GPS World

Tag: NAVIMOON

  • A mess in Boston? Moon navigation? GNSS to the rescue

    A mess in Boston? Moon navigation? GNSS to the rescue

    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.

    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.

    The Elios 2 indoor inspection UAV is encased in a collision-tolerant frame to protect both the drone and the environment it’s inspecting. (Photo: © Flyability)
    The Elios 2 indoor inspection UAV is encased in a collision-tolerant frame to protect both the drone and the environment it’s inspecting. (Photo: © Flyability)

    Lunar Pathfinder

    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)
    Artist illustration of the Pathfinder mission. (Image: SSTL)

    The Lunar Pathfinder satellite. (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)
    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)
    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 Skydio 2+ quadcopter drone. (Image: Skydio)
    The Skydio 2+ quadcopter drone. (Image: Skydio) 

    Tony Murfin
    GNSS Aerospace

  • The Moon: Where no satnav has gone before

    The Moon: Where no satnav has gone before

    News from the European Space Agency

    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)
    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.”

    Relaying signals for multiple lunar missions
    Relaying signals for multiple lunar missions

    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.”

    Lunar Pathfinder will relay communications from orbital and surface missions
    Lunar Pathfinder will relay communications from orbital and surface missions

    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.

    Laser ranging station
    Laser ranging station

    “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.”

     

    Galileo 'side lobe' signals
    Galileo ‘side lobe’ signals

    Finding ultra-faint satnav signals

    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)
    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)
    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.

  • SpacePNT to develop GPS/Galileo receiver for Lunar Pathfinder spacecraft

    SpacePNT to develop GPS/Galileo receiver for Lunar Pathfinder spacecraft

    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)
    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.