Shuttle TPS inspection using triangulation scanning technology

Abstract

With the loss of the Space Shuttle Columbia, there has been intense focus at NASA on being able to detect and characterize damage that may have been sustained by the orbiter during the launch phase. To help perform this task, the Neptec Laser Camera System (LCS) has been selected as one of the sensors to be mounted at the end of a boom extension to the Shuttle Robotic Manipulator System (SRMS). A key factor in NASA's selection of the LCS was its successful performance during flight STS-105 as a Detailed Test Objective (DTO). The LCS is based on a patented designed which has been exclusively licensed to Neptec for space applications.The boom will be used to position the sensor package to inspect critical areas of the Shuttle's Thermal Protection System (TPS). The operational scenarios under which the LCS will be used have required solutions to problems not often encountered in 3D sensing systems. For example, under many of the operational scenarios, the scanner will encounter both commanded and uncommanded motion during the acquisition of data. In addition, various ongoing studies are refining the definition of what constitutes a critical breach of the TPS. Each type of damage presents new challenges for robust detection. This paper explores these challenges with a focus on the operational solutions which address them.

STS-128 on-orbit demonstration of the TriDAR targetless rendezvous and docking sensor

“…This configuration takes advantage of the complementary nature of these two ranging technologies to provide 3D data at both short and long range without compromising on performance [6]. The laser triangulation subsystem is largely based on the Laser Camera System (LCS) used to inspect the Space Shuttle's thermal protection system after each launch [7]. By multiplexing the two active subsystem's optical paths, the TriDAR can provide the functionalities of two 3D scanners into a compact package.…”

The complementary nature of triangulation and ladar technologies

“…first pulse or last pulse, the range measurement will be associated with the center of the beam aim even though they come from different locations within the spot. Generally, the position of the measurement will only be precise to within about a half of the spot size relative to the center position, and the aim of the † Range precision is only reported up to 12 m and so is extrapolated by the dotted line to 25 center position is uncertain to the galvanometer aiming precision. Since these are independent errors, they can be added as root-sum-squares.…”

“…Larger scale inspection is becoming more critical in space applications such as scanning the shuttle fleet on orbit 24,25 , the International Space Station, and future spacecraft and habitats. The criteria for this type of inspection usually consist of a maximum spatial resolution and tight range precision requirements, with acquisition speed also a concern.…”

“…An updated design has been selected for inspection of the shuttle Thermal Protection System for returning the shuttles to flight 25 . LCS peak measurement algorithms are capable of measuring the peak with a precision better than 1/64 th of a detector pixel 27 (50 µm pitch) which has been confirmed in practice.…”