Amateur Deep Space Tracking

Many radio amateurs are familiar with tracking amateur satellites that orbit the Earth in low orbits or high elliptical orbits. Several tracking programs and all required orbital parameters are available for tracking these satellites.

But soon spacecraft carrying an amateur radio payload will be launched towards the Moon and beyond. If amateurs want to track these spacecraft they will need suitable tracking software and orbital elements to be able to calculate the positions of these spacecraft.

Calculations

Unfortunately none of the currently available tracking programs, used for satellite tracking by amateurs, is suitable for deep space tracking. But fortunately two free, open source software packages for Windows, Linux and Mac are available, that will enable deep space tracking:

General Mission Analysis Tool (GMAT)
Home page, Download page

SciLab, including CelestLab, CelestLabX and Aerospace Blockset

Probably most amateurs will prefer GMAT, because it is most user friendly, has a lot of documentation and help files, and contains many sample scripts. Scripts that are created by other amateurs can be used without having much knowledge or experience with GMAT.

Measurements

It is not certain that orbital elements for all deep space spacecraft carrying amateur radio payloads will be made available to radio amateurs. Therefore amateurs may need to measure these orbital elements themselves through doppler and ranging measurements. So amateurs will need to set up their own Amateur Deep Space Network, similar to NASA's DSN, ESA's Estrack, etc. This will require some stations with large enough antennas and with equipment to carry out doppler and ranging measurements to determine direction and distance to the spacecraft. This new development is an interesting challenge for radio amateurs.

For the direction to the spacecraft its celestial coordinates, i.e. its Right Ascension and Declination, must be determined. The Right Ascension is derived from the midpoint of the measured doppler curve, while the Declination is derived from the amplitude of the doppler curve. The distance to the spacecraft is determined using the measured delay of the received downlink signals.

Using GMAT

For practicing purposes I created a simple script for a Cubesat that is launched towards the Moon. It is a Cubesat that has no propulsion.

It shows how the Moon's gravity forces affect the Cubesat's orbit. You can play with the orbital elements to see how the orbit changes when the satellite's flyby distance to the Moon changes.

The Chinese LongJiang 2 microsat, carrying an amateur radio payload, was launched towards the Moon at 21:25 UTC on 2018-05-20. This script for LongJiang 2 can be used to track this spacecraft in its high elliptical orbit around the Moon. This script contains the most recent orbital data, published on 2018-06-15. New views have been added. Note that the ContactLocater report shows the exact AOS and LOS times, also indicating the periods when the spacecraft passes behind the Moon.

The groundstation used in these scripts is a random location in New York City. You can change this to your location by updating the values under the GroundStation tab.

Note that GMAT sometimes uses conventions that are different from what amateurs are used to. E.g. GMAT uses this convention for azimuths: 0 degrees is South, +90 degrees is East, -90 degrees is West and 180/-180 degrees is North. So to convert to the usual convention, you will need to convert azimuth values by subtracting these values from 180. I made a Python script that performs these conversions, while also calculating doppler shift values for a user defined frequency.

Note that this script only works with a ReportFile1.txt file that is defined exactly like that file in the CubesatMoon_NYC.script and LongJiang2_NYC.script mentioned above. The output file TrackingData.txt is in the same directory as ReportFile1.txt and the Tracking.py Python script.


You can find further information on space flight on this very informative set of pages. Deep space navigation is covered in chapter 13.




PA0DLO   2018-06-15