[meteorite-list] Searching for the Grandest Asteroid Tour

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 6 Apr 2007 15:26:46 -0700 (PDT)
Message-ID: <200704062226.l36MQks25814_at_zagami.jpl.nasa.gov>


Searching for the Grandest Asteroid Tour
Jet Propulsion Laboratory
April 05, 2007

Asteroids are Earth's closest celestial neighbors, sometimes passing
closer to Earth than even the Moon. And yet, to date, only two
spacecraft have ever remained in proximity to one of these bodies. Last
month, orbit mechanics experts from around the world met to discuss
methods for finding the best possible spacecraft trajectory, or flight
path, for visiting a sequence of asteroids. The gathering was part of
the second Global Trajectory Optimisation Competition, organized by JPL.

The idea of an asteroid grand tour is a celestial analogue to the Grand
Tour embarked upon by Renaissance travelers seeking to further their
cultural knowledge of Europe. Just as the traveler had to judge
carefully which cities to visit based on his or her available resources,
so must designers of a spacecraft flight path contend with limited
resources and constraints. Such restrictions include the rocket's
ability to launch the spacecraft into space, the strength of the
spacecraft's thruster, orbital positions of the various asteroids over
time, and the spacecraft's longevity.

Determining the best possible trajectory within these constraints, out
of the many good ones, is not a trivial matter. It requires a
big-picture, or global, view of all the possibilities, that is, it
requires global optimization. There are many possible approaches, each
with its own strengths and weaknesses.

The inspiration for this problem was the need to study closely different
types of asteroids. By visiting a member of each of four different
asteroid groups, a spacecraft would provide insights into their chemical
composition, their structural characteristics, how they formed, and
which might be suitable for future space mining operations. Such
insights would also be critical should the need ever arise to deflect an
asteroid that is found to be on an Earth-threatening trajectory.

The problem posed by JPL's Outer Planets Mission Analysis Group for the
second competition was to design a flight path for visiting four
asteroids-- one from each group -- in the shortest amount of flight time
and with the least amount of propellant. With almost 1,000 asteroids to
choose from, more than 41 billion asteroid sequences could be
considered. That's far too many to study individually in the short time
allocated for the competition, even with the fastest computers, largest
computer clusters and best algorithms.

Fourteen teams - from Europe, Russia, China and the U.S. - sought the
elusive best possible trajectory. Their search took place over a period
of four weeks late last year, at the end of which they submitted their
top solution to be ranked against those of the other teams.

The winning trajectory was found by a team from the Polytechnic of
Turin, Italy. Two professors, Lorenzo Casalino and Guido Colasurdo,
along with Ph.D. student Matteo Rosa Sentinella and graduate student
Francesco Cacciatore, successfully and quickly screened out billions of
possible asteroid sequences to focus on the most practical ones. Their
winning trajectory, involving visits of four different asteroids in just
over nine years, was followed by trajectories from a Russian team (the
Moscow Aviation Institute and the Khrunichev State Research and
Production Space Center), and a team from the European Space Agency's
Advanced Concepts Team.

The workshop where the various teams convened for their discussions took
place in Sedona, Ariz., in conjunction with the Space Flight Mechanics
Meeting of the American Astronautical Society and the American Institute
of Aeronautics and Astronautics.

Did the competition yield the best possible trajectory? With such
complexity, it is likely impossible to say, but an educated guess, and
the insights gained by comparing the various teams' methods, would
suggest that there is still some room for improvement. The Turin team,
as winners of this year's competition, will now be organizing the Third
Global Trajectory Optimisation Competition, where various teams will
again have the opportunity to test their mettle in solving the most
challenging problems currently faced by spacecraft trajectory designers.

The Global Trajectory Optimisation Competition was instituted in 2005 by
Dario Izzo of the European Space Agency's Advanced Concepts Team. As
winners of the first competition, the JPL team organized this latest
one, with support from NASA's In-Space Propulsion Program.

For further information about asteroids and the Near-Earth Object
Program, visit: http://neo.jpl.nasa.gov

For further information about the Global Trajectory Optimisation
Competition series, visit:
http://www.esa.int/gsp/ACT/mad/op/GTOC/index.htm .


Media contact: DC Agle 818-393-9011
Received on Fri 06 Apr 2007 06:26:46 PM PDT

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