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Availability: Archived at NSSDC, accessible from elsewhere


This description was generated automatically using input from the Planetary Data System.

Data Set Overview ==================

This dataset consists of data products derived from data collected by an Inertial Measurement Unit (IMU) on the Phoenix spacecraft during its entry into the martian atmosphere. The DATA/ directory contains two data files (PHXPROFILE.TAB and PHXCOMPACT.TAB). PHXPROFILE.TAB contains time ordered records of smoothed acceleration, derived velocity, derived position, derived atmospheric properties and other derived quantities. PHXCOMPACT.TAB contains position and atmospheric properties at 1 km vertical intervals. PHXPROFILE.TAB is the more comprehensive set of results. PHXCOMPACT.TAB is intended for those users who are only interested in the atmospheric properties.

Parameters ===========

PHXPROFILE.TAB contains the following items.

Time (relative to reference time, seconds) UTC_TIME Radial distance (m) RADIAL_DISTANCE Areocentric latitude (degrees north) LATITUDE Areocentric longitude (degrees east) LONGITUDE X-component of position (m) X_POSITION Y-component of position (m) Y_POSITION Z-component of position (m) Z_POSITION Element 0 of quaternion (dimensionless) Q0 Element 1 of quaternion (dimensionless) Q1 Element 2 of quaternion (dimensionless) Q2 Element 3 of quaternion (dimensionless) Q3 X-component of velocity (m/s) X_VELOCITY Y-component of velocity (m/s) Y_VELOCITY Z-component of velocity (m/s) Z_VELOCITY Speed of spacecraft relative to atmosphere (m/s) VREL X-component of acceleration (m s^(-2)) X_ACCELERATION Y-component of acceleration (m s^(-2)) Y_ACCELERATION Z-component of acceleration (m s^(-2)) Z_ACCELERATION Angle of attack (degrees) ALPHA Axial force coefficient, CA (dimensionless) CA Normal force coefficient, CN (dimensionless) CN Mach number (dimensionless) MA Knudsen number (dimensionless) KN Density (kg m^(-3)) RHO Pressure (Pa) PRESS Temperature (K) TEMP

This data file also contains 1-sigma uncertainties for those items. Units for the uncertainties in item XXX are the same as for item XXX. Those names, which are derived from the above names, are as follows:


PHXCOMPACT.TAB contains the following items.

Radial distance (m) MRADIAL_DISTANCE Altitude (km) MALTITUDE Density (kg m^(-3)) MRHO Pressure (Pa) MPRESS Temperature (K) MTEMP

This data file also contains 1-sigma uncertainties for those items. Units for the uncertainties in item XXX are the same as for item XXX. Those names, which are derived from the above names, are as follows:


Timing ====== All data products in this dataset are derived from PDS volume PHXASE_0001 [CATLINGETAL2008], which expresses times with respect to a UTC reference time of 2008-05-25T23:30:47.918. All times in this dataset are expressed relative to the UTC reference time of 2008-05-25T23:00:00.000. Thus a time of 0.000 in [CATLINGETAL2008] would be written as 1847.918 seconds in this dataset.

Coordinate Systems ================== All data products in this dataset are derived from 200 Hz IMU measurements in DATA/IMU_A_EDR_M.TAB of PDS volume PHXASE_0001 [CATLINGETAL2008]. These acceleration measurements are given in an XYZ cartesian frame fixed relative to the spacecraft. Specifically, the Phoenix mechanical frame, also known as the PHX_LANDER frame or the M frame, which has NAIF ID -84001. This spacecraft frame is neither inertial nor fixed relative to Mars. The spacecraft is axisymmetric about the Z axis in this frame. The data products in PDS volume PHXASE_0001 [CATLINGETAL2008] were transmitted to Earth in a different frame, the IMU frame, and then transformed into the M frame before being archived. During the course of the preparation of this dataset, it was discovered that a preliminary version of the appropriate transformation matrix had been used. The preliminary matrix corresponds to the spacecraft as designed, not as built. The vector accelerations and angular velocities in DATA/IMU_A_EDR_M.TAB of PDS volume PHXASE_0001 [CATLINGETAL2008] should be multiplied by the following matrix to transform them into the actual M frame. [New X] = [ 0.99991267 -0.00087993926 -0.013188274 ] [Old X] [New Y] = [ 0.00090164837 0.99999798 0.0016463352 ] [Old Y] [New Z] = [ 0.013186473 -0.0016580001 0.99991177 ] [Old Z] Where the vector with components [New X, New Y, and New Z] is the corrected vector, the vector with components [Old X, Old Y, and Old Z] is the vector from DATA/IMU_A_EDR_M.TAB in PDS volume PHXASE_0001, and the XYZ axes refer to the M frame. Further details are given in DOCUMENT/REPORT.LBL.

Acceleration measurements included in this dataset (X_ACCELERATION, Y_ACCELERATION, Z_ACCELERATION and associated uncertainties) are expressed in the Phoenix cruise frame, also known as the PHX_LANDER_CRUISE frame or the C frame, which has NAIF ID -84000. The spacecraft is axisymmetric about the X axis in this frame. The relationship between the M and C frames is stated in DOCUMENT/EDRSIS.LBL of PDS volume PHXASE_0001 [CATLINGETAL2008]. Axial accelerations are parallel to the X axis of the C frame and normal accelerations are perpendicular to the X axis of the C frame.

Position and velocity (X_POSITION, Y_POSITION, Z_POSITION and associated uncertainties; X_VELOCITY, Y_VELOCITY, Z_VELOCITY and associated uncertainties) are given in an XYZ cartesian frame whose origin is at the center of mass of Mars. The +Z axis passes through the north pole and the +X axis passes through the equator at zero degrees east areocentric longitude at a specified time. The +Y axis completes a right-handed set. The specified time is the UTC reference time of 2008-05-25T23:00:00.000. Position is also given as radial distance, areocentric latitude, and areocentric longitude. This is the standard spherical polar coordinate system found in mathematical textbooks. Longitude increases to the east. Altitude is defined as radial distance minus the radial distance from the center of mass of Mars to the landing site, 3376.3 km. Altitude is not referenced to any equipotential surface. The orientation of Phoenix is described by the quaternion that relates the C frame to the J2000 frame, which is defined by the Earth's mean equator and equinox at the J2000.0 epoch. The convention that quaternion [Q0, Q1, Q2, Q3] corresponds to a rotation about the axis parallel to the vector QV = [Q1, Q2, Q3] by an angle 2 cos-1(Q0) was adopted.

Data Processing ===============

Data processing for PHXPROFILE.TAB is described in DOCUMENT/REPORT.LBL. Many aspects of the reconstruction were similar to the reconstruction reported in PDS volume MERIMU_2001 [WITHERS&MURPHY2009]. Not all data products are defined at all timesteps. Data products derived in the atmospheric structure reconstruction are not defined above about 130 km nor below about 15 km. Such data products are given the null value -1 in the PHXPROFILE.TAB. The contents of PHXCOMPACT.TAB were derived from the contents of PHXPROFILE.TAB. The dependent variable in PHXCOMPACT.TAB is altitude, which is defined as the difference between the radial distance to Phoenix and the radial distance to the landing site (3376.3 km). The prefix M is used frequently in PHXCOMPACT.TAB to distinguish variables in PHXCOMPACT.TAB from similar variables in PHXPROFILE.TAB. This M stands for mean, since many of the values contained in PHXCOMPACT.TAB are averages of values reported in PHXPROFILE.TAB. A series of altitude levels were defined as 1 km, 2 km, ..., 146 km and labelled as MALTITUDE. Each value of MRADIAL_DISTANCE was defined as the sum of the corresponding value of MALTITUDE and 3376.3 km. Each value of SIGMA_MRADIAL_DISTANCE was defined as the arithmetic mean of SIGMA_RADIAL_DISTANCE for all data points in PHXPROFILE.TAB whose value of RADIAL_DISTANCE is within 0.5 km of the relevant value of MRADIAL_DISTANCE. SIGMA_MALTITUDE was defined to equal SIGMA_MRADIAL_DISTANCE. Each value of MRHO was defined as the geometric mean of all values of RHO whose value of RADIAL_DISTANCE is within 0.5 km of the relevant value of MRADIAL_DISTANCE. Values of SIGMA_MRHO, MPRESS, SIGMA_MPRESS and SIGMA_MTEMP were defined similarly. MTEMP was calculated from MRHO and MPRESS using the same ideal gas law as was used to produce TEMP in PHXPROFILE.TAB. If all DENSITY values in PHXPROFILE.TAB whose values of RADIAL_DISTANCE are within 0.5 km of a given value of MRADIAL_DISTANCE in PHXCOMPACT.TAB are null (-1), then all atmospheric properties at this MRADIAL_DISTANCE in PHXCOMPACT.TAB are given the null value -1.

Acronyms ======== AAS American Astronautical Society AIAA American Institute of Aeronautics and Astronautics ASCII American Standard Code for Information Interchange ASE Atmospheric Structure Experiment ASTG Atmospheric Science Theme Group BWG Beam Wave Guide CA California CD Compact Disc CD-ROM Compact Disc Read-Only Memory CM Centre of Mass CO Colorado D/L Downlink DSN Deep Space Network DVI Device Independent file format EDL Entry, Descent and Landing EDR Experiment Data Record EDT Eastern Daylight Time EPS Encapsulated Postscript ET Ephemeris Time FL Florida HASI Huygens Atmospheric Structure Instrument HEF High Efficiency HIRISE High Resolution Imaging Science Experiment ID Identifier IDL Interactive Data Language, a computer programming language IMU Inertial Measurement Unit ITAR International Traffic in Arms Regulations JPG Joint Photographic Experts Group JPL Jet Propulsion Laboratory LM Lockheed Martin LMA Lockheed Martin Astronautics LMST Local Mean Solar Time Ls The angle between the Mars-Sun line and the Mars-Sun line at the northern hemisphere vernal equinox, known as the areocentric longitude of the Sun LSB Least Significant Bit LST Local Solar Time MA Massachusetts MECA Microscopy, Electrochemistry, and Conductivity Analyzer MEGDR Mission Experiment Gridded Data Records MET Meteorological MEX Mars Express MGS Mars Global Surveyor MIMU Minature IMU MOLA Mars Orbiter Laser Altimeter MPL Mars Polar Lander MRO Mars Reconnaissance Orbiter MSP Mars Surveyor Program NAIF Navigation and Ancillary Information Facility NASA National Aeronautics and Space Administration ODY Mars Odyssey ORT Operational Readiness Test PDF Portable Document Format PDS Planetary Data System PDT Pacific Daylight Time PHX Phoenix PS Postscript RA Robotic Arm RAC Robotic Arm Camera RLG Ring Laser Gyroscope SCLK Spacecraft Clock SIS Software Interface Specification SPICE An information system provided by the Navigation and Ancillary Information Facility SSI Surface Stereo Imager TEGA Thermal and Evolved Gas Analyzer TCM Trajectory Correction Maneuver TBD To be determined UA University of Arizona UHF Ultra High Frequency USA United States of America UTC Coordinated Universal Time WA Washington

These data are available on-line from the Planetary Data System (PDS) at:

Alternate Names

  • PHX-M-ASE-5-EDL-RDR-V1.0


  • Planetary Science: Atmospheres

Additional Information


Questions and comments about this data collection can be directed to: Dr. David R. Williams



NameRoleOriginal AffiliationE-mail
Dr. Andrew N. FazakerleyData ProviderUniversity College,
Dr. Paul WithersGeneral ContactBoston
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