DIAPASON (D1-A)

About This Satellite

Diapason, or D-1A, was a French experimental satellite combining scientific measurements with a test of sustained operation in orbit. Its instruments included Doppler experiments, while its power system paired solar cells with a nickel-cadmium battery supplied by Saft. Keeping the electronics powered through eclipse was part of making the experiment useful beyond a successful launch.

Sunlight generation and eclipse storage had different jobs

Saft describes solar panels generating electricity and the battery supplying it during orbital eclipse. A satellite could therefore continue operating when Earth blocked direct sunlight. The battery was an energy store within the spacecraft power system, not an independent source expected to run unrecharged for the entire mission.

Telemetry let engineers learn from hardware in orbit

CNES analysed telemetry on Diapason and its battery and returned performance information to the manufacturers. That feedback connected a scientific flight with later engineering improvements. It also distinguishes reported electrical performance from an assumption that every experiment remained equally useful throughout the mission.

Mission reference: Saft: Diapason 1A power system and in-flight engineering feedback. Editorial review: 2026-09-15.

The launch and its preparation survive in a contemporary film

CNES's 1966 documentary follows D-1A manufacturing, environmental testing, transport, launch-site integration, and tracking preparations. The archive identifies launch on February 17, 1966 aboard Diamant-A2 from Hammaguir in Algeria. This gives the profile a mission-specific visual reference: it is footage and documentation of this spacecraft's preparation, rather than a generic modern satellite illustration.

Reference: CNES film archive: Diapason, construction through the February 17, 1966 launch.

Doppler geodesy used changing radio frequency, not map photography

An Institut geographique national paper published in UN conference proceedings identifies Diapason and Diademe as French satellites carrying stable-frequency transmitters for geodetic work. In this method, relative radial motion changes the received frequency. Ground observations of that change support geometric measurements with suitable receivers and processing. The paper's separate performance figures for TRANSIT must not be reassigned to Diapason merely because both used Doppler techniques.

Reference: C. Boucher, IGN: Geodesy by Doppler Satellite, UN conference proceedings.

Battery endurance is a component-level result

Saft's fiftieth-anniversary report states that the battery supplied power for six years against an initially planned two-year mission. This is a useful result about the power system. It should not be expanded into an exact spacecraft shutdown date, a six-year guarantee of continuous scientific coverage, or evidence of present-day transmission from the object.

Reference: Saft International 34: Diapason battery endurance versus the initial mission plan.

Reading this orbital snapshot

Based on TLE epoch: 2026-09-05. Estimated altitude ranges from 497 km at perigee to 2,294 km at apogee, a difference of 1,797 km. The orbital period is about 113.7 minutes. Eccentricity 0.11558 shows why a single altitude cannot describe the whole path. In a two-body approximation, perigee speed is 1.26 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 34.09 degrees implies approximate geocentric ground-track limits of 34.1 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 2016 · GCAT: S02016 (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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