Recent research on reusable launchers indicates that those vehicles require a more complex design and higher technology performance levels than actual expendable launchers. The need for an advanced Health Monitoring System (HMS) appears then to be unavoidable to assure the concept of reusability at an affordable cost without affecting the overall mission risk. After a brief reminder on mission risk management aspects and then possible ways to reduce the risks inherent to any system operation, the sensor specifications of this advanced integrated HMS are fully deduced from the environmental and operational requirements, according to the NDE sensing technique in review and the corresponding final detection objectives. Some short examples are given all the way long to show what has already been developed and where the most difficult problems remain (including also remote controlled systems like space probe, deep-see submarine,etc.). With the help of an advanced integrated multi-sensor network (hardware) and the use of an expert system (software), damage detection, monitoring and prognosis are performed to deduce the safety state of any subsystem or associated operation. Then the information is used to modify accordingly the mission scenario if imposed to maintain an acceptable level of risk.
Ion beam figuring is a deterministic optical fabrication technique which efficiency has been mainly demonstrated on large optics these last years. One of the disadvantages of ion figuring is the high surface temperature of the workpiece. Temperature aspects have already ben mentioned by some authors but are weakly detailed. Therefore thermal effects on BK7 and Zerodur, mainly surface figure distortions and surface temperature measurements, have been investigated here in more detail.
The frequency domain approach of Scansar problems suffers, numerically speaking, from the constrained smallness of the unit of azimuth increment. This unit is equal to the displacement of the craft between two consecutive transmission times, whatever the burst length, the latter conditioning the resolution of the coherent reconstruction. Thus a large oversampling occurs. There are three main ways of action to save computational effort: (1) The simplest one is to go out of the frequency domain with a dimension reduced transform operating on a cheap manipulation of the full frequential product. (2) The second one is to build the frequential input from several transforms at a dimension close to the burst, thus taking advantage of the initial zero padding. (3) The third one is to modify the 'static' template pipe in order to avoid repetitive operations in the signal pipe. A simple situation will be met where this policy is immediate. A much more intricate case of application leads to a hybrid algorithm connected with the SPECAN approach. The difference between the hybrid algorithm and Specan rests in the strictly diagonal character of the initial transformation performed on the burst in the Specan case, contrary to a narrow band matrix multiplication for the more general hybrid approach. The main lines of conclusion of this study are that, assorted with carefully designed numerical procedures, the frequency domain approach for Scansar is convenient, mainly, for coherent processing of rather longs bursts. More particularly, it combines well with frequential azimuth multilook. In the case of too short bursts, it becomes weaker than direct algebraic manipulation, but it gives an easy way for preparation of the needed static transformation matrices. The comparison with SPECAN approach is less easy, as the nets of points locations for reconstruction do not match. Nevertheless, a static transformation generalizes the Specan concept to prescribed grid by approximations coming from the hybrid algorithm. That new way could be challenging. The important theoretical part of this paper is clarified by illustrative means and some quicklook alternatives discussed in the function of, among other things, the imaging scenario, the required resolution, and the bursts length.