Identification from flight data of the Italian Unmanned Space vehicle

Identification methodologies for processing flight data are frequently used to validate and improve a pre-flight aerodynamic data-base and, specifically, to reduce the associated uncertainties. This paper describes the process applied for the identification of the aerodynamic model of the Italian Unmanned Space Vehicle. The identification problem is solved through a multi-step approach, where the aerodynamic coefficients are identified first and, in a following phase, a set of model parameters are updated. The methodology was applied to actual flight data, gathered during the second flight test performed by the Italian Aerospace Research Centre

Robustness Analysis for Terminal Phases of Re-entry Flight

Advancements in the current practices used in robustness analysis for FCS design refinement by introducing a method that takes into account nonlinear effects of multiple uncertainties over the whole trajectory, to be used before robustness is finally assessed with MC analysis has been reported. Current practice in FCS robustness analysis for this kind of application mainly relies on the theory of linear time-invariant (LTI) systems. The method delivers feedback on the causes of requirement violation and adopts robustness criteria directly linked to the original mission or system requirements, such as those employed in MC analyses. The nonlinear robustness criterion proposed in the present work is based on the practical stability and/or finite time stability concepts. The practical stability property improves the accuracy in robustness evaluation with respect to frozen-time approaches, thus reducing the risk of discovering additional effects during robustness verification with Monte Carlo techniques

A linear time-varying approach for robustness analyses of a re-entry flight technology demonstrator

A novel robustness analysis technique is proposed for atmospheric re-entry applications. The problem is stated as a finite time stability (FTS) analysis of linear time-varying (LTV) systems on a compact time domain, subject to bounded variations in initial state and unknown parameters. The FTS property is formulated as the inclusion of all the possible system trajectories into a pre-specified time-varying subset of the state space. Based on assuming the involved sets are polytopes, the proposed approach allows deducing the system FTS from the property verification on a limited number of numerically computed system trajectories. An additional result is presented which allows determination of a conservative estimate of the maximum norm-bound of time-varying perturbations under which the LTV system remains finite time stable. Results of the application of the proposed technique to a re-entry technology demonstrator are presented which demonstrate its effectiveness in complementing conventional linear time invariant-based analyses. Results also show that it is computationally viable and allows linking the system robustness to a quantitative analysis of the system trajectory dispersion around the nominal one due to concurrent initial state dispersion and uncertain parameters effects, which aids in evaluating mission objectives fulfillment

GNC Post Flight Analysis of the Italian Dropped Transonic Flight Tests

The Italian Aerospace Research Centre (CIRA), in the framework of the Unmanned Space Vehicles (USV) Program, has developed several advanced Guidance, Navigation and Control technologies for the Terminal Area Energy Management (TAEM) phase of a re-entry ight. These technologies were in-flight tested during the first two dropped transonic flight tests (DTFT1 and DTFT2) of the program. These missions allowed CIRA to investigate critical technological aspects related to the autonomous execution of a typical TAEM phase of a re-entry flight, from a velocity of about Mach 2 down to the typical Approach/Landing Interface speed of Mach 0.5 and below. This paper presents flight tests results and post flight data analysis of these missions. How technological innovations in the Guidance, Navigation and Control domain can contribute to a more autonomous, more safe and less costly future generation of reusable launch vehicles is well stated in open literature. In the USV program, focus was given to adaptive guidance with on-line trajectory re-planning capabilities and to robust and fault tolerant control, as key enabling technologies for atmospheric re-entry and hypersonic flight. Obviously, the complexity of such missions also required dedicated research on advanced methodologies in the field of robustness analysis, design and verification of GNC systems for highly uncertain and non-linear systems. Methodologies for vehicle model identification from flight data have been also included in this technological road map to maximize the scientific return from the flight tests. Model identification methodologies for processing flight data are frequently used to validate and improve a pre-flight aerodynamic data-base and, specifically, to reduce the associated uncertainties. However in this field conventional techniques need to be improved because the USV flight tests have a non-stationary trajectory and specific identification manoeuvres should be avoided being hazardous for the mission. More specifically, the problem of the identification of the aerodynamic model of the Italian Unmanned Space Vehicle was solved through a multi-step approach, where the aerodynamic coefficients are identified first and, in a following phase, a set of model parameters are updated. The methodology was applied to actual flight data, acquired during the two dropped transonic flight tests

Advanced GN&C Technologies for TAEM: Flight Test Results of the Italian Unmanned Space Vehicle

This paper describes the guidance, navigation and control challenges posed by the Unmanned Space Vehicles Program. Within the framework of this program the Italian Aerospace Research Center has conceived several advanced GN&C technologies useful in the Terminal Area Energy Management phase of a re-entry flight pattern. These technologies were flight tested during the first two dropped transonic flight tests (DTFT1 and DTFT2) of the program. More specifically, this paper will present the design of the adaptive guidance algorithms developed to accomplish the mission objectives of the DTFT2 flight test. Flight results will be shown in order to state the performance of the guidance strategy putting in evidence, where possible, its most promising aspects for future TAEM applications

A hybrid approach to robustness analyses of flight control laws in re-entry applications

The present paper aims at improving the efficiency of the robustness analyses of flight control laws with respect to conventional techniques, especially when applied to vehicles following time-varying reference trajectories, such as in an atmospheric re-entry. A nonlinear robustness criterion is proposed, stemming from the practical stability framework, which allows dealing effectively with such cases. A novel approach is presented, which exploits the convexity of linear time varying systems, coupled to an approximate description of the original nonlinear system by a certain number of its time-varying linearizations. The suitability of the approximating systems is evaluated in a probabilistic fashion making use of the unscented transformation technique. The effectiveness and potentials of the method are ascertained by application to the robustness analysis of the longitudinal flight control laws of the Italian Aerospace Research Center (CIRA) experimental vehicle USV

Multi-step strategy for rotorcraft model identification from flight data

The availability of suitable methods for system identification from flight data of rotorcraft models is a key factor to enhance the competitiveness of the rotorcraft industry in the development process of new vehicles. Indeed, reliable simulation models provided by the identification techniques can be used for the design and validation of the vehicle flight control system. It allows minimizing the number of in flight experimental tests and consequently reducing costs and risks related to flight testing. Identification methodologies generally fall into two categories: frequency-domain and time-domain. Each approach has inherent strengths and weaknesses. Much of the published works on rotorcraft identification deals primarily with frequency-domain methods, which work well at mid and high frequencies associated with the dynamics of the vehicle control inputs and the aero-elastic behaviour of the blades. On the other hand, time-domain methods, which are well assessed for the identification of fixed wing aircraft, provide accurate models at the low frequency scale that is related to the vehicle flight mechanics. In this paper a hybrid time-frequency identification approach is described. The identification process was carried out in the framework of a multi-step strategy and a specific methodology was selected to comply with each step objective. The hybrid time-frequency approach allowed exploiting the advantage of both time and frequency methods, maximizing the information content extracted from the flight data and obtaining an identified model applicable in the whole frequency range of interest. Furthermore the multi-step strategy decomposed the complex starting problem in simplified sub-problems, which are easier to be solved. The proposed methodology was applied to simulated data of the UH60 Black Hawk, generated using the FLIGHTLAB multi-body simulation environment. Preliminary results showed the effectiveness of the proposed identification strategy in terms of convergence and capability of extracting from flight data relevant information on the vehicle dynamic behaviour. Future works will be focused on the refinement of the structure of the rotorcraft model used for identification purpose and on the application of the proposed methodology to set of data gathered during actual rotorcraft flight tests

Superhydrophobic coatings as anti-icing systems for small aircraft

Traditional anti-icing/de-icing systems, i.e., thermal and pneumatic, in most cases require a power consumption not always allowable in small aircraft. Therefore, the use of passive systems, able to delay the ice formation, or reduce the ice adhesion strength once formed, with no additional energy consumption, can be considered as the most promising solution to solve the problem of the ice formation, most of all, for small aircraft. In some cases, the combination of a traditional icing protection system (electrical, pneumatic, and thermal) and the passive coatings can be considered as a strategic instrument to reduce the energy consumption. The effort of the present work was to develop a superhydrophobic coating, able to reduce the surface free energy (SFE) and the work of adhesion (WA) of substrates, by a simplified and non-expensive method. The developed coating, applied as a common paint with an aerograph, is able to reduce the SFE of substrates by 99% and the WA by 94%. The effects of both chemistry and surface morphology on the wettability of surfaces were also studied. In the reference samples, the higher the roughness, the lower the SFE and the WA. In coated samples with roughness ranging from 0.4 and 3 μm no relevant variations in water contact angle, nor in SFE andWA were observed

Unconventional integrated navigation systems based on redundancy of traditional navigation sensors

In this work several unconventional navigation systems are presented that include redundancy of traditional navigation sensors. Main focus is on sensor architectures, while sensor fusion algorithms will be treated as a secondary aspect. Specifically, an analysis of systems with multiple IMUs, Gyro-free INS and GPS derived attitude has been performed. Several reasons justify the application of architectures with redundant navigation sensors; the most relevant obviously concerns the capability to detect and identify some faults. Anyway, sensor redundancy also allows increasing the accuracy of some measurements (as for example in multiple IMU’s systems) or avoiding the use of some sensors, which may have disadvantages in terms of costs or accuracy, without renounce to their measurements (as for example in Gyro-free INS). In fact these systems are based on the application of pseudo-measurements