Lunar habitat concept employing the space shuttle external tank

The space shuttle external tank, which consists of a liquid oxygen tank, an intertank structure, and a liquid hydrogen tank, is an expendable structure used for approximately 8.5 min during each launch. A concept for outfitting the liquid oxygen tank-intertank unit for a 12-person lunar habitat is described. The concept utilizes existing structures and openings for both man and equipment access without compromising the structural integrity of the tank. Living quarters, instrumentation, environmental control and life support, thermal control, and propulsion systems are installed at Space Station Freedom. The unmanned habitat is then transported to low lunar orbit and autonomously soft landed on the lunar surface. Design studies indicate that this concept is feasible by the year 2000 with concurrent development of a space transfer vehicle and manned cargo lander for crew changeover and resupply.     

Synthesis Techniques for a Class of SSB-AM-PM Signals

This paper develops synthesis techniques for a particular type of single-sideband sinusoidal carrier which is phase modulated by a subcarrier. Mathematical expressions for signal efficiency, sensitivity of design to parameter variation, and ratio of peak to average power are derived and incorporated in a computer program. Given the desired power ratios for modulated signal components, the program solves for the corresponding modulation parameters and evaluates signal efficiency, design sensitivity, and peak to average power ratio. A sample signal design is presented for clarity.     

Optical communication systems for avionics

Avionic information processing and transmission requirements are increasing geometrically, with no end in sight, The only feasible way to meet them is to incorporate fiber-optic communication systems into avionic platforms, Such systems can be employed to replace standard electronic components, to augment existing systems, or to enable new technologies. In this paper, we survey the field of low-power communication systems from the avionics engineering perspective. We review the fundamental merits of optical fiber for information transmission and discuss various information modulation schemes. These modulation techniques determine the performance requirements for laser transmitters, We describe the horizontal- and vertical-cavity semiconductor lasers currently available for these systems, and measure their performance against the additional environmental constraints of avionics platforms. Finally, we outline expected near- and far-term trends in system and device development     

Observations of interplanetary shocks: Recent progress

Interplanetary shock observations since the prior Solar Terrestrial Physics Symposium in 1978 are reviewed. Since the interval coincides with the recent solar maximum, emphasis is placed on shocks associated with transient solar phenomena, including coronal transients and eruptive prominences as well as flares. A good correlation between shocks and Storm Sudden Commencements has persisted into the recent maximum. Shocks have been identified that are associated with disappearing filaments and coronal transients rather than with flares. Significant progress has been made in the indirect observation of shocks near the Sun as a result of radio wave measurements in interplanetary space and measurement of the scintillation and spectral broadening of spacecraft radio transmissions. Preliminary results regarding the thickness of interplanetary shocks have appeared. Several quasi-parallel shocks propagating more nearly along, rather than across, the magnetic field have been identified. The plasma drivers accompanying interplanetary shocks have received increased attention and distinctive features have been found in electron, ion and magnetic field data.     

Regolith X-Ray Imaging Spectrometer (REXIS) Aboard the OSIRIS-REx Asteroid Sample Return Mission

The Regolith X-ray Imaging Spectrometer (REXIS) is the student collaboration experiment proposed and built by an MIT-Harvard team, launched aboard NASA’s OSIRIS-REx asteroid sample return mission. REXIS complements the scientific investigations of other OSIRIS-REx instruments by determining the relative abundances of key elements present on the asteroid’s surface by measuring the X-ray fluorescence spectrum (stimulated by the natural solar X-ray flux) over the range of energies 0.5 to 7 keV. REXIS consists of two components: a main imaging spectrometer with a coded aperture mask and a separate solar X-ray monitor to account for the Sun’s variability. In addition to element abundance ratios (relative to Si) pinpointing the asteroid’s most likely meteorite association, REXIS also maps elemental abundance variability across the asteroid’s surface using the asteroid’s rotation as well as the spacecraft’s orbital motion. Image reconstruction at the highest resolution is facilitated by the coded aperture mask. Through this operation, REXIS will be the first application of X-ray coded aperture imaging to planetary surface mapping, making this student-built instrument a pathfinder toward future planetary exploration. To date, 60 students at the undergraduate and graduate levels have been involved with the REXIS project, with the hands-on experience translating to a dozen Master’s and Ph.D. theses and other student publications.     

A General Model for Switching Converters

A low frequency, small signal model, valid for all types of converters, both in the heavy and the light mode of conduction, is developed in block diagram form. The model provides a clear insight into the behavior of such converters and enhances the respective contributions of input and output filters.     

High Dynamic GPS Receiver Using Maximum Likelihood Estimationand Frequency Tracking

A new high dynamic global positioning system (GPS) receiver ispresented and its performance characterized by analysis,simulation, and demonstration. The demonstration receiver is abreadboard model capable of tracking a single simulated satellitesignal in pseudorange and range rate. Pseudorange and range rateestimates are made once every 20 ms, using a maximum likelihoodestimator, and are tracked by means of a third-order fadingmemory filter in a feedback configuration. The receiver trackspseudorange with rms errors of under 1 m when subjected tosimulated 50 g, 40 g/s circular trajectories. The tracking thresholdis approximately 28 dB·Hz, which provides 12 dB margin relativethe the minimum specified signal strength, assuming 3.5 dB systemnoise figure and 0 dB antenna gain.     

Subjective vertical before and after space flight

Three scientist astronauts on the D1 spacelab mission participated in a series of orientation experiments before and after exposure to orbital weightlessness. Each subject was tilted about a roll axis at 15 deg intervals up to +/-90 deg. At each angle the subject set a luminous line to what he perceived to be the vertical. The results of these tests are presented.     

Ionospheric response of equatorial and low latitude F-region during the intense geomagnetic storm on 24–25 August 2005

In this investigation, we present and discuss the response of the ionospheric F-region in the South American and East Asian sectors during an intense geomagnetic storm in August 2005. The geomagnetic storm studied reached a minimum Dst of −216 nT at 12:00 UT on 24 August. In this work ionospheric sounding data obtained of 24, 25, and 26 August 2005 at Palmas (PAL; 10.2° S, 48.2° W; dip latitude 6.6° S), São José dos Campos (SJC, 23.2° S, 45.9° W; dip latitude 17.6° S), Brazil, Ho Chi Minh City, (HCM; 10.5° N, 106.3° E; dip latitude 2.9° N), Vietnam, Okinawa (OKI; 26.3° N, 127.8° E; dip latitude 21.2° N), Japan, are presented. Also, the GPS observations obtained at different stations in the equatorial and low-latitude regions in the Brazilian sector are presented. On the night of 24–25 August 2005, the h′F variations show traveling ionospheric disturbances associated with Joule heating in the auroral zone from SJC to PAL. The foF2 variations show a positive storm phase on the night of 24–25 August at PAL and SJC during the recovery phase. Also, the GPS-VTEC observations at several stations in the Brazilian sector show a fairly similar positive storm phase on 24 August. During the fast decrease of Dst (between 10:00 and 11:00 UT) on 24 August, there is a prompt penetration of electric field of magnetospheric origin that result in abrupt increase (∼12:00 UT) in foF2 at PAL, SJC (Brazil) and OKI (Japan) and in VTEC at IMPZ, BOMJ, PARA and SMAR (Brazil). OKI showed strong oscillations of the F-region on the night 24 August resulted to the propagation of traveling atmospheric disturbances (TADs) by Joule heating in the auroral region. These effects result a strong positive observed at OKI station. During the daytime on 25 August, in the recovery phase, the foF2 observations showed positive ionospheric storm at HCM station. Some differences in the latitudinal response of the F-region is also observed in the South American and East Asian sectors.