EXPLORER 20

About This Satellite

Explorer 20 investigated the topside ionosphere, the ionized region above the main electron-density peak. NASA's programme review records observations from August 25, 1964 through December 29, 1965, totalling about 1,450 hours. Its fixed-frequency soundings helped researchers study plasma resonances and small-scale ionospheric irregularities, complementing the Alouette and ISIS missions.

The spin rate itself became a useful engineering observation

The review describes an initial spin rate of 1.53 revolutions per minute after antenna deployment, declining to about 0.47 after a year. Tracking that change helped extend investigations of spacecraft spin decay. The rotating spacecraft was therefore not an ideal platform with a permanently fixed spin rate; its own behaviour had to be measured and understood.

The ion probe did not deliver the intended science data

NASA explicitly records that the ion-probe experiment failed to yield scientific data. Nevertheless, experience integrating a direct-measurement probe with long sounder antennas informed later spacecraft. The successful sounder results should not be used to imply that every instrument succeeded, or to invent a usable ion-temperature dataset from the probe.

Mission reference: NASA NSSDC: Explorer 20 results in the Alouette-ISIS programme review. Editorial review: 2026-09-14.

Three experiments asked different questions

NASA's historical inventory lists a fixed-frequency sounder, an ion probe, and a galactic radio-noise receiver on the 44.5 kg spacecraft, launched by Scout on August 25, 1964. A sounder investigates a response to transmitted radio signals, while the probe was intended to sample the immediate plasma environment. The radio-noise receiver had a different observing role again; the payload list is not a list of three imaging cameras.

Reference: NASA Historical Data Book: Explorer 20 characteristics and payload inventory.

Fixed frequencies revealed detail that a sweep treated differently

A NASA-hosted programme account explains that Explorer 20 data were used mainly for fine structure in ionospheric irregularities and plasma resonances. Although electron-density profiles could also be derived, Alouette 1 supplied plentiful ionograms better suited to that task. Explorer 20's value was therefore not simply a larger quantity of the same data: its observing method supported a different emphasis within the programme.

Reference: NASA-hosted Alouette-ISIS account: fixed-frequency soundings and direct-measurement limitations.

Reading this orbital snapshot

Based on TLE epoch: 2026-09-05. Estimated altitude ranges from 851 km at perigee to 994 km at apogee, a difference of 143 km. The orbital period is about 103.5 minutes. Eccentricity 0.00979 indicates a nearly circular path. In a two-body approximation, perigee speed is 1.02 times apogee speed. These are mean-element estimates, not instantaneous measurements. Distance per orbit uses an ellipse approximation.

Saved build snapshot. If a valid TLE is retrieved, this explanation and the orbit panel update together. Otherwise this dated snapshot is retained.

Ground track is not sensor coverage

An inclination of 79.90 degrees implies approximate geocentric ground-track limits of 79.9 degrees north and south. This is a prograde orbit, moving in the same general direction as Earth rotation. The plotted line marks the point beneath the object. It does not represent camera coverage, radio reception, or a guaranteed visible pass.

Accuracy and missing information

The introductory record describes the build snapshot. The orbital snapshot explanation and orbit panel share any successfully retrieved TLE; check the displayed epoch. Reentered objects retain historical data only. Mission history is not rewritten by TLE updates. TLE/SGP4 positions are predictions and can change after maneuvers or updated observations. The 14-day stale-data cutoff is a display safeguard, not an accuracy guarantee. Local passes are geometric predictions, not a visibility forecast. No verified operator or mission status means unknown, not active. Do not use this catalog for collision avoidance or operational flight decisions.

Catalog sources: CelesTrak SATCAT: NORAD 870 · GCAT: S00870 (source update 2026 Sep 4 2345:57). Supplementary metadata: SatNOGS DB, retrieved 2026-09-05T12:57:25.375Z. Page assembled 2026-09-15. GCAT phase codes describe trajectory phases, not mission health.

Learn more: TLE data · Perigee and apogee · Ground tracks · JOT (Jewawud Live Orbital Map)

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