arXiv subjects

Rasmus Maråk

Publications and source records attributed to Rasmus Maråk.

3 recordsLinked to original sources

arXiv2026

The SHARPEx space-to-space VLBI experiment

Space is the next frontier for ultra-high resolution imaging of astrophysical sources with very long baseline interferometry (VLBI). The limited size of the Earth and atmospheric absorption and turbulence at high frequencies prevent order-of-magnitude resolution improvements from current black hole imaging with the ground-based Event Horizon Telescope. A two or three-element submm space-based array like SHARP would image the thin black hole photon ring and measure the black hole spin and spacetime. Here, we present the SHARP Experiment (SHARPEx) mission concept. SHARPEx will demonstrate key enabling technologies for space-to-space VLBI, including clock syntonization between two satellites, on-board correlation, and sub-wavelength relative orbit determination. SHARPEx will consist of two CubeSat or SmallSat platforms carrying small (~1 m diameter) antennas, observing at cm wavelengths. While SHARPEx will be a technical demonstrator, a SHARPEx-type follow-up mission with enhanced intersatellite link properties (range and bandwidth) may produce images of bright AGN with unprecedented resolution and fidelity.

astro-ph.IM↗

arXiv2024

Rapid Distributed Fine-tuning of a Segmentation Model Onboard Satellites

Segmentation of Earth observation (EO) satellite data is critical for natural hazard analysis and disaster response. However, processing EO data at ground stations introduces delays due to data transmission bottlenecks and communication windows. Using segmentation models capable of near-real-time data analysis onboard satellites can therefore improve response times. This study presents a proof-of-concept using MobileSAM, a lightweight, pre-trained segmentation model, onboard Unibap iX10-100 satellite hardware. We demonstrate the segmentation of water bodies from Sentinel-2 satellite imagery and integrate MobileSAM with PASEOS, an open-source Python module that simulates satellite operations. This integration allows us to evaluate MobileSAM's performance under simulated conditions of a satellite constellation. Our research investigates the potential of fine-tuning MobileSAM in a decentralised way onboard multiple satellites in rapid response to a disaster. Our findings show that MobileSAM can be rapidly fine-tuned and benefits from decentralised learning, considering the constraints imposed by the simulated orbital environment. We observe improvements in segmentation performance with minimal training data and fast fine-tuning when satellites frequently communicate model updates. This study contributes to the field of onboard AI by emphasising the benefits of decentralised learning and fine-tuning pre-trained models for rapid response scenarios. Our work builds on recent related research at a critical time; as extreme weather events increase in frequency and magnitude, rapid response with onboard data analysis is essential.

cs.LG↗

arXiv2023

Trajectory Optimisation of a Swarm Orbiting 67P/Churyumov-Gerasimenko Maximising Gravitational Signal

Proper modelling of the gravitational fields of irregularly shaped asteroids and comets is an essential yet challenging part of any spacecraft visit and flyby to these bodies. Accurate density representations provide crucial information for proximity missions which rely heavily on it to design safe and efficient trajectories. This work explores using a spacecraft swarm to maximise the measured gravitational signal in a hypothetical mission around the comet 67P/Churyumov-Gerasimenko. Spacecraft trajectories are simultaneously propagated with an evolutionary optimisation approach to maximise overall signal return. The propagation is based on an open-source polyhedral gravity model using a detailed mesh of 67P and considers the comet's sidereal rotation. We compare performance on a mission scenario using one and four spacecraft. The results show that the swarm achieved almost twice the single spacecraft coverage over a fixed mission duration. However, optimising for a single spacecraft results in a more effective trajectory. Overall, this work serves as a testbed for efficiently designing a set of trajectories in this complex gravitational environment balancing measured signals and risks in a swarm scenario. The codebase and results are publicly available at https://github.com/rasmusmarak/TOSS

astro-ph.EP↗