ASTRA 5B (EGNOS/PRN 123)

ASTRA 5B, catalogued by NORAD under ID 39617 and carrying the international designator 2014-011B, is a geostationary communications satellite operated by SES S.A., one of the world's leading satellite fleet operators. Launched in March 2014, the spacecraft occupies a slot above the equator and serves broadcasting and data distribution needs across Eastern Europe. It is also known by the alternate designation Astra 3C, and plays a secondary role as part of the European Geostationary Navigation Overlay Service (EGNOS), operating under the pseudorandom noise code PRN 123 — a relatively unusual dual role that makes it notable among the broader Astra fleet.

Mission and Purpose

ASTRA 5B was conceived as SES's 56th satellite, positioned to extend and strengthen the company's broadcasting capabilities in the Eastern European market. The spacecraft was placed at the 31.5° East orbital position, which had been identified by SES as a key slot for reaching audiences across Eastern Europe via direct-to-home (DTH) satellite television, as well as supporting digital terrestrial television (DTT) distribution infrastructure and cable head-end reception. This orbital longitude had been developed by SES specifically to address the growing demand for high-quality broadcast services in that region, where satellite distribution remained a primary pathway for multichannel television delivery.

Beyond its primary role in broadcasting, ASTRA 5B carries a navigation payload that integrates it into the EGNOS network. EGNOS — the European Geostationary Navigation Overlay Service — is a satellite-based augmentation system (SBAS) developed under the auspices of the European Space Agency, the European Commission, and EUROCONTROL. Its function is to improve the accuracy, reliability, and integrity of GPS positioning signals over European territory, making it particularly valuable for safety-critical applications such as civil aviation approaches, maritime navigation, and precision agriculture. By hosting an EGNOS transponder and transmitting under the PRN 123 pseudorandom noise identifier, ASTRA 5B contributes real-time correction and integrity data to GPS users across its coverage zone. This kind of hosted payload arrangement — where a commercial communications satellite carries a secondary navigation or augmentation payload — is an efficient use of on-orbit resources and has become an increasingly common model in the industry.

The combination of high-capacity broadcast services and navigation augmentation in a single platform reflects a broader trend in satellite operations toward multimission spacecraft that maximize the return on launch investment. For SES, it also deepened the company's relationship with European institutional space programs, complementing its commercial broadcasting business with a public-service infrastructure role.

Orbit and Tracking

ASTRA 5B resides in a near-perfect geostationary orbit, as reflected in its current tracked parameters. The spacecraft has an apogee of 35,803 km and a perigee of 35,787 km, giving it an extremely low eccentricity — the difference of only 16 km between the highest and lowest points of its orbit is characteristic of a well-maintained, operationally active geostationary satellite. Its orbital inclination is just 0.1°, meaning it deviates only fractionally from the equatorial plane, which is consistent with active station-keeping operations that counteract the natural tendency of geostationary satellites to drift in inclination over time due to gravitational perturbations from the Moon and Sun.

The orbital period of 1,436.2 minutes — very close to the 1,436-minute sidereal day — confirms that the satellite completes one orbit in very nearly the same time it takes Earth to rotate once relative to the stars. This synchronization is the defining characteristic of a geostationary orbit and is what allows the satellite to remain effectively stationary above a fixed point on the equator as seen from the ground. For broadcast and navigation applications alike, this stationarity is essential: it allows receiving antennas to be fixed rather than tracking, dramatically reducing the cost and complexity of ground infrastructure.

ASTRA 5B was launched on March 21, 2014, and remains in orbit as of the time of this writing, with no reentry or decay date recorded in the catalog. As a commercial geostationary satellite, it is expected to have an operational design life measured in decades, after which it would typically be moved to a graveyard orbit — a supersynchronous disposal orbit several hundred kilometers above the geostationary ring — to free up its operational slot.

The satellite is tracked by the U.S. Space Surveillance Network and maintained in the public catalog under NORAD ID 39617. Its COSPAR international designator, 2014-011B, indicates it was the second catalogued object from the 11th launch of 2014, reflecting its shared launch vehicle with at least one other payload.

Design and Operator

Specific details regarding the manufacturer and the satellite's mass are not recorded in the publicly available catalog data for this object. What is known is that ASTRA 5B was built to serve both commercial communications and institutional navigation augmentation roles, requirements that typically drive the selection of a large, high-power geostationary bus capable of hosting multiple distinct payload types.

SES S.A., the Luxembourg-headquartered operator of the Astra fleet, is one of the largest commercial satellite operators in the world by number of spacecraft and by total capacity managed. The Astra brand under which this satellite flies has historically been associated with direct-to-home television distribution in Europe, with the Astra orbital positions at 19.2° East and 28.2° East being among the most densely populated geostationary slots on the Clarke Belt in terms of active transponders. The 31.5° East position represented a more recent expansion of the Astra footprint, targeting audiences not comprehensively served by the earlier western positions.

SES has a long track record of integrating hosted payloads onto its commercial satellites, and the EGNOS payload carried by ASTRA 5B is consistent with the company's approach to working with European institutions. Hosting arrangements of this kind generally involve the commercial operator providing power, structural support, and telemetry services for the secondary payload, with the institutional customer retaining operational control of the payload itself.

Significance and Current Status

ASTRA 5B holds a distinctive place in the SES catalog as one of the few Astra-branded satellites to carry a dual role that bridges commercial broadcasting and institutional safety-of-life navigation services. Its contribution to EGNOS under PRN 123 places it within a network that underpins aviation safety across Europe, a responsibility that contrasts with — and complements — its role in delivering television channels and broadband services to households and cable operators.

The satellite's designation as Astra 3C reflects SES's internal naming conventions, which sometimes assign a satellite a series designation based on its slot family alongside a commercial brand name that emphasizes mission or customer identity. The simultaneous use of both names in the catalog — ASTRA 5B and Astra 3C — can occasionally cause confusion among researchers, but both identifiers refer to the same physical object in the same orbital slot.

As of the current catalog data, ASTRA 5B remains in its operational geostationary orbit with no indication of retirement or disposal. Its orbital parameters — closely matched apogee and perigee, near-zero inclination — are consistent with a satellite receiving regular station-keeping maneuvers, suggesting it remains under active operational control. For users across Eastern Europe, it continues to serve as a primary or supplementary source of broadcast signal distribution, while for the European navigation community, its EGNOS transponder continues to contribute to the integrity monitoring and correction infrastructure that underpins precision GPS use across the continent.

The launch of ASTRA 5B in 2014 also marked a moment of maturation in the Eastern European broadcast satellite market, as operators and broadcasters increasingly invested in dedicated orbital resources for that region rather than relying on spillover coverage from satellites positioned for Central and Western European audiences. In that sense, the satellite represents both an infrastructure milestone for SES and a broader marker of the region's growing importance to European satellite communications.

How to Spot It

ASTRA 5B is a geostationary satellite and, like all objects in that orbit, it does not move visibly across the sky as seen from Earth's surface. From any fixed ground location, a geostationary satellite appears as a stationary point relative to the background stars, distinguishable only by its lack of proper motion when observed over time. At roughly 35,800 km altitude — nearly three times the diameter of the Earth away — visual detection requires optical aid, and casual naked-eye observation is not feasible.

For observers with telescopes or sensitive cameras, geostationary satellites can occasionally be identified as faint, stationary points of reflected sunlight, most visible during twilight hours when the satellite is illuminated by the Sun but the sky background is dark enough to permit contrast. ASTRA 5B would appear near the celestial equator when observed from mid-latitudes, fixed at the position corresponding to 31.5° East longitude projected outward to geostationary altitude. Dedicated satellite-tracking software using its NORAD ID 39617 will provide precise azimuth and elevation data for any observer location.