NASA has initiated orbital testing of its Passive Electronically Scanned Array Experiment for Terrestrial Communications (PExT), a next-generation wideband optical and RF communications payload. Deployed aboard a CubeSat from the International Space Station (ISS), this experimental platform aims to validate high-throughput data links using both laser and Ka-band technologies—offering significant implications for future military SATCOM architectures and resilient space-based C4ISR networks.
PExT Overview: A Dual-Mode Wideband Communications Pathfinder
The PExT system is designed to evaluate hybrid optical/RF communication capabilities in low Earth orbit (LEO). It integrates a narrow-beam laser terminal with a Ka-band radio frequency transceiver on a 6U CubeSat bus. The goal is to demonstrate gigabit-per-second-class downlink rates while maintaining compact form factors suitable for small satellites or distributed LEO constellations.
Developed under NASA’s Space Communications and Navigation (SCaN) program and managed by NASA’s Glenn Research Center in Cleveland, Ohio, PExT represents a key step toward enabling resilient high-throughput space-to-ground links. The mission also supports broader U.S. government efforts—particularly those led by the Department of Defense (DoD)—to leverage commercial satellite technologies for secure tactical data relay.
According to NASA officials, the system will test multiple parameters including beam pointing accuracy, atmospheric interference effects on laser comms, adaptive modulation schemes in Ka-band transmissions, and interoperability with ground terminals developed under other SCaN initiatives.
Deployment from ISS via Nanoracks
PExT was launched aboard Northrop Grumman’s Cygnus NG-20 cargo resupply mission on January 30, 2024. After docking with the ISS and completing initial checks, the CubeSat was deployed into orbit using Nanoracks’ Bishop Airlock—a commercial airlock module designed to support small satellite deployments from the station.
This deployment method offers several advantages over traditional rideshare launches. It allows precise insertion into lower orbits ideal for early-stage technology demonstration missions while leveraging ISS infrastructure for pre-deployment health checks. Additionally, it enables real-time coordination with ground stations already supporting ISS operations.
Optical Comms in Focus: Laser Links as Future Backbone
The centerpiece of PExT’s capability is its onboard optical terminal—a miniaturized laser communication system capable of transmitting data at rates exceeding 1 Gbps under optimal conditions. Laser comms offer several advantages over traditional RF systems:
- Higher bandwidth: Optical frequencies enable significantly greater data throughput than microwave bands.
- LPI/LPD characteristics: Narrow-beam lasers reduce interception risk and electromagnetic interference susceptibility—key attributes for military applications.
- Spectrum relief: Using optical frequencies bypasses congested RF bands increasingly saturated by commercial SATCOM operators.
PExT’s laser terminal will attempt downlinks to ground stations equipped with adaptive optics systems capable of mitigating atmospheric distortion—a major challenge in free-space optical communication (FSOC). Successful trials would validate key components needed for future DoD hybrid SATCOM architectures that blend RF resilience with optical capacity.
Ka-Band Transceiver Adds Redundancy and Tactical Relevance
In parallel with its laser payload, PExT includes a compact Ka-band transceiver operating in frequencies commonly used by military SATCOM systems such as WGS (Wideband Global SATCOM). This dual-mode approach allows comparative analysis between RF and optical performance under identical orbital conditions—including cloud cover impacts on link availability.
The Ka-band node will test adaptive coding/modulation techniques optimized for dynamic LEO geometries. It also serves as a fallback channel when atmospheric conditions inhibit FSOC operations—mirroring redundancy strategies being explored by U.S. Space Force programs like Protected Tactical Enterprise Service (PTES).
Implications for Military Space Communications
PExT is part of a broader trend toward disaggregated satellite architectures where small platforms deliver specialized capabilities rather than relying solely on large geostationary assets. In contested environments where kinetic or electronic threats may target traditional SATCOM nodes, proliferated LEO constellations offer survivability through redundancy and maneuverability.
If successful, PExT could inform future DoD acquisitions involving hybrid RF/optical terminals integrated into CubeSats or hosted payload configurations. Potential applications include:
- Tactical ISR data exfiltration from theater sensors via secure FSOC links
- Resilient command-and-control channels immune to jamming/spoofing
- Low-latency battlefield networking between airborne platforms and ground units
The U.S. Space Development Agency (SDA) has already signaled interest in incorporating FSOC into its Transport Layer architecture—a mesh network of LEO satellites designed to support Joint All-Domain Command & Control (JADC2). Lessons learned from NASA’s PExT could accelerate TRL maturation across these defense programs.
A Collaborative Pathway Toward Operationalization
PExT is not operating in isolation—it builds upon prior NASA experiments such as the Laser Communications Relay Demonstration (LCRD) launched in December 2021 aboard STPSat-6 under DoD auspices. While LCRD focused on geosynchronous relay scenarios using larger spacecraft buses, PExT brings similar capabilities into smaller form factors suitable for rapid deployment missions or attritable assets.
The program also benefits from partnerships with industry players developing ground segment solutions compatible with both FSOC and Ka-band reception—including General Atomics Electromagnetic Systems and MIT Lincoln Laboratory among others involved in adaptive optics R&D.
Next Steps and Evaluation Timeline
The initial checkout phase will last several weeks as engineers assess thermal stability, power budgets, attitude control performance during pointing maneuvers, and link acquisition success rates under varying environmental conditions. Data collected will inform design refinements ahead of potential follow-on missions or operational prototypes funded through SCaN or DoD innovation pathways like DIU or AFWERX.
If technical milestones are met within expected timelines—estimated at Q3–Q4 2024—the platform may be considered as part of future joint demonstrations involving DoD users seeking assured connectivity across denied environments or degraded infrastructure scenarios.
