INMARSAT integrity channels for global navigation satellite systems

The transmission of integrity information using a signal format compatible with the Global Positioning System (GPS) and relayed through a geostationary satellite repeater, which will be critical in achieving high integrity and availability of global navigation by satellite is discussed. The inclusion of navigation repeaters designed to fulfil this function, the next generation of INMARSAT spacecraft, INMARSAT-3 is examined. The global navigation satellite system (GNSS) integrity channel (GIC) will employ pseudorandom codes in the same family as, but distinct from, the codes reserved by GPS. The data format of the basic integrity channel is designed to convey user range error information for 24 to 40 satellites. A closed-loop timing compensation technique will be used at the uplinking Earth station, to make the signal's clock and carrier Doppler variations identical to those that would result from an onboard signal source. Therefore, the INMARSAT-3 satellites will increase the number of useful navigation satellites available to any user, and can also function as sources of precise timing. There is also a possibility that wide area differential corrections can be carried on the same signal     

Latitudinal influences on the quiet daytime D-region

Four versions of a steady-state quiet D-region model are presented. They differ from each other as a result of latitudinal differences in total neutral particle concentrations, nitric oxide concentrations and cosmic ray ionization rates. The total ion concentration profiles of all four versions have minima near 70 km which range from about 10⁸ m^?3 at high latitudes to 3.5 × 10⁷ m^?3 at equatorial latitudes for a solar zenith angle of 60°. Neutral density differences among the four cases result in important vertical shifts for the respective D-region profiles relative to one another. A “C-layer” is evident for the high and mild-latitude models at large solar zenith angles. The altitude where the negative ion/electron concentrations ratio is unity varies from about 63 to 67 km. The computed results are compared briefly with the extensive data base in the literature.     

The instrument IKS and its calibration

The IKS infrared spectro-photometer will fly on board the VEGA platforms. It is designed to characterize the size, temperature and emissivity of the Comet Halley nucleus, to identify the major gaseous components of the inner coma and to detect the emission of the cometary grains. This paper presents the “calibration” experiments required to reduce the raw data: (i) absolute wavelength calibration of the filter wheels; (ii) modeling of the internal signal, as a function of the temperature of the different sub-systems; (iii) absolute and spectral responsivities of each of the spectrometric and photometric channels, as a function of the wavelength and position of the source in the field of view. Finally, we shall indicate the expected S/N ratios.     

Adaptive Array Bandwidth with Tapped Delay-Line Processing

The bandwidth of adaptive arrays with tapped delay lines behind the elements is examined. Such processing offers improved bandw over that attainable with quadrature hybrid processing. The performance of a two-element array with four types of processing (equarature hybrids, single delay lines, 3-tap delay lines, and 5-tap delay lines) is compared. It is shown that with half-wavelength element spacing, a quadrature hybrid and single delay-line processor are inadequate at 10-percent bandwidth. A 3-tap processor is adeq however, up to 40-percent bandwidth.     

V.L.A. observations of flare build-up in coronal loops

Very Large Array (V.L.A.) measurements at 20 cm wavelength map emission from coronal loops with second-of-arc angular resolution at time intervals as short as 3.3 seconds. The total intensity of the 20 cm emission describes the evolution and structure of the hot plasma that is detected by satellite X-ray observations of coronal loops. The circular polarization of the 20 cm emission describes the evolution, strength and structure of the coronal magnetic field. Preburst heating and magnetic changes that precede burst emission on time scales of between 1 and 30 minutes are discussed. Simultaneous 20 cm and soft X-ray observations indicate an electron temperature $\text{T}{}_{\mathrm{e}}\textcolor{red}{}\text{2.5 × 10}{}^7\text{K}$ and electron density $\text{N}{}_{\mathrm{e}}\textcolor{red}{}\text{10}{}^{10}\text{cm}{}^{\mathrm{?3}}$ during preburst heating in a coronal loop that was also associated with twisting of the entire loop in space. We also discuss the successive triggering of bursts from adjacent coronal loops; highly polarized emission from the legs of loops with large intensity changes over a 32 MHz change in observing frequency; and apparent motions of hot plasma within coronal loops at velocities V > 2,000 kilometerspersecond.     

Growth and development of plants flown on the STS-3 Space Shuttle mission

Pre-germinated pine seedlings and germinating oat and mung bean seeds were flown on the STS-3 Space Shuttle mission. Overall, the seedlings grew and developed well in space. Some oat and mung bean roots, however, grew upward. Lignin content was slightly lower in flight tissues and protein content was higher.     

Instantaneous Frequency Estimation Using Adaptive Linear Predictor Weights

A computationally efficient scheme for estimating the digital instantaneous frequencies of narrowband inputs is introduced. The frequency estimates are obtained by searching for minima of the inverse input power spectrum. This spectrum is estimated at each input sample from the weights of an adaptive linear predictor which uses the LMS (least mean square) algorithm to update its weights. The related minima are sought via an iterative search algorithm, referred to as the iterative frequency estimator. This algorithm is computationally more efficient than available methods, and also provides a higher resolution. Simulation results are included; these include tracking of random message sequences in FM signals, and the formant frequency estimation of speech.     

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.     

Systolic time intervals after a seven-day orbital flight.

Heart rate, systolic time intervals (pre-ejection period, left ventricular ejection time , ejection friction, stroke volume and QT interval of two cosmonauts (Leonid Popov--L.P. and Dumitru Prunariu--D.P.) were studied before, during, and after an ergometric bicycle exercise test performed before and after the seven-day Soviet-Romanian orbital flight on the Soyuz 40-Salyut 6 Complex in May 1981. For this purpose one precordial electrocardiogram (ecg) and the ear photodensitopram (den) were recorded stimulaneously. The method used permitted recording even during exercise, Ecg and den signals were stored on magnetic tape, processed in an analogue device and in a digital computer. The data obtained after landing suggest a slight cardiac deconditioning in L.P., demonstrated especially by augmentation of the pre-ejection period, which was unchanged in D.P. corresponding to a sympathoadrenergic hypertonia. The seven-day orbital flight has not produced important cardiovascular changes.     

FIGARO: An experiment for pulsar and variable source studies in the MeV range

We present a large area, balloon borne, NaI(Tl) detector for low-energy gamma rays with temporal signature : FIGARO.The main detector is a mosaic of 12 NaI(Tl) tiles 22.5 × 15 × 5 cm, for a total geometric area of 4050 cm².In the energy band 140 keV - 6 MeV, the expected background counting rate at float altitude is in the range of two to three thousands counts per second.For pulsar analysis the expected 3δ sensitivity for 5 hours exposition time is 2.5 10^?4 ph/cm².s.MeV (150–500 keV) 1.5 10^?4 ph/cm².s.MeV (1–6 MeV). This performance, together with the large effective area and the relatively short duration of a balloon flight, make FIGARO particularly suitable for the identification of sources by means of temporal analysis.For objectives in the Northern sky, including the Crab pulsar, a transmediterranean flight is planned for the summer of 1982 ; a Southern mission is scheduled in Brazil for the fall of 1983 (Vela, PSR 1822-09).