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Space missions are becoming more and more challenging, requiring fast and adaptive reactions to external stimuli that can be obtained with higher level of on-board autonomy. Because of such requirements, Guidance Navigation and Control technologies are increasing in complexity and, as a consequence, demand a more structured validation plan, to be started already during the preliminary stages of the mission. GMV standard for the Design, Development, Validation and Verification of GNC technologies is an incremental validation that starts with unitary testing of functions and modes up to flight code run inside representative processors and with engineering/qualification sensor models in close loop. The critical review of requirements allows for the derivation of GNC subsystem specification and for a preliminary design of GNC modes and functions necessary to achieve mission objectives. First step is functions unitary testing, but using previous experience and heritage, it is possible to test the algorithms in a representative closed loop GNC prototype already in phase A-B1. Model-In-the-Loop simulations demonstrate the feasibility of the preliminary design and the robustness of the selected solutions using Monte Carlo test campaigns. Being able to perform such tests during the preliminary stages of the development allows for efficient iterations at system level, giving valuable contributions for trade-offs that involve other subsystems. A fast prototyping based on autocoding is performed as following step, verifying the GNC code in Software-In-the-Loop tests. To demonstrate the feasibility of the design, the Processor-In-the-Loop step is then a key point of the incremental validation in order to verify the behaviour of the GNC code in a representative Hardware and to identify the computational resources required through code profiling. At this stage it is possible that specific function/algorithm (e.g. Image Processing) turns out to be too demanding for a space qualified processor like a LEON. In this case, a HW-SW co-design is performed in order to get advantage of the HW acceleration that an FPGA can offer. An estimation of the required resources and HW units is an essential input for Spacecraft system in order to perform budget activities and interfaces between subsystems. Furthermore, this high level of simulations fidelity, allows to take into account also operations constraints, defining a detailed time line of the different mission phases. In the final stage of the incremental validation Hardware-In-the-Loop is performed, including representative sensors in the loop (e.g. camera in a vision-based GNC). Two environments are foreseen for the HIL tests: an optical test bench where the images are generated on a high resolution screen and only a picture of it is taken; a robotic test bench (platform-art(c)) that re-creates a space-like scenario in terms of illumination conditions and simulated gravity using a dedicated laboratory with robotic arms. The platform-art(c) tests are the most complex to set-up and to execute, but there is a clear advantage in terms of representativeness because no artificial image is generated and the camera directly takes a picture of the target mock-up. This paper will include the details on GMV DDVV approach, which allows to perform end-to-end GNC simulations at very early phases of the mission to bring into considerations aspects normally not really considered in detail till later mission phases. GMV standard allows (through very fast iteration loops and full algorithms/SW coherence approach) algorithms updates/iteration till phases where they should be nominally frozen (thus, gaining flexibility and introduction of last techniques in the late phases of the mission. Copyright 2019 by by GMV aerospace and defence. Published by the EUCASS association with permission. A. Pellacani, M. Graziano

The Asteroid Impact and Deflection Assessment mission (AIDA) is a joint mission between ESA and NASA to demonstrate the kinetic impactor technique for planetary defence. A NASA spacecraft, DART, will impact the moon of the Didymos asteroid binary system and the HERA spacecraft, from ESA, will get closer to investigate what was the effect of such impact. The HERA mission is based on the extensive work done by the Agency and European industry between 2011 and 2016 in the frame of the Asteroid Impact Mission (AIM). In order to be able to detect the slightest change to the system and better understand the effect of the impact, close proximity operations are baselined in the mission timeline. Both AIM and HERA missions share the vision of a highly autonomous system, which is necessary to allow such close proximity operations. As it is the first time that a binary asteroid system will be studied from such a short distance, it is also important to remark the value of the scientific return of the mission. In order to guarantee a high level of autonomy, the first step is to give to the Spacecraft enough on-board information to estimate its position with respect to the asteroids and, based on that estimation, to act accordingly following a preloaded sequence of commands or objectives. To achieve this requirement, a vision based GNC has been designed, which includes image processing algorithms and a navigation filter capable of processing the visual information and to get the desired estimation. The HERA GNC baseline presented here will not only use a visual camera but also several other payloads, involving data fusion with a hyperspectral/thermal camera and a laser altimeter (PALT). These additional instruments will be able to increase the robustness of the strategy: the hyperspectral/thermal imager will be able to see where the AFC is limited by shadows and phase angle issues; PALT will be able to give observability on the radial direction, which is poorly estimated in a vision based GNC (especially if the low gravity environment does not allow stable orbits and hyperbolic arcs are preferred for safety reasons). HERA close proximity operations have been investigated and the design will be consolidated by the end of Phase B1. A specific distance of 8 km is identified from a GNC driving factor. If the Spacecraft will be outside the 8km sphere centred in the main asteroid, the AFC will give a full visibility of the body and centroiding techniques can be used for the state estimation. For closer fly-bys the entire camera FoV will be covered by the asteroid and a feature tracking technique is baselined to maintain the relative state estimation. Image Processing and navigation functions have been designed taking into account this factor and a detailed designed showed its feasibility taking into account ground segment operations and pushing the validation of the on-board algorithms up to TRL 5/6 with Hardware-In-the-Loop tests. This paper will include the consolidated strategies of the vision based GNC designed for the HERA mission, together with the test campaign results. Additionally, the required future developments will be addressed.

BACKGROUND AND PURPOSE: Ceramic-on-ceramic articulation is an attractive alternative to metal-on-polyethylene (PE) bearings, but little is known about the in vivo effects induced by dissemination of alumina wear debris in the periprosthetic tissues. We hypothesized that wear debris is not the main factor responsible for loosening and failure of the implant but that mechanical problems caused by incorrect surgical technique, prosthetic design, or trauma, may cause instability of the implants and result in production of wear debris. PATIENTS AND METHODS: Clinical, radiographic, laboratory, and microbiological data from 30 consecutive patients with failed alumina-on-alumina arthroplasties, 19 with screwed socket and 11 with press-fit socket, were systematically collected and evaluated. Retrieved peri-implant tissues and prosthesis wear were also analyzed. RESULTS AND INTERPRETATION: Loosening was due to malpositioning, primary mechanical instability, trauma, or infection. Bone stock was generally preserved, even if screwed implants showed higher levels of osteolysis. Variable implant wear and tissue macrophage reaction were present but activation of giant cells/osteoclasts was not induced, and no correlation between histocytic reaction and the level of osteolysis was found. These findings indicate that, in contrast to the situation with metal-on-PE bearings, wear debris and occasional osteolysis were the effect rather than the cause of failure of ceramic-on-ceramic implants, and that press-fit socket fixation was the socket fixation design of preference.