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A dust storm on聽Mars聽and a minor wobble in the spacecraft鈥檚 trajectory have given scientists something to think about, but leaders of NASA鈥檚 Curiosity mission said Thursday that they are on track for a Sunday landing 鈥� the delivery of the largest and most ambitious machine ever sent to another planet.

鈥淭hings are almost too quiet,鈥� Pete Theisinger, the mission鈥檚 project manager, said Thursday at the Jet Propulsion Laboratory in La Canada Flintridge as Curiosity barreled toward聽Mars聽at 7,987 mph. 鈥淚鈥檓 waiting for the other shoe to drop.鈥�

Curiosity, a roving lab that will scour聽Mars聽for the ingredients of life, is scheduled to land 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聽Mars聽rovers. Its landing requires a dizzying sequence of pyrotechnics and on-the-fly adjustment, all done automatically because聽Mars聽is 154 million miles distant, too far for the swift communication needed to guide the landing from Earth.

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鈥檚 landing site but large enough that it could kick up a pesky cloud of dust.

In theory, that could affect the accuracy of Curiosity鈥檚 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, 鈥渋t would have to be the great-grandmother of all dust storms.鈥�

Scientists also determined in recent weeks that Curiosity was on course to hit the Martian atmosphere about 13 miles east of the optimal 鈥渆ntry point.鈥� Last weekend, they conducted a routine trajectory correction 鈥� a 鈥渂urn,鈥� in pop-science parlance. The operation was a success, but imperfect. The spacecraft鈥檚 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鈥檚 landing target is an ellipse of land 12 miles wide, allowing for considerable wiggle room. What鈥檚 more, the craft has been equipped with a self-correcting navigation system called 鈥済uided entry鈥� 鈥� thrusters that can correct miles鈥� worth of error in trajectory.

Adam Steltzner, a leader of the JPL team overseeing the spacecraft鈥檚 landing, said an error of just 3,000 feet could easily be 鈥渇lown out鈥� 鈥� absorbed by the sophisticated navigation system. Scientists have two other opportunities for corrective 鈥渂urns,鈥� but said it was unlikely they would use them.

鈥淲e are doing everything we can to make sure that we are going to the right place,鈥� said Tomas Martin-Mur, the mission鈥檚 navigation team chief. 鈥淚 am confident that we will get there and get there safely.鈥�

Also Thursday, scientists revealed that Curiosity already has delivered results, even before it lands.

Curiosity鈥檚 instruments are expected to yield a new understanding of聽Mars鈥� history and environment. The mission鈥檚 impact doesn鈥檛 end there, however. Curiosity is also expected to pave the way for future聽Mars missions, including the first human exploration. President Obama has set a goal of sending an astronaut to Mars聽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鈥檚 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.聽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鈥檚 ability to foster life.

About a year ago, scientists realized they could turn RAD on early, that they didn鈥檛 need to wait for Curiosity to get to聽Mars. The instrument was turned on 10 days after launch and was active for most of the spacecraft鈥檚 81/2-month journey to聽Mars. It has already sent home a significant amount of data.

RAD measured radiation encountered by Curiosity along the way, outside the craft and inside, where an astronaut would be housed during a human-exploration 鈥渃ruise.鈥�

Although 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 鈥� 鈥渘ot a full, lifetime dose, but not insignificant,鈥� said Don Hassler, RAD鈥檚 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鈥檚 exposure.

漏2012 Los Angeles Times

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