[meteorite-list] 'J' Marks the Spot for Rosetta's Lander

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon, 15 Sep 2014 13:16:42 -0700 (PDT)
Message-ID: <201409152016.s8FKGgBK028870_at_zagami.jpl.nasa.gov>


'J' Marks the Spot for Rosetta's Lander
Jet Propulsion Laboratory
September 15, 2014

The European Space Agency's Rosetta's lander, Philae, will target Site
J, an intriguing region on comet 67P/Churyumov-Gerasimenko that offers
unique scientific potential, with hints of activity nearby, and minimum
risk to the lander compared to the other candidate sites. The 220-pound
(100-kilogram) lander is scheduled to reach the surface on November 11,
where it will perform in-depth measurements to characterize the nucleus.
Rosetta is an international mission spearheaded by the European Space
Agency with support and instruments provided by NASA.

Site J is on the "head" of the comet, an irregular shaped world that is
just over 2.5 miles (four kilometers) across at its widest point. The
decision to select Site J as the primary site was unanimous. The backup,
Site C, is located on the "body" of the comet.

"As we have seen from recent close-up images, the comet is a beautiful
but dramatic world - it is scientifically exciting, but its shape makes
it operationally challenging," says Stephan Ulamec, Philae Lander
Manager at the German Aerospace Center (DLR) in Cologne. "None of the
candidate landing sites met all of the operational criteria at the
100-percent level, but Site J is clearly the best solution."

Over the weekend, the Landing Site Selection Group of engineers and
scientists from Philae's Science, Operations and Navigation Center at
the National Center of Space Studies of France (CNES), the Lander
Control Center at DLR, and scientists representing the Philae Lander
instruments and ESA's Rosetta team, met at CNES, Toulouse, France, to
consider the available data and to choose the primary and backup sites.

A number of critical aspects had to be considered, not least that it had
to be possible to identify a safe trajectory for deploying Philae to the
surface and that the density of visible hazards in the landing zone
should be minimized. Once on the surface, other factors come into play,
including the balance of daylight and night-time hours, and the
frequency of communications passes with the orbiter.

The descent to the comet is passive and it is only possible to predict
that the landing point will be within a "landing ellipse" (typically a
few hundred meters) in size. For each of Rosetta's candidate sites, a
larger area -- four-tenths of a square mile (one square kilometer) --
was assessed. At Site J the majority of slopes are less than 30-degrees
relative to the local vertical, reducing the chances of Philae toppling
over during touchdown. Site J also appears to have relatively few
boulders, and it receives sufficient daily illumination to recharge
Philae and continue science operations on the surface beyond the initial
battery-powered phase.

Provisional assessment of the trajectory to Site J found that the
descent time of Philae to the surface would be about seven hours, a
length that does not compromise the on-comet observations by using up
too much of the battery during the descent.

Both Sites B and C were considered as the backup, but C was preferred
because of a higher illumination profile and fewer boulders. Sites A and
I had seemed attractive during first rounds of discussion, but were
dismissed at the second round because they did not satisfy a number of
the key criteria.

A detailed operational timeline will now be prepared to determine the
precise approach trajectory of Rosetta in order to deliver Philae to
Site J. The landing must take place before mid-November, as the comet is
predicted to grow more active as it moves closer to the sun.

"There's no time to lose, but now that we're closer to the comet,
continued science and mapping operations will help us improve the
analysis of the primary and backup landing sites," says ESA Rosetta
flight director Andrea Accomazzo from the European Space Operations
Centre in Darmstadt, Germany. "Of course, we cannot predict the activity
of the comet between now and landing, and on landing day itself. A
sudden increase in activity could affect the position of Rosetta in its
orbit at the moment of deployment and in turn the exact location where
Philae will land, and that's what makes this a risky operation."

All commands for Philae's descent will be uploaded prior to the lander's
separation from the Rosetta orbiter. Once deployed from Rosetta,
Philae's descent will be autonomous, with the lander taking images and
other observations of the comet's environment.

Philae will touch down at the equivalent of walking pace and then use
harpoons and ice screws to fix itself onto the comet's surface. It will
then make a 360-degree panoramic image of the landing site to help
determine where and in what orientation it has landed. The initial
science phase will then begin, with other instruments analyzing the
plasma and magnetic environment, and the surface and subsurface
temperature. The lander will also drill and collect samples from beneath
the surface, delivering them to the on-board laboratory for analysis.
The interior structure of the comet will also be explored by sending
radio waves through the surface toward Rosetta.

"No one has ever attempted to land on a comet before, so it is a real
challenge," says Fred Jansen, the ESA Rosetta mission manager from the
European Space Research Technology Center, Noordwijk, the Netherlands.
"The complicated 'double' structure of the comet has had a considerable
impact on the overall risks related to landing, but they are risks worth
taking to have the chance of making the first ever soft landing on a comet."

The landing date should be confirmed on September 26 after further
trajectory analysis and the final Go/No Go for a landing at the primary
site will follow a comprehensive readiness review on October 14.

Launched in March 2004, Rosetta was reactivated in January 2014 after a
record 957 days in hibernation. Composed of an orbiter and lander,
Rosetta's objectives since arriving at comet 67P/Churyumov-Gerasimenko
earlier this month are to study the celestial object up close in
unprecedented detail, prepare for landing a probe on the comet's nucleus
in November, and track its changes through 2015, as it sweeps past the sun.

Comets are time capsules containing primitive material left over from
the epoch when the sun and its planets formed. Rosetta's lander will
obtain the first images taken from a comet's surface and will provide
comprehensive analysis of the comet's possible primordial composition by
drilling into the surface. Rosetta also will be the first spacecraft to
witness at close proximity how a comet changes as it is subjected to the
increasing intensity of the sun's radiation. Observations will help
scientists learn more about the origin and evolution of our solar system
and the role comets may have played in seeding Earth with water, and
perhaps even life.

Rosetta is an ESA mission with contributions from its member states and
NASA. Rosetta's Philae lander is provided by a consortium led by the
German Aerospace Center, Cologne; Max Planck Institute for Solar System
Research, Gottingen; National Center of Space Studies of France (CNES),
Paris; and the Italian Space Agency, Rome. NASA's Jet Propulsion
Laboratory in Pasadena, California, a division of the California
Institute of Technology, manages the U.S. participation in the Rosetta
mission for NASA's Science Mission Directorate in Washington.

For more information on the U.S. instruments aboard Rosetta, visit:


More information about Rosetta is available at:


DC Agle Jet Propulsion Laboratory, Pasadena, Calif.
agle at jpl.nasa.gov Dwayne Brown
Headquarters, Washington
dwayne.c.brown at nasa.gov

Markus Bauer
European Space Agency, Noordwijk, Netherlands
markus.bauer at esa.int

Received on Mon 15 Sep 2014 04:16:42 PM PDT

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