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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Charter and activities of the SIRTF in-orbit checkout focus integrated products team and optical performance of the CTA

We describe a strategy to determine the initial mirror spacing by quantitatively evaluating the shapes of the images formed by the telescope using the Infrared Array Camera and other science instruments. We show that this information can be used to predict the direction and magnitude of the secondary mirror move that will result in the telescope best focus. The tools used to evaluate focus position and optical quality of the in orbit CTA have been qualified during the BRUTUS test are here described.

Integrated↗
NASA NTRS1983

Fused silica mirror development for SIRTF

An advanced design, lightweight, fuse-quartz mirror of sandwich construction was evaluated for optical figure performance at cryogenic temperatures. A low temperature shroud was constructed with an integral mirror mount and interface to a cryostat for use in a vacuum chamber. The mirror was tested to 13 K. Cryogenic distortion of the mirror was measured interferometrically. Separate interferometry of the chamber window during the test permitted subtraction of the small window distortions from the data. Results indicate that the imaging performance of helium cooled, infrared telescopes will be improved using this type of mirror without correction of cryogenic distortion of the primary mirror.

Barnes, W. P., Jr.↗
NASA NTRS1984

Thermal and cryogenic design study for space infrared telescope facility (SIRTF)

A study was conducted to determine the ability of an all superfluid helium design to meet the performance requirements of background limited to 200 micrometer, and a two year lifetime for a one meter class free flying infrared observatory. Both a 98 deg and 28.5 deg inclination orbits were examined, and aperture shade designs were developed for both orbits. A unique forebaffle cooling design significantly reduces the sensitivity to aperture heat loads. With certain restrictions on observing modes, the study determined that an all superfluid helium Dewar will meet the temperature and lifetime requirements. A dual cryogen SFHe/SH2 system was also investigated for the 28.5 deg orbit and found to provide a more constant forebaffle temperature but with only a slight improvement in lifetime.

Urbach, A. R.↗
NASA NTRS1984

Pointing and control system design study for the space infrared telescope facility (SIRTF)

The design and performance of pointing and control systems for two space infrared telescope facility vehicles were examined. The need for active compensation of image jitter using the secondary mirror or other optical elements was determined. In addition, a control system to allow the telescope to perform small angle slews, and to accomplish large angle slews at the rate of 15 deg per minute was designed. Both the 98 deg and the 28 deg inclination orbits were examined, and spacecraft designs were developed for each. The results indicate that active optical compensation of line-of-sight errors is not necessary if the system is allowed to settle for roughly ten seconds after a slew maneuver. The results are contingent on the assumption of rigid body dynamics, and a single structural mode between spacecraft and telescope. Helium slosh for a half full 4000 liter tank was analyzed, and did not represent a major control problem.

Lorell, K. R.↗
NASA NTRS1986

A SIRTF interdiciplinary scientist proposal

Segal's chronometric cosmology provides an adequate fit to the radio source counts only for an unrealistic choice of spectral index. Since the typical observed spectral index of 0.75 gives a completely unacceptable X squared = 136 with 24 (or fewer) degrees of freedom, it is concluded that the actual Universe does not fit the chronometric model. Counts of ultraviolet excess quasistellar objects also show a steep N(S) curve that the chronometric cosmology cannot explain. Claims to the contrary by Segal, Loncaric, and Segal (1980) and Segal and Nicoll (1986) depend on a seemingly innocuous assumption that in fact destroys the power of the N(S) test. Even though the chronometric model gives a better fit that other non-evolving models it must be ruled out along with all non-evolving cosmologies.

Wright, E. L.↗
NASA NTRS1986

Moderate resolution spectroscopy for the Space Infrared Telescope Facility (SIRTF)

The conceptual design presented for a low-to-moderate resolution IR spectrometer is expected to allow the spectroscopic study of objects whose location ranges from within the solar system to distant galaxies, with far greater sensitivity than previously available for the study of faint objects. The low resolution mode will allow detailed continuum radiation studies to be conducted, while the moderate resolution mode will facilitate studies encompassing the IR spectral signatures of small outer solar system bodies and the nature of more luminous active galaxies and QSOs at greater distances. The five spectrometer modules share a common aperture, and all gratings share a single scan mechanism. All heat sources other than the detectors operate at 7 K and are separated from the 4 K cold station. Two-dimensional area detector arrays are used in the 2.5- to 120-micron bands to simultaneously monitor adjacent regions in extended objects and to measure the background near point sources.

Houck, J. R.↗
NASA NTRS1988

SIRTF nod maneuvers

The response of the Space Infrared Telescope Facility's attitude control system to a nod command is studied under a wide variety of conditions. Several engineering issues are explored: the effects of variations in the structural model, relocation of sensors and actuators, the influence of the fine guidance sensor sampling period, resolution and noise on the system response, torque and rate integrating gyro noise and disturbances. Simulation results using control moment gyros and reaction wheels as actuators are presented.

Rajan, N.↗
NASA NTRS1990

Space Infrared Telescope Facility (SIRTF) implementation plans

This paper describes the Space Infrared Telescope Facility (SIRFT) mission planned by NASA for a launch by a Titan IV launch vehicle near the end of this decade. Special attention is given to the SIRFT's scientific goals, instruments, and technology. The cryogenically cooled SIRFT will utilize three scientific instruments, the Infrared Array Camera, the Infrared Spectrograph, and the Multiband Imaging Photometer for SIRFT and will achieve sensitivities 100 to 10,000 times greater than previous space telescope missions. During its five or six years of operation, SIRFT is expected to yield information on the formation and evolution of galaxies and stars and the solar-system phenomena and supernovae, as well as on the formation of other solar systems.

Spehalski, Richard J.↗