ESA GNC Conference Papers Repository

PODIUM is a compact spacecraft navigation unit designed to provide interplanetary missions with autonomous position and velocity estimations. The unit will make use of Pulsar X-ray observations to measure the distance and distance rate from the host spacecraft to the Solar System Barycenter. Such measurements will then be used by the onboard orbit determination function to estimate the complete orbital elements of the spacecraft. The design aims at 6 kg of mass and 20 W of power, in a volume of 150 mm by 240 mm by 600 mm. The Pulsar X-Ray navigation has been theoretically addressed in various papers and was demonstrated by SEXTANT/NICER on the International Space Station (ISS). The aim of the activity carried out by the SENER-DEIMOS-IEEC industrial consortium under ESA contract is to define a preliminary design for the unit, tackling the overall unit architecture, the optical and thermomechanical design, the unit avionics and SW, and a preliminary concept of function, performance, and operation. PODIUM is designed to minimize the impact on the mission operational and accommodation constraints. The architecture is based on a grazing incidence X-ray telescope with focal distance limited to 50 cm. The effective area was designed to be at least 50 cm2 for photon energies in the range 0.2-10 keV, and 60 cm2 are achieved for the majority of the pulsars in our pulsar catalogue, requiring nesting of several mirrors in the Wolter-1 geometry. Grazing incidence angles are very small, below 2 deg. The FOV size determines the aperture of the optics and is related to the maximum number of nested mirrors to accommodate. The current target FOV is 0.25 deg. The pulsars’ photon arrivals are detected with a single pixel Silicon Drift Detector (SDD) sensor with timing accuracy below 1µsec. This leads to a maximum expected position accuracy of 30 m. The unit has no gimbaling to meet the applicable power, size and mass requirements. Instead, the host spacecraft shall slew and point to allow pulsar observation. The avionics architecture is based on a radiation hardened LEON4 processor, to allow a synchronous propagation task and measurement generation and orbit determination step in an asynchronous task. PODIUM will enable higher autonomy and lower cost for interplanetary missions. L2 space observatories and planetary flybys are the current reference use cases. Onboard autonomous state estimation can reduce the ground support effort required for navigation and orbit correction/maintenance computation, and reduce the turnaround time, thus enabling more accurate maneuvers, reducing the orbit maintenance mass budget.