Here's how astronomers use DSN to connect with James Webb

Sandy Kwan, the mission interface manager for Webb within the DSN, mentions in an official release that “each mesmerizing Webb image that has graced our screens would not have been possible without the support of the DSN antennas and personnel, the backbone of interplanetary communication.”

NASA's Jet Propulsion Laboratory (JPL) in Southern California manages and operates the DSN primarily.

Communication with Webb through DSN 

The DSN antennas have been carefully placed at three distinct sites across the planet, each about 120 degrees apart.

DSN antennas are mainly located at Goldstone (California), Canberra (Australia), and Madrid (Spain). 

Because the Earth revolves, the network of antennae enables scientists to communicate with Webb at nearly any time of the day.

Despite this, Webb is still not a call away through DSN. Given the telescope's distance from the Earth, the communication process between Webb and the DSN is quite different and difficult. 

“On average, the Webb mission operations center connects with the observatory at least 2-3 times in a 24-hour period. There are mission planners at STScI where the Mission Operations Center (MOC) is located, mission schedulers at JPL, and of course at the DSN complexes. The mission planners at STScI work together with the mission schedulers at JPL to create contacts with Webb,” said Kari Bosley, the lead Webb mission planner at the Space Telescope Science Institute (STScI). 

NASA's Goddard Space Flight Center's Flight Dynamics Facility maintains track of the "view periods" when the Webb is facing the Earth in its orbit and visible from any of the three separate DSN stations. This helps us to stay in touch with Webb. 

The different antennas of DSN sites 

According to the official release, the DSN sites are outfitted with antennas of various sizes, including 70 meters (230 feet in diameter), 34 meters (111 feet in diameter), and 26 meters (85 feet in diameter). The DSN stations communicate with Webb via 34-meter antennae, with 70-meter antennas serving as backup. 

Webb is mostly reliant on S-band and Ka-band radio frequencies. 

All commands are sent to the Webb through the lower bandwidth S-band. It is also used to receive telemetry data on Webb's overall health and safety, as well as for range to determine Webb's position and trajectory. 

“We use Ka-band to downlink stored science and engineering data and some telemetry from the spacecraft. If we used S-band to downlink data, it would take many days to download each day’s data. With Ka-band, it takes much less time, and we can usually completely download all of the stored data in a couple of hours,” explained Bosley. 

Scientists highlight that there are times when the established contact with Webb is short and sometimes even long. The majority of contact with Webb via DSN last between two and six hours. 

As the telescope is constantly making science observations and collecting data 24/7, it is critical to downlink as much data as possible in each such contact. At times when there is no communication, the telescope continues to conduct scientific observations on its own. 

“These data are stored on a solid-state recorder and downlinked on our next contact. After the Webb MOC at STScI receives the data and ingests them into the Barbara A. Mikulski Archive for Space Telescope for processing and calibration, the observers will receive the data from their observations,” concluded the statement.