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Beidou Satellites Misclassification - Bert Hubert's writings
2 months ago
- The author is deeply involved in GNSS monitoring and uses automated orbit matching via TLEs and the sgp4 library.
- Four Chinese BeiDou satellites (C21/C22 and C25/C26) are misidentified due to swapped tracking codes after paired launches.
- Official BeiDou designations indicate C21 as MEO03 and C22 as MEO04, but US Space Control Squadron data shows different matches.
- The misclassification seems to be a simple reversal (e.g., M11 and M12 swapped), which is easy to correct.
Galileo Notes: Ephemeris, Anomalies, I/NAV, SFRBX - Bert Hubert's writings
2 months ago
- The author uses a Navilock NL-8012U with a u-blox 8 chipset, configuring it via u-center to enable Galileo and NMEA 4.1 for raw data.
- Galileo ephemeris parameters in semi-circle units require multiplication by π for calculations.
- Eccentric anomaly is computed through iteration (E = M + e * sin(E)), often in 10 iterations.
- True anomaly can be calculated using an approximation formula for near-circular orbits, with extra terms for elliptical orbits (e.g., e=0.162).
- Extracting ephemeris parameters from I/NAV messages involves parsing word types 1-4 with specific bit positions and sign handling.
- Coordinates in ECEF GTRF are derived using standard orbital mechanics, and elevation is calculated as 90° minus the angle between user and satellite vectors.
GPS, Galileo & More: How do they work & what happened during the big outage? - Bert Hubert's writings
2 months ago
- Navigation satellites transmit precise timing signals and orbital data (ephemeris), allowing receivers to calculate position via multilateration.
- Receivers use additional satellites to correct internal clock inaccuracies, essential for meter-level accuracy due to the speed of light.
- Different GNSS systems (GPS, Galileo, GLONASS, BeiDou) use varied orbital and clock correction methods, with Galileo and BeiDou updating more frequently.
- The July 2019 Galileo outage occurred when control center equipment malfunctioned stopped regular updates, causing ephemeris to become ambiguous after 3.5 days due to missing week numbers.
- GLONASS uniquely employs Moscow time and encodes satellite position via integration of motion equations, including gravitational perturbations.
- Each GNSS broadcasts its offset from UTC and handles leap seconds; dual-frequency receivers can virtually eliminate ionospheric errors.
- The Galmon project openly monitors all navigation satellites, displaying real-time data on parameters like IOD, ephemeris age, SISA, and pseudorange residuals.
The State of Galileo as seen by an outsider - Bert Hubert's writings
2 months ago
- Galileo is a civilian EU GNSS managed by the European Commission, built by ESA, and operated by the GSA via Spaceopal, with a complex multi-layered governance structure.
- The July 2019 week-long outage was caused by multiple simultaneous failures (backup unavailable, mishandled upgrade, system anomalies), but communication was poor and the EC blamed a single person.
- The constellation has only 21 functional satellites (below 24), leading to coverage gaps, and frequent 'No Accuracy Prediction Available' (NAPA) status due to ground software issues.
- Software fixes are slow due to a long chain from vendor to ESA to GSA to Spaceopal, and many satellite failures are expected before the next launch (likely 2021).
- The galmon.eu open source project provides independent 24/7 monitoring of Galileo and other GNSS, uncovering under-reported issues.
- Galileo's search and rescue component performed well and remained available during the outage.
- EU governance upheavals (creation of EU Space Agency) and tensions with ESA may further delay improvements.
- The author recommends better transparency, independent monitoring, and structural reforms to address communication and expertise gaps.
The July Galileo Outage: What happened and why - Bert Hubert's writings
2 months ago
- The July Galileo outage was caused by multiple simultaneous failures: backup system unavailable, mishandling of new equipment during an upgrade, an anomaly in the system reference time, and a non-normal configuration.
- Communication during the outage was poor, with the European Commission being the sole communicator and far removed from operations.
- Galileo's operational complexity involves many organizations, leading to slow resolution of ground-based software problems and a culture of secrecy.
- Despite the outage, the constellation could restart in a few days, but 5% of satellites are often unavailable due to software issues.
- The SDD allows for up to 6.9 days of outage in a 30-day period, so the outage technically met minimum performance levels.
The new Galmon.eu Weekly Galileo Report - Bert Hubert's writings
2 months ago
- Announcement of the first full Galmon.eu Weekly Galileo Report, summarizing a good week with minimal issues.
- The report is a blog post version of an earlier Twitter thread, available via email or online.
- Motivation: to provide helpful public insight into Galileo's performance, despite existing internal reporting.
- Galileo is important for European independence in satellite navigation, though its technical and managerial systems are complex.
- A 6-day outage a year ago highlighted a lack of public transparency, prompting the creation of a worldwide GNSS monitoring platform.
- The platform, built with over 60 station operators and open data sources, enables near real-time reporting.
- Many helpful individuals within the Galileo project (engineers, scientists, etc.) educated the author, but the culture remains closed, with anonymous communication.
- The report aims to increase visibility and serve as a public reference, contributing to the project's improvement.
Multi-Signal GNSS & the Curious Case of Galileo E24: Part 1 - Bert Hubert's writings
2 months ago
- Multi-frequency GNSS removes over 99% of ionospheric delay by combining signals at different frequencies.
- Galileo uses an 'ionosphere-free clock combination' as its official time signal, but internal satellite delays cause small clock offsets.
- Single-band receivers (like phones) must apply a correction term (BGDE1E5a/b) to compensate for the combined clock adjustment.
- Galileo has two clock combinations (E1/E5a and E1/E5b), each with separate clock parameters (af0) that receivers must match correctly.
- Satellite E24 shows a persistent ~5 nanosecond (1.5 meter) clock bias in correction feeds, due to a mismatch in clock references.
- NAVCAST corrections convert E1/E5a clocks to E1/E5b clocks, causing the bias, which is resolved by using I/NAV clock parameters.
- The issue arises from an undocumented RTCM standard and the choice of I/NAV as the reference clock for corrections.
- Offline SP3 files also show the bias, but only when compared to the wrong clock reference (I/NAV instead of F/NAV).
- The af0 parameters between F/NAV and I/NAV clocks differ by 5.8789 ns for E24, closely matching the observed bias.
GNSS Jamming and Spoofing, aka Galileo's Authentication Algorithm Part 3 - Bert Hubert's writings
2 months ago
- GNSS jamming is a denial-of-service attack that stops positioning, but spoofing is more dangerous as it can deceive receivers into believing false locations.
- Spoofing detection is critical; turning spoofing into jamming makes it easier to handle, while undetected spoofing can lead to catastrophic outcomes.
- Meaconing involves recording and replaying authentic GNSS signals from one location to another, making it hard to detect without additional checks like precise clocks or multiple receivers.
- Receivers can use multiple techniques to detect spoofing, including monitoring signal strength, cross-checking satellite data from multiple constellations, and using RAIM (Receiver Autonomous Integrity Monitoring).
- OSNMA adds digital signatures to navigation messages to authenticate content, but it cannot fully protect against timing-based attacks or meaconing without precise time references.
- Advanced spoofing attacks may require multiple transmitters to mimic satellite parallax, raising the bar significantly for attackers.
- Receiver manufacturers often do not implement robust spoofing detection features, leaving commodity devices vulnerable to simple attacks.
- OSNMA is a valuable tool but not a complete solution; it works best alongside physical and software-based detection methods to raise the difficulty of successful attacks.
Galileo's Ground Segment Problem - Bert Hubert's writings
2 months ago
- Galileo's ground segment has limited uplink capacity, often contacting only 13 of 24 satellites simultaneously, causing occasional accuracy issues.
- On September 25, 2020, satellite E11 accumulated a 5-meter error due to lack of ground contact, highlighting the need for more robust communication.
- Aging satellites like E11 require frequent ephemeris updates every 10 minutes, but without ground contact they continue broadcasting a healthy status, potentially misleading users.
- On October 27, 2020, two new dishes were added to the ground segment, partially addressing the capacity problem.
- The ground segment's underinvestment (despite Galileo's €10 billion cost) contrasts with satellite reliability, leading to chronic uplink shortages and calls for autonomous fault signaling.
- Adding 'Working Without Guarantee' functionality to all satellites would improve system integrity by marking them faulty if out of contact.
Leap seconds: Causing Bugs Even When They Don't Happen - Bert Hubert's writings
2 months ago
- Leap seconds are controversial due to Earth's variable rotation, affecting timekeeping.
- Navigation satellites like GPS, Galileo, and BeiDou use monotonic clocks unaffected by leap seconds, broadcasting offset to UTC.
- Leap seconds are pre-announced months in advance, transmitted with truncated week number and day to save bandwidth.
- The last leap second was in December 2016; since then, no new leap seconds have occurred, leading to a 256-week gap.
- Bugs emerge when systems misinterpret leap second data, e.g., U-Blox receivers reporting a false imminent leap second, and a gpsd bug causing a 1024-week time jump.
- Negative leap seconds may be needed in the future due to Earth's rotation speeding up, posing potential software issues.
- GLONASS handles time differently by incorporating leap seconds directly, which can cause glitches during leap second events.
MCH2022: DNA and GPS/Galileo/GNSS Talks - Bert Hubert's writings
2 months ago
- MCH2022 was a large hacker camp event in the Netherlands, originally planned for 2021 but delayed due to COVID-19, with over 3500 attendees.
- The event was a success thanks to many volunteers and teams, and nearly all talks are available online.
- First talk: 'Hacking the genome' covered DNA basics, gene editing, its potential, and ethical considerations.
- Second talk: 'How GPS/Galileo really work' explained GNSS technology, the galmon.eu monitoring project, vulnerabilities like spoofing/jamming, and open-source receivers.
- Both talks include slides and video links.
Show HN: Sidereon: GNSS and Astrodynamics (Python, Rust, JavaScript, C, Elixir)
2 months ago
- Sidereon provides a Rust core for GNSS and astrodynamics, including SGP4, SPP/RTK/PPP, RINEX, observation quality control, RTCM/NTRIP streams, frames/time, ionosphere, and conjunction calculations.
- The engine is verified against reference implementations like Vallado, Skyfield, IGS, teqc, and IERS.
- It supports idiomatic interfaces in Rust, Python, C, Elixir, and WebAssembly, with a single verified codebase across languages.
- The engine runs client-side in browsers via WebAssembly, enabling real-time calculations (global coverage, close-approach screening, orbit determination) without server calls.
- Cargo installation is available via 'cargo add sidereon' and crates.io.

Beidou Satellites Misclassification - Bert Hubert's writings

Galileo Notes: Ephemeris, Anomalies, I/NAV, SFRBX - Bert Hubert's writings

GPS, Galileo & More: How do they work & what happened during the big outage? - Bert Hubert's writings

The State of Galileo as seen by an outsider - Bert Hubert's writings

The July Galileo Outage: What happened and why - Bert Hubert's writings

The new Galmon.eu Weekly Galileo Report - Bert Hubert's writings

Multi-Signal GNSS & the Curious Case of Galileo E24: Part 1 - Bert Hubert's writings

GNSS Jamming and Spoofing, aka Galileo's Authentication Algorithm Part 3 - Bert Hubert's writings

Galileo's Ground Segment Problem - Bert Hubert's writings

Leap seconds: Causing Bugs Even When They Don't Happen - Bert Hubert's writings

MCH2022: DNA and GPS/Galileo/GNSS Talks - Bert Hubert's writings

Show HN: Sidereon: GNSS and Astrodynamics (Python, Rust, JavaScript, C, Elixir)