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Late Breaking News - Patchedconics got Strategic Space Fund of Japan Government
Patchedconics and Tohoku University hire a Postdoc or a Research Fellow.
Workplace: Tohoku University (Sendai City). Employment period: 3.5 years*. A doctoral degree may not be required.
Required qualifications and abilities: Expert knowledge of astrodynamics (orbit and navigation), and a basic understanding capability of GNSS-related open-source software and programming skills. Knowledge of radio communications is a plus.
* If successful in the selection process for the on-orbit demonstration phase. If unsuccessful, the period is 1.5 years.
Please apply actively.
The team also invites universities’ ground stations globally who participate in the project.
Contact via 'Contact Us' tab above immediately.

ASYNCHRONOUS ONE-WAY RANGE (AOWR) SCHEME
Background
The primary challenge of GNSS positioning in the cislunar region stems from its geometric configuration. GNSS positioning relies on determining four parameters—three-dimensional position and time offset—by measuring distances from satellites distributed across a wide solid angle. However, in the cislunar region, all GNSS satellites appear clustered in nearly the same direction, making it inherently difficult to accurately resolve these four parameters. The AOWR method, by contrast, measures only two parameters—distance and time offset—through telemetry exchanges between individual pairs of satellites, enabling these measurements regardless of geometric constraints. Consequently, by incorporating carrier phase synchronization, the positioning error, which exceeded 1 km in the LuGre spacecraft’s flight data, can be reduced by a factor of 1,000.
Fundamentals The AOWR method involves exchanging telemetry information between a pair of transceivers, which can be considered as a ground station and a spacecraft as in Figure 1 below. A simpler explanation, in a static configuration without relative velocity, is illustrated in the diagram Figure 2 below. If the ground station's clock is ahead of the spacecraft's, the pseudo-distance measured by the spacecraft—based on telemetry information received and referencing the ground station's clock at the time of transmission—will appear longer by the amount of the time difference. Conversely, the pseudo-distance measured by the ground station will appear shorter. Thus, the two sets of measurements contain dual information representing two distances and two time-differences. Adding these two quantities yields the actual distance, while subtracting them yields the time difference. This is the principle of the AOWR method. Although details are omitted, this 'duality' persists even when relative velocity is present. The details are omitted here. The team has developed the SDR (Software-Defined=Radio) board preparing for the on-orbit-demonstration.(Figure 3)

APPLICATIONS
Application 1a: Self-Positioning in Transport Vehicles Accessing the Lunar Polar Region
The aforementioned results pertain to applications for determining the position of a spacecraft from Earth. However, accurately determining the position of a spacecraft or transport vehicle—especially when it is approaching a designated landing area—is challenging from the ground. The method proposed here involves using radio beacons (markers) installed and deployed on the lunar surface. Even during early lunar exploration, if limited to specific regions such as the polar areas, small radio beacons equipped with AOWR devices can be easily integrated into deployable payloads (such as landers) and networked. Since the locations of these radio beacons can be precisely determined through terrain and optical measurements, positioning services can be provided to approaching spacecraft by synchronizing the clocks of all radio beacons to a single master clock. (Because the spacecraft travels at high speed, clock synchronization is essential.)
The proposed solution is to adopt the AOWR method, which synchronizes multiple clocks simultaneously in real time. The master clock only needs to be installed on the spacecraft receiving the positioning service ('Self-Positioning'). This system operates without relying on infrastructure such as pre-installed navigation satellite constellations like GNSS. It can also be applied to return the spacecraft to the lunar gateway (or base) with high relative navigation accuracy. This demonstrates the high applicability of the AOWR-Alone method, which enables the gradual expansion of the positioning service coverage area. (Figure 4) In the early stages of lunar exploration, the number of spacecraft is expected to be small, so the navigation system should be designed to be much simpler. The proposed research and development focus is the AOWR-Alone method.
Application 1b: Positioning of Lunar Terrain Vehicles (LTVs)
The lower-left diagram illustrates the 'Self-Positioning' method of a spacecraft flying in orbit, as described in Application 1a. The key point is that an LTV located on the lunar surface within the triangular area formed by the radio beacons can always maintain communication with the spacecraft as on Figure 5. In other words, the spacecraft can continuously exchange distance information with the LTV while maintaining self-positioning. (Even outside this triangular area, although accuracy may degrade, positioning remains possible.)
Application 2: Self-Positioning in the Cislunar Region Using AOWR-Alone Configuration
The proposed AOWR-Alone system is an AOWR-exclusive configuration that employs three or more AOWR ground stations. See Figure 6. Thanks to the simultaneous synchronization of clocks across multiple AOWR units, even with short baseline lengths, the dilution of precision (DOP) can be significantly reduced compared to a GNSS-only system using only three AOWR ground stations. Accuracy can be further enhanced by utilizing carrier phase synchronization, making the system highly practical.
Unlike GNSS, the code synchronization correlation time in the AOWR-Alone system can be freely adjusted. Under current conditions, a correlation time of 200 milliseconds is expected to be achievable. The figure below illustrates an example where three AOWR support stations are positioned on the Earth's surface. Using the same baseline length, these stations—with a 3-meter aperture and a transmit power of approximately 5 W—enable the spacecraft to perform near-real-time positioning at lunar distances or between connected near-Earth planets, such as SEL2 points. This is possible even with a patch array antenna and a transmit power of approximately 1 W. A key feature of the AOWR method is its ability to synchronize the timing of a large number of devices simultaneously, thereby facilitating a gradual expansion of the range over which positioning services can be provided. In this AOWR-Alone method, DOP is assessed in Figure 7. The baseline length is less than the effective baseline that GNSS uses to receive signals via side lobes, and is approximately the same as the diameter of the Earth. The accuracy degradation index (PDOP) corresponding to this method is approximately 200, which is slightly higher than the PDOP of GNSS alone via the baseline. The RMS position error value of 39m shown above is calculated from code correlation with a PDOP of 100; by using carrier phase tracking, the RMS error is reduced to approximately 1 meter. This makes it possible to improve the positioning results in the LuGre demonstration mission to 1/1000. Carrier phase tracking in this method is GNSS-independent and can operate autonomously. (Note that the integration of carrier phase tracking into the AOWR method has already been completed.)

TECJNOLOGY DEVELOPMENT STATUS
AOWR-Alone ('Self-Positioning') Flight Experiments Using Drones
Applications utilize the AOWR method's capability to simultaneously synchronize multiple clocks in real time. This function is highly practical for a wide range of applications. Two drone flight tests were conducted to demonstrate their application in transport operations within the lunar polar region and asteroid exploration. Drones were used in these experiments to eliminate multipath interference, which makes wireless experiments near the ground surface unfeasible. During the flights, the drone hovered at an altitude of 50 meters before gradually descending in a circling pattern toward the ground. See Figure 8.
The results of the two demonstrations are presented below. Preliminary experiments confirmed that the positioning function operated correctly, with positioning results closely matching those obtained using GPS. The measurement interval for the AOWR method is 6 seconds.
The second drone test was also successfully conducted and the flight profile is presented in Figure 9. The results are as follows: Initialization of the carrier phase requires several minutes, so during hovering, fluctuations in positioning accuracy are observed due to the effects of code correlation. However, once carrier phase tracking begins, the positioning accuracy becomes highly precise. Because the antenna used had relatively narrow directivity, some radio markers became unresponsive at low altitudes during descent, resulting in areas where positioning was lost. This issue can be avoided by using a wide-directivity antenna. The orange line represents experimental results of extrapolating clock information by referencing the drift rate obtained during flight. Although the 6-second interval is still long and the drift rate extrapolation is not entirely accurate, this ranging interval can be further shortened, allowing for improved results in future experiments.
The positioning results are compared with that via GPS as in Figure 10. It exhibits the good agreement between them.
The drone and the radio markers used are shown in Figure 11.