ESA’s Celeste LEO-PNT demonstrator mission set to launch in December

Celeste becomes the name of ESA’s LEO-PNT mission, that will "mediate: between Galileo and the rest of the world. The name was announced during the celebration of 30 years of European satellite navigation, in September 2025 with two actors enacting a fictional conversation between Galileo Galilei and his imagined great granddaughter Celeste, a satellite navigation engineer working at the ESA. (Credit: ESA / M. Polo)

The European Space Agency (ESA) has confirmed plans to launch the first two satellites in its low-Earth orbit (LEO) positioning navigation and timing (PNT) constellation in the second half of December 2025. The launch will use a Rocket Lab Electron Vehicle, marking Europe’s first venture into LEO-based satellite navigation.

The LEO-PNT in-orbit demonstrator mission, called Celeste, aims to test satellite navigation capabilities in LEO and evaluate its integration with existing medium-Earth orbit (MEO) systems.

Celeste features a constellation of ten satellites that will fly close to Earth to test innovative signals across various frequency bands. The first two Celeste satellites, built in parallel by GMV and Thales Alenia Space, are set to launch in the coming months.

The dedicated Electron rocket launch will place both satellites in orbit at 510 km altitude. The launch window extends for three months beginning in mid-December 2025, with operations conducted from Rocket Lab’s New Zealand facility.

ESA Director of Navigation, Javier Benedicto, said, “We are thrilled to see the LEO-PNT demonstration advancing so quickly, with less than two years between mission kick-off and launch. This launch ensures the first European LEO-PNT satellites are in space before spring 2026, crucial for bringing the frequencies into use in compliance with the International Telecommunications Union.”

Galileo’s “Daughter Mission”

The name Celeste pays homage to Maria Celeste, Galileo Galilei’s daughter, as the two shared a strong emotional and intellectual bond, with the daughter honoring her father’s astronomical interest. This symbolic connection links the pioneering work of the father of modern astronomy to contemporary navigation systems, with Celeste serving as a bridge between Galileo’s groundbreaking discoveries and today’s satellite-based positioning technology.

The demonstrator satellites for Galileo, launched in 2005 and 2008, were called GIOVE, after the Italian word for Jupiter. This name also paid tribute to Galileo’s achievements in discovering the planet’s four largest Moons which were used to determine longitude from anywhere on Earth.

System Advantages

The initial Pathfinder A satellites are CubeSats measuring 12U and 16U formats, comparable to suitcase size and weighing approximately 20 kg to 30 kg. These satellites will broadcast in L-band and S-band frequencies and operate for at least six months following orbital commissioning.

The larger, more complex Pathfinder B satellites will follow, incorporating additional payloads to test innovative signals across multiple frequency bands and demonstrate expanded services.

LEO-PNT satellites will supplement existing GNSS constellations by providing enhanced coverage in challenging environments. The system aims to improve navigation services in deep urban areas, under heavy foliage, in polar regions and potentially indoor locations where current MEO satellites face limitations.

The complete demonstrator constellation, expected to be operational by 2027, will assess how LEO navigation systems can integrate with existing GNSS infrastructure. The mission will also test interoperability with 5G and 6G communication standards.

Preparing for Launch

Satellite integration and testing of Pathfinder A hardware and software continues ahead of the December launch. ESA and industrial teams plan to complete testing during summer 2025, with qualification and acceptance reviews scheduled for autumn.

“Pathfinder A satellites have already paid off, even before launch,” said Roberto Prieto-Cerdeira, ESA’S LEO-PNT project manager. “The experience gathered during their development is helping to identify critical technologies, system design trade-offs, design choices and optimised approaches and processes, paving the way for future phases of LEO-PNT. Having them in orbit and validating their signals and algorithms is a major additional achievement.”

Future Plans

Following the demonstrator mission, ESA plans to propose an in-orbit preparatory phase at the agency’s November Ministerial Council meeting. This phase would focus on technology development and industrialization, potentially leading to an operational system integrated with EU GNSS infrastructure.

The Celeste demonstrator is part of FutureNAV, an ESA Navigation program designed to maintain Europe’s position at the forefront of satellite navigation technology.

The mission receives backing from 15 ESA member states: Austria, Belgium, Finland, France, Germany, Hungary, Italy, Norway, Poland, Portugal, Romania, Spain, Sweden, Switzerland and the United Kingdom. More than 50 entities from 14 countries participate in the two development consortia awarded contracts in 2024.