Explorer 47, also designated IMP‑6 (International Monitoring Platform‑6), was a United States scientific satellite launched as part of NASA’s Explorer program. It was the sixth spacecraft in the Interplanetary Monitoring Platform series, designed to study the interplanetary medium, solar wind, cosmic rays, and magnetospheric phenomena.
Launch and Spacecraft
- Launch vehicle: Thor‑Delta 225
- Launch site: Cape Canaveral Air Force Station, Launch Complex 17A (CCAFS LC‑17A)
- Launch date: 26 October 1972, 13:10 UTC
- Spacecraft bus: IMP‑6, a cylindrical spin‑stabilized design, approximately 1.5 m in diameter and 3 m in length, with a total mass of ~ 280 kg (including propellant).
Mission Objectives
- Measure the physical properties of the solar wind (velocity, density, temperature).
- Observe energetic particles, including galactic and solar cosmic rays.
- Study the Earth's magnetosphere and its interaction with the solar wind.
- Provide continuous monitoring of interplanetary magnetic fields.
Scientific Instruments
Explorer 47 carried a suite of sensors, including:
- Plasma Analyzer: Determined solar wind ion composition and distribution.
- Magnetometer: Measured vector magnetic fields in the interplanetary space.
- Cosmic‑Ray Detectors: Detected protons, electrons, and heavier nuclei across a broad energy range.
- Particle Telescope: Recorded directional fluxes of energetic particles.
- Plasma Wave Instrument: Monitored electric and magnetic wave phenomena.
Operational History
- The spacecraft entered a heliocentric orbit after Earth escape, remaining in a near‑circular orbit at approximately 0.9 AU from the Sun, with an orbital period of ~ 365 days.
- Data collection commenced shortly after checkout and continued uninterrupted for over 11 years.
- Contact with the satellite was lost on 29 February 1984, marking the end of the mission.
Scientific Contributions
Explorer 47 contributed to a long‑term dataset on solar wind variability and magnetospheric dynamics, complementing observations from earlier IMP missions and later spacecraft (e.g., ISEE, Voyager). Its measurements helped refine models of solar‑terrestrial coupling, the structure of interplanetary magnetic fields, and the behavior of cosmic‑ray modulation over solar cycles.
Program Context
- The Explorer program, initiated in 1958, comprises a series of low‑cost scientific satellites.
- IMP‑6 (Explorer 47) followed IMP‑5 (Explorer 33) and preceded IMP‑7 (Explorer 51).
- Data from the IMP series informed the design of subsequent heliophysics missions, including the Advanced Composition Explorer (ACE) and the Parker Solar Probe.
Reference
- NASA’s National Space Science Data Center (NSSDC) mission archive for Explorer 47 (IMP‑6).
All information presented is derived from publicly available NASA records and accepted scientific literature.
