Flight Question Positioning of GeoSync/Molniya orbits around objects other than Earth

[Hlynkacg]

I've been messing on Mars and trying to place a satellite in a stable GeoSync (MarsSynch?) or Molniya-type orbit directly over Olympus but thus far have been unsuccessful.

I've tried placing a "Target vessel" using the SCN Editor but have not been able to translate orbital parameters into a reliable ground track. Is there anyone else here who's tried this or can give me some some hints?

 

[Jarvitä]

I've been messing on Mars and trying to place a satellite in a stable GeoSync (MarsSynch?) or Molniya-type orbit directly over Olympus but thus far have been unsuccessful.

(my apologies for being slightly offtopic)

Can't help you there, but I just wanted to point out that technically, the correct term is "Areosynchronous". But than again, it's unlikely to see use, as the JPL people also tend to use "Martian geology" instead of "Areology", the generic terms for orbital apses, etc.

 

[krashkart]

http://en.wikipedia.org/wiki/Geostationary_orbit#Derivation_of_geostationary_altitude

This paragraph appears after the equations for a geostationary orbit:

Now, by the same formula, let us find the geostationary orbit of an object in relation to Mars (an areostationary orbit). The geocentric gravitational constant GM (which is μ) for Mars has the value of 42,828 km3s-2, and the known rotational period (T) of Mars is 88,642.66 seconds. Since ω = 2π/T, using the formula above, the value of ω is found to be approx 7.088218×10-5 s-1. Thus, r3 = 8.5243×1012 km3, whose cube root of is 20,427 km; subtracting the equatorial radius of Mars (3396.2 km) we have 17,031 km.

:tiphat:

 

[Wishbone]

I'll look into that, thanks for the reminder. The idea behind Molniya is not only to have a high dwell time in the apoapsis, but also to keep AgP from moving around due to oblateness. That's why the first Molniya launches were less than successful - the chosen inclination did not zero out perigee rotation.

 

[krashkart]

I wouldn't know right offhand how to set up a tundra- or Molniya-type orbit around Mars, as I have never done that. However, if I understand correctly such an orbit around Earth 'hovers' over the high latitudes for about twelve hours and then swings quickly through periapsis. So, if you wanted to set up a similar orbit around Mars then your travel through the highest portion of orbit should be about half a day there. What should the final inclination be, though? :hmm:

I may just have to try this. The question is, should I base my orbital timing on a Mars sidereal day, or a Mars solar day? :hmm:

Disclaimer: I make no claims nor assumptions whatsoever to being an expert. Someone will be along shortly to correct me where I am wrong.

 

[Wishbone]

Must admit that I am as clueless as advertised. The (prograde) critical inclination should be the same as around Earth, regardless of the exact value of J2. 63.435 degrees. More results to follow.

SMa: 20427.68 km
Ecc: 0.8

Inclination (equatorial) 63.435
LPe 255 (vary to get close to Olympus in apoapsis)

Map MFD certainly is of little help since at high enough altitudes the track disappears (I'm posting this as a bug!)

 

[Hlynkacg]

Thanks for the info.

Map MFD certainly is of little help since at high enough altitudes the track disappears (I'm posting this as a bug!)

And yes this ^ was giving me trouble as well.

 

[Wishbone]

Am re-posting the test scenario here, since not everybody frequents the bug forum. The inclination is finetuned to have almost zero perigee rotation rate, periapsis is at 400 km above the areoid.

BEGIN_DESC
Delta Glider is near apoapsis, Shuttle PB is whooshing by Mars.
END_DESC

BEGIN_ENVIRONMENT
  System Sol
  Date MJD 51982.5388331969
END_ENVIRONMENT

BEGIN_FOCUS
  Ship GL-01
END_FOCUS

BEGIN_CAMERA
  TARGET GL-01
  MODE Extern
  POS 4.00 -151.30 -30.80
  TRACKMODE TargetRelative
  FOV 50.00
END_CAMERA

BEGIN_HUD
  TYPE Surface
END_HUD

BEGIN_MFD Left
  TYPE Orbit
  PROJ Ship
  FRAME Ecliptic
  ALT
  REF Mars
  TARGET PB-01
END_MFD

BEGIN_MFD Right
  TYPE Map
  REF Mars
  OTARGET PB-01
  POS 0.00 0.00
END_MFD

BEGIN_SHIPS
GL-01:DeltaGlider
  STATUS Orbiting Mars
  RPOS -14383890.30 -18420649.13 28768323.48
  RVEL -337.210 -159.256 -274.435
  AROT -52.54 -57.19 90.78
  AFCMODE 7
  PRPLEVEL 0:0.553000 1:0.900000
  NAVFREQ 0 0 0 0
  XPDR 0
  AAP 0:0 0:0 0:0
END
PB-01:ShuttlePB
  STATUS Orbiting Mars
  RPOS -6760434.36 -3816659.06 -3329050.86
  RVEL 2011.109 1714.944 -1028.643
  AROT 39.41 -16.44 12.57
  AFCMODE 7
  PRPLEVEL 0:1.000000
  NAVFREQ 0 0
END
END_SHIPS