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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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NASA NTRS2000

Development of the Circadian Timing System in Rat Pups Exposed to Microgravity during Gestation

Ten pregnant Sprague Dawley rat dams were exposed to spaceflight aboard the Space Shuttle (STS-70) for gestational days 11-20 (G 11-20; FILT group). Control dams were maintained in either a flight-like (FIDS group) or vivarium cage environment (VIV group) on earth. All dams had ad lib access to food and water and were exposed to a light-dark cycle consisting of 12 hours of light (- 30 lux) followed by 12 hours of darkness. The dams were closely monitored from G 22 until parturition. All pups were cross-fostered at birth; each foster dam had a litter of 10 pups. Pups remained with their foster dam until post-natal day 21 (PN 21). Pup body mass was measured twice weekly. At PN14 FILT pups had a smaller body mass than did the VIV pups (p < 0.01). Circadian rhythms of body temperature and activity of pups from two FILT dams (n = 8), two FIDS dams (n = 9) and two VIV dams (n = 7) were studied starting from age PN 21. All pups had circadian rhythms of temperature and activity at this age. There were no significant differences in rhythms between groups that could be attributed to microgravity exposure. We also examined the development of neural structures involved in circadian rhythmicity: the retina, the intergeniculate leaflet (IGL) and the circadian pacemaker, the suprachiasmatic nucleus (SCN). There were small differences between the flight and control groups at very early stages of development (G 20 and PN3) which indicated that the development of both the SCN and the IGL. These results indicate that exposure to the microgravity environment of spaceflight during this embryonic development period does not affect the development of the circadian rhythms of body temperature and activity, but may affect the early development of the neural structures involved in circadian timing.

Fuller, Charles A.↗

NASA NTRS2012

GMSK Modulation for Deep Space Applications

Due to scarcity of spectrum at 8.42 GHz deep space Xband allocation, many deep space missions are now considering the use of higher order modulation schemes instead of the traditional binary phase shift keying (BPSK). One such scheme is pre-coded Gaussian minimum shift keying (GMSK). GMSK is an excellent candidate for deep space missions. GMSK is a constant envelope, bandwidth efficien modulation whose frame error rate (FER) performance with perfect carrier tracking and proper receiver structure is nearly identical to that of BPSK. There are several issues that need to be addressed with GMSK however. Specificall, we are interested in the combined effects of spectrum limitations and receiver structure on the coded performance of the X-band link using GMSK. The receivers that are typically used for GMSK demodulations are variations on offset quadrature phase shift keying (OQPSK) receivers. In this paper we consider three receivers: the standard DSN OQPSK receiver, DSN OQPSK receiver with filte ed input, and an optimum OQPSK receiver with filte ed input. For the DSN OQPSK receiver we show experimental results with (8920, 1/2), (8920, 1/3) and (8920, 1/6) turbo codes in terms of their error rate performance. We also consider the tracking performance of this receiver as a function of data rate, channel code and the carrier loop signal-to-noise ratio (SNR). For the other two receivers we derive theoretical results that will show that for a given loop bandwidth, a receiver structure, and a channel code, there is a lower data rate limit on the GMSK below which a higher SNR than what is required to achieve the required FER on the link is needed. These limits stem from the minimum loop signal-to-noise ratio requirements on the receivers for achieving lock. As a result of this, for a given channel code and a given FER, there could be a gap between the maximum data rate that BPSK can support without violating the spectrum limits and the minimum data rate that GMSK can support with the required FER depending on the type of GMSK receiver that is used.

Communications↗

NASA NTRS1984

Vacuum-deposited optical coatings experiment (A0138-4)

The stability of various vacuum deposited optical coatings exposed to the space environment were analyzed. A wide range of optical components manufactured by vacuum deposition, such as metallic and multidielectric reflective coatings in the UV range, metal dielectric interference filtes in the UV and IR ranges, narrow-bandpass filters int he near-UV and visible ranges, selective metallic mirrors in the range from 1500 to 2500 A. antireflective and reflective IR coatings, beam splitters in the visible and IR ranges, and optical surface reflection (OSR) coatings were developed. Many of these components were incorporated into scientific and technical experiments flown on balloons and rockets as well as on Symphonie, Meteosate, OTS, D2-B, TIROS n, and others. It appears that these components operate successfully in flight.

Malherbe, A.↗

NASA NTRS1984

Superconducting Nbti and Pb(cu) Bandpass Filters

Superconducting Nb0.45Ti0.55 and Pb electroplated on Cu bandpass microwave filtes were constructed to investigate their low loss properties at 4.7 K. An interdigital stripline filter configuration was selected as the optimum structure for future applications. The filter was designed to operate at 8.45 GHz with an equal ripple bandwidth of 0.15 GHz. The insertion loss and the noise temperature contribution were measured at 4.7 K. In addition, the insertion loss was studied as a function of out of band power (up to 1 watt) and temperature (4.7 K up to T(c)). Results of an oxygen free high conductivity Cu filter are included for comparison.

Bautista, J. J.↗

NASA NTRS1996

Adaptive Orbit Determination for Interplanetary Spacecraft

The interplanetary orbit problem has been traditionally solved using least-squares techniques. Due to operational limitations of this method, a Kalman filter approach has been proposed for future missions which includes all spacecraft and measurement modeling states in the filter.

adaptive↗