A few weeks ago somebody posted pseudo-keps to the -bb and from the looks of the queries and comments, many have installed them on their tracking programs. Which brings to question. Are there any pseudo-keps for the planets?
73,
Jeff WB3JFS
Are there any pseudo-keps for the planets?
Actually, the word planet comes from the meaning "wanderers" because that is what stumped the early astronomers thousands of years ago. They do not have regular motion about Earth... And Copernicus finally figured it out... They rotate around the sun.
Bob
Hi Bob,
You are correct on the term planets being "wonderers". If I recall correctly, that came from the Greek skywatchers.
Yes, many thought the Earth was the center of the solar system. I'm sure more believed it was the center of the universe as well! In any case, with the Sun as the center of the solar system, that was some wild "outside of the box" thinking since the church frowned upon any type of "new findings" that disputed what the church layed down. Can you imagine being ostracized, if nothing more serious, in stating and believing that the Sun, not the Earth, was the center of the solar system? WOW! You'd be excommunicated and strung up.
Since the planets revolve around the Sun ,and not the Earth, there can't be any Keps. Keps are based on the Earth being the center of an orbiting object. I should've recalled that. However, my thinking at the time was if there are programs which display where to find planets in the sky, like Starry Night, then there'd have to be a form of calculation to determine it. I just thought of using the wrong type of calculation.
73,
Jeff WB3JFS
----- Original Message ----- From: "Robert Bruninga" [email protected] To: "'Jeff Yanko'" [email protected]; [email protected] Sent: Friday, February 26, 2010 5:31 AM Subject: RE: [amsat-bb] Planet Pseudo-Keps
Are there any pseudo-keps for the planets?
Actually, the word planet comes from the meaning "wanderers" because that is what stumped the early astronomers thousands of years ago. They do not have regular motion about Earth... And Copernicus finally figured it out... They rotate around the sun.
Bob
You saying that if I lived on another planet or in another star system then my satellites wouldn't have keps and I couldn't use my software to track them?
That sounds rediculous.
On 27-Feb-10 09:43, Jeff Yanko wrote:
Since the planets revolve around the Sun ,and not the Earth, there can't be any Keps. Keps are based on the Earth being the center of an orbiting object.
Since the planets revolve around the Sun, and not the Earth, there can't be any Keps. Keps are based on the Earth being the center of an orbiting object.
You're saying that if I lived on another planet or in another star system then my satellites wouldn't have keps and I couldn't use my software to track them?... That sounds rediculous.
Yep. "keps" (as we use the term here regularly) either in AMSAT format or in NASA two-line format are just inputs to an "Earth orbit" propogator that predicts where a satellite is around Earth based on the laws of physics.
If you lived on Mars, and had a "Mars Orbit Propogator" then you could download "Martian Keps" from the Martians and track Martian satellites. But the Martian tracking program would not be able to track earth satellies, just as ours Earth based programs cannot track theirs. Because the size and mass of Mars is different from Earth, so the propogators have to be different... or something like that. I'm on the limit of my meager knowledge here...
Bob, Wb4APR
I would have to guess that this is entirely possible otherwise Mars and Moon missions would be shots-in-the-dark. The software to do this is most likely completely different from that which predicts simple satellites around one planet. Tracking other planets relative to ours would be more like predicting angles and velocities from one LEO to another LEO. The software would need to contain the "keps" of the solar system, and then give results from the perspective of one of the satellites. This software probably already exists, but in the proprietary domain.
On second thought, the software that runs the fully-automated personal telescopes already does most of this, except for the relative velocity part.
73's Auke
----- Original Message ----- From: "Jeff Yanko" [email protected] To: [email protected] Sent: Friday, February 26, 2010 2:09 AM Subject: [amsat-bb] Planet Pseudo-Keps Which brings to question. Are there any pseudo-keps for the
planets?
73,
Jeff WB3JFS
Keplerian Elements have nothing to do with the Earth. To say it only applies to earth orbiting objects would be like saying Newton's laws of motion only apply to the earth.
They are mathematical descriptions of the motion of one body orbiting another in an unperturbed orbit using the 6 degrees of freedom of the orbiting body - i.e the 6 key elements of the keps.
They predate computers and software; circa 1605.
This not to say that they are universally applicable. Larger or smaller as in galactic or subatomic with perturbed orbits - all bets are off.
Your statement is correct, however there is an issue of context. Most satellite tracking software uses Simplified General Perturbations No. 4 (SGP4) as an orbit propagator. SGP4 is one of several orbit propagation algorithms that presume the Earth to be the central attracting body (as both origin and major attracting mass). As such, the associated Keplerian elements are in the context of an Earth-orbiting satellite as are the corresponding output positions and velocities. This is a convenient simplifying assumption for Earth-orbiting satellites and also since Earth station coordinates use the center of the Earth as the origin.
Certainly, there are orbit propagation (and ephemeris interpolation) methods that have a different (or a flexible choice of) attracting body (and therefore a different origin and central mass). In using such an algorithm, the software must also (1) know the mass of the central attracting body, (2) compute the Earth's position relative to the origin (the attracting body) and (3) also determine its orientation relative to (for example) the Sun's coordinate system. This requires an additional translation (i.e., vector subtraction) and a re-orientation (i.e., coordinate transformation). These are fairly simple to code into a library and thus simple to use. However, the software needs to have that additional logic already embedded.
I do not know of a method in which the Keplerian elements of a planet orbiting the Sun could be used to produce any sort of meaningful answer in software that propagates orbit using an Earth-centered propagator. Indeed, there's nothing wrong with the physics, but one must pay attention to the simplifying assumptions underlying the implemented algorithms.
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of ve4yz Sent: Saturday, February 27, 2010 11:41 AM To: [email protected] Subject: [amsat-bb] Re: Planet Pseudo-Keps
Keplerian Elements have nothing to do with the Earth. To say it only applies to earth orbiting objects would be like saying Newton's laws of motion only apply to the earth.
They are mathematical descriptions of the motion of one body orbiting another in an unperturbed orbit using the 6 degrees of freedom of the orbiting body - i.e the 6 key elements of the keps.
They predate computers and software; circa 1605.
This not to say that they are universally applicable. Larger or smaller as in galactic or subatomic with perturbed orbits - all bets are off.
_______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Auke de Jong, VE6PWN wrote:
On second thought, the software that runs the fully-automated personal telescopes already does most of this, except for the relative velocity part.
The US government will do that for us via the JPL HORIZONS tracking system http://ssd.jpl.nasa.gov/?horizons The data below show that as this being written I should point my antennas to the south, a little less than half way up from horizon to my zenith. Jupiter is moving away from me at about six and a half kilometers per second, and a "dit" leaving my keyer will take the better part of an hour to reach it's target.
No charge to use this, US hams pay for this with our taxes. That being said you Canadians are welcome to send me cash gifts, and I will be glad to pay the appropriate US income tax on it!
-Joe KM1P
******************************************************************************* Revised: Dec 17, 2009 Jupiter 599
PHYSICAL DATA (updated 2009-Jan-28): Mass (10^24 kg) = 1898.13+-.19 Density (g/cm^3) = 1.326 Equat. radius (1 bar) = 71492+-4 km Polar radius (km) = 66854+-10 Volumetric mean radius= 69911+-6 km Flattening = 0.06487
Rotation period = 9h 55m 29.685s Rot. rate(10^-4 rad/s) = 1.75865 m = w^2a^3/GM = 0.089195 Hydrostatic flat., fh = 0.06509 Inferred rot. period = 9.894+-0.02 hr ks = 3*J2/m = 0.494 Mom. of inert. I/MRo^2= 0.254 I/MRo^2 (upper bound) = 0.267 Rocky core mass (Mc/M)= 0.0261 Y factor (He/H ratio) = 0.18+-0.04
GM (km^3/s^2) = 126,686,511 GM 1-sigma (km^3/s^2) = +-100 Equ. grav, ge (m/s^2) = 24.79 Pol. grav, gp (m/s^2) = 28.34
Geometric albedo = 0.52 Visual magnitude V(1,0)= -9.40 Vis. mag. (opposition)= -2.70 Obliquity to orbit = 3.12 deg Sidereal orbit period = 11.862615 yr Sidereal orbit period = 4332.820 d Mean daily motion = 0.0831294 deg/d Mean orbit velocity = 13.0697 km/s
Atmos. temp. (1 bar) = 165+-5 K Heat flow/mass (x10^7) = 15 erg/gm*s Planetary Solar Const = 50.5 W/m^2 Dipole tilt/offset = 9.6deg/0.1Rp Escape velocity (km/s)= 59.5 Mag.dip.mom(gauss-Rp^3)= 4.2 Aroche(ice)/Rp = 2.76 Hill's sphere rad. Rp = 740 *******************************************************************************
******************************************************************************* Ephemeris / WWW_USER Sat Feb 27 10:15:04 2010 Pasadena, USA / Horizons ******************************************************************************* Target body name: Jupiter (599) {source: JUP230} Center body name: Earth (399) {source: DE405} Center-site name: (user defined site below) ******************************************************************************* Start time : A.D. 2010-Feb-10 17:00:00.0000 UT Stop time : A.D. 2010-Feb-10 20:00:00.0000 UT Step-size : 5 minutes ******************************************************************************* Target pole/equ : IAU_JUPITER {East-longitude -} Target radii : 71492.0 x 71492.0 x 66854.0 km {Equator, meridian, pole} Center geodetic : 288.845300,42.2925472,49.999402 {E-lon(deg),Lat(deg),Alt(km)} Center cylindric: 288.845300,4762.18349,4303.3386 {E-lon(deg),Dxy(km),Dz(km)} Center pole/equ : High-precision EOP model {East-longitude +} Center radii : 6378.1 x 6378.1 x 6356.8 km {Equator, meridian, pole} Target primary : Sun {source: DE405+DE408} Interfering body: MOON (Req= 1737.400) km {source: DE405} Deflecting body : Sun, EARTH {source: DE405} Deflecting GMs : 1.3271E+11, 3.9860E+05 km^3/s^2 Atmos refraction: NO (AIRLESS) RA format : HMS Time format : CAL RTS-only print : NO EOP file : eop.100226.p100520 EOP coverage : DATA-BASED 1962-JAN-20 TO 2010-FEB-26. PREDICTS-> 2010-MAY-19 Units conversion: 1 AU= 149597870.691 km, c= 299792.458 km/s, 1 day= 86400.0 s Table cut-offs 1: Elevation (-90.0deg=NO ),Airmass (>38.000=NO), Daylight (NO ) Table cut-offs 2: Solar Elongation ( 0.0,180.0=NO ) ***************************************************************************************************************** Date__(UT)__HR:MN Azi_(a-appr)_Elev dAZ*cosE d(ELV)/dt APmag S-brt delta deldot 1-way_LT ***************************************************************************************************************** $$SOE 2010-Feb-10 17:00 *m 163.9922 35.9868 867.85 184.19 -2.02 5.31 8.8974883901E+08 6.3227121 49.464711 2010-Feb-10 17:05 *m 165.4872 36.2310 871.25 167.40 -2.02 5.31 8.8975073674E+08 6.3287606 49.464817 2010-Feb-10 17:10 *m 166.9922 36.4517 874.35 150.38 -2.02 5.31 8.8975263628E+08 6.3348429 49.464922 2010-Feb-10 17:15 *m 168.5063 36.6486 877.14 133.15 -2.02 5.31 8.8975453766E+08 6.3409553 49.465028 2010-Feb-10 17:20 *m 170.0287 36.8215 879.61 115.74 -2.02 5.31 8.8975644087E+08 6.3470944 49.465134 2010-Feb-10 17:25 *m 171.5582 36.9700 881.74 98.16 -2.02 5.30 8.8975834593E+08 6.3532567 49.465240 2010-Feb-10 17:30 *m 173.0940 37.0941 883.54 80.44 -2.02 5.30 8.8976025284E+08 6.3594385 49.465346 2010-Feb-10 17:35 *m 174.6348 37.1934 884.98 62.60 -2.02 5.30 8.8976216161E+08 6.3656364 49.465452 2010-Feb-10 17:40 *m 176.1796 37.2679 886.07 44.67 -2.02 5.29 8.8976407224E+08 6.3718469 49.465558 2010-Feb-10 17:45 *m 177.7272 37.3175 886.79 26.68 -2.02 5.29 8.8976598473E+08 6.3780662 49.465664 2010-Feb-10 17:50 *m 179.2766 37.3420 887.15 8.64 -2.02 5.29 8.8976789909E+08 6.3842910 49.465771 2010-Feb-10 17:55 *t 180.8265 37.3415 887.15 -9.40 -2.02 5.28 8.8976981532E+08 6.3905176 49.465877 2010-Feb-10 18:00 *m 182.3758 37.3159 886.77 -27.44 -2.02 5.28 8.8977173341E+08 6.3967424 49.465984 2010-Feb-10 18:05 *m 183.9233 37.2653 886.03 -45.43 -2.02 5.27 8.8977365338E+08 6.4029620 49.466091 2010-Feb-10 18:10 *m 185.4680 37.1897 884.93 -63.36 -2.02 5.27 8.8977557520E+08 6.4091726 49.466197 2010-Feb-10 18:15 *m 187.0086 37.0893 883.48 -81.19 -2.02 5.27 8.8977749889E+08 6.4153709 49.466304 2010-Feb-10 18:20 *m 188.5441 36.9643 881.67 -98.90 -2.02 5.26 8.8977942444E+08 6.4215531 49.466411 2010-Feb-10 18:25 *m 190.0734 36.8147 879.52 -116.48 -2.02 5.26 8.8978135184E+08 6.4277158 49.466519 2010-Feb-10 18:30 *m 191.5955 36.6408 877.04 -133.88 -2.02 5.26 8.8978328108E+08 6.4338554 49.466626 2010-Feb-10 18:35 *m 193.1093 36.4429 874.24 -151.10 -2.02 5.25 8.8978521216E+08 6.4399685 49.466733 2010-Feb-10 18:40 *m 194.6139 36.2212 871.13 -168.11 -2.02 5.25 8.8978714507E+08 6.4460514 49.466841 2010-Feb-10 18:45 *m 196.1085 35.9760 867.72 -184.89 -2.02 5.25 8.8978907980E+08 6.4521008 49.466948 2010-Feb-10 18:50 *m 197.5921 35.7077 864.04 -201.43 -2.02 5.25 8.8979101634E+08 6.4581130 49.467056 2010-Feb-10 18:55 *m 199.0640 35.4166 860.08 -217.70 -2.02 5.25 8.8979295468E+08 6.4640847 49.467164 2010-Feb-10 19:00 *m 200.5234 35.1031 855.88 -233.69 -2.02 5.24 8.8979489480E+08 6.4700124 49.467271 2010-Feb-10 19:05 * 201.9698 34.7676 851.44 -249.38 -2.02 5.24 8.8979683669E+08 6.4758927 49.467379 2010-Feb-10 19:10 * 203.4023 34.4105 846.78 -264.78 -2.02 5.24 8.8979878034E+08 6.4817222 49.467488 2010-Feb-10 19:15 * 204.8206 34.0323 841.92 -279.85 -2.02 5.24 8.8980072573E+08 6.4874975 49.467596 2010-Feb-10 19:20 * 206.2242 33.6333 836.87 -294.60 -2.02 5.24 8.8980267285E+08 6.4932152 49.467704 2010-Feb-10 19:25 * 207.6125 33.2141 831.66 -309.02 -2.02 5.25 8.8980462167E+08 6.4988721 49.467812 2010-Feb-10 19:30 * 208.9853 32.7751 826.29 -323.09 -2.02 5.25 8.8980657218E+08 6.5044648 49.467921 2010-Feb-10 19:35 * 210.3423 32.3168 820.79 -336.82 -2.02 5.25 8.8980852435E+08 6.5099901 49.468029 2010-Feb-10 19:40 * 211.6831 31.8396 815.17 -350.20 -2.02 5.25 8.8981047818E+08 6.5154447 49.468138 2010-Feb-10 19:45 * 213.0077 31.3441 809.45 -363.23 -2.02 5.25 8.8981243363E+08 6.5208255 49.468247 2010-Feb-10 19:50 * 214.3158 30.8308 803.64 -375.91 -2.02 5.26 8.8981439068E+08 6.5261292 49.468355 2010-Feb-10 19:55 * 215.6074 30.3001 797.76 -388.24 -2.02 5.26 8.8981634931E+08 6.5313528 49.468464 2010-Feb-10 20:00 * 216.8824 29.7525 791.82 -400.21 -2.02 5.26 8.8981830950E+08 6.5364932 49.468573 $$EOE ***************************************************************************************************************** Column meaning:
TIME
Prior to 1962, times are UT1. Dates thereafter are UTC. Any 'b' symbol in the 1st-column denotes a B.C. date. First-column blank (" ") denotes an A.D. date. Calendar dates prior to 1582-Oct-15 are in the Julian calendar system. Later calendar dates are in the Gregorian system.
The uniform Coordinate Time scale is used internally. Conversion between CT and the selected non-uniform UT output scale has not been determined for UTC times after the next July or January 1st. The last known leap-second is used over any future interval.
NOTE: "n.a." in output means quantity "not available" at the print-time.
SOLAR PRESENCE (OBSERVING SITE) Time tag is followed by a blank, then a solar-presence symbol:
'*' Daylight (refracted solar upper-limb on or above apparent horizon) 'C' Civil twilight/dawn 'N' Nautical twilight/dawn 'A' Astronomical twilight/dawn ' ' Night OR geocentric ephemeris
LUNAR PRESENCE WITH TARGET RISE/TRANSIT/SET MARKER (OBSERVING SITE) The solar-presence symbol is immediately followed by another marker symbol:
'm' Refracted upper-limb of Moon on or above apparent horizon ' ' Refracted upper-limb of Moon below apparent horizon OR geocentric 'r' Rise (target body on or above cut-off RTS elevation) 't' Transit (target body at or past local maximum RTS elevation) 's' Set (target body on or below cut-off RTS elevation)
RTS MARKERS (TVH) Rise and set are with respect to the reference ellipsoid true visual horizon defined by the elevation cut-off angle. Horizon dip and yellow-light refraction (Earth only) are considered. Accuracy is < or = to twice the requested search step-size.
Azi_(a-appr)_Elev = Airless apparent azimuth and elevation of target center. Corrected for light-time, the gravitational deflection of light, stellar aberration, precession and nutation. Azimuth measured North(0) -> East(90) -> South(180) -> West(270) -> North (360). Elevation is with respect to plane perpendicular to local zenith direction. TOPOCENTRIC ONLY. Units: DEGREES
dAZ*cosE d(ELV)/dt = The rate of change of target center apparent azimuth and elevation (airless). d(AZ)/dt is multiplied by the cosine of the elevation angle. TOPOCENTRIC ONLY. Units: ARCSECOND/MINUTE
APmag S-brt = Target's approximate apparent visual magnitude & surface brightness. For planets and satellites, values are available only for solar phase angles in the range generally visible from Earth. This is to avoid extrapolation of models beyond their valid (data-based) limits. Units: NONE & VISUAL MAGNITUDES PER SQUARE ARCSECOND
delta deldot = Range ("delta") and range-rate ("delta-dot") of the target center relative to the observer at the instant light seen by the observer at print-time would have left the target center (print-time minus down-leg light-time); the distance traveled by a light ray emanating from the center of the target and recorded by the observer at print-time. "deldot" is a projection of the velocity vector along this ray, the light-time-corrected line-of-sight from the coordinate center, and indicates relative motion. A positive "deldot" means the target center is moving away from the observer (coordinate center). A negative "deldot" means the target center is moving toward the observer. Units: KM and KM/S
1-way_LT = 1-way down-leg light-time from target center to observer. The elapsed time since light (observed at print-time) would have left or reflected off a point at the center of the target. Units: MINUTES
Computations by ... Solar System Dynamics Group, Horizons On-Line Ephemeris System 4800 Oak Grove Drive, Jet Propulsion Laboratory Pasadena, CA 91109 USA Information: http://ssd.jpl.nasa.gov/ Connect : telnet://ssd.jpl.nasa.gov:6775 (via browser) telnet ssd.jpl.nasa.gov 6775 (via command-line)
*****************************************************************************************************************
participants (8)
-
Auke de Jong, VE6PWN -
Bob Bruninga -
Jeff Yanko -
Joe Fitzgerald -
Ken Ernandes -
Nigel Gunn G8IFF/W8IFF -
Robert Bruninga
-
ve4yz