Presumable it is largely a coincidence that Juno arrives at the perfect moment for American pride in NASA's achievements, but not entirely. The video below of the trajectory, released in July 2011 just before it launched, only states it will arrive at Jupiter in July 2016:

How were the small adjustments made so that the craft would arrive in such a timely fashion? Was it due to the juggling always involved in launch dates, or was more involved?

Edit: There are a range of possible launch dates and possible trajectories on missions, there is margin built in to missions, and a number of precedents for things being done for public relations reasons. July 4th is nearing and this question will occur to others, and at the moment there is no answer out there. If the answer is it is entirely coincidence, it seems that should be possible to demonstrate, and it would be especially nice to have a sense of how much play there is in launch dates, and how much fuel would be involved in making a minor adjustment in deep space to change arrival time by a day or two, and how much that might affect a mission of this kind (a polar orbit of Jupiter). Or some reference point for the decision process.

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    $\begingroup$ For those of us working on planetary projects, there is clearly some sort of universal attractor that puts major mission events on or near holidays, in order to assure that we don't get that time off. $\endgroup$ – Mark Adler Jun 21 '16 at 16:45
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    $\begingroup$ @MarkAdler That's what I was thinking--this alignment is really not convenient for those working on the projects. $\endgroup$ – called2voyage Jun 21 '16 at 17:06
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    $\begingroup$ Oh, simply the universe loves me, knows my space geek nature and gives me birthday presents. $\endgroup$ – SF. Jun 22 '16 at 21:42
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    $\begingroup$ @MarkAdler - Oh come on, scientists and engineers don't take vacations ;) $\endgroup$ – honeste_vivere Jun 28 '16 at 17:55
  • $\begingroup$ @SF Happy Birthday :] $\endgroup$ – kim holder Jul 5 '16 at 15:29

There have been four major US planetary probe events on (or scheduled for) 4th July. This compares to approximately a hundred "major events" for US planetary probes. At least one (Viking) was somewhat intentional - it had to be around early July and the 4th was deliberately picked - while others may fall into this category.

  • Viking 1 landing, 1976 (delayed to July 20, itself nicely symbolic...)
  • Mars Pathfinder landing, 1997
  • Deep Impact flyby/impact, 2005
  • Juno arrival, 2016.

Of these, the first was partly dictated by celestial mechanics and partly by date preference. Launch windows dictated an arrival at Mars around early July, and when the Viking mission planners sat down in 1970, they made the deliberate choice of 4th July out of a roughly one-week window:

Martin remarked that even if Viking had safely touched down on the Fourth of July, the landing "would have been lost among the Tall Ships," a reference to the publicity given the bicentennial parade of ships in New York harbor. That historic date had been chosen in 1970 after a preliminary trajectory analysis singled out the first week in July 1976 for a landing, but the Red Planet had not cooperated. The bicentennial was celebrated without a Viking on Mars.

(On Mars: Exploration of the Red Planet, ch. 10)

Pathfinder did not hang around in Mars orbit, and so the landing date was entirely dependent on the trajectory. Again, this would mean that it was probably an arbitrary selection of a target date in a longer window. I have not as yet been able to confirm that they did pick 4th July as a nicer date than 3rd or 5th, but this seems to have been generally assumed at the time.

Deep Impact - I've not been able to find anything on this one way or another. I suspect it was mostly coincidence - there cannot be much flexibility in the rendezvous window with a comet! The mission was originally planned to launch at the end of December 2004, and delayed two weeks until 12 January; a press kit for a proposed intermediate launch date of 8 January still expected a 4th July impact, but it seems this was driven by orbital and observation opportunities more than symbolism:

An impact on 4 July would not only be one day before the comet's perihelion, but would also mark an American national holiday. This solution roughly optimised several parameters, including lighting conditions and launcher performance, and the impact was scheduled for a one-hour window where it could be tracked by Deep Space Network antennas in both Australia and California, and the effect of the strike could be observed by the large telescopes in Hawaii and in space.

Juno - I've not been able to find anything either way as yet. I suspect it may fall into the category of "we have a broad window, pick an arbitrary date in the middle".

These are all American dates. It's worth considering the experience of other countries. The most obvious example in recent years is North Korea; more or less every launch attempt there is near an anniversary, if not on the specific day. Most prominently, the Kwangmyŏngsŏng-3 launch attempt was timed for what would have been Kim Il-Sung's hundredth birthday.

In the USSR, Soyuz 1 was scheduled to coincide with Lenin's birthday, and it's possible the resulting launch pressures may have contributed to the failure of that flight. I can't immediately find a reference to any other launches being timed around major anniversaries, but I'm sure there were some!

  • $\begingroup$ In addition to April 22 being Lenin's birthday, 1967 was also majorly important in the USSR due to being the fiftieth anniversary of the October Revolution. They were initially targeting their lunar landing for 1967 because of this; when that fell through, they tried to go for a circumlunar mission, but weren't able to do that either. $\endgroup$ – DylanSp Jun 22 '16 at 19:43
  • $\begingroup$ For Souyz 1, May Day was also coming up; in "Challenge to Apollo", Asif Siddiqi states that "there is reason to believe that the Soyuz flight was timed to roughly coincide with the anniversary." He doesn't cite a source, though. See [here|history.nasa.gov/SP-4408pt2.pdf], page 78 of the PDF (printed page 577). $\endgroup$ – DylanSp Jun 22 '16 at 20:14

I had thought that July the 4th was deliberately chosen, as it had been for a few previous missions where the celestial mechanics ended up with a range of dates that included July the 4th. However it turns out that the optimization happened to end up with the arrival right on July 4th (in the US time zones anyway), so they left it there.

From an interview with Scott Bolton:

“We did not actually select July 4,” Bolton told FoxNews.com during a June interview. “Celestial mechanics selected it.”

I confirmed this with a JPL mission designer. The arrival date was originally in August. That date was changed, not to make it July the 4th, but rather to separate the Juno launch date from the MSL launch date as much as possible for logistical reasons. When they moved the launch as much as they could while satisfying all the other constraints, like Earth visibility of JOI, the arrival happened to land on July 4th. There they left it.

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    $\begingroup$ This was what I thought initially, but I could not confirm, and then I got in touch with Warren. It's interesting how these subtle differences could have been lost to the public if this discussion had not occurred. $\endgroup$ – called2voyage Jul 5 '16 at 12:15

I can almost guarantee that it was a coincidence. Essentially they have a launch window, with an entry for each day of the launch window. Depending on the launch date, they will arrive at the given day.

I can almost guarantee if it didn't make the most sense from a spacecraft point of view, they would have adjusted the arrival to July 5th, to make it easier for the team working on the spacecraft. But as Mark joked, major mission events frequently happen on or near major holidays.

  • $\begingroup$ There has got to be a bit of wiggle room, and some adjustability... there is a lot more involved in launch timing than the ideal moment to launch, and all missions have to have margin, which if things go well can be employed for such things as convenient timing. Because the arrival could not possibly have been timed better, which is an awfully big coincidence. $\endgroup$ – kim holder Jun 21 '16 at 17:05
  • $\begingroup$ I'm pretty sure NASA doesn't hate it's employees... There is wiggle room, but they will always use the time for such things that best meets engineering and scientific objectives, over personal objectives. $\endgroup$ – PearsonArtPhoto Jun 21 '16 at 17:07
  • $\begingroup$ @called2voyage well, that sounds like a follow-up question... $\endgroup$ – kim holder Jun 21 '16 at 17:12
  • $\begingroup$ Yep, the question could be an example of the Texas sharpshooter fallacy. $\endgroup$ – user10509 Jun 22 '16 at 7:33
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    $\begingroup$ I would also argue that the 3 arguably had the most important event happen on July 4th. Also, the fact that Viking was delayed a few weeks is indicative that delaying a bit was a good thing, possibly for personnel reasons. As the Viking lander deployed from orbit, it could easily be delayed. $\endgroup$ – PearsonArtPhoto Jun 22 '16 at 16:11

At one of the recent talks at JPL, this exact question was raised. Basically, if there's a significant anniversary date that falls within a launch or arrival window, it's possible for the MDNAV team to push the launch/landing/orbital insertion/rendezvous/etc. towards the significant date by making fairly minor changes to the mission.

E.g. to advance or delay arrival by a few days, you can make fairly small trajectory adjustments early on.

You can even make pretty significant changes well after launch depending on the delta-v budget you have. Sure, there's an element of luck involved to have the option to make the dates line up with significant events, but mission designers often do have the ability to nudge towards those dates if it's within a few days.

I mean, think about it. Juno's launch window was 22 days. And this was its trajectory:

How far does Jupiter move in a couple of days? How much is that trajectory going to change if its arrival were delayed or advanced by a week?


On good authority (Warren Robinson of Lockheed Martin Space Systems, speaking unofficially and not on behalf of Lockheed Martin):

Yes, the July 4th Jupiter arrival was a deliberate choice of the Principal Investigator and Customer team, made way back in the early days of the program. Given the nature of orbital mechanics, the navigation could have fine tuned the date multiple times to be something different, but have done an excellent job keeping it precisely on the original plan.

NASA has a great love for having spacecraft events on July 4th, including Deep Impact hitting comet Tempel-1 on July 4th 2005, and even the Viking 1 Lander was originally scheduled to land on the Bi-centennial (July 4th 1776), though it end up delay as the program concluded the original landing location was too dangerous and a more suitable site was required. It ultimately touched down on July 20th of that year.

The plan with multiple gravity assists to arrive at Jupiter on July 4th was actively maintained by the navigation team. I would have to go back and play with some numbers, but I suspect it was not the most efficient trajectory, but honestly the difference is down in the noise (mere grams of propellant). So yes, the trajectory correction burns in deep space were adjusted to maintain this timing.

Same was true for the Deep Impact mission.

For the Viking missions to Mars, the conop was different in that an orbiter/lander carrier was inserted into Mars orbit the month before and the July 4th planned landing date wasn't dependent on in-flight trajectory maneuvers.

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    $\begingroup$ Let me say i appreciate them working on a national holiday for the sake of national pride in NASA :) $\endgroup$ – kim holder Jun 27 '16 at 15:22
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    $\begingroup$ Alas, it turns out that Warren is not correct. $\endgroup$ – Mark Adler Jul 5 '16 at 2:52

I believe my comments were a bit misunderstood. There wasn't a grand conspiracy to place the event on July 4th, and thus inconvenience the people flying the spacecraft. Rather, when based upon the replan a new arrival date had to be selected, this one was what came out balancing a bunch of different parameters. And then the navigation team did an outstanding job making it work and getting the spacecraft there on the plan, with almost unheard of levels precision in the different events (DSM, Earth-fly-by and JOI). So July 4th is a great day for Juno!

  • $\begingroup$ So to clarify: July 4th wasn't preselected before calculating the mission requirements, but after balancing parameters it was chosen out of a few possible options. Correct? $\endgroup$ – called2voyage Jul 5 '16 at 15:34

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