Onboard Flight Software Research Articles

Point Mascon Global Lunar Gravity Models

Lunar gravitational models are generated using sets of point mass potentials (mascons) fit to the GRGM1200A representation derived from GRAIL mission data. Point mass ensembles allow for simple modeling of a gravity potential and its partial derivatives. The new point mascon models are intended to be low- to medium-resolution replacements for spherical harmonics models in mission planning applications or onboard flight software. The design space of how to parameterize the mascons is explored. The chosen configuration uses equally weighted point mass potentials and requires the successive solutions to thousands of nonlinear optimization problems that adjust the mascon locations. A database of models that vary in resolution is generated and disseminated as supplementary material, with the highest-fidelity model demonstrating equivalent accuracy and memory footprint to a spherical harmonics truncation. Gravitational acceleration and gravity gradient evaluation runtimes are roughly two to eight times faster for the new mascon models when compared with spherical harmonics models with equivalent error, depending on the model fidelity and the computational environment.

High-Resolution Image and Video CubeSat (HiREV): Development of Space Technology Test Platform Using a Low-Cost CubeSat Platform

In this paper, we present high-resolution image and video CubeSat (HiREV), the first constructed 6 U platform to reach the space technology test bed stage, developed by the Korea Aerospace Research Institute (KARI). The CubeSat system is a low-cost platform that has been widely applied to various space missions, from missions involving earth observation to deep space. Despite the emergence of the CubeSat technology worldwide, the CubeSat market in Korea is still in the beginning stages, and a standard testing platform is also in demand. For this reason, KARI is starting to develop a 6 U CubeSat platform, which includes a less than 3 U bus system and greater than 3 U payload space. HiREV has been developed with locally manufactured parts, creating a domestic commercial off-the-shelf infrastructure for CubeSat and 3 m resolution camera payload development. Core flight software has also been applied as an on-board flight software system. Presently, we have developed the main system, while HiREV is under space environmental testing.

Libration point stationkeeping using the θ-D technique

Unstable orbits about the collinear libration points require stationkeeping maneuvers to maintain the nominal path. A new method for stationkeeping such unstable orbits is proposed here using continuous thrust. The stationkeeping challenge is formulated as a nonlinear optimal control problem in the framework of the circular restricted three-body problem with the Sun and Earth/Moon center of mass as the two primaries. A recently developed control technique known as the “θ-D controller” is employed to provide a closed-form suboptimal feedback solution to this nonlinear control problem. In this approach an approximate solution to the Hamiltonian-Jacobi-Bellman (HJB) equation is found by adding perturbation terms to the cost function. The controller is designed such that the actual (numerically integrated) trajectory tracks a predetermined Lissajous reference orbit with good accuracy. Numerical results employing this method demonstrate the potential of this approach with stationkeeping costs varying between 0.52 ∼ 0.68 m/s per year (the range depending on the particular simulation parameters used), which is of the same order of magnitude as other methods using discrete maneuvers with halo orbits. The costs are modest and the method provides flexibility in selecting the “tightness” of the control versus fuel consumption. The algorithm is well-suited for integration with onboard flight software, as the nonlinear optimal control law is solved in closed-form and the Riccati equation must only be solved once, resulting in a computationally efficient controller.

Odin two years in-orbit, staying alive and continuously tuned-in

Odin is a Swedish-led, scientific, three-axis stabilised, fine-pointing, small satellite that provides high-quality spectroscopy data in the optical, mm and submm regions. End-users are atmosphere and astronomy scientists in Canada, France, Finland and Sweden. The satellite had in February 2003 accomplished its design goal, two years lifetime in-orbit, and it continues to work well. Satellite parameters as well as operational procedures have been adjusted frequently during the lifetime of Odin. Operational changes and improvements cover almost all areas, like power management, data taking, cooler operation, thermal control, payload configuration and calibration, star tracker handling and, perhaps most important, attitude reference generation. The on-board flight software has on several occasions been updated. Some of the improvements were planned already before launch, while others are a consequence of adapting to gathered experience in-orbit. Today Odin has implemented sophisticated measurement strategies that either increases pointing accuracy or creates more efficient aeronomy research than originally planned for.

Design, Implementation, and Validation of KOMPSAT-2 Software Simulator

In this paper, we present design features, implementation, and validation of a satellite simulator subsystem for the Korea Multi-Purpose Satellite-2 (KOMPSAT-2). The satellite simulator subsystem is implemented on a personal computer to minimize costs and trouble on embedding onboard flight software into the simulator. An object-oriented design methodology is employed to maximize software reusability. Also, instead of a high-cost commercial database, XML is used for the manipulation of spacecraft characteristics data, telecommand, telemetry, and simulation data. The KOMPSAT-2 satellite simulator subsystem is validated by various simulations for autonomous onboard launch and early orbit phase operations, anomaly operation, and science fine mode operation. It is also officially verified by successfully passing various tests such as the satellite simulator subsystem test, mission control element system integration test, interface test, site installation test, and acceptance test.