From Newsgroup: sci.space.news


http://m.esa.int/Our_Activities/Space_Science/Rosetta/Rosetta_finale_set_for_30_September

Rosetta finale set for 30 September
European Space Agency
30 June 2016

Rosetta is set to complete its mission in a controlled descent to the
surface of its comet on 30 September.

The mission is coming to an end as a result of the spacecraft's ever-increasing

distance from the Sun and Earth. It is heading out towards the orbit of Jupiter, resulting in significantly reduced solar power to operate the
craft and its instruments, and a reduction in bandwidth available to downlink scientific data.

Combined with an ageing spacecraft and payload that have endured the
harsh environment of space for over 12 years - not least two years
close to a dusty comet - this means that Rosetta is reaching the
end of its natural life.

Unlike in 2011, when Rosetta was put into a 31-month hibernation for the
most distant part of its journey, this time it is riding alongside the
comet. Comet 67P/Churyumov-Gerasimenko's maximum distance from the
Sun (over 850 million km) is more than Rosetta has ever journeyed before.
The result is that there is not enough power at its most distant point
to guarantee that Rosetta's heaters would be able to keep it warm
enough to survive.

Instead of risking a much longer hibernation that is unlikely to be survivable,

and after consultation with Rosetta's science team in 2014, it was
decided that Rosetta would follow its lander Philae down onto the comet.

The final hours of descent will enable Rosetta to make many once-in-a-lifetime measurements, including very-high-resolution imaging, boosting Rosetta's science return with precious close-up data achievable only through such
a unique conclusion.

Communications will cease, however, once the orbiter reaches the surface,
and its operations will then end.

"We're trying to squeeze as many observations in as possible
before we run out of solar power," says Matt Taylor, ESA Rosetta
project scientist. "30 September will mark the end of spacecraft
operations, but the beginning of the phase where the full focus of the
teams will be on science. That is what the Rosetta mission was launched
for and we have years of work ahead of us, thoroughly analysing its data."

Rosetta's operators will begin changing the trajectory in August
ahead of the grand finale such that a series of elliptical orbits will
take it progressively nearer to the comet at its closest point.

"Planning this phase is in fact far more complex than it was for
Philae's landing," says Sylvain Lodiot, ESA Rosetta spacecraft
operations manager. "The last six weeks will be particularly challenging
as we fly eccentric orbits around the comet - in many ways this will
be even riskier than the final descent itself.

"The closer we get to the comet, the more influence its non-uniform
gravity will have, requiring us to have more control on the trajectory,
and therefore more manoeuvres - our planning cycles will have to
be executed on much shorter timescales."

A number of dedicated manoeuvres in the closing days of the mission will conclude with one final trajectory change at a distance of around 20 km
about 12 hours before impact, to put the spacecraft on its final descent.

The region to be targeted for Rosetta's impact is still under discussion,
as spacecraft operators and scientists examine the various trade-offs involved, with several different trajectories being examined.

Broadly speaking, however, it is expected that impact will take place
at about 50 cm/s, roughly half the landing speed of Philae in November
2014.

Commands uploaded in the days before will automatically ensure that the transmitter as well as all attitude and orbit control units and instruments are switched off upon impact, to fulfill spacecraft disposal requirements.

In any case, Rosetta's high-gain antenna will very likely no longer
be pointing towards Earth following impact, making any potential communications

virtually impossible.

In the meantime, science will continue as normal, although there are still many risks ahead. Last month, the spacecraft experienced a "safe
mode" while only 5 km from the comet as a result of dust confusing
the navigation system. Rosetta recovered, but the mission team cannot
rule out this happening again before the planned end of the mission.

"Although we'll do the best job possible to keep Rosetta safe
until then, we know from our experience of nearly two years at the comet
that things may not go quite as we plan and, as always, we have to be
prepared for the unexpected," cautions Patrick Martin, ESA Rosetta's
mission manager.

"This is the ultimate challenge for our teams and for our spacecraft,
and it will be a very fitting way to end the incredible and successful
Rosetta mission."

Notes for Editors
Details regarding the end of mission scenario are subject to change. Further information will be announced once available.

Background information on ending Rosetta's mission on the comet was
published on the blog last year: From one comet landing to another -
planning Rosetta's grand finale

For further information, please contact:
Markus Bauer
ESA Science and Robotic Exploration Communication Officer
Tel: +31 71 565 6799
Mob: +31 61 594 3 954
Email: markus.bauer@esa.int

Matt Taylor
ESA Rosetta Project Scientist
Email: matt.taylor@esa.int

Sylvain Lodiot
Rosetta Spacecraft Operations Manager
Email: sylvain.lodiot@esa.int

Patrick Martin
Rosetta Mission Manager
Email: patrick.martin@esa.int

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