A Spectacular Mission to a Celestial Traveller
8 July, 2005
Canberra DSN and Deep Impact
The personnel at the Canberra Deep Space Communication Complex (CDSCC), as part of NASA's Deep Space Network (DSN) have played a key role in the Deep Impact rendezvous with Comet Tempel 1 on the 4th of July - that of maintaining the link between the spacecraft and the Earth as its impactor payload collided with this mysterious celestial traveller.

The DSN used specially assigned radio frequencies for this link that were about a hundred times higher than would be used to listen to an FM radio station. The telecommunications link provided three main interactions that were vital to Deep Impact - tracking, command, and telemetry.

• The tracking data measures the distance from the spacecraft to the Earth; the navigators use these measurements to guide Deep Impact toward Comet Tempel 1.
• The command link provides a channel for control of the spacecraft and its computers and subsystems by the mission controllers at the Jet Propulsion Laboratory (JPL).
• The telemetry link gives engineers a view into the operation of the spacecraft to ensure that all on-board tasks are being properly conducted. The telemetry link also brings the scientific measurements of the on-board telescopes and spectrometer to the science investigators.

For the critical events such as important command sessions, spacecraft maneouvres, and observations of the comet the DSN provided redundant coverage from two stations.

The DSN conducts ground operations from its control center at JPL in the Space Flight Operations Facility and via the Deep Space Communication Complexes, which include the 70-metre antenna in Canberra, Australia, as well as those in California, USA, and Madrid, Spain. The DSN is the major link that deep space missions have with their engineering and science teams.

The Deep Impact event was somewhat unique in that it is observable by both Earth-based and space-based telescopes. Coordinating the encounter across a number of observing instruments adds to the complexity and to the richness of the results.

With the help of its sister stations in the DSN, the Canberra Complex provided continuous link support as Deep Impact approached the comet. Because of the volume of data and its importance at that exact time, overlapping coverage was considered necessary from two of the DSN's three 70-metre antennas around the world.

For the impact event itself, the 70-metre antenna in Canberra had the spacecraft in view and provided the real-time telemetry channel ensuring that the unique data was captured and returned to anxious scientists at JPL.

The spectacular flash from the moment of impact sent cheers not only through the assembled teams at JPL in Pasadena, California, but also at the CDSCC in Canberra, Australia.

It was an amazing sight, and a spectacular success for all involved. A proud moment for the men and women behind the scences within the DSN, especially here in Canberra, and our colleagues around the Network and at NASA and JPL.

For further information on the Deep Impact Mission, visit http://deepimpact.jpl.nasa.gov

Article written by Glen Nagle - Manager, Education and Outreach