Journal of the Astronautical Sciences最新文献

The geosynchronous (GSO) debris environment is continually evolving. Regular monitoring of the region is consequently of great importance, though the trade-off between coverage and sensitivity makes this challenging for the population of optically faint debris, where collecting area becomes a pivotal factor. Surveys conducted with large-aperture telescopes have provided crucial insights into the nature of this largely uncharacterised population. In this paper, we revisit a survey conducted with the 2.54 m Isaac Newton Telescope (INT), presenting an overhaul of the astrometric calibration and object detection stages of the original analysis pipeline. We apply a blind stacking technique to boost target recovery, unearthing 25 tracklets previously missed by single-frame extraction methods, and pushing the sensitivity limit fainter by 1 magnitude. The same algorithm is applied to a contemporaneous dataset, captured with a 36 cm astrograph, enabling performance benchmarking through the attempted recovery of INT detections from commercial-off-the-shelf observations. We achieve sub-arcsecond astrometric accuracy through a combination of improved star trail centroiding and iterative distortion fitting, allowing short arc initial orbit solutions to be obtained. High-cadence light curves extracted for trailing detections indicate that faint fragments are proportionally more variable than bright derelicts, with many exhibiting photometric signatures of rapid tumbling, often straddling the image noise floor. Lastly, we present preliminary findings from a follow-up multi-national observation campaign, utilising telescopes in Australia, Japan and La Palma. As space traffic management concerns begin to extend beyond GSO altitudes, scientifically-driven surveys of high-altitude orbits have an important role to play in characterising the faint debris environment.

In Low Earth Orbit (LEO), atmospheric drag is the largest contributor to trajectory prediction error. The current thermospheric density model used by the Combined Space Operations Center (CSpOC) in operations is the High Accuracy Satellite Drag Model (HASDM). Since HASDM is not available for use outside of the US Government, satellite operators are left to determine what publicly available, open-source density model they should integrate into their internal operational software. Given the ever more challenging nature of operations in LEO, it is imperative for satellite operators to update legacy density models to a state-of-the-art density model to provide improved trajectory predictions for collision risk assessment and vital day-to-day operational decisions. This article outlines four operations-ready thermospheric density models, describing their performance, computation time, required space weather inputs, and notes for implementation. Operations-ready models include the Drag Temperature Model (DTM), the Jacchia-Bowman 2008 (JB2008) model, the US Naval Research Laboratory Mass Spectrometer and Incoherent Scatter radar 2.0 (NRLMSIS 2.0) model, and the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM). US Government operational density models, HASDM and the Whole Atmosphere Model and Ionosphere Plasmasphere Electrodynamics (WAM-IPE) model, are included for comparison. Models are evaluated against global HASDM density and local GRACE-FO satellite accelerometer densities and Swarm mission densities. Additionally, comparisons between HASDM and WAM-IPE nowcast and forecast density are revealed for the first time publicly.

Supplementary information: The online version contains supplementary material available at 10.1007/s40295-025-00558-8.

A next-generation Mars Network is investigated to determine a configuration optimized for both communications and positioning performance for surface users. A previously proposed 6000 km altitude, 3-satellite equatorial constellation that was found to be optimal for communications to surface users located in the latitude range from 60°S to 60°N is shown to be deficient for surface positioning. Inclining the 3-satellite configuration between 30° and 50° improves positioning performance to users in this latitude range; however, due to a lack of coverage this improvement is primarily seen for positioning when using tracking data collected over long timespans. Moving to an inclined 6-satellite case and using a Walker 6/2/0 delta configuration, at selected inclinations and altitudes, greatly improves the positioning solution performance over shorter timescales, with the best performance obtained with orbits inclined at 50°. Also examined were continuous coverage global constellations that were compared to the Walker 50°: 6/2/0 configurations. The single fold continuous coverage Walker 55.7°:7/7/5 constellation slightly improves the positioning performance and provides more uniform and continuous coverage to the poles, which the Walker 50°:6/2/0 case cannot. Finally, a Walker 57.1°: 8/8/2 constellation that provides continuous twofold coverage was examined; however, the high altitude required for this case reduces its communication performance and yields poorer positioning performance relative to the Walker 55.7°:7/7/5. It is concluded that a next generation Mars Network with focused support to users between 60°S and 60°N that the Walker 50°: 6/2/0 is the best positioning and communications performance while, for continuous coverage global coverage, the Walker 55.7°: 7/7/5 is superior.

Asteroid impact monitoring systems search for potential collisions of near-Earth objects (NEOs) with the Earth over 100 years. A necessary condition for an impact is the intersection between the orbit of the asteroid and the orbit of the Earth. This condition is measured by the Minimum Orbit Intersection Distance (MOID), which can be computed reliably for longer periods of time to identify when an Earth impact is possible. As the orbit is propagated into the future, the uncertainty in position grows faster than the uncertainty in the MOID. If the MOID is low but the position along the orbit is unknown, we compute an analytical approximation of the frequency of close encounters for a given distance. The NEO population spreads widely in orbital uncertainty, which we consider by propagating multiple samples from the initial orbital uncertainty distribution. We demonstrate and validate the methodology for 99942 Apophis, whose MOID is secularly increasing at a slow rate that still allows for future deep encounters. We apply this methodology to the NEO population, and for a large fraction we rule out the crossing of Earth's orbit in the next 1000 years. Otherwise, we rank NEOs in terms of how long their MOID will be low, long-term frequency of close encounters, and frequency relative to the background close encounter frequency for objects of similar size. These rankings identify NEOs that should be prioritized for future tracking and orbit refinement.

Thermospheric mass density knowledge remains a primary driver of operational uncertainty for Low Earth Orbit operations, yet current sources of density observations suffer from limited latency, accuracy, and/or licensing issues. The growing body of Precise Orbit Determination data from emerging Low Earth Orbit constellations offers a promising source of thermospheric mass density measurements. Realising this potential requires the application of methods which can convert Precise Orbit Determination data into reliable density observations. This work provides an assessment of the Energy Dissipation Rate technique. Using a simulated constellation of up to eighteen Starlink-like satellites, we quantify the relationship between the quality of retrieved mass densities and four major influencing factors: Precise Orbit Determination noise level, drag acceleration magnitude, estimation fit-span, and the number of co-orbital spacecraft whose independent density estimates are averaged. Densities retrieved via the Energy Dissipation Rate method are also compared with densities that have been assimilated into a background density model. We identify conditions under which non-assimilated retrievals can outperform their assimilated counterparts, demonstrating the benefits of averaging data from multiple satellites along the same orbital track. Our results reveal three rules of thumb that describe how retrieval error scales as a function of fit-span, satellite count, and drag level. Doubling the fit-span roughly halves the RMS percentage error; adding co-orbital satellites reduces error as $\sim N^{-0.6}$ (unassimilated) or $\sim N^{-0.25}$ (assimilated); and drag-acceleration sensitivity follows a logistic response with the steepest gains between $2\times {10}^{-8}$ and $2\times {10}^{-7}m{s}^{-2}$ . Together, these findings provide the first systematic quantification of how density-retrieval errors scale with Precise Orbit Determination noise, drag-acceleration level, fit-span, and satellite count. The resulting analytical approximation captures over 89% of the variance in simulated retrieval errors and is intended to support the design of next-generation assimilative thermospheric mass density models.

Discovered by the ATLAS survey on December 27, 2024, asteroid 2024 YR₄ represented one of the most significant impact risks ever detected. Roughly 60 m in size, this asteroid reached a 3% probability of impacting the Earth on December 22, 2032. We discuss the orbit and impact analyses carried by the three impact monitoring systems Sentry, Aegis, and NEODyS. The orbit solution proved to be remarkably stable and the impact probability behaved according to expectations as the uncertainty decreased thanks to additional observations, i.e., the impact probability initially increased as the Earth remained within the core of the uncertainty region and then dropped as the Earth moved towards the tail and eventually outside of the uncertainty region. Although the risk of an Earth impact has been ruled out, there remains a 4% probability of a lunar impact on December 22, 2032. To confirm or more likely rule out that possibility, we need to wait until new astrometric data become available, e.g., during the 2028 apparition.

Supplementary information: The online version contains supplementary material available at 10.1007/s40295-026-00576-0.

This paper presents a practical, computationally efficient approach to spacecraft angular velocity estimation using the finite difference (FD) differentiation of star tracker attitude measurements. Intended for gyro-free applications such as within the star tracker processors themselves, this technique is not reliant on external sensors. Although prior studies have proposed similar finite difference techniques, this study provides a more accurate and rigorous model of angular velocity covariance. Additionally, we derive an analytical model of optimal measurement timing to balance noise and bias in the finite difference estimates. A series of simulations validates the revised covariance models and benchmarks the performance of the finite difference rate estimator against a conventional Multiplicative Extended Kalman Filter (MEKF). Although the FD estimates show significant latency-induced bias, the standard deviation of the measurements are improved by 40% or more compared to the MEKF.

This study describes exploratory, in-situ experimentation to measure Very Low Frequency (VLF) plasma waves (1-35 kHz) at times when a space physics satellite equipped with a radio plasma wave receiver conjuncts with other space objects. The objective was to learn if a secondary space object's rapid passage near another satellite is detectable. If so, this would offer a new avenue to infer the presence of space debris in Earth orbit. Space objects in Earth's ionosphere develop a region of ion density rarefactions in the wake of their orbital motion which could serve as the basis for object detection. In 2022 the Canadian space physics satellite CASSIOPE used its radio plasma physics package during conjunctions with other satellites and recorded ambient electric field data at times prior to, during and after the time of closest approach of CASSIOPE and the secondary object. CASSIOPE is designed to measure Earth's aurora, particles, fields and has an eccentric 330 × 1200 km orbit which fortuitously samples a variety of plasma regimes in Earth's ionosphere to test this approach. This orbit regularly crosses the altitudes of highly populated orbital shells such as Starlink, Iridium and OneWeb offering regular conjunction opportunities to attempt measurement of plasma oscillations. CASSIOPE collected electric field measurements using its crossed-dipole Radio Receiver Instrument (RRI) which detects plasma electric field oscillations. CASSIOPE sampled 35 conjunctions using the RRI from 4 March to 10 June 2022. It was surmised that if CASSIOPE traversed an ion density rarefaction the RRI should produce broadband noise at times correlating with the time of closest approach. Of the 35 conjunctions sampled, 3 exhibited VLF broadband noise somewhat correlated to the time of closest approach but were difficult to differentiate from background ambient auroral activity. One conjunction showed strong temporal correlation where a conjuncting Starlink appears to have threaded the magnetic field line between itself and CASSIOPE which also traversed the Starlink's wake. All other conjunctions where the secondary object passed behind CASSIOPE or were quite distant (~ 5-10 km) from CASSIOPE did not show wave power exceeding the ambient background. The CASSIOPE findings indicate that sensing of ion density rarefactions in space object wakes does not appear practical to implement and clear, repeatable signatures from known space object conjunctions were not identified during this investigation.

This paper uses a motion primitive approach to automatically generate constrained spacecraft trajectories for Neptunian system exploration. Motion primitives are generated as smaller building blocks of motion that summarize periodic orbits and arcs along stable and unstable manifolds of selected orbits in the Neptune-Triton circular restricted three-body problem. The sequential composability of these motion primitives is represented by a graph that also incorporates path and maneuver constraints. This graph is searched using a k-best paths algorithm to generate multiple motion primitive sequences. These sequences are transformed into an array of geometrically diverse initial guesses. After corrections and optimization, the resulting tradespace of continuous, constrained trajectories with impulsive maneuvers is analyzed. This approach is applied to two planar trajectory design scenarios in the Neptunian system: high-energy insertion into a Neptune-centered science orbit after interplanetary arrival and low-energy transfers between science orbits centered around each of Neptune and Triton.

Supplementary information: The online version contains supplementary material available at 10.1007/s40295-025-00545-z.

This paper documents the results from the highly successful Lunar flashlight Optical Navigation Experiment with a Star tracker (LONEStar). Launched in December 2022, Lunar Flashlight (LF) was a NASA-funded technology demonstration mission. After a propulsion system anomaly prevented capture in lunar orbit, LF was ejected from the Earth-Moon system and into heliocentric space. NASA subsequently transferred ownership of LF to Georgia Tech to conduct an unfunded extended mission to demonstrate further advanced technology objectives, including LONEStar. From August to December 2023, the LONEStar team performed on-orbit calibration of the optical instrument and a number of different OPNAV experiments. This campaign included the processing of nearly 400 images of star fields, Earth and Moon, and four other planets (Mercury, Mars, Jupiter, and Saturn). LONEStar provided the first on-orbit demonstrations of heliocentric navigation using only optical observations of planets. Of special note is the successful in-flight demonstration of (1) instantaneous triangulation with simultaneous sightings of two planets with the LOST algorithm and (2) dynamic triangulation with sequential sightings of multiple planets.