An experimental demonstration set-up for detecting potential temperature defects on harness of cables with reflectometry
Creators: name:  N. GREGIS 
name:   M. CARTRON 
name:   M. SLIMANI 
name:   D. MONCHAUX 
name:   D. BESSON 
Publisher: name: Proceedings of  the 9th European Conference for Aerospace Sciences. Lille, France, 27 June - 1 July, 2022
Year: 2022
Subjects: REUSABLE SYSTEMS
SYSTEM DESIGN
REUSABLE LAUNCH VEHICLES

description: In a context of Reusable Launch Vehicles (RLV), preventive maintenance is the solution to ensure reliable and safe reuse of the system for extending its useful life. In particular, cables are critical components of the space launch system subject to harsh environmental conditions such as mechanical stress, heat, vibration etc., which can lead to severe damage and affect the overall functionality of the system. In [1], we proposed a monitoring system, based on electrical reflectometry technique, where embedded sensors are deployed on the harness of the vehicle. We showed, through numerical simulations based on a rough model that thermal defects can be detected. However, this model integrates only brutal temperature change and does not considers progressive temperature variations along the cable. In this study, we propose more accurate models, taking into account local thermal effect on the cable. We included in the ABCD frequency method a mesh description of the cable to allow a thinner description of the cable while considering a progressive temperature profile. We proposed a combination of a mesh description and the ABCD calculus method and optimized the meshs parameters to reduce side effects on simulations. Using a previously given law linking temperature variations and materials variation, we could generate the impact on reflectometry for each cell of the mesh and mitigate the unwanted reflections created by this new model. Then, two cases were considered. First, we focused on a dramatic drop of the temperature on a local part of the cable, for temperatures ranging from -50 C to -200 C. This can happen, for example, when the thermal protection around the ergol tanks is damaged and the cable is exposed to very low temperature. Second, we considered an important raise of the temperature of a part of a cable up to 180C, as it could happen with the presence of a hot spot near a reactor, for instance. For both cases, numerical simulations were conducted taking into account a cable network used for power distribution with the presence of local thermal defects in different places of the cable. We equipped the cable with temperature sensors and used a reflectometry measurement tool. We then measured TDR signals. The response of reflectometry sensors shows that hot and cold spots can be detected and located. To prove the validity of the proposed models, experimental test beds were set to reproduce the same scenario as in simulation. For low temperatures, we immerged part of a cable in a tank full of liquid nitrogen and made several reflectometry measurements with an electronic board similar to the one described in [1]. In addition, an oven was used to locally heat a portion of the cable. The experimental results showed great similarities between the simulations and the measurements. All this work provides an experimental validation of a newly designed model describing the cable damage due to local temperature change, and lays the proof of the capability of our reflectometry sensors to detect and locate such types of defects on a typical cable used in Space Launch Vehicles.