Bill Hersman, LiDAR Space; Mike Briggs, LiDAR Space; Jan Distelbrink, LiDAR Space; Jeff Ketel, LiDAR Space; Steve Ketel, LiDAR Space; Iulian Ruset, LiDAR Space
Keywords: LiDAR, diode-pumped alkali laser, FADOF, Lethal Non-Trackable debris,
Abstract:
A new time-of-flight (TOF) LiDAR technology will soon provide full synoptic space domain awareness (SDA), promising small debris sensitivity and spatio-temporal precision unmatched by any existing or planned system. It leverages Diode-Pumped Alkali Laser (DPAL) technology, which has been under development by government labs worldwide due to its potential as a high-power directed energy weapon. Our team developed unique DPAL pump lasers that are wavelength-stabilized and optically narrowed by external-cavity feedback through a Faraday Anomalous Dispersion Optical Filter (FADOF). Their ultra-narrow pump linewidth can extend the DPAL operational regime to low pressure, where the output line is only minimally altered by gas collisions. We recognized that a mode-locked adaptation of our low-pressure DPAL can produce a train of nanosecond-scale pulses and fast-rastering can distribute the pulses so each one interrogates an independent spatial volume. Furthermore, we recognized that a sensor is commercially available that can fully exploit the laser’s characteristics: single-photon sensitivity, rise and fall times in the tens of nanoseconds regime, multi-pixel high-resolution, and nanosecond-precision timing, which can be preceded by an ultra-narrow bandpass FADOF. Over the past year we matured the world’s only low-pressure, mode-locked, unidirectional, triangular-ring DPAL and demonstrated it as a short-pulsed LiDAR illuminator. We showed that the pulse wavelength was pico-tunable, viewable through a FADOF atomic line filter, retiring essentially all elements of scientific risk. We operated it routinely and autonomously, raising Technical Readiness to Level 5.
When the system is deployed in a few years, two telescopes will synergistically comprise a TOF-LiDAR: the DPAL LiDAR illuminator will transmit short pulses at the atomic-line wavelength upward, while its companion atomic-line-filtered single-photon sensor will trigger selectively only on its reflections. The benefits of this system will be manifold and significant. In addition to nanosecond timing precision, the transmit and receive sides also offer few-square-meter x-y definition, yielding a few-cubic-meter spatial precision in three dimensions. Pulses will outshine the sun by many orders of magnitude within the ultra-narrow spectral bandpass, allowing daytime operation. An image intensifier allows triggering at few-photon threshold levels, enabling discovery and tracking of resident space objects (RSOs) in the Lethal Non-Trackable (LNT) class, down to few-centimeter sizes. Pulse rates in the tens to hundreds of kilohertz distributed by a fast raster will search thousands of cubic kilometers every second to discover new uncatalogued debris every hour. Real-time tasking and orbit determination, even for closely spaced objects, becomes feasible. One system will be able to complete a comprehensive survey of a half-trillion cubic kilometers of low-earth orbit within a decade. A worldwide network of a dozen systems could interrogate most of the low-earth orbit region yearly, gain custody of one-hundred thousand new LNT RSOs in its first year, provide updates of all catalogued items daily, and allow real-time tasking for conjunction prediction or monitoring suspicious objects’ behavior for concealment, camouflage, deception, or maneuver (CCDM) activity, while also providing resilience to weather and adversaries.
With scientific validation completed, we will devote the coming year to engineering considerations, performance improvements, power and size scaling, and next-generation prototyping. We have completed sourcing custom micro-optics to allow greater power density and ordered additional diode array stacks, leading to a new sixteen-kilowatt layout. Procurement is nearly completed for the new unstable ring resonator design which will scale the pulse brightness, with the goal of producing 400mJ pulses at 40kHz. We have fast-raster elements in-house for high-speed rotational balancing and subsystem integration. We have selected a camera, sensor, and image intensifier. Soon, we will begin sourcing transmit and receive telescope optics. We see no obstacle to completing modest-power testing within eighteen months on terrestrial and celestial targets. With further scale-up, safety integration, and site selection, we expect to deploy the first installation of what will become a next-generation, worldwide SDA network within three to four years.
Date of Conference: September 16-19, 2025
Track: SDA Systems & Instrumentation