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This study assessed the System Design Of Future Communications Satellites Using High Temperature Superconductors.
Previously there has been much work performed on HTS technology and it has been clearly demonstrated that the technology offers significant benefit to RF performance. However, this is the first time in which the overall system impact of the technology on a telecommunications satellite has been evaluated, taking into account accommodation, cooling and programmatic factors in addition to RF performance.
The principal question that has been asked during this study is: "For the same mission, can the use of HTS technology result in a smaller, cheaper spacecraft?"
The introduction of HTS into a telecommunications payload is technically challenging in two distinct areas:
1) maintaining the HTS material at the required temperature (77K) in orbit whilst minimizing the requirement for active cooling, and
2) establishing a spacecraft architecture that lends itself to ground testing.
The HTS payload was designed so that all the HTS components were located in the large feed arrays. This had the advantage that:
In addition, this arrangement permitted the introduction of a chilled region (~180K) in which the LNAs could be located, thereby enabling reduced system noise and hence potential G/T improvements (1 to 2 dB). The concept is illustrated below:
The payload is cooled using large pulse tube coolers. This type of cooler offers the potential for growth to the powers required and is being actively developed, thus raising the possibility that such development will occur.
HTS has been shown to provide several potential benefits for RF systems, including:
It was hoped that the satellite system level savings resulting from these benefits would outweigh the impact of introducing a cryogenic cooling system.
Whilst the use of HTS technology in the payload itself resulted in mass and power savings, an analysis of the thermal implementation showed that a considerable penalty had to be paid in order to include and support the coolers. In total, a dry mass penalty (after converting power demand into power subsystem mass) of approximately 720 kg was calculated.
The cost of implementing an HTS payload were found to be considerable, the non-recurring cost might be in the order of 20 M¬ whilst the recurring cost might be in the order of 35 M¬ (including test and launch costs).
Overall, the impact of HTS technology on a communications satellite business case is negative. However, there are factors (improved G/T due to system noise temperature and increased capacity due to HTS enabled narrower filter bandwidths) that may have a positive impact.
A payload concept was selected that is being developed as part of an advanced mobile study. The scenario that was selected is a mixed L plus S-Band mission on a single platform with added C-to-C capacity with RF processing.
The payload consists of C-band feeder links and two user links in L and S-band with global coverage and is strongly based on Astrium's assumptions regarding a next generation mobile service spacecraft.
A high level synthesis of the characteristics of the selected payload is given in the following table:
|Payload scenario||Future Mobile Mission|
|Payload DC power||19 kW|
|Payload dissipation||16.5 kW|
|Payload mass||2700-2800 kg|
|Number of reflectors
Size of each reflector
|Number of active SSPAs||426|
The payload architecture used for this assessment is shown below. Items identified in blue are where HTS material is employed.
Click for larger image
The study has addressed the following:
In order to objectively assess the impact of HTS on the spacecraft, the performance of the reference payload, realised with conventional technology, was kept constant, thereby permitting like-for-like comparison.
The study commenced early in 2002 and concluded with a final presentation in October 2003.