Winter Boon From Deep Space
|Location of Stardust trajectory. View from above the solar plane Credit: NASA/JPL|
Have you ever wondered how NASA obtains those beautiful pictures of planets and distant moons? In between a spacecraft’s camera and photography printers at Pasedena’s Jet Propulsion Laboratory is an array of big dishes called NASA’s Deep Space Network. This network has completed a number of upgrades to help support the fleet of more than two dozen spacecraft touring the solar system. Among the upgrades is the addition of a new 34-meter (110-foot) antenna near Madrid, Spain, which began operations on Nov. 1.
The Deep Space Network, managed by NASA’s Jet Propulsion Laboratory, Pasadena, Calif., is a worldwide network of antennas that supports interplanetary spacecraft missions, and some near-Earth missions. With antennas in Spain; near Canberra, Australia; and in California‘s Mojave Desert, the network has the ability to provide radio communications with spacecraft at all times. The three sites are spaced approximately one-third of the way around Earth from each other so they cover spacecraft in any direction as the world turns.
Among the missions supported by the network are the Mars Exploration Rovers that will land on Mars in January; the Stardust mission that will collect comet dust in January; the Cassini-Huygens mission that will probe the rings and moons of Saturn beginning in July; and the Genesis mission which is collecting solar wind particles for return to Earth in September. All these mission can be tracked live as they traverse deep space.
"We have upgraded our network to accommodate the unprecedented level of activity this winter," said Peter Doms, manager of the Deep Space Network [DSN] systems program at JPL. "It’s the large number of these events that we need to support; that is the reason for these upgrades."
The Madrid antenna is the biggest piece of about $54 million worth of improvements to the network. "These upgrades will allow us to be right there when the missions need us," said Doms. Other upgrades include improving the capabilities of existing antennas at all three of the network’s tracking complexes; modifying the antennas to "listen" to more than one spacecraft at a time; adding more powerful transmitters; replacing some older hardware and software with more reliable equipment; and adding a new navigation capability to help the Mars rovers land on their targets.
|Huygens parachutes onto Titan. ESA’s Huygens probe descends through Titan’s mysterious atmosphere to unveil the hidden surface (artist’s impression) Credit: ESA|
Each complex consists of several deep space stations equipped with large parabolic reflector antennas and ultra sensitive receiving systems that include a 70-meter-diameter (230-foot) antenna; a 34-meter-diameter (110-foot) high-efficiency antenna; at least one 34-meter (110-foot) beam waveguide antenna; and a 26-meter-diameter (85-foot) antenna.
"To give you an idea of how sensitive these antennas are, if we were to "listen" to one spacecraft in the outer solar system by Jupiter or Saturn for 1 billion years and add up all the signal we collected, it would be enough power to set off the flash bulb on your camera once," said Doms. One a signal is received it begins its journey to the printers: the DSN data are relayed using microwave links, communications satellites, land lines, and submarine cables to their final destinations.
Mission projections for the period of November 2003 to February 2004 indicate the greatest need for increased communications capacity will be at the Madrid complex. The new antenna in Madrid will add about 70 hours of spacecraft-tracking time per week for the rovers and orbiters during the periods when Mars is in view of Madrid. The added hours represent a 33-percent increase from the station’s current capacity of 210 hours per week.
In Australia, other NASA-funded upgrades were completed this summer on the Parkes Radio Telescope. Owned by the Australian Commonwealth Scientific and Industrial Research Organization, the 64-meter (210-foot) antenna is located near the town of Parkes, Australia. With upgrades to handle the current deep space transmission standards, Parkes will take on some of the Deep Space Network workload.
Parkes will provide backup support for a large number of critical mission events and will also provide coverage for missions that would otherwise receive less during periods of conflicts. The major improvement is adding a microwave system that allows for reception in the X-band frequency currently used by all missions. The amount of solid paneling on the Parkes antenna was also increased to offer better performance. Among Parkes’ many noteworthy science contributions, the telescope was the star of the Australian movie, "The Dish", since it proved the critical link that brought to 600 million people globally the live images from the first moonwalk of Neil Armstrong. Surviving a driving rain storm and winds up to 60 mile per hour– about three times greater than the dish was rated to survive– the western Australian outpost became the world’s only link on July 21, 1969. Without Parkes, one of the most stunning events of the century would have been just fuzzy TV static.
|Solar flares issue strong electromagnetic bursts, as photographed by the SOHO spacecraft and transmitted by the DSN.
In addition to the 2004 boon of new missions, ongoing support for NASA and European probes is ongoing. The Deep Space Network supports downlink from the main solar observatory (SOHO), which monitors space weather and flare activity. Called SOHO, the Solar and Heliospheric Observatory had proven to be a huge hit on the internet, as millions could view real-time images of the Sun, discover comets, or check space weather for flares, prominences, or sunspots.
Since 2001, the Mars Odyssey spacecraft has sent back spectacular images of the red planet, via the Deep Space Network.
During its Jan. 2, 2004 encounter with its target, Stardust will fly within 75 miles of comet Wild 2’s main body, close enough to trap small particles from the coma, the gas-and-dust envelope surrounding the comet’s nucleus. Stardust will be traveling at about 13,400 miles per hour and will capture comet particles traveling at the speed of a bullet fired from a rifle. The main camera, built for NASA’s Voyager program, will transmit the closest-ever comet pictures back to Earth. It is the first U.S. sample-return mission since the last moon landing in 1972.
Next summer, NASA’s Cassini spacecraft, first launched in 1997, is scheduled to go into orbit around Saturn and its moons for four years. The piggybacking Huygens probe is scheduled to plunge into the hazy Titan atmosphere and land on the moon’s surface. The Huygens probe is geared primarily towards sampling the atmosphere. The probe is equipped to take measurements and record images for up to a half an hour on the surface. But the probe has no legs, so when it sets down on Titan’s surface its orientation will be random. And its landing may not be by a site bearing organics.
|An artist’s rendition of 2001 Mars Odyssey as it entered orbit.
NASA’s Genesis mission was designed to collect solar wind samples (10-20 milligrams). The spacecraft was launched in August of 2001 and is now collecting particles coming off the sun. The samples will be returned to Earth in September 2004.
Future methods of improved communications to deep space probes are under study. In order to maximize the science return from spacecraft operating on and around Mars, NASA is planning to place a communications relay satellite — a Mars Telesat — into orbit around Mars in 2009. This satellite will be designed for a lifetime of at least six years, with a goal of ten years, and will be placed into a high Mars orbit that will enable it to cover a large fraction of the martian surface every few hours. The Telesat will not only substantially increase the total volume of data that can be returned from Mars, it will also provide essential telemetry relay during critical events such as Mars landings, orbital entries, and the launch of samples from the martian surface.
The most recent advance is the implementation of communications systems operating at Ka-band. This capability, to be fully demonstrated on the 2005 Mars Reconnaissance Orbiter, will provide a data rate from Mars of more than 2 megabits/second. In addition to its role as a relay at various radio frequencies, the Telesat will carry the first deep space optical communications payload. This technology uses laser light instead of radio waves to dramatically expand the data "pipeline" to Earth. As the first operational test of optical communications for planetary missions, this experiment on the Mars Telesat will help to alleviate one of the fundamental constraints on solar system exploration.
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