L. E. Gonzalez

Photometric and Spectroscopic Observations of SN 1990E in NGC 1035: Observational Constraints for Models of Type II Supernovae

We present 126 photometric and 30 spectral observations of SN 1990E spanning from 12 days before B maximum to 600 days past discovery. These observations show that SN 1990E was of type II-P, displaying hydrogen in its spectrum, and the characteristic plateau in its light curve. SN 1990E is one of the few SNe II which has been well observed before maximum light, and we present evidence that this SN was discovered very soon after its explosion. In the earliest spectra we identify, for the first time, several N II lines. We present a new technique for measuring extinction to SNe II based on the evolution of absorption lines, and use this method to estimate the extinction to SN 1990E, A(V) = 1.5 +/- 0.3 mag. From our photometric data we have constructed a bolometric light curve for SN 1990E and show that, even at the earliest times, the bolometric luminosity was failing rapidly. We use the late-time bolometric light curve to show that SN 1990E trapped a majority of the gamma rays produced by the radioactive decay of Co-56, and estimate that SN 1990E ejected an amount of Ni-56 virtually identical to that of SN 1987A.

Optical Light Curves of the Type I[CLC]a[/CLC] Supernovae SN 1990N and SN 1991T

We present UBVRI light curves for the bright Type Ia supernovae SN 1990N in NGC 4639 and SN 1991T in NGC 4527, based on photometry gathered in the course of the Calan/Tololo supernova program. Both objects have well-sampled light curves starting several days before maximum light and spanning well through the exponential tail. These data supersede the preliminary photometry published by Leibundgut et al. and Phillips et al. The host galaxies for these supernovae have (or will have) accurate distances based on the Cepheid period-luminosity relationship. The photometric data in this paper provide template curves for the study of the general population of Type Ia supernovae and accurate photometric indices, needed for the Cepheid-supernova distance scale.

Performance of Satellite Communications On The Move Systems in the Presence of Antenna Pointing Errors

On the move satellite communications is a major new capability that is being sought by the Army to support new operational concepts. Because of their size and weight, small aperture terminals are very attractive in such communications on the move applications. These terminals have wide beamwidths and may increase interference to adjacent satellite systems. Also, motion induced antenna pointing errors are unavoidable in communications on the move systems and these will increase the interference level to adjacent satellites. In order to limit interference to adjacent satellite systems, the International Telecommunications Union (ITU) and the Federal Communications Commission (FCC) have established strict recommendations and rules on the off-axis emissions and antenna gain patterns. These recommendations and rules do not account for the motion induced antenna pointing errors and, in the presence of such errors, the transmit power spectral density from these terminals will be so small that only very low data rates can be realized. In order to facilitate communications on the move systems, a modification to the relevant existing ITU recommendations was proposed. In this paper we will examine the bit-error-rate (BER) performance of communications on the move systems subject to those suggested modifications. Analysis carried out in this paper shows that the motion induced antenna errors can have a significant impact on the BER performance

Optical light curves of the type ia supernovae 1990n and 1991t

We present UBVRI light curves for the bright Type Ia supernovae SN 1990N in NGC 4639 and SN 1991T in NGC 4527, based on photometry gathered in the course of the Calan/Tololo supernova program. Both objects have well-sampled light curves starting several days before maximum light and spanning well through the exponential tail. These data supersede the preliminary photometry published by Leibundgut et al. and Phillips et al. The host galaxies for these supernovae have (or will have) accurate distances based on the Cepheid period-luminosity relationship. The photometric data in this paper provide template curves for the study of the general population of Type Ia supernovae and accurate photometric indices, needed for the Cepheid-supernova distance scale.

A plausible CONOPS for frequency reuse at Ka-band on WGS system

The Department of Defense (DOD) demand for satellite communications (SATCOM) bandwidth is increasing. To meet this demand, the DOD will implement dual-polarization frequency reuse to increase bandwidth utilization.

Relative performance of mobile networks in the Ku, commercial Ka and government Ka bands

In the past 10 years mobile satellite networks have gained a strong foothold in the commercial Ku-band and now attention is turning to mobile networks in the commercial and government Ka-bands. Examples of new Ka-band commercial systems abound (Inmarsat-5, ViaSat-1 and Jupiter-1) and WGS is just opening up the government Ka-band in a big way. Land, sea, and aero communications-on-the-move (COTM) applications are being proposed and developed in each of these bands.

“A regulatory study and recommendation for EIRP Spectral Density requirement/allowance for SOTM terminals at Ka-Band on WGS system”

The Armys WIN-T program is developing a new class of terminals for satellite on-the-move (SOTM) missions. The initial target satellites were commercial Ku-band satellites however, the ultimate goal is the Wideband Global System (WGS). WGS will consist of a geosynchronous constellation of at least six spacecrafts with X and Ka-band capable transponders. WGS is the newest department of defense (DOD) transponded satellite system. Earth Terminals (ET) that will utilize WGS will need to conform to MIL-STD-188-164A [1]. Currently, the DOD is in the process of updating MIL-STD-188-164A to add mobile satellite communications (SATCOM) requirements. One of the parameters that will be addressed is the off-axis equivalent isotropically radiated power (EIRP) Spectral Density (ESD) for ground mobile terminals. The ESD value is an extremely important parameter that will drive the achievable throughput, spectral efficiency, and adjacent satellite interference (ASI) levels of SOTM terminals and networks. The World Radio Regulations has designated the earth-to-space 30–31 GHz Ka-band, which is the band used by WGS, with a usage designation of co-primary fixed satellite (FSS) and mobile satellite service (MSS). This means that the same criteria used to analyze commercial Ku-band FSS is not applicable. This paper looks at the system impacts of operating small mobile terminals at the 30–31 GHz Ka-band. It develops a methodology to analyze the overall performance impacts for SOTM networks, giving particular consideration to performance and the transmission impacts to adjacent satellite networks (ASN). The ASI will be quantified in terms of Equivalent Satellite Link Noise Temperature (ESLNT)[2] and its equivalent delta-T over T (delta-T/T). The analysis will examine ASI using the ESD limits provided by SMDC/ARSTRAT for WGS. Finally, based on this analysis, the paper will propose an off-axis ESD limits for inclusion in the update to MIL-STD-188-164B.

Capacity and regulatory study on the potential use of satellite on the move terminals at X-band

The Army is evaluating the potential use of military X-band, in support of satellite on- the-move (SOTM) missions, to satisfy much needed war-fighting bandwidth. Over the next 5 years, the Wideband Global SATCOM (WGS) constellation will be placed in orbit. It will consist of a geosynchronous constellation of at least five X and Ka capable satellites. The WGS X- band payload is significantly more powerful than the existing Defense Satellite Communications System (DSCS) constellation and will also allow cross- banding between X and Ka on orbit. Initial US Army CERDEC analysis of WGS and experiments on a similar commercial X- band payload (XTAR) has shown the feasibility of operating small (18 inch and smaller apertures) mobile terminals at X- band with reasonable spectral efficiency. This paper expands upon the work performed to date at the CERDEC to look closely at the system impacts of operating small mobile terminals at X-band. It develops a methodology to analyze the overall performance impacts and terminal design goals. Finally, it proposes a new standard for these X-band mobile terminals.

Optimized loading of NCW networks on WGS

The Wideband Global Satellite (WGS) system represents an order of magnitude increase in capacity over the existing Defense Support Communications Satellite (DSCS) system. In addition to adding capability in the X-band and a Ka-band, WGS adds a unique digital channelizer. The digital channelizer greatly increases the flexibility of the WGS payload over previous satellite systems. It allows an individual 125 MHz transponder to be decomposed into as many as 48 sub-channels, each of which can be given its own transfer gain, be cross-banded between X-band and Ka-band, be combined with other sub-channels (fanned-in), or be duplicated in multiple downlinks (fanned-out). However, with increased flexibility comes the following planning challenge. Given all of the possible options, how does an operator configure the WGS satellite to most efficiently serve a given network?

Spectral Efficiency of Mobile VSAT Systems

Satellite communication systems based on very small aperture terminals (VSAT) are important for the military in on-the-move communications applications. The performance of these systems depends on many parameters, including, the transmit and receive antenna aperture sizes and the specific satellite employed in the system. In this paper we will compute the spectral efficiency of the VSAT system for different sets of these parameters. We will consider the commercial Ku-band and all the applicable regulatory issues will be addressed in this analysis. It is demonstrated that these regulatory issues play a significant role in determining the performance of the VSAT system.