(41C) Tracking Satellites in Elliptical Orbits
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08-20-2019, 09:49 AM
Post: #1
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(41C) Tracking Satellites in Elliptical Orbits
An extract from Computer program and sample problem for tracking OSCAR , Ham Radio, MAR 1981 (pgs. 46-50)
"The altitude and velocity of a satellite in a circular orbit are nearly constant. However, both altitude and velocity are always changing during an elliptical orbit … The spot on the earth surface directly beneath the satellite is called the subsatellite point. A plot of the path of this point is the ground track and must include the effects of earth rotation. If the altitude and subsatellite point are known at a given time, the azimuth and elevation can be found using the same equations as for circular orbits … A program for the HP-41C programmable calculator and printer was written to test the equations and to learn more about elliptic orbits …" Excellent documentation. BEST! SlideRule |
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08-20-2019, 10:28 PM
Post: #2
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RE: (41C) Tracking Satellites in Elliptical Orbits
Excellent post. If you check Celestrak or Heavens Above you can get the "two line element" which is a description of a satellites orbit cataloged by NORAD and other authorities. You can find the orbital elements for the ISS and your hp41 will faithfully point you to an orbiting object you can easily see with the naked eye.
I am still trying to wrangle my own variant but it was largely an exercise to play with an Advantage ROM and I got lost in the matrix math. It does have a simple parser that will pull a TLE out of extended memory and parse it into the individual fields. I have always meant to graft it on this code. https://github.com/twdeckard/HP41CX-PLAN41 There are other hp41 routines that are rumored to be in AMSAT libraries but I've never surfaced them. Here is my code, but everything after the parser is worthless. Offered for a better coder than I ... Code:
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08-21-2019, 12:55 AM
Post: #3
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RE: (41C) Tracking Satellites in Elliptical Orbits
(08-20-2019 10:28 PM)twdeckard Wrote: There are other hp41 routines that are rumored to be in AMSAT libraries but I've never surfaced them. An extract from AMSAT Orbit magazine (JAN-FEB/1983 pg. 19) … "Calculator Program Orders The AMSAT Software Exchange address listed previously handles only programs for microcomputer systems. Orders for and inquiries about programs for calculators such as HP-41C should be directed to: AMSAT Calculator Program Library, John Montague, W0RUE, Box 541, Willenie, MN 55090." BEST! SlideRule |
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08-21-2019, 02:29 AM
Post: #4
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RE: (41C) Tracking Satellites in Elliptical Orbits
Thanks! Its not far from me in space, but pretty far in time. I'll stuff an envelop in the time machine and see what happens.
Todd |
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08-21-2019, 07:30 AM
(This post was last modified: 08-21-2019 07:32 AM by Ángel Martin.)
Post: #5
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RE: (41C) Tracking Satellites in Elliptical Orbits
In case you want to test it, this program is included in the LATLON module available in the CL Library, with id# = "LTLN". The program label is LBL "SATRACK".
Stay tuned for a couple of new compilation ROMS including programs from several papers contributed by SlideRule. Slow train coming... but here at last! "To live or die by your own sword one must first learn to wield it aptly." |
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08-21-2019, 11:45 AM
Post: #6
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RE: (41C) Tracking Satellites in Elliptical Orbits
(08-21-2019 07:30 AM)Ángel Martin Wrote: In case you want to test it, this program is included in the LATLON module available in the CL Library, with id# = "LTLN". The program label is LBL "SATRACK". Greetings Angel! I would very much like to experiment with it. I do not have a CL, can you point me to the original FOCAL? Best Todd |
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08-21-2019, 12:11 PM
Post: #7
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RE: (41C) Tracking Satellites in Elliptical Orbits
Greetings Angel,
Unless you have it readily at hand I may be able to fish for myself. I downloaded LATLON.ROM from Mr. Dalrymple's site and converted it to .raw and .txt with the most excellent utilities available on Mr. Furlow's site but at first blush it doesn't contain SATRACK? This evening I will experiment. Todd |
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08-21-2019, 11:27 PM
Post: #8
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RE: (41C) Tracking Satellites in Elliptical Orbits
I had to use Free42 (also excellent) as the .raw file had muitiple ends.
I love the fact that there are still experts and tools for this platform. I am going to reactivate the original project and I will also graft the TLE parser onto this routine. Code:
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11-05-2021, 07:42 AM
Post: #9
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RE: (41C) Tracking Satellites in Elliptical Orbits
(08-21-2019 11:27 PM)twdeckard Wrote: I am going to reactivate the original project and I will also graft the TLE parser onto this routine. It's been a while... so i was wondering if you had a chance to look int this projext since? Pls. update us on the progress... I noticed strange code lines in the INPSTA routine. There are inputs of value pairs (say a,b) but only the second value (b) is stored in a data register R30, R31 and R39. As this is done repeated times all the ä) values entered are lost due to stack overflow... I suppose this wasn't intended? Cheers, ÁM "To live or die by your own sword one must first learn to wield it aptly." |
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11-23-2021, 09:08 PM
(This post was last modified: 11-23-2021 09:13 PM by twdeckard.)
Post: #10
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RE: (41C) Tracking Satellites in Elliptical Orbits
Greetings Angel,
thank you for your gracious follow up. I never made much progress on the project. All my energy was squandered on the Arduino driven antenna rotor drive and alas that is quite dusty as well. Here is an early test: https://www.youtube.com/watch?v=VG5L5oP2...j_&index=4 Here is the unit running in sky survey mode: https://www.youtube.com/watch?v=3rMM7kyH..._&index=14 The telescope provided quite some amusement for my neighbor across the street when I teased him that based on the 300K noise I was picking up was throwing off my survey of the cosmic background radiation and probably a sign of some alien presence -- an elaborate aluminum foil ET appeared in his window a few days later. Here is an actual attempt at a contact over an amateur radio satellite. This one was funny. There are several attempts that worked. https://www.youtube.com/watch?v=O5nFwU_w...j_&index=3 You are correct the INPUTSTA is flawed. Early in the projects I generally "rough" in the application to see if it will even fit in the mighty HP41 calculator before I really dive in. Here was the last variant of the code but again, I never carried it across the finish line. Thank you for your inquiry -- I really enjoy the forum and the community. Code: ; SATTRK |
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