Posted on 11/17/2005 8:32:34 PM PST by strategofr
JPL D-8822, Small Mission Design Team, Exploration Initiative Studies Office, NASA Jet Propulsion Laboratory, October 1991.
The Jet Propulsion Laboratory (JPL) Exploration Initiative Studies (EIS) Office, established in September 1989, was the successor of JPL's Mars Rover Sample Return (MRSR) Development Flight Project Office [read] and the Space Exploration Initiative (SEI) Precursor Task Team [read]. Beginning in late 1990, the EIS Office Small Mission Design Team (SMDT) studied a Mars Sample Return (MSR) mission conducted on "a smaller and more affordable scale" than MRSR using microtechnology developed for the Strategic Defense Initiative (SDI) anti-missile system. The SMDT notes that SDI microtechnology is designed for short-duration military operations; it would thus need long-duration space testing before it could be applied to MSR. The SMDT derived its MSR concept from the Direct Return microspacecraft alternative in Martin Marietta's October 1990 MRSR Delivery and Return Study final report [read] prepared for NASA's Johnson Space Center. Martin Marietta aided the SMDT's study at its own expense. The design team acknowledges that the SEI Synthesis Group's May 1991 report [read] did not include MSR among its recommended robotic precursors to a piloted Mars mission, but asserts that MSR is, nonetheless, "a valid candidate for a robotic Mars mission in the SEI context as well as a science mission on its own." The proposed SMDT MSR flight system includes the following five hardware elements:
* The Sample Return Lander (SRL) weighs 145.7 kilograms with 37.2 kilograms of nitrogen tetroxide oxidizer and hydrazine fuel in its four spherical tanks. It has three foldable landing legs providing 50 centimeters of ground clearance, three main engines, four steering rocket clusters, a Radioisotope Thermal Generator (RTG) for electric power and heating, nine kilograms of science instruments, separate booms for imager, weather station, and antenna, a support ring for the Mars Ascent and Return Vehicle (MARV), an underslung "parking garage" platform for the Mini-rover, a pair of Mini-rover ramps, and sample loading gear. The design team opts for an RTG over solar panels because dust storms can coat the latter, reducing their electricity output and limiting SRL lifetime. The lander measures 2.47 meters across its legs and stands 2.3 meters tall from its footpads to the MARV's dome-shaped nose. The antenna boom adds a further 84 centimeters of height.
* The two-stage MARV weighs 491.4 kilograms with 401.4 kilograms of liquid chloropentafluoride (CPF) oxidizer and hydrazine fuel (a high-energy propellant combination under development for SDI). The MARV first stage measures 1.38 meters tall and 1.13 meters in diameter and has three main engines. The second stage, which nests inside the first stage and carries the Sample Return Capsule (SRC) on its front, measures 1.07 meters tall and 69.8 centimeters in diameter. The SMDT places the second stage upside-down within the first stage, so that its single engine faces in the direction of flight during first-stage operation. This arrangement facilitates sample loading by placing the SRC near the ground. (The joint Langley/JPL MSR study team opted for a similar design approach in 1975 [read].)
* Sample Return Capsule (SRC): The SMDT considered both conical "Apollo" and spherical shapes for its SRC. A spherical SRC would not have to precisely orient itself for Earth atmosphere entry, but would need a heatshield over its entire surface. It would thus have 1.5 times a conical SRC's volume, which would demand a larger MARV diameter, with knock-on effects throughout the MSR spacecraft design. The SMDT's conical SRC measures 50 centimeters across its bowl-shaped heatshield by 29.1 centimeters tall and weighs 18.8 kilograms with a 0.5-kilogram sample inside.
* The 17-kilogram Mini-Rover is "a mobile instrument platform" designed "to bring science instruments to the samples and to bring the samples back to the lander." It rolls across Mars' surface on three pairs of 12.7-centimeter-diameter wheels. Each wheel sports independent suspension, steering, and power, enabling the little automated explorer to turn within its own length, surmount rocks up to 19 centimeters tall, and reach a speed of 0.57 kilometers per hour on a smooth hard surface. The Mini-rover measures 46.7 centimeters wide, 64.9 centimeters long from its rear-mounted RTG to its front-mounted sample scoop, and 34.9 centimeters tall (not including its top-mounted whip antenna). Two forward-mounted imagers provide stereo views, and three rock analysis instruments aid sample selection. Communication between Earth and Mini-rover is relayed primarily through a Communications Orbiter (CO) in Mars orbit, though relay through the SRL is typical when the Mini-rover is within line of sight. Mostly the Mini-rover drives itself, though controllers on Earth can teleoperate it if necessary using a Computer-Assisted Remote Driving (CARD) technique. CARD takes into account the long trip time for radio signals between Earth and Mars (up to 45 minutes).
* The 2.2-meter-tall Blunt Cone Aeroshell (BCA) contains the other four MSR flight system elements from Earth launch until just before Mars landing. It consists of a 3.5-meter-diameter heatshield and a conical aft cover containing a radio system, navigation sensors, 12 thrusters for course corrections and attitude control, and the landing parachute. With 12.5 kilograms of nitrogen tetroxide/hydrazine propellants in its tanks the BCA weighs 261.6 kilograms.
Total MSR flight system weight comes to 917 kilograms. The SMDT assumes that its MSR mission will be part of a Mars program spanning 2001-2011 that will also see a network of weather/seismic surface stations akin to MESUR [read], site survey landers and orbiters, and communications relay orbiters. The first MSR launch might occur as early as 2003, though the team favors the 2007 Earth-Mars transfer opportunity. The 2007 mission occurs as follows:
1. MSR flight system launches (November 21-December 20, 2006): An Atlas IIAS launch vehicle boosts two MSR flight systems toward Mars. The twin spacecraft separate from the spent Atlas IIAS upper stage and each other to coast to Mars independently. A second Atlas IIAS launches another MSR flight system pair no less than 10 days later.
2. MSR flight system Earth-Mars transfer: The 2005 and 2007 Mars transfer opportunities are unfavorable, meaning that a spacecraft needs more energy to reach Mars than in the 2001, 2003, 2009, and 2011 opportunities. To compensate for this, the SMDT invokes a low-energy Type IV trajectory, which sees the MSR flight systems circle the Sun slightly more than one and a half times en route to Mars. Spacecraft following more commonly used Type I and II trajectories typically need between six and 12 months to reach Mars, with as little as four months possible - the MSR flight systems launched in 2007 need about 26 months. Fifteen days after Earth launch, the MSR flight systems use thrusters on the BCA to perform course corrections that space their Mars arrival times at least 24 hours apart.
3. Communications Orbiter (CO) launches (September 5-October 4, 2007): Two Delta 7925 rockets launch one CO each toward Mars on Type II trajectories.
4. CO Mars orbit arrival (August 2008): The twin COs fire rocket motors to slow down so Mars' gravity can capture them. After they reach Mars orbit, they provide navigation data to controllers on Earth, who use these to target the MSR flight systems to landing sites on Mars no larger than 50 kilometers across. One functional CO in Mars orbit is sufficient to perform the MSR mission.
5. MSR flight system Mars landings (January 19-March 1, 2009): Each MSR flight system enters Mars' atmosphere directly from its interplanetary trajectory with no stop in Mars orbit. Landings occur in daylight to permit surface imaging during descent. Scientists use descent images to create maps of the terrain up to 10 kilometers from the SRL touchdown point for Mini-rover traverse planning. The BCA heatshield separates 10 kilometers above Mars and the parachute opens. The SRL, with MARV, SRC, and Mini-rover on board, then separates from the aft cover, unfolds its legs, and fires its main engines. A "simple" hazard avoidance system using a "multi-laser ranger" lets the SRL steer past boulders, crevices, and steep slopes to a soft landing. Immediately after touchdown the SRL extends its imager boom and takes a panorama while controllers on Earth locate the lander to within five meters using descent images and CO data.
6. Sampling operations begin after a five-day post-landing SRL checkout. In many MSR plans that include a rover, the lander includes a robot arm that can serve as a backup sample collector. To save weight and cut complexity, the SMDT relies entirely on the Mini-rover to collect samples. During surface mission Days 6 through 17, a single Mini-rover collects a contingency sample (soil and, if possible, a pebble) within the terrain visible to the SRL imager. Ramps deploy from opposite sides of the SRL and the Mini-rover rolls down the least-obstructed one to the surface. The Mini-rover's sampling arm carries a scoop, a removable sample canister, and an Alpha Proton X-Ray Spectrometer (APXS) for determining rock and soil composition. The Mini-rover images a prospective sampling site, tips its arm down to place the scoop in contact with the surface, then rolls forward to drive the scoop into the ground. The arm then tips up so the sample spills backward into the sample canister. Tipping the arm also tilts the APXS into position for operation. The Mini-rover images the sampling site again, then returns to the lander and ascends a ramp into its garage. There it hands the full sample canister to the "carousel" sample handler and picks up an empty canister. It then returns to the surface to continue sampling. Assuming that the contingency sample traverse succeeds, the other Mini-rovers deploy from their SRLs on Day 18 (March 18, 2009). The SMDT acknowledges that samples collected near the SRL might contain contaminants deposited by the main engines; thus, if any of the Mini-rovers succeed in collecting additional samples beyond the contamination zone, the carousel will likely discard the contingency sample. The Mini-rovers each conduct 10 traverses, collecting one 100-gram sample per traverse. Scientists select five samples from each Mini-rover for Earth return, bringing the total sample from each landing site to 0.5 kilograms. Traverses occur only in daylight, with about seven hours spent rolling per day. Controllers lengthen the traverses to perhaps 10 kilometers as they gain experience. Each Mini-rover might cover a total of 40 kilometers. Sample collection continues until Day 120 (June 29, 2009).
7. MARV ascent to Mars orbit (July 7-23, 2009): Preparations for MARV liftoff begin on surface mission Day 131 (June 30, 2009). The sample-laden carousel on each SRL is raised into the cylindrical Sample Canister Assembly (SCA) in the SRC. Meanwhile, each Mini-rover plants a seismometer 10 meters away from its lander, then moves away a safe distance (several hundred meters). On July 7, 2009, controllers begin a one-day countdown to the first MARV launch. Launches then occur four days apart. The Mini-rovers attempt to image MARV ascent. Science instruments on the SRLs continue to radio data to Earth after MARV liftoff, thus contributing to the Mars surface science network.
8. MARV Mars orbit departure (July 25-August 3, 2009): The MARV second stages separate from their spent first stages in 200-kilometer circular orbit. They spin for stabilization, then ignite their engines to leave Mars orbit three days apart. Mini-rover exploration resumes after the last MARV second stage departs for Earth.
9. MARV Mars-Earth transfer: The MARV second stages follow low-energy Type IV trajectories, reaching Earth's vicinity after about nine months.
10. SRC Earth recovery (May 2010): The MARV second stages reach Earth over several days. Each ejects its SRC two days prior to Earth arrival then fires its engine to change course so that it misses Earth. The SRC reenters Earth's atmosphere directly and deploys a parachute, then an aircraft snatches it in mid-air.
The SMDT envisions that its MSR mission will occur over two Earth-Mars transfer opportunities. Two months after the 2007 MARV second stages depart Mars, two Atlas IIAS rockets launch four more MSR flight systems from Florida. Because the 2009 Earth-Mars transfer opportunity is favorable, the spacecraft follow Type II (conjunction class) trajectories leading to Mars landings in September 2010. They depart Mars in August 2011 and reach Earth in July 2012. If all the MSR flight systems from the 2007 and 2009 opportunities succeed, then as much as four kilograms of martian materials from eight widely scattered sites will reside in Earth laboratories less than six years after the first MSR flight system launch. The SMDT notes that an MSR mission cost of less than $2 billion might restore enthusiasm for the concept, which the costly (about $10 billion) MRSR design had quashed. The team, however, offers no cost estimate for its program, explaining that
the capability to cost missions using rovers and a high degree of new microtechnology is not mature enough for a cost estimate to be made concurrently with the design...nor is it credible to say at this time whether the mission could be done for $2B[illion] or less.
Just a proposal.
About 1% as nutty as sending people along.
They're talking about launching a year from now and they haven't built hardware yet? Yeah, right...
"They're talking about launching a year from now and they haven't built hardware yet? Yeah, right."
I was unable to place a date on this article. It is probably very old.
"About 1% as nutty as sending people along."
Upon reflection, I retract the "almost nutty" comment. The idea is really kind of cool.
Ah, you are correct. The top of the article says 1991. Ancient history. Heck, 2003 is ancient history when planning missions...
300 pounds of hardware doesn't seem to match the 'micro' description closely.
"300 pounds of hardware doesn't seem to match the 'micro' description closely."
too heavy or too light?
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.