<div dir="auto">Thank you Thomas, this is very useful advice. I’ll ask Jan King directly about these model “implications” as soon as he’s back from vacation, which should be the 25th. </div><div dir="auto"><br></div><div dir="auto">-mdt</div><div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sun, Feb 21, 2021 at 03:57 Thomas Parry via Ground-Station <ground-station@lists.openresearch.institute> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;padding-left:1ex;border-left-color:rgb(204,204,204)"><div dir="ltr"><p class="MsoNormal" style="text-align:justify">I'm not sure if you're still wondering about the original question, but I passed it on to my friend who's day job is modelling re-entry simulations. This was his response:</p><p class="MsoNormal" style="text-align:justify"><br></p><p class="MsoNormal" style="text-align:justify">"The 2020 release of GMAT (<a href="https://sourceforge.net/projects/gmat/files/GMAT/GMAT-R2020a/" target="_blank">https://sourceforge.net/projects/gmat/files/GMAT/GMAT-R2020a/</a>) seems to have the MSISE90 atmospheric model. This is one of the best ones at present to use for re-entry simulations since it can model the whole atmosphere up to 1000 km. It also has extensive options for things like solar flux, and can even return different values based upon longitude, latitude, and the time of year. </p><p class="MsoNormal" style="text-align:justify"><u></u> <u></u></p><p class="MsoNormal" style="text-align:justify">The only one that’s better for this application is the NRLMSISE00 model, which as far as I know is calculated using the same methods (spherical harmonics) but with additional measurements. The other packages that are mentioned (STK/HPOP) appear to have options for multiple models, including both MSISE90 and NRLMSISE00."</p><p class="MsoNormal" style="text-align:justify"><br></p><p class="MsoNormal" style="text-align:justify">I hope that helps.</p><p class="MsoNormal" style="text-align:justify">If there are any more questions I can you put you contact with him to tap his expertise.</p><p class="MsoNormal" style="text-align:justify"><br></p><p class="MsoNormal" style="text-align:justify">Cheers,</p><p class="MsoNormal" style="text-align:justify">Thomas</p></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sat, 30 Jan 2021 at 22:51, Thomas Parry <<a href="mailto:yrrapt@gmail.com" target="_blank">yrrapt@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;padding-left:1ex;border-left-color:rgb(204,204,204)"><div dir="auto">This is not my area of expertise at all. But I have heard people that do know what they're talking about say its very hard to analytically predict re-entry at low altitudes with real satellite geometries.<div dir="auto"><br></div><div dir="auto">With a spherical satellite everything is well behaved but with different drag coefficients at different angles<span style="font-family:sans-serif"> from square-ish satellites</span> the behaviour becomes chaotic and the window of possible solutions widens dramatically. </div><div dir="auto"><br></div><div dir="auto">Not really a useful answer but maybe a interesting thing to think about. </div><div dir="auto"><br></div><div dir="auto">Cheers, </div><div dir="auto">Thomas </div><br><br><div class="gmail_quote" dir="auto"><div dir="ltr" class="gmail_attr">On Sat, 30 Jan 2021, 22:03 , <ground-station-request@lists.openresearch.institute> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;padding-left:1ex;border-left-color:rgb(204,204,204)">Send Ground-Station mailing list submissions to<br>
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Today's Topics:<br>
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1. GMAT vs. STK/HPOP - call for help (Michelle Thompson)<br>
<br>
<br>
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<br>
Message: 1<br>
Date: Fri, 29 Jan 2021 17:28:20 -0800<br>
From: Michelle Thompson <<a href="mailto:mountain.michelle@gmail.com" rel="noreferrer" target="_blank">mountain.michelle@gmail.com</a>><br>
To: Michelle Thompson via Ground-Station<br>
<ground-station@lists.openresearch.institute><br>
Subject: [Ground-station] GMAT vs. STK/HPOP - call for help<br>
Message-ID:<br>
<CACvjz2UOeHpUmGgtvqTS=Y4WQ4_XDLyQRu_7=<a href="mailto:qw13bY_hzevFg@mail.gmail.com" rel="noreferrer" target="_blank">qw13bY_hzevFg@mail.gmail.com</a>><br>
Content-Type: text/plain; charset="utf-8"<br>
<br>
For the Debris Mitigation presentation to the FCC, we want to give answers<br>
(and show our work) about how much delta-v we need for some of the proposed<br>
orbits for minimum viable amateur spacecraft in the Amateur Radio Satellite<br>
Service.<br>
<br>
There's a question that Jan King and I have about a critical altitude and<br>
low surface_area:mass ratio spacecraft. It occurred to us that we really<br>
might want to compare results across two or more software packages to build<br>
some confidence.<br>
<br>
Jan has a set of results from a spreadsheet from SMAD.<br>
<br>
<a href="https://smad.com/" rel="noreferrer noreferrer" target="_blank">https://smad.com/</a><br>
<br>
The calculation under review is around 165km with a relatively lightweight<br>
6U spacecraft. It's acting like it wants to do some strange things. Is this<br>
physics, or at a limit of the model?<br>
<br>
We have a couple of people who are good or are getting good at GMAT.<br>
<br>
<a href="https://software.nasa.gov/software/GSC-17177-1" rel="noreferrer noreferrer" target="_blank">https://software.nasa.gov/software/GSC-17177-1</a><br>
<br>
Question: Are the atmospheric models in GMAT good enough for this<br>
calculation?<br>
<br>
Does anyone have access to STK/HPOP to run this calculation, for<br>
comparison?<br>
<br>
<a href="https://www.agi.com/products/stk" rel="noreferrer noreferrer" target="_blank">https://www.agi.com/products/stk</a><br>
<br>
<a href="https://help.agi.com/stk/11.0.1/Content/hpop/hpop.htm" rel="noreferrer noreferrer" target="_blank">https://help.agi.com/stk/11.0.1/Content/hpop/hpop.htm</a><br>
<br>
Thank you,<br>
-Michelle W5NYV<br>
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</blockquote></div></div>
</blockquote></div>
</blockquote></div></div>-- <br><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div dir="ltr">-Michelle W5NYV<br><br><div dir="ltr">"Potestatem obscuri lateris nescis."<br></div><div><br></div></div></div></div></div></div></div></div>