STS Spectrometers Help NASA Evaluate Radiation Models


When NASA’s Space Shuttle program ended in 2011, the U.S. agency focused its attention on deep space exploration. Within the decade, NASA’s Orion Spacecraft will take humans “farther than they’ve ever gone before,” with an ultimate destination of Mars.

Ocean Optics STS spectrometers could be along for ride. The spectrometers are being evaluated as part of a heat shield testing system, critical to safely returning astronauts to Earth.

To learn more about the Orion mission and its heat shield design, we interviewed several members of the Orion team: Rachel Kraft, public affairs specialist and NASA spokeswoman; Joe Olejniczak, manager, Multi-Purpose Crew Vehicle (MPVC), Orion Aerosciences; and Doug Holland, Orion Heat Shield Spectrometer (OHSS), project engineer.

Orion Spacecraft

Figure 1. As the Orion Spacecraft returns to Earth, onboard spectrometers will gather spectral data from the heat shield during re-entry.

Ocean Optics: Tell us about the Orion Spacecraft mission and the status of the project. What is Orion’s role in future space exploration?

Kraft: Orion is NASA’s spacecraft that will send humans far beyond Earth on deep space missions, including as part of NASA’s journey to Mars. Engineers are currently manufacturing and assembling Orion for a late 2018 mission that will send the uncrewed spacecraft more than 40,000 miles beyond the moon in the first test, with the Space Launch System rocket NASA is also developing to send Orion and other payloads to deep space. Astronauts will first venture far into space in Orion in the 2021 timeframe.

Ocean Optics: Orion will have onboard spectrometers that measure the heat shield during re-entry. What will you learn from those measurements?

Olejniczak: The spectrometer will measure the radiation from hot gas surrounding the vehicle. This gas is so hot [up to 4,000 °F], that the radiation from it produces a significant amount of the energy that goes into the vehicle. These spectral measurements will allow us to refine and validate our radiation heating models, enabling NASA to improve and optimize the design of Thermal Protection Systems (TPS) for high speed Earth entry.

flight prototype of the Orion Heat Shield Spectrometer 2

Figure 2. This flight prototype of the Orion Heat Shield Spectrometer includes STS UV (190-650 nm) and NIR (650-1100 nm) spectrometers.

Ocean Optics: Why evaluate a microspectrometer like our STS model for the heat shield?

Holland: One of the goals of all space systems is to minimize size, weight and power. When spectrometers become small enough they can start being considered for inclusion into space flight systems.

Ocean Optics: With that in mind, how has the evolution of spectrometers to very small sizes, greater modularity and simpler interfaces benefitted space researchers?

Holland: In addition to meeting the need to reduce size and mass, simpler interfaces allow less complicated circuitry, thus increasing the reliability of the end system.

Ocean Optics: Some of the work on the OHSS involved collaboration with university faculty and students. How did that work?

Holland: The OHSS has been developed as university collaboration. We work with the University of Texas at Austin on mechanical design and analysis; Northern Arizona University on electronics component testing; the University of Arizona on fiber optic cable system design; and Texas State University on ground software. The university students and faculty members collaborate with NASA engineers on research, design, development and testing of the system. Some of these collaborations are done as a part of a Senior Design Project (also known as a capstone design project). Texas State University is participating in the Texas Space Grant Consortium Design Challenge* in addition to this work being their senior design project.

spectral output for STS-UV and STS-NIR spectrometers 3

Figure 3. In preliminary lab testing, engineers combined the spectral output for STS-UV and STS-NIR spectrometers. This extended wavelength range will be required for the project.

Ocean Optics: Now that you have done some engineering builds, when will testing begin? What are some the challenges of instruments designed for space flight?

Holland: Testing has already begun. We are currently performing environmental tests to determine the changes in signal characteristics with temperature. Flight certification testing will begin in spring 2017.

The challenges of instruments designed for the space environment are many. These include: a) space radiation, which changes dramatically depending on where in space you are operating; b) being able to go from one atmosphere pressure to a vacuum and back; c) not creating electromagnetic interference that could affect other spacecraft systems; d) being able to withstand the shock and vibration characteristics of the entire mission cycle – at launch, in space operations, during re-entry and landing; e) requiring the absolute minimum size, weight and power; f) being able to survive large temperature differences and still operate with acceptable performance; and g) continuing to operate after being subjected to salt water during splashdown.

Ocean Optics: We appreciate your careful consideration of these questions and willingness to share material with our readers.

* Learn more about the design challenge Texas State took on.

Note: All images shown here are courtesy of NASA.