Exploration of Mars over the next ten years will focus on climate,
life, and resources, with determination of the presence of water and
the nature of current and past hydrologic cycles as key elements of
the exploration strategy. Autonomous rovers capable of kilometers of
traverse distances, in-situ measurements of soil and rock properties,
and sample caching for subsequent return sample missions will be
important components of missions designed to meet these objectives.
Two deployments using the Rocky 7 rover to Mars-like sites in the
Mojave Desert are described in these pages, one in December
1996 and one in May 1997. The experiments are designed to: (a)
evaluate the ability of rovers to conduct autonomous traverses, (b)
maneuver instrumented robotic arms to acquire in-situ geochemical
data, and to acquire and cache samples, and (c) better understand how to
conduct long-term mission operations at low cost.
The following paragraphs give an overview of Mars rover missions over
the next decade to provide background for understanding the rationale
for field experiments in the Mojave Desert.
Mobility
A major element of Mars Rover Missions will be the ability of a rover
to traverse autonomously a complex area (soils littered with blocks,
with some bedrock exposures) with only waypoint information provided
by uplink telemetry. Descent images can be used to place the rover
on the surface and to define initial targets for the traverses. Then
on-board, stereo imagers (blue and red
bands would be suitable, with the visual acuity of the human eye and
standing at least 1 m above the surface) could acquire data for the traverse
area. The data would be downlinked and viewed by scientists and
mission specialists. Scientists would then update targets or
destination points for traverses, and mission specialists would select
waypoints to guide the rover to the locations. The on-board system
should then be able to process the data and provide commands to drive
the system to the desired locations. Selected science imaging data
could be acquired along the way and downlinked. The downlinked
science image data would be examined by scientists to determine if
mid-course changes are necessary because of the discovery of
interesting surfaces; e.g., rocks that show cross bedding.
In-Situ Measurements
A second key aspect of Mars Rover missions will be the determination of
the composition and mineralogy of soils and rocks. The first step
would be an analysis of multispectral imaging data to find areas of
interest. Then a point reflectance or emission spectrometer would be
used to acquire spectral reflectance or emission spectra for key
regions, using a single pixel or modest array of spectral data for the
target of interest. The rover would be commanded to go to the target.
Once positioned, an arm would be used to get instrumentation close to
the relevant surfaces. Instruments of interest might be a close-up
imager and one or more instruments that would determine mineralogy
and/or chemistry for the selected surfaces. Rock surfaces might be
vertical, horizontal, or inclined at some angle between vertical and
horizontal. Therefore, the arm should be able to position the
instrument in a horizontal position at a height above the surface of
20 to 30 cm and to be able to measure the inclination of the rock
surfaces. Also, the arm should be able to place instruments in the
nadir (down-pointing) position on the surface. The activities should
be accomplished by commanding waypoint positions using stereo imaging
data. All measurements should be downlinked. The exact sequence of
events (close up imaging first or geochemistry/mineralogy first, etc.)
should be commandable.
Sample Acquisition and Caching
A key aspect of Mars sample return is the ability to select materials,
including atmosphere, soils and rocks. Sampling the atmosphere is the
easiest to accomplish, once the rover is away from the landing site
and any lingering effects of degassing of airbags or rocket exhaust
imbedded into the surface soils are removed. Opening a valve,
letting in the required amount of atmosphere and sealing the container
after sample acquistion are all that are required. Collection of soils
could be done as bulk material scooped from the surface and placed
into containers that can be sealed after sample acquisition. Some
processing of soils, including removing fines and examining the coarse
fraction with close-up imaging (for unweathered lithic fragments) is
also of interest. This might be accomplished by use of a rake.
Selection and manipulation of rocks using a rover will pose
technological challenges. Yet rocks probably offer the best ties to
geology (and climatic history) since they are highly likely to have
local origins, as opposed to soils. Available evidence suggests soils
on Mars are complex, with a large wind-blown component and some
cementation by salts. Thus it is important to be able to select
rocks, using the types of measurements described in the previous
section, and to then place them in containers that can be sealed. If
the work were done by a human, the rocks would also be processed by
breaking away unneeded sections and keeping the best pieces (e.g., the
limestone portions of a multimict sample). The kinds of rovers that
might operate in the next decade will probably have the ability to
acquire small rocks. This might be done by collection of rock
fragments from raked soils.
The rocky surface of Mars as seen by Viking Lander 1.
Mission Operations
Operation of a rover on Mars will probably be done in a geographically
distributed environment to minimize costs and dislocations of
engineers and scientists over the course of a long rover mission.
For instance, two Earth years might be needed to rove several to tens of
kilometers.
The rocky surface of Mars as seen by Viking Lander 1.