Editing 3029: Sun Avoidance

{{comic
| number    = 3029
| date      = December 25, 2024
| title     = Sun Avoidance
| image     = sun_avoidance_2x.png
| imagesize = 311x403px
| noexpand  = true
| titletext = C'mon, ESA Solar Orbiter team, just give the Parker probe a LITTLE nudge at aphelion. Crash it into the sun. Fulfill the dream of Icarus. It is your destiny.
}}

==Explanation==
{{incomplete|Created by a SANTA BOT FLYING TOO CLOSE TO THE SUN (SKILL ISSUE). Do NOT delete this tag too soon.}}

The comic shows the end of a table of human missions, both terrestrial and space-based, ranked by how far they stayed away from the {{w|Sun}}.

The vast majority of these missions have been on Earth, a few on the Moon, and most of the rest in Earth orbit, so about 157 million km from the Sun. There have also been 8 probes sent to the outer planets; they could be at the top of the list if this were shown, but only if they started by flying directly away from the Sun, at at time when the Earth was farthest from the Sun. Else they would have been closer to the Sun at the start than all missions on Earth when Earth was farthest. It is not how far away the mission ends but how close it comes at closest approach to the Sun.

Most space probes try not to get too close to the Sun, because it's extremely hot{{Citation needed}} and their equipment (especially the electronics) are not designed to work at such temperatures and radiation levels. If they have to venture into the inner Solar System, either because the mission is to an inner planet or other body there or to use {{w|gravity assist}} of Mercury or Venus, mission planners will design the trajectory so it remains tens of millions of kilometers away from the Sun, to minimize the Sun's effect on the spacecraft.

This comic was posted the day after December 24, 2024, when the {{w|Parker Solar Probe}} made its closest approach to the Sun. As a result, it has set a new record for the worst failure in solar avoidance. This mission needs to be really close to the Sun so it can make close-up analysis of its corona and magnetic field. It has been engineered with special solar shields to protect it from the extreme heat and radiation.

Obviously the joke is to mischaracterize Parker's impressively close approach to the Sun as a failure to avoid it. Earth and everything on it travel at an {{w|Earth's orbit|average of 29.78 km/s}} in a direction 90 degrees to the direction of the Sun, and the majority of this "sideways" relative velocity must be shed to bring Parker's orbit closer to the Sun. Just to bring a mass of approximately 67 metric tons directly to an orbit crossing Mercury requires a rocket the size of the Saturn V stack. Parker masses about ten times that and it's Christmas 2024 perihelion was just 6.1 million kilometers versus Mercury's 46 million kilometers. The Parker mission designers needed an extremely ''high'' degree of skill to plot a course with very minor adjustments that resulted in the seven gravity assists from Venus that were needed to get this close to the sun — and should rank well above all the missions that went nowhere near the Sun and therefore showed no skill avoiding it.

The next closest mission that's still in operation (the {{w|Helios (spacecraft)|Helios}} missions ended in 1985) is the {{w|European Space Agency}}'s {{w|Solar Orbiter}}. The title text jokes that it should nudge Parker so it crashes into the Sun fulfilling the supposed dream of {{w|Icarus}}, a character from Greek mythology who flew too close to the Sun using wings crafted by his father {{w|Daedalus}}, and fell into the sea because the beeswax in the wings melted. Flying too close to the Sun is a saying that relates to Icarus, whose dream may have been to fly even closer to the Sun (or just so high that he was), but the 'reality' was instead a fall ''out'' of the sky and into the sea, making the title text somewhat metaphorically mixed.

The title text additionally suggests that the Solar Orbiter could be repurposed to nudge the Parker Probe into a Sun-striking trajectory, as their orbits do technically overlap, although it would take some time (and very precise operation) to coordinate the Orbiter such that it could somehow send the Probe into a full terminal Sun-dive to cement its position as being the closest mission to the Sun (or, in terms of the comic, aquiring a "last place" position in Sun-avoidance that can only ever be equalled, and never overtaken). But it would be be difficult to accomplish the feat, as the mission had not been designed with this degree of capability in reserve, and it would not be easy to give the amount/timing of nudge needed without potentially damaging/destroying both craft.

Note that falling into the Sun, starting from Earth, needs almost as much effort as it would take to launch a probe ''from'' the surface of the Sun (assuming one could be) and out into Earth's orbit, which might involve reversing the {{w|Gravity assist|gravitational slingshots}} used to save some effort. The possible advantage for a Sun-destined probe is that it can end by taking advantage of {{w|aerobraking}} in its {{w|Stellar atmosphere|thickening atmosphere}}, but this would mean surviving higher tempereratures for even longer than Parker probe is designed to hopefully withstand; it would take further development to have a probe with a good chance of surviving long enough to make useful studies all the way up to not missing the Sun at all, or could only be considered as beyond the end of any practical mission.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[Header:] Sun Avoidance Skill Leaderboard

:[A table with three columns, all with underlined headers.]
:<u>Rank</u>
:<u>Mission</u>
:<u>Sun Nearest Miss</u>
:[First 'row', 'Rank', is of extra height and over several lines, using vertical and horizontal ellipses between the two endpoints to indicate a range of ranks in the first column, the first visible digit of the larger number being cut off by the left frame edge:] 1. ⋮ … ⋮ 4303857.
:[Across both the 'Mission' and 'Sun Nearest Miss' columns, the first row has some text spread across two lines, within a framing pair of large square brackets to match the Rank range:] All other expeditions in human history
:[A simple row, with all three columns separately populated, the first columns Rank number is also cut off across the first visible digit.]
:4303858.
:Mariner-10
:69.0 million km
:[Another row, likewise.]
:4303859.
:Helios 1
:46.4 million km
:[Another row.]
:4303860.
:BepiColombo
:45.8 million km
:[Another row, with a yet more significant Ranking digit now partly visible due to non-proportional spacing, itself being cut off in the stead of the now fully visible next digit.]
:24303861.
:Messenger
:45.3 million km
:[Another row, back to the original pre-cutoff.]
:4303862.
:Solar Orbiter
:43.8 million km
:[Another row.]
:4303863.
:Helios 2
:43.3 million km
:[Final row.]
:4303864.
:Parker
:6.17 million km

:[Caption below the panel:]
:Congratulations to the Parker Solar Probe for setting a new record for "Worst Job Avoiding the Sun."

==Trivia==
This comic was released on Christmas Day of 2024, but makes no reference to Christmas. This year marks the first time in xkcd's 20 year history (of releasing comics around Christmas), that there have been no [[:Category:Christmas|Christmas comics]] released during those days. Also all nine times before this year, when a release day fell on Christmas Day, that comic has always been about Christmas.

It might explain why this comic was released on Christmas Day instead of a Christmas comic, if [[Randall]] found the accomplishments of the Parker Solar Probe more interesting than Christmas itself. It would not be the first accomplishment mentioned on or around Christmas, however, with the others having been given a seasonal spin.<!-- consider links, e.g. to James Webb Advent Calendar?-->

{{comic discussion}}

[[Category:Space probes]]