next up previous
Next: KECK OBSERVATORY AND THE Up: NETWORK PERFORMANCE Previous: NETWORK PERFORMANCE

Reliability Issues

While network performance was perhaps not at the level desired, due to developing infrastructure in Hawaii and idiosyncrasies within the outdated SunOS 4.1.4 operating system, issues of network reliability had far greater impact on our remote observing operation. The experimental and limited nature of the ACTS program has created a number of difficulties which one would almost certainly not face if using a more developed and/or commercial satellite system. For example, we have been forced to await replacement of two transmitters, the operating system, and several other HDR components, due to hardware failures. The Internet connection to the HDR, which is required for operation, has also proved unreliable. Although the ACTS personnel and BBN have been extremely cooperative in restoring service on such occasions, the impact of the reliability issue is that at least one observer must be sent to Hawaii to use the telescope, in case of ACTS-related equipment malfunctions.

The remote nature of most high-quality observing sites exacerbates this problem. BBN maintains only a small field office in Hawaii, making HDR maintenance costly and time-consuming. A truly remote site, which would most benefit from remote observing techniques, also requires the highest degree of robustness from the equipment. In our opinion, the ACTS system is insufficiently robust to provide true remote observing with large (i.e., highly competitive) telescopes, due primarily to its limited scope and experimental nature. However, one of the ACTS Project's primary goals is to stimulate commercial high-speed communications satellite development. These systems may eventually play a role in remote astronomical observing systems.

Another difficulty we have encountered is that the transmitters in the ACTS HDR stations are not designed to run continuously, due to the finite lifetime of certain critical components, but rather must be switched on and off as needed. This method of operation demands human intervention at the beginning and end of every satellite session, a procedure that has been non-trivial to organize and would prove difficult in more remote observatory locations. The Hawaii location itself poses an additional problem due to the large yearly rainfall at the location of the HDR in Honolulu. Because the uplink frequency of 30 GHz at which ACTS operates is highly susceptible to rain fade, we have lost several runs in the past year due to rain in Honolulu. In essence, the use of the ACTS system for remote observing adds a weather constraint such that it must be clear (i.e., not raining) at both of the ground station sites, as well as at the observatory itself! Noting ACTS rain fade compensation capabilities, we suggest that this is another area in which future commercial high-speed communications satellites may provide improvements.


next up previous
Next: KECK OBSERVATORY AND THE Up: NETWORK PERFORMANCE Previous: NETWORK PERFORMANCE
Patrick Shopbell
3/17/1998