probe is more away from the earth, then the probe is eclipsed by the planet.
Another issue observed is a small position difference from JPL/Horizons to my ephemerris using SPICE. It happend, because JPL/Horizons uses TDB as time reference and I’m using UTC. Then, exists a difference of few secconds produced by the leap seconds.
As I was write in my last post, one of the challenges of the amateur-DSN stations is get the ephemeris of the space probes to get the position and deldot for the doppler. JPL Horizons helps, but dont give info about the planetary space probes. How solve it? The solution is use the same data and tools that are using the mission control Every mission, have a dataset called kernel that contains info about position, instruments and clock onboard, mission operations, etc… this data is public and is controlled by NASA / NAIF and can be obtenied from here.
The Nasa NAIF, proces a toolkit called SPICE to use this data. This toolkit is available in a lot of programming languages and have a good documentation. Using a small piece of code from Achim Vollhardt DH2VA that he was send-me in 2006 and after some years googling a lot, finally I build my own planetary probes ephemeris generator.
In the next post the results…
One of the challenges of the amateur-DSN stations to track planetary and solar system space-probes is the position and frecuency accuracy. Currently all the stations are using the ephemeris provided by the JPL Horizons system. This is a cool system and can be used online using telnet, using a web interface or via email and provide-us the position, range and deldot of the select target, then using this data can track easy the probes and calculate the doppler.
Due that the JPL Horizons is a service for the main public basically for amateurs and space anthussiastas, they can not provide ephemeris for probes or missions that are orbiting a planet because this kind of missions not are static and depends of the stage of the mission.
The solution provided by Horizons is track the planet is orbiting the probe, for example to track MRO, MEX and MO have to track Mars. It works because the position difference is minimal, a typical difference of less of 0.05 deg and it not makes a sense in our small dishes. The amateur-DSN members are detecting space propbes that are orbiting a planet during years with good results, but we have some troubles like taht we dont know when the probe is eclipsed by the planet and, and we dont know the exact frequency where is the probe, because the probe and planet have a differnt deldot. Now I’m working in generate my own ephemeris, to get the data of the probes that are orbiting planets.
Today I continued updating the downconverter for X-band deep space probes. Having the local oscillator selected, today was the mixer selection. Up today I was using a RHG mixer purchased in 2006, but from the 2006 up today I purchased another units, but not tested up today.
After test the 5 units, looks that I have a unit perfect for 8.4 GHz it is a Aertech 8500 this mixer look more of 4 dB better that the RHG mixer used up today.
Now only need check the low noise amplifier to see the performance and decide if I build a new one. I’m very anxious to receive space probes again!