The Precision Clock Mk IV is a highly accurate, GPS-disciplined clock built by the author. It uses a combination of a Rubidium oscillator for short-term stability and a GPS receiver for long-term accuracy, achieving sub-microsecond precision. The clock features a custom-designed circuit board and firmware, and includes several output options, including a 1PPS (pulse-per-second) signal, a configurable frequency output, and a serial interface for time and status information. The project documentation thoroughly details the design, build process, and testing results.
GPS is increasingly vulnerable to interference, both intentional and unintentional, posing a significant risk to critical infrastructure reliant on precise positioning, navigation, and timing (PNT). While GPS is ubiquitous and highly beneficial, its inherent weaknesses, including low signal power and lack of authentication, make it susceptible to jamming and spoofing. The article argues for bolstering GPS resilience through various methods such as signal authentication, interference detection and mitigation technologies, and promoting alternative PNT systems and backup capabilities like eLoran. Without these improvements, GPS risks being degraded or even rendered unusable in critical situations, potentially impacting aviation, maritime navigation, financial transactions, and other vital sectors.
HN commenters largely agree that GPS is vulnerable to interference, both intentional and unintentional. Some highlight the importance of alternative positioning systems like Galileo, Beidou, and GLONASS, as well as inertial navigation for resilience. Others point out the practicality issues of backup systems like Loran-C due to cost and infrastructure requirements. Several comments emphasize the need for robust electronic warfare protection and redundancy in critical systems relying on GPS. A few discuss the potential for improved signal authentication and anti-spoofing measures. The real-world impacts of GPS disruption, such as on financial transactions and emergency services, are also noted as compelling reasons to address these vulnerabilities.
Jeff Geerling's blog post highlights Beidou Position System (BPS), China's independently developed global navigation satellite system, as a lesser-known alternative to GPS. He details its development, global coverage, and increasing accuracy, emphasizing its potential as a backup or even primary navigation system, particularly for those needing to operate independently of US-controlled infrastructure. Geerling shares his experience testing BPS receivers, noting its comparable performance to GPS in his basic experiments and the growing availability of BPS-compatible devices. He concludes by advocating for greater awareness of BPS as a viable option in the GNSS landscape.
HN commenters discuss the viability and practicality of BPS, noting it's largely theoretical and faces significant hurdles. Several point out the immense infrastructure investment required for terrestrial positioning systems like BPS, especially compared to the established satellite-based GPS. Some question the accuracy claims and highlight potential interference issues in dense urban environments. Others express skepticism about BPS's resistance to jamming and spoofing, crucial for critical infrastructure. A few comments mention Loran-C as a more mature terrestrial alternative, although it has its limitations. Overall, there's a consensus that while intriguing, BPS lacks the development and backing to become a serious competitor to GPS in the foreseeable future.
GPS jamming and spoofing are increasing threats to aircraft navigation, with potentially dangerous consequences. A new type of atomic clock, much smaller and cheaper than existing ones, could provide a highly accurate backup navigation system, independent of vulnerable satellite signals. These chip-scale atomic clocks (CSACs), while not yet widespread, could be integrated into aircraft systems to maintain precise positioning and timing even when GPS signals are lost or compromised, significantly improving safety and resilience.
HN commenters discuss the plausibility and implications of GPS spoofing for aircraft. Several express skepticism that widespread, malicious spoofing is occurring, suggesting alternative explanations for reported incidents like multipath interference or pilot error. Some point out that reliance on GPS varies among aircraft and that existing systems can mitigate spoofing risks. The potential vulnerabilities of GPS are acknowledged, and the proposed atomic clock solution is discussed, with some questioning its cost-effectiveness and complexity compared to other mitigation strategies. Others suggest that focusing on improving the resilience of GPS itself might be a better approach. The possibility of state-sponsored spoofing is also raised, particularly in conflict zones.
NASA has successfully demonstrated the ability to receive GPS signals at the Moon, a first for navigating beyond Earth’s orbit. The Navigation Doppler Lidar for Space (NDLS) experiment aboard the Lunar Reconnaissance Orbiter (LRO) locked onto GPS signals and determined LRO’s position, paving the way for more reliable and autonomous navigation for future lunar missions. This achievement reduces reliance on Earth-based tracking and allows spacecraft to more accurately pinpoint their location, enabling more efficient and flexible operations in lunar orbit and beyond.
Several commenters on Hacker News expressed skepticism about the value of this achievement, questioning the practical applications and cost-effectiveness of using GPS around the Moon. Some suggested alternative navigation methods, such as star trackers or inertial systems, might be more suitable. Others pointed out the limitations of GPS accuracy at such distances, especially given the moon's unique gravitational environment. A few commenters highlighted the potential benefits, including simplified navigation for lunar missions and improved understanding of GPS signal behavior in extreme environments. Some debated the reasons behind NASA's pursuit of this technology, speculating about potential future applications like lunar infrastructure development or deep space navigation. There was also discussion about the technical challenges involved in acquiring and processing weak GPS signals at such a distance.
This paper explores the feasibility of using celestial navigation as a backup or primary navigation system for drones. Researchers developed an algorithm that identifies stars in daytime images captured by a drone-mounted camera, using a star catalog and sun position information. By matching observed star positions with known celestial coordinates, the algorithm estimates the drone's attitude. Experimental results using real-world flight data demonstrated the system's ability to determine attitude with reasonable accuracy, suggesting potential for celestial navigation as a reliable, independent navigation solution for drones, particularly in GPS-denied environments.
HN users discussed the practicality and novelty of the drone celestial navigation system described in the linked paper. Some questioned its robustness against cloud cover and the computational requirements for image processing on a drone. Others highlighted the potential for backup navigation in GPS-denied environments, particularly for military applications. Several commenters debated the actual novelty, pointing to existing star trackers and sextants used in maritime navigation, suggesting the drone implementation is more of an adaptation than a groundbreaking invention. The feasibility of achieving the claimed accuracy with the relatively small aperture of a drone-mounted camera was also a point of contention. Finally, there was discussion about alternative solutions like inertial navigation systems and the limitations of celestial navigation in certain environments, such as urban canyons.
Researchers have demonstrated a method for using smartphones' GPS receivers to map disturbances in the Earth's ionosphere. By analyzing data from a dense network of GPS-equipped phones during a solar storm, they successfully imaged ionospheric variations and travelling ionospheric disturbances (TIDs), particularly over San Francisco. This crowdsourced approach, leveraging the ubiquitous nature of smartphones, offers a cost-effective and globally distributed sensor network for monitoring space weather events and improving the accuracy of ionospheric models, which are crucial for technologies like navigation and communication.
HN users discuss the potential impact and feasibility of using smartphones to map the ionosphere. Some express skepticism about the accuracy and coverage achievable with consumer-grade hardware, particularly regarding the ability to measure electron density effectively. Others are more optimistic, highlighting the potential for a vast, distributed sensor network, particularly for studying transient ionospheric phenomena and improving GPS accuracy. Concerns about battery drain and data usage are raised, along with questions about the calibration and validation of the smartphone measurements. The discussion also touches on the technical challenges of separating ionospheric effects from other signal variations and the need for robust signal processing techniques. Several commenters express interest in participating in such a project, while others point to existing research in this area, including the use of software-defined radios.
Summary of Comments ( 66 )
https://news.ycombinator.com/item?id=44144750
HN commenters were impressed with the clock's accuracy and the detailed documentation. Several discussed the intricacies of GPS discipline and the challenges of achieving such precise timekeeping. Some questioned the necessity of this level of precision for a clock, while others appreciated the pursuit of extreme accuracy as a technical challenge. The project's open-source nature and the author's willingness to share their knowledge were praised. A few users also shared their own experiences with similar projects and offered suggestions for improvements, like adding a battery backup. The aesthetics of the clock were also a topic of discussion, with some finding the minimalist design appealing.
The Hacker News post titled "Precision Clock Mk IV" linking to mitxela.com/projects/precision_clock_mk_iv has generated a moderate number of comments, primarily focused on the technical aspects of the clock's design and implementation.
Several commenters delve into the specifics of GPS discipline and its limitations. One commenter questions the necessity of an expensive Rubidium oscillator given the clock's reliance on GPS, sparking a discussion about the importance of holdover performance and maintaining accuracy when the GPS signal is lost. This thread explores various scenarios where GPS might be unavailable, like indoor use or intentional jamming, and how a Rubidium oscillator mitigates these issues. Another commenter highlights the intricacies of achieving nanosecond-level accuracy, pointing out the challenges introduced by cable length and signal propagation delays within the system itself.
The discussion also touches upon the choice of using a Raspberry Pi Pico and its suitability for this application. Some commenters suggest alternative microcontrollers with potentially better performance characteristics, while others defend the Pico's adequacy given the project's requirements. This leads to a brief comparison of different microcontroller platforms and their respective strengths and weaknesses.
Further comments explore the clock's display technology and potential improvements. One commenter suggests using e-paper for lower power consumption, while another raises the possibility of incorporating a Network Time Protocol (NTP) server functionality.
A few commenters express general admiration for the project's complexity and the author's dedication. They praise the detailed documentation and the open-source nature of the design.
While the overall number of comments isn't exceptionally high, the discussion provides valuable insights into the technical challenges and design choices involved in building a high-precision clock. The comments offer a range of perspectives, from questioning specific design decisions to suggesting alternative approaches and appreciating the overall accomplishment. The conversation remains focused on the technical merits of the project and avoids straying into unrelated topics.