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From The "JPL Universe"
April 17, 1998

Engineering, art come together in DS2 'spider'

By SUZANNE D'MELLO, New Millennium Program outreach coordinator

In January 1999, Deep Space 2's twin probes will take off for Mars riding piggyback aboard the Mars Polar Lander spacecraft. The experimental mission is designed to test a number of advanced, miniature instruments and systems inside the probes to see if they can perform experiments beneath Martian soil after surviving crushing impacts on landing and extremely cold temperatures.

On their journey to the red planet, each probe will be housed in a protective shell that will be attached to the larger spacecraft with a device called a "spider," which is part of an overall attachment structure. The spider is so-called because its curved, three-legged frame resembles the body of that arthropod.

What is striking about this seemingly fragile piece of aluminum is that it's not only functional hardware--needing to withstand the extreme conditions of launch and travel into deep space--but with its spare, elegant, Art Deco-like form, is industrial design at its most beautiful.

Satish Krishnan, 23, who designed the spider, was just a few months out of college when assigned the task by DS2's mechanics lead engineer, Tom Rivellini, in late 1996. Rivellini provided Krishnan with an initial concept, which required that the egg- shaped shell be held on to at three, equidistant points.

With a preliminary design of a three-pronged structure in hand, Krishnan worked closely with Rivellini, structural analysts Darshan Sutharshana and Faz Keyvenfar, manufacturing engineer Bob Moncada, machinist Nelson Leiva, and DS2's graphics designer, Frank Ramirez, during the year it took to complete the part. "This had to be a collaboration from the very start," Krishnan pointed out. "The very nature of this part required it."

Heavily constrained by issues of cost and manufacturability while working concurrently in JPL's "faster, better, cheaper" era, he adapted his design several times on the advice of the others. The single most important question that Krishnan faced in creating the spider was whether to make it one part or three. "We knew that making the spider a single part would be very difficult," he said, "but assembly of three parts would have been a nightmare because of the tolerance mismatches we'd have to contend with--tolerance is the degree of precision required in a dimension. So we decided to bite the bullet and make it a single part."

"This is the toughest part I've ever worked on," admitted Moncada, who added, "The part wouldn't have been as rigid or strong if it had been three pieces, and this was the cleanest, easiest way to mount the shell inside the spider."

Making the spider a single part was not that much easier a task, either. The finished spider, which weighs a mere 590 grams (1.3 pounds), had to be crafted out of a giant, 250-kilogram (550-pound) billet of aluminum.

Why such a large chunk? Detailed drawings hadn't yet been created when Krishnan decided to make the device a single part instead of three. Ordering a large billet of metal ensured that engineers would have plenty of material to work with once Krishnan figured out the outer dimensions of the spider.

Leiva machined the spider into its final shape using the process of "undercutting" to hollow out the legs of the spider. Undercutting, a process invented by JPL engineer Don Bickler for the Mars Pathfinder mission, is an innovative way of hollowing out a piece of metal without having to cut it in two. Bickler used the process for the Sojourner rover's "rocker bogie" suspension system, which allowed the rover to negotiate the Martian terrain with its system of joints that rotated and conformed to the contour of the ground.

To drill holes in the precise locations that Krishnan had pinpointed in the legs of the spider, Leiva used a series of fine tools, knowing that if he was off by even an infinitesimal amount the part wouldn't be functional. At one point he even had to contend with having the material move while he tried to machine it. After consulting with materials engineers the problem was solved, and Leiva completed the spider in October 1997.

The device has since successfully passed all its tests and Krishnan is very pleased with its design. "I think when you look at this part, what makes it interesting is the method we used to hollow it out," he said. "I don't think it would have actually looked as neat if we had used an alternative method."

Though Krishnan may be indebted to Bickler for the aesthetics of his design, he also has Leiva's extraordinary craftsmanship to thank for producing an industrial device that is a perfect blend of functionality and beauty.

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