Spectroscopic evaluation of polyurea crosslinked aerogels,as a substitute for RTV-based chromatic calibration targets for spacecraft

Room temperature vulcanizing (RTV)-based components have been used on Mars Pathfinder, the Mars rovers, Spirit and Opportunity, as well as the Phoenix Lander as a support matrix for pigmented panoramic camera calibration targets. RTV 655 has demonstrated superiority to other polymers due to its unique range of material properties namely mechanical stability between −115 and 204 °C and UV radiation tolerance. As a result, it has been the number one choice for many space-related missions. However, due to the high mass density and the natural tendency for electrostatic charging RTV materials have caused complications by attracting and retaining dust particles (Sabri et al., 2008). In the current project we have investigated the relevant properties of polymer-reinforced (crosslinked) silica aerogels with the objective of substituting RTV-based calibration targets with an aerogel based design. The lightweight, mechanical strength, ability to accept color pigments, and extremely low dust capture makes polyurea crosslinked aerogels a strong candidate as a chromatic standard for extraterrestrial missions. For this purpose, the reflection spectra, gravimetric analysis, and low temperature response of metal oxide pigmented, polyurea crosslinked silica aerogels have been investigated and reported here.     

An overview of RADOM results for earth and moon radiation environment on Chandrayaan-1 satellite

The RADiatiOn Monitor (RADOM) is a miniature dosimeter-spectrometer that flew onboard the Chandrayaan-1 lunar mission in order to monitor the local radiation environment. Primary objective of the RADOM experiment was to measure the total absorbed dose, flux of surrounding energetic particles and spectrum of the deposited energy from high energy particles both en-route and in lunar orbit. RADOM was the first experiment to be switched on after the launch of Chandrayaan-1 and was operational until the end of the mission. This paper summarizes the observations carried out by RADOM during the entire life time (22 October 2008–31 August 2009) of the Chandrayaan-1 mission and compares the measurement by RADOM with the radiation belt models such as AP-8, AE-8 and CRRESS.     

Output Signal-to-Noise Ratios for Amplitude-Modulated Noise-Like Lasers

A general expression of the output SNR of a photodetector is derived for a noise-like laser amplitude-modulated by a stationary Gaussian random modulating signal in the presence of a background light. The electric field Vx(t) of the noise-like laser is assumed to be a stationary narrowband Gaussian random process with zero mean. Two types of modulating signal are considered, the baseband and bandpass modulating signals. More specifically, the effects of the center frequency of the modulating signal, the modulating degree, the bandwidth ration of the noise-like laser to the modulating signal, the effective average quantum rate, and input CNR on output SNR are studied. The detection characteristics of the noise-like laser are also made clear by comparison with the case of a coherent laser.     

Some Electrical/Electronic Areas Requiring Emphasis in Preparation for Future Space Programs

A panel session held at the 1965 Aerospace Conference, Houston,Tex., June 23, 1965. Panelists discussed Life-Suppport interfaces with Electric Power; Communications; Navigation; System Integration for Future Space Programs; and Reliability.     

What Are Special About Ground-Level Events?

Ground level events (GLEs) occupy the high-energy end of gradual solar energetic particle (SEP) events. They are associated with coronal mass ejections (CMEs) and solar flares, but we still do not clearly understand the special conditions that produce these rare events. During Solar Cycle 23, a total of 16 GLEs were registered, by ground-based neutron monitors. We first ask if these GLEs are clearly distinguishable from other SEP events observed from space. Setting aside possible difficulties in identifying all GLEs consistently, we then try to find observables which may unmistakably isolate these GLEs by studying the basic properties of the associated eruptions and the active regions (ARs) that produced them. It is found that neither the magnitudes of the CMEs and flares nor the complexities of the ARs give sufficient conditions for GLEs. It is possible to find CMEs, flares or ARs that are not associated with GLEs but that have more extreme properties than those associated with GLEs. We also try to evaluate the importance of magnetic field connection of the AR with Earth on the detection of GLEs and their onset times. Using the potential field source surface (PFSS) model, a half of the GLEs are found to be well-connected. However, the GLE onset time with respect to the onset of the associated flare and CME does not strongly depend on how well-connected the AR is. The GLE onset behavior may be largely determined by when and where the CME-driven shock develops. We could not relate the shocks responsible for the onsets of past GLEs with features in solar images, but the combined data from the Solar TErrestrial RElations Observatory (STEREO) and the Solar Dynamics Observatory (SDO) have the potential to change this for GLEs that may occur in the rising phase of Solar Cycle 24.     

RF band high resolution sounding of building structures and works

A subsurface radar using a multi-frequency signal has been developed. It is designated for surveying building structures and works. The characteristic feature of this device is the possibility of obtaining sounding plane radio images featuring a high resolution attaining 1…2 cm. The main applications of this device includes the survey of building structures to reveal their heterogeneities and defects and the investigation of premises to detect bugging devices     

Evaporation and ignition of droplets in combustion chambers modeling and simulation

Computer simulation of liquid fuel jet injection into heated atmosphere of combustion chamber, mixture formation, ignition and combustion need adequate modeling of evaporation, which is extremely important for the curved surfaces in the presence of strong heat and mass diffusion fluxes. Combustion of most widely spread hydrocarbon fuels takes place in a gas-phase regime. Thus, evaporation of fuel from the surface of droplets turns to be one of the limiting factors of the process as well. The problems of fuel droplets atomization, evaporation being the key factors for heterogeneous reacting mixtures, the non-equilibrium effects in droplets atomization and phase transitions will be taken into account in describing thermal and mechanical interaction of droplets with streaming flows. In the present paper processes of non-equilibrium evaporation of small droplets will be discussed. As it was shown before, accounting for non-equilibrium effects in evaporation for many types of widely used liquids is crucial for droplet diameters less than 100 μm, while the surface tension effects essentially manifest only for droplets below 0.1 μm. Investigating the behavior of individual droplets in a heated air flow allowed to distinguish two scenarios for droplet heating and evaporation. Small droplets undergo successively heating, then cooling due to heat losses for evaporation, and then rapid heating till the end of their lifetime. Larger droplets could directly be heated up to a critical temperature and then evaporate rapidly. Droplet atomization interferes the heating, evaporation and combustion scenario. The scenario of fuel spray injection and self-ignition in a heated air inside combustion chamber has three characteristic stages. At first stage of jet injection droplets evaporate very rapidly thus cooling the gas at injection point, the liquid jet is very short and changes for a vapor jet. At second stage liquid jet is becoming longer, because evaporation rate decreases due to decrease of temperature. But combustion of fuel vapor begins which brings to increase of heat flux to droplets and accelerates evaporation. The length of the liquid jet decreases again and remains constant slightly oscillating.     

Bandwidth maximization for satellite laser communication

Free space optical communication between satellites networked together can make possible high speed communication between different places on Earth. The basic free space optical communication network includes at least two satellites. In order to communicate between them, the transmitter satellite must track the beacon of the receiver satellite and point the information optical beam in its direction. The pointing systems for laser satellite communication suffer during tracking from vibration due to electronic noise, background radiation from interstellar objects such as Sun, Moon, Earth, and Stars in the tracking field of view, and mechanical impact from satellite internal and external sources. Due to vibrations the receiver receives less power. This effect limits the system bandwidth for given bit error rate (BER). In this research we derive an algorithm to maximize the communication system bandwidth using the transmitter telescope gain as a free variable based on the vibration statistics model and the system parameters. Our model makes it possible to adapt the bandwidth and transmitter gain to change of vibration amplitude. We also present an example of a practical satellite network which includes a direct detection receiver with an optical amplifier. A bandwidth improvement of three orders of magnitude is achieved in this example for certain conditions, as compared with an unoptimized system