Press Release

The Deep Space Network – NASA Science News

By SpaceRef Editor
June 6, 2001
Filed under ,

NASA’s traffic control system for interplanetary spacecraft is bracing for a
flurry of activity in deep space.

On April 28, 2001, a weak radio signal reached Earth from
beyond the orbit of Pluto. It was NASA’s Pioneer 10 spacecraft, struggling
to communicate with ground controllers, its message riding on a radio signal
that registered just a billionth of a trillionth of a watt.

How do you listen to a transmission that couldn’t make a lightbulb glow in a
billion years? It’s all in a day’s work for NASA’s extraordinary Deep Space
Network (DSN).

The DSN is a global system for communicating with interplanetary spacecraft.
The largest and most sensitive scientific telecommunications system in the
world, it also performs radio and radar astronomy observations for the
exploration of the solar system and the universe.

“Communicating with missions in deep space is difficult,” said Joseph
Statman, Manager of the Deep Space Mission System Engineering Office at
NASA’s Jet Propulsion Laboratory (JPL). “It requires extremely large
antennas, huge transmitters and very sensitive receivers.”

The DSN consists of three clusters of antennas spaced approximately 120
degrees apart around the world: at Goldstone, in California’s Mojave Desert;
near Madrid, Spain; and near Canberra, Australia. “The strategy here is, no
matter where the spacecraft is, you’re always in contact with it,” explained
Statman. Each complex is situated in semi-mountainous, bowl-shaped terrain
to shield against radio frequency interference.

DSN locations in Spain, Australia, and California are approximately 120
degrees apart in longitude, which enables continuous observation and
suitable overlap for transferring the spacecraft radio link from one complex
to the next.

The centerpiece of every DSN facility is an enormous 70-meter diameter
antenna (230-foot) capable of tracking spacecraft more than 16 billion
kilometers (10 billion miles) from Earth. Arrayed around that dish is an
assortment of 34-meter, 26-meter, and 11-meter antennas. The 26-meter
antennas feature a double-axis astronomical mount that allows them to point
low on the horizon to pick up fast-moving, Earth-orbiting satellites as soon
as they come into view. These can track at up to three degrees per second.

DSN antennas communicate with far-flung spacecraft at radio frequencies of
2.2 GHz, 8.4 GHz, and 32 GHz. For comparison, the lowest frequency, 2.2 GHz,
is about the same as radio waves that cook food inside household microwave
ovens.

All of the antennas communicate directly with the Deep Space Operations
Center at JPL in Pasadena, CA. The center staff directs operations,
transmits commands and oversees the quality of spacecraft telemetry and
navigation data delivered to network users.

NASA recently announced it’s upgrading the DSN to handle a surge in
interplanetary traffic.

“We’re getting ready for a crunch period beginning in November 2003,” said
Rich Miller, head of planning and commitments at JPL. That’s when the U.S.,
Europe and Japan all will have missions arriving at Mars. These include
NASA’s 2003 Mars Exploration Rovers, the ESA Mars Express Mission, and the
Japanese Nozomi spacecraft. At the same time Stardust and Deep Space 1 will
be encountering comets and a third comet mission named “CONTOUR” will
launch. And, of course, other ongoing missions will have continuing
communications needs.

“[These new] missions all happen to lie in the same part of the sky,” said
Statman, who described the area where the spacecraft will cluster as a slice
of the sky with Mars in the middle. “We need to track them but we don’t have
enough antennas.”

Madrid will receive a new 34-meter antenna that will increase available
spacecraft-tracking time by about 105 hours per week when Mars is in view.
The Madrid complex’s current capacity is 315 hours.

“The tracking capacity is proportional to the number of antennas at each
location,” said Statman. “At the moment, Madrid is the most crucial site for
an upgrade simply because we need more tracking time there.”

Goldstone already supports as many as 420 hours per week of deep space
communication, a figure that will balloon to 525 hours when an existing
antenna comes online in 2003. “Both the Japanese and the Europeans have
tracking antennas in Australia,” says Statman, so they can help with the
communications load at that longitude.

As part of the upgrade, older hardware and software systems will be phased
out and replaced with ones that are more reliable and, in some cases,
automated. Also, Madrid and Canberra will receive processing equipment that
will allow operators to combine signals from multiple on-site antennas,
increasing their sensitivity to distant transmissions. Goldstone can already
do that.

Every bit of extra sensitivity is welcome, says Statman. The total signal
power arriving at a network antenna from a spacecraft transmitting from the
outer solar system is 20 million times weaker than the power level from a
modern digital watch battery!

Teasing out faint signals from space probes isn’t all the DSN does — it’s a
powerful scientific instrument in its own right. The Goldstone 70-meter
antenna, for example, doubles as a powerful solar system radar. It captures
radar images of planets and passing asteroids, searches for water on the
Moon, and helps pick landing sites on Mars. Together, the three DSN
facilities along with other antennas around the world form a powerful Very
Long Baseline Interferometer that can peer into the hearts of quasars,
measure Earth’s continental drift — even test general relativity.

Astronomers used the Goldstone radar to image near-Earth asteroid 1999 KW4
when it passed by Earth last month. They discovered the space rock was a
binary!

Not bad for a bit of moonlighting!

NASA’s Deep Space Network truly is an international treasure, and it’s about
to become even better. For more information about DSN and its ongoing
upgrades, please visit the Deep Space Network home page from JPL
( http://deepspace.jpl.nasa.gov ).

SpaceRef staff editor.