For decades, Global Navigation Satellite Systems (GNSS) have transformed the way modern platforms navigate. From aircraft and UAVs to maritime vessels and autonomous systems, GNSS provides a widely available source of positioning, navigation and timing information.
But what happens when that signal is no longer available?
As defence platforms operate in increasingly complex and contested environments, GNSS-denied and GNSS-degraded conditions are becoming an important consideration in the design of modern navigation systems.
The challenge is no longer simply achieving accurate navigation under normal conditions. It is maintaining reliable navigation when one of the primary sources of navigation information is disrupted, degraded or unavailable.
What is a GNSS-denied environment?
A GNSS-denied environment is an operating environment in which a platform cannot reliably obtain usable information from satellite navigation systems.
This can occur for several reasons, including:
- Jamming, where radio-frequency interference prevents a receiver from acquiring or maintaining GNSS signals.
- Spoofing, where false GNSS signals are introduced, potentially causing a receiver to calculate an incorrect position.
- Signal obstruction, caused by buildings, terrain, structures or other physical environments.
- Environmental conditions that affect signal availability or quality.
- Intentional electromagnetic interference in contested or sensitive operating environments.
The result can be a loss of positioning information or a reduction in navigation accuracy and reliability.
For a modern autonomous or crewed platform, this can have significant consequences.
Why GNSS resilience matters
GNSS is deeply integrated into modern navigation architectures. It can provide positioning and timing information to navigation systems, autopilots, mission computers and other onboard technologies.
When GNSS becomes unavailable, platforms may need to rely on alternative sources of information.
Inertial Navigation Systems (INS), for example, can continue operating without external signals. However, inertial systems accumulate errors over time. Without an external reference to correct these errors, navigation accuracy can progressively degrade.
This creates a fundamental challenge:
How can a platform maintain reliable navigation when GNSS cannot be trusted?
The answer increasingly involves combining multiple navigation technologies rather than relying on a single source.
From GNSS dependence to navigation resilience
Modern navigation architectures can combine information from several sensors and technologies, depending on the platform and mission.
These may include:
- Inertial sensors
- Visual navigation
- Terrain or scene-based navigation
- Radar-based navigation
- Stellar navigation
- Magnetic sensors
- GNSS, when available
Each technology has its own strengths and limitations.
The objective of a resilient navigation architecture is therefore not necessarily to replace GNSS, but to reduce dependence on any single navigation source.
GNSS can remain the primary navigation reference when it is available, while alternative technologies provide additional information when its performance degrades.
The role of stellar navigation
One of the most established alternatives to satellite-based navigation is also one of the oldest: the stars.
Celestial navigation has been used for centuries by mariners and aviators to determine position and orientation using celestial objects as references.
Modern optical technology enables this principle to be applied in a very different way.
Advanced optical sensors can identify stars and other celestial references and use their known positions to determine the orientation of a platform. Combined with navigation algorithms and other onboard sensors, this information can contribute to navigation without depending on GNSS signals.
For defence platforms operating in GNSS-denied or GNSS-degraded environments, stellar navigation can therefore provide an additional source of navigation information.
Stellar navigation for demanding defence applications
Applying stellar navigation to modern defence platforms requires more than simply identifying stars.
Navigation systems must be capable of operating within the constraints of real platforms, including limited size, weight and power, rapid manoeuvres and changing environmental conditions.
The ability to provide reliable navigation information while integrating with existing onboard systems is therefore a key consideration.
STELION, developed by SOLAR MEMS, applies optical sensing and stellar navigation principles to support navigation in GNSS-degraded and GNSS-denied environments.
The STELION family includes solutions for heading, geolocation and navigation, providing complementary navigation information that can be integrated into broader platform architectures.
Beyond a single navigation source
GNSS denial is only one part of the navigation challenge.
Modern defence platforms may also need to operate in environments involving rapid manoeuvres, limited visibility, complex terrain, electromagnetic interference and other demanding conditions.
Navigation systems must therefore be designed around the complete operational environment rather than a single failure scenario.
This is particularly relevant for autonomous platforms, where navigation information may directly influence flight control, mission execution and the ability to operate safely.
As autonomy increases, so does the importance of having navigation systems capable of maintaining reliable information under changing conditions.
The future of resilient navigation
The growing challenge of GNSS-denied environments is driving interest in navigation technologies that can operate independently of satellite signals.
The future is unlikely to depend on a single replacement for GNSS. Instead, resilient navigation will increasingly involve complementary technologies working together, combining different sources of information to create a more robust navigation architecture.
Optical and stellar navigation can form part of this approach, providing platforms with access to an external reference that does not depend on GNSS signals.
The underlying principle is remarkably simple:
When the signal from satellites is no longer available, the sky can provide another reference.
As defence platforms become more autonomous and operating environments become increasingly challenging, resilient navigation will play an increasingly important role in enabling reliable operation.
And sometimes, the answer to a modern navigation challenge can be found in one of the oldest navigation references of all, the stars.
Discover STELION
STELION is SOLAR MEMS’ family of optical navigation technologies developed to support platforms operating in GNSS-degraded and GNSS-denied environments.
Explore the STELION technology and discover how stellar navigation can contribute to the next generation of resilient navigation architectures.For maritime, aerospace and defense operators, that difference is the gap between a controlled contingency and an unplanned one.