Citation
Abstract
In this article the performance of the 32-GHz (Ka-band) deep-space link is compared to that of the 8.41-GHz (X-band) link through emulation. Sky brightness time series from water vapor radiometers (WVRs) and advanced WVRs (AWVRs) were used to emulate the effects of increased system noise temperature (SNT) and line-of-sight atmospheric attenuation due for both X-band and Ka-band. Models for Deep Space Network (DSN) ground antennas were used to obtain ground antenna gain and system noise temperature performance. Mars Reconnaissance Orbiter (MRO) X-band and Ka-band capabilities with slightly different coding and data rates were chosen for the spacecraft link design and emulation. A total of 207 passes (69 per DSN complex) from MRO’s DSN tracking schedule were selected for these emulations. For each pass, the actual link geometry was used to design and emulate the link. The Ka-band link was designed so that the expected pass capacity is maximized with at most two data rates, subject to a minimum availability requirement (MAR). Two X-band link designs were used. The first design approach, similar to Ka-band, maximized the expected link capacity with at most two data rates subject to a MAR. The second design approach was similar to the current MRO link design practice. In this approach, the X-band link was designed for operations above 20 deg elevation with a single data rate that has at least 1 dB of margin over 90 percent supportable data rate at 20 deg elevation. The analysis provides continuity and completeness statistics as well as delay-throughput performance characteristics for both Ka-band and X-band. The analysis indicates that the optimized X-band link has only a 2-dB advantage over current practice in terms of capacity and the Ka-band link offers an approximately 5.5-dB advantage over current practice (normalized for onboard DC power used). The analysis also indicates that even with a 99 percent MAR, the Ka-band link suffers an order of magnitude more losses than the current X-band practice. Therefore, it is recommended that the Ka-band link be designed for maximum expected capacity and additional onboard storage and retransmission schemes be used to assure data completeness, provided that the delay requirements on the data are not too stringent.
Details
- Volume
- 42-178
- Published
- August 15, 2009
- Pages
- 1–56
- File Size
- 1.5 MB