A Scientific Rationale for Mobility in Planetary Environments (1999) / Chapter Skim
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3 Technological Capabilities
3 Technological Capabilities
Pages 28-52
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What are the associated needs for sample acquisition? · Terrestrial field demonstrations.
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But mission scientists want to retain some control over the rover and its operations. If they do, in the words of the Mars 2001 Science Definition Team, "the rover would spend most of its time stationary waiting for instructions from home and so distances traveled would be greatly reduced as would the number of analyses, images ...."~6
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Smith, Space Activities of the United States, CIS, and Other Launching Countries/Organizations: 1957-1994, Congressional Research Service 95-873 SPR, Library of Congress, Washington, D.C., 1995, p.
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Antennae \ I_ TV cameras /~ Solar panels 5~ FIGURE 3.1.1 This sketch shows the basic features of the former Soviet Union Lunokhod rover. Two such vehicles were deployed on the Moon in the early 1970s.
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The chemical data returned included some surprises, such as rocks with sufficient SiO2 that quartz appears in their calculated "normative" mineral compositions, and with higher SiO2 than any of the known martian meteorites or any martian soils. Sojourner was originally designed to conduct a 7-day mission on the martian surface.
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Sojourner's principal scientific instrument, the rear-mounted alpha-proton x-ray spectrometer, is visible on the extreme left, below the solar array. Photograph courtesy of the Jet Propulsion Laboratory.
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· Total mass · Payload mass · Range · Lifetime 100 to 1000 kg 35 to 150 kg 0.1to10kmperday months to years Minirovers are more modest, battery- and solar-powered vehicles developed in the context of the austere Mars mission concepts that were devised in the early 1 990s. The smaller vehicles in this class might not, in general, be capable of travel far from their landing sites.
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The Athena rover, scheduled to be deployed by a future Mars Surveyor mission, represents a significant step in achieving some of these objectives. Although it is similar in its mobility design to Sojourner, it is much larger and some 50 percent more massive (Figure 3.1~.
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Courtesy of Brian Wilcox, Jet Propulsion Laboratory.
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Balloons The former Soviet Union's Vega 1 and 2 spacecraft deployed balloons in Venus's atmosphere in 1985 (see Box 3.5~. These drifted with the prevailing winds at fixed altitude in the atmosphere, surviving for almost two Earth days.
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The hopper was designed to sample 10 sites during its 4-hour, batterypowered lifetime.4 FIGURE 3.4.1 Hopping is an appealing means of providing mobility in a low-gravity environment. The former Soviet Union planned to use hoppers to undertake multipoint measurements on the martian moon, Phobos, in the late 1 980s as part of the ambitious, but unsuccessful, Phobos program.
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5 Nepholometer windows Meteorology block Illuminatlon detector Y i -Straps FIGURE 3.5.1 This diagram illustrates the general arrangement of the instruments carried by the balloons released into Venus's atmosphere by the former Soviet Union's Vega spacecraft in 1985. Illustration reprinted, adapted, from R.S.
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They traveled more than 11,000 km, with Vega 1 going slightly farther, covering 109 degrees of longitude, just 4 more degrees than its successor, Vega 2.2 The balloons alternated between 25 minutes of data gathering (often taking measurements every 90 seconds in order to conserve power) and 5 minutes of Earth-relay.3 The Vega balloons were tracked interferometrically by an international array of antennae that included NASA's Deep Space Network.4 Both balloons fulfilled nearly all of their planned science objectives.
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· Touchdown. The ability to touch down is important because it would allow study of the atmospheric boundary layer structure, permit sample collection, and provide for soft deployment of geophysical or atmospheric surface stations.
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Another disadvantage is, ironically, a consequence of the balloon's inherent advantages as a platform for high-resolution imagery and spectroscopy, which generate such large volumes of information that necessary data rates may stress the uplink capabilities to, and on-board memory of, a relay orbiter. Future Developments Several development thrusts are clearly called for, which include the following: planets; · Studying the use of reversible fluids for altitude control of balloons on Venus and Titan; · Studying methods to attain altitude control with an infrared-heated balloon in the atmospheres of the giant · Designing science instruments that are of significantly smaller mass than those currently available; and · Devising techniques to increase data rates by at least an order of magnitude.
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From page 43... ...
The Mars Polar Pathfinder Discovery mission concept envisages the use of a 22-cm-long thermal probe to measure the thermal profile and conduct optical measurements of the ice to a depth of some 150 m in Mars's northern polar cap.4i An exciting analog for Europa exists on Earth; about 4 km beneath the surface of the antarctic ice cap is a large body of water, Lake Vostok, that is about the size of Lake Ontario. It is likely that both the ice above Lake Vostok and the lake itself harbor microorganisms that have been isolated from the active Earth's atmosphere and hydrosphere for a very long time, perhaps for as long as 105 to 106 years.42 43 Whether the ice and the putative water
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These studies should be carried out by a consortium of scientists and engineers, many of whom will not be directly associated with NASA. SAMPLE ACQUISITION A review of the various documents outlining plans for future space exploration is sufficient to gain a sense of the importance of sample acquisition.44 These sample-acquisition plans cannot succeed unless devices capable of collecting samples are present on landers and, even more importantly, on mobile platforms.
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From page 45... ...
The Mars Polar Lander, scheduled to touch down on the northern edge of Mars's southern polar cap in 1999, for example, will be equipped with a 2-m robotic arm with a microscope camera at its tip. Similarly, the Mars Surveyor 2001 lander may be equipped with an arm designed to collect soil samples and deliver them to instruments for analysis.
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The nominal sample acquisition area was a 15 m2 sector in front of the lander. The Viking sample collection assembly consisted of a head attached to a 3-m furlable boom (Figure 3.6.1~.
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The lid top was a metal sieve with 2-mm-diameter holes, designed to deliver sifted samples to the instruments. The Viking sample collection assembly successfully: · Collected soil from a variety of locations within the sample collection area around the landing site, · Pushed a moderately sized rock approximately 12 to 15 cm away from the lander,3 and · Rolled over a moderately sized rock and collected soil from beneath it.
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Finally, the total systems, including human operators, must undergo testing under conditions as similar as possible to those to be experienced on other solar system bodies. Various balloon and acrobat concepts have undergone field testing on Earth in anticipation of deployment on Venus, Mars, or Titan.5i Rovers have been tested extensively for many years; important recent examples include tests of the Mars Pathfinder Sojourner rover using a simulated Mars surface environment, and the field tests of Rocky 7 at Lavic Lake, California,52 and of Nomad in the Atacama Desert of Chile.53
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From page 49... ...
Lessons Learned from Sojourner Operations Operation of the Sojourner rover on the Mars Pathfinder mission also provided opportunities for field testing, both on Earth (operational readiness tests) and in the martian environment.
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With the twice-da~ly communications sessions scheduled for future Mars Surveyor missions, this downtime could amount to 90 percent. Field demonstrations offer a ready means to develop and validate schemes for autonomous operations and to develop techniques for their harmonious integration with the limited periods when mission scientists will be in the control loop.
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Dias, United States Planetary Rover Status, JPL Publication 90-6, Jet Propulsion Laboratory, Pasadena, Calif., 1989.
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From page 52... ...
57. Office of Space Science, National Aeronautics and Space Administration, Report of the Mars Surveyor 2001 Science Definition Team, National Aeronautics and Space Administration, Washington, D.C., 1997, p.
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