Talk:Queqiao-2

Easy to understand.

Should have picture to scale. Signal from antenna of the satellite can reach Earth. 1.47.134.193 (talk) 13:03, 3 June 2024 (UTC)

Substantial errors apparently in stated orbital parameters

Scott Tilley, a well respected observer of space objects claims that the orbit is nothing like the 62.4 degree 200 x 16000 km orbit claimed. He claims it's in an 119.25 degree 1992 x 18679 km orbit (re-rounded the values myself). Looks like China was claiming incorrect parameters. https://x.com/coastal8049/status/1837741079828816114 Ergzay (talk) 10:58, 23 September 2024 (UTC)

An amateur observer posting orbital parameters is not a primary source, which is what data in Wikipedia should be based on. Moreover, in this case Scott Tilley has made the mistake of not taking into account that it is practically impossible to distinguish a certain lunar orbit from its mirror image on the orbital plane of the Moon around the Earth using Doppler observations alone. The inclinations of an orbit and its mirror image add up to 180º, which suggests that the value of 119.25º obtained by Scott is the consequence of this mistake, because 62.4º+119.25º is close to 180º. I am reverting this edit. Daniestevez (talk) 21:47, 23 September 2024 (UTC)

@Daniestevez A doppler invert would not have drastically different orbital parameters. China has lied many times in the past about it's space vehicles. Please restore these edits. Ergzay (talk) 22:26, 23 September 2024 (UTC)

For the sake of correctness, I should say that this sentence that I said is wrong: "The inclinations of an orbit and its mirror image add up to 180º, which suggests that the value of 119.25º obtained by Scott is the consequence of this mistake, because 62.4º+119.25º is close to 180º." I made a mistake when calculating how this mirroring affects the Keplerian parameters. The correct effect is that the RAAN and argument of periapsis change by 180 degrees, but the inclination is maintained. There are still two orbits that give nearly the same Doppler, but in an orbit like the one for Queqiao-2, one has the apoapsis over the lunar north pole and the other over the lunar south pole, since this mirroring inverts north and south. The orbit with the apoapsis over the north pole can likely be discarded, because the Queqiao-2 mission goals are to provide communications over the south pole.

Reviewing Scott's results again I now have the feeling that they are correct. Additionally, it appears that there is other circumstantial evidence within the spacecraft tracking community for the spacecraft having been injected in a retrograde orbit rather than a prograde orbit. From the point of view of orbital dynamics, both the inclinations 62º and 118º give the same frozen orbit behaviour, so it is possible that mission planning decided to change to a 118º orbit after the sources that cite at 62º orbit were published. I would attribute to that the change from 62º to 118º inclination, rather than the political sentence "China has lied many times in the past about it's space vehicles." that you have mentioned.

Regardless of whether Scott's findings are correct or not, this does not change the fact that Wikipedia should not be based on information in tweets. Tweets haven't been peer-reviewed, etc. Specifically, the kind of discussion that we're now having in this talk page about whether some technical information is correct or not should not happen in Wikipedia. Wikipedia should be based on sources for which this discussion has already taken place (via peer review or other means). I'm basically saying what Wikipedia:Reliable Sources says. Daniestevez (talk) 07:59, 24 September 2024 (UTC)

Reliable sources says to not use information from Twitter as a source if there is sufficient reason to doubt the information. It is a low quality source, but it IS a source. Once higher quality sources are available the twitter source can be replaced. Given that you agree now with the accuracy with Scott's analysis I will restore the edits. Ergzay (talk) 02:18, 26 September 2024 (UTC)

I disagree with your changes, but I will not waste any more time reverting them. My position is that those Tweets are not appropriate sources for Wikipedia, even if they are factually correct. If other editors come across this discussion, they might want to chime in.

Additionally, you have failed to understand the difference between reporting apoapsis and periapsis as altitudes versus reporting them as radii. The information that you have written in the article, "Periselene altitude 1,991.69 km, Aposelene altitude 18,678.5 km", is largely incorrect. You have copied numbers from a tweet into the article without even understanding them.

My position for this article is that the periapsis and apoapsis altitudes were given as 200 km and 16000 km respectively in official press releases in several news sources (these were cited before in the Wikipedia article; example: https://spacenews.com/chinas-queqiao-2-relay-satellite-enters-lunar-orbit/). With the understanding that these values are rounded off (it is understood that the zeros will not be zeros in the exact value), the periapsis and apoapsis that Scott found are compatible with these values. The citation of these news articles is highly preferable to Scott's tweet as a source for Wikipedia, and the approximate values are good enough for Wikipedia (Wikipedia doesn't need to list the most accurate orbital information, and in fact it omits other Keplerian parameters). Likewise these news sources cited an orbital period of 24 hours, which can be understood as an approximation and is within a 10% error of the value of 26.2 hours given by Scott. So the value of 24 hours and the news articles citation are still preferable. Finally, the inclination of the orbit should have never been listed in Wikipedia. The previous citation for a 62º inclination is a Chinese article that appears to discuss several types of orbits for lunar exploration (including low orbits, high elliptical orbits and others), and mentions the required inclination of a high elliptical orbit that achieves frozen eccentricity. This inclination depends on the eccentricity, and a table with several example values is given. The article does not seem to mention Queqiao-2 specifically, so it is not an appropriate source either. I would simply refrain to mention the inclination of the orbit in Queqiao-2's Wikipedia page, since an appropriate source is not available. Daniestevez (talk) 06:07, 26 September 2024 (UTC)