Lunar Pathfinder Minisatellite Mission
Following the European Space Agency Ministerial Council Space19+ meeting in Seville at which the UK Space Agency confirmed it will invest £374 million per year with ESA, Surrey Satellite Technology Ltd (SSTL) is pleased to announce the kick-off for the implementation phase of its Lunar data-relay spacecraft, Lunar Pathfinder. 1)
Figure 1: Lunar Pathfinder is a Commercial Lunar Mission Support Service to provide data services via S-band and UHF links to lunar assets, and an X-band link to Earth (image credit: SSTL)
Phil Brownnett, SSTL’s Managing Director said “Lunar Pathfinder will be the first commercial service to address the need for data relay around the Moon, and will not only demonstrate an innovative business idea, but we fully expect it to also stimulate the emerging Lunar market. By pioneering a commercial solution and service delivery model in lunar orbit, SSTL and ESA are opening the door to providing services to the solar system, and contributing to the scientific progress of deep space exploration.”
The Lunar Pathfinder spacecraft is designed to provide affordable communications services to lunar missions via S-band and UHF links to lunar assets on the surface and in orbit around the Moon, and an X-band link to Earth. As early as Q4 2022, the 280 kg Lunar Pathfinder spacecraft will be a mission enabler for polar and far-side missions, which, without direct line of sight of the Earth, would otherwise have to procure their own communications relay spacecraft. Lunar Pathfinder is a more cost effective alternative to Direct-to-Earth solutions and a credible alternative to institutional deep-space ground stations, offering orbiters and near-side missions a better availability, enhanced safety and improved data-rate.
”The Moon is a cornerstone of ESA’s exploration strategy,” says David Parker, ESA’s director of human and robotic exploration, “this decade we will see humans and robots visit uncharted territory and return with new discoveries, communications is key to send scientific and operational data to Earth.”
“We are returning to the Moon with commercial and international partners, and the Lunar Pathfinder mission will be an integral part.”
To support booming demand from Lunar missions and a clear goal in the scientific community to undertake detailed study and analysis of the Aitken Basin, Lunar Pathfinder intends to operate in a stable elliptical orbit to provide long duration visibility of the Southern Lunar Hemisphere each day, with maximum opportunities for the transmission and reception of data between Earth and the lunar surface. NASA’s Artemis program also calls for “landing the first American woman and next American man at the South Pole of the Moon by 2024, followed by a sustained presence on and around the Moon by 2028” and Lunar Pathfinder is accordingly working towards a launch in Q4 2022 to support early NASA missions.
In parallel to the Lunar Pathfinder mission SSTL has been working on future plans for a constellation of spacecraft around the Moon, capable of providing enhanced communications, as well as navigation services for the Lunar market as it grows from exploration to commercial exploitation and even tourism.
Acting both as technology and service demonstrator, Lunar Pathfinder is the opportunity for scientific and commercial mission developers to support the development, test and standardization of Lunar communication infrastructure, and for emerging off-planet telecommunications to acquire experience of lunar asset operations and off-planet service delivery. Lunar Pathfinder is thus laying the foundation to support sustainable science and exploration for the next twenty years and beyond – bringing with it the possibility that when humans next set foot on the Moon we will be hearing not “Houston we’ve landed” but instead “Guildford ....
Figure 2: Illustration of the Lunar Pathfinder mission in lunar orbit providing its services (image credit: SSTL)
Figure 3: Lunar Pathfinder, first mission in 2023 (image credit: SSTL)
Agreements & Development Status
• March 18, 2021: ESA’s Lunar Pathfinder mission to the Moon will carry an advanced satellite navigation receiver, in order to perform the first ever satnav positioning fix in lunar orbit. This experimental payload marks a preliminary step in an ambitious ESA plan to expand reliable satnav coverage – as well as communication links – to explorers around and ultimately on the Moon during this decade. 4)
- Due for 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 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.
- Javier adds: "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.”
- This high sensitivity receiver’s main antenna was developed through ESA’s General Support Technology Program, with the receiver’s main unit developed through ESA’s NAVISP (Navigation Innovation and Support Program).
- 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 to achieve unprecedented orbit determination accuracy on an autonomous basis.”
Figure 4: Galileo 'side lobe' signals. Navigation satellites – such as Europe's Galileo, the US GPS, Russia’s GLONASS or their Japanese, Chinese and Indian counterparts – aim their antennas directly at Earth. Any satellite orbiting above these constellation can only hope to detect signals from over Earth’s far side, but the majority are blocked by the planet. For a position fix, a satnav receiver requires a minimum of four satellites to be visible, but this is most of the time not possible if based solely on front-facing signals. Instead, satnav receivers in higher orbits can make use of signals emitted sideways from navigation antennas, within what is known as ‘side lobes’. Just like a flashlight, radio antennas shine energy to the side as well as directly forward (image credit: ESA)
- Lunar Pathfinder’s receiver is projected to achieve positioning accuracy of around 100 m – more accurate than traditional ground tracking.
- The availability of satnav will allow the performance of ‘Precise Orbit Determination’ for lunar satellites, notes 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. 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.
Figure 5: The moon. A high-definition image of the Mars Australe lava plain on the Moon taken by Japan’s Kaguya lunar orbiter in November 2007 (image credit: JAXA/NHK)
- 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 go on to establish a Lunar Communication and Navigation Service.
Figure 6: Lunar Pathfinder will fly in a frozen elliptical orbit, focused on covering the Moon's south pole, highlighted as a prime target for future exploration (image credit: SSTL)
• October 2, 2020: Just as we navigate our way around Earth's surface using the connection between our phones and navigation satellites high above us, our missions use the very same satellites to navigate their way in space. 5)
- To pinpoint a location accurately, a receiver – in our phones or on a spacecraft – needs to collect and combine signals from at least four navigation satellites. The receiver determines its distance from each of the satellites by measuring the time that it takes for the signal to travel from the satellite to the receiver.
- Navigation satellites orbit in MEO, about 22,000 km, above Earth's surface. As they point in the direction of Earth, any spacecraft between them and Earth are served well by their signal. But around ten years ago, engineers started demonstrating that spacecraft outside the orbit of navigation satellites could also navigate in space using 'spill over' signal from the satellites.
- Then in 2012 two Discovery & Preparation studies explored a seemingly radical question: could this spill over signal even be used to navigate our way around the Moon, and if so, what kind of receiver would we need to build to be able to use these signals?
- The studies were very successful, finding that indeed, the signal from navigation satellites orbiting Earth could be used to navigate the Moon's surface. But with the signal being so weak, they found that a new type of receiver would need to be built, and at the time there was no clear application for this.
Figure 7: GPS satellites – like those of Galileo, Russia’s GLONASS or their Japanese, Chinese and Indian counterparts – aim their antennas directly at Earth. Any satellite orbiting above the GPS constellation can only hope to detect signals from over Earth’s far side, but the majority are blocked by the planet. For a position fix, a satnav receiver requires a minimum of four satellites to be visible, but this is most of the time not possible if based solely on front-facing signals. Instead, GIOVE-A has been able to make use of signals emitted sideways from GPS antennas, within what is known as ‘side lobes’. Just like a flashlight, radio antennas shine energy to the side as well as directly forward (image credit: ESA)
- Fast-forwarding eight years, and ESA has invested in the development of such a receiver, and is exploring whether it could be demonstrated on the Lunar Pathfinder mission. ESA is collaborating with SSTL (Surrey Satellite Technology Ltd) and GES (Goonhilly Earth Station) on this mission, which will provide exciting new opportunities for science and technology demonstration. In particular, it will help lay the groundwork for providing navigation services around the Moon, currently studied through two ESA NAVISP activities and culminating in the Moonlight initiative.
- "We have now accurate simulation results that show that navigation signals may be used at Moon orbit and provide good performances," adds Dr Javier Ventura-Traveset, Head of the Galileo Science Office and in charge of coordinating all GNSS Moon activities for ESA's Navigation Directorate. “And with an innovative receiver in Lunar Pathfinder, we could have the first ever experimental evidence of this. This is exciting!
- "Furthermore, we are also studying how existing navigation constellations may be complemented by additional Moon-orbiting satellites, providing additional ranging signals for an optimal navigation service including Moon landing and Moon surface operations. This is being done as part of the ESA NAVISP program and through the ESA Moonlight initiative."
Figure 8: SSTL, GES (Goonhilly Earth Station) and ESA have signed a collaboration agreement for Commercial Lunar Mission Support Services at the Space Symposium in Colorado Springs as of 17 April 2028. This innovative commercial partnership for exploration aims to develop a European lunar telecommunications and navigation infrastructure, including the delivery of payloads and nanosatellites to lunar orbit (image credit: SSTL)
- "The Discovery & Preparation studies have been eye-openers and they are currently being followed up by a NAVISP activity aiming to develop the highly sensitive spaceborne navigation receiver planned to fly on board Lunar Pathfinder," notes ESA Radio Navigation Engineer Pietro Giordano. "This technology will enable improved performances and much more cost-effective ways to navigate and operate missions to and around the Moon."
- It is thanks to the pioneering Discovery & Preparation studies that ESA was confident enough to invest in the new receiver. This success story demonstrates the importance of investigating in blue sky research where real-world applications are not immediately apparent. Discovery & Preparation specializes in such research and is therefore pivotal in laying the path for ESA’s future activities.
• 23 October 2019: ESA and NASA reaffirmed their interest in working with commercial service providers as well as international partners on missions to the Moon in a joint statement signed at the 70th annual International Astronautical Congress last week. 8)
- The statement supports the ‘Lunar Pathfinder’ mission, ESA’s first Moon partnership with European industry, addressing communication and navigation needs for future lunar exploration.
- The ‘Lunar Pathfinder’ partnership helps lay the foundation for providing communications, navigation, and operations services around the Moon. Its communications relay service is intended to link the Earth and the lunar surface.
Figure 9: David Parker ESA’s Director of Human and Robotic Exploration and Thomas Zurbuchen NASA's Associate Administrator for Science signed a joint statement that welcomed the ‘Lunar Pathfinder’ mission, ESA’s first Moon partnership, during the 70th annual IAC. Alice Bunn, director of International Policy at the UK Space Agency, and Sir Martin Sweeting, founder and executive chairman of Surrey Satellite Technology Ltd. (SSTL), were also present during the signature (image credit: ESA)
- “We are working together to make the commercial lunar economy a reality,” says David Parker ESA’s Director of Human and Robotic Exploration. “We want to act as an anchor customer and institutional broker for gaining access to non-European markets. ESA supports a competitive ecosystem of European space providers.”
- Commercialization is gaining momentum in the space arena and both ESA and NASA confirmed their intention to work on lunar services with the UK Space Agency earlier this year.
- In the joint statement, NASA and ESA reiterated their interest to identify the elements of this potential cooperation and formalize an interagency agreement in the future.
- The two agencies have also committed to working together to supplement NASA’s own communications capabilities with those of ESA and its partners.
- NASA also confirmed its interest in having a variety of communication and navigation services to serve its robotic missions, including lunar surface activities, starting as early as end of 2022.
• 17 April 2018: ESA has signed a collaboration agreement with Surrey Satellite Technology Ltd (SSTL) and Goonhilly Earth Station (GES) for Commercial Lunar Mission Support Services at the Space Symposium in Colorado Springs, USA. This innovative commercial partnership for exploration aims to develop a European lunar telecommunications and navigation infrastructure, including the delivery of payloads and nanosats to lunar orbit. 9)
- The partnership allows for a low-risk, phased approach to implementing a sustainable, long-term commercial service and will support lunar scientific and economic development across Europe and the rest of the world. The agreement includes the upgrade of the Goonhilly Earth Station for commercial deep space services and the development of the space segment with a lunar pathfinder mission. The cooperation also encompasses the commercial and regulatory support to catalyze the lunar economy and provide affordable access to the lunar environment, and ultimately deep space.
- The agreement was signed by Sir Martin Sweeting, founder and Executive Chairman of SSTL, Ian Jones, founder and Chief Executive of GES and David Parker, Director of Human and Robotic Exploration at ESA.
- David Parker commented, “The agreement between ESA and SSTL/GES establishes ESA’s first partnership for providing commercial services in support of lunar missions. The Lunar Pathfinder mission would provide exciting new opportunities for science and technology demonstration and open deep space access to new actors.”
- Sir Martin Sweeting commented, “I am delighted that this collaboration agreement will enable new, and regular, mission opportunities to the Moon, which I believe is the next frontier for commerce and sustainable solar system exploration and exploitation.”
- Following the recent announcement of the GES ground segment upgrade to form the world’s first deep space commercial node, the partners are now jointly committed to the developing the Lunar Pathfinder space segment for a low cost “Ride and Phone Home” capability. The Lunar Pathfinder mission will offer a ticket to lunar orbit for payloads and nanosats onboard an SSTL lunar mothership spacecraft, which will provide communications data relay and navigation services between customer payloads and the GES Deep Space ground station.
- The £1m per kilogram ticket for a flight opportunity in the 2022 timeframe includes end-to-end mission service which supports the integration, transportation and deployment of payloads, the provision of data relay and navigation services via the dedicated ESA ESTRACK deep space network, and a simple web-based interface for payload operations and return of mission data.
- Private and agency Lunar landers, rovers and surface impactors will also be able to sign up to use the lunar communications and navigation services provided by the mothership either for primary mission operations, to provide additional capacity, or as a back-up service. For prospecting, exploring, and ultimately utilizing the far side of the Moon, this communications relay service will be a mission enabler, providing the vital bridge between Earth and the lunar surface. Exploring the far side of the Moon, particularly the South Pole Aitkin Basin, is a key area for future robotic and human exploration due to its chemical and mineral composition. The stable elliptical orbit of the mothership will allow for long duration visibility of the Southern Lunar Hemisphere each day, with maximum opportunities for the transmission and reception of data between Earth and the lunar surface.
1) ”SSTL Kicks-Off Lunar Pathfinder Communications Mission,” SSTL, 5 February 2020, URL: https://www.sstl.co.uk/media-hub/latest-news/
2) ”Lunar Mission Services,” SSTL, 2020, URL: https://www.sstl.co.uk
3) ”Lunar Mission Services,” SSTL, URL: https://www.sstl.co.uk/what-we-do/lunar-mission-services
4) ”Galileo will help Lunar Pathfinder navigate around Moon,” ESA Applications, 18 March 2021, URL: https://www.esa.int/Applications/Navigation/Galileo_will_help_Lunar_Pathfinder_navigate_around_Moon
5) ”ESA Discovery studies lay path to navigating the Moon,” ESA Enabling & Support, 02 October 2020, URL: https://www.esa.int/Enabling_Support/Preparing_for_the_Future/
6) Information provided by Joelle Sykes of SSTL.
7) ”Lunar Mission Flyer,” a handout of SSTL, November 2019, URL: https://www.sstl.co.uk
8) ”A pathway for communicating at the Moon,” ESA Science & Exploration, 23 October 2019, URL: https://www.esa.int/Science_Exploration/
signs collaboration agreement for commercial Lunar missions,” ESA
Science & Exploration, 17 April 2018, URL: https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (email@example.com).