MARS PATHFINDER
Mars Pathfinder was launched on December 4, 1996 at 1:58:07 am EST on a
Delta II rocket. After an uneventful journey, the spacecraft safely
landed on the surface of Mars on July 4, 1997. Its landing on the Ares
Vallis plain was confirmed at 1:07 p.m. EDT. The air bag landing system,
tested at Glenn's Plum Brook Station in Sandusky, Ohio, performed well.
The first set of data was received shortly after 5:00 p.m. followed by
the release of images at 9:30 p.m. The Sojourner rover, with three Lewis
components, then began its Martian trek and returned images and other
data over the course of three months. After operating on the surface of
Mars three times longer than expected and returning a tremendous amount
of new information about the red planet, NASA's Mars Pathfinder mission
completed the last successful data transmission cycle from Pathfinder at
6:23 a.m. EDT on Sept. 27, 1997.
NASA's Glenn Research Center has a long history of involvement with missions to Mars. Glenn managed the launch of the Mariner, Viking and Mars Observer missions. NASA Glenn was a key participant in the Mars Pathfinder mission, an engineering proof-of-concept mission. The intent was to demonstrate the successful deployment of scientific instruments, including a small rover, on a planetary body and to gain engineering design information.
NASA Glenn has been involved in the Mars Pathfinder Mission nearly from the beginning. The Mars Solar Energy Model provided an early demonstration that sufficient solar energy is available at Mars to provide operating power for a spacecraft and lander. This solar energy model was incorporated into the computer model used by JPL to design solar arrays for the Pathfinder lander, and the Sojourner Rover.
The Jet Propulsion Laboratory, which is heading the Pathfinder mission, requested Glenns' aid in several areas. To help meet mission objectives, Glenns' Plum Brook Station was used to test the Pathfinder airbag landing system for JPL. To help meet science objectives, JPL requested that Glenn develop a means to obtain information on the abrasiveness and adherence properties of Mars soil and dust. Consequently, Glenn developed three flight sensors for experiments on the Pathfinder Microrover, named "Sojourner." Also delivered were several small tungsten points for removing electrostatic charge accumulated during rover surface operations.
The Wheel Abrasion Experiment (WAE) gathered soil abrasion information by observing a special rover wheel wear. The center section on one of the rover's six wheels was coated with thin layers of nickel, aluminum, and platinum. Changes in the metal layers' reflectance due to wear were detected by a photocell.
The Materials Adherence Experiment (MAE) was designed to determine how much dust lands on the solar array of the Sojourner Rover. It did this by using two sensors: a solar cell sensor, which measured how much light was obstructed by dust landing on a transparent cover, and a quartz crystal monitor, which measured the mass of dust deposited on the array. Some initial measurement of dust settling data has been made available.
Tests and calculations confirmed the possiblity that the rover would accumulate a large static charge during its surface operations. Since actual martian conditions are unknown, JPL followed Lewis' recommendations and added discharge points to the rover's antenna as a precaution. If the rover accumulated electric charge, some, or all of it should have been removed to the atmosphere through the discharge points.
NASA's Glenn Research Center has a long history of involvement with missions to Mars. Glenn managed the launch of the Mariner, Viking and Mars Observer missions. NASA Glenn was a key participant in the Mars Pathfinder mission, an engineering proof-of-concept mission. The intent was to demonstrate the successful deployment of scientific instruments, including a small rover, on a planetary body and to gain engineering design information.
NASA Glenn has been involved in the Mars Pathfinder Mission nearly from the beginning. The Mars Solar Energy Model provided an early demonstration that sufficient solar energy is available at Mars to provide operating power for a spacecraft and lander. This solar energy model was incorporated into the computer model used by JPL to design solar arrays for the Pathfinder lander, and the Sojourner Rover.
The Jet Propulsion Laboratory, which is heading the Pathfinder mission, requested Glenns' aid in several areas. To help meet mission objectives, Glenns' Plum Brook Station was used to test the Pathfinder airbag landing system for JPL. To help meet science objectives, JPL requested that Glenn develop a means to obtain information on the abrasiveness and adherence properties of Mars soil and dust. Consequently, Glenn developed three flight sensors for experiments on the Pathfinder Microrover, named "Sojourner." Also delivered were several small tungsten points for removing electrostatic charge accumulated during rover surface operations.
The Wheel Abrasion Experiment (WAE) gathered soil abrasion information by observing a special rover wheel wear. The center section on one of the rover's six wheels was coated with thin layers of nickel, aluminum, and platinum. Changes in the metal layers' reflectance due to wear were detected by a photocell.
The Materials Adherence Experiment (MAE) was designed to determine how much dust lands on the solar array of the Sojourner Rover. It did this by using two sensors: a solar cell sensor, which measured how much light was obstructed by dust landing on a transparent cover, and a quartz crystal monitor, which measured the mass of dust deposited on the array. Some initial measurement of dust settling data has been made available.
Tests and calculations confirmed the possiblity that the rover would accumulate a large static charge during its surface operations. Since actual martian conditions are unknown, JPL followed Lewis' recommendations and added discharge points to the rover's antenna as a precaution. If the rover accumulated electric charge, some, or all of it should have been removed to the atmosphere through the discharge points.
- Imager For Mars Pathfinder (IMP)
- Alpha Proton X-Ray Spectrometer (APXS)
- APXS Deployment Mechanism
- Atmospheric Structure Instrument/Meteorology Package (ASI/MET)
Imager For Mars Pathfinder (IMP)
The Imager For Mars Pathfinder is a stereo imaging system with color
capability provided by a set of selectable filters for each of the two camera
channels. It has been developed by a team lead by the University
Of Arizona with contributions from the Lockheed
Martin Group, Max Planck Institute
For Aeronomy in Lindau, Germany, the Technical
University Of Braunschweig in Germany and the Ørsted
Laboratory, Niels Bohr Institute for Astronomy, Physics and Geophysics
in Copenhagen, Denmark. It consists of three physical subassemblies: (1)
camera head (with stereo optics, filter wheel, CCD and pre-amp, mechanisms
and stepper motors); (2) extendable mast with electronic cabling; and (3)
two plug-in electronics cards (CCD data card and power supply/motor drive
card) which plug into slots in the Warm Electronics Box within the lander.
Azimuth and elevation drives for the camera head are provided by stepper
motors with gear heads, providing a field of regard of ±180 degrees
in azimuth and +83 degrees to -72 degrees in elevation, relative to lander
coordinates. The camera system is mounted at the top of a deployable mast,
a continuous longeron, open-lattice type provided by Able Manufacturing,
Inc. When deployed, the mast provides an elevation of 1.0 m above the lander
mounting surface.
The focal plane consists of a CCD mounted at the foci of two optical paths where it is bonded to a small printed wiring board, which in turn is attached by a short flex cable to the preamplifier board. The CCD is a front-illuminated frame transfer array with 23 micrometer square pixels. Its image section is divided into two square frames, one for each half of the stereo FOV's. Each has 256x256 active elements. A 256x512 storage section (identical to the imaging section) is located under a metal mask. The imp focal plane and electronics are nearly identical copies of the comparable subsystem employed in the Huygens Probe Descent Imaging Spectroradiometer (DISR), using the Loral 512X512 CCD.
The stereoscopic imager includes two imaging triplets, two fold mirrors separated by 150 mm for stereo viewing, a 12-space filter wheel in each path, and a fold prism to place the images side-by-side on the CCD focal plane. Fused silica windows at each path entrance prevent dust intrusion. the optical triplets are an f/10 design, stopped down to f/18 with 23-mm effective focal lengths and a 14.4 degree field of view. The pixel instantaneous field of view is one milliradian. The filter wheel four pairs of atmospheric filters, two pairs of stero filters, eleven individual geologic filters (which, when combined with the two pairs of stereo filters, result in thirteen distinct geologic filters) and one diopter or close-up lens, designed to acquire images of magnetic, wind-blown dust which adheres to a small magnet located on the IMP tip plate.
Full panoramas of the landing site are acquired during the mission using the stereo baseline provided by the camera optics. Additionally, monoscopic panoramas are acquired both prior and subsequent to the mast deployment, yielding vertically displaced stereo pairs with approximately 80 cm baseline. Images of a substantial portion of the visible surface are acquired in multispectral images with as many as eight spectral bands.
The focal plane consists of a CCD mounted at the foci of two optical paths where it is bonded to a small printed wiring board, which in turn is attached by a short flex cable to the preamplifier board. The CCD is a front-illuminated frame transfer array with 23 micrometer square pixels. Its image section is divided into two square frames, one for each half of the stereo FOV's. Each has 256x256 active elements. A 256x512 storage section (identical to the imaging section) is located under a metal mask. The imp focal plane and electronics are nearly identical copies of the comparable subsystem employed in the Huygens Probe Descent Imaging Spectroradiometer (DISR), using the Loral 512X512 CCD.
The stereoscopic imager includes two imaging triplets, two fold mirrors separated by 150 mm for stereo viewing, a 12-space filter wheel in each path, and a fold prism to place the images side-by-side on the CCD focal plane. Fused silica windows at each path entrance prevent dust intrusion. the optical triplets are an f/10 design, stopped down to f/18 with 23-mm effective focal lengths and a 14.4 degree field of view. The pixel instantaneous field of view is one milliradian. The filter wheel four pairs of atmospheric filters, two pairs of stero filters, eleven individual geologic filters (which, when combined with the two pairs of stereo filters, result in thirteen distinct geologic filters) and one diopter or close-up lens, designed to acquire images of magnetic, wind-blown dust which adheres to a small magnet located on the IMP tip plate.
Full panoramas of the landing site are acquired during the mission using the stereo baseline provided by the camera optics. Additionally, monoscopic panoramas are acquired both prior and subsequent to the mast deployment, yielding vertically displaced stereo pairs with approximately 80 cm baseline. Images of a substantial portion of the visible surface are acquired in multispectral images with as many as eight spectral bands.
A number of atmospheric imvestigations are carried out using imp images.
aerosol opacity is measured periodically by imaging the Sun through two
narrow-band filters. Dust particles in the atmosphere are characterized
by observing Phobos at night. Water vapor abundance is measured by imaging
the Sun through filters in the water vapor absorption band and in the spectrally
adjacent continuum. Images of wind socks located at several heights above
the surrounding terrain are used to assess wind speed and direction.
A magnetic properties investigation is included as part of the IMP investigation. A set of magnets of differing field strengths will be mounted to a plate and attached to the lander. Images taken over the duration of the landed mission are used to determine the accumulation of magnetic species in the wind-blown dust. Multispectral images of these accumulations may be used to differentiate among likely magnetic minerals.
The IMP investigation also includes the observation of wind direction using a small wind sock mounted above a reference grid, and a calibration and reference target mounted to the lander.
A magnetic properties investigation is included as part of the IMP investigation. A set of magnets of differing field strengths will be mounted to a plate and attached to the lander. Images taken over the duration of the landed mission are used to determine the accumulation of magnetic species in the wind-blown dust. Multispectral images of these accumulations may be used to differentiate among likely magnetic minerals.
The IMP investigation also includes the observation of wind direction using a small wind sock mounted above a reference grid, and a calibration and reference target mounted to the lander.
Alpha Proton X-Ray Spectrometer
This instrument is a foreign-provided derivative of instruments flown
on the Russian Vega and Phobos missions and identical to the unit that was
planned for flight on the Russian
Mars '96 missions. Accordingly, the instrument has extensive, applicable
flight heritage. With the mobility provided by the microrover
and a deployment mechanism, the APX Spectrometer not only acquires spectra
from the ubiquitous martian dust, but more importantly, is deployed to distinct
rock outcroppings, thereby analyzing the native rock composition for the
first time. The alpha and proton spectrometer portions are provided by the
Max Planck Institute, Department
of Chemistry, Mainz Germany. The x-ray spectrometer portion is provided
by the University
Of Chicago.
This elemental composition instrument consists of alpha particle sources
and detectors for back-scattered alpha particles, protons and X-Rays. The
APX Spectrometer will determine elemental
chemistry of surface materials for most major elements except hydrogen.
The analytical process is based on three interactions of alpha particles
with matter: elastic scattering of alpha particles by nuclei, alpha-proton
nuclear reactions with certain light elements, and excitation of the atomic
structure of atoms by alpha particles, leading to the emission of characteristic
X-Rays. The approach used is to expose material to a radioactive source
that produces alpha particles with a known energy, and to acquire energy
spectra of the alpha particles, protons and X-Rays returned from the sample.
Such an instrument can identify and determine the amounts of most chemical
elements.
The basis of the alpha mode of the instrument is the dependence of the energy spectrum of alpha particles scattered from a surface on the composition of the surface material. The method has the best resolving power for the lighter elements.
The basis of the alpha mode of the instrument is the dependence of the energy spectrum of alpha particles scattered from a surface on the composition of the surface material. The method has the best resolving power for the lighter elements.
The proton spectra for alpha particles interacting with elements with atomic
numbers from 9 to 14 are very characteristic of the individual elements,
reflecting the resonance nature of the nuclear interactions involved. The
proton mode allows their detection and measurement.
The addition of a third detector for X-Rays Results in a significant extension of the accuracy and sensitivity of the instrument, particularly for the heavier, less abundant elements. Alpha sources produce characteristic X-Rays for a range of elements, giving an instrument sensitivity that can approach the ppm level.
The APXS sensor head is mounted external to the Rover chassis on a deployment mechanism (described below). This mechanism places the APXS in contact with rock and soil surfaces. The APXS electronics are mounted within the rover, in a temperature-controlled environment.
The addition of a third detector for X-Rays Results in a significant extension of the accuracy and sensitivity of the instrument, particularly for the heavier, less abundant elements. Alpha sources produce characteristic X-Rays for a range of elements, giving an instrument sensitivity that can approach the ppm level.
The APXS sensor head is mounted external to the Rover chassis on a deployment mechanism (described below). This mechanism places the APXS in contact with rock and soil surfaces. The APXS electronics are mounted within the rover, in a temperature-controlled environment.
APXS Deployment Mechanism
The deployment mechanism supports the APXS under launch and landing loads
and provides a means for positioning the APXS with a single actuator. The
linkage allows the APXS to be placed at a variety of elevations above nominal
ground level and at a variety of rotational orientations. The mounting of
the APXS to the deployment mechanism permits about 20 degrees of compliance
motion as the APXS is placed in contact with the sample. A set of contact
closures on the APXS front aperture ring indicate to the Rover
that the positioning is complete, thereby terminating the positioning motions.
Atmospheric Structure Instrument/Meterology Package
The ASI/MET is an engineering subsystem which acquires atmospheric information
during the descent of the lander through the atmosphere and during the entire
landed mission. It is implemented by JPL as a facility experiment, taking
advantage of the heritage provided by the Viking mission experiments.
Data acquired during the entry and descent of the lander permits the reconstruction of profiles of atmospheric density, temperature and pressure from altitudes in excess of 100 km to the surface.
The accelerometer portion of the ASI is provided by the Attitude And Information Management subsystem of the lander. It consists of x-, y- and z-axis sensors. Several gain states are provided to cover the wide dynamic range from the micro-g accelerations experienced upon entering the atmosphere to the peak deceleration and landing events in the range of 30 to 50 g's.
The ASI/MET instrument hardware consists of a set of temperature, pressure and wind sensors and an electronics board for operating the sensors and digitizing their output signals. Temperature is measured by thin wire thermocouples mounted on a meteorological mast that is deployed after landing. The location of one thermocouple is chosed to measure atmospheric temperature during descent, and three more monitor atmospheric temperatures 25, 50, and 100 cm above the surface during the landed mission. Pressure is measured by a Tavis magnetic reluctance diaphragm sensor similar to that used by Viking, both during descent and after landing. The wind sensor employs six hot wire elements distributed uniformly around the top of the mast. Wind speed and direction 100 cm above the surface are derived from the temperatures of these elements
Data acquired during the entry and descent of the lander permits the reconstruction of profiles of atmospheric density, temperature and pressure from altitudes in excess of 100 km to the surface.
The accelerometer portion of the ASI is provided by the Attitude And Information Management subsystem of the lander. It consists of x-, y- and z-axis sensors. Several gain states are provided to cover the wide dynamic range from the micro-g accelerations experienced upon entering the atmosphere to the peak deceleration and landing events in the range of 30 to 50 g's.
The ASI/MET instrument hardware consists of a set of temperature, pressure and wind sensors and an electronics board for operating the sensors and digitizing their output signals. Temperature is measured by thin wire thermocouples mounted on a meteorological mast that is deployed after landing. The location of one thermocouple is chosed to measure atmospheric temperature during descent, and three more monitor atmospheric temperatures 25, 50, and 100 cm above the surface during the landed mission. Pressure is measured by a Tavis magnetic reluctance diaphragm sensor similar to that used by Viking, both during descent and after landing. The wind sensor employs six hot wire elements distributed uniformly around the top of the mast. Wind speed and direction 100 cm above the surface are derived from the temperatures of these elements
During entry and descent, the sampling of acceleration, pressure and temperature data is optimized to the vertical rate of decent through the atmosphere. After landing, considerable flexibility in data averaging and sampling is provided to measure the variation of temperature, surface pressure and wind on short, diurnal, and seasonal time scales over the life of the mission.
Three wind socks are located at various heights on the meterology mast to determine the speed and direction of winds at the Pathfinder landing site. The wind socks will be imaged repeatedly by the IMP. The orientations of the wind socks will be measured in the images to determine the wind velocity at three heights above the surface. This information can then be used to estimate the aerodynamic roughness of the surface in the vicinity of the lander, and to determine the variation in wind speed with height. Because the Viking landers had wind sensors at only one height, such a vertical wind profile has never been measured on Mars. This new knowledge will help to develop and modify theories for how dust and sand particles are lifted into the martian atmosphere by winds, for example. Because erosion and deposition of wind-blown materials has been such an important geologic process on the surface of Mars, the results of the wind sock experiment will be of interest to geologists as well as atmospheric scientists.
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