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.

“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 (@MBTA) March 29, 2022

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)

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)

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 Skydio 2+ quadcopter drone. (Image: Skydio) 

Tony Murfin
GNSS Aerospace