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CX2SA > SATDIG 01.10.17 19:02l 966 Lines 35805 Bytes #999 (0) @ WW
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To : SATDIG@WW
Today's Topics:
1. Upcoming ARISS Contact Schedule as of 2017-10-01 06:00 UTC
(AJ9N@xxx.xxxx
2. Re: WISP replacement? (John Melton)
3. Conventions for apogee and perigee altitudes? (Phil Karn)
4. Re: WISP replacement? (or Live digipeating?) (Edson W. R. Pereira)
5. Re: Conventions for apogee and perigee altitudes? (Alan)
6. R60SAT Special Call on the air. Sputnik-1 60 Year Celebration
(Steve Nordahl)
7. Falconsat-3 and APRS HT's? (Robert Bruninga)
8. Re: Falconsat-3 and APRS HT's? (JoAnne K9JKM)
9. Re: Conventions for apogee and perigee altitudes? (Phil Karn)
----------------------------------------------------------------------
Message: 1
Date: Sun, 1 Oct 2017 01:42:24 -0400
From: AJ9N@xxx.xxx
To: amsat-bb@xxxxx.xxx
Subject: [amsat-bb] Upcoming ARISS Contact Schedule as of 2017-10-01
06:00 UTC
Message-ID: <332310.77831f18.4701da40@xxx.xxx>
Content-Type: text/plain; charset="UTF-8"
Upcoming ARISS Contact Schedule as of 2017-10-01 06:00 UTC
Quick list of scheduled contacts and events:
Kugluktuk High School, Kugluktuk Nunavut, Canada, telebridge via IK1SLD
The ISS callsign is presently scheduled to be IR?ISS
The scheduled astronaut is Paolo Nespoli IZ?JPA
Contact is a go for Option #5: Tue 2017-10-03 15:32:57 UTC 30 deg
****************************************************************************
**
International Space Station Astronauts are Calling CQ Students ? (***)
ARISS-US program education proposal deadline is November 15, 2017
September 18, 2017: The Amateur Radio on the International Space
Station (ARISS) program is seeking proposals from U.S. schools,
museums, science centers and community youth organizations to host
radio contacts with an orbiting crew member aboard the International
Space Station (ISS) between July 1 and December 31, 2018.
Each year, ARISS provides tens of thousands of students with oppor-
tunities to learn about space technologies and space communications
through the exploration of Amateur Radio. The program provides
learning opportunities by connecting students to astronauts aboard
the International Space Station (ISS) through a partnership between
NASA, the American Radio Relay League, the Radio Amateur Satellite
Corporation and other Amateur Radio organizations and worldwide
space agencies. The program?s goal is to inspire students worldwide,
to pursue interests and careers in science, technology, engineering
and mathematics (STEM) through Amateur Radio.
Educators overwhelmingly report that student participation in the
ARISS program inspires an interest in STEM subjects and in STEM
careers. Ninety-two percent of educators who have participated in
the program have indicated that ARISS provided ideas for encourag-
ing student exploration, discussion, and participation, and 78
percent said that ARISS was effective in stimulating student
interest in STEM.
ARISS is looking for organizations that will draw large numbers
of participants and integrate the contact into a well-developed
education plan. Students can learn about satellite communications,
wireless technology, science research conducted on the space
station, what it is like to work in space, radio science, and any
related STEM subject. Students learn to use Amateur Radio to talk
directly to an astronaut and ask their STEM-related questions.
ARISS will help educational organizations locate Amateur Radio
groups who can assist with equipment for this once-in-a-lifetime
opportunity for students.
The proposal deadline for 2018 contacts is November 15, 2017.
The ARISS website has additional details on expectations, proposal
guidelines, and the proposal form. See:
http://www.ariss.org/hosting-an-ariss-contact-in-the-us.html
****************************************************************************
**
ARISS is always glad to receive listener reports for the above contacts.
ARISS thanks everyone in advance for their assistance. Feel free to send
your reports to aj9n@xxxxx.xxx or aj9n@xxx.xxx.
Listen for the ISS on the downlink of 145.8? MHz.
****************************************************************************
***
All ARISS contacts are made via the Kenwood radio unless otherwise noted.
****************************************************************************
***
Several of you have sent me emails asking about the RAC ARISS website and
not being able to get in. That has now been changed to
http://www.ariss.org/
Note that there are links to other ARISS websites from this site.
****************************************************************************
Looking for something new to do? How about receiving DATV from the ISS?
If interested, then please go to the ARISS-EU website for complete
details. Look for the buttons indicating Ham Video.
http://www.ariss-eu.org/
If you need some assistance, ARISS mentor Kerry N6IZW, might be able to
provide some insight. Contact Kerry at kbanke@xxxxxxxxx.xxx
****************************************************************************
ARISS congratulations the following mentors who have now mentored over 100
schools:
Satoshi 7M3TJZ with 124
Gaston ON4WF with 123
Francesco IK?WGF with 119
Sergey RV3DR with 100
****************************************************************************
The webpages listed below were all reviewed for accuracy. Out of date
webpages were removed and new ones have been added. If there are
additional
ARISS websites I need to know about, please let me know.
Note, all times are approximate. It is recommended that you do your own
orbital prediction or start listening about 10 minutes before the listed
time.
All dates and times listed follow International Standard ISO 8601 date and
time format YYYY-MM-DD HH:MM:SS
The complete schedule page has been updated as of 2017-10-01 06:00 UTC.
(***)
Here you will find a listing of all scheduled school contacts, and
questions, other ISS related websites, IRLP and Echolink websites, and
instructions for any contact that may be streamed live.
http://www.amsat.org/amsat/ariss/news/arissnews.rtf
http://www.amsat.org/amsat/ariss/news/arissnews.txt
Total number of ARISS ISS to earth school events is 1161.
Each school counts as 1 event.
Total number of ARISS ISS to earth school contacts is 1120.
Each contact may have multiple schools sharing the same time slot.
Total number of ARISS supported terrestrial contacts is 47.
A complete year by year breakdown of the contacts may be found in the
file.
http://www.amsat.org/amsat/ariss/news/arissnews.rtf
Please feel free to contact me if more detailed statistics are needed.
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
The following US states and entities have never had an ARISS contact:
Arkansas, Delaware, South Dakota, Wyoming, American Samoa, Guam, Northern
Marianas Islands, and the Virgin Islands.
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
QSL information may be found at:
http://www.ariss.org/qsl-cards.html
ISS callsigns: DP?ISS, IR?ISS, NA1SS, OR4ISS, RS?ISS
****************************************************************************
The successful school list has been updated as of 2017-09-30 06:00 UTC.
http://www.amsat.org/amsat/ariss/news/Successful_ARISS_schools.rtf
Frequency chart for packet, voice, and crossband repeater modes showing
Doppler correction as of 2005-07-29 04:00 UTC
http://www.amsat.org/amsat/ariss/news/ISS_frequencies_and_Doppler_correction
.rtf
Listing of ARISS related magazine articles as of 2006-07-10 03:30 UTC.
http://www.amsat.org/amsat/ariss/news/ARISS_magazine_articles.rtf
Check out the Zoho reports of the ARISS contacts
https://reports.zoho.com/ZDBDataSheetView.cc?DBID=412218000000020415
****************************************************************************
Exp. 52 on orbit
Randy Bresnik
Paolo Nespoli IZ?JPA
Sergey Ryazanskiy
Exp. 53 on orbit
Mark Vande Hei KG5GNP
Alexander Misurkin
Joe Acaba KE5DAR
****************************************************************************
73,
Charlie Sufana AJ9N
One of the ARISS operation team mentors
------------------------------
Message: 2
Date: Sun, 1 Oct 2017 07:55:38 +0100
From: John Melton <john.d.melton@xxxxxxxxxx.xxx>
To: Douglas Quagliana <dquagliana@xxxxx.xxx>
Cc: Paul Stoetzer <n8hm@xxxx.xxx>, "amsat-bb@xxxxx.xxxx
<amsat-bb@xxxxx.xxx>, Robert Switzer <robert_switzer@xxx.xxx>
Subject: Re: [amsat-bb] WISP replacement?
Message-ID:
<CABBykh2RRfbLTi=7kbZNzn+k6MTnk4vNwpPdhunc_YWuLixd1A@xxxx.xxxxx.xxx>
Content-Type: text/plain; charset="UTF-8"
I am away cycling in Italy and France at the moment but will try to help if
needed when I get home next week.
It has been a long time since I wrote the original code!
-- John g0orx/n6lyt
On 30 Sep 2017 21:12, "Douglas Quagliana" <dquagliana@xxxxx.xxx> wrote:
> All,
> I'd like to get pbpg running with a soundcard modem on Linux. First, I'm
> just trying to get pbpg running.
>
> I was able to download pbpg-2.2.1.tar.gz from the AMSAT website, and
> after a little work I got it to compile and got it installed, but it
> doesn't seem to run properly on my Linux box. I have kernel version 4.4.75
> on this machine, but I could try another kernel version or a completely
> different distro quite easily.
>
> I strongly suspect I'm "doing it wrong" and there's some more missing
> setup and config (for example, the "configure/make/make install" didn't
> create the control FIFO (/etc/pbpg/pb-fifo) nor any of the
> /var/spool/pbpg/satellite-name directories.
>
> I think I'm missing a required step. Is there more install/config
> documentation somewhere besides what comes with pbpg-2.2.1.tar.gz ?
>
> Douglas KA2UPW/5
>
>
> On Thu, Sep 28, 2017 at 11:23 AM, Edson W. R. Pereira <ewpereira@xxxxx.xxx
> >
> wrote:
>
> > The Linux version of PB and PG talks to a pseudo TNC using the native
> Linux
> > AX.25 sockets. It has been more than two decades since I have last used
> the
> > native AX.25 sockets and, as far as I can remember, it was not trivial. I
> > suggest modifying the PB and PB software to speak the AX.25 KISS over TCP
> > protocol and talk with DireWolf, a software TNC that implements the G3RUH
> > GFSK 9600 bps modem. DireWolf can be found here:
> >
> > https://github.com/wb2osz/direwolf
> >
> > I will try modifying PB and PG to use the KISS protocol as soon as I can
> > spare some time.
> >
> > DireWolf could be used with a classic transceiver via soundcard and also
> to
> > a SDR receiver such as GQRX or GNURadio and a classic (or SDR)
> transmitter.
> > The software modem could also be implemented directly in GNUradio as
> well.
> >
> > It will be a blast to operate a PACSAT BBS again.
> >
> > 73, Edson PY2SDR
> >
> >
> > On Thu, Sep 28, 2017 at 12:55 PM, Paul Stoetzer <n8hm@xxxx.xxx> wrote:
> >
> > > The Linux tools (PacSatTools and PB/PG) are distributed as source
> > > code. That code could potentially serve as a guide for how to encode
> > > files and interface with a KISS TNC.
> > >
> > > See https://www.amsat.org/falconsat-3/
> > >
> > > 73,
> > >
> > > Paul, N8HM
> > >
> > > On Thu, Sep 28, 2017 at 11:18 AM, Robert Switzer via AMSAT-BB
> > > <amsat-bb@xxxxx.xxx> wrote:
> > > > Don't know if this is opensource ( a quick search only found the old
> > > WiSP32 download setup.exe), but this as well as other old programs (I'm
> > > thinking Nova, but perhaps others?) would be best
> > > > served by getting it out there in the public domain.
> > > > The other option is to reverse engineer if someone has a working
> copy.
> > > >
> > > >
> > > >
> > > >
> > > > On Thursday, September 28, 2017 9:19 AM, Andrew Glasbrenner <
> > > glasbrenner@xxxxxxxxxx.xxx> wrote:
> > > >
> > > >
> > > > For all our talented coders out there, a replacement for the
> venerable
> > > WISP
> > > > software would be well received, and allow much more utilization of
> > this
> > > > satellite resource. Anyone interested?
> > > >
> > > >
> > > >
> > > > 73, Drew KO4MA
> > > >
> > > > _______________________________________________
> > > > Sent via AMSAT-BB@xxxxx.xxx. AMSAT-NA makes this open forum
> available
> > > > to all interested persons worldwide without requiring membership.
> > > Opinions expressed
> > > > are solely those of the author, and do not reflect the official views
> > of
> > > AMSAT-NA.
> > > > Not an AMSAT-NA member? Join now to support the amateur satellite
> > > program!
> > > > Subscription settings: http://www.amsat.org/mailman/
> listinfo/amsat-bb
> > > >
> > > >
> > > >
> > > > _______________________________________________
> > > > Sent via AMSAT-BB@xxxxx.xxx. AMSAT-NA makes this open forum
> available
> > > > to all interested persons worldwide without requiring membership.
> > > Opinions expressed
> > > > are solely those of the author, and do not reflect the official views
> > of
> > > AMSAT-NA.
> > > > Not an AMSAT-NA member? Join now to support the amateur satellite
> > > program!
> > > > Subscription settings: http://www.amsat.org/mailman/
> listinfo/amsat-bb
> > > _______________________________________________
> > > Sent via AMSAT-BB@xxxxx.xxx. AMSAT-NA makes this open forum available
> > > to all interested persons worldwide without requiring membership.
> > Opinions
> > > expressed
> > > are solely those of the author, and do not reflect the official views
> of
> > > AMSAT-NA.
> > > Not an AMSAT-NA member? Join now to support the amateur satellite
> > program!
> > > Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
> > >
> > _______________________________________________
> > Sent via AMSAT-BB@xxxxx.xxx. AMSAT-NA makes this open forum available
> > to all interested persons worldwide without requiring membership.
> Opinions
> > expressed
> > are solely those of the author, and do not reflect the official views of
> > AMSAT-NA.
> > Not an AMSAT-NA member? Join now to support the amateur satellite
> program!
> > Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
> >
> _______________________________________________
> Sent via AMSAT-BB@xxxxx.xxx. AMSAT-NA makes this open forum available
> to all interested persons worldwide without requiring membership. Opinions
> expressed
> are solely those of the author, and do not reflect the official views of
> AMSAT-NA.
> Not an AMSAT-NA member? Join now to support the amateur satellite program!
> Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
>
------------------------------
Message: 3
Date: Sun, 1 Oct 2017 02:30:40 -0700
From: Phil Karn <karn@xxxx.xxx>
To: amsat-bb@xxxxx.xxx
Subject: [amsat-bb] Conventions for apogee and perigee altitudes?
Message-ID: <89c8b173-c835-da1c-dfda-193850fb646d@xxxx.xxx>
Content-Type: text/plain; charset=utf-8
I've been returning to satellite tracking software after a while (I
wrote some early AMSAT tools in the early 1980s) and am wondering if
there has ever been a resolution of the exact definitions of "apogee
height" and "perigee height".
The simple geometric definitions of "perigee" and "apogee" are the
points where the spacecraft is the closest to or farthest from the
center of the earth. This is easy if you assume the earth is a perfect
sphere; all you need is the semimajor axis a and the eccentricity e:
apogee = a * (1+e) - earth_radius
perigee = a * (1-e) - earth_radius
But reality is more complicated than that. For a nonequatorial orbit the
apogee and perigee usually occur over some point off the equator where
the earth's radius is smaller than at the equator. You can correct for
this given the inclination and the argument of perigee, which together
tell you the latitude at which apogee and perigee occur; one will occur
in the northern hemisphere and the other will occur in the southern
hemisphere at the opposite latitude.
There's a complication here in that this is geocentric latitude, while
we more often use geodetic latitude on a daily basis. Converting
geodetic latitude to geocentric is fairly easy, but converting in the
other direction is like Kepler's equation: apparently there's no closed
form solution so you have to iterate.
But this is a relatively minor detail. The real problem comes when you
have a satellite with a relatively high inclination and an argument of
perigee close to 0 or 180 degrees; in this situation the satellite can
easily be farther from the earth's surface than *either* the calculated
apogee or perigee!
The ISS is a case in point at the moment. Using element set 906, which
has an argument of perigee of about 329 degrees I calculate an apogee of
408 km and a perigee of 402.4 km assuming an oblate earth and ignoring
the distinction between geodetic and geocentric latitude (which is
relatively small for this argument of perigee). But near the
southernmost point of its orbit, I calculate an altitude of about 421
km, well above both the perigee and apogee heights because the earth's
surface through the poles is more elliptical than the ISS's orbit.
So what conventions do people use? How meaningful do people expect these
figures to be? For a low altitude orbit like the ISS, the difference in
drag between 402 and 421 km is actually quite significant. At the very
least it would be nice if everybody used the same convention.
------------------------------
Message: 4
Date: Sun, 1 Oct 2017 08:00:05 -0300
From: "Edson W. R. Pereira" <ewpereira@xxxxx.xxx>
To: Robert Bruninga <bruninga@xxxx.xxx>
Cc: Robert Switzer <robert_switzer@xxx.xxx>, "amsat-bb@xxxxx.xxxx
<amsat-bb@xxxxx.xxx>, Paul Stoetzer <n8hm@xxxx.xxx>
Subject: Re: [amsat-bb] WISP replacement? (or Live digipeating?)
Message-ID:
<CALNQy4_SLjRYPPHcMmP4yNC79WCeq3iU4hn3Pk_WiJCKCpBnvg@xxxx.xxxxx.xxx>
Content-Type: text/plain; charset="UTF-8"
Bob,
Digipeating through PFS3-1 is on, but it would be really nice to use the
digipeater for live QSOs and not unattended beacons.
73, Edson PY2SDR
On Sat, Sep 30, 2017 at 8:31 PM, Robert Bruninga <bruninga@xxxx.xxx> wrote:
> It was possible to enable digipeating in a PACSAT protocol satellite. I
> wonder if it should be considered?
> I know I'd like it... ;-)
>
> Live Real-time satellite operations.
>
> I remember 20 years ago, I worked for a month and finally got a PACSAT
> ground station to work. Did one pass. Once I saw that it was a hands off,
> automatic process, with nothing to do during the pass but just watch it
> work, I lost interest and never went back...
>
> I wanted something live...
>
> Bob, WB4APR.
>
> On Sat, Sep 30, 2017 at 3:09 PM, Douglas Quagliana <dquagliana@xxxxx.xxx>
> wrote:
>
>> All,
>> I'd like to get pbpg running with a soundcard modem on Linux. First,
>> I'm
>> just trying to get pbpg running.
>>
>> I was able to download pbpg-2.2.1.tar.gz from the AMSAT website, and
>> after a little work I got it to compile and got it installed, but it
>> doesn't seem to run properly on my Linux box. I have kernel version 4.4.75
>> on this machine, but I could try another kernel version or a completely
>> different distro quite easily.
>>
>> I strongly suspect I'm "doing it wrong" and there's some more missing
>> setup and config (for example, the "configure/make/make install" didn't
>> create the control FIFO (/etc/pbpg/pb-fifo) nor any of the
>> /var/spool/pbpg/satellite-name directories.
>>
>> I think I'm missing a required step. Is there more install/config
>> documentation somewhere besides what comes with pbpg-2.2.1.tar.gz ?
>>
>> Douglas KA2UPW/5
>>
>>
>> On Thu, Sep 28, 2017 at 11:23 AM, Edson W. R. Pereira <
>> ewpereira@xxxxx.xxx>
>> wrote:
>>
>> > The Linux version of PB and PG talks to a pseudo TNC using the native
>> Linux
>> > AX.25 sockets. It has been more than two decades since I have last used
>> the
>> > native AX.25 sockets and, as far as I can remember, it was not trivial.
>> I
>> > suggest modifying the PB and PB software to speak the AX.25 KISS over
>> TCP
>> > protocol and talk with DireWolf, a software TNC that implements the
>> G3RUH
>> > GFSK 9600 bps modem. DireWolf can be found here:
>> >
>> > https://github.com/wb2osz/direwolf
>> >
>> > I will try modifying PB and PG to use the KISS protocol as soon as I can
>> > spare some time.
>> >
>> > DireWolf could be used with a classic transceiver via soundcard and
>> also to
>> > a SDR receiver such as GQRX or GNURadio and a classic (or SDR)
>> transmitter.
>> > The software modem could also be implemented directly in GNUradio as
>> well.
>> >
>> > It will be a blast to operate a PACSAT BBS again.
>> >
>> > 73, Edson PY2SDR
>> >
>> >
>> > On Thu, Sep 28, 2017 at 12:55 PM, Paul Stoetzer <n8hm@xxxx.xxx> wrote:
>> >
>> > > The Linux tools (PacSatTools and PB/PG) are distributed as source
>> > > code. That code could potentially serve as a guide for how to encode
>> > > files and interface with a KISS TNC.
>> > >
>> > > See https://www.amsat.org/falconsat-3/
>> > >
>> > > 73,
>> > >
>> > > Paul, N8HM
>> > >
>> > > On Thu, Sep 28, 2017 at 11:18 AM, Robert Switzer via AMSAT-BB
>> > > <amsat-bb@xxxxx.xxx> wrote:
>> > > > Don't know if this is opensource ( a quick search only found the old
>> > > WiSP32 download setup.exe), but this as well as other old programs
>> (I'm
>> > > thinking Nova, but perhaps others?) would be best
>> > > > served by getting it out there in the public domain.
>> > > > The other option is to reverse engineer if someone has a working
>> copy.
>> > > >
>> > > >
>> > > >
>> > > >
>> > > > On Thursday, September 28, 2017 9:19 AM, Andrew Glasbrenner <
>> > > glasbrenner@xxxxxxxxxx.xxx> wrote:
>> > > >
>> > > >
>> > > > For all our talented coders out there, a replacement for the
>> venerable
>> > > WISP
>> > > > software would be well received, and allow much more utilization of
>> > this
>> > > > satellite resource. Anyone interested?
>> > > >
>> > > >
>> > > >
>> > > > 73, Drew KO4MA
>> > > >
>> > > > _______________________________________________
>> > > > Sent via AMSAT-BB@xxxxx.xxx. AMSAT-NA makes this open forum
>> available
>> > > > to all interested persons worldwide without requiring membership.
>> > > Opinions expressed
>> > > > are solely those of the author, and do not reflect the official
>> views
>> > of
>> > > AMSAT-NA.
>> > > > Not an AMSAT-NA member? Join now to support the amateur satellite
>> > > program!
>> > > > Subscription settings: http://www.amsat.org/mailman/l
>> istinfo/amsat-bb
>> > > >
>> > > >
>> > > >
>> > > > _______________________________________________
>> > > > Sent via AMSAT-BB@xxxxx.xxx. AMSAT-NA makes this open forum
>> available
>> > > > to all interested persons worldwide without requiring membership.
>> > > Opinions expressed
>> > > > are solely those of the author, and do not reflect the official
>> views
>> > of
>> > > AMSAT-NA.
>> > > > Not an AMSAT-NA member? Join now to support the amateur satellite
>> > > program!
>> > > > Subscription settings: http://www.amsat.org/mailman/l
>> istinfo/amsat-bb
>> > > _______________________________________________
>> > > Sent via AMSAT-BB@xxxxx.xxx. AMSAT-NA makes this open forum available
>> > > to all interested persons worldwide without requiring membership.
>> > Opinions
>> > > expressed
>> > > are solely those of the author, and do not reflect the official views
>> of
>> > > AMSAT-NA.
>> > > Not an AMSAT-NA member? Join now to support the amateur satellite
>> > program!
>> > > Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
>> > >
>> > _______________________________________________
>> > Sent via AMSAT-BB@xxxxx.xxx. AMSAT-NA makes this open forum available
>> > to all interested persons worldwide without requiring membership.
>> Opinions
>> > expressed
>> > are solely those of the author, and do not reflect the official views of
>> > AMSAT-NA.
>> > Not an AMSAT-NA member? Join now to support the amateur satellite
>> program!
>> > Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
>> >
>> _______________________________________________
>> Sent via AMSAT-BB@xxxxx.xxx. AMSAT-NA makes this open forum available
>> to all interested persons worldwide without requiring membership.
>> Opinions expressed
>> are solely those of the author, and do not reflect the official views of
>> AMSAT-NA.
>> Not an AMSAT-NA member? Join now to support the amateur satellite program!
>> Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
>>
>
>
------------------------------
Message: 5
Date: Sun, 1 Oct 2017 06:48:48 -0500
From: "Alan" <wa4sca@xxxxx.xxx>
To: <amsat-bb@xxxxx.xxx>
Subject: Re: [amsat-bb] Conventions for apogee and perigee altitudes?
Message-ID: <000001d33aab$3f22f2f0$bd68d8d0$@xxxxx.xxx>
Content-Type: text/plain; charset="us-ascii"
Phil,
One of my hobbies is to periodically calculate the apogee and perigee of a
few satellites to monitor their decay rates. (The total energy of the orbit
can be parameterized in terms of the sum of the apogee and perigee, which is
ultimately what you want for this purpose.) When I started this, I surveyed
the results of tracking programs, and found the same chaos you report. At
least some use an average, others a mean radius. This is certainly _part_
of the explanation for hearing satellites when they are reported to be below
the horizon, diffraction and refraction being other factors.
I decided that for my purposes, trends, it didn't matter so long as I stuck
with one. I finally chose the NASA Debris Assessment Software program which
is the official tool for calculating lifetimes, etc. Unfortunately the
program is a black box, or at least not documented in the program notes, but
there are hints that is uses a more sophisticated model than a simple
sphere.
I expect for amateur purposes, a simple sphere is fine.
73s,
Alan
WA4SCA
<-----Original Message-----
<From: AMSAT-BB [mailto:amsat-bb-bounces@xxxxx.xxxx On Behalf Of Phil
<Karn
<Sent: Sunday, October 01, 2017 04:31 AM
<To: amsat-bb@xxxxx.xxx
<Subject: [amsat-bb] Conventions for apogee and perigee altitudes?
<
<I've been returning to satellite tracking software after a while (I
<wrote some early AMSAT tools in the early 1980s) and am wondering if
<there has ever been a resolution of the exact definitions of "apogee
<height" and "perigee height".
<
<The simple geometric definitions of "perigee" and "apogee" are the
<points where the spacecraft is the closest to or farthest from the
<center of the earth. This is easy if you assume the earth is a perfect
<sphere; all you need is the semimajor axis a and the eccentricity e:
<
<apogee = a * (1+e) - earth_radius
<perigee = a * (1-e) - earth_radius
<
<But reality is more complicated than that. For a nonequatorial orbit the
<apogee and perigee usually occur over some point off the equator where
<the earth's radius is smaller than at the equator. You can correct for
<this given the inclination and the argument of perigee, which together
<tell you the latitude at which apogee and perigee occur; one will occur
<in the northern hemisphere and the other will occur in the southern
<hemisphere at the opposite latitude.
<
<There's a complication here in that this is geocentric latitude, while
<we more often use geodetic latitude on a daily basis. Converting
<geodetic latitude to geocentric is fairly easy, but converting in the
<other direction is like Kepler's equation: apparently there's no closed
<form solution so you have to iterate.
<
<But this is a relatively minor detail. The real problem comes when you
<have a satellite with a relatively high inclination and an argument of
<perigee close to 0 or 180 degrees; in this situation the satellite can
<easily be farther from the earth's surface than *either* the calculated
<apogee or perigee!
<
<The ISS is a case in point at the moment. Using element set 906, which
<has an argument of perigee of about 329 degrees I calculate an apogee of
<408 km and a perigee of 402.4 km assuming an oblate earth and ignoring
<the distinction between geodetic and geocentric latitude (which is
<relatively small for this argument of perigee). But near the
<southernmost point of its orbit, I calculate an altitude of about 421
<km, well above both the perigee and apogee heights because the earth's
<surface through the poles is more elliptical than the ISS's orbit.
<
<So what conventions do people use? How meaningful do people expect these
<figures to be? For a low altitude orbit like the ISS, the difference in
<drag between 402 and 421 km is actually quite significant. At the very
<least it would be nice if everybody used the same convention.
<
<
<
<_______________________________________________
<Sent via AMSAT-BB@xxxxx.xxx. AMSAT-NA makes this open forum available
<to all interested persons worldwide without requiring membership. Opinions
<expressed
<are solely those of the author, and do not reflect the official views of
AMSAT-
<NA.
<Not an AMSAT-NA member? Join now to support the amateur satellite
<program!
<Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
------------------------------
Message: 6
Date: Sun, 1 Oct 2017 11:37:34 +0000 (UTC)
From: Steve Nordahl <ns3l@xxxxx.xxx>
To: AMSAT BB <amsat-bb@xxxxx.xxx>
Subject: [amsat-bb] R60SAT Special Call on the air. Sputnik-1 60 Year
Celebration
Message-ID: <213132842.595853.1506857854889@xxxx.xxxxx.xxx>
Content-Type: text/plain; charset=UTF-8
Keep your eye out for "R60SAT" a special call on the air from European
Russia celebrating "Sputnik-1 The First Artificial Earth Satellite"
Steve NS3L
R60SAT Callsign Page
|
|
|
| | |
|
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|
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R60SAT Callsign Page
R60SAT personal biography | |
|
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Message: 7
Date: Sun, 1 Oct 2017 11:20:33 -0400
From: Robert Bruninga <bruninga@xxxx.xxx>
To: amsat bb <amsat-bb@xxxxx.xxx>
Subject: [amsat-bb] Falconsat-3 and APRS HT's?
Message-ID:
<CALdCfNLtSjVGS2yP2jMbE_CEKdZna1aiCH2jYDSO7=C-MSs8uA@xxxx.xxxxx.xxx>
Content-Type: text/plain; charset="UTF-8"
I was confused. I thought FALCONSAT-3 was a PACSAT protocol store and
forward system because I thought I saw people trying to get the old PB and
BG code, But the AMSAT web page says it is 9600 baud GMSK up and down.
https://www.amsat.org/falconsat-3/
435.103 MHz down and 145.840 up DIGI call of PFS3-1. While of course
setting 5 memores to chase the Doppler the full 20 KHz during the pass.
So I am surrprised that I havent heard of anyone making contacts with any
ole' APRS HT or Mobile... All of these radios can do 9600 baud and APRS
natively..
Im under Kitchen arrest until 1st grandkid arrives soon and cannot play.
If I missed something, ignore me. Ill go back under my domestic rock...
Bob, WB4APR
------------------------------
Message: 8
Date: Sun, 1 Oct 2017 10:37:25 -0500
From: "JoAnne K9JKM" <joanne.k9jkm@xxxxx.xxx>
To: "'amsat bb'" <amsat-bb@xxxxx.xxx>
Subject: Re: [amsat-bb] Falconsat-3 and APRS HT's?
Message-ID: <59d10bb6.c4e0240a.45cde.db31@xx.xxxxxx.xxx>
Content-Type: text/plain; charset="us-ascii"
Hi Bob,
> So I am surprised that I havent heard of anyone making contacts with any
> ole' APRS HT or Mobile... All of these radios can do 9600 baud and APRS
> natively.
There doesn't seem to be much discussion on the amsat-bb but the Satellite
Forum on QRZ.com has a lot of examples of setup and QSOs ... with photos and
screenshots (which we couldn't see the graphics on the good 'ol -bb anyways)
https://forums.qrz.com/index.php?threads/falconsat.582133/
and on the AMSAT-NA group on Facebook
--
73 de JoAnne K9JKM
k9jkm@xxxxx.xxx
------------------------------
Message: 9
Date: Sun, 1 Oct 2017 09:47:17 -0700
From: Phil Karn <karn@xxxx.xxx>
To: amsat-bb@xxxxx.xxx
Subject: Re: [amsat-bb] Conventions for apogee and perigee altitudes?
Message-ID: <5f0e549e-43af-3eee-7917-9ee1c4b540f9@xxxx.xxx>
Content-Type: text/plain; charset=utf-8
On 10/1/17 04:48, Alan wrote:
> I expect for amateur purposes, a simple sphere is fine.
>
I'm interested in what others are doing so I can be at least somewhat
consistent with their results.
My current method for computing apogee and perigee seems to give results
that match many of the online tracking programs. That is, find the
geometric apogee and perigee and subtract the radius of the earth under
those points. I can't easily tell if they make the correction for
geodetic latitude because the effect is small and the results are
usually not given with a lot of precision. But you do end up with weird
oddities like seeing the ISS at an altitude that exceeds calculated
apogee. As long as everybody is happy with that little anomaly, I'm
happy too.
If you want to compute the energy in a (decaying) orbit, there's a
simple and straightforward formula:
specific orbital energy = -GM/(2*a)
where 'GM' (also known as mu) is the earth's gravitational parameter =
3.986004418e14 m^3/s^2 and 'a' is the orbit's semi-major axis in meters.
The specific energy is the sum in joules of the satellite's kinetic and
potential energy per kilogram of its mass. Because of energy
conservation, it will remain constant for any satellite in any
trajectory unless it is gaining or losing energy from thrust, drag, or
gravitational exchanges with a third body. It is always negative for a
closed orbit because potential energy is zero at infinity and
increasingly negative as you get closer. A positive specific energy
means a hyperbolic (escape) trajectory.
For the ISS I calculate a specific energy of about -29.38 MJ/kg.
Problem is, you can't recover the semimajor axis from the apogee and
perigee unless you know how they're computed. And if they're done the
way I described, you also need the latitude of apogee and perigee so you
can add the right earth radius, and that in turn usually requires
knowing the inclination and argument of perigee, the latter changing
steadily with time.
But if you have the mean motion or period you can compute the semi major
axis from it using Kepler's third law:
a = (GM*P^2)^1/3
where the period P is expressed in seconds/radian
= seconds/revolution / (2*pi), or
a = (GM/N^2)^1/3
where the mean motion N is expressed in radians/sec
= rev/day * 2 * pi/86400.
So all you really need to compute specific energy and track decay is the
satellite's period. That's it! Forget apogee and perigee...
You can also track the specific angular momentum of the satellite, which
must also remain constant absent external forces besides simple 2-body
gravity:
h = sqrt(GM * a(1-e^2))
The units of specific angular momentum are m^2/s, or area per time. This
is where Kepler's second law comes from: the satellite sweeps out equal
areas in equal time because that represents the satellite's (conserved)
specific angular momentum.
In fact, we could describe an orbit with the angular momentum vector,
which points normal to the orbit plane and defines RAAN and inclination,
and the eccentricity vector, which points at perigee and defines the
argument of perigee and the eccentricity. The two together define the
mean motion, and if the epoch corresponds to a specific point on the
orbit that sets the mean anomaly. That's all 6 Keplerian elements.
--Phil
------------------------------
Subject: Digest Footer
_______________________________________________
Sent via amsat-bb@xxxxx.xxx.
AMSAT-NA makes this open forum available to all interested persons worldwide
without requiring membership. Opinions expressed
are solely those of the author, and do not reflect the official views of
AMSAT-NA.
Not an AMSAT member? Join now to support the amateur satellite program!
http://www.amsat.org/mailman/listinfo/amsat-bb
------------------------------
End of AMSAT-BB Digest, Vol 12, Issue 241
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