ISS Risk Mitigation

Space Portable Spectroreflectometer (SPSR)

SPSR Hardware


The SPSR is a handheld device designed to take measurements of the absorption capabilities of solar materials, reflecting mirrors, solar power systems, and other spacecraft external surfaces on-orbit.

Shuttle-Mir Missions

SPSR measurements are made by first placing the instrument on the surface to be examined. Monochromatic light shining onto the surface through an aperture (located on the bottom side of the instrument) is reflected back into an integrating sphere. The reflectance is obtained as a function of wavelength; energy not reflected is absorbed by the surface.

A rigidized tether was provided to aid in positioning the SPSR and holding it stable on the Mir surface during data collections. One end of the tether was attached to a fitting on the SPSR and the other onto a mechanism that locked onto a handrail. However, the Kvant II handrail was slightly too large for the mechanism to lock properly. In order to keep the SPSR stable, a crewmember held the locking mechanism as secure as possible. While conducting the experiment, the display faded, preventing feedback for proper positioning of the SPSR. The astronauts proceeded anyway, working from memory to complete five data collection runs.

Reflectance signals were measured for each data run; each run consisted of 100 individual data points of reflectance as a function of wavelength. Data from position sensors on the bottom of the SPSR were recorded for each of these 100 points. Data from position sensors allowed correction of the data for imperfect positioning. Only data from a radiator on the Kvant II module was obtained during the EVA.

Although the data are still being evaluated, it appears that the leading edge cutoff of the high reflectance, which occurs in the visible region, is very sharp. This would indicate that the surface is relatively clean and not significantly contaminated. This is interesting considering other areas of obvious contamination on Mir. The NASA-6 crewmember did report that the surface appeared almost pristine. There is degradation of the reflectance curve and therefore increased solar absorptivity, but this Kvant II radiator had been in orbit for nearly 10 years.

There is reason to believe that the corrected curve is indicating an absolute reflectance that is too low and some systematic error in the correction may exist. In other ground and flight data, reflectance degradation beyond 1 micron has not been observed.

The SPSR functioned well, except for the anomaly with the display and the handrail tether. Researchers have been successful in correcting the reflectance data using the position data. This is encouraging since it indicates that perfect positioning of the SPSR may not be necessary. Adequate positioning is desirable since the correction does increase errors in the reflectance curve. The data from the Kvant II radiator indicates minimal contamination and some degradation of the coating due to increased solar absorptivity.

Earth Benefits
Over the years data obtained in ground simulations and from flight experiments have been relied on to predict spacecraft degradation. Ground simulations are the primary means by which the effects on materials and systems are predicted. However, accurate simulation of the space environment is impossible and compromises have to be made in this approach. The long life expectations for future spacecraft combined with low degradation requirements demand that our understanding of subtle, long-term effects be accurate. The SPSR experiment on Mir can be used to provide data to validate ground test facilities and prediction models for material behavior in space. Comparison with other flight experiments and ground data can allow determination of effects and damage mechanisms of the Mir environment on materials.

Wilkes DR, Carruth MR, "In-Situ Materials Experiments on the Mir Station," SPIE Conference on Optical System contamination: Effects, Measurements and Control VI, San Diego, CA, SPIE Vol. 3427.

Space Portable Spectroreflectometer, Final Report Contract NAS8-38970. AZ Technology Report 91-1-117-D0006. November 1993.

Principal Investigators
Ralph Carruth
NASA/Marshall Space Flight Center

Jim Zwiener
Rachel Kamanetzky
Don Wilkes
Stanislav Naumov

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Page last updated: 07/16/1999

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