Hi We had a low pass over here minutes ago and i felt the keps BY70-1 are wrong . I start to hear 25 seconds before . Does anyone feels the same ? 73
If you are still using yesterday's TLE set, then you will indeed find that BY70-1 is now about half a minute earlier. The problem is that the TLEs for this satellite are not stable yet in the first days after the launch. The right value for e.g. the decay rate has not yet been established. So for the time being you need to make sure you use the most recent TLE set that is available.
By the way, the two SuperView satellites are now using their own propulsion system to increase their altitude, preventing an early decay. As BY70-1 does not have any propulsion, it is stuck in its low orbit.
73, Nico PA0DLO
On 30-12-16 13:42, PY5LF wrote:
Hi We had a low pass over here minutes ago and i felt the keps BY70-1 are wrong . I start to hear 25 seconds before . Does anyone feels the same ? 73 _______________________________________________ Sent via AMSAT-BB@amsat.org. 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
Nico Thank you for the explanation. I got the fresh Tles from Celestrack today, but looks not correct. Regards
2016-12-30 11:14 GMT-02:00 Nico Janssen hamsat@xs4all.nl:
If you are still using yesterday's TLE set, then you will indeed find that BY70-1 is now about half a minute earlier. The problem is that the TLEs for this satellite are not stable yet in the first days after the launch. The right value for e.g. the decay rate has not yet been established. So for the time being you need to make sure you use the most recent TLE set that is available.
By the way, the two SuperView satellites are now using their own propulsion system to increase their altitude, preventing an early decay. As BY70-1 does not have any propulsion, it is stuck in its low orbit.
73, Nico PA0DLO
On 30-12-16 13:42, PY5LF wrote:
Hi We had a low pass over here minutes ago and i felt the keps BY70-1 are wrong . I start to hear 25 seconds before . Does anyone feels the same ? 73 _______________________________________________ Sent via AMSAT-BB@amsat.org. 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
18:20 pass not as strong as prior passes. Only got a few moments of full-quieting audio. Contacts with W5ACM and KC7M. As before, the second half of the pass was much better (nothing heard at all until just before indicated TCA), so perhaps the bird is late compared to the Keps. Worked it almost into the ground before LOS. I'm using 2016-083C, updated from Celestrak right before the pass. Playing with polarization seemed to help, but I'm assuming the bird's antennas are linear, right? Possibly my relays are getting dirty.
One question, for scale... We know that the satellite will not last "long", given it's crippled orbit. How long? Days? Weeks? Months?
Greg KO6TH
Nico Janssen wrote:
If you are still using yesterday's TLE set, then you will indeed find that BY70-1 is now about half a minute earlier. The problem is that the TLEs for this satellite are not stable yet in the first days after the launch. The right value for e.g. the decay rate has not yet been established. So for the time being you need to make sure you use the most recent TLE set that is available.
By the way, the two SuperView satellites are now using their own propulsion system to increase their altitude, preventing an early decay. As BY70-1 does not have any propulsion, it is stuck in its low orbit.
73, Nico PA0DLO
On 30-12-16 13:42, PY5LF wrote:
Hi We had a low pass over here minutes ago and i felt the keps BY70-1 are wrong . I start to hear 25 seconds before . Does anyone feels the same ? 73 _______________________________________________ Sent via AMSAT-BB@amsat.org. 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@amsat.org. 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
When I put keps for BY70-1 into SatPC32 (either yesterday's keps or today's), it pops up a box that says, "E/A - Fehler 105." SatPC32 freezes up.
Does anyone know what this error code means? Anyone else getting it?
Mark,
I also get the “E/A-Fehler 105.” error message when I add BY70-1 to a satellite group in SatPC32. Other people don’t have the problem.
The error message (in German) means I/O Error 105 in the Delphi programming environment, which I believe is an error writing to a file.
What I can’t yet answer is how to fix the problem. We may have a file permissions problem.
Anybody have a solution or know where to look?
73, Steve N9IP
-- Steve Belter, seb@wintek.com
On 12/30/16, 1:20 PM, "AMSAT-BB on behalf of Mark Johns via AMSAT-BB" <amsat-bb-bounces@amsat.org on behalf of amsat-bb@amsat.org> wrote:
When I put keps for BY70-1 into SatPC32 (either yesterday's keps or today's), it pops up a box that says, "E/A - Fehler 105." SatPC32 freezes up.
Does anyone know what this error code means? Anyone else getting it?
--
Mark D. Johns, KØMDJ Decorah, Iowa USA EN43
"Heaven goes by favor; if it went by merit, you would stay out and your dog would go in." ---Mark Twain
----- Original Message ----- From: Greg D ko6th.greg@gmail.com To: AMSAT-BB AMSAT-BB@amsat.org Sent: Friday, December 30, 2016 12:43 PM Subject: Re: [amsat-bb] BY70-1
18:20 pass not as strong as prior passes. Only got a few moments of full-quieting audio. Contacts with W5ACM and KC7M. As before, the second half of the pass was much better (nothing heard at all until just before indicated TCA), so perhaps the bird is late compared to the Keps. Worked it almost into the ground before LOS. I'm using 2016-083C, updated from Celestrak right before the pass. Playing with polarization seemed to help, but I'm assuming the bird's antennas are linear, right? Possibly my relays are getting dirty.
One question, for scale... We know that the satellite will not last "long", given it's crippled orbit. How long? Days? Weeks? Months?
Greg KO6TH
Nico Janssen wrote:
If you are still using yesterday's TLE set, then you will indeed find that BY70-1 is now about half a minute earlier. The problem is that the TLEs for this satellite are not stable yet in the first days after the launch. The right value for e.g. the decay rate has not yet been established. So for the time being you need to make sure you use the most recent TLE set that is available.
By the way, the two SuperView satellites are now using their own propulsion system to increase their altitude, preventing an early decay. As BY70-1 does not have any propulsion, it is stuck in its low orbit.
73, Nico PA0DLO
On 30-12-16 13:42, PY5LF wrote:
Hi We had a low pass over here minutes ago and i felt the keps BY70-1 are wrong . I start to hear 25 seconds before . Does anyone feels the same ? 73 _______________________________________________ Sent via AMSAT-BB@amsat.org. 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@amsat.org. 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@amsat.org. 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@amsat.org. 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
I was hoping someone with a better memory, or Erich would chime in on this but here goes. I would first add this line to the Doppler.SQF file...
BY70-1,436200,145920,FM,FM,Nor,0,0,Voice V/U
Then add this line to the subTone.SQF file...
BY70-1,67.0,$3F,1 (for an Icom, I'm not sure of other rigs) RTFM
Then I download the keps from nasa.all (I was fudging them in for a day) and you should be good to go when you add BY70-1
73 Jeff kb2m
-----Original Message----- From: AMSAT-BB [mailto:amsat-bb-bounces@amsat.org] On Behalf Of Stephen E. Belter Sent: Friday, December 30, 2016 4:01 PM To: Mark Johns; AMSAT-BB
Subject: Re: [amsat-bb] BY70-1
Mark,
I also get the “E/A-Fehler 105.” error message when I add BY70-1 to a satellite group in SatPC32. Other people don’t have the problem.
The error message (in German) means I/O Error 105 in the Delphi programming environment, which I believe is an error writing to a file.
What I can’t yet answer is how to fix the problem. We may have a file permissions problem.
Anybody have a solution or know where to look?
73, Steve N9IP
-- Steve Belter, seb@wintek.com
On 12/30/16, 1:20 PM, "AMSAT-BB on behalf of Mark Johns via AMSAT-BB" <amsat-bb-bounces@amsat.org on behalf of amsat-bb@amsat.org> wrote:
When I put keps for BY70-1 into SatPC32 (either yesterday's keps or today's), it pops up a box that says, "E/A - Fehler 105." SatPC32 freezes up.
Does anyone know what this error code means? Anyone else getting it?
--
Mark D. Johns, KØMDJ Decorah, Iowa USA EN43
"Heaven goes by favor; if it went by merit, you would stay out and your dog would go in." ---Mark Twain
----- Original Message ----- From: Greg D ko6th.greg@gmail.com To: AMSAT-BB AMSAT-BB@amsat.org Sent: Friday, December 30, 2016 12:43 PM Subject: Re: [amsat-bb] BY70-1
18:20 pass not as strong as prior passes. Only got a few moments of full-quieting audio. Contacts with W5ACM and KC7M. As before, the second half of the pass was much better (nothing heard at all until just before indicated TCA), so perhaps the bird is late compared to the Keps. Worked it almost into the ground before LOS. I'm using 2016-083C, updated from Celestrak right before the pass. Playing with polarization seemed to help, but I'm assuming the bird's antennas are linear, right? Possibly my relays are getting dirty.
One question, for scale... We know that the satellite will not last "long", given it's crippled orbit. How long? Days? Weeks? Months?
Greg KO6TH
Nico Janssen wrote:
If you are still using yesterday's TLE set, then you will indeed find that BY70-1 is now about half a minute earlier. The problem is that the TLEs for this satellite are not stable yet in the first days after the launch. The right value for e.g. the decay rate has not yet been established. So for the time being you need to make sure you use the most recent TLE set that is available.
By the way, the two SuperView satellites are now using their own propulsion system to increase their altitude, preventing an early decay. As BY70-1 does not have any propulsion, it is stuck in its low orbit.
73, Nico PA0DLO
On 30-12-16 13:42, PY5LF wrote:
Hi We had a low pass over here minutes ago and i felt the keps BY70-1 are wrong . I start to hear 25 seconds before . Does anyone feels the same ? 73 _______________________________________________ Sent via AMSAT-BB@amsat.org. 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@amsat.org. 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@amsat.org. 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@amsat.org. 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
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Thanks, Steve. Good to know it's not just me. Let me know if you figure it out. I will do likewise.
Steve (and others),
I wrote directly to Erich, the SatPC32 author, about this problem. FYI, below is his very nice reply:
Mark, Happy New Year! I don't remember my comment in 2006. You are right - since the problem is specific to only one satellite it doesn't make sense to completely re-install the program, I think. Perhaps you proceed step-by-step: Run SatPC32 with configuration #1 (menu "Setup") and group "Standard". Choose nasa.all as Keps file. Leave Doppler.SQF and SubTone.SQF and (eventually) Prior.SQF unchanged, that means WITHOUT entries for BY70-1. Make sure that there is at least one ident letter free for a new satellite.
Then open menu "Satellites" and add BY70-1 from the "Available" list to the "Selected" list and click the "OK" button. A new ident letter should appear. Click on it to switch to BY70-1. Does that cause already the io 105 error?
SatPC32 saves the "Selected" list of group "Standard" in the text file "Standard.Sat" in the SatPC32 DATA folder (path can be seen in footline of menu "Satellites" ). Is there something unusual with that file? At its end it should show: BY70-1 - The minus char below the name indicates that the option "Show On/Off" (menu "Satellites") is unchecked (no asterix in front of the satellite name). Attention: Make first hidden files and folders visible using the Windows File Explorer, because the folder "AppData" in the path is hidden by default. 73s, Erich, DK1TB
As long as we don't have stable TLEs it is not possible to perform an analysis to determine the expected lifetime. But my initial guestimate would be somewhere between 2 and 6 months.
73, Nico
On 30-12-16 19:43, Greg D wrote:
18:20 pass not as strong as prior passes. Only got a few moments of full-quieting audio. Contacts with W5ACM and KC7M. As before, the second half of the pass was much better (nothing heard at all until just before indicated TCA), so perhaps the bird is late compared to the Keps. Worked it almost into the ground before LOS. I'm using 2016-083C, updated from Celestrak right before the pass. Playing with polarization seemed to help, but I'm assuming the bird's antennas are linear, right? Possibly my relays are getting dirty.
One question, for scale... We know that the satellite will not last "long", given it's crippled orbit. How long? Days? Weeks? Months?
Greg KO6TH
Nico Janssen wrote:
If you are still using yesterday's TLE set, then you will indeed find that BY70-1 is now about half a minute earlier. The problem is that the TLEs for this satellite are not stable yet in the first days after the launch. The right value for e.g. the decay rate has not yet been established. So for the time being you need to make sure you use the most recent TLE set that is available.
By the way, the two SuperView satellites are now using their own propulsion system to increase their altitude, preventing an early decay. As BY70-1 does not have any propulsion, it is stuck in its low orbit.
73, Nico PA0DLO
On 30-12-16 13:42, PY5LF wrote:
Hi We had a low pass over here minutes ago and i felt the keps BY70-1 are wrong . I start to hear 25 seconds before . Does anyone feels the same ? 73 _______________________________________________ Sent via AMSAT-BB@amsat.org. 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@amsat.org. 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@amsat.org. 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
I put the parameters from yesterday's TLEs into NASA's DAS software. The mass is listed at 2 kg, so the unknown variable is the cross sectional surface area. It's a 2U cubesat with deployed solar panels. With one estimate, I got 6 days, which is obviously wrong. With another estimate, I got 96 days.
73,
Paul, N8HM
On Fri, Dec 30, 2016 at 14:45 Nico Janssen hamsat@xs4all.nl wrote:
As long as we don't have stable TLEs it is not possible to perform
an analysis to determine the expected lifetime. But my initial
guestimate would be somewhere between 2 and 6 months.
73, Nico
On 30-12-16 19:43, Greg D wrote:
18:20 pass not as strong as prior passes. Only got a few moments of
full-quieting audio. Contacts with W5ACM and KC7M. As before, the
second half of the pass was much better (nothing heard at all until just
before indicated TCA), so perhaps the bird is late compared to the
Keps. Worked it almost into the ground before LOS. I'm using
2016-083C, updated from Celestrak right before the pass. Playing with
polarization seemed to help, but I'm assuming the bird's antennas are
linear, right? Possibly my relays are getting dirty.
One question, for scale... We know that the satellite will not last
"long", given it's crippled orbit. How long? Days? Weeks? Months?
Greg KO6TH
Nico Janssen wrote:
If you are still using yesterday's TLE set, then you will indeed find
that BY70-1 is now about half a minute earlier. The problem is that
the TLEs for this satellite are not stable yet in the first days after
the
launch. The right value for e.g. the decay rate has not yet been
established. So for the time being you need to make sure you use the
most recent TLE set that is available.
By the way, the two SuperView satellites are now using their own
propulsion system to increase their altitude, preventing an early decay.
As BY70-1 does not have any propulsion, it is stuck in its low orbit.
73,
Nico PA0DLO
On 30-12-16 13:42, PY5LF wrote:
Hi
We had a low pass over here minutes ago and i felt the keps BY70-1 are
wrong .
I start to hear 25 seconds before . Does anyone feels the same ?
73
Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available
to all interested persons worldwide without requiring membership.
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of AMSAT-NA.
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program!
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of AMSAT-NA.
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AMSAT-NA.
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And when we know this, re-entry window, wouldn't it be neat if someone could catch it on video coming back in?
Joe WB9SBD Sig The Original Rolling Ball Clock Idle Tyme Idle-Tyme.com http://www.idle-tyme.com On 12/30/2016 12:43 PM, Greg D wrote:
18:20 pass not as strong as prior passes. Only got a few moments of full-quieting audio. Contacts with W5ACM and KC7M. As before, the second half of the pass was much better (nothing heard at all until just before indicated TCA), so perhaps the bird is late compared to the Keps. Worked it almost into the ground before LOS. I'm using 2016-083C, updated from Celestrak right before the pass. Playing with polarization seemed to help, but I'm assuming the bird's antennas are linear, right? Possibly my relays are getting dirty.
One question, for scale... We know that the satellite will not last "long", given it's crippled orbit. How long? Days? Weeks? Months?
Greg KO6TH
Nico Janssen wrote:
If you are still using yesterday's TLE set, then you will indeed find that BY70-1 is now about half a minute earlier. The problem is that the TLEs for this satellite are not stable yet in the first days after the launch. The right value for e.g. the decay rate has not yet been established. So for the time being you need to make sure you use the most recent TLE set that is available.
By the way, the two SuperView satellites are now using their own propulsion system to increase their altitude, preventing an early decay. As BY70-1 does not have any propulsion, it is stuck in its low orbit.
73, Nico PA0DLO
On 30-12-16 13:42, PY5LF wrote:
Hi We had a low pass over here minutes ago and i felt the keps BY70-1 are wrong . I start to hear 25 seconds before . Does anyone feels the same ? 73 _______________________________________________ Sent via AMSAT-BB@amsat.org. 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@amsat.org. 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
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On 12/30/16 05:14, Nico Janssen wrote:
By the way, the two SuperView satellites are now using their own propulsion system to increase their altitude, preventing an early decay. As BY70-1 does not have any propulsion, it is stuck in its low orbit.
Thanks for this explanation. I was wondering why the Superview satellites were in stable near-circular orbits at ~520 km if the launch vehicle malfunctioned.
I've grabbed all the historical elements sets from space-track.org for both Superview spacecraft and for BY70-1. There are quite a few. I want to look at BY70-1's change in specific orbital energy over time to estimate the power being dissipated around the spacecraft as it decayed.
The specific orbital energy is the sum of the potential and kinetic specific energy at any given time. It's constant in any 2-body orbit in the absence of drag and thrust: negative for a closed orbit (circular, elliptical) and positive for a hyperbolic (escape) trajectory. It's exactly 0 for a parabolic escape trajectory. The specific orbital energy in joules per kilogram is
E = -mu/(2*a)
where mu is the earth's gravitational parameter (3.986004418e14 m^3/s^2) and 'a' is the semimajor axis in meters. The semimajor axis can be computed from the mean motion as
rt = 86400 / (MM*2*pi) a = cube_root(mu*rt^2)
where MM is the mean motion in revolutions per day (from the TLE set) and mu is again the earth's gravitational parameter. The intermediate variable rt is the time in seconds it takes for the mean anomaly to increase by 1 radian, i.e, the time to complete 1/(2*pi) of an orbit.
--Phil
Very interesting stuff, Phil.
Brings to mind a couple of questions on the subject of a decaying orbit...
#1, is there some more-or-less constant altitude where an object is considered to have stopped orbiting and started re-entering the atmosphere, or does it vary with mass of the object, speed, etc.
#2, in the case of a spacecraft with radio TX capability, should we expect it to stop transmitting at some point prior to actual re-entry (for some electrical or RF reason) or do objects normally keep transmitting until they fail structurally due to heat & mechanical break-up?
Thanks!
-Scott, K4KDR Montpelier, VA USA
==============================================
-----Original Message----- From: Phil Karn Sent: Friday, February 24, 2017 12:35 AM To: amsat-bb@amsat.org Subject: Re: [amsat-bb] BY70-1
On 12/30/16 05:14, Nico Janssen wrote:
By the way, the two SuperView satellites are now using their own propulsion system to increase their altitude, preventing an early decay. As BY70-1 does not have any propulsion, it is stuck in its low orbit.
Thanks for this explanation. I was wondering why the Superview satellites were in stable near-circular orbits at ~520 km if the launch vehicle malfunctioned.
I've grabbed all the historical elements sets from space-track.org for both Superview spacecraft and for BY70-1. There are quite a few. I want to look at BY70-1's change in specific orbital energy over time to estimate the power being dissipated around the spacecraft as it decayed.
The specific orbital energy is the sum of the potential and kinetic specific energy at any given time. It's constant in any 2-body orbit in the absence of drag and thrust: negative for a closed orbit (circular, elliptical) and positive for a hyperbolic (escape) trajectory. It's exactly 0 for a parabolic escape trajectory. The specific orbital energy in joules per kilogram is
E = -mu/(2*a)
where mu is the earth's gravitational parameter (3.986004418e14 m^3/s^2) and 'a' is the semimajor axis in meters. The semimajor axis can be computed from the mean motion as
rt = 86400 / (MM*2*pi) a = cube_root(mu*rt^2)
where MM is the mean motion in revolutions per day (from the TLE set) and mu is again the earth's gravitational parameter. The intermediate variable rt is the time in seconds it takes for the mean anomaly to increase by 1 radian, i.e, the time to complete 1/(2*pi) of an orbit.
--Phil
On 2/23/17 21:47, Scott wrote:
Very interesting stuff, Phil.
Brings to mind a couple of questions on the subject of a decaying orbit...
#1, is there some more-or-less constant altitude where an object is considered to have stopped orbiting and started re-entering the atmosphere, or does it vary with mass of the object, speed, etc.
Well, atmospheric density decays exponentially with altitude, so there's no well-defined upper edge. There's the Karman Line that many people consider the traditional "edge of space", set quite arbitrarily to a nice round 100 km. But even a satellite at, say, 500 km will come down in a number of years because it's already re-entered the atmosphere and losing energy to air drag. (Strictly speaking, you could say that it never "re-enters" the atmosphere because it never left it in the first place.)
Karman reportedly chose 100 km as about where an aircraft moving at orbital velocity would be just barely able to generate enough lift to support its own weight. I.e., that would be the highest altitude conceivably reachable with a winged aircraft. I'm not sure how he got that result since it would depend on the size and shape of the wings, the aircraft weight, etc. And of course no real aircraft can get *anywhere* near 100 km with lift, to say nothing of achieving orbital velocity with current aircraft propulsion. (Even with a rocket engine Space Ship One could only briefly visit space; it had only about 4% of the energy needed to attain a minimal orbit.)
From memory, most meteors and decaying spacecraft break up below the
Karman line, in the mesosphere at maybe 70-80 km. The mesosphere is the hardest region of the atmosphere to study since it's too high for balloons and too low for satellites. It can only be briefly visited with sounding rockets (or well protected re-entering spacecraft.)
So I can't give you an exact altitude, but I could say that an object "stops orbiting" when its vacuum perigee (i.e., its projected trajectory if you ignore the atmosphere) goes negative. As long as the vacuum perigee is positive you could say that the satellite is still in orbit, if not for long given the rate at which it's losing energy to drag (and causing the instantaneous vacuum perigee to decrease). And that assumes the spacecraft remains in one piece.
Just before re-entry, Apollo 11 was in a highly elliptical earth orbit with a vacuum perigee of 38.5 km. But it lost so much energy to drag that its vacuum perigee went negative well before it could reach that original 38.5 km point. Had the vacuum perigee been too high, then when it got to perigee it would have retained enough energy to fly back out into space. Mike Collins wrote in his book that he carefully monitored total spacecraft energy during entry, and he breathed a huge sigh of relief when it fell below that required to maintain an orbit.
#2, in the case of a spacecraft with radio TX capability, should we expect it to stop transmitting at some point prior to actual re-entry (for some electrical or RF reason) or do objects normally keep transmitting until they fail structurally due to heat & mechanical break-up?
Well, that depends on how much of the drag heat gets into the electronics and whether they get too hot to function before structural failure. The air is so thin in the upper mesosphere and the velocity is still so high that heating effects probably overwhelm aerodynamic forces, so initial structural failure probably comes from melting, not mechanical pressure.
--Phil
Here's a first calculation of the power dissipation in BY70-1 during its decay.
The highest will be for the period between the last two sets before decay, which have epochs:
Fri Feb 17 17:37:01.530336 2017 UTC Fri Feb 17 22:00:25.286112 2017 UTC
i.e., roughly 4.5 hours apart. The specific orbital energy at the first epoch was -3.044e7 J/kg and -3.054e7 J/kg at the second.
The energy decreased by 100 kJ/kg during this time, so over 4.5 hours that's an average of about 6.2 watts per kilogram. Multiply that by the (unknown?) mass of the spacecraft to determine the actual drag power dissipation in watts.
Depending on how much of that heat was conducted into the spacecraft, I suppose it would have shown up as a temperature increase in telemetry but not necessarily enough to cause the electronics to fail.
Decay was about 2.25 hours after the last eleset, and obviously the power dissipation rose quite sharply toward the end of that interval...
Phil
Very interesting Phil, it seems to make sense that this calculation could be used in reverse to calculate the energy needed raise the perigee height of a GTO orbit. Assuming a flight to GTO was available to a 1U or 3U cubesat, if the perigee is not raised the satellite will not stay in orbit very long, if I understand it correctly. Given the limited size of the spacecraft and the prohibition on volatile propellants this poses a difficult challenge. It would be interesting to determine if enough thrust can be generated by electrical thrusters to accomplish this ?
- Howie AB2S
________________________________ From: AMSAT-BB amsat-bb-bounces@amsat.org on behalf of Phil Karn karn@ka9q.net Sent: Friday, February 24, 2017 12:53 AM To: amsat-bb@amsat.org Subject: Re: [amsat-bb] BY70-1
Here's a first calculation of the power dissipation in BY70-1 during its decay.
The highest will be for the period between the last two sets before decay, which have epochs:
Fri Feb 17 17:37:01.530336 2017 UTC Fri Feb 17 22:00:25.286112 2017 UTC
i.e., roughly 4.5 hours apart. The specific orbital energy at the first epoch was -3.044e7 J/kg and -3.054e7 J/kg at the second.
The energy decreased by 100 kJ/kg during this time, so over 4.5 hours that's an average of about 6.2 watts per kilogram. Multiply that by the (unknown?) mass of the spacecraft to determine the actual drag power dissipation in watts.
Depending on how much of that heat was conducted into the spacecraft, I suppose it would have shown up as a temperature increase in telemetry but not necessarily enough to cause the electronics to fail.
Decay was about 2.25 hours after the last eleset, and obviously the power dissipation rose quite sharply toward the end of that interval...
Phil _______________________________________________ Sent via AMSAT-BB@amsat.org. 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 AMSAT-BB Info Pagehttp://www.amsat.org/mailman/listinfo/amsat-bb www.amsat.org To see the collection of prior postings to the list, visit the AMSAT-BB Archives. Using AMSAT-BB: To post a message to all the list members, send ...
On 2/24/17 07:55, Howie DeFelice wrote:
Very interesting Phil, it seems to make sense that this calculation could be used in reverse to calculate the energy needed raise the perigee height of a GTO orbit. Assuming a flight to GTO was available to a 1U or 3U cubesat, if the perigee is not raised the satellite will not stay in orbit very long, if I understand it correctly. Given the limited size of the spacecraft and the prohibition on volatile propellants this poses a difficult challenge. It would be interesting to determine if enough thrust can be generated by electrical thrusters to accomplish this ?
- Howie AB2S
It would be most relevant if you can use a tether to form an electric motor with the earth's magnetic field to raise your orbit.
Otherwise, things are much more complicated with a chemical or electrical rocket because you have to carry your reaction mass with you and then put energy into it to blow it out the nozzle at high speed.
There's a fundamental tradeoff in rocketry between rocket power and propellant mass flow rate. You can produce a given amount of thrust with high power and a low propellant mass flow rate, or with low power and a high propellant mass flow rate.
E.g., to produce a thrust of 1 N with a mass flow rate of 1 kg/s, you have to eject it at 1 N / 1 kg/s = 1 meter/sec. Ignoring relativity, the kinetic energy in 1 second of exhaust (1 kg) will therefore be
1/2 mv^2 = 1/2 * 1 kg * (1 m/s)^2 = 0.5 joules
and since you need 0.5 joules every second, the required power will be 0.5 watts (assuming 100% efficiency).
If you double the exhaust velocity to 2 m/s, you can drop the mass flow rate to only 1/2 kg/s and still get 1 N of thrust (1/2 kg/s * 2 m/s = 1 N). But you'll now need a power of
0.5 * 0.5 kg/s * (2 m/s)^2 = 1 watt
i.e., twice as much power for that same 1 newton of thrust.
So, which do you have more of, propellant mass or energy? In a chemical rocket the energy is stored in the unburned propellant, so the energy per unit mass is set by the propellant chemistry. That's why every propellant combination has a theoretical specific impulse, e.g. 455 seconds for hydrogen/oxygen in vacuum. Specific impulse is just effective exhaust velocity divided by g = 9.8 m/s^2, so the theoretical exhaust velocity for hydrogen/oxygen is 4,462 m/s.
But in an electric rocket the energy source is external to the propellant mass, so the energy/mass ratio can vary; you decide how fast to eject it. If mass is cheaper than energy, then you want a low exhaust velocity. If energy is cheaper than mass, then you want a high exhaust velocity.
Since the rocket is free to move, the kinetic energy it produces will be split between the payload/rocket itself (which you want) and the exhaust (which is effectively wasted). The only way to get 100% of the energy into the payload/rocket and none into the exhaust is to set the exhaust velocity equal to the current velocity of the rocket so that the exhaust comes out stationary. Of course, velocity is relative so you measure it relative to the reference frame in which the rocket is initially stationary. So to minimize energy consumption you want to increase the exhaust velocity as the rocket accelerates. That's the exact idea behind the VASIMR (Variable Specific Impulse Magnetoplasma Rocket).
The recent "EM drive" hype notwithstanding, I know of only one way to produce thrust in vacuum without some kind of propellant: the photon rocket. Even a flashlight will work, but let's do the numbers. The momentum of a photon is equal to its energy divided by the speed of light, so to get 1 newton of thrust from a 100% efficient photon rocket requires a power input of 1 N * c = 300 megawatts!
That kind of power in space requires either a very large solar array or a very big nuclear reactor (which still needs a very large radiator to reject waste heat).
But there's a simpler way to power a photon rocket with the sun. Instead of turning solar photons into electricity and back into photons, why not use solar photons directly? Voila -- that's what a solar sail does. The thrust produced by a solar sail per unit area is equal to the incident solar power per unit area divided by the speed of light. At 1 AU that's about 1361 W/m^2, so the thrust will be 1361 W/m^2 / c = 4.54 micro newton/m^2. That's actually units of pressure, so solar radiation pressure at 1 AU is 4.54 micropascal on a sail normal to the sun that simply absorbs solar photons. If you reflect them back, you'll get twice as much, 9.08 micropascal. Doesn't seem like much, but you'll get it continuously, no local power source or propellant mass needed.
The one big problem with solar sails is that you can't use them in low orbits because they'll generate far more drag than thrust.
73, Phil
Thanks Phil, that explanation cleared up many questions. I had been thinking about ways to use the earths magnetic field to raise perigee by storing energy in capacitors and pulsing something along the lines of a magnetorquer with a high current pulse at the right time and vector. The problem, I think, is that I would need to generate the thrust at apogee where the earths magnetic field is weakest.
- Howie AB2S
________________________________ From: Phil Karn karn@ka9q.net Sent: Saturday, February 25, 2017 12:41 AM To: Howie DeFelice; amsat-bb@amsat.org Subject: Re: [amsat-bb] BY70-1
On 2/24/17 07:55, Howie DeFelice wrote:
Very interesting Phil, it seems to make sense that this calculation could be used in reverse to calculate the energy needed raise the perigee height of a GTO orbit. Assuming a flight to GTO was available to a 1U or 3U cubesat, if the perigee is not raised the satellite will not stay in orbit very long, if I understand it correctly. Given the limited size of the spacecraft and the prohibition on volatile propellants this poses a difficult challenge. It would be interesting to determine if enough thrust can be generated by electrical thrusters to accomplish this ?
- Howie AB2S
It would be most relevant if you can use a tether to form an electric motor with the earth's magnetic field to raise your orbit.
Otherwise, things are much more complicated with a chemical or electrical rocket because you have to carry your reaction mass with you and then put energy into it to blow it out the nozzle at high speed.
There's a fundamental tradeoff in rocketry between rocket power and propellant mass flow rate. You can produce a given amount of thrust with high power and a low propellant mass flow rate, or with low power and a high propellant mass flow rate.
E.g., to produce a thrust of 1 N with a mass flow rate of 1 kg/s, you have to eject it at 1 N / 1 kg/s = 1 meter/sec. Ignoring relativity, the kinetic energy in 1 second of exhaust (1 kg) will therefore be
1/2 mv^2 = 1/2 * 1 kg * (1 m/s)^2 = 0.5 joules
and since you need 0.5 joules every second, the required power will be 0.5 watts (assuming 100% efficiency).
If you double the exhaust velocity to 2 m/s, you can drop the mass flow rate to only 1/2 kg/s and still get 1 N of thrust (1/2 kg/s * 2 m/s = 1 N). But you'll now need a power of
0.5 * 0.5 kg/s * (2 m/s)^2 = 1 watt
i.e., twice as much power for that same 1 newton of thrust.
So, which do you have more of, propellant mass or energy? In a chemical rocket the energy is stored in the unburned propellant, so the energy per unit mass is set by the propellant chemistry. That's why every propellant combination has a theoretical specific impulse, e.g. 455 seconds for hydrogen/oxygen in vacuum. Specific impulse is just effective exhaust velocity divided by g = 9.8 m/s^2, so the theoretical exhaust velocity for hydrogen/oxygen is 4,462 m/s.
But in an electric rocket the energy source is external to the propellant mass, so the energy/mass ratio can vary; you decide how fast to eject it. If mass is cheaper than energy, then you want a low exhaust velocity. If energy is cheaper than mass, then you want a high exhaust velocity.
Since the rocket is free to move, the kinetic energy it produces will be split between the payload/rocket itself (which you want) and the exhaust (which is effectively wasted). The only way to get 100% of the energy into the payload/rocket and none into the exhaust is to set the exhaust velocity equal to the current velocity of the rocket so that the exhaust comes out stationary. Of course, velocity is relative so you measure it relative to the reference frame in which the rocket is initially stationary. So to minimize energy consumption you want to increase the exhaust velocity as the rocket accelerates. That's the exact idea behind the VASIMR (Variable Specific Impulse Magnetoplasma Rocket).
The recent "EM drive" hype notwithstanding, I know of only one way to produce thrust in vacuum without some kind of propellant: the photon rocket. Even a flashlight will work, but let's do the numbers. The momentum of a photon is equal to its energy divided by the speed of light, so to get 1 newton of thrust from a 100% efficient photon rocket requires a power input of 1 N * c = 300 megawatts!
That kind of power in space requires either a very large solar array or a very big nuclear reactor (which still needs a very large radiator to reject waste heat).
But there's a simpler way to power a photon rocket with the sun. Instead of turning solar photons into electricity and back into photons, why not use solar photons directly? Voila -- that's what a solar sail does. The thrust produced by a solar sail per unit area is equal to the incident solar power per unit area divided by the speed of light. At 1 AU that's about 1361 W/m^2, so the thrust will be 1361 W/m^2 / c = 4.54 micro newton/m^2. That's actually units of pressure, so solar radiation pressure at 1 AU is 4.54 micropascal on a sail normal to the sun that simply absorbs solar photons. If you reflect them back, you'll get twice as much, 9.08 micropascal. Doesn't seem like much, but you'll get it continuously, no local power source or propellant mass needed.
The one big problem with solar sails is that you can't use them in low orbits because they'll generate far more drag than thrust.
73, Phil
On 2/27/17 10:37, Howie DeFelice wrote:
Thanks Phil, that explanation cleared up many questions. I had been thinking about ways to use the earths magnetic field to raise perigee by storing energy in capacitors and pulsing something along the lines of a magnetorquer with a high current pulse at the right time and vector. The problem, I think, is that I would need to generate the thrust at apogee where the earths magnetic field is weakest.
If you're going to use the earth's magnetic field to change orbit, you want a linear force, not a torque as you'd use for attitude control.
A straight conductor will experience a Lorentz force perpendicular to both the current flow and the ambient magnetic field. Problem is, how do you close the circuit to keep the current flowing? If you run a second conductor through the same magnetic field, it will experience an equal and opposite Lorentz force. If it's physically separated from the first conductor (i.e. forming a loop), the result will be a net torque, not a net linear force.
So you need one of two things. Option #1 is a gradient in the magnetic field. If your "forward" conductor is in a stronger part of the field, it will experience a greater Lorentz force for a given current than the "return" conductor in a weaker part of the field. You'll then get a net linear force, along with plenty of torque.
The other possibility is to use something not attached to your spacecraft as the return conductor so you won't feel the opposing Lorentz force. But what conductor is there in space??
LEO is actually within the ionosphere, and that's your return path. This is in fact how tethers have been used so far to either add or remove energy from a satellite orbit.
Some years ago N6NKF and I looked at how much linear force you could get from a practical magnetorquer coil. (I think it was when Oscar 13 was decaying, so that was 20 years ago!) I don't remember the exact result but I do remember it being negligible.
Here's a wild idea I just had. I wonder if it would be practical to build an ion thruster for use in the ionosphere that uses the ambient ions as your reaction mass? Think of it as vaguely analogous to the Bussard Ramjet in science fiction. You'd collect both protons and electrons and accelerate the protons rearward and the electrons forward to maintain charge balance. The protons, being much more massive, would result in a net forward thrust. You could also see this as analogous to an airplane, only the "propellers" are electric fields that work on an ambient atmosphere that is ionized.
Phil
participants (11)
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Greg D -
Howie DeFelice -
Jeff Griffin -
Joe -
Mark Johns -
Nico Janssen -
Paul Stoetzer -
Phil Karn -
PY5LF -
Scott -
Stephen E. Belter