A dust storm on Mars and a wobble in Curiosity's trajectory give scientists something to think about, but mission leaders say they're on track for a Sunday landing.
"Things are almost too quiet," Pete Theisinger, the mission's project manager, said Thursday at the Jet Propulsion Laboratory in La Cañada Flintridge as Curiosity barreled toward Mars at 7,987 mph. "I'm waiting for the other shoe to drop."
Curiosity, a roving lab that will scour Mars for the ingredients of life, is scheduled to land at 10:31 PDT Sunday in an ancient geological feature known as the Gale Crater. It is a complex operation. At 1,982 pounds, Curiosity is five times heavier than previous Mars rovers. Its landing requires a dizzying sequence of pyrotechnics and on-the-fly adjustment, all done automatically because Mars is 154 million miles distant, too far for the swift communication needed to guide the landing from Earth.
PHOTOS: A rover called Curiosity
At a briefing Thursday, scientists said satellites had discovered a dust storm swirling south of Gale Crater. Earlier this week, the storm was more than 600 miles from Curiosity's landing site but large enough that it could kick up a pesky cloud of dust.
In theory, that could affect the accuracy of Curiosity's landing mechanism, but scientists said the craft had been engineered to guard against nasty weather and that storms like this are common and typically dissipate in a day or two. To pose a real threat, Theisinger said, "it would have to be the great-grandmother of all dust storms."
Scientists also determined in recent weeks that Curiosity was on course to hit the Martian atmosphere about 13 miles east of the optimal "entry point." Last weekend, they conducted a routine trajectory correction — a "burn," in pop-science parlance. The operation was a success, but imperfect. The spacecraft's new trajectory will send it into the Martian atmosphere at a point roughly 3,000 feet from where scientists had planned after the correction.
However, Curiosity's landing target is an ellipse of land 12 miles wide, allowing for considerable wiggle room. What's more, the craft has been equipped with a self-correcting navigation system called "guided entry" — thrusters that can correct miles' worth of error in trajectory.
Adam Steltzner, a leader of the JPL team overseeing the spacecraft's landing, said an error of just 3,000 feet could easily be "flown out" — absorbed by the sophisticated navigation system. Scientists have two other opportunities for corrective "burns," but said it was unlikely they would use them.
"We are doing everything we can to make sure that we are going to the right place," said Tomas Martin-Mur, the mission's navigation team chief. "I am confident that we will get there and get there safely."
Also Thursday, scientists revealed that Curiosity has already delivered results, even before it lands.
Curiosity's instruments are expected to yield a new understanding of Mars' history and environment. The mission's impact doesn't end there, however. Curiosity is also expected to pave the way for future Mars missions, including the first human exploration. President Obama has set a goal of sending an astronaut to Mars by the 2030s.
That would be no small matter. Rather than the three days it took to reach the moon, an astronaut would endure a nine-month trip there and then another one to get home. Scientists are still trying to understand how they might guard against radiation astronauts would encounter. It's a critical issue. Carrying a proper radiation shield would be both vital and burdensome.
Curiosity was equipped with a device, known as RAD, to measure radiation once the craft arrives. Mars, because of its thin atmosphere and weak magnetic field, lacks the ability to repel or absorb radiation, a trait that could have affected the planet's ability to foster life.
About a year ago, scientists realized they could turn RAD on early, that they didn't need to wait for Curiosity to get to Mars. The instrument was turned on 10 days after launch and was active for most of the spacecraft's 81/2-month journey to Mars. It has already sent home a significant amount of data.
RAD measured radiation encountered by Curiosity along the way, both outside the craft and inside, where an astronaut would be housed during a human-exploration "cruise."
Though scientists are still digesting the data, early indications are that radiation outside the spacecraft carrying Curiosity was perhaps 100 times higher than inside the craft. Still, levels inside might have been a full fifth of the amount of radiation that NASA allows its astronauts to face over the course of their career — "not a full, lifetime dose, but not insignificant," said Don Hassler, RAD's principal investigator. A better understanding of deep-space radiation could help determine everything from spacecraft construction to when a human-exploration mission might launch to limit an astronaut's exposure.