Talk:Molniya orbit

Redirect needed
"Molyniya orbit" needs to redirect to this article. Surely, that is a misspelling of a kind (a misspelling of a transliterated world in the Russian alphabet). However, those of us who are not Russians, and not Slavs, do things like that - such as those whose native language is English and their second language is German, French, Spanish, etc.

Words that start with "moly" are more familiar to us, such as molybdenum, and words that start off "mol" + vowel, such as molecule, molar, mole, and Moline.

Just to throw a little humor onto the subject, a noted cartoonist made a drawing of a street scene in Moscow that stated that the entire Russian language looks like "Kaopectate" with the backwards "K" ! It is too bad that I can't type one of those here. 98.81.25.132 (talk) 02:30, 5 October 2010 (UTC)

Mentioning of Kepler's Laws
I think that at least mentioning Kepler's Laws for ellipical orbits is important for an article like this one, hence I added that information. Kepler's Third Law is the crucial one concerning Molniya orbits, and it is also important that one focus of an elliptical orbit is always located at the center of the primary object in the system. (The Sun for the Solar System; the Earth for the Earth-Moon system, and for artificial satellites; and Jupiter for the jovian system and its many moons.)

It is also important to mention in the text that the perigees of Molniya orbits are always over the Southern Hemisphere, which consists of 80% ocean and just 20% land, and the Molniya satellites do not dilly-dally over such an unpopulated place. There apogees are always designed to be A.) Over central Eurasia once per day, and B.) Over central North America once per day.

Also, the title of this other Wikipedia article is as follows: Van Allen radiation belt, which makes it more self-explanatory than other forms of the title would be. 98.81.25.132 (talk) 02:48, 5 October 2010 (UTC)

Source = Wikipedia
The source given for the initial HEO statement itself references the Wikipedia as the source for this statement, this is circular. —Preceding unsigned comment added by 91.89.172.190 (talk) 02:04, 26 December 2009 (UTC)

Sirius Satellite Radio
This article claims that SSR uses satellites in Molniya orbits, defined as having a 12-hour period. However, SSR's own article states that they use 24-hour orbits, which could be Tundra orbits, but not Molniya. —The preceding unsigned comment was added by Pakaran (talk • contribs) 18:28, 13 February 2007 (UTC).


 * And in fact, the tracking site linked from this article confirms that they have 24 hour (or rather, 1 sidereal day) periods.    -- Pakaran 18:35, 13 February 2007 (UTC)

Van Allen belt
The article states that: "A Molniya orbit is not suitable for manned spacecraft as it repeatedly crosses the high-energy Van Allen belt." However, it would seem that any long range space mission whould have to pass through the radiation, such as the Moon mission, say. Or does the "not suitable" in this sentense mean something like "not advisable" rather then "impossible"? Maxim K 22:11, 24 October 2007 (UTC)


 * Manned missions would generally be flown on a trajectory to avoid the worst of the Van Allen radiation and thus to pass quickly through the thinnest part of the belt (see here, for example).  Since the path of the Molniya orbit is effectively fixed by the orbital element parameters needed to achieve the Molniya configuration then I guess that it would be difficult to configure a Molniya orbit to avoid the Van Allen radiation in this way.   Moreover the fact that an object in a Molniya orbit would repeatedly pass through the Van Allen belts on each orbit would make the radiation issue much more of a problem.   In this case, I think that "not suitable" is probably the correct language.   It's not "impossible" (the manned spacecraft *could* be constructed with large amounts of shielding I suppose) with enough money being spent. MarkPos 12:11, 25 October 2007 (UTC)


 * OK thank you, that's sort of what I suspected but wasn't sure. I like that website. Maxim K 08:18, 26 October 2007 (UTC)

Orbital period and dwell time
The article says "The most typical Molniya-type orbits have a period of 12 hours, making them appear over Russia twice a day, for about eight hours." If the Earth's rotation means the apogee alternates over two points on the surface, as the linked chart suggests, does that mean Russia is visited only once a day? -- Regregex 20:06, 29 October 2007 (UTC)


 * Yes, you are correct of course.  It's obvious really... after 12 hours the satellite has made one orbit and returns to the apogee, but the Earth has only made a half-rotation and thus the apogee is now over a point on the Earth 180 degrees away in longitude.   The dwell over one apogee is around eight hours, therefore three satellites in three orbital planes are required to provide service to one region, e.g. Russia, and as a "by-product" service could also be provided to the other region on the opposite side of the Earth, if required.   If no-one else does it first I'll try and tidy up the article a bit to correct this point. -- MarkPos( User Page 11:28, 30 October 2007 (UTC)

Altitude
Can somebody cite typical apogee and perigee values? Allowing for the retrograde motion shown in the illustrations I presume apogee is a beyond the geosynchoronous orbit- I've seen about 40,000 km suggested but don't know whether this is typical.

Was the Russian satellite that knocked out an Iridium on 12th February 2009 on a Molniya orbit? MarkMLl (talk) 08:50, 13 February 2009 (UTC)

Rewrite?
The text should really be radically re-written

The basic principle is that one uses a highly eccentric orbit with apogee over the norther hemisphere and perigee over the southern hemisphere. As the apogee is as high as (about) 40000 km almost half of the Earth is visible from the high part of the orbit and as the sub-satellite point then is in the polar region this is essentially the northern hemisphere, i.e. for example Russia and Canada.

Certainly the high part of every orbit gives coverage of Russia (and also of Canada!)! The "12 hour period" is to have repetitive optimized communication pattern from day to day very similar to orbit design for XMM and Integral. In fact, the phase of the spacecraft in its 12 hour orbit (relative to the phase of the Earth in its rotation) will have been carefully optimized to make the best possible use of both of the 2 daily passes.

The 63.4 deg inclination is in principle just a technical detail although an interesting one. But the perturbations from Sun/Moon will also be important for the stability of this highly eccentric orbit, it is probably not enough to inhibit the J2 precession by using a 63.4 deg inclination to get a "frozen" argument of perigee!


 * To mention "Sun-synchronous orbit" is absolutely irrelevant here!
 * What is an "inclined equatorial orbit"?????

Some pictures showing the coverage circle for a few points of both the 2 daily passes (with optimized orbital phase!) would also be nice but to carry out a full new "mission analysis" for a Moniya orbit just to write a small WIKI article would certainly be an "over-kill"

Stamcose (talk) 09:24, 4 July 2011 (UTC)

Actually, to understand this, just use Google Earth! If you select latitude 63.4 N and different longitudes, for example 0 deg and 180 deg, and select a high "Eye altitude",say 35000 km, you see all of Russia, Greenland and Canada! Well off apogee, say at altitude 30000 km and latitude 60 deg N, it is the same. The optimization of the orbital is to extend the coverage as far as possible away from apogee!

Stamcose (talk) 10:06, 4 July 2011 (UTC)

If somebody wants to use Google Earth as described above the following table for the hours -3, -2, .. ,3 is useful

Long shift  Latitude      Altitude 1.819904  55.502632     31381.4    0.806301   60.172752     36207.4    0.217108   62.646281     38967.4   -0.000000   63.430000     39867.3   -0.217108   62.646281     38967.4   -0.806301   60.172752     36207.4   -1.819904   55.502632     31381.4

Use:

Assume a certain apogee longitude, for example 10 deg East

For apogee-3 hours add 1.819904 deg to the apogee longitude => 11.8 deg East

Check the visibility of the Earth using Google Earth using 11.8 deg E,  55.5 deg North,  altitude 31381 km.

To check the other apogee, subtract 180 deg to the longitude. In this example this other apogee longitude is 170 deg West.

Note how slowly the sub-satellite longitude changes! The steerable antenna will move very slowly!

Stamcose (talk) 09:04, 5 July 2011 (UTC)


 * I can't say much about the technical argument being made here, but the article obviously requires many inline citations in order to make it possible to easily verify the sources claimed. N2e (talk) 12:08, 24 November 2011 (UTC)

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External links modified (February 2018)
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Suggestion
This is a nice little article! I'd love to also see a section explaining who conceived and how the concept of the Molniya Orbit was developed, a bit of historical context. For instance, I suspect the Soviets used Molniya orbits because Geostationary just wasn't available to them (and, as is pointed out in the header, such orbits aren't as useful to a high latitude country like the Soviet Union). --Neopeius (talk) 21:18, 6 January 2019 (UTC)
 * Cheers, added a sentence *or two to history - but couldn't find anything more detailed. I suspect there might be somthing in Russian langugue sources... Spacepine (talk) 11:26, 6 March 2019 (UTC)

Additional information?
Would it be worth mentioning in the Orbital inclination section that $$\csc i + \cot i = \phi$$, the golden ratio? Thus:

$$i = 2 \arccot \phi \approx 63.4\deg$$, which is a direct result of the triangle formed by $$4-5\sin^2 i=0$$. LegendoftheGoldenAges85, Team M (talk &#124; worse talk) 00:27, 23 June 2021 (UTC)