KPL/IK \beginlabel PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM RECORD_BYTES = "N/A" ^SPICE_KERNEL = "MGS_MOLA_V26.TI" MISSION_NAME = "MARS GLOBAL SURVEYOR" SPACECRAFT_NAME = "MARS GLOBAL SURVEYOR" DATA_SET_ID = "MGS-M-SPICE-6-V1.0" KERNEL_TYPE_ID = IK PRODUCT_ID = "MGS_MOLA_V26.TI" PRODUCT_CREATION_TIME = 2001-06-27T17:43:39 PRODUCER_ID = "NAIF/JPL" MISSION_PHASE_NAME = "N/A" PRODUCT_VERSION_TYPE = ACTUAL PLATFORM_OR_MOUNTING_NAME = "MGS NADIR DECK" START_TIME = "N/A" STOP_TIME = "N/A" SPACECRAFT_CLOCK_START_COUNT = "N/A" SPACECRAFT_CLOCK_STOP_COUNT = "N/A" TARGET_NAME = MARS INSTRUMENT_NAME = "MARS ORBITER LASER ALTIMETER" NAIF_INSTRUMENT_ID = -94040 SOURCE_PRODUCT_ID = "N/A" NOTE = "See comments in the file for details" OBJECT = SPICE_KERNEL INTERCHANGE_FORMAT = ASCII KERNEL_TYPE = INSTRUMENT DESCRIPTION = "MGS Mars Orbiter Laser Altimeter instrument parameters SPICE I-Kernel File. This file also contains MOLA Frame definitions and location of the MGS antenna phase centers and center of gravity for some spacecraft configurations. " END_OBJECT = SPICE_KERNEL \endlabel MOLA Instrument Kernel =========================================================================== This instrument kernel (I-kernel) contains the Mars Orbiter Laser Altimeter (MOLA) instrument mounting offset, instrument frame definition and instrument location. Version and Date -------------------------------------------------------- Version 2.6 -- June 26, 2001 Added section describing various timing delays used by the MOLA team in the instrument data processing. Improved description of the instrument frame. Added FOV definition. Re-arranged sections of the file. Added "name-to-NAIF ID" mapping keywords. Version 2.5 -- December 5, 2000 Replaced pre-flight measured mounting alignment offsets with flight calibrated offsets (in both ``Euler Angles'' keyword and MOLA frame definition.) Version 2.4 -- January 28, 1998 Added explanations regarding antenna phase center locations. Version 2.3 -- January 16, 1998 Added coordinates of the receiving LGA geometric centers. Version 2.2 -- May 27, 1998 Added section containing coordinates of the HGA and LGAs geometric centers in stowed position. Version 2.1 -- August 25, 1997 Z coordinate of MOLA was changed to be 1.9202 meters (old value 1.9116 meters) after confirmation from Rich Hund of LMA. Version 2.0 -- August 19, 1997 Section specifying location of MOLA, s/c center of mass and s/c frame origin was added. Version 1.2 -- August 11, 1997 Frame definition was corrected to represent the correct transformation sense. Version 1.1 -- June 19, 1997 The MOLA frame definition section was added to support utilization of the SPICE system FRAMES capabilities. Version 1.0 -- November 26, 1996 Initial Release. References -------------------------------------------------------- 1. ``MGS Alignment Transformation'', by Richard A. Hund, November 26, 1996. 2. ``MGS Payload Data Sheet'' by C.Kloss, October 31, 1995, 3. ``C-kernel Required Reading'' 4. ``Kernel Pool Required Reading'' 5. ``Frames Required Reading'' 6. ``MGS Mission Specification. Mission Requirements and Vehicle Description'', MDC 95H0026B, MGS REV B. APRIL 1996. 7. ``Nadir Equipment Deck. Science Instrument Configuration" DWG, 23 Jan 1995; provided by Carl Kloss. 8. Phone message from Jon Nichols re. location of the spacecraft's center of mass during mapping phase of the mission; August 13, 1997. 9. E-mail message from William Adams, LMA re. location of the HGA and LGA phase center locations; January 27, 1999. 10. Complete set of mechanical drawings for the MGS spacecraft. 11. E-mail from Greg Neumann providing official flight MOLA mounting alignment offsets (based on Rowlands et al., 1999 and article in JGR MGS issue); December 4, 2000 12. E-mails from Greg Neumann explaining timing delays used in the MOLA data processing; December 5, 2000 and December 6, 2000 Implementation Notes -------------------------------------------------------- This file is used by the SPICE system as follows: programs that make use of this I-kernel must `load' the kernel, normally during program initialization. Loading the kernel associates data items with their names in a data structure called the `kernel pool'. The SPICELIB routine FURNSH loads a kernel file into the pool as shown below. CALL FURNSH ( I_kernel_name ) In order for a program or subroutine to extract data from the pool, the SPICELIB routines GDPOOL and GIPOOL are used. See [4] for more details. This file was created and may be updated with a text editor or word processor. MOLA NAIF ID -------------------------------------------------------- The following NAIF ID is assigned to the MOLA instrument: Instrument NAIF ID --------------------------- MOLA -94040 --------------------------- The keywords in this data block make this name/ID mapping available within the SPICE toolkit. \begindata NAIF_BODY_NAME += ( 'MGS_MOLA' ) NAIF_BODY_CODE += ( -94040 ) \begintext Naming Conventions -------------------------------------------------------- All names referencing values in this I-kernel start with the characters `INS' followed by the NAIF MOLA instrument ID (-94040). The remainder of the name is an underscore character followed by the unique name of the data item. For example, the MOLA offset relative to the spacecraft frame, given as three Euler angles, is specified using two items: INS-94040_EULER_ANGLES INS-94040_EULER_AXES The upper bound on the length of the name of any data item is 32 characters. If the same item is included in more then one file, or if the same item appears more than once within a single file, the latest value supersedes any earlier values. MOLA mounting offset -------------------------------------------------------- This section describes the offset of the MOLA instrument fixed frame (the frame fixed to the alignment cube on the MOLA) relative to the Mars Global Surveyor spacecraft frame. From the offset, given as three rotation angles -- ROLL, PITCH and YAW, a rotation matrix can be constructed that will transform the components of a vector expressed in the spacecraft frame to components expressed in the MOLA instrument fixed frame. For example, if x y and z are the components of a vector expressed in the spacecraft frame, X Y and Z will be the components of the same vector expressed in the MOLA instrument fixed frame: [ X ] [ ] [ x ] | Y | = | ROT | | y | [ Z ] [ ] [ z ] where ROT is the rotation matrix constructed from the rotation angles as follows: [ ] [ ] [ ] [ ] [ ROT ] = [ YAW ] [ PITCH ] [ ROLL ] [ ] [ ] [ ] [ ] Z Y X where each of three matrixes on the right side represent a coordinate frame rotation by the given angle around the indicated axis. See the SPICELIB routine EUL2M for more information about constructing a rotation matrix from a set of rotation angles. The following pre-flight measured values of ROLL, PITCH and YAW are provided in [1]: ROLL = 0.021 (degrees) PITCH = 359.995 (degrees) YAW = 0.059 (degrees) These values were provided in the versions 1.0 through 2.4 of this IK file (Nov'96 through Dec'00) in radians in the following keyword: INS-94040_EULER_ANGLES = ( 0.000366519143 6.283098040717 0.001029744259) In December 2000, starting with IK version 2.5, these values were replaced with the flight calibrated offsets provided by Greg Neumann [11]: ROLL = -0.0029 (degrees) PITCH = 359.9914 (degrees) YAW = 0.059 (degrees) The keyword INS-94040_EULER_ANGLES contains these values, in radians, in the following order: INS-94040_EULER_ANGLES = ( ``ROLL'' ``PITCH'' ``YAW'' ) The keyword INS-94040_EULER_AXES contains integer codes of the corresponding axes of rotations (1 -- X, 2 -- Y, 3 -- Z). \begindata INS-94040_EULER_ANGLES = ( -0.0000506145 6.283035209 0.001029744259 ) INS-94040_EULER_AXES = ( 1 2 3 ) \begintext Instrument Frame Definition -------------------------------------------------------- The MOLA instrument frame, MGS_MOLA, is defined as follows: -- +Z is the receiver boresight; nominally co-aligned with the s/c +Z axis; -- +Y nominally points in the same direction as the s/c +Y axis; -- +X completes the right hand frame; nominally points in the same direction as the s/c +X axis; This picture illustrates the MGS_MOLA frame: ^+Zmola | | +Xmola.|_. +Ymola \ o------> ._________________. .____\_/. ._________________. | \ | | / | | o| |o | | / | ^+Zsc \ | ._________________. .___|___. ._________________. | | | /__|__\ +Xsc and +Xmola /_o------> +Ysc are out of the page +Xsc The frame definition in the data section below incorporate the in-flight calibrated alignment angles provided in the section ``MOLA mounting offset'' above. Note that angles in the frame definitions are specified for "from instrument to base (relative to) frame" transformation. \begindata FRAME_MGS_MOLA = -94040 FRAME_-94040_NAME = 'MGS_MOLA' FRAME_-94040_CLASS = 4 FRAME_-94040_CLASS_ID = -94040 FRAME_-94040_CENTER = -94 TKFRAME_-94040_SPEC = 'ANGLES' TKFRAME_-94040_RELATIVE = 'MGS_SPACECRAFT' TKFRAME_-94040_ANGLES = ( 0.0000506145, -6.283035209, -0.001029744259 ) TKFRAME_-94040_AXES = ( 1, 2, 3 ) TKFRAME_-94040_UNITS = 'RADIANS' \begintext Timing Corrections -------------------------------------------------------- Two timing offsets (errors) were taken into in computing the observation geometry in the MOLA team in their processing: -- the MOLA internal timing error; -- the CK time tag adjustment error; Greg Neumann, MOLA team, described the first of these errors, internal timing error, in [12] as follows: "The MOLA internal timing error is 117 ms, plus or minus a millisecond. ... the actual MOLA fire time was 117 ms later than the time recorded in the instrument packet ... [thus] the code ... to get MGS inertial position at [MOLA] fire time is: bias = 30./256.d0 ! 0.1171875 s is best guess of MOLA timing bias call spkgeo(MARS,stime+bias,REF, MO,vtarg,lttim) " The keyword in this data section contain the value, in seconds, that should added to the raw MOLA observation time tag to adjust it to the time when the shot actually happened: \begindata INS-94040_MOLA_TIMING_BIAS = ( 0.1171875 ) \begintext The second error, CK time tag error, also described by Greg in [12] has to do with adjusting the time that is used to read the s/c orientation from the "2.3 seconds corrected" mapping CK files (see CK comments for details): "... Both in systematic mapping and in the programmed maneuvers, we find the filter latency is about 1.1 - 1.2 seconds ... The question of why the timing offset of the [input to the] C-kernels appears not to have changed from the aerobraking filter to the mapping filter (1.15 seconds to 2.3 seconds) is unresolved ... [therefore] ... to get the correct pointing .. [one has to] remove half of the 2.3-second offset applied to the C-kernel in the processing. The code I use to get pointing at a nominal MOLA fire time stime, obtained from the PEDRs, is: abias=-1.150D0 ! best guess for mapping after 2.3 added call sce2t (MO, stime+abias, sclkdp) call ckgp (MOPLAT, sclkdp, toldp, REF, cmat, clkodp, found) " Thus, the analysis done by the MOLA team shows that the offset of -2.3 seconds, that has been applied to the original s/c orientation appears telemetry during mapping phase before it was written to the CK files, to be incorrect -- instead of -2.3 it should have been -1.15 seconds, as during pre-mapping mission phases. To compensate these "over-corrected" CK data a half of this offset should be "taken back" during reading of the CK files by subtracting -1.15 seconds from the CK pointing request time. This small diagram illustrates this offset: CK request time at "true" which correct s/c MOLA fire orientation is stored time | | | <...................... | | 1.15 seconds must | | be subtracted to get | | correct orientation | | | | V V ............................................ . 2.3 seconds were subtracted . . by the ground s/w making CK files . V . @ @ ......................> @ ^ ^ 1.15 seconds were ^ | | added by AACS filter | | | | | | | time tag "true" time for time tag in CK file which s/c orientation in s/c TLM was determined The keyword in this data section contain the value, in seconds, that should added to the corrected MOLA observation time tag to obtain the correct s/c orientation from the "2.3 seconds corrected" mapping CK files: \begindata INS-94040_CK_TIMING_BIAS = ( -1.15 ) \begintext Laser Transmitter -------------------------------------------------------- The laser transmitter beam divergence, from [2], is 0.25 mrad. Unit are in radians \begindata INS-94040_LASER_BEAM_DIVERGENCE = ( 0.00025 ) \begintext Altimeter Receiver FOV -------------------------------------------------------- The altimeter receiver field of view (FOV), from [2], is a cone of 0.85 mrad. The following set of keywords defines the receiver FOV according to the SPICE FOV standard (i.e. in the form that it can be utilized by the GETFOV/getfov_c routines): \begindata INS-94040_FOV_FRAME = 'MGS_MOLA' INS-94040_FOV_SHAPE = 'CIRCLE' INS-94040_BORESIGHT = ( 0.0000000000000000 0.0000000000000000 +1.0000000000000000 ) INS-94040_FOV_BOUNDARY_CORNERS = ( 0.0000000000000000 +0.0004249999646376 +0.9999999096875100 ) \begintext This keyword specifying the FOV extent was provided in the IK file version 1.0 through 2.5, prior to SPICE FOV definition standard was introduced. In this keyword the angular extent of the FOV cone is given in radians. \begindata INS-94040_RECEIVER_FOV = ( 0.00085 ) \begintext MOLA and s/c center of mass locations -------------------------------------------------------- The locations of the MOLA instrument [ref. 6,7] and the s/c center of mass for stowed (launch) [ref. 6] and nominal mapping [ref. 8] configuration are specified relative to the s/c fixed which is defined as follows: - origin of the frame is located at the intersection of the s/c--launch vehicle interface plane and the spacecraft's central axis, i.e at the center of the bottom of the propulsion unit nozzle; - Z axis is along s/c central axis; positive Z direction is from s/c bottom towards nadir equipment deck; - X axis is perpendicular to Z axis and points thought the side of the s/c which high gain antenna is mounted on; positive X direction is from the center of the s/c toward HGA side; - Y axis completes X and Z axes to right hand frame. The locations coordinates are given in meters. \begindata INS-94040_MOLA_LOC = ( 0.3383 0.3126 1.9202 ) INS-94040_SC_LAUNCH_CG_LOC = ( -0.0010 -0.0007 1.1320 ) INS-94040_SC_MAPPING_CG_LOC = ( 0.0298 0.0718 0.9970 ) \begintext MGS Antenna Locations (stowed configuration). -------------------------------------------------------- Five MGS antennas -- main HGA, "FRONT" and "BACK" transmitting LGAs (LGAF & LGAB) and "+X side" and "-X side" receiving LGAs (RLGA+X & RLGA-X) -- are shown on the diagrams below for the HGA in stowed configuration: MGS S/C "-Y" Side View: ------------------------------------------------- ^ S/C +Z Axis | | | +39.318" |<----------->| | | | +39.318" | |<--------->| | | | | | +20.72" | | |<-->| | | -25.81"| |<----->| LGAB __LGAF | | @=| |=@ ---------------- | | | | __ ^ | | |__|/ | | | +-----------+ / | | | | | / | |+81.46" | | | / | | | | || | | RLGA-X | | || HGA | ------ | ----- @=| || | ^ | ^ |-----------| \ | | | | | | \ | | | | | \ | | | | | +31.75" \__| | | | | |<----->| | | | | | | RLGA+X |+66.15" | | | |=@ --- | | | +----+-+----+ ^ | | |+49.94" / | \ |+17.56" | | | / | \ | | | v / | \ v v v -------- +----o----+ ------------------------ ---> | S/C Frame S/C +X Axis | Origin MGS S/C Top View: ------------------------------------------------- ^ S/C +Y Axis | | __ RLGA+X / | | +-----------+ / | v | | |=@/ ------------ 0"| | S/C Frame | / | |+5.29" v | Origin || HGA | | ---- @=| o ||__ | ------------ ---> ^ RLGA-X || | | ^ ^ ^ S/C +X Axis | | || | | | | | || | | |-28.18" | +----+-+----+| | | | |-30.05" | |\__| v | | |=@ --- v @=|__| --------------------- LGAB LGAF The HGA center, coordinates of which are given below, is considered to be at the geometric center of the outside (big diameter) circle of the antenna. This point can also be considered the phase center of the antenna because it is located on the antenna boresight axis and the near field distribution is essentially unchanged along the boresight direction of the antenna throughout the near-field region. The LGA centers, coordinates of which are given below, are considered to be at the geometric center of the 1.45" x 1.45" square-shaped active element of the antenna. This point can also be considered the phase center of the antenna because, in practice, for square circular polarized patch antennas (with LGAs are), the phase center is approximately located in the center of the copper patch. i.e. in the MGS LGA case, in the center of the nearly square "top" of the LGA. MGS Antenna Center locations, in inches: s/c X s/c Y s/c Z -------- -------- --------- HGA 39.318 0.0 66.15 "FRONT" LGA 39.318 -28.18 81.46 "BACK" LGA 20.72 -30.05 81.56 "+X SIDE" RLGA 31.75 5.29 17.56 "-X SIDE" RLGA -25.81 0.00 49.94 Same, in meters: s/c X s/c Y s/c Z -------- -------- --------- HGA 0.999 0.000 1.680 "FRONT" LGA 0.999 -0.716 2.069 "BACK" LGA 0.526 -0.763 2.072 "+X SIDE" RLGA 0.806 0.134 0.446 "-X SIDE" RLGA -0.655 0.000 1.268 The data keywords below contain coordinates in meters. \begindata INS-94040_HGA_STOWED_LOC = ( 0.999 0.000 1.680 ) INS-94040_FRONT_LGA_STOWED_LOC = ( 0.999 -0.716 2.069 ) INS-94040_BACK_LGA_STOWED_LOC = ( 0.526 -0.763 2.072 ) INS-94040_+X_RLGA_LOC = ( 0.806 0.134 0.446 ) INS-94040_-X_RLGA_LOC = ( -0.655 0.000 1.268 ) \begintext Platform ID -------------------------------------------------------- This number is the NAIF instrument ID of the platform on which the instrument is mounted. \begindata INS-94040_PLATFORM_ID = ( -94000 ) \begintext