Whirlwind of Signals Expected from Mars
Dec. 15, 2003 -- The first thing controllers hope to hear as the earliest of three Mars probes touches down on the Red Planet on Christmas day is a nine-tone ditty by the British rock band, Blur. From that point on, Mars will only get noisier.
If all goes to plan, three probes will be exploring Mars' surface by the end of January and relaying everything they learn back to Earth directly or by way of two orbiters that are now zipping around the planet.
NASA is bracing for the communications crunch.
"From Christmas eve until the end of January we're going to be here around the clock," said Roger Gibbs, project manager for the Mars Odyssey orbiter at the Johnson Space Center, in Pasadena, Calif.
Singing Beagle 2
Mission planners for the European Space Agency's Beagle 2 lander solicited the craft's unique arrival tune as a way of drawing a little more attention to the Beagle's planned Christmas day landing on Mars.
"We have to announce our arrival and normally we send back some piece of gobbledygook but we wanted to have something that was instantly recognizable," Beagle 2's lead scientist Colin Pillinger told the BBC.
The Beagle may sing, but unlike the two NASA rovers that are due to touch down in January, it can't talk directly to receivers on Earth. Instead, it will relay all information through one of three orbiters.
Most of the Beagle's reports will arrive via the Mars Express — the European orbiter that's now heading toward the planet. But for the Beagle's first 10 days on Mars, NASA's Odyssey orbiter will do most of the listening as the Express reorients itself into a comfortable orbit.
Odyssey will then send Beagle's reports to one of three sites of giant listening dish stations posted in Spain, Australia and California, known collectively as the Deep Space Network (DSN).
Rich Miller, manager of the DSN, said his team began adding equipment to the network last spring when they realized they'd be facing an onslaught of communications from the Mars bound vehicles. The biggest improvement was the addition of a 110-foot antenna near Madrid, Spain, which began working Nov. 1.
"We feel prepared now," said Miller.
Silent Landing
Despite the extra arrangements, there will be no avoiding a brief, tense silence as each rover drops to Mars. In 1999, that pause grew into anguish as engineers slowly realized the rover did not survive its descent.
This time, Mark Adler, mission manager for Spirit — the first NASA rover to drop to Mars — is hoping the communication blackout will only be temporary.
"The whole landing event takes about five minutes from the time it enters the atmosphere," he said about the planned Jan. 4 landing. "Then it will be a couple more minutes at least before it stops bouncing and rolls to a stop."
Just how soon Adler's team hears from Spirit (and later, Opportunity) depends on whether the ATV-sized robot lands with its dish antenna directed toward Earth or away.
If the rover happens to roll to a stop with the dish facing home, it should transmit an 'All OK' signal within 10-15 minutes — the time it takes light to travel the some 100 million miles to Earth.
"It's about a 50-50 chance we'll hear that quickly," said Adler.
If the dish isn't in range, engineers must wait for one of two other sets of calls. The first are what Adler calls very simple "smoke signals" relayed to one of the orbiters during the spacecraft's descent to the planet. Once an orbiter is in range (after a few hours), it will send the data down to Earth.
Another possible first signal could arrive from the rover's low-gain antenna. This antenna sends less data at a lower rate, but it doesn't need to be pointing to Earth to work, so it's more reliable. That signal could arrive the following evening Earth Pacific time or by the next morning, Mars time.
Seeing Mars in 20-20
Considering the distance the signals travel — some 100 million miles — the lapse isn't terribly long. But, for Adler, the time will drag.
"Landing is a violent process, so you don't want to breathe a sigh of relieve until you know it's safely on the planet," he said. "That will feel like an eternity."
Once settled into their new digs, the Beagle will communicate and receive orders mostly through its partner spacecraft, the Mars Express, while the two NASA rovers will be sending and receiving signals directly with the Deep Space Network on Earth half the time at a rate of 13,000 bits per second.
For transmitting big chunks of data, such as chemical spectrum readings and images, the NASA rovers will send relay streams at 128,000 bits per second to one of two orbiters — the Mars Global Surveyor or the Mars Odyssey as they pass overhead.
Nearly all the information from the rovers will then be relayed right to NASA's Mars Web site. Steve Squyres, principal investigator for the Mars Exploration Rovers, says if all goes to planned, people will be able to see Mars "like they've never seen it before."
"The quality of the images will be equivalent to human 20-20 vision," he said. "And I have no idea what we'll see."