[Ground-station] Potential Phase 4 - Gateway interference

[Leffke, Zachary]

We have an AOE undergraduate student (senior) working on building Gateway orbits in STK for exactly this type of modelling.  It’s a bit more complicated than just dropping a new bird in from a TLE database, especially with the unknowns in the specific Gateway orbit.  It starts with candidate NRHO trajectories built up in matlab.  Once that’s up to a workable simulation and has been vetted by some of our researchers that have more of an AOE background than me (like, PhDs in this stuff), I (and/or some of my ECE students) can use the Communications Toolbox in STK to model exactly this sort of thing.  In addition to the Amateur Radio work we hope to participate in for this sort of thing, having accurate Gateway orbit modelling available will be useful and important to a number of projects VT hopes to participate in related to the Gateway and Lunar missions in the relatively near future.

We had to do a similar analysis for ground to LEO to GEO interference in the 401 MHz band as part of a study to show we would not degrade the NOAA DCS geo transponder’s capabilities with three LEO 1U cubesats (and their associated GSs) operating in the same band in order to get our Part 5 licenses for the VCC mission.  There are ITU recs for this that help in the analysis method (the thresholds and limits and such may or may not directly apply, but maybe useful as a guide, we’re in a different service).  All very straightforward and easy to execute in STK, once the orbits are established.

It will be a while before the student is done developing his part of the simulations, but things are progressing well.  I wouldn’t see this as a path for a short term answer, but is something we can use to refine the analysis as the various 10 GHz projects progress and their mission specific details can be added into the simulations (antenna patterns, power levels, bandwidths of operation, etc.).  This type of problem is perfect fodder for AOE/ECE collaborations for undergrad students.  Don’t anyone hold your breath, but when we have something worth reporting we’ll shoot it out to the team.

Also, this does require multiple toolboxes that are in the ‘Pro’ version of STK, so reproducing the results will be difficult unless you are also part of the Educational Alliance program with AGI (we have access to the pro version for education purposes at VT, and for research).  Therefore, I highly recommend pursuit of the Python method (or similar) Michelle mentioned.  Eventually, people are going to need to figure out where to point their antennas and ‘the moon’ might not be accurate enough……figuring out how to track Gateway with FOSS tools will go a long way to stimulating activity and getting people on the air.

-Zach, KJ4QLP
--
Research Associate
Aerospace & Ocean Systems Lab
Ted & Karyn Hume Center for National Security & Technology
Virginia Polytechnic Institute & State University
Work Phone: 540-231-4174
Cell Phone: 540-808-6305

From: Ground-Station <ground-station-bounces at lists.openresearch.institute> On Behalf Of Michelle Thompson via Ground-Station
Sent: Friday, February 14, 2020 4:19 PM
To: KENT BRITAIN <wa5vjb at flash.net>
Cc: Michelle Thompson via Ground-Station <ground-station at lists.openresearch.institute>
Subject: Re: [Ground-station] Potential Phase 4 - Gateway interference

OK I see what you mean.

In doing a BOE for GEO, the occlusion is longer lasting, because the moon moves more slowly across the sky than a lower satellite, but the outcome appears to be the same. It's rare.

If we can put this on a single slide, for that one time someone with authority requires an answer, then the work to come up with numbers is worth it. I think Kent is correct in the order of magnitude for LEO and pretty close numerically.

I am interested in generating a solid number. Does anyone have good software for this, or want to write up a python script that encapsulates the problem?

-Michelle W5NYV



On Fri, Feb 14, 2020 at 1:07 PM KENT BRITAIN <wa5vjb at flash.net<mailto:wa5vjb at flash.net>> wrote:
Interference would be rare, and momentary.

OK, the bird goes though a 360 deg arc in about 80 minutes.

So in a typical overhead pass that's about 4 deg a min..
( Yes, a lot of variables in that equation! )

The antenna beam is 6 deg if we allow for the -10 dB points.
So 90 seconds would put the 2nd bird well out of the pattern from the
ground station.

Lots of orbits, a parallel orbit is not impossible, but in most cases they
would only be in common view of the ground dish for a minute or so.
I'll let someone else do this calculation.  Take two LEO Birds, and when
looking from a common point on the ground, how often do they pass within
6 deg of each other?    Not often I suspect.    Kent WA5VJB



On Friday, February 14, 2020, 1:17:53 PM CST, Michelle Thompson <mountain.michelle at gmail.com<mailto:mountain.michelle at gmail.com>> wrote:


Good point on frequency management.

We plan to use (up to) the entire 10MHz amateur allocation.

Gateway appears to be using less.

Given that one can model this as a narrowband interferer to a broader band signal, in your opinion, can we accept or ignore the potential interference?

-Michelle W5NYV



On Fri, Feb 14, 2020 at 10:20 AM KENT BRITAIN <wa5vjb at flash.net<mailto:wa5vjb at flash.net>> wrote:
The typical Direct TV style dish looks at 1/4000 th of the sky.
Well, we only see 1/2 of the sky at any given time, so even if both birds are visible
at the same time, only 1/2000 of the time would they both be in the same beam
even if on the same frequency.

Yea, can crunch these numbers several ways but with a little frequency management
interference is going to be pretty rare.    Kent WA5VJB




On Friday, February 14, 2020, 12:03:12 PM CST, Michelle Thompson via Ground-Station <ground-station at lists.openresearch.institute<mailto:ground-station at lists.openresearch.institute>> wrote:


With AREx and Lunar Orbiting Platform Gateway (usually just called "Gateway") developing and progressing, Paul KB5MU brought up something we need to check on.

If Gateway uses the 10GHz amateur downlink (and they plan to) how much impact do other 10GHz payloads present? QO-100, Phase 4X, CatSat, etc.?

I think any interference or outages are going to be very small, but I'd like to have an answer before someone like ARISS asks.

If we all use DVB-S2/X, then it would seem that there would be a potential for brief interference.

Assuming 10GHz downlinks from Gateway
1) how often would potential interference occur for GEO, HEO, LEO?
2) is there anything that we (or Gateway) should do about it?
3) is there anything that we (or Gateway) could do about it?

Goal: Quantify and document.

-Michelle W5NYV

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