Research Items (4)
The total shift of focus and dependence from ground-based architectures to reliable on-board autonomous systems is a prime necessity for navigation of small satellites if they are to venture beyond Earth. Navigation systems would need to provide higher accuracy levels, generally constrained by stringent transfer trajectories. Research on autonomous navigation by Spaceflight Dynamics division at SRM University considered an articulated navigation technique with the goal to maximize accuracy in both orbiting and cruise phases of the mission. Optical navigation is considered as primary navigation method for orbiting profile phases, while Milli-Second X-Ray Pulsar based navigation for the cruise phase. The navigation methods are theoretically investigated in a Low Lunar Orbit, which is being considered in the mission design for SRMSAT-2, a student designed lunar orbiter. Use of optical navigation is a developed concept and furthering its use to account for versatility to minimize hardware requirements by using same optical hardware in all the orbiting or close approach phases is important. In the paper, star occultation method is considered and investigated. The work lays down basic geometry of star occultation measurement problem. The performance evaluation is then laid out utilizing a non-standard EKF form with truth model simulation. Observability analysis and scope of improvements are then inferenced from the analysis. Primary attention in the work is given to maximizing the state acquisition accuracy to improve independence and reliability of the navigation system. The hardware layout for achieving reasonable orbit determination accuracy is then laid down.
SRMSAT 2 is a progressive conceptual student small satellite mission and a step forward in deep space exploration, pushing horizons of robust small satellites to regimes beyond earth. Currently in the preliminary design phase, the mission is directed towards the design of a small orbiter spacecraft to orbit and study moon in a Low Lunar Orbit (LLO). The propulsion system of the spacecraft is a crucial design factor considering the constraint put in by mass and volume. The paper is focused on the design of a propulsion system for a small satellite which can be considered and optimized for other future missions. The paper contains trade-off studies of different propulsion systems and propellants available and the criteria for choosing the best for the system. The design will include various propellant study, mass calculation, and estimation by considering the inputs from the trajectory, the number of thrusters and their placements and finally the design of the tank and propellant feed system.
SRMSAT 2 is a progressive conceptual student small satellite mission and a step forward in deep space exploration, pushing horizons of robust small satellites to regimes beyond earth. Currently in the preliminary design phase, the mission is directed towards the design of a small orbiter spacecraft to orbit and study moon in a Low Lunar Orbit (LLO). The extent of small satellites’ reach to the moon has been limited mainly, due to conventional direct transfers requiring higher ∆v and incorporation of complex propulsion systems for the same. Thus, the mission is being designed to insert a small-satellite in an LLO achieved by a Weak Stability Boundary capture following the Low Energy Transfer to Lagrangian Equilibrium point via a low energy trajectory through invariant manifolds, an elementary component of Earth-Moon system in Circular Restricted Three Body Problem. Main components of the preliminary mission include design of Propulsion, TT&C, ADCS, GNC, Power, On-Board Computer and Thermal Design and Control subsystems coherent with mission requirements for spacecraft to endure harsh environment during Earth-orbiting, trans-lunar and Moon-orbiting phases. The paper describes mission design methodology as well as preliminary subsystem designs for the spacecraft.
Satellite constellations have become a popular choice for sufficing needs ranging from terrestrial navigation (GPS) to communication relay in space (TDRSS). With the increasing popularity of small satellite applications, a small satellite constellation would be the most cost-efficient solution for smaller applications. A constellation of small satellites can be used for beam forming applications like directional transmission and spatial filtering in satellite communication, high resolution imaging etc. Critical challenge for a beam forming constellation would be the precise positioning of each spacecraft in their orbits and attitude based on their position. Traditional ground tracking utilizing Doppler and Ranging for position determination wouldn’t render accuracy of the order of meters expected for positioning requirements for precision beam forming. The paper lays out simplified relative autonomous navigation process to precisely determine orbit on board as well as relative positions of each spacecraft, layout of a less complex hardware system for navigation (not requiring communication between the spacecraft), operations encompassed and performance of synchronized attitude orbit data optimized for stationkeeping and attitude control suitable for beamforming in a small satellite constellation around moon. On orbit navigation means independence from ground tracking and lower hardware complexity. Lower hardware complexity offers cost-efficient inclusion of more than one systems to better fulfill navigation and station keeping accuracy requirements for a beam forming constellation.