Rosetta blog: From one comet alighting to another: formulation Rosetta’s grand finale

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As announced in Jun along with acknowledgment of a mission’s extension, Rosetta teams are formulation to finish a operational proviso of a goal in a tranquil impact of a orbiter on a aspect of Comet 67P/Churyumov-Gerasimenko during a finish of Sep 2016. While a specific sum of a trajectories and impact site are still underneath discussion, ESA’s Rosetta Spacecraft Operations Manager Sylvain Lodiot, Project Scientist Matt Taylor, and goal manager Patrick Martin, share some credentials information on a formulation of this thespian goal finale.

Why will a goal come to an end?
Following perihelion in August, Comet 67P/C-G and Rosetta are now relocating divided from a Sun and behind out towards a circuit of Jupiter. This creates a series of challenges:

Reduced solar power
As a comet recedes from a Sun, a volume of object descending on Rosetta’s solar panels will dump significantly. As a energy drops, it will not be probable to work all of a systematic instruments during a same time. Ultimately, a indicate will be reached where Rosetta would have to be put behind in hibernation, as it was for a 31 months heading adult to Jan 2014. However, this time Rosetta will follow a comet out over a circuit of Jupiter on a 6.5-year tour around a Sun, serve from a source of energy than ever before.

On tip of this, a booster will have been in space for over 12 years, dual of them spent in a comet’s dry environment, with plunge of a solar arrays coming to serve revoke a accessible power.

Solar conjunction
By September-October 2016, Rosetta and a comet will seem really tighten to a Sun as seen from a Earth, creation a uplinking of operational commands and a downlinking of systematic information intensely challenging. On 1 Oct 2016, a booster will enter a duration of conjunction, i.e. it will be behind a Sun as seen from Earth.

Reduced information rates distant from Earth
The increasing stretch from Earth and apparent vicinity to a Sun lead to a poignant dump in information rates. By early Jul 2016, we should be removing 91kbps around NASA’s DSN 70m belligerent stations and usually 22 kbps around ESA’s ESTRACK 35m stations. By comparison, by midst Sep 2016, these rates will dump to 57 kbps around DSN and usually 14 kbps around ESTRACK, identical to a 1995 epoch dial-up modem. Access to NASA’s bigger dishes is not always guaranteed, due to a high direct for their use by other missions.

These low information rates, total with reduced energy availability, will lead to problems starting in Aug 2016, as a instrument teams and scholarship operations formulation teams during ESAC work to understanding with power-sharing issues and a much-reduced scholarship information download capacity.

Rosetta will be a prolonged proceed from home by Sep 2016. Click to revisit a Where is Rosetta? interactive tool.

Rosetta will be a prolonged proceed from home by Sep 2016. Click to revisit a “Where is Rosetta?” interactive tool.

Why can’t we put a booster behind into hibernation?
In principle, Rosetta could be put behind into hibernation and awakened several years after as a comet starts to proceed a Sun again. In practice, however, this does not seem possible.

First and foremost, a comet’s aphelion – limit stretch from a Sun – is serve than Rosetta gifted during a prior hibernation between 2011 and 2014. There will not be adequate energy to control a spacecraft, including, for example, a thermal control of a booster – definition it could solidify – and not be means to come out of hibernation during all.

Second, Rosetta relies on diesel to stratagem around a comet as it carries out a systematic measurements, and this is ever depleting, tying any renewed post-hibernation operations.

Third, a booster and scholarship instruments are aging and will be good over their favoured handling lifetime post-hibernation.

These constraints led a Science Working Team to cruise scenarios that would see a goal finish in Sep 2016. Taking into comment a accessible resources, a SWT motionless that a ultimate finish would be to first make a delayed proceed to a comet, removing behind to within 10 km and even closer. Getting this tighten has not been probable for most of a past year due to a high activity of a comet, and there is most to be gained scientifically in questioning a low altitude segment of a comet’s coma and study a post-perihelion aspect in good detail. Then Rosetta would begin a slow descent towards a surface, holding systematic information during really low altitudes, and ultimately leading to a tranquil impact, culmination this landmark systematic goal with Rosetta fasten Philae on a aspect of a comet.

In a meantime, a arriving months of Rosetta operations will see a renewed concentration on tighten vicinity to a comet as a activity continues to drop, as good as investigations of formerly uncharted territories during incomparable distances around a comet, including a tail region.

Rosetta coming comet 67P/C-G from afar.

Rosetta coming comet 67P/C-G from afar. Spacecraft: ESA/ATG medialab; Comet image: ESA/Rosetta/NAVCAM

What does a alighting unfolding now demeanour like?
We are still deliberating a method of events that will take place in Rosetta’s final weeks. Operations really tighten to a comet will be really formidable and challenging, even some-more so than a arena designed by a moody dynamics group in 2014 to broach Philae to a surface.

The pivotal reason is that a closer Rosetta gets to a comet, a some-more critical a non-uniform gravitational intensity will become. This will have a poignant impact on a trajectory, with outrageous perturbations in a round tallness – a farthest indicate from a comet on an elliptical circuit – expected. This will need most some-more control on a arena and therefore many some-more manoeuvres – a formulation cycles will be reduced significantly.

The extended devise is to fly Rosetta in bound, highly-elliptical firm orbits that will take us as tighten as probable to a comet in a final dual months of a mission, with flyby distances reduction than 1 km from a aspect towards a end: a instruments will be means to collect good systematic data, including implausible images. In a final days of a mission, Rosetta will be on ever-closer firm elliptical orbits. We will afterwards perform a final stratagem to put Rosetta on a controlled, delayed collision march with Comet 67P/C-G. Subject to probable changes formed on final moody dynamics analyses, a tranquil impact is foreseen to take place on 30 Sep 2016.

Credits: ESA-C.Carreau

Credits: ESA-C.Carreau

Will we be means to promulgate with Rosetta during a final descent?
During a final ‘collision trajectory’, a spacecraft’s high-gain receiver will be Earth-pointing, creation it probable to get behind telemetry and systematic information all a proceed down to contact. However, once impact has occurred, it is rarely doubtful that any serve communication with a Rosetta will occur.

Why can’t we sojourn in hit with Rosetta on a surface?
There are dual tools to this question: will Rosetta continue to duty on a surface, and if so, will we be means to accept any information from it?

Rosetta was not designed for a landing. Even underneath a delayed impact, a really vast solar panels might be damaged, and some of a instrument booms adhering out from a physique of a booster might bend or snap off. Under a really low sobriety of a comet, a booster might tumble, serve deleterious it.

Furthermore, as Rosetta is solar-powered, to be means to work it would have to land in a fully-illuminated partial of a comet. As a comet rotates during a 12.4-hour day, a arrays would expected indicate divided from a Sun, shortening a energy next a operational threshold.

Critically, even if Rosetta were to duty on a aspect for a while, it would be intensely formidable to communicate. If a high-gain receiver points divided from a Earth only half a degree, we would remove line-of-sight hit with belligerent stations on Earth. In addition, a booster course (for instance for high benefit receiver and solar array pointing) relies on operational star trackers; it could be that Rosetta lands ‘face down’ with a star trackers indicating into a aspect and a instruments indicating ‘up’ into space.

All in all, it is foreseen that Rosetta’s goal will finish during a indicate of hit on to a aspect of Comet 67P/C-G, a mystic culmination to an epic tour travelling roughly 20 years of formulation and preparation, and 12 years in space.

More sum on a finish of goal unfolding will be supposing when they are known.

Note: on a favoured goal finish date of 30 Sep 2016, Rosetta and a comet will be 573 million km (3.8 AU) from a Sun and 720 million km (4.8 AU) from Earth. The one-way vigilance transport time will be approximately 40 minutes.

Source: Rosetta blog