Geometry Drives Selection Date for 2011 Mars Launch

Feature May 20, 2010

GEOMETRY DRIVES SELECTION DATE FOR 2011 MARS LAUNCH

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2010-171&cid=release_2010-171

Planners of NASA's next Mars mission have selected a flight schedule that will use
favorable positions for two currently orbiting NASA Mars orbiters to obtain maximum
information during descent and landing.

Continuing analysis of the geometry and communications options for the arrival at Mars
have led planners for the Mars Science Laboratory, or Curiosity, to choose an Earth-to-
Mars trajectory that schedules launch between Nov. 25 and Dec. 18, 2011. Landing will
take place between Aug. 6 and Aug. 20, 2012. Due to an Earth-Mars planetary alignment,
this launch period actually allows for a Mars arrival in the earlier portion of the landing
dates under consideration.

"The key factor was a choice between different strategies for sending communications
during the critical moments before and during touchdown," said Michael Watkins,
mission manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "The shorter
trajectory is optimal for keeping both orbiters in view of Curiosity all the way to
touchdown on the surface of Mars. The longer trajectory allows direct communication to
Earth all the way to touchdown."

The simplicity of direct-to-Earth communication from Curiosity during landing has appeal
to mission planners, in comparison to relying on communications relayed via NASA's
Mars Odyssey, which has been orbiting Mars since 2001, and NASA's Mars
Reconnaissance Orbiter, in operation since 2006. However, the direct-to-Earth option
allows a communication rate equivalent to only about 1 bit per second, while the relay
option allows about 8,000 bits or more per second.

Landing on Mars is always difficult, with success uncertain. After an unsuccessful
attempted Mars landing in 1999 without definitive information on the cause of the
mishap, NASA put a high priority on communication during subsequent Mars landings.

"It is important to capture high-quality telemetry to allow us to learn what happens during
the entry, descent and landing, which is arguably the most challenging part of the
mission," said Fuk Li, manager of NASA's Mars Exploration Program at JPL. "The
trajectory we have selected maximizes the amount of information we will learn to
mitigate any problems."

Curiosity will use several innovations during entry into the Martian atmosphere, descent
and landing in order to hit a relatively small target area on the surface and set down a
rover too heavy for the cushioning air bags used in earlier Mars rover landings. In a "sky-
crane" maneuver during the final minute of arrival, a rocket-powered descent stage will
lower Curiosity on a tether for a wheels-down landing directly onto the surface.

Even though Curiosity won't be communicating directly with Earth at touchdown, data
about the landing will reach Earth promptly. Odyssey will be in view of both Earth and
Curiosity, in position to immediately forward to Earth the data stream it is receiving
during the touchdown. Odyssey performed this type of "bent-pipe" relay during the May
25, 2008, arrival of NASA's Phoenix Mars Lander.

Curiosity will rove extensively on Mars, carrying an analytical laboratory and other
instruments to examine a carefully selected landing area. It will investigate whether
conditions there have favored development of microbial life and its preservation in the
rock record. Plans call for the mission to operate on Mars for a full Martian year, which is
equivalent to two Earth years.

Consideration of landing sites for the mission narrowed to four finalist candidates in
November 2008. The candidate sites are still being analyzed for safety and science
attributes.

Curiosity is managed by JPL for NASA's Science Mission Directorate in Washington.
JPL also manages the Mars Odyssey and Mars Reconnaissance Orbiter missions, in
partnership with Lockheed Martin Space Systems, Denver.

More information about NASA's Mars Science Laboratory is at:
http://www.nasa.gov/msl .

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