ESA's Rosetta spacecraft is scheduled to orbit 67P/Churyumov–Gerasimenko after it reaches the comet by mid-2014:

Rosetta's main objective is to rendezvous with, and enter orbit around, comet 67P/Churyumov-Gerasimenko and to perform observations of the comet's nucleus and coma. During the period that Rosetta orbits the comet, 67P/Churyumov-Gerasimenko will reach the closest point to the Sun in its orbit, allowing for the consequent increase in activity to be measured. A lander, named Philae, will be deployed and it will attempt to make the first ever controlled landing on a comet.

(source: ESA's Rosetta Fact Sheet)

Rosetta's 67P/Churyumov–Gerasimenko rendezvous

Trajectory of the Rosetta Space Probe (source: Wikipedia)

As the comet approaches the Sun, ejected materials will increase its coma and tails in size and particle density due to increase in radiation pressure, solar wind, and heat exchange on the Sun-facing surface of the comet.

What I'm curious is, what (if any) adjustments in orbital trajectory are planned by ESA due to this increase in particle density (either it having a deceleration effect on spacecraft's inertia, or to avoid collision with larger comet's debris), and which or the coma and tails (dust tail, ion tail,...) is the spacecraft's orbit planned to intersect along the comet's path around the Sun. In essence, what are ESA's estimates regarding particle density the Rosetta spacecraft will have to travel through while orbiting 67P/Churyumov–Gerasimenko, and the acceptable / planned for margins of error?

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    $\begingroup$ From what I understand, finding even marginally stable orbits around bodies like this is difficult due to irregular mass distributions, and I imagine they're going to need to do quite a bit to control the orbit. I don't know about specific considerations for the tail and coma though, good question. $\endgroup$
    – user29
    Commented Jul 26, 2013 at 16:04

2 Answers 2


Since my question didn't yet receive an answer, I did some digging around of my own. This should be considered as a temporary answer, before more precise ones will be actually possible.

The answer is, that for the time being, we don't know yet, because we don't yet know what orbit around 67P/Churyumov–Gerasimenko will be first attempted, or is indeed the most desirable one. And we likely won't know until the Rosetta spacecraft is awaken from its hibernation mode it's currently in (entered on 8 June 2011) to conserve energy, and it makes its own observations of the 67P/Churyumov–Gerasimenko.

Approach itself will be based on ground observations alone, due to onboard camera capabilities, but orbital maneuvers after approach will be determined based on Rosetta's observations, too, presumably during last stages of the approach in May 2014:

The deep sleep is made necessary by the craft's enormous distance from the Sun and the weakness of the sunlight falling on its solar panels, which cannot produce enough electricity to power the probe fully. (Source: ESA)

It is scheduled to be awoken from this deep sleep, or hibernation, on January 2014, when it will begin its preliminary observations and a controlled slow approach to the comet's core, where it will enter a slow speed (relative to comet's core) orbit around it, to about 25 metres per second. Calculations to Rosetta's approach and orbiting trajectory will be made synchronous to its own observations:

As Rosetta drifts towards the heart of the comet, the mission team will try to avoid any comet dust and achieve good comet illumination conditions. The first camera images will dramatically improve calculations of the comet’s position and orbit, as well as its size, shape and rotation. (Source: ESA)


    Artist’s impression of Rosetta approaching the nucleus of Comet 67P/Churyumov-Gerasimenko. Source and hi-res image at: ESA

Rosetta spacecraft's approach and orbit will be operated from the ground, but the spacecraft does have ability to react to observed conditions on its own, since the communication with the ground control can take up to 50 minutes in a single direction:

Rosetta will be operated from the ground. It is impossible to have the manoeuvres for the whole mission programmed before the launch because adjustments will have to be made at each stage of the journey. At the appropriate time, commands will be sent from Earth to adjust the spacecraft’s trajectory. But instructions from the ground can take up to 50 minutes to reach the spacecraft, so to overcome the delay, Rosetta must have the ‘intelligence’ to look after itself. This is done by its on-board computers, whose tasks include data management and attitude and orbit control. If any problems arise during the cruise, back-up systems will ensure that the spacecraft can remain operational during critical mission phases. For example, the spacecraft will automatically position itself with the solar panels facing the Sun, to avoid it becoming powerless. (Source: ESA)

Short of the last two quotes above, I wasn't able to find any additional source of information on what orbit around 67P/Churyumov–Gerasimenko would be considered most desirable, or estimated trajectory corrections for the spacecraft due areas of increased particle density it might be flying through, especially as the comet approaches the Sun and slingshots past it (November 2014 – December 2015), and the coma and tails increase in size and density.


I sincerely hope that my answer contributes in a meaningful way. I found a very nice visualisation of the manouvers that the Rosetta will go through after catching up to 67P (see below).


It seems as if the short answer to your question may indeed be 'yes' but I guess anything may happen when the spacecraft reaches its target and the 'we don't know yet' may be equally relevant. From the animation it seems as if ESA is planning to approach 67P from the sunny side to avoid the coma and tail as much as possible.


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