The Navigation Support Office at the Mission Control Centre of the European Space Operations Center (ESOC) has been tasked with providing independent precise orbit determination for European space missions. ESOC, which is based in Darmstadt, Germany, is a part of the of the European Space Agency (ESA). ESA aims to use high-quality signals from Galileo alongside GPS to sharpen the orbital positioning levels for future space missions.
The Navigation Support Office has used the positive results of the Copernicus Sentinel-6 mission — one of the first missions to fly a joint Galileo-GPS capable receiver, which improved positioning capabilities — to prove to ESA mission teams that future missions can harness the power of Galileo to improve positioning accuracy.
Missions in the works
Proba-3 is a precision formation flying mission that aims to launch in 2024. The mission consists of two small satellites launched together that will separate to fly in tandem to prepare for future multi-satellite missions flying as one virtual structure. This mission will require millimeter-scale positioning precision and use a variety of positioning methods, including optical, radio and laser links and GNSS such as Galileo.
The ESA-supported Lunar Pathfinder will be launched into lunar orbit in 2024 with the intent of using it as a communication satellite for future moon missions. The spacecraft will incorporate a specially designed GPS- and Galileo-capable receiver that aims to demonstrate the feasibility of positioning fixes from 400,000 km away.
The future of Galileo
Galileo serves Europe and the world with accurate and reliable navigation services as well as a catalyst for future space missions — making it a critical aspect of both everyday life and the enhancement of accurate navigation. The constellation will continue to grow with 10 more Galileo first-generation satellites planned for launch in the next few years. Second-generation Galileo satellites with enhanced capabilities are being built for testing and qualification at ESA’s European Space Technology and Research Centre as well.
The European Space Agency (ESA) is looking for companies interested in helping create a constellation of lunar satellites to connect and guide missions to the Moon. Creating lasting telecommunications and navigation links with the Moon will enable sustainable space exploration for the hundreds of lunar missions that are due to launch within the next few decades, ESA stated.
The companies would provide telecommunications and navigation services to these lunar missions, under its Moonlight initiative.
ESA is completing two studies with two consortia of space companies based in Europe that assess the business case and the technical solutions for building and operating a constellation of lunar satellites. ESA is asking any space firms to indicate whether they would like to become involved in the ambitious project — or simply to develop lunar telecommunication and navigation technologies and products. The deadline is Oct. 28.
Artist’s rendering: NASA
On Sept. 19, ESA Director General Josef Aschbacher and NASA Administrator Bill Nelson signed a joint statement on lunar exploration cooperation at the International Astronautical Congress in Paris.
The lunar Gateway will be an outpost in orbit around the Moon. It will serve as the staging point for both robotic and crewed exploration of the lunar south pole.
ESA’s European Service Modules will power all Artemis Orion spacecraft to the Moon and back. ESA will also provide refueling elements for Gateway and a communications module that will pave the way for Moonlight.
ESA has already initiated the Lunar Pathfinder project to provide initial communications services to early lunar missions, which will also help to prepare for the next stage with Moonlight. The Lunar Pathfinder will also include a navigation payload demonstrator, which will allow positioning in lunar orbit using GPS and Galileo systems for the first time, and is due to launch in 2025.
Space companies in Europe and Canada will be invited to tender for the initial Moonlight work in December.
This month our UAV and GNSS news ranges from a drone diving into the Boston subway to a GNSS receiver designed for Moon orbit. We also look at the types of drones heading to Ukraine to help fight the Russian invasion and rescue citizens from demolished buildings.
Boston cleanup
Bostonians’ morning commutes were disrupted at the end of March after 100 tons of demolition debris fell nine stories onto ground directly above subway tunnels, and the Massachusetts Bay Transport Authority (MBTA) closed the Orange and Green lines as a precaution.
The bad news got worse. A construction worker was killed when part of a parking garage under demolition collapsed. Apparently his jackhammer-construction vehicle — in the midst of demolition work — fell nine stories when the floor near the edge of the building buckled and crumbled away.
MBTA was concerned that damage could have occurred to the subway under the building from the huge amount of debris that fell on the ground above a tunnel. The agency closed the line passing through that section of the system. Hundreds of morning commuters were turned away from the subway at nearby station entrances and were directed to buses hastily brought on as temporary shuttles around the closed subway sections.
MBTA wanted to immediately, but carefully, inspect the tunnel for damage, but was concerned for the safety of its inspection personnel. As news of the disaster circulated, the Massachusetts Department of Transportation (MassDOT) Aeronautics Division became aware of the subway issue, and proposed a rapid solution to the dilemma — to fly a drone through the tunnel. The drone would transmit high-resolution video and gather data on the status of both tracks and tunnel structure.
Soon after, Bostonians were able to watch a 29-second video collected by the drone that was sent into the subway tunnel.
“As we work to safely restore service following the Gov Center Garage accident, we teamed with @MassDOT Aeronautics to scan Orange & Green Line tunnels with a drone. This allowed us to safely assess tunnel conditions before sending engineers in for in-depth structural inspections.” pic.twitter.com/LHGUfiou9r
MBTA was then able to gauge that live inspections would be safe. The tunnel was ultimately assessed as being sound and, following test trains being run, service was restored.
It has been difficult to establish which drone was used for these initial visual tunnel inspections, but in 2021 the Aeronautics Division was operating multiple drones, including the DJI Matrice, Inspire, Phantom and Mavic, as well as a few fixed-wing and multi-rotor models manufactured by Yuneec, SenseFly and Delair.
Flyability provides the Elios 2 drone, specifically built for indoor inspection, for such places as inside underground tunnels. Similar “caged” inspection drones include Droneball 360 by Imaze, the Skycopter Cobra drone, the Asio Caged Inspection Drone and several others.
Turning our attention to space, the European Space Agency (ESA) will conduct a mission to place a refrigerator-sized satellite in orbit around the Moon. Of course, there have been many successful efforts to put things in lunar orbit since Russia first achieved the feat with Lunar 10 in 1966. NASA’s Lunar Reconnaissance Orbiter followed in 2009, along with India’s Chandrayaan-2 orbiter and its failed lander.
ESA has contracted Surrey Satellite Technology Ltd. (SSTL) in Guildford, UK, to develop the Lunar Pathfinder communications relay satellite — the first part of a project to provide communications and navigation for the Moon. This capability will enable assets on the lunar surface to communicate directly with the Pathfinder via S-band and UHF, which will then relay their signals onwards to Earth using X-band.
The satellite will also carry a laser retro-reflector and a space-weather payload designed to assess the radiation environment in orbit. This should help support landers carrying astronauts, such as the NASA Artemis, by broadcasting radiation intensity to the surface.
Artist illustration of the Pathfinder mission. (Image: SSTL)
The Lunar Pathfinder satellite. (Image: SSTL)The Pathfinder satellite will carry a few passenger payloads, but the most interesting to us might be the highly sensitive GNSS receiver, which will attempt to make position fixes from lunar orbit using GPS and Galileo satellites in Earth orbit.
The NaviMoon receiver designed by SpacePNT in Switzerland was implemented and tested by European Engineering & Consultancy, which added a special low-noise amplifier of its own design — essential for detecting minute satnav signals at 20 times the distance they usually travel to Earth’s surface from Earth orbit. In addition, antennas on GNSS satellites are designed for transmissions towards the Earth’s surface, not out toward space, further decreasing the signal strength in the vicinity of the Moon.
As you might expect, the view of the various constellations of GNSS satellites from orbit around the Moon is extremely limited. To give the NaviMoon receiver any sort of chance of picking up signals when they are in view, an onboard dynamic force model provides the receiver with its anticipated location along its orbit, and also derives the apparent direction from which signals should be observed. Even detecting a single satnav signal could assist the receiver in creating a position fix. SSTL will also reorient the Lunar Pathfinder satellite from time to time to enable the receiver to gain access to GNSS signals from Earth.
Measurements from Earth using laser ranging, aimed at the laser retro-reflector on the satellite, will be used as “truth” against which the position fixes by the NaviMoon receiver will be verified.
UAVs for Ukraine
Meanwhile, as the war in Ukraine continues to rage on, AeroVironment has been contracted by the U.S. Army to supply its RQ-20 Puma AE for use in Ukraine for almost $20 million. The package includes reconnaissance/surveillance and target acquisition kits, spares, logistics support and training for operators in Ukraine.
The Puma has an endurance of about three hours, carries a gimbaled visual/IR camera and is equipped with dual GPS receivers.
AeroVironment’s Puma is hand-launched. (Photo: Lance Cpl. Frank Cordoba/U.S. Marine Corps)
U.S. drone manufacturers have donated hundreds of other recon drones to Ukraine. The AeroVironment Quantix Recon drone takes off and lands vertically, but flies rapidly as a fixed-wing observation platform. While its endurance is not as long as the Puma’s, it flies faster so it can return with information more quickly.
Quantix lands vertically, but flies fixed wing. (Photo: AeroVironment)
Brinc has also donated and sold its Lemur tactical drones to Ukraine for use in disaster recovery work in devastated buildings throughout the country. The rugged quadrotor drone has two-way voice communications, video and lidar, and has proven itself in difficult building-collapse search and recovery operations in confined spaces. Skydio has apparently donated and sold quadrotor drones to Ukraine with multi-view video from six 200-degree color cameras, also for use in collapsed building search and recovery.
The test version of a unique satellite navigation receiver has been delivered for integration testing on the Lunar Pathfinder spacecraft.
The NaviMoon satnav receiver is designed to perform the farthest ever positioning fix from Earth, employing signals that will be millions of times fainter than those used by smartphones or cars on Earth.
The NaviMoon receiver and low-noise amplifier. (Photo: SSTL)
“This engineering model of our NaviMoon receiver is the very first piece of hardware to be produced in the context of ESA’s Moonlight initiative, to develop dedicated telecommunications and navigation services for the Moon,” explained Javier Ventura-Traveset, head of ESA’s Navigation Science Office and manager of ESA lunar navigation activities.
“It will be flown aboard the Lunar Pathfinder mission into orbit around the Moon, from where it will perform the furthest satellite navigation positioning fix ever made, at more than 400,000 kilometers away to an accuracy of less than 100 meters,” Ventura-Traveset said. “This represents an extraordinary engineering challenge, because at such a distance the faint Galileo and GPS signals it uses will be barely distinguishable from background noise. This demonstration will imply a true change of paradigm for lunar orbiting navigation.”
The washing-machine-sized Lunar Pathfinder is being built as a commercial mission by Surrey Satellite Technology Ltd. (SSTL), in the United Kingdom. ESA is funding guest payloads for it, including the 1.4-kg NaviMoon receiver that will be accommodated beside the spacecraft’s main X-band transmitter that links it with Earth.
“Receiving physical hardware for a mission is always fantastic,” said Lily Forward, SSTL system engineer. “This engineering model receiver will be integrated into our FlatSat Test Bed version of the mission to test that all our systems communicate and work together properly, ahead of receiving the flight-model receiver and antenna later this year.”
This will be SSTL’s first full-fledged mission beyond Earth, she added. “Laying the foundations for numerous scientific missions that will come after it, Lunar Pathfinder is a communications relay satellite, intended to serve assets on both the nearside and farside, orbiting in an elliptical lunar frozen orbit for prolonged coverage over the South Pole — a particular focus for future exploration. Then, during regular intervals, we will orient the spacecraft towards Earth to test out the NaviMoon receiver.”
Satnav position fixes from the receiver will be compared with conventional radio ranging carried out using Lunar Pathfinder’s X-band transmitter as well as laser ranging performed using a retroreflector contributed by NASA and developed by the KBR company.
“This will be the first time these three ranging techniques will be used together in deep space,” explained ESA navigation engineer Pietro Giordano. “There is a long heritage of lunar laser ranging, going back to the Apollo missions, and the retroreflector we are using is an evolution from NASA’s Lunar Reconnaissance Orbiter. The combination of all ranging techniques will improve the orbit estimation further, potentially beyond what radio ranging can achieve.
“In principle, this could mean that future missions could navigate themselves to the Moon autonomously using satellite navigation signals alone with no help from the ground.”
The satnav signals employed here on Earth are already vanishingly faint, equivalent to a single pair of car headlights shining all across Europe. By the time these signals reach the Moon, they have crossed distances of more than 20 times further, attenuating through space like ripples from a stone splashed in water.
“Adding to the difficulty, the satnav constellations are not designed to transmit up into space, but to keep their antennas facing Earth,” Giordano said. “So we are reliant on much weaker side-lobe signals, like light spilling from the sides of a flashlight. To be able to make use of these signals, we turned to a specialist in space-based satellite navigation, whose signal-processing techniques have really proven the magic ingredient.”
Testing the NaviMoon receiver and Low Noise Amplifier engineering models at SSTL ahead of integration testing. The flight models of the receiver and amplifier will be delivered later in 2022. (Photo: SSTL)
SpacePNT, based in Switzerland, oversaw the NaviMoon receiver design. “We began working on the idea of lunar-distance satnav positioning back in 2013 as something of a scientific challenge,” said Cyril Botteron, company head.
“The combination of Galileo dual-frequency signals with those of the existing GPS satellites is what started to make it feasible,” Botteron said. “Although, along with the extreme sensitivity that is demanded, the other big problem is that from the Moon all the satnav satellites are in the same narrow geometry of sky around Earth, periodically rotating out of view.”
Lunar navigation satellites will ultimately help guide Moon landings, such as with the European Large Logistic Lander. (Image: ESA)
The solution that SpacePNT came up with leverages more than half a century of lunar exploration. The company installed a dynamic software model of all the forces acting upon the satellite into the receiver, including the gravitational influences of the Moon, Earth, Sun and planets as well as the very slight push from sunlight itself — solar radiation pressure — along with factors such as clock error and the radio signal direction.
“As we experience a given acceleration the receiver can judge it is most probably at one particular point in its orbit,” Botteron said. “Usually a satnav receiver needs signals from four satellites to fix its position, but with this approach, less than four signals is still enough to obtain useful information, constraining the model to minimize any error drift.”
European Engineering & Consultancy (EECL) in the UK was assigned the task of turning SpacePNT’s design into fully tested hardware, and also designed the crucial low-noise amplifier that sifts through noise to boost usable signals.
Artist’s impression of the Lunar Pathfinder satellite built by Surrey Satellite Technology Ltd. (SSTL) that will provide communications and navigation services for the Moon.
NASA and its international partners are planning a return to our natural satellite. The following three papers — presented at the Institute of Navigation (ION) GNSS+ conference Sept. 20–24, 2021 — discuss the role of GNSS in lunar exploration. The full papers are available at www.ion.org/publications/browse.cfm.
Using GPS for Time Transfer
NASA and the European Space Agency have conceptualized the initial framework for a GPS-like constellation for the Moon, which will ensure uninterrupted navigation and communication services for future lunar missions. The authors designed a smallsat-based Lunar Navigation Satellite System (LNSS) with time-transfer from Earth-GPS to alleviate the size, weight and power (SWaP) and timing stability requirements of the onboard clocks. A timing filter corrects the lower grade clock when Earth-GPS signals are available and propagates these clock estimates forward in time when no Earth-GPS signals are available. The authors analyzed their proposed time-transfer technique using high-fidelity simulations of an LNSS satellite with an onboard chip-scale atomic clock for three cases of elliptical lunar frozen orbits.
Bhamidipati, Sriramya, Mina, Tara, Gao, Grace, “Design Considerations of a Lunar Navigation Satellite System with Time-Transfer from Earth-GPS,” https://doi.org/10.33012/2021.18021
GNSS Nav for Moon Missions
The authors show the potential of autonomous GNSS signal-based navigation for a set of Moon scenarios. This technology could be a game changer for the future of lunar exploration, representing an extremely low cost and effective alternative for Moon navigation. Results show that not only autonomous GNSS navigation for lunar orbiters is possible, but it also delivers good navigation performance. In fact, navigation with root-mean-square (RMS) errors on the order of 50–100 meters were obtained for scenarios of high interest, such as for the planned Lunar Pathfinder and near-rectilinear halo orbit of the Lunar Gateway space station around the Moon.
Mangialardo, Marco, Jurado, María Manzano, Hagan, David, Giordano, Pietro, Ventura-Traveset, Javier, “The full Potential of an Autonomous GNSS Signalbased Navigation System for Moon Missions,” https://doi.org/10.33012/2021.18040
Finding the best lunar orbit
A continuous and reliable lunar positioning and timing system, such as a GNSS-like constellation, is considered essential infrastructure for lunar exploration. The authors focus on halo orbits with the aim of defining an optimal halo constellation for supporting and delivering a navigation service on the Moon. This paper shows the performance of a GNSS-like constellation deployed in Halo orbits around Earth-Moon L1 and L2 collinear libration points. Different phases have been considered, from a minimum number of satellites able to provide a local PNT service on the South Pole (Initial Operational Capability), to a final, extended constellation able to cover the whole lunar surface (Final Operational Capability).
Musacchio, Daniele, Iess, Luciano, Carosi, Mattia, Capolicchio, Jacopo, Eleuteri, Massimo, Stallo, Cosimo, Di Lauro, Carmine, “Design of Earth Moon Halo Orbits for a Global Lunar PNT Service,” https://doi.org/10.33012/2021.18020
Artist’s impression of SSTL’s Lunar Pathfinder satellite that will provide communications services around the Moon. (Image: SSTL)
News from the European Space Agency (ESA)
ESA is going to the Moon — in collaboration with its international partners — and seeks to build a lasting lunar link to enable sustainable space exploration.
The agency has now evaluated initial ideas to create a network of lunar telecommunications and navigation satellites.
Creating a commercial telecommunications and navigation service for the Moon will allow many of the dozens of planned lunar missions to share the same infrastructure to communicate with Earth, as well as to find their way on the lunar surface.
The service is needed because the planned missions are becoming regular trips to Earth’s natural satellite rather than one-off expeditions.
Using a shared telecommunications and navigation service will reduce the design complexity and weight of individual missions, making them more cost-efficient.
Lowering the ticket price to lunar exploration could also empower a wider group of ESA member states to launch their own national lunar missions, inspiring the next generation of scientists and engineers.
Call for Ideas
The call for ideas for how to use a lasting link with the Moon is open until April 30. People working for commercial companies, universities or governmental organizations are welcome to suggest how they would like to use a lunar communications and navigation service.
This diagram presents a notional preliminary top-level system concept for a lunar communications and navigation service. (Image: ESA)
Concept Reviews Completed
Two consortia of companies have now completed their system concept reviews, which set out how to create the lunar constellation, under ESA’s Moonlight initiative to identify the best way to create a lasting link with the Moon. The reviews set out the business and technical analysis needed to identify and justify a number of feasible system concepts for creating the lunar network.
The next step will be to define a detailed system architecture and identify the most suitable partnership models between private space companies and ESA.
Telespazio leads the first consortium. The consortium includes:
satellite operators Inmarsat and Hispasat
manufacturing companies such as Thales Alenia Space Italy, OHB System in Germany and Canadian space technology company MDA
Italian Aerospace Logistics Technology Engineering Company (ALTEC)
small and medium-sized enterprises such as Nanoracks Europe and Argotec
universities and research centers such as SEE Lab, SDA Bocconi and Politecnico di Milano.
The second consortium is spearheaded by Surrey Satellite Technology Limited, both in the service prime capacity through its lunar services brand SSTL Lunar and as the satellite manufacturer. The consortium includes:
satellite manufacturer Airbus
satellite network providers SES, based in Luxembourg, and Kongsberg Satellite Services, based in Norway
the Goonhilly Earth Station in the UK
British satellite navigation company GMV-NSL.
Artemis Program and Pathfinder
NASA’s Artemis program will use several of ESA’s service modules to return humans to the Moon, including the ESPRIT communications module for the lunar Gateway’s living quarters for astronauts. With its European industrial partner, ESA is helping to build the Lunar Pathfinder, showcasing lunar communications service provision by providing initial services to early lunar missions, including a complete lunar navigation in-orbit demonstration.
The Moonlight initiative builds on both the ESPRIT communications module and the Lunar Pathfinder.
Swiss company SpacePNT will develop an advanced spaceborne GPS/Galileo receiver to demonstrate for lunar navigation and positioning.
A vision of the NAVIMOON receiver. (Image: SpacePNT)
The European Space Agency (ESA) has selected SpacePNT to develop an advanced spaceborne GPS/Galileo receiver to demonstrate the use of terrestrial satellite navigation signals or real-time and autonomous orbit determination and positioning, navigation and timing (PNT).
The receiver will be carried aboard the ESA-SSTL Lunar Pathfinder spacecraft, which will be placed in orbit around the Moon.
The contract includes the development, qualification and delivery of one proto-flight model (PFM) and two engineering models of the NAVIMOON receiver. NAVIMOON is the high-sensitivity version of SpacePNT’s NAVILEO high-performance GNSS spaceborne receiver.
The NAVIMOON receiver implements high-sensitivity algorithms able to receive and process signals extremely attenuated coming from the spillover (side lobes) around the Earth of signals transmitted by satellite navigation systems. It combines these signals’ measurements with advanced on-board orbital filters to achieve onboard the spacecraft in real time an unprecedented target orbit determination accuracy of 100 meters root-mean-square (rms) at Moon altitude, which is well above the typical accuracy that can be achieved with terrestrial radio ranging that involves the use of costly deep-space-station ground infrastructures.
Given the high interest in Moon exploration and colonization (more than 50 commercial and governmental missions have been announced between now and 2024), it is expected that this NAVIMOON receiver technology will play a significant role in the next decade not only on Earth-Moon transfer orbits, but also to provide enhanced PNT services for users on the Moon. Deployment of a lunar constellation will allow the provision of lunar navigation in Moon-obstructed areas.
For this project, SpacePNT will partner with EECL from the UK. EECL will work as a subcontractor and bring significant space expertise to the electronics design, manufacturing and qualification of the receiver.
Europe’s Lunar Pathfinder mission to the Moon will carry an advanced satellite navigation receiver to perform the first satellite navigation positioning fix in lunar orbit. The experimental payload marks a preliminary step in an ambitious European Space Agency (ESA) plan to expand reliable satnav coverage — as well as communication links — to explorers around and ultimately on the Moon during this decade.
Due to launch by the end of 2023 into lunar orbit, the public-private Lunar Pathfinder comsat will offer commercial data-relay services to lunar missions, while also stretching the operational limits of satnav signals.
Navigation satellites like Europe’s Galileo constellation are intended to deliver positioning, navigation and timing services to our planet, so most of the energy of their navigation antennas radiates directly towards the Earth disc, blocking its use for users further away in space.
“But this is not the whole story,” explains Javier Ventura-Traveset, leading ESA’s Galileo Navigation Science Office and coordinating ESA lunar navigation activities. “Navigation signal patterns also radiate sideways, like light from a flashlight, and past testing shows these antenna side lobes can be employed for positioning, provided adequate receivers are implemented.”
Just like people or cars on the ground, satellites in low-Earth orbit rely heavily on satnav signals to determine their orbital position, and since ESA proved higher orbit positioning was possible, a growing number of satellites in geostationary orbit today employ satnav receivers.
But geostationary orbit is 35,786 km up, while the Moon is more than ten times further away, at an average distance of 384 000 km. In 2019 however, NASA’s Magnetospheric Multiscale Mission acquired GPS signals to perform a fix and determine its orbit from 187,166 km away, close to halfway the Earth-Moon distance.
“This successful experimental evidence provides us high confidence since the receiver we will embark on Lunar Pathfinder will have a significantly improved sensitivity, employ both Galileo and GPS signals and will also feature a high-gain satnav antenna,” Javier added.
The main challenge will be overcoming the limited geometry of satnav signals all coming from the same part of the sky, along with the low signal power.
The high-sensitivity receiver’s main antenna was developed through ESA’s General Support Technology Programme, with the receiver’s main unit developed through ESA’s Navigation Innovation and Support Programme, NAVISP.
The receiver project is led by ESA navigation engineer Pietro Giordano. “The high sensitivity receiver will be able to detect very faint signals, millions of times weaker than the ones received on Earth. The use of advanced on-board orbital filters will allow for unprecedented orbit determination accuracy on an autonomous basis,” Giordano said.
Lunar Pathfinder’s receiver is projected to achieve positioning accuracy of around 100 meters — more accurate than traditional ground tracking.
Once in a stable elliptical orbit over the lunar south pole, Lunar Pathfinder will relay signals from other Moon missions. (Image: ESA)
The availability of satnav will allow the performance of ‘Precise Orbit Determination’ for lunar satellites, said Werner Enderle, head of ESA’s Navigation Support Office. “Traditional orbit determination for lunar orbiting satellites is performed by radio ranging, using deep space ground stations,” Enderle said. “This Lunar Pathfinder demonstration will be a major milestone in lunar navigation, changing the entire approach. It will not only increase spacecraft autonomy and sharpen the accuracy of results, it will also help to reduce operational costs.”
While lunar orbits are often unstable, with low-orbiting satellites drawn off course by the lumpy mass concentrations or mascons making up the Moon, Lunar Pathfinder is planned to adopt a highly stable “frozen” elliptical orbit, focused on the lunar south pole – a leading target for future expeditions. Earth — and its satnav constellations — should remain in view of Lunar Pathfinder for the majority of testing. The main challenge will be overcoming the limited geometry of satnav signals all coming from the same part of the sky, along with the low signal power.
Lunar Pathfinder’s demonstration that terrestrial satnav signals can be employed to navigate in lunar orbits will be an important early step in ESA’s Moonlight initiative. Supported through three ESA Directorates, Moonlight will establish a lunar communication and navigation service.
“Over this coming decade, ESA aims to contribute to building up a common communications and navigation infrastructure for all lunar missions based on dedicated lunar satellites,” explained Bernhard Hufenbach, managing commercialisation and innovation initiatives for space exploration at ESA. “Moonlight will allow to support missions that cannot use Earth satnav signals, such as landers on the far side and is planning to cover the current gap towards the needs expressed by the Global Exploration community, targeting positioning accuracy below 50 meters.”
As well as facilitating lunar exploration, these satnav signals might one day become a tool for science in their own right, used, for example, to perform reflectometry across the lunar surface; sounding the scant dusty exosphere that surrounds the Moon or by providing a common time reference signal across the Moon, to be used for fundamental physics or astronomy experiments.
Javier noted that Lunar Pathfinder’s satnav experiment also will have larger consequences. “This will become the first-ever demonstration of GPS and Galileo reception in lunar orbit, opening the door to a complete way to navigate spacecraft in deep space, enabling human exploration of the Moon,” he said.
