SES-15 (WAAS/PRN 133)

SES-15, catalogued by NORAD as object 42709 and carrying the international designator 2017-026A, is a geostationary communications satellite operated by the Luxembourg-based satellite fleet operator SES. Launched on May 17, 2017, the spacecraft occupies a near-perfect equatorial geostationary orbit and remains operational as of the latest catalog update. Among its most publicly significant roles is its participation in the Wide Area Augmentation System (WAAS), a satellite-based augmentation system managed by the United States Federal Aviation Administration that improves the accuracy and integrity of GPS signals for aviation navigation across North America. In this capacity the satellite is identified by the WAAS pseudorandom noise code PRN 133.

Mission and Purpose

SES-15 serves a dual-purpose role that distinguishes it from many conventional commercial communications satellites. On one level, it functions as part of the SES fleet providing broadband and video broadcasting services. On another, it hosts a WAAS payload operated on behalf of the FAA, making it an integral part of civil aviation infrastructure across the United States and neighboring regions.

WAAS works by receiving GPS signals at a network of precisely surveyed ground reference stations, computing corrections for timing errors, ionospheric disturbances, and satellite orbit inaccuracies, and then broadcasting those corrections via geostationary satellites — including SES-15 — to aircraft equipped with WAAS-capable receivers. This allows suitably equipped aircraft to achieve positioning accuracy well within the tolerances required for approach and landing procedures at thousands of airports. The assignment of PRN 133 to SES-15 identifies it uniquely within the WAAS signal architecture, allowing receivers to distinguish its augmentation signal from those of other WAAS satellites.

The broader commercial communications mission of the satellite is not fully detailed in publicly available catalog records, and specific transponder configurations or frequency bands in use are not confirmed in the verified technical record for this entry. What is clear is that SES-15 was procured and positioned as part of SES's ongoing strategy to serve the North American market, offering capacity over a region where demand for both broadband connectivity and aviation-grade navigation augmentation is substantial.

Orbit and Tracking

SES-15 occupies a geostationary orbit with an apogee of 35,797 km and a perigee of 35,793 km, giving it an orbital profile that is, for practical purposes, perfectly circular. Its inclination is 0.0°, meaning the satellite travels along the equatorial plane without any measurable north-south drift relative to Earth's surface. The orbital period is 1,436.2 minutes — almost exactly 24 hours — which is precisely the defining characteristic of a geostationary orbit: the satellite completes one revolution in the same time it takes Earth to rotate once, causing it to appear stationary when viewed from the ground.

The remarkably small difference between apogee and perigee — just 4 km — reflects the high degree of orbital maintenance that geostationary operators routinely perform. Station-keeping maneuvers, carried out using onboard propulsion, counteract the gravitational perturbations from the Moon and Sun and the slight non-uniformities in Earth's own gravitational field, all of which would otherwise cause the satellite to drift in both longitude and inclination over time. Without these periodic corrections, a geostationary satellite would gradually develop an inclined, figure-eight ground track visible from the surface.

For tracking purposes, NORAD catalog ID 42709 is the primary identifier used in two-line element sets (TLEs) distributed by space surveillance networks. Because SES-15 is geostationary, its TLE is updated relatively infrequently compared to low-Earth orbit objects — its position changes slowly and predictably, and the main variables requiring correction are the fine adjustments resulting from station-keeping burns. Users querying this object in orbital databases will find it essentially fixed over a single equatorial longitude, consistent with its role as a communications relay requiring stable, uninterrupted line-of-sight contact with fixed ground antennas and aircraft receivers.

Design and Operator

SES-15 was designed and manufactured by Boeing Defense, Space & Security (now part of Boeing's space division), drawing on Boeing's heritage of commercial geostationary satellite construction. The spacecraft has a launch mass of 2,300 kg, a figure that places it in the medium class of geostationary communications satellites. Boeing's commercial satellite platforms are known for their flexible payload accommodation and on-orbit reliability, attributes that align with a mission requiring both commercial bandwidth delivery and the high-availability demands of aviation navigation augmentation.

The satellite was designed with a service life of at least 15 years from launch, a typical design horizon for geostationary assets intended to amortize their considerable development and launch costs over a long operational period. Having launched in May 2017, the satellite would be expected to remain viable well into the 2030s under normal operational conditions, assuming propellant reserves — which ultimately limit geostationary satellite lifespans through the depletion required for station-keeping — hold out across that timeframe.

SES is one of the world's largest satellite operators by fleet size and orbital slot holdings, headquartered in Betzdorf, Luxembourg. The company manages a diverse portfolio of geostationary and medium-Earth orbit assets serving broadcast, broadband, government, and mobility markets globally. SES-15 represents one of the operator's North American deployments, integrated both into the company's commercial service offerings and into a public safety infrastructure role through the WAAS agreement with the FAA. The satellite is listed with SES as both operator and owner country in the international catalog, reflecting the company's role as the responsible party for the spacecraft's orbital operations.

The launch vehicle and launch site details for the May 17, 2017 mission are part of the historical record of this deployment, though specific launch provider details are not enumerated in the verified catalog data presented here. The launch date corresponds to a period of active commercial geostationary launch activity, and the satellite successfully reached its operational geostationary slot following an anticipated transfer orbit phase after separation from its launch vehicle.

Current Status and Significance

As of the most recent catalog data, SES-15 remains in orbit with no decay or reentry date recorded — it continues to function as an active on-orbit asset. Its persistence in a near-perfectly circular geostationary orbit with zero inclination is consistent with an operationally maintained satellite receiving regular station-keeping attention from its ground control teams.

The satellite's significance extends beyond its commercial role. Its inclusion in the WAAS constellation under PRN 133 means that every WAAS-equipped aircraft operating in or transiting North American airspace may be relying, in part, on the signal this satellite transmits for navigation correction data. This makes SES-15 a quietly critical piece of transportation infrastructure, even though it is not a government-owned spacecraft. The arrangement reflects a broader trend in which government navigation augmentation systems are hosted on commercial satellite platforms, distributing the cost and operational burden while leveraging the reliability and positioning of established commercial operators.

From a space situational awareness perspective, geostationary objects like SES-15 are among the more straightforward to track, given their predictable, nearly stationary positions. However, they are also among the most valuable orbital slots, and the geostationary arc remains one of the most congested and contested regions of near-Earth space. SES-15's continued operation in a well-maintained near-zero-eccentricity orbit reflects responsible orbital stewardship consistent with the long-term value of geostationary real estate.

At end of operational life, geostationary satellites are typically boosted into a "graveyard" orbit several hundred kilometers above the geostationary belt, removing them from the congested operational arc and preserving valuable slots for future users. Planning for such a disposal maneuver requires retaining sufficient propellant throughout the satellite's operational life — a consideration that operators like SES factor into mission planning from the outset.

How to Spot It

SES-15 is not a practical visual observation target for most sky watchers. Geostationary satellites orbit at approximately 35,800 km altitude — roughly 100 times higher than the International Space Station — making them far too faint to see with the naked eye under any ordinary conditions. At that distance, even a 2,300 kg spacecraft subtends an angle far below the threshold of unaided human vision, and the satellite does not move against the star background in any perceptible way, appearing effectively stationary.

With a sufficiently powerful telescope and precise pointing coordinates, experienced observers have been known to glimpse geostationary satellites as faint, unmoving points of light against drifting star fields during long-exposure imaging. For SES-15, the relevant orbital position is fixed along the equatorial geostationary arc, and its longitude can be inferred from its operational role and orbital parameters. However, casual visual observation is not considered feasible, and this satellite is of most interest to trackers working with RF receiving equipment capable of detecting its WAAS or commercial signals rather than optical observers.