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Spacecraft Instrument Tracks

Some instruments measure from a fixed site; some measure while moving. A satellite is the ultimate moving platform, and two sibling dexes hold what its instruments measured along the orbit — one slot = one instrument's full measurement record: spacecraft_particle_counts for radiation counters, spacecraft_field_measurements for field instruments like magnetometers.

The dexes hold the particle instruments of Explorer 4 (1958), Explorer 7 (1959–1961) and Injun 1 (1961–1962) — three of them satellites of James Van Allen's own group in the first years after Explorer 1 discovered that Earth is wrapped in belts of trapped radiation — plus Explorer 12's magnetometer. Explorer 4's track is the oldest measured data on TerraPulse by roughly forty years; Injun 1's is over 830,000 readings at one-second cadence.

🛰️ Readings
1,848,405
📟 Tracks
10
📅 Span
1958–1965
⏱️ Time resolution
0.01 s

The tracks

  • Explorer 4, charged-particle detector — 23,865 rows, July 26 to September 21, 1958, across 347 telemetry-station passes: a UTC timestamp, seven count-rate channels from the four onboard detectors (two Geiger tubes, two scintillators), and the spacecraft's position.
  • Explorer 7, trapped radiation and solar protons — 376,243 rows from launch day (October 13, 1959, 22:41 UT) to the instruments' documented last day of operation (February 28, 1961, 19:21 UT), timestamped to the hundredth of a second with latitude, longitude, and altitude on every row.
  • Explorer 7, heavy primary cosmic rays — 17,237 ion-chamber rows over mission days 0–231.
  • Injun 1, all six experiments merged — 831,499 one-second records from Van Allen's University of Iowa satellite, June 30, 1961 to August 31, 1962: cadmium-sulfide detectors, Geiger tubes, an electron spectrometer, solid-state proton detectors, and an aspect magnetometer, every row geolocated with B and L values. The archive's own 1971 caveats ride along verbatim — including that the proton channels are contaminated after July 9, 1962, and that the photometer never saw anything but the rocket body that failed to separate.
  • Telstar 1, proton and electron radiation — 112,677 records across 3,170 telemetry passes, from launch day (July 10, 1962) to February 21, 1963 — the day its radiation-damaged transmitter failed. Nine measured counting-rate channels per record, with geocentric radius and sub-satellite position; the decoded orbit matches the documented one to the third decimal.
  • Telstar 2, proton and electron radiation — 120,625 records across 2,060 telemetry passes, from launch day (May 7, 1963 — the first pass begins 29 minutes after liftoff, over Johannesburg) to May 7, 1965, nine days before the two-year timer shut the transmitter off. The archive's catalogue page claims the record ends in April 1964; the restored tapes carry a further year, and this dex holds all of it. Where a pass file's header was damaged in restoration, its calendar day was restored only when tape order pinned it uniquely — those rows are flagged, and the ambiguous ones were dropped rather than guessed.
  • Injun 3, all detectors merged — 208,036 eight-second records from Van Allen's second Iowa satellite, December 1962 to October 1963, every row geolocated: GM tubes, scintillators, electron spectrometers (including the channel that counted the artificial "Starfish" electrons), a proton spectrometer, photometers and VLF receivers.
  • Relay 1, proton-electron counters — 13,791 records from NASA's experimental comsat, December 1962 to May 1964, monitoring the belts at ten-second resolution across nineteen detector channels.
  • Explorer 12, fluxgate magnetometer — 6,626 ten-second-averaged field readings from launch day (August 16, 1961) through September 15: field magnitude in gammas and orientation angles, each with its own standard deviation from the same 32-point average. The angles are spacecraft-referenced, the record says so, and the surviving archive carries no per-row position — the ephemeris-merged tape was never recovered, and the page won't pretend otherwise.
  • Mariner 2, fluxgate magnetometer — 137,817 field readings from the first spacecraft to reach another planet, on its 1962 cruise to Venus. This is the platform's first interplanetary track: the position is heliocentric, roughly one astronomical unit from the Sun, and the field is given in radial, tangential, and normal components with the magnitude verified against them. It arrives as plain text — no tape to decode.

Two kinds of columns get special honesty treatment. The magnetic-coordinate values (B and L) were computed by the original investigators from a geomagnetic field model — they are carried as organizing coordinates and flagged model_derived; the measurements in this dex are the count rates and the clock. And where the archive's own documentation for a column label is currently unreachable, the column is carried verbatim under a positional name rather than guessed at.

The decode

These files sat on NASA's archive flagged as "highly encoded." They turned out to be EBCDIC — 1950s IBM/CDC mainframe tape text, in three distinct tape dialects: fixed 120-byte marked records with a packed month/day/hour field and an end-of-day "hour 24" convention (Explorer 4); fixed 114-column records interleaved with tape block-control words (Explorer 7 trapped radiation); and 80-byte marked records timed in mission days and decimal hours (Explorer 7 cosmic rays); and a fourth for Explorer 12's magnetometer: little-endian record prefixes with IBM "overpunch" digits — letters standing for signed digits — and eight-digit floats, cross-checked against a 1970 NSSDC memo found beside the data. A handful of records in 1.59 million carried a corrupt byte — each was dropped and documented, not guess-repaired. Every decode recipe rides in the dex's provenance, so anyone can go from NASA's raw tape bytes to these rows.

Provenance

NASA SPDF — every track comes from the Space Physics Data Facility's open archive: the Explorer trees (SPMS-00015, SPHE-00282/00064, SPMS-00648), the Iowa Injun masters (SPMS-00023, SPMS-00018), the Bell Labs Telstar records (SPMS-00277, SPMS-00654), Relay 1 (SPMS-00434), and the Mariner 2 magnetometer — investigator-supplied records of US missions, restored by NSSDC and served openly by NASA.

Scope

Ten slots across two kinds, and growing. Any spacecraft instrument whose along-orbit measurements we hold becomes a new slot — and when an instrument measures a different phenomenon, it gets a sibling kind rather than a stretched one. The dex family flexes to fit the data's natural shape, which is exactly how dexes get made here.