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<div dir="ltr" data-setdir="false">Easily!</div><div dir="ltr" data-setdir="false"><br></div><div dir="ltr" data-setdir="false">Have a look at the typical Satellite TV dish these days.</div><div dir="ltr" data-setdir="false">A very narrow beam left/right, but a wide beam up/down.</div><div dir="ltr" data-setdir="false"><br></div><div dir="ltr" data-setdir="false">In Radar they are called a Banana Peel Dish <br></div><div dir="ltr" data-setdir="false">Very wide, but not very high.</div><div dir="ltr" data-setdir="false"><br></div><div dir="ltr" data-setdir="false">Of course there are limits. What gain at the rec antenna is necessary?</div><div dir="ltr" data-setdir="false">Widening the beam does reduce gain.<br></div><div dir="ltr" data-setdir="false"><br></div><div dir="ltr" data-setdir="false">Kent<br></div><div dir="ltr" data-setdir="false"><br></div><div><br></div>
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On Monday, March 23, 2020, 2:36:48 PM CDT, Ron Economos via Ground-Station <ground-station@lists.openresearch.institute> wrote:
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<p>Back of the napkin calculation suggests that the gateway could be
offset from the Moon by up to 10 degrees. Can the pattern be that
oval?</p>
<p>Ron W6RZ<br clear="none">
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<div class="ydpfab05c3dyiv8787339469yqt8163925353" id="ydpfab05c3dyiv8787339469yqt15044"><div class="ydpfab05c3dyiv8787339469moz-cite-prefix">On 3/23/20 10:52, KENT BRITAIN via
Ground-Station wrote:<br clear="none">
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<div dir="ltr">Hi Michelle</div>
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<div dir="ltr">I wouldn't rule out a
dish/feed that puts out an Oval pattern much like</div>
<div dir="ltr">the FAA RADARS. Now
pointing at the moon would be enough.</div>
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<div dir="ltr">Tips of the oval to match the
satellite's max distance from the moon.<br clear="none">
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<div dir="ltr">Kent WA5VJB<br clear="none">
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<div> On Monday, March 23, 2020, 12:46:03 PM CDT, Michelle
Thompson via Ground-Station
<a shape="rect" class="ydpfab05c3dyiv8787339469moz-txt-link-rfc2396E" href="mailto:ground-station@lists.openresearch.institute" rel="nofollow" target="_blank"><ground-station@lists.openresearch.institute></a> wrote: </div>
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<div dir="ltr">Thank you Zach, super helpful. I am
really looking forward to seeing what your students
can achieve. Is anyone at the point where they would
be interested in a teleconference or recording a ~15
minute video presentation?<br clear="none">
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It's clear from simply drawing the orbit in my
notebook based on Frank Bauer's presentations that
simply tracking the moon will result in too much loss
over the week it takes for Gateway to zip around the
moon (at microwave). We assumed we'd need to track,
but getting real numbers means the link budgets and
antenna assumptions get more real. <br clear="none">
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GMAT is up and running and I'm working through
tutorials. They're well done! GMAT has a MATLAB and
python interface. <br clear="none">
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I learned about Poliastro at the Open Source Cubesat
Workshop. See more about it here: <a shape="rect" href="https://docs.poliastro.space/en/stable/" rel="nofollow" target="_blank">https://docs.poliastro.space/en/stable/</a><br clear="none">
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<div dir="ltr">-Michelle W5NYV<br clear="none">
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<div class="ydpfab05c3dyiv8787339469ydp91b4a5bfyiv6360139489gmail_attr" dir="ltr">On Mon, Mar 23, 2020 at 9:42 AM Leffke,
Zachary via Ground-Station
<a shape="rect" class="ydpfab05c3dyiv8787339469moz-txt-link-rfc2396E" href="mailto:ground-station@lists.openresearch.institute" rel="nofollow" target="_blank"><ground-station@lists.openresearch.institute></a>
wrote:<br clear="none">
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<p class="ydpfab05c3dyiv8787339469ydp91b4a5bfyiv6360139489MsoNormal"><span style="font-size:11pt;font-family:Calibri, sans-serif;color:black;">Hi Michelle and
Everyone!</span></p>
<p class="ydpfab05c3dyiv8787339469ydp91b4a5bfyiv6360139489MsoNormal"><span style="font-size:11pt;font-family:Calibri, sans-serif;color:black;">We need FOSS
tools for this sort of thing for both
mission analysis and design as well as for
tracking programs for the Amateur Radio
community. SGP4 and TLEs from celestrak
aren’t going to cut it for this kind of
mission. Pointing ‘at the moon’ is
probably not going to be sufficient for
Gateway, especially with tighter microwave
beams and the NRHO of the Gateway. I am
unfamiliar with GMAT, and encourage as
many folks as possible to look into it as
Michelle mentioned. I just wanted to let
folks know that I am pulling a couple
parallel threads related to the Gateway
and modelling its orbit.</span></p>
<p class="ydpfab05c3dyiv8787339469ydp91b4a5bfyiv6360139489MsoNormal"><span style="font-size:11pt;font-family:Calibri, sans-serif;color:black;"> </span></p>
<p class="ydpfab05c3dyiv8787339469ydp91b4a5bfyiv6360139489MsoNormal"><span style="font-size:11pt;font-family:Calibri, sans-serif;color:black;">Thread 1 (mission
modelling, nearer term). AGI’s STK (not
FOSS) and a few VT AOE students.</span></p>
<p class="ydpfab05c3dyiv8787339469ydp91b4a5bfyiv6360139489MsoNormal"><span style="font-size:11pt;font-family:Calibri, sans-serif;color:black;">I mentioned in a
previous thread that we have a senior AOE
student working on building models in STK
for Lunar Gateway (with help from two grad
students). That is progressing fairly
well (despite all the remote work /
COVID-19 isolation) and we expect the
student to be finished by end of the
semester with a basic model that we can
build upon. For those that aren’t aware,
System’s Tool Kit (STK) is a powerful
orbital/trajectory modelling tool from
Analytical Graphics Incorporated (AGI) and
includes tools like a communications
toolbox for modelling antenna patterns,
transmitters, receivers, performing link
analysis, etc. etc. It also has the
‘astrogator’ tool which is a required
package for modelling the
orbits/trajectories for things that are a
bit more complicated than SGP4 and
LEO/MEO/GEO. The downside of STK is that
it is hyper-expensive for individual
users. We are fortunate at VT to be part
of the AGI academic partnership and have
access to the Pro version (with the comms
toolbox), and the Lunar Gateway problem is
a good learning experience for students.
GMAT is widely considered to be the open
source alternative to STK, but for the
moment I’m sticking with what I know and
have access to. Perhaps results can be
compared from one to the other in order to
double check ourselves once things are a
bit more ‘ripe.’</span></p>
<p class="ydpfab05c3dyiv8787339469ydp91b4a5bfyiv6360139489MsoNormal"><span style="font-size:11pt;font-family:Calibri, sans-serif;color:black;"> </span></p>
<p class="ydpfab05c3dyiv8787339469ydp91b4a5bfyiv6360139489MsoNormal"><span style="font-size:11pt;font-family:Calibri, sans-serif;color:black;">Thread 2. Open
Source Tools – Python, NAIF (SPK files),
and JPL HORIZONS</span></p>
<p class="ydpfab05c3dyiv8787339469ydp91b4a5bfyiv6360139489MsoNormal"><span style="font-size:11pt;font-family:Calibri, sans-serif;color:black;">I am currently
playing around with a python package
called Skyfield (<a shape="rect" href="https://rhodesmill.org/skyfield/" rel="nofollow" target="_blank">https://rhodesmill.org/skyfield/</a>)
that is a follow on to the popular pyephem
module. For modelling major bodies
(planets, moons, etc.) Skyfield uses
ephemerides from NASA/JPL in the form
‘.bsp’ files. More specifically it uses a
subset of SPICE files from NASA’s NAIF
group (<a shape="rect" href="https://naif.jpl.nasa.gov/naif/" rel="nofollow" target="_blank">https://naif.jpl.nasa.gov/naif/</a>),
which is a defined format for modelling a
LOT of things related observation geometry
in the solar system. The ‘bsp’ files used
in skyfield are actually Type 2 and/or
Type 3 SPK files in the SPICE system (out
of 21 possible Types), that it accesses
through a separate module called
‘jplephem’. To over-simplify it a bit,
think of SPKs as containing the
coefficients for various regressions of
trajectory/orbit data that is derived from
spacecraft tracking data (like ranging
from DSN). The different ‘Types’ of SPKs
are related to what kind of regression and
form of the equation is used (Chebyshev
polynomials, Lagrange interpolation,
Hermite Interpolation, etc.). Skyfield
reads in the coefficients, sets up the
equations, you feed it a time, it pumps it
through the equation returns a position,
and then computes the ‘additional info’
most users are interested in (like az, el,
range, range rate). Related, but slightly
different from SPICE SPK files is the JPL
HORIZONS database (<a shape="rect" href="https://ssd.jpl.nasa.gov/horizons.cgi" rel="nofollow" target="_blank">https://ssd.jpl.nasa.gov/horizons.cgi</a>),
which contains a number of ephemerides for
comets, asteroids, planets, and a large
number of spacecraft in the Solar System.
HORIZONS can be queried through a web
interface and/or a telnet interface, and
there is a python package called
Astroquery that provides a python API for
access (via the telnet interface).
HORIZONS can provide observational data
(think az, el, range, range rate), state
vector information (think time series of
position and velocity), and/or orbital
elements. I am currently trying to figure
out how to merge the two and get HORIZONS
to export an SPK of various Spacecraft
(currently using LRO as the ‘standin’ for
Gateway). HORIZONS definitely exports
SPKs, but at the moment it looks like only
for asteroids and comets and in a type
that is not currently supported by
Skyfield. The ultimate goal is to be able
to import a non-Earth Orbit spacecraft
into Skyfield as a ‘body’ so that the rest
of the code would flow like normal. As an
alternative…(though a hack in my current
opinion, might change) skyfield can be
‘bypassed’ and HORIZONS can be directly
queried for observer data.</span></p>
<p class="ydpfab05c3dyiv8787339469ydp91b4a5bfyiv6360139489MsoNormal"><span style="font-size:11pt;font-family:Calibri, sans-serif;color:black;"> </span></p>
<p class="ydpfab05c3dyiv8787339469ydp91b4a5bfyiv6360139489MsoNormal"><span style="font-size:11pt;font-family:Calibri, sans-serif;color:black;">I would encourage
folks to take a look at the skyfield
github page (<a shape="rect" href="https://github.com/skyfielders/python-skyfield/" rel="nofollow" target="_blank">https://github.com/skyfielders/python-skyfield/</a>)
and look for some of the issues related to
this. Contributing to Skyfield supporting
various SPK types might go a good ways
towards FOSS tools for tracking non-earth
orbiting vehicles (like gateway…..or for
use in an ‘Amateur DSN’ context). Also,
generating SPKs for spacecraft from the
HORIZONS database data ultimately for use
with Skyfield (and other tools) is also a
good way to help…there is another python
module called SpiceyPy (<a shape="rect" href="https://pypi.org/project/spiceypy/" rel="nofollow" target="_blank">https://pypi.org/project/spiceypy/</a>)
that can be used to create SPKs. Assuming
Gateway data shows up in HORIZONS (or on
the NAIF site), this could be the
alternative to Celestrak/Space-Track for
where Hams go to get data for tracking
spacecraft not in Earth Orbit. Eventually
there may need to be an alternative site
set up (maybe ORI, maybe AMSAT) where just
the SPKs can be downloaded, maybe produced
from HORIZONS data, to alleviate strain on
the HORIZONS telnet interface (not sure
what the limits are here). Finally, I
should also mention that SPICE files have
support in multiple languages, not just
Python (see the NAIF link above for more
details), but again, I’m sticking with the
tool I know for now. SPKS can also be
used in GMAT. At the end of the day….SPK
files seem to be the way the ‘pros’ do it,
maybe we should consider it ourselves.</span></p>
<p class="ydpfab05c3dyiv8787339469ydp91b4a5bfyiv6360139489MsoNormal"><span style="font-size:11pt;font-family:Calibri, sans-serif;color:black;"> </span></p>
<p class="ydpfab05c3dyiv8787339469ydp91b4a5bfyiv6360139489MsoNormal"><span style="font-size:11pt;font-family:Calibri, sans-serif;color:black;">All good stuff!
GMAT should definitely be explored for
mission modelling and analysis purposes.
At VT we’re trying to get a handle on STK
modelling for the same purpose.
Personally, I’m looking into
Skyfield+Python+NAIF+HORIZONS for ultimate
application in ‘real time tracking’
programs (to feed antenna controllers,
Doppler tuning, etc.). Can ‘gpredict’
(and popular windows equivalents) be
modified to include this type of
tracking? I encourage as many folks as
possible to start thinking about this and
these kinds of questions and either jump
in on what’s already going on or come up
with other ways to do it.</span></p>
<p class="ydpfab05c3dyiv8787339469ydp91b4a5bfyiv6360139489MsoNormal"><span style="font-size:11pt;font-family:Calibri, sans-serif;color:black;"> </span></p>
<p class="ydpfab05c3dyiv8787339469ydp91b4a5bfyiv6360139489MsoNormal"><span style="font-size:11pt;font-family:Calibri, sans-serif;color:black;">-Zach, KJ4QLP</span></p>
<p class="ydpfab05c3dyiv8787339469ydp91b4a5bfyiv6360139489MsoNormal"><span style="font-size:11pt;font-family:Calibri, sans-serif;color:black;">--
</span></p>
<p class="ydpfab05c3dyiv8787339469ydp91b4a5bfyiv6360139489MsoNormal"><span style="font-size:11pt;font-family:Calibri, sans-serif;color:black;">Research
Associate</span></p>
<p class="ydpfab05c3dyiv8787339469ydp91b4a5bfyiv6360139489MsoNormal"><span style="font-size:11pt;font-family:Calibri, sans-serif;color:black;">Aerospace &
Ocean Systems Lab</span></p>
<p class="ydpfab05c3dyiv8787339469ydp91b4a5bfyiv6360139489MsoNormal"><span style="font-size:11pt;font-family:Calibri, sans-serif;color:black;">Ted & Karyn
Hume Center for National Security &
Technology</span></p>
<p class="ydpfab05c3dyiv8787339469ydp91b4a5bfyiv6360139489MsoNormal"><span style="font-size:11pt;font-family:Calibri, sans-serif;color:black;">Virginia
Polytechnic Institute & State
University</span></p>
<p class="ydpfab05c3dyiv8787339469ydp91b4a5bfyiv6360139489MsoNormal"><span style="font-size:11pt;font-family:Calibri, sans-serif;color:black;">Work Phone:
540-231-4174</span></p>
<p class="ydpfab05c3dyiv8787339469ydp91b4a5bfyiv6360139489MsoNormal"><span style="font-size:11pt;font-family:Calibri, sans-serif;color:black;">Cell Phone:
540-808-6305</span></p>
<p class="ydpfab05c3dyiv8787339469ydp91b4a5bfyiv6360139489MsoNormal"><span style="font-size:11pt;font-family:Calibri, sans-serif;color:black;"> </span></p>
<p class="ydpfab05c3dyiv8787339469ydp91b4a5bfyiv6360139489MsoNormal"><b><span style="font-size:11pt;font-family:Calibri, sans-serif;">From:</span></b><span style="font-size:11pt;font-family:Calibri, sans-serif;"> Ground-Station
<a shape="rect" class="ydpfab05c3dyiv8787339469moz-txt-link-rfc2396E" href="mailto:ground-station-bounces@lists.openresearch.institute" rel="nofollow" target="_blank"><ground-station-bounces@lists.openresearch.institute></a>
<b>On Behalf Of </b>Michelle Thompson via
Ground-Station<br clear="none">
<b>Sent:</b> Sunday, March 22, 2020 1:52
PM<br clear="none">
<b>To:</b> Michelle Thompson via
Ground-Station
<a shape="rect" class="ydpfab05c3dyiv8787339469moz-txt-link-rfc2396E" href="mailto:ground-station@lists.openresearch.institute" rel="nofollow" target="_blank"><ground-station@lists.openresearch.institute></a><br clear="none">
<b>Subject:</b> [Ground-station] Gateway
update + Gateway orbit modeling</span></p>
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<p class="ydpfab05c3dyiv8787339469ydp91b4a5bfyiv6360139489MsoNormal">Things
are moving on Gateway (lunar station)!<br clear="none">
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I’m trying to find an orbit model so we
can make progress on a ground station
design. JAMSAT asked for help at AMSAT-NA
Symposium and I said yes. We’ve been
talking ever since and are at the stage of
writing formal commitments to AREx, the
project from ARISS that is working to put
amateur radio on the Gateway. <br clear="none">
<br clear="none">
Yes, I know, everything could be canceled
or delayed. But, the work we’re doing is
entirely re-usable and is exactly in line
with our payload project.<br clear="none">
<br clear="none">
I have not yet found a published orbital
model for Gateway, but from the meetings
and presentations and documents, I know
it’s a near rectilinear halo orbit with a
7 day period. It’s highly elliptical,
going from 3,000 (wikipedia) or 7,000
(Frank Bauer) out to 70,000 km. I am
trying to get clarification on the
perilune (closest distance to moon).<br clear="none">
<br clear="none">
I have GMAT from NASA successfully
installed and over 1000 pages of
documentation to go along with it.<br clear="none">
<br clear="none">
I don’t know anything about modeling
orbits other than what I learned in AP
Physics in high school, but I’m willing to
try to get something nailed down and
reviewed enough to help us with 1)
tracking 2) link budgets and 3) antenna
repercussions.<br clear="none">
<br clear="none">
Plus, surely an animation of what things
look like would be super fun and help
everyone spread the word about this really
neat amateur radio opportunity. <br clear="all">
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So if you know anything
about GMAT and can answer
some newbie questions (as
soon as we have some)
please speak up. If you're
interested in installing
it and trying to help with
this, then go here and get
it stood up on your
machine: <br clear="none">
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<a shape="rect" href="https://sourceforge.net/projects/gmat/" rel="nofollow" target="_blank">https://sourceforge.net/projects/gmat/</a><br clear="none">
<br clear="none">
-Michelle W5NYV</p>
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