The ACTS Satellite and the Plan for the High Speed Network

Throughout the design process of the hardware and software for the Keck Telescope the possibility of implementing remote observing from Waimea, the location of the Keck headquarters in Hawaii , (and eventually from California once suitable networks became affordable) was kept in mind. The instruments, their motors, and detectors are run through workstations that are located in the control room of the Keck Telescope dome. All the instrument and telescope control software was written using X Window System displays. It is not necessary during normal night time operation to go out to the instrument on the telescope to make any adjustments or changes. The main deterrent to the implementation of remote observing has always been the problem of obtaining an affordable and reliable connection with adequate bandwidth. NASA's Advanced Communications Technology Satellite was built as a prototype system to explore new modes of high speed transmission for digital data. It provides this capability at rates reaching up to OC-12 via advanced on-board switching and multiple dynamically hopping spot beam antennas for selected areas of the United States, including Pasadena and Hawaii , although the steerable antenna used to reach sites not in the continental U.S. is only capable of OC-3 speed. The 20-30 GHz frequency band, not previously used by a communication satellite, is utilized, with extensive rain fade compensation. ACTS was launched in September, 1993. In response to an announcement of opportunity issued by NASA , a proposal was submitted by JPL for the use of ACTS as part of a network for the remote control of the Keck Telescope and its instruments, as well as to work on other issues closely related to remote observing. This proposal was chosen for funding and allocated several nights per week of ACTS satellite time for an 18 month period. BBN has designed and built the high data rate (HDR) ground stations that provide a gateway at these high data rates between ACTS and ground based fiber optic networks or interfaces to supercomputers. Five of the HDR terminals have been built and they are allocated to the various ACTS experiments for pre-determined lengths of time, then moved to another location. Because of the delay in finishing these complex groundstations, all ACTS experiments until recently used the smaller and much slower T1 portable ground stations.

The network that we are in the process of establishing runs using the ATM protocol from Caltech to Mauna Kea , Hawaii . Its overall layout is given in Figure 1. The first leg runs at OC-3 from the Caltech campus to JPL through optical fiber, then through the HDR at JPL up to the satellite. The downlink from the satellite is through the HDR in Honolulu.

 

Figure 1: Layout of the high speed network used for remote observing with the Keck Telescope.

We have negotiated a contract with GTE Hawaiian Telephone for a T3 link from Honolulu to the Keck Telescope on the summit of Mauna Kea , with a drop at Keck headquarters in Waimea. The completion of the underwater inter-island fiber optic cable in early 1995 by GTE Hawaiian Telephone was an important step towards making this network possible. There are serious problems in the capacity of existing equipment in the link between Waimea and Hale Pohaku, a point half way up Mauna Kea , after which fiber optic cable has already been laid to the summit. Plans to upgrade this segment have been under discussion for several years, and sources for the necessary funding exist since part of this segment services all the astronomical facilities on Mauna Kea . However, their implementation has been delayed far beyond the point anticipated at the time we proposed our ACTS experiment. Because of these limitations, our network runs through some existing telephone company microwave stations along the Saddle Road and then from the Saddle Road up to Hale Pohaku through two portable microwave antennae which GTE Hawaiian Telephone has provided specifically for this project Several vendors are supplying ATM hardware for this network. Newbridge Networks supplied the ATM switches used by GTE Hawaiian Telephone, while JPL uses Fore Systems switches, and the Caltech switch is made by SynOptics . Fore ATM SBus cards are used as the interface into the Sun SPARC 20/51 workstations at each end of the network. This mixed vendor environment is a stringent test of the compatibility among these vendors in the relatively new ATM environment. It will also be of interest to see how well ATM performs in a network with so many different physical media, from satellite links to microwave, as well as the usual optical fiber.