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| Professor of astronomy Steven Squyres talks about one of his rover "children" at a teacher workshop held at the Doubletree hotel in Cocoa Beach, Fla., on June 25. Robert Barker/University Photography |
CAPE CANAVERAL, Fla., June 26 -- Steven Squyres talks about his two Mars rovers, Spirit and Opportunity, the way a parent would describe two beloved -- and individually unique -- children.
"Spirit is our firstborn," he told a group of about 75 Cornell alumni attending a briefing June 25 at the Best Western hotel in Cape Canaveral, Fla. "Spirit has the most quirks, a little more personality than Opportunity has. Opportunity is not quite as quirky."
Referring to the rovers by the names recently selected by NASA from thousands submitted by schoolchildren, Squyres gave his audience an overview of the Mars Exploration Rover (MER) mission on a day when the firstborn was already safely launched on its journey to Mars, and the younger child was still sitting atop a Delta II Heavy rocket on pad 17B at Cape Canaveral Air Force Station.
"She's been a real good spacecraft so far," he said of Spirit. "On Friday of last week (June 20, 2003), we had our first critical event, a trajectory correction." This maneuver, known as a TCM, aimed the spacecraft more precisely toward its landing site on Mars next January, a depression called Gusev crater. The burn of the rockets "went perfectly," he reported. "The TCM moment was the coolest moment for me so far. Twelve of us, members of the science team, were on the fourth floor of the Space Sciences building [at Cornell]. As it's happening 3 million kilometers away, we're watching our spacecraft do stuff. It was really a neat thing having our bird out there."
Spirit is now in a "quiescent cruise" mode, Squyres said. "We'll do our first cruise check in 3 to 3 1/2 weeks -- the first time we'll turn our instruments on in space. We'll know then whether or not the instruments are healthy."
While the science team had to work out numerous quirks and details on Spirit, that rover's launch went smoothly, with only a couple of minor delays due to weather. Opportunity's development, on the other hand, went more smoothly than Spirit's, but its launch has presented more difficulties, resulting in a delay of several days while NASA replaced cork insulation that was incorrectly installed on one of the rocket stages. The new insulation then had to be painted, Squyres noted, because "you can't launch an ugly rocket."
That, said Squyres, brings up another difference between the two rovers. Spirit was launched on Boeing's reliable, much-used Delta II rocket. Opportunity will leave Earth atop a Delta II Heavy -- making its inaugural flight. Its nine solid-fuel boosters have flown only three times previously.
"The reason we're using the Delta II Heavy is because the best time to launch was when we launched Spirit," Squyres explained. "The planets are farther apart now, and we need a heavier rocket to get to Mars."
By coincidence, Cornell has had part "ownership" of the Delta II Heavy for some time. It was the rocket that was due to put the Space Infrared Telescope Facility (SIRTF), an orbiting observatory, into space April 27. James Houck, professor of astronomy at Cornell, is the lead investigator on one of the observatory's instruments. Because NASA needed the rocket for the rover, said Squyres, it postponed SIRTF just six days before the scheduled launch and "literally peeled the SIRTF logo off" and "slapped a rover label" on the rocket. He joked, "Not only did we bump SIRTF, we stole their rocket." He added that Houck was "very gracious" about giving up his rocket. SIRTF's new launch date is Aug. 23.
Although outwardly twins, the rovers have unique voices. "They transmit radio signals on two different frequencies so we know who we're talking to," Squyres said.
Spirit and Opportunity also have individual destinations. "Their two landing sites are very different from each other," Squyres said.
Gusev crater, Spirit's landing site, appears to be an ancient lakebed, and there is evidence that a river once flowed into it. Opportunity will land at Meridiani Planum, a smooth plain, halfway around the planet from Gusev, to try to discover if the the significant deposits of the gray mineral hematite in the crater are an indication that the area was once covered with water.
In spite of these minor personality differences, Spirit and Opportunity have the same larger goal: to advance human knowledge that "deepens our understanding of the nature of our universe" and helps us "better understand our role in the cosmos," said proud father Squyres.