[amsat-bb] Tracking Non Earth Orbit Spacecraft......how?

Zach Leffke zleffke at vt.edu
Mon Oct 17 22:24:08 UTC 2016

Thanks for the response Nico.  Pete, WA6WOA, also recommend I take a 
look at the Horizons system as well.  I gave it a quick once over, and 
actually logged into the telnet interface and played around a bit.  It 
definitely looks like the type of thing I'm looking for.  Next step for 
me is to learn the API and figure out how to integrate with my existing 
Python tools.  Also, changing how I think about satellite orbits and 
tracking algorithms is also probably a requirement for me (I'm an EE 
type, not an AOE type, so probably time to learn a little more about how 
these tracking algorithms actually work).

Not being familiar with the system yet (or deep space tracking in 
general), my only concern at the moment is the frequency with which they 
update the system.  TLEs get updated pretty regularly and need to be 
refreshed by the client software.  My cursory examination of the 
HORIZONS system seems to indicate that they give ephemerides that cover 
much longer windows, possibly indicating that they don't update the data 
as frequently? Hopefully there is something about Deep Space tracking 
that is different, not requiring such frequent updates.  I have a sense 
that I'm not thinking about 'scale' correctly yet.  Like maybe these 
objects are so far out, that errors that might creep into the SGP4+TLE 
algorithms relatively quickly (requiring the weekly or bi-weekly 
updates) take a lot longer to creep up and matter with the deep space 

My concern here is primarily related to the Cube Quest Challenge stuff.  
I think this is being launched as part of the Orion mission to the Moon 
in the next couple years.  Can we expect ephemeris data to be quickly 
added to the HORIZONS system soon after launch and after the TLI burn 
for the Orion mission?  Maybe I'm just wrong about how frequently they 
update the info.  Since this system is being run by JPL, I'm assuming 
(maybe hoping?) that the datasets on HORIZONS get updated every time 
they conduct ranging operations on active missions with the DSN (kind of 
like TLEs get updated every time NORAD does RADAR tracking for things 
closer in)?  Hopefully, this will then include the Orion Mission 
relatively quickly so that the community can quickly pull the tracking 
data required to compute pointing angles for their ground stations to 
monitor the CQC bird.

Thanks for the pointers folks.  In only a few emails, I've got some 
great stuff to look into, and a whole new area to look into and learn 
about!  Fun stuff!  Keep them coming!


Zach, KJ4QLP

Research Associate
Ted & Karyn Hume Center for National Security & Technology
Virginia Polytechnic Institute & State University
Work Phone: 540-231-4174
Cell Phone: 540-808-6305

On 10/17/2016 5:08 PM, Nico Janssen wrote:
> Zach,
> Good questions. In the near future deep space tracking will become vital
> for radio amateurs. So we should prepare for that.
> There are no simple solutions. But it may be helpful to start studying 
> the
> JPL HORIZONS system:
> http://ssd.jpl.nasa.gov/?horizons
> Tracking information on a number of deep space missions is provided by
> this system, e.g. Cassini, DSCOVR, Juno, LRO, MRO and the Voyagers.
> 73,
> Nico PA0DLO
> On 17-10-16 17:35, Zach Leffke wrote:
>> Hello all,
>>     This might be slightly off topic, but I'm betting someone on this 
>> list can point me in the right direction.  I'm looking for ways to 
>> track spacecraft that are not in Earth Orbit (NEO?...did I just 
>> invent another acronym?...probably not.).  I'm trying to figure out 
>> ways to track man made space vehicles sent to places like the Moon, 
>> Mars, the Lagrange Points, and beyond.  As I understand it, TLEs + 
>> SGP4 are not the appropriate model for things not in the vicinity of 
>> Earth.  I'm hoping to find a similar technique though for looking up 
>> current orbital parameters for the Non-Earth satellites (like pulling 
>> TLEs from celestrak) in some kind of database that contains current 
>> elements for the spacecraft (NASA servers somewhere?), and then 
>> compute pointing angles from a location on earth so I can figure when 
>> and where to point an antenna to receive signals from these spacecraft.
>> I believe this may be relevant to those on this list that might be 
>> interested in tracking the Cube Quest Challenge amateur radio cubesat 
>> that will be sent to the moon in the near future.  After the 
>> trans-lunar injection burn, the cubesat will be ejected from the 
>> deployer.  I'd like to be able to track this satellite as it travels 
>> to the moon, and potentially help receive data from the bird's 10 GHz 
>> Downlink.  But.......where do I point my antenna and when?
>> For spacecraft that are already orbiting the Moon, OK, easy enough.  
>> Unless the antenna has a very narrow beamwidth, I can use any 'ole 
>> EME tracking package to point my antenna 'at the moon' and with the 
>> beamwidths I'm working with, the satellite is probably in the main 
>> beam.  But what about the initial journey to the moon?  Also, for the 
>> CQC, the cubesat will not immediately enter Lunar orbit (that is 
>> where the 'Challenge' part comes in). So simply pointing at the Moon 
>> may not work reliably.
>> To get a little more detail......but hopefully not too much......
>> I like using a python module called 'pyephem' for all (well...most) 
>> things related to antenna pointing.  This handy module works well 
>> with TLE formats for Earth orbiters, contains a built in database for 
>> objects in the solar system, and a decent number of 'fixed' celestial 
>> objects like stars.  It has the ability to import new objects in the 
>> 'Xephem' format, for things like comets and other bodies.  If 
>> possible I'd like to use this feature to track other space probes 
>> like the Lunar Reconnaissance Orbiter, various Mars missions, 
>> Satellites at Lagrange Points (ACE/DISCOVR), etc. etc.
>> Does anyone on the list have experience with this type of thing that 
>> they might be willing to share?  I believe folks from AMSAT-DL 
>> participated in the ISEE-3 reboot mission, so how did they know when 
>> and where to point the Bochum antenna for this? Again, I'm looking 
>> for a technique that hopefully involves downloading current 'orbital 
>> parameters' of some standard format type (Like TLEs from celestrak, 
>> but for non Earth Orbiters) and then importing those parameters into 
>> pyephem (by possibly converting whatever gets downloaded into the 
>> 'Xephem' format?) in order to integrate this kind of capability into 
>> my current, python-based, tracking software.  Does anyone know of any 
>> publicly available databases that store current orbital or tracking 
>> data for non-earth orbiting spacecraft?  Any tutorials out there 
>> about the algorithms used to compute deep space spacecraft position 
>> from the orbital elements and thus the pointing angles (Like SGP4 + 
>> coordinate system math, but for non-earth orbiters)?  Any software 
>> libraries anyone is familiar with for this (I prefer python, but am 
>> open to other languages)?
>> Any and all advice, thoughts, info, papers, links, etc. would be 
>> greatly appreciated.
>> Sincerely,
>> Zach, KJ4QLP

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