Assessment and Mission Planning Capability for Quantitative Aerothermodynamic Flight Measurements Using Remote Imaging

Abstract

High resolution calibrated infrared imagery of vehicles during hypervelocity atmospheric entry or sustained hypersonic cruise has the potential to provide flight data on the distribution of surface temperature and the state of the airflow over the vehicle. In the early 1980's NASA sought to obtain high spatial resolution infrared imagery of the Shuttle during entry. Despite mission execution with a technically rigorous pre-planning capability, the single airborne optical system for this attempt was considered developmental and the scientific return was marginal. In 2005 the Space Shuttle Program again sponsored an effort to obtain imagery of the Orbiter. Imaging requirements were targeted towards Shuttle ascent; companion requirements for entry did not exist. The engineering community was allowed to define observation goals and incrementally demonstrate key elements of a quantitative spatially resolved measurement capability over a series of flights. These imaging opportunities were extremely beneficial and clearly demonstrated capability to capture infrared imagery with mature and operational assets of the US Navy and the Missile Defense Agency. While successful, the usefulness of the imagery was, from an engineering perspective, limited. These limitations were mainly associated with uncertainties regarding operational aspects of data acquisition. These uncertainties, in turn, came about because of limited pre-flight mission planning capability, a poor understanding of several factors including the infrared signature of the Shuttle, optical hardware limitations, atmospheric effects and detector response characteristics. Operational details of sensor configuration such as detector integration time and tracking system algorithms were carried out ad hoc (best practices) which led to low probability of target acquisition and detector saturation. Leveraging from the qualified success during Return-to-Flight, the NASA Engineering and Safety Center sponsored an assessment study focused on increasing the probability of returning spatially resolved scientific/engineering thermal imagery. This paper provides an overview of the assessment task and the systematic approach designed to establish confidence in the ability of existing assets to reliably acquire,

The Hythirm Project: Flight Thermography of the Space Shuttle During Hypersonic Re-Entry

“…Advancements in capability led to additional insight gained during the imaging attempts with a land-based system in 1999 6,7 . This methodical approach was continued with incremental experience gained during attempts associated with the 2005-6 ad-hoc missions flown in support of RTF 13,15 . Presently, an optical asset identified for a HYTHIRM mission will spend a significant length of time in preparation using the rigorously developed and validated pre-mission planning tools.…”

“…Based upon the imagery successes during the Shuttle RTF and recognizing the tremendous technical opportunity that the Shuttle BLT flight tests offered, the NASA Engineering and Safety Center (NESC) sponsored the formation of a team of technical experts to assess existing imaging capability within the US and to develop and validate a mission planning tool set 13,20,21 . The overall goal of the assessment team was to then utilize the validated mission planning tools to determine the viability of obtaining global temperature measurements on a hypersonic flight vehicle using one or more of the nation's …”

“…Collectively, a reduction in uncertainties in the prediction of both transition onset and turbulent heating can remove unnecessarily large TPS margins that currently translate to reduced payload capability and degraded mission performance. In anticipation of a Shuttle flight test program, an effort was made prior to the first return to flight mission (STS-114) after the Columbia accident (STS-107) to establish whether or not remote imaging could provide quantitative global surface temperature on the windward surface of the Shuttle during boundary layer transition at high Mach number 13,15 . The ensuing Space Shuttle sponsored effort was leveraged from post STS-107 recommendations made to NASA management to improve imaging capability during ascent and entry.…”

“…Quantitatively, if surface temperatures associated with a hypersonic laminar and/or fully turbulent boundary layer flow can be inferred from calibrated in flight imagery, they could be used to verify engineering models or numerical predictive methods and associated turbulence models. While most aerospace applications of infrared thermography have been limited to wind tunnel testing, this measurement technique has been utilized during several Shuttle entries over the past 25 years to obtain flight data [6][7][8][9][10][11][12][13][14][15] . The renewed interest in thermal imagery during Shuttle entry was initially motivated by the desire to reduce uncertainties associated with an empirical strategy to predict BLT onset.…”

Infrared Imaging of Boundary Layer Transition Flight Experiments

“…9, the HYTHIRM project has multiple tasks, such as establishing an understanding of the capabilities and experience of national assets to obtain IR imagery, developing simulation and radiance modeling tools, and validation of the use of those tools and assets, that in the end are intended to allow recommendations of the best observation strategy for imaging the Shuttle during reentry in support of the Shuttle BLT FE. However, a recognized long-term goal of the HYTHIRM project is also to seek other opportunities to obtain global IR aerothermal data as possible support for other flight projects.…”