Feb 27, 2010 08:43:51 AM, bruninga(a)usna.edu 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.
>> 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 (and Nigel) -
That's pretty accurate. Although the laws of physics apply universally around all the planets, the specific implementations of orbit mechanics software are location dependent. You gave one example--size and mass of the Earth vs Mars. Other examples are the oblateness of the planet (how flattened at the poles is Mars vs Earth) and the effects of other objects such as the moon and other planets. (The effects of the earth's moon on an earth-orbiting satellite will be different from the effects of Deimos and Phobos on a Mars-orbiting satellite.)
Although the equations are all the same, most programs (that are publicly distributed) "assumes" the earth as the core body, and embeds those assumptions into the software. I think STK (Satellite Tool Kit) by Analytical Graphics may have the ability to analyze non-Earth geometries, but it's hardly within the realm of amateurs. (A full-up version costs something like US$50,000.)
Is there a "easy" way of figuring out where/when a given apogee will at a given lat.long? I want to try to predetermine when the apogee will be on AO-7 to favor the northern hemisphere. To "maybe" help in dx contacts. The difference is only bout 17km in altitude, it just might streeeetch the footprint enough. Also just how much does the 17km add to the footprint?
73 Bob W7LRD
I came across this info, might be of some value.
Ref: The Satellite Experimenters Handbook, Pg 9-6
Max Dist (range) = 2R * arcos [R/(R+h)]
Where R = 6,371 km and
h = 1,459 km at Apogee (AO-7)
h = 1,440 km at Perigee (AO-7)
Therefore the maximum possible communication distance via AO-7 at Apogee =
Therefore the maximum possible communication distance via AO-7 at Perigee =
The difference in range from apogee to perigee appears to be only 33 km.
73, Pierre ZS6BB
I'll be on from the EL17 / EL18 line tomorrow (Friday) on two SO50 passes (local AOS at 26/1840Z and 26/2022Z) as well as AO27 which switches to VOX at 26/1957Z.
We're taking Saturday off, but I'll operate from the EL28 / EL29 line on Sunday on the four AO27 and SO50 passes between 28/1800-2050Z.
Jim, ND9M / VQ9JC
Corpus Christi, TX / EL17
Hello 910 owners
I am trying to get my AG-25 preamp running. In the set mode- I set the pre 144 to on. Should I then be able to measure 12v at the 2M antenna output to run the preamp? I get nothing.
73 Bob W7LRD
We have been trying many weeks to have a simple QSO, with several near misses. At 2120Z via AO-7 I got a, "you are 5/1 here". At 7504 km not a record, but a real fun effort. Next is Eric-PA1TNO, I may have to go portable on a nearby mountain.
73 Bob W7LRD
At 05:07 PM 2/25/2010 +0000, Bob- W7LRD <w7lrd(a)comcast.net> wrote:
>Hello Is there a "easy" way of figuring out where/when a given apogee will
>at a given lat.long?Â I want to try to predetermine when the apogee will
>be on AO-7 to favor the northern hemisphere.Â To "maybe" help in dx
>contacts.Â The difference is only bout 17km in altitude, it just might
>streeeetch the footprint enough.Â Also just how much does the 17km add to
>the footprint?Â 73 Bob W7LRD
OK, Now to answer your question Bob.
If you want that extra 15km of altitude you get with AO-7 at apogee, the
next time AO-7 will be having apogees at the most northern latitudes it
reaches will be on orbits around June 17th to the 18th. Apogee will occur
around 78 degrees N Lat.
To night at abt 9.17 gmt on AO7 , mode B Bob W7LRD and myself confirmed working each other ,exchanged reports etc and was very workable below 0.3 deg ! althrough not a record cn87 to io92bx works out to be 7504.52 km distance but may well be a United Kingdom A07 record?? thanks Bob and thanks for all you guys on A07 ! -Paul 2E1EUB