Space traffic management: concepts and practices

The value of a space traffic management system must weigh the historical and legally entrenched concept of the freedom of operation in near-Earth orbit against the potential benefits of a new regulatory regime. Most spacefaring nations do not yet exert control over the selection of orbital parameters for new space systems within their own countries, much less in an international context. The need for and potential effectiveness of such intrusive space traffic management in the foreseeable future have not yet been clearly established.     

Military qualification of a high-reliability, light-weight 24 V/30Ah aircraft battery

The United States Navy has flown Valve Regulated Lead-Acid Batteries (VRLA) for approximately 18 years. The first VRLA aircraft batteries were cylindrical cell design and evolved to a prismatic design to save weight, volume, and to increase rate capability. This paper discusses the next generation of the VRLA aircraft battery. The HORIZON composite grid VRLA design reduces weight, increases high rate performance, and is expected to increase service life. This paper discusses the weight reduction over the present 30 Ah prismatic VRLA aircraft battery design; improvements in high rate engine start performance, and present status of the development effort. Finally, the paper discusses the applications for the 30 Ah composite grid VRLA aircraft battery, and shows the future application opportunities for light-weight VRLA, both in the military and commercially     

Geology of the Icy Satellites

In the last 25 years, the explorations of the Voyager and Galileo missions have resulted in an entirely new view of the icy worlds orbiting the giant outer planets. These objects show a huge diversity in their characteristics, resulting from their formation histories, internal processes and interactions with their space environments. This paper will review the current state of knowledge about the icy satellites and discuss the exciting prospects for the upcoming Cassini/Huygens mission as it begins a new era of exploration of the Saturn satellite system.     

CO2 crop growth enhancement and toxicity in wheat and rice.

The effects of elevated CO2 on plant growth are reviewed and the implications for crop yields in regenerative systems are discussed. There is considerable theoretical and experimental evidence indicating that the beneficial effects of CO2 are saturated at about 0.12% CO2 in air. However, CO2 can easily rise above 1% of the total gas in a closed system, and we have thus studied continuous exposure to CO2 levels as high as 2%. Elevating CO2 from 340 to 1200 micromoles mol-1 can increase the seed yield of wheat and rice by 30 to 40%; unfortunately, further CO2 elevation to 2500 micromoles mol-1 (0.25%) has consistently reduced yield by 25% compared to plants grown at 1200 micromoles mol-1; fortunately, there was only an additional 10% decrease in yield as the CO2 level was further elevated to 2% (20,000 micromoles mol-1). Yield increases in both rice and wheat were primarily the result of increased number of heads per m2, with minor effects on seed number per head and seed size. Yield increases were greatest in the highest photosynthetic photon flux. We used photosynthetic gas exchange to analyze CO2 effects on radiation interception, canopy quantum yield, and canopy carbon use efficiency. We were surprised to find that radiation interception during early growth was not improved by elevated CO2. As expected, CO2 increased quantum yield, but there was also a small increase in carbon use efficiency. Super-optimal CO2 levels did not reduce vegetative growth, but decreased seed set and thus yield. The reduced seed set is not visually apparent until final yield is measured. The physiological mechanism underlying CO2 toxicity is not yet known, but elevated CO2 levels (0.1 to 1% CO2) increase ethylene synthesis in some plants and ethylene is a potent inhibitor of seed set in wheat.     

Present needs,capabilities, and future prospects in rocket technology for space research

The paper is a review of the past, present, and future of rocket technology, relating these to the propulsion requirements for exploration of the solar system. It reviews the U.S.A. approach to planning its launch-vehicle programs for space exploration, covers the present capabilities of the U.S.A. family of launch vehicles, and discusses some technology possibilities for future propulsion systems.     

Ambiguities in Spacebornene Synthetic Aperture Radar Systems

Several aspects of range and azimuth (time delay and Doppler) ambiguities in spaceborne synthetic aperture radars (SARs) are examined. An accurate method to evaluate the ratio of the intensities of the ambiguities to that of the signal is described. This method has been applied to the nominal SAR system on SEASAT and the variations of this ratio as a function of orbital latitude and attitude control error are discussed. It is also shown that the detailed range migration-azimuth phase history of an ambiguity is different from that of a signal. The images of ambiguities are, therefore, dispersed. Several examples of such dispersed images observed by the SEASAT SAR are presented. These dispersions are eliminated when the processing parameters are adjusted appropriately. Finally, a method is described which uses a set of multiple pulse repetition frequencies to determine the absolute values of the Doppler centroid frequencies for SARs with high carrier frequencies and relatively poor attitude measurements.     

A hard X-ray experiment for long-duration balloon flights

The Naval Research Lab has developed a balloon-borne hard X-ray experiment which is designed for 60- to 90-day flight durations soon to be available with around the world Sky Anchor or RACOON balloon flights. The experiment's scintillation detector is sensitive to the 15 – 250 keV X-ray energy range. The experiment includes three microcomputer systems which control the data acquisition and provide the orientation and navigation information required for global balloon flights. The data system supports global data communications utilizing the GOES satellite as well as high bit rate communications through L-band li line-of-site transmissions     

Fluid volumes changes induced by spaceflight

The blood volume (BV), plasma volume (PV), and extracellular fluid volume changes produced in crewmembers during spaceflights of 11-84 days were compared to changes after 14 or 28 days of bedrest. Spaceflight and bedrest produce approximately equal BV changes but the recorded PV change after spaceflight was less. However, the diurnal change in PV may explain the smaller decreases recorded after spaceflight. The cardiovascular deconditioning caused by spaceflight and bedrest was compared using the mean heart rate response to lower body negative pressure (LBNP) testing at -50 mmHg pressure. These tests show approximately equal LBNP produced heart rate changes after bedrest and spaceflight. A countermeasure which includes 4 hr of LBNP treatment at -30 mmHg and the ingestion of one l. of saline was studied and found capable of returning the heart rate response and the PV of bedrested subjects to control (prebedrest) levels suggesting that it would be useful to the crewmembers after a spaceflight.     

Minimizing space radiation exposure during extra-vehicular activity

Continued assembly of the International Space Station (ISS) requires numerous extra-vehicular activities (EVAs). Prudent radiological safety practices require minimizing additional exposures to crewmen during these periods. The spatial distribution of the “normal” trapped proton and electron radiation sources in low Earth orbit is strongly governed by the geomagnetic field. It is possible to use ISS trajectory information to estimate crew exposures during EVAs and to identify periods that can result in minimal EVA crew exposures through avoidance of these trapped radiation regions. Such exposure minimization planning can also accommodate the unforeseen development of a solar proton event. An EVA exposure estimation tool, EVADOSE, is described and applied to various EVA exposure scenarios. Procedures and parameters that influence EVA exposures are discussed along with techniques to minimize crew exposures.