Talk:Near-rectilinear halo orbit

okay but what is it? - What does "near-rectilinear" mean

It would help to say what "near-rectilinear" means. —Tamfang (talk) 19:26, 11 July 2020 (UTC)

Agree completely, Tamfang. There was a tag in the article from June 2020 asking that "near-rectilinear" be explained, but User:Soumya-8974 removed the tag in October 2020, without the answer to the question ever being provided.

I will re-add the tag asking that this be clarified. N2e (talk) 17:57, 11 February 2021 (UTC)

Tag has been removed and still no real useful explanation what the term means. CFLeon (talk) 04:41, 23 September 2021 (UTC)

Intro says "has slightly curved, so near straight sides, " - Seems clear enough ? - Rod57 (talk) 14:12, 19 February 2022 (UTC)

I came here hoping to find a definition but went away confused. I did orbital mechanics 55 years back when orbits were well behaved ellipses. A few minutes OR came up with NR means that some segments of the orbit have a greater curvature than those of an elliptical orbit of the same maximum diameter, and other segments have a curvature less than that of an elliptical orbit of the same maximum diameter (taking maximum diameter being that of the smallest circle that contains the whole of the orbit). In the extreme case all segments have zero curvature with four points with infinite curvature (i.e. a rectangle although there need not be four such points, but any number greater than 2). Such a non-elliptical orbit would require at least two other bodies - hence the reference to the three body problem. For the two other bodies to remain separate one must orbit the other so the orbit is unlikely to be stable (some artificial thrust would be required) and also unlikely to be closed. I think the references to L1 and L2 are to the Lagrange points as the specific orbit mentioned goes outside one of them (L2) and so is a halo orbit (A halo orbit is a periodic, three-dimensional orbit near one of the L1, L2 or L3 Lagrange points).77.44.114.237 (talk) 16:55, 22 February 2022 (UTC)

I'm not confident enough in this answer to put it in the article, but I believe the following is a correct, and somewhat simplified statement that answers "what actually is it?". An NRHO is an orbit around a Lagrange point, that flies close to one of the bodies that establishes the Lagrange point. It's a "halo orbit" because it's around a Lagrange point, and it's "near recti-linear" because it's not an ellipse (being more flattened than an ellipse due to gravitational oddities in the path (namely flying so close to the moon). The main interesting thing here (IMHO) is that the CAPSTONE spacecraft is NOT in orbit around the moon, per se, but rather in an orbit around the Earth-Moon L1 point, and the orbit flies really close to the moon (indeed around it, rather than in front of it.) If someone could confirm this understanding, could we put a statement like this in the article to simplify the article for non-experts? Tim Bird (talk) 18:54, 9 February 2023 (UTC)

Why Halo?

'Near rectilinear' seems clear enough. However, I thought Halo orbits were around Lagrange points. The orbit depicted seems to be a polar orbit around the moon. The Lagrange points are all in the plane of the moon's orbit so I don't see how it is an orbit around a Lagrange point but maybe it is related in some way? crandles (talk) 23:24, 28 February 2021 (UTC)

The Moon's Hill sphere extends out to about 60,000 km - the planned orbit for Lunar Gateway meanwhile goes out to distance of 70,000 km and thus reaches well outside of where the Moon's gravitational potential dominates over the Earth's. According to this source there's four such stable orbits, two for each pole, and two extending inwards or outwards, and I understand they can be described as a special case halo orbit in a wide trajectory around L1 or L2 with a very close approach to the Moon once per cycle. 93.103.223.236 (talk) 09:33, 5 May 2021 (UTC)

Your source seems to use "L1 and "L2" as labels with no clear connection to the Earth-moon Lagrange points 1 & 2. Maybe the ones that are in the L1/2 plane that go around L1 or L2 (as well as the moon) rotate with and stay near that L1/2 plane. Seems a misuse of the term halo orbit. - Rod57 (talk) 14:20, 19 February 2022 (UTC)

Mention of L2 is confusing

"to be orbiting Earth-Moon L2 " seems superfluous and confusing (need to see if any of the 3 refs mention L2). - Rod57 (talk) 13:35, 19 February 2022 (UTC)

Solution to 3-body problem - dubious

"NRHO orbits are one theoretical solution to the classic three-body problem in gravitational mechanics" seems dubious and needing a reference. Might be true of halo orbits around L1 or L2 points, but not of all NRHOs. - Rod57 (talk) 13:42, 19 February 2022 (UTC)

In the case of the Capstone orbit, it appears to be a case of Euler's 3-body problem (qv) in which one of the bodies has negligible mass (i.e. the lunar orbiting satellite). 47.204.70.29 (talk) 17:26, 28 June 2022 (UTC)

I edited the article to incorporate all the comments here on the talk page. I think its a bit more clear, now. 67.198.37.16 (talk) 03:37, 5 July 2022 (UTC)

Are NRHO a type of halo orbit

"A near-rectilinear halo orbit (NRHO) is a type of halo orbit that has slightly curved, so near straight sides, between close passes with an orbiting body." - seems a contradiction since halo orbit says they are not around a central body. & "close passes" seems confusing. NRHO seems to describe a near rectilinear orbit where thrusters rather than gravity are causing the orbit. Who defined NRHO, and is NASA misusing or redefining the term (in connection with Gateway) ? - Rod57 (talk) 14:14, 19 February 2022 (UTC)

What is the advantage of NRHO?

The article does not say what is the rationale for using an NRHO. From my reading it seems to have

• less time blocked by the moon from earth communication
• less time blocked by the moon from sunlight (for power generation)
• is useful as an intermediate location near the moon, but requiring less energy to reach than lunar orbit

According to these articles:

https://sservi.nasa.gov/wp-content/uploads/ger-downloads/day1/Whitley-LunarSurface-GER3-Workshop-20171130.pdf, page 5 "Gateway Staging Orbit Trade".

https://www.esa.int/Enabling_Support/Operations/Angelic_halo_orbit_chosen_for_humankind_s_first_lunar_outpost

But I don't know enough to be sure. Ttulinsky (talk) 08:34, 28 August 2022 (UTC)

In lede - rectilinear vs. rectangular?

Currently the article lede describes NRHO as "a halo orbit with slightly curved – or nearly straight – sides." While perhaps true in certain reference frames (seehttps://www.researchgate.net/figure/92-synodic-resonant-NRHO-in-various-rotating-frames_fig3_342147097) that description doesn't capture the essence of the trajectories. Further, it seems to confuse the reader into thinking rectilinear is directly related to rectangular. Is there a source for this description? (sdsds - talk) 03:00, 27 January 2024 (UTC)