What in tarnation is a Distant Retrograde Orbit (DRO)?

For those wondering what I'm waving my hands about these days about here's a THREAD about what a DRO is and why it may be something you hear a lot more of soon... (1/n) Image
A DRO is a long term STABLE orbit for a very small mass object around the smaller of two much larger bodies that are in a two-body orbital system. As the Earth has a Moon, one could place a spacecraft in a DRO of the Moon. (2/n) web.archive.org/web/2015011122… Image
The general parameters of a DRO are about +/- 70000km form the Moon along the axis to the Earth and between 70000-110000km on the perpendicular axis. The period is around 13-14 days. This is why it's call 'distant'.
Most lunar orbits can be rather unstable due to MASCONS, require periodic station keeping (fuel). A DRO offers a stable (decades+), low cost place to come and park your spacecraft or asteroid of that matter. (3/n) science.nasa.gov/science-news/s… Image
A DRO of the Moon as seen from above orbits around the Earth-Moon L1 and L2 points and is called retrograde as it orbits in the direction opposite of the Moon's orbital motion around Earth. From Earth it would appear to move around the Moon in a periodic manner over weeks. (4/n) ImageImage
#NASA plans on placing the first SLS EM-1 mission into a DRO. If #Change5 is now presently in a DRO then it would be the first time a man made object has used such an orbit. (5/n) ntrs.nasa.gov/api/citations/… Image
What else could a DRO be used for? If you wanted to bring something from deep space you could park it in a Lunar DRO fairly cheaply. Say you had an asteroid you wanted to mine? (6/n) nasa.gov/content/what-i…
If China has sent #Change5 into deep space Earth-Sun L1 point over 1.5 million km away return to the Earth-Moon system, used the Moon's gravity in two encounters to navigate to a DRO it would be an impressive demonstration of astrogation. Image

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More from @coastal8049

13 Jan
The last observation before #Change5 'disappeared' after Dec 2nd, was 19 degrees from the Moon on the western side. Perhaps just before a burn!? This as you will see is significant to understand CE5's present trajectory and why I'm pretty much convinced it is in a DRO now. (1/n) Image
The geometry of Dec 2nd timing is curious to say the least. If you examine this plot you'll not there are a number of possible DROs. If you measure the elongation angles for the second closest to the Moon you get ~19 degrees. (2/n) Image
I'm not sure if it's required or just easier, but #NASA is using the elongation point to do their insertions to a DRO. It's referred to as a Distant Retrograde Insertion (DRI) of course! Image
Read 8 tweets
9 Jan
#Change5 DRO state vector estimate with rationale.

Amateurs lost signal ~2021-12-03. About 3 integer periods of ~13 days, which is around the optimal DRO period. We appear to be seeing spacecraft at eastern elongation now. So... (1/n)
From what I understand of DRO insertion geometry one likes to enter DRO from one of the elongation points not the EM-L1 or EM-L2 points. This insertion burn occurred ~ 2021-12-03. SOURCE: ntrs.nasa.gov/api/citations/…
Location of #Change5 this evening is within error bars of rough location of a hacked together state vector estimate is. (2/n)
Read 4 tweets
9 Jan
Could #Change5 be in a Distant Retrograde Orbit (DRO) of the Moon pulling off a space first?

CE5 is ~15deg east of the Moon suggesting it is ~100000km distant from the Moon. I made a model DRO in GMAT seeded it with a start from EM-L2 around 2021-12-01 00:00 UTC, Hmmm... (1/n)
Examining papers on the upcoming #NASA SLS EM-1 mission that will use a DRO reveals the geometry somewhat fits the limited observations we have of #Change5 since it was recovered a couple of days ago. (2/n) SOURCE: ntrs.nasa.gov/api/citations/…
Range estimates based on SNR of #Change5 X-band signal appear to be consistent with it being approximately at a lunar distance. If it is in a DRO this would be a first scoping the upcoming #NASA SLS EM-1 mission. (3/n)
Read 4 tweets
9 Oct 21
March 2021 - 18SPCS reported that YUNHAI 1-02 [44547, 2019-063A] had broken up. Since the breakup report, amateurs have monitored radio emissions on 1704MHz. As the spacecraft straddles the terminator it was lost in the glare of daylight until now...
@18SPCS reported that YUNHAI 1-02 broke up and amateurs noticed it continued to emit. The following thread should catch you up on some of these facts.
@planet4589 later noted an anomolly in the @SpaceTrackOrg catalogue with a report indicating 48078, 1996-051Q: "Collided with satellite". See this great thread to learn more about his analysis and the tie to YUNHAI 1-02.
Read 7 tweets
16 Jan 21
Well well well, the mystery of what the signal on ~992.4MHz/~1000.44MHz and FM audio on ~998.94MHz from the Meridian satellites is resolved. It's SECAM TV channels from Turkmenistan. SECAM channel spacing is 8MHz and video carrier to audio carrier is 6.5MHz which matches.
I mused a few weeks about about the curious nature of the 15.625MHz sub-carriers around the primary.
Here you can find some info on the SECAM channel frequencies. Look up France, Eastern Europe, Former Soviet Union, French overseas territories and former French colonies in Africa, North Korea, Vietnam...
Read 7 tweets
15 Dec 20
Steffan Watkins provided a wealth of AIS data from MarineTraffic about the journey of Yuan Wang 3 to the #Change5 re-entry skip point in the Arabian Sea. The data reveals that the ship did some interesting stop and goes prior to arriving on station to look at what? THREAD.
2020-12-10 UTC between 18:30 & 22:30, Mars was at the zenith when they stopped and set just before they got underway again. Perhaps providing support for TIANWEN-1 on the way to Mars?
2020-12-11 UTC between 14:20 & 22:05 more TIANWEN-1 watching at the zenith again it appears. The Mars bound probe has a big signal on X-band which is also used by #Change5.
Read 8 tweets

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