Speaker
Mr
Massimo Vetrisano
(DEIMOS SPACE SLU)
Description
This work presents the general architecture and capabilities of the HADES software developed at Deimos Space SLU. Detailed models about the close proximity environment about Near Earth asteroids and the involved operations are often required during preliminary assessment of mission requirements especially under the presence of uncertainties. It is vital to assess the compliance to the mission requirements in terms of safety and illumination. These play an important role in the selection of control techniques and operational orbits.
The developed software deals with the high-fidelity modelling of spacecraft operations at irregular shape asteroids. The first version of HADES which includes the main GNC functionalities has been developed and tested.
The spacecraft dynamics considers all the possible perturbations, i.e. third body effect from the Sun, the SRP and irregular gravity field of the rotating asteroid. The software uses both spherical harmonics and actual asteroid’s shapes. In the first case the coefficients can be given from actual data or they are calculated on the size of user-defined ellipsoid; in the second case the gravity field is reconstructed from the asteroid tetrahedral mesh. The software can handle any operational orbit, with particular care paid to inertial and body fixed hovering.
One important aspect when designing proximity operations is to evaluate how the different control techniques and on-board instruments affect the performance of the system.
Different control techniques based on both continuous and discrete methods have been considered and implemented. The manoeuvre execution itself can be affected by errors in the magnitude and in direction.
The spacecraft orbit determination is performed through a performance models or by on-board measurements, a navigation camera and a LIDAR, which are processed by an Unscented H-infinity Filter (UHF). The latter was selected for its ability to deal with unfiltered biases and non-Gaussian distribution of the measurements. The visibility and illumination condition are considered for the image processing, with the measurements affected by the attitude and pointing errors.
HADES can employ different levels of accuracy between the assumed environment knowledge and the model used in the controller and in the UHF. For instance the gravity could be modelled from the shape, but the correction manoeuvre and the trajectory estimate could be calculated by a limited number of spherical harmonics. Also the shape model could be known with a certain error.
HADES comes with a Monte Carlo (MC) module which allows drawing more noticeable statistical parameters, such as the control budget, accuracy of the estimation and control systems, or the occurrence of failures when the controller cannot maintain the orbit.
Different examples applied to the case of the asteroid Dydimos will be shown for inertial and body-fixed hovering, with some MC analyses for the station keeping of the Asteroid Impact Mission (AIM) for different levels of system and dynamics uncertainties.
Finally the ongoing activity on the asteroid deflection by low push methods, i.e. laser ablation, ion-beam shepherd and gravity tractor will be shown.
The present tool was developed within the European Commission funded Stardust project under the Marie Curie scheme.
| Applicant type | First author |
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Primary author
Mr
Massimo Vetrisano
(DEIMOS SPACE SLU)
Co-author
Mr
Juan Luis Cano
(Elecnor Deimos)
