# Fastest time to Sun Earth L2 (or L1)?

Of all the past, present or planned probes to SE-L2 (or L1*) which has or will take the shortest amount of time to arrive from leaving low earth orbit, or from passing that location if the probe doesn't enter LEO before heading to L2 (*or L1 it the travel time is similar)?

Arrival at the general location of L2 is sufficient, I'm not concerned about the length of time it takes to enter a Lissajous orbit.

• I didn't know if an orbit closer to the sun would have different requirements, which would lead to different travel times. Feb 17, 2020 at 13:38
• L2 is more "energetic" in terms of Jacobi constant than L1 Feb 17, 2020 at 15:19
• @uhoh To you downvote observation, I'll add a bonus tomorrow, if that might make it worth someone's time. If someone wants to point to the way to do the leg work myself I'm all for it, that is if I'm up for the challenge. My physics education ended as I was getting ready for the Classical Mechanics class at my university, decades ago. Feb 17, 2020 at 17:07
• It could be @uhoh, I do not know what happens because CRTBP non-linearities can come into play. I just wanted to remark that L1 and L2 are not the same in terms of energy. Feb 18, 2020 at 9:16
• I wonder if a community wiki might be the way to go here. The lack of answers suggests no-one knows the fastest time for sure. But a community wiki would allow someone to post the probe/space telescope/satellite/whatever that took the shortest time they know. Then someone can amend that with one they know took less time, and we might get a good approximate answer to OP's question. Feb 20, 2020 at 7:44

I think the best bet for answering this question will be a community wiki, in which we post what we know for several different L1/L2 orbiters. I'll start.

L1 - the fastest I know:

L1 - other:

L2 - the fastest I know:

• Gaia was launched on the 19th of December 2013 and reached L2 orbit on January 8th 2014 - so a mere 20 days! In fact, the report of its entering L2 orbit may have been published a few hours after this happened, so it may be as little as 19 days and X hours!

L2 - other missions:

• According to the European Space Agency, Planck was launched on the 14th of May 2009 and reached L2 orbit on the 3rd of July. So that's 50 days.

• Herschel was launched on May 14th 2009, along with Planck. According to Wikipedia, it reached L2 "approximately sixty days after launch". Still, its observation mission didn't get started until the autumn.

• Chang'e 2 reached the L2 point by a rather different route - it had an earlier mission which required it to be orbiting the Moon. When that was complete, it left that orbit on June 8th 2011 and arrived on August 25th - 78 days. So that's slower and it's a route starting at high instead of low Earth orbit, but I thought it might interest the OP anyway.

• Spektr-RG apparently took 100 days to reach L2.

L2 - planned missions:

L2 - cancelled missions:

Craft that I don't have the full information for:

• WIND was launched on the 1st of November 1994 into "a double-lunar-swingby orbit near the ecliptic plane with an apogee from 80 to 250 RE and a perigee of 5 to 10 RE". It was inserted into halo orbit around L1 some time in November 1996, after making several observations in its previous orbit. If "RE" means "Earth Radiuses", this was a high-Earth orbit that may have been designed to eventually bring it close to L1. It looks like it exited its "halo" orbit and entered "petal" orbits in June 1996, in preparation for exiting L1 orbit. It moved to L2, and I don't think it got close enough to Earth to be in LEO, whether or not it resumed an Earth-centric orbit. It returned to L1 in early 2004.

I do not believe that it broke the record for LEO - Lagrange travel time, but the information sources I have examined were incomplete and I could only work out a partial picture.

• WMAP was launched on the 30th of June, 2001. Sources claim that it took about three months to reach L2. I'd put that down as roughly 90 days - except that one NASA page quotes the three month figure but also gives a date of August 10 2001 - which would be less than two months. The press release announcing its arrival at L2 is dated October 3 2001, so this would give us a travel time of 95 days. However, a published research paper states "By 10 August 2001, WMAP was sufficiently stable in its L2 orbit for CMB data taking to commence." So we either have 41 days or 95 days, and disagreement as to exactly what counted as a stable L2 orbit may be the reason.

Anyone who can beat these records, I've made this a community wiki, so please edit them in!

• +1 for initiative! The problem with using "wikiblurbs" for comparison is that they can be wrong, or not directly comparable. For example, if a spacecraft approaches a halo orbit along a stable manifold trajectory, there is no well-defined point where you can say definitively that it's reached orbit. For those trajectories that have well-defined insertion burns, then we can note those. Anyway, let's see how it goes...
– uhoh
Feb 20, 2020 at 9:31
• @uhoh Thanks for that. I admit that I don't understand orbital mechanics well enough to follow your point, but I do certainly understand that there is potential inaccuracy in the figures. They're all I've got to go by, but maybe someone with information allowing for more accurate and comparable times-to-orbit will edit this answer. Feb 22, 2020 at 9:47
• Okay the wiki really helps! I can have a look to see how much can be deduced from the data in Horizons
– uhoh
Feb 22, 2020 at 10:08
• WIND could be a tricky one to research (directory.eoportal.org/web/eoportal/satellite-missions/…) (en.wikipedia.org/wiki/WIND_(spacecraft)) - it's moved between Earth-centric orbit, L1 orbit, L2 orbit, L1 again and I don't yet have the full information on how long any of these traversals took or whether it temporarily entered into Earth orbit on the way. Feb 22, 2020 at 16:31
• @uhoh It looks like WMAP was an example of the problem you describe. At the very least, I've got contradictory dates as to when it reached L2 orbit. Feb 22, 2020 at 17:38