 |
Above: image of Nozomi approaching Mars
The Japanese word nozomi means “hope,” and that is just what scientists involved in the current Nozomi Mars Mission are getting from York University.
When the Japanese spacecraft was launched in July 1998, the idea was that it would head toward Mars to study its atmosphere and ionosphere. However, the launch of Nozomi failed to provide it with enough energy to achieve a Mars trajectory directly, and the spacecraft has been forced to take the scenic route to the red planet.
Nozomi’s new pathway involves two slingshot-type swingbys of the Earth. For these swingbys, mission scientists needed outside held. That’s when York stepped in.
“We have been responding to a Japanese request for assistance in the Nozomi rescue,” said Professor Wayne Cannon, Department of Physics & Astronomy, Faculty of Pure & Applied Science. “My research group offered VLBI (Very Long Baseline Interferometry) as Nozomi does a final swingby of Earth to gain energy for its onward flight.
“VLBI is a radio astronomical technique developed in Canada in 1967 for combining signals from remotely sited radio observatories with no physical connection between them,” explained Cannon. “The signals are recorded at each observatory using ultra-high-precision atomic clocks as a time reference. The recorded signals are then delivered to a special purpose signal-processing facility where they can be interferometrically combined using the atomic time reference from each station.”
York has been conducting VLBI observations of Nozomi since March 2003. “Our objective is to assist Japanese flight controllers to plan a manoeuvre of Nozomi on May 31 in advance of the swingby of Earth on June 19,” said Cannon.
“The intention is for the swingby to send Nozomi off on a correct trajectory to Mars and not have it go off somewhere else and get lost. Our last VLBI observations of the spacecraft were on May 15 and we plan some more observations after the swingby to verify that the trajectory is correct and the spacecraft is indeed headed for Mars.”
For many years, Cannon’s research group at York University has been using the 46-m-diameter antenna (right) of the Algonquin Radio Observatory in Algonquin Park, Ontario, to do VLBI for a variety of research purposes. His group has developed a world standard VLBI system at York University that is now used in more than a dozen countries around the world, including Japan.
“We have been collaborating with Japanese VLBI research groups at the Institute for Space and Astronautical Science and the Communications Research Lab in Japan for many years,” said Cannon. “We have had Japanese VLBI scientists come and spend up to a year at York working with us. When the Japanese science teams decided to use VLBI techniques to rescue Nozomi, they thought of us.”
How does VLBI work? As Cannon explained, using VLBI on microwave signals transmitted from the spacecraft, the VLBI interference output provides a precise timing delay that permits scientists to determine the position of the spacecraft relative to the interferometer baseline. In this case, the baseline extends from the Algonquin Radio Observatory to similar VLBI antennas located in Japan.
“We also compare the VLBI timing delay from spacecraft signals to the VLBI timing delay for signals from nearby quasars to add precision to the measurements. The quasars we use are ‘nearby’ the spacecraft only in an angular sense. The quasars are actually very powerful, point-like radio sources located at the farthest reaches of the observable universe, but they provide a very stable frame of reference for this sort of measurement,” said Cannon.
“VLBI techniques allow us to determine the celestial position of Nozomi with a precision of a few milli-arc seconds. This is an angle about the size of the diameter of a dime held up in Vancouver and viewed from Toronto.”
If all goes well Nozomi will enter an orbit around Mars in January 2004 and then will begin its real mission – to study the planet’s upper atmosphere and its interaction with the solar wind. The spacecraft carries 14 instruments from five countries, including one from Canada. The Thermal Plasma Analyser (TPA) is a Canadian instrument being carried to Mars by Nozomi on behalf of the Canadian Space Agency and a group of Canadian scientists led by Professor Andrew Yau of the University of Calgary, a graduate of York’s Department of Physics & Astronomy.
Nozomi will investigate the structure, composition and dynamics of Mars’ ionosphere, study the effects of the solar wind, investigate how Mars’ atmosphere leaks out into space, and monitor interactions between the solar wind and Mars’ weak magnetic field. In addition it will be studying dust levels in Mars’ upper atmosphere and dust particles that are able to make it into orbit around the planet.
