[meteorite-list] Geometry Drives Selection Date for 2011 Mars Launch (MSL)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 21 May 2010 09:40:49 -0700 (PDT)
Message-ID: <201005211640.o4LGenuA021399_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.cfm?release=2010-171

Geometry Drives Selection Date for 2011 Mars Launch
Jet Propulsion Laboratory
May 20, 2010

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.

Guy Webster 818-354-6278
Jet Propulsion Laboratory, Pasadena, Calif.
guy.webster at jpl.nasa.gov

2010-171
Received on Fri 21 May 2010 12:40:49 PM PDT