EXPLORER 29 (GEOS 1)

About This Satellite

GEOS 1, also cataloged as Explorer 29, launched on November 6, 1965. Its role was geodesy: measuring Earth through precise observations of a satellite. It brought several agencies' tracking instruments onto one spacecraft, allowing different observing systems to examine a common target rather than relying only on separate satellites and unrelated measurements.

One target connected several measuring techniques

The payload combined Navy Doppler tracking, Army SECOR electronic ranging, Air Force optical beacons, and NASA laser reflectors and range/range-rate equipment. Their agreement was itself useful evidence. NASA's programme history explains that comparisons could reveal errors in one system by reference to the others, an important step toward a consistent geodetic network.

A laser reflector is not an onboard laser

For laser ranging, the spacecraft carried corner-cube reflectors. The laser measurement depended on light sent from a ground station and returned by the satellite. This differs from an Earth-observing lidar that transmits from orbit; drawing an onboard scanning laser would misrepresent this part of GEOS 1's equipment.

Mission reference: NASA GEOS-C press kit: historical background on GEOS 1. Editorial review: 2026-09-14.

An array of reflectors changes the returned pulse

NASA's 1972 GEOS-1 analysis treated the geometry of the corner-cube array to predict the shape of the laser return. Its calculated pulse depended on viewing orientation as well as time. The spacecraft could not simply be treated as a single mathematical reflecting point: the arrangement of real optical components mattered to interpreting a precise range measurement.

Reference: NASA NTRS: GEOS-1 laser pulse return shape analysis.

A geometric model has explicit limits

The same study deliberately excluded optical interference and atmospheric perturbations. Its pulse-shape prediction was therefore not a complete error budget for an actual observation. When comparing a plotted orbit with historical laser results, retain that distinction: a catalog trajectory and a calibrated measurement of returned light answer different questions and should not be presented as interchangeable data.

Reference: NASA NTRS: assumptions and limits of the GEOS-1 return-pulse model.

Reading this orbital snapshot

Based on TLE epoch: 2026-09-05. Estimated altitude ranges from 1,120 km at perigee to 2,268 km at apogee, a difference of 1,148 km. The orbital period is about 120.3 minutes. Eccentricity 0.07111 shows why a single altitude cannot describe the whole path. In a two-body approximation, perigee speed is 1.15 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 59.38 degrees implies approximate geocentric ground-track limits of 59.4 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 1726 · GCAT: S01726 (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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