Alternatives to GPS, compared

Inertial navigation

An inertial navigation system integrates accelerometer and gyroscope measurements to track position without any external signal. It is the backbone of almost every resilient navigation design — but its errors accumulate. Groves characterises navigation-grade systems (gyro bias around 0.01°/hour) as keeping horizontal drift within about 1.5 km in the first hour, while tactical-grade sensors (1–100°/hour) provide a stand-alone solution for only a few minutes.¹

Use it for: short-term continuity and as the core that other sources correct. Watch for: cost and size rising steeply with grade.

Vision and terrain-referenced navigation

Cameras can track motion (visual odometry) or match imagery to reference maps; terrain-referenced methods match measured terrain height to elevation databases. A recent review notes that vision-based navigation struggles in adverse weather, low light and low visibility, and that terrain methods struggle over uniform or featureless landscapes or where databases are outdated.²

Celestial navigation

Star trackers provide an absolute attitude reference that does not drift, and have long been used on high-altitude aircraft and spacecraft. Their limits are environmental: they work best above cloud, and daytime use requires filtering the strong sky background.³ On their own they constrain attitude and heading more directly than position.

LEO PNT, signals of opportunity and eLoran

These approaches replace or supplement GNSS with other radio signals: dedicated low-Earth-orbit navigation services, signals from communications satellites or terrestrial transmitters, or the terrestrial eLoran system. In the US DOT's 2021 demonstrations, static outdoor positioning from two LEO-based services measured 75.0 m and 333.2 m, while eLoran timing accuracy in 72-hour bench tests was around 80–115 ns.⁴ Research on Doppler positioning from broadband LEO constellations reports metre-level results in simulation, noting those satellites were not designed for navigation.⁵

Watch for: these are still radio signals, so they share some exposure to interference, and terrestrial systems depend on transmitter infrastructure.

Magnetic anomaly navigation (MagNav)

Earth's crust contains magnetic minerals that create small, spatially varying anomalies in the magnetic field. A MagNav system measures the local field with a magnetometer and matches it against magnetic anomaly maps to estimate position.⁶ It is passive — nothing is transmitted — and the signal source cannot be switched off.

The published research is candid about the difficulties:

• The vehicle is the dominant noise source. The magnetometer sees the aircraft's own field as well as Earth's; separating them is the central challenge.⁶ The classical linear compensation model dates to Tolles and Lawson in 1950, and newer work augments it with machine learning.⁷
• Altitude acts as a low-pass filter. The fine-scale anomaly features that help most with accuracy fade as altitude increases.⁸
• Maps are a patchwork. High-accuracy magnetic maps do not exist everywhere; survey line spacing in North American databases ranges from about 2 km to over 400 km.⁸ Global compilations such as EMAG2v3 provide 2-arc-minute grids at 4 km altitude,⁹ while national surveys can be much finer — Canada's aeromagnetic compilation is gridded at 200 m and 1 km.¹⁰
• The field varies in time. Daily variation of roughly 20–40 nT at mid-latitudes, and far more during magnetic storms, must be accounted for.⁸

With a high-quality map at low altitude, academic flight-data work has reported navigation accuracy of 13 m DRMS.⁸ Results depend heavily on platform, altitude and map, so treat any single figure — including vendor-reported flight-test results — as conditional. An open flight dataset from the US Department of the Air Force and MIT, flown near Ottawa, Ontario, is available for algorithm development.¹¹

Gravity-aided navigation

Gravity-aided navigation matches measured gravity against gravity maps, and is attractive at sea and underwater. A 2026 preprint reports a quantum-gravimeter maritime trial in which position error over an 83 km track fell from about 26 km (unaided inertial) to 4.1 km, with performance limited by the resolution of the available gravity map.¹² Evidence is early and largely company-reported.

Putting them together

The strongest designs pair an inertial core with at least two aiding sources whose failure modes differ — for example, a radio-based source and a passive, map-matched one — plus integrity monitoring to reject a source that disagrees.

Where Orbital Quantum fits

Orbital Quantum is a Canadian company developing True North Navigation™ quantum magnetometer modules for GPS-independent positioning. The approach reads the structure of Earth's magnetic field with a quantum magnetometer array and matches the live signature against a known field model to resolve position.

Read more on how True North Navigation works, or see Founder's Edition access on orbitalquantum.com.

Sources

1. Groves, P. D. — Navigation using inertial sensors, IEEE AESS Magazine (2015) — discovery.ucl.ac.uk
2. Satellite Navigation (Springer) — review of GNSS-denied UAV navigation (2025) — link.springer.com
3. MDPI Engineering Proceedings — Celestial navigation in GNSS-denied environments (2025) — www.mdpi.com
4. US DOT / Volpe — Complementary PNT and GPS Backup Technologies Demonstration Report (Jan 2021) — www.transportation.gov
5. Allahvirdi-Zadeh, El-Mowafy & Wang — NAVIGATION 72(2) (2025) — navi.ion.org
6. Gnadt et al. — Signal enhancement for magnetic navigation challenge problem (2020) — arxiv.org
7. Gnadt, Wollaber & Nielsen — Derivation and extensions of the Tolles–Lawson model (2022) — arxiv.org
8. Canciani, A. J. — Absolute positioning using the Earth’s magnetic anomaly field, AFIT dissertation (2016) — scholar.afit.edu
9. NOAA NCEI — EMAG2v3 Earth Magnetic Anomaly Grid — www.ncei.noaa.gov
10. Government of Canada Open Data — Canadian aeromagnetic data compilation — open.canada.ca
11. DAF-MIT AI Accelerator — Open flight data for magnetic navigation research (Zenodo) — zenodo.org
12. Everitt et al. — quantum gravimetric maritime navigation trial, preprint (Aug 2026) — arxiv.org