[meteorite-list] Robotic Comet Explorers Could Be Given New Lives
From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Oct 12 13:17:52 2005
Robotic comet explorers could be given new lives
BY STEPHEN CLARK
October 10, 2005
The future may not be empty for a pair of NASA space probes that are
wrapping up their primary missions this year, as the agency plans to
formally announce the availability of the platforms this fall to gather
proposals from the academic and science communities.
The Deep Impact and Stardust projects are both part of NASA's Discovery
program, which aims to develop high-performance and ambitious missions
for lower costs than earlier robotic space explorers. Expenses are
capped at several hundred million dollars for prime missions, and teams
are urged to be ready to launch within 36 months from the official start
of the project.
A formal Announcement of Opportunity is expected to be released this
fall, though the date could be pushed into the winter if a Congressional
inquiry into last year's solicitation is not completed in time. Details
of the inquiry could not be obtained, other than it covered the
"guidelines followed and decisions made" in 2004's Announcement of
Opportunity, according to Discovery program scientist Susan Niebur.
Proposals will be due 120 days after the announcement is released, and a
decision will be made in the months following the receipt, Niebur said.
Missions starting from scratch are to be conducted for a cost to NASA of
less than $450 million and must be launched by the end of May 2013.
Missions of opportunity - like those possible for Deep Impact and
Stardust - are constrained to a cost of $35 million to the government.
"The evaluation criteria will be similar to criteria used in previous
Discovery program Announcements of Opportunity, that is, scientific
merit, scientific implementation merit and feasibility, and technical
merit and feasibility," Niebur said in response to written questions.
"The last criterion will have to include the appropriateness of the
proposed investigation for the available hardware and consumables," she
Deep Impact's thrusters completed a trajectory correction burn July 20
that put the craft in a storage orbit, followed on August 9 by the
placement of the spacecraft into deep sleep by ground controllers. Its
course will bring it toward Earth for a speedy fly-by on December 31, 2007.
"This maneuver will keep the spacecraft in the vicinity of the inner
planets, thereby making the task of tracking and communicating with it
easier," said Andy Dantzler, Director of the Solar System Division of
NASA's Science Mission Directorate.
"The spacecraft is being offered as is. Proposers must include mission
management and spacecraft operations in the total proposed funding."
Stardust is on the final leg of its trip back to Earth after streaking
past comet Wild 2 in early 2004. During the high-speed encounter,
Stardust collected microscopic samples of the
comet's dusty environment to be returned to Earth in a small capsule for
study by scientists in laboratories on the ground. Its sensitive aerogel
collector plates were also exposed to space for several months en route
to Wild 2 to retrieve interplanetary dust samples.
The material will parachute to the ground in Utah on January 15 of next
year, while the main spacecraft will continue in its solar orbit after
releasing the return capsule. A divert burn will allow Stardust to miss
Earth, and officials estimate around 44 pounds of propellant will remain
inside its on-board reservoirs.
"Proposals to reuse the Stardust spacecraft are also welcome," Niebur
said. "It is anticipated that the consumables available on Stardust will
make this more challenging, however, NASA is willing to consider
proposals that are able to propose within the stated constraints."
Stardust has been in space - and thus using propellant reserves - since
1999 while covering a total distance of over three billion miles, while
Deep Impact was recently launched in January for the comparatively short
trip to Tempel 1.
The propulsion system aboard Stardust is relatively modest compared to
many deep space missions. The monopropellant design uses just hydrazine
given the low-energy trajectory Stardust's primary mission took. Deep
Impact's thrusters are also fueled by hydrazine and were designed to
provide for a mission total of just over 600 feet per second of velocity
Estimates indicate that about 143 pounds of Stardust's hydrazine fuel
will have been used by January, leaving about a quarter of the craft's
original lot of propellant left in the tank. Almost 35 pounds of fuel
currently remains aboard Deep Impact - enough for a change in velocity
of around 213 feet per second.
Stardust carries a small group of instruments that includes a cometary
and interstellar dust analyzer, a dust flux monitoring device that
detects particles around the craft, and an optical navigation camera.
"Deep Impact and Stardust were engineered first and foremost to be able
to achieve their prime missions, interaction with comets Tempel 1 and
Wild 2. Although these primary missions have been the top priority, each
has some capacity remaining that we are willing to make available to the
space science community," explained Niebur.
Other missions under the Discovery program umbrella have included the
NEAR-Shoemaker asteroid orbiter, 1997's historic Mars Pathfinder
mission, the Lunar Prospector, the Genesis solar wind catcher, the
failed CONTOUR cometary mission, and the MESSENGER probe currently en
route to orbit the planet Mercury. Two more flights are on the books for
launch next year and in 2008.
Deep Impact achieved its objective on July 4, when a 816-pound
copper-laden impactor earlier released from a mothership smacked
into comet Tempel 1 at over six miles per second.
Though the collision destroyed the impactor, the mothership completed a
close fly-by of the comet to observe the affects of the impact in great
scientific detail. Its high-resolution camera captured impressive images
of the impact and the debris ejected away from the comet's surface. The
instrument contains an 11.8-inch aperture telescope, an infrared
spectrometer, and a multi-spectral camera. The fly-by craft also carries
a medium-resolution camera as a backup.
Ball Aerospace and Technologies Corporation of Colorado, the prime
contractor for Deep Impact, built the instruments.
The high-resolution camera traces its heritage to work done by Ball on
the Wide Field Camera 3, which was developed for the Hubble Space
Telescope but is stranded on the ground due to the questionable
possibility of a future space shuttle servicing mission to Hubble. Deep
Impact's imager is sensitive enough to resolve a car from a distance
equal to the width of the state of Colorado.
About the size of a typical sports utility vehicle - and weighing 1,430
pounds at launch - the fly-by spacecraft could use its optical and
science suite to study other valuable targets in the solar system.
One such possible destination is Boethin, which is a Jupiter family
comet that orbits the Sun about every 11 years. Deep Impact could use
its unique cameras and spectrometer as it flies past to add its
characteristics to the ever-growing database of closely observed comets.
The Earth fly-by in late 2007 could be used as a gravity assist maneuver
to slingshot Deep Impact toward Boethin by around the end of 2008.
The mission extension to comet Boethin comes from a proposal being
planned by the University of Maryland, which was the institution
responsible for science operations and analysis for this summer's impact
at Tempel 1.
Scientists have also long been advocating a similar mission to create
craters on an asteroid, dubbed Deep Interior.
"It would be helpful to have a similar type of mission go to an asteroid
and compare the results," said Deep Impact Co-investigator Lucy McFadden
of the University of Maryland. "That mission is Deep Interior. It has
been proposed in the past to NASA's Discovery program, but has not been
Deep Interior would use radio reflection data to determine the structure
of the asteroid, which scientists have long hypothesized as widely
varying from dense rock to "rubble piles" with potential internal voids.
It could also carry with it explosives to be released on the asteroid to
blast 100-foot craters in the surface for further studies. The
spacecraft could visit several near-Earth objects during its mission.
"Would we want to do the same thing to a different type of comet? I
don't want to answer that question until we have analyzed the results
from this comet. It depends on what picture we piece together from
observing beneath this comet's surface," McFadden said.
Comets and asteroids are on the radar screen of scientists because they
are ancient relics left over from the earliest period of the formation
of the solar system. It is believed that material remaining from the
early solar system could still be harbored inside the icy comets, while
asteroids - essentially mini-planets - give researchers clues about how
Received on Wed 12 Oct 2005 01:16:16 PM PDT