The newest antennae are beam waveguide structures. These dont use a centrally mounted feed-horn system like the older antennae (known as high efficiency) they are replacing; instead, their most sensit
The newest antennae are beam waveguide structures. These dont use a centrally mounted feed-horn system like the older antennae (known as high efficiency) they are replacing; instead, their most sensitive electronic components are below ground in a pedestal room. Using a series of precision-machined radio frequency reflective mirrors, the radio signal can be brought down from the reflector into this room, providing easy access for the maintenance crew as well as far more efficient thermal control for the delicate electronics. Perhaps the most valuable advantage of the beam waveguide design lies in its ability to be easily expanded: by locating the electronics in the underground room, it was a relatively simple task to upgrade to such things as the Ka-band frequency requirements of the Saturn explorer Cassini mission, for example.
The ability to array several beam waveguide antennae dramatically improves performance by allowing more of the signal to be captured, and thus enabling higher data rates. Combining the signals of four 34m antennae creates an equivalent capability of a single, but much more expensive, 70m antenna. This in itself is an important factor as it means there is now a backup mechanism to enable a downtime period on the Goldstone 70m antenna for repair or upgrade, as the 34m array will be able to fulfil DSN tracking commitments.
By strategically locating the antenna clusters at 120-degree intervals, continual observation of spacecraft can be maintained as the Earth rotates, enabling unmanned spacecrafts to receive commands and transmit data to their project managers on Earth. The ability to use unmanned crafts to automate the process of scientifically investigating the solar system is vital to NASAs exploration plans, and the use of DSN in providing the all-important two-way link to control navigation and receive data and imaging is key.
While theres little doubt that these steerable, high-gain, parabolic reflector antenna clusters make the DSN the biggest, most sensitive, scientific telecommunications system in the world, it isnt without its problems. Not least of those is the small matter of available bandwidth on a system that is increasingly becoming overloaded, with 40 active missions fighting for network time each month. Missions that carry a high profile, such as the ill-fated Mars Polar Lander, carry an equally high priority on the DSN network, further reducing the available bandwidth.
As we enter the new millennium, you might be forgiven for assuming that technology is helping to overcome these bandwidth problems, but unfortunately it seems the reverse is true. Since payload restrictions are such that spacecraft space is severely limited, on-board communications equipment has to be compact and lightweight to the extreme. Bearing in mind that DSN communicates with crafts travelling in the furthest reaches of the solar system, and that the aforementioned payload restrictions result in low-power data transmission equipment with the equivalent power of a 20W refrigerator light bulb, you can appreciate why these weak signals require as much as 18 hours a day on the network.