Multiple CubeSat altimeters can work independently or corporately to form altimeter constellations. Different configurations of the constellations can acquire distinguished advantages: improved spatial/temporal sampling and high cross-track resolution, which will be helpful for observations of oceanic small-scale structures and weather forecasting. Compared to single conventional altimeters, CubeSat altimeter constellations may achieve better performances with lower costs. To fully understand these systems, this article focuses on the performance analysis and methodology for CubeSat altimeter constellations. Besides the typical analyses of the resolution, revisit, and absolute sea surface height (SSH) accuracy, the performance analysis was conducted by considering the characteristics of multiple measurements provided by CubeSat altimeter constellations. Local and global spatial sampling performances are investigated for various constellations and compared by sampling density and swath size. Moreover, relative SSH accuracy is introduced and evaluated based on the spatial structure functions of errors to effectively evaluate the measurement performance. Related system requirements on power, delta-v, etc., to achieve the performance are also discussed, which ensures that the analysis fits the boundary conditions of implementation. Finally, different concepts of the CubeSat altimeter constellations are compared, where their limitations and possible solutions are also discussed.

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Orbiting Low Frequency Array for Radio Astronomy (OLFAR) is a radio astronomy mission that has been studied since 2010 by several Dutch universities and research institutes. The mission aims at producing sky maps by collecting cosmic signals at ultra-low wavelengths regimes, below the 30 MHz frequency band. A satellite swarm comprising more than 10 satellites equipped with passive antennas will be deployed in space where the radio frequency interference can be minimized, e.g., on the far side of the moon. So far, several studies have been devoted to design the space segment, which consists of the payload and platform elements. However, the ground segment, particularly the mission planning system has not yet been designed in detail. In this paper, a systematical mission planning method for OLFAR is presented after a mission planning problem is formulated based on the current satellite design. @en

Employing a satellite swarm for radio astronomy has been continuously addressed in the Orbiting Low Frequency ARray (OLFAR) project. A 100 km diameter of aperture array constructed by distributed satellites will be able to provide sky maps of better than 1 arc-minute spatial resolution at 10 MHz. However, an orbit design strategy for the swarm satellites that ensures safe intersatellite distances and relative orbit stability has not yet been developed. In this paper, a new method for OLFAR orbit design is proposed. A deterministic solution is presented based on three algebraic constraints derived here, which represent three orbit design requirements: collision avoidance, maximum baseline rate, and uvw-space coverage. In addition, an idea for observation planning over the mission lifetime is presented.

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Formation reconfiguration with impulsive maneuvers has been continuously addressed in recent decades. The studies mostly focused on in-plane formation reconfiguration since the out-of-plane motion is independently controlled by a single burn. Most in-plane reconfiguration studies, meanwhile, rely on tangential maneuvers because of fuel efficiency and controllability of the orbital energy, compared to radial maneuvers. In this paper, the perspective differs that little influence of the radial maneuvers on the orbital energy is considered as a benefit rather than a drawback. By employing radial burns only, an effect of the thrust errors on the semimajor axis control error can be minimized. Both numerical simulations and sensitivity analysis demonstrate the robustness of the proposed radial impulsive burns compared to the conventional tangential impulsive control schemes.@en

In the original article [https://doi.org/10.2514/1.G004933], the fifth element of the relative orbit elements (ROE) vector should be δiy, the y component of the relative inclination vector. Therefore: The correct notation for Eq. (1) is. (Formula presented).

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The tremendous progress of small satellite technologies in recent years brings unique opportunities for satellite radar altimetry. Flying radar altimeters onboard a group of small satellites could provide better swath observation, an equivalent or even improved performance and coverage at a much lower price, while complementing large satellite missions. To this end, a feasibility study of a Ka-band altimeter CubeSat constellation for ocean monitoring, called AltiCube, is being carried out by the Delft University of Technology, under the support of the European Space Agency. This paper provides an overview of the AltiCube mission study. First, the potential observation products and performance of five constellation/formation concepts are analyzed. Then the requirements on the platform are discussed based on these concepts. The main focus is on the payload performance and the needed delta-V for the constellation/formation maintenance. Based on the assessment with respect to performance, platform, technological readiness level, cost and other factors, the along-track comb formation (consisting of five identical CubeSats) is selected. Further details of its system design is given in the paper. The selected CubeSat altimeter along-track comb formation shows the capability to map the ocean sub-mesoscale structures, which is extremely hard to monitor using traditional large spaceborne radar altimeters.

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