The Pioneer project used engineering data extracted from the MDRs to monitor and control the spacecraft, while scientific data, also extracted from the MDRs, was converted into formats specific to each experiment and supplied to the experimenter groups.
Far beyond the original expectations17,
telemetry is now seen to be of value for the investigation of the Pioneer anomaly, as the MDRs, specifically
the telemetry data contained therein, are helpful in the construction of an accurate model of the spacecraft
during their decades long journey, including a precise thermal profile, the time history of propulsion system
activation and usage, and many other potential sources of on-board disturbances. After recent recovery
efforts [397], this data is available for investigation.
The total amount of data stored in these MDR files is approximately 40 GB [397]. According to the
original log sheets that record the transcription from tape to magneto-optical media, only a few days worth
of data is missing, some due to magnetic tape damage. One notable exception is the Jupiter encounter
period of Pioneer 10. According to the transcription log sheets, DOY 332–341 from 1973 were not available
at the time when the magnetic tapes on which the MDRs were originally stored were transcribed to more
durable magneto-optical media.
Other significant periods of missing data are listed in Table 3.5. It is not known why these records are not present, except that we know that very few days are missing due to unreadable media (i.e., the cause is missing, not damaged, tapes.)
Spacecraft | Year | Days of the Year (DOY) |
Pioneer-10 | 1972 | 133–149 |
1973 | 004–008, 060–067, 332–341 | |
1974 | 034–054 | |
1979 | 025–032, 125–128, 137–157, 171–200 | |
1980 | 173–182, 187–199, 248–257 | |
1983 | 329–348 | |
1984 | 346–359 | |
Pioneer-11 | 1973 | 056–064, 067–080, 082–086, 088–094 |
1980 | 309–330, 337–365 | |
1982 | 318–365 | |
1983 | 001–050 | |
1984 | 343–357 | |
1990 | 081–096 | |
So, the record is fairly complete. But how good is the data? Over forty billion bytes were received by the DSN, processed, copied to tape, copied from tape to magneto-optical disks, then again copied over a network connection to a personal computer. It is not inconceivable that the occasional byte was corrupted by a transmission or storage error. There are records that contain what is apparently bogus data, especially from the later years of operation. This, plus the fact that the record structure (e.g., headers, synchronization sequences) is intact suggests reception errors as the spacecraft’s signal got weaker due to increasing distance, and not copying and/or storage errors.
The MDRs contain no error detection or error correction code, so it is not possible to estimate the error rate. However, it is likely to be reasonably low, since the equipment used for storage and copying is generally considered very reliable. Furthermore, any errors would likely show up as random noise, and not as a systemic bias. In this regard, the data should generally be viewed to be of good quality insofar as the goal of constructing an engineering profile of the spacecraft is considered.
MDRs are a useless collection of bits unless information is available about their structure and content. Fortunately, this is the case in the case of the Pioneer 10 and Pioneer 11 MDRs.
The structure of an MDR is shown in Appendix C (see also [402]). The frame at the beginning and at
the end of each 1344-bit record contained information about the DSN station that received the data, and
included a timestamp, data quality and error indicators, and the strength of the received signal. The
middle of the record was occupied by as many as four consecutive data frames received by the
spacecraft.
The MDR header is followed by four data frames (not all four frames may be used, but they are all present) of 192 bits each. Lastly, an additional 8 words of DSN information completes the record. The total length of an MDR is thus 42 words of 32 bits each.
The 192-bit data frames are usually interpreted as 64 3-bit words or, alternatively, as 32 6-bit words. The Pioneer project used many different data frame formats during the course of the mission. Some formats were dedicated to engineering telemetry (accelerated formats). Other formats are science data formats, but still contain engineering telemetry in the form of a subcommutator: a different engineering telemetry value is transmitted in each frame, and eventually, all telemetry values are cycled through.
The Pioneer spacecraft had a total of 128 6-bit words reserved for engineering telemetry. Almost all
these values are, in fact, used. A complete specification of the engineering telemetry values can be found in
Section 3.5 (“Data Handling Subsystem”) of [292]. When engineering telemetry was accelerated to the
main frame rate, four different record formats (C-1 through C-4) were used to transmit telemetry
information. When the science data formats were in use, an area of the record was reserved for a
subcommutator identifier and value.
The formats are further complicated by the fact that some engineering telemetry values appear only in subcommutators, whereas others only appear at the accelerated (main frame) rate.
In the various documentation packages, engineering data words are identified either by mnemonic, by the letter ‘C’ followed by a three-digit number that runs from 1 through 128, or most commonly, by the letter ‘C’ followed by a digit indicating which ‘C’ record (C-1 through C-4) the value appears in, and a two-digit number between 1 and 32: for instance, C-201 means the first engineering word in the C-2 record.
|
|
|
Parameters | Subsystem | Telemetry words |
|
|
|
|
|
|
TEMPERATURES
|
||
|
|
|
RTG fin root temps | Thermal | C 201, C202, C203, C204 |
RTG hot junction temps | Thermal | C220, C219, C218, C217 |
TWT temperatures | Communications | C205, C206, C207, C228, C223, C221 |
Receiver temperatures | Communications | C222, C227 |
Platform temperatures | Thermal | C301, C302, C304, C318, C319, C320 |
PSA temperatures | Thermal | C225, C226 |
Thruster cluster temps | Propulsion | C309, C326, C310, C311, C312, C328, C325 |
SRA/SSA temperatures | ACS | C303, C317 |
Battery temperature | Power | C115 |
Propellant temperature | Propulsion | C327 |
N2 tank temperature | Propulsion | C130 |
Science instr temps | Science | E101, E102, E109, E110, E117, E118, E125, E128, |
E201, E209, E213, E221 | ||
|
|
|
VOLTAGES
|
||
|
|
|
Calibration voltages | Data handling | C 101, C102, C103 |
RTG voltages | Power | C110, C125, C131, C113 |
Battery/Bus voltages | Power | C106, C107, C117, C118, C119 |
TWT voltages | Communications | C224, C230 |
Science instr voltages | Science | E119, E129, E210, E211, E217, E220 |
|
|
|
CURRENTS
|
||
|
|
|
RTG currents | Power | C 127, C105, C114, C123 |
Battery/Bus currents | Power | C109, C126, C129 |
Shunt current | Power | C122, C209 |
TWT currents | Communications | C208, C211, C215, C216 |
Science instr currents | Science | E111, E112, E113 |
|
|
|
PRESSURE
|
||
|
|
|
Propellant pressure | Propulsion | C 210 |
|
|
|
OTHER ANALOG
|
||
|
|
|
TWT power readings | Communications | C231, C214 |
Receiver readings | Communications | C111, C212, C232, C121, C229, C213 |
|
|
|
BINARY/BIT FIELDS
|
||
|
|
|
Conscan | Communications | C313, C314, C315, C316 |
Stored commands | Electrical | C305, C306, C307 |
Thruster pulse counts | Propulsion | C329, C321, C322, C330 |
Status bits | Data handling | C104 |
Power | C128 | |
Electrical | C120, C132, C324, C332 | |
Communications | C308 | |
Power switches | Electrical | C108, C124 |
Roll attitude | Data handling | C112, C116 |
Precession | ACS | C403, C411, C412, C415, C416, C422, C423, C424, |
C425, C428, C429, C430 | ||
Spin/roll | Data handling | C405, C406, C407, C408, C417 |
Delta v | ACS | C413, C414, C426 |
ACS status | Propulsion | C409 |
ACS | C410, C427, C431, C432 | |
Star sensor | ACS | C404, C419, C420, C421 |
|
|
|
SCIENCE INSTRUMENTS
|
||
|
|
|
Status/housekeeping | Science | E108, E124, E130, E202, E224, E131, E132, E208 |
JPL/HVM readings | Science | E103, E104, E105, E106, E107, E203, E204, E205 |
UC/CPI readings | Science | E114, E115, E116, E206, E212, E214, E215, E216 |
GE/AMD readings | Science | E122, E123, E222, E223 |
GSFC/CRT readings | Science | E126, E127 |
LaRC/MD readings | Science | E207 |
|
|
|
Pioneer 10 and 11 telemetry data is very relevant for a study of on-board systematics. The initial
studies of the Pioneer anomaly [24, 27
, 194, 390
] and several subsequent papers [28, 391
, 392
, 393
] had
emphasized the need for a very detailed investigation of the on-board systematics. Other researchers also
focused their work on the study of several on-board generated mechanisms that could contribute to an
anomalous acceleration of the spacecraft [164, 245, 327]. Most of these investigations of on-board
systematics were not very precise. This was due to a set of several reasons, one of them is insufficient
amount of actual telemetry data from the vehicles. In 2005, this picture changed dramatically when this
critical information became available.
Table 3.6 summarizes all available telemetry values in the C (engineering) and E (science) telemetry formats. The MDRs also contain a complete set of science readings that were telemetered in the A, B, and D formats.
As this table demonstrates, telemetry readings can be broadly categorized as temperature, voltage, current readings; other analog readings; various binary counters, values, and bit fields; and readings from science instruments. Temperature and electrical readings are of the greatest use, as they help to establish a detailed thermal profile of the spacecrafts’ major components. Some binary readings are useful; for instance, thruster pulse count readings help to understand maneuvers and their impact on the spacecrafts’ trajectories. It is important to note, however, that some readings may not be available and others may not be trusted. For example, thruster pulse count readings are only telemetered when the spacecraft is commanded to send readings in accelerated engineering formats; since these formats were rarely used late in the mission, we may not have pulse count readings for many maneuvers. Regarding reliability, we know from mission status reports about the failure of the sun and star sensors; these failures invalidate many readings from that point onward. Thus it is important to view telemetry readings in context before utilizing them as source data for our investigation.
On-board telemetry not only gives a detailed picture of the spacecraft and its subsystems, but this picture is redundant: electrical, thermal, logic state and other readings provide means to examine the same event from a multitude of perspectives.
In addition to telemetry, there exists an entire archive of the Pioneer Project documents for the period from 1966 to 2003. This archive contains all Pioneer 10 and 11 project documents discussing the spacecraft and mission design, fabrication of various components, results of various tests performed during fabrication, assembly, pre-launch, as well as calibrations performed on the vehicles; and also administrative documents including quarterly reports, memoranda, etc. Information on most of the maneuver records, spin rate data, significant events of the craft, etc. is also available.
http://www.livingreviews.org/lrr-2010-4 | ![]() This work is licensed under a Creative Commons License. Problems/comments to |