EXPLORER 30

About This Satellite

Explorer 30, also known as SOLRAD 8, launched on November 19, 1965 to measure solar X-ray and ultraviolet emission. Standardized detectors allowed observations to be compared with other SOLRAD experiments. The measurements were radiation signals, not resolved photographs of sunspots or individual structures on the solar surface.

A failed memory changed how the data could be collected

NASA's experiment catalog reports that the core memory failed at launch, leaving real-time collection only. The distinction matters when reading a mission-wide coverage claim: an observing programme intended to monitor the Sun could still have gaps in its received data.

Detector saturation and changing orientation limited the record

The catalog reports useful observations from November 27, 1965 to August 24, 1967, but explicitly notes saturated Lyman-alpha and shortest-wavelength X-ray detectors at normal viewing angles. Slowing rotation also degraded the viewing geometry during the second year. The date range does not guarantee usable measurements in every channel throughout that interval.

Mission reference: NASA NSSDC solar-physics catalog: SOLRAD 8 instruments and data limitations. Editorial review: 2026-09-15.

Rotation swept the detectors across the Sun

NASA's earlier mission inventory describes fourteen photometers around the satellite's equatorial belt, with the spin axis perpendicular to the Sun-satellite line. Each rotation brought them into view of the Sun. The detector arrangement explains why spin and aspect angle affected measurement quality: the sensors did not remain continuously pointed at the Sun like a modern stabilized telescope.

Reference: NASA NSSDC: Explorer 30 photometer arrangement and spin geometry.

Small gas thrusters controlled spin, not a solar destination

The US Navy's research history describes gas thrusters producing thousandths of a pound of thrust, first used to spin-stabilize the SOLRAD series on SOLRAD 8. It independently gives the November 19, 1965 launch date, unlike the November 18 entry in the earlier NSSDC inventory. These thrusters supported spacecraft attitude behaviour; observing the Sun did not require SOLRAD 8 to leave Earth orbit.

Reference: US Naval history: SOLRAD 8 launch date and gas-thruster spin stabilization.

Reading this orbital snapshot

Based on TLE epoch: 2026-09-05. Estimated altitude ranges from 654 km at perigee to 851 km at apogee, a difference of 196 km. The orbital period is about 99.9 minutes. Eccentricity 0.01377 shows why a single altitude cannot describe the whole path. In a two-body approximation, perigee speed is 1.03 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 59.71 degrees implies approximate geocentric ground-track limits of 59.7 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 1738 · GCAT: S01738 (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)

Satellite Details