NASA's Deep Space Network (DSN) provides communications and other services for planetary exploration missions as well as other missions beyond geostationary orbit, supporting both NASA and international users. The DSN comprises three antenna complexes in Goldstone, California; Madrid, Spain; and Canberra, Australia.
Currently the DSN supports 35+ spacecraft or service users, counting all those with regular requirements for scheduled time on any antenna. The mission users span a wide range of distance and orbit type: high Earth orbit, lunar orbit, solar orbit, probes at Mercury, Venus, Mars, and Saturn (and en route to Jupiter and Pluto/Charon), and to comets and asteroids, out to the two Voyager spacecraft in interstellar space. Ground-based users conduct radio science and radio astronomy using the antennas, including coordinated programs with international partners. Other activities that must be scheduled include routine and special maintenance, calibration, engineering, and test activities. The collected set of DSN users imposes a very wide range of usage requirements on the network due to differing designs and operating modes. Some users require occasional contacts of only a few hours per week, but this ranges up to continuous coverage during certain mission phases, such as postlaunch and during critical mission events. At the present time, a typical week includes between 400 and 500 scheduled activities on the antennas of the three DSN complexes.
The process of scheduling the DSN is complex and time-consuming. There is significantly more demand for DSN services than can be handled by the available antennas. There are numerous constraints on the antennas and on the timing of communications supports, due to spacecraft and ground operations rules and preferences. Most DSN users require a firm schedule around which to build spacecraft command sequences, weeks to months in advance.
The Service Scheduling Software (SSS) was developed to support automated scheduling of these assets and facilitate resolving conflicts within the schedule. Currently there are several distributed teams who work with missions and other users of the DSN to determine their service needs, provide these as input to an initial draft schedule, then iterate among themselves and work with the users to resolve conflicts and come up with an integrated schedule. This effort has a goal of a conflict-free schedule by eight weeks ahead of the present, which is frequently hard to meet in practice. In addition to asset contention, many other factors such as upcoming launches (and their slips) contribute to the difficulty of building up an extended conflict-free schedule.
The SSS software is actively used to schedule DSN activities. Since 2011, it has performed mid-range scheduling for the Deep Space Netowrk (DSN). In 2017, it was extended to support realtime changes to the schedule.
There are three primary features of SSS to improve the scheduling process.
- Automated scheduling of activities with a request-driven approach (as contrasted with the previous activity-oriented approach that specified individual activities).
- Unifying the scheduling software and databases into a single integrated suite covering real time out through as much as several years into the future.
- A peer-to-peer collaboration environment for DSN users to view, edit, and negotiate schedule changes and conflict resolutions.