Mapping planet Earth for better positioning: ESA's GENESIS mission

Mapping planet Earth for better positioning: ESA’s GENESIS mission

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10/20/2022
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ESA’s Navigation Directorate is planning a new satellite, the results of which will enable the generation of an updated global model of the Earth – the International Terrestrial Reference Frame, used for everything from land surveying to measuring sea level rise – with an accuracy of up to 1 mm while tracking ground movement of only 0.1 mm per year. This improvement will have an immediate impact on numerous applications in navigation and earth sciences, including improving the accuracy of the Galileo navigation system. This mission, called GENESIS, will be proposed to next month’s ESA Ministerial Council meeting.

GENESIS

GENESIS will work by combining and co-locating all four main technologies currently used for geodetic measurements on Earth, for the first time on board a satellite in orbit at 6,000 km altitude on the same platform. This satellite also receives one of the most precisely determined orbits of all objects in space, down to the millimeter scale.

“Measurements are all about precise reference points,” explains Javier Ventura-Traveset, Head of ESA’s Galileo Navigation Science Office.

Precise earth measurement from space

“Thanks to GENESIS, we will improve the accuracy of the Earth-Space Reference System by about an order of magnitude. This is essential for positioning and navigating in civil society and for proper georeferencing of all geospatial information. GENESIS will also make it possible to improve the ‘precise orbit determination’ of Galileo and other satellites and in turn immediately improve their positioning performance as we will have a more accurate reference for the exact distances their signals travel from space to the ground.”

The data collected by GENESIS will not only improve our knowledge of the orbits of Galileo – and other GNSS satellites of the Global Navigation Satellite System – but also allow “phase center calibration” of GNSS antennas, identifying the offset between their mechanical and electrical centers plays a key role in many aspects of positioning, navigation and timing.

Geodetic payloads on the GENESIS satellite

In addition, the high-precision orbital tracking that GENESIS needs to fulfill its mission will enable one of the most accurate modeling yet of the nongravitational forces acting on satellites in space — such as solar radiation pressure, which is a slight but steady pressure that objects in orbit date from receive sunshine itself.

GENESIS itself will be a relatively small meter-scale satellite, but the challenge is to synchronize and cross-calibrate its quartet of payloads in a very stable environment, and to map their positions relative to the satellite’s center of mass to within a millimeter or less throughout the entire mission duration.

International Terrestrial Reference Framework

A new look at our home planet

Equivalent benefits will accrue to many other space missions, such as the radar altimetry satellites used to track sea level rise, as well as earth-based science and location-based services.

Javier adds: “Thanks to GENESIS, we will improve the current accuracy of the International Terrestrial Reference Frame (ITRF), which forms the basis for all space-based and ground-based observations in navigation and geosciences, and therefore its improvement will bring great benefits in all related applications. GENESIS outcomes will also strengthen many everyday location-based services, such as land surveying, intelligent transportation systems, precision farming and infrastructure maintenance.”

Global Geodetic Observing System stations worldwide

The ITRF, in turn, is constructed from a grid of specific reference points: Global Geodetic Observing System stations distributed around the globe, whose positions are precisely and regularly mapped using a quartet of space-based geodetic techniques.

Javier adds: “The problem is that when all these methods are combined to generate ITRFs, they are affected by the accuracy with which we determine the difference coordinates between the reference points of each technique, called local bindings, and by some systematic errors, Structure of the overall error level.”

Laser range to the satellite

“But now, by running them all together from the same satellite, and with the instruments properly calibrated and synchronized, we can identify and correct for these distortions over time and achieve much higher overall accuracy and stability.” GENESIS, in turn, becomes a dynamic geodetic observatory in space, efficiently complementing existing ground-based infrastructure and offering a breakthrough in improving the accuracy and consistency of the Earth’s frame of reference.”

Combined scientific measurements

GENESIS will start with the following geodetic payloads, which are used today to determine the position of observation stations:

Receiver for the global navigation satellite system Satellite navigation, also known as satnav, is one of the most widely used geodetic techniques. The positioning of a given location is continuously fixed, using multiple satellite navigation constellations for added accuracy, and becomes more precise over time to within millimeter range, additionally revealing gradual drifts due to earth movements.
Satellite Laser Ranging In this measurement method, laser pulses bounce back from a retroreflector on board a satellite and then measure their round-trip times to determine the distance the laser light has traveled to within a few millimeters.
DORIS receiver France’s Doppler Orbitography and Radiopositioning Integrated by Satellite, or DORIS system, has been in operation for three decades and has become a standard data source for the ITRF. DORIS signals from satellites are compared to those coming from a 60-strong network of receiver stations spread across the planet in terms of their ‘Doppler shift’ – frequency increases on approach and decreases on departure – to determine their relative position to be determined to the nearest centimetre.
VLBI Very Long Baseline Interferometry (VLBI) began as a radio astronomy technique that precisely combines observations of celestial objects such as quasars from multiple radio telescopes to achieve resolution equivalent to that of a single giant telescope. For geodesy, the technique can be reversed so that the exact times of joint observations of celestial targets can deduce the exact distance between locations. An artificial radio source on board GENESIS will therefore serve as a common target for several VLBI stations on Earth and will transmit on at least two frequency bands.

One or more of these instruments, once properly qualified and characterized with the GENESIS mission, could potentially also be flown on future Galileo satellites.

Very long baseline interferometry

Strong scientific and international support

Following the publication of a Scientific White Paper and the recent ESA GNSS Scientific Colloquium in Sofia, Bulgaria, the proposed mission has received very strong support from the scientific community as well as interest from NASA.

NAV for CM22 fact sheet

In addition, the potential of this mission was also recently recognized during the UN International Committee on GNSS 16th Meeting 9-14 October in Abu Dhabi highlighting the multiple benefits of this mission for precise navigation, geodesy, earth science and climate change monitoring.

Recently, an ESA “Request for Information” for the GENESIS mission was published in order to collect further contributions from industrial partners who could carry out the mission after approval.

Continue to FutureNAV

GENESIS is supported by ESA’s Directorate of Navigation FutureNAV programme, which also includes in-orbit demonstration satellites for a low-Earth satellite navigation constellation. The FutureNAV programme, including GENESIS, is up for decision at the next ESA Ministerial Council in November.

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