Unclassified

The Wideband Global SATCOM (WGS) system is currently operational in the Pacific Ocean using WGS1 (175E). GBS traffic is supported in that theater today using the Digital Video Broadcast by Satellite (DVB-S) and operates using terminals originally designed for operation using the UHF Follow-On satellite (UFO8). These terminals can now operate over WGS1 and UFO8. GBS is planned to migrate to the Joint IP Modem (JIPM) in 2010. The JIPM will use the second generation DVB-S2 which represents a quantum leap in capability over DVB-S in terms of its power and bandwidth efficiency. Further, the JIPM allows hub-spoke operation between a control center at a Teleport and the remote terminals equipped with a remote Modem. This paper will address the data rate performance of GBS terminals using the current DVB-S and the JIPM DVB-S2 over WGS1 (175E), WGS2 (60E) and WGS3 (12W). First, a reference link is defined based on the Next Generation Receive Terminal (NGRT). Next, data rates will be determined for the reference link based on measured WGS1 data. Finally, global availability maps will be determined for the reference link when operating over WGS1, WGS2, and WGS3 using WGS Ka-band beams.

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RELATIONSHIP OF SPECTROMETER MEASUREMENTS TO SPECTRAL RADIANCE AND EMISSIVITY
The deflection of the spectrometer recorder when viewing the plasma will be given by where C is a calibration constant independent of wavelength, Np is the blackbody radiance function (Planck's radiation law) at the temperature of the plasma, E X is spectral emissivity and 6 (k) is the slit function. Ideally 0(X) could be replaced by a delta function, but practically it is a function sharply peaked at the wavelength setting of the instrument. Over the wavelength interval where s(X) gives significant contributions, Nkp is nearly constant and can be removed from the integration. Hence, where the bar over the spectral emissivity means an effective value.
The spectral emissivity is determined by two measurements. In the first measurement the radiance of a radiation source is determined. The recorder deflection when viewing the source is given by When only the plasma is observed the deflection is R.
From the alternating P signal it is possible to determine the peak-to-peak amplitude which is If the source has a spectral emissivity which varies slowly over a wavelength interval equal to the width of the slit function, then Combining equations 3, 5 and 6 gives RA = R s (l-I X ) or k =(Re

RA) /R s (8)
Once the effective spectral emissivity has been determined, equation 2 can be used to obtain a value for N X.

III. TYPICAL FLAME TEMPERATURE MEASUREMENTS
The results of experiments reported in Reference I are described here. By changing the word plasma to flame and the subscript p to f the analysis of the preceding section is applicable. A term for background radiation essential for experiments with flames but nonessential for plasma, has been omitted.

IV. REQUIREMENTS FOR EXTENDING THE METHOD TO LABORATORY PLASMAS
A.

Wavelength Interval
The wavelength range investigated should include the peak of the blackbody curve. For a 2000"K flame the peak occurs between I and 2 micron.
For a 8000"K plasma from an electric arc, the peak is in the visible region.
Arc plasmas can be examined in an experimentally more favorable region.
However, for temperatures above about 15000"K the difficulties of conducting experiments in the ultraviolet region are encountered. B.

Source Requirements
The discussion leading to equation 6 has placed a slow-variationwith-wavelength restriction on the source spectral emissivity. If is known and if 0(k) is known, the restriction is removed.
A requirement that the source radiative temperature exceed the plasma temperature might be expected. In principle,the source temperature need not be greater. However, from experimental limitations it is necessary to have RA/Rp sufficiently large to avoid signal-to-noise problems. In order to neglect background radiation, the source must be many times brighter.
If RA were larger than R., equation 7 would yield negative values for This cannot occur since R is always longer than RA: regardless of source temperature relative to plasma temperature. Assuming that plasma temperature exceeds 15000*K and that one is willing to pay the price of There is sufficient variety of radiative processes occurring in a plasma arc jet so as to make the method attractive. The radiance is not dependent solely on a few atomic lines.

VI. CONCLUSIONS
It seems feasible to extrapolate the technique to continuous plasma with temperature up to about 15000 0 K. Above that temperature, plasmas are usually of a transient nature imposing severe requirements on the chopper and spectrometer. Also at higher temperatures a suitable radiation source may not be available. A maser, which can be tuned, would appear to be the answer to the source problem.
The method provides a temperature determined from many different radiative processes, i.e., atomic transitions, radiative recombination, molecular electronic transitions, and bremsstrahlung. This experimental technique appears to have advantages, when compared to spectroscopic methods focusing on a particular radiative process, such as atomic transitions. The method readily finds and determines the extent of isolated departtures from equilibrium provided such an equilibrium exists.