Aercamsprint

Although their spacewalk had lasted far longer than the six hours originally planned, and Scott and Doi had accomplished a significant amount of their objectives, there were a number of tasks that had been omitted. One of these was an odd, beachball-like contraption known as 'AERCam/Sprint' - or the Autonomous EVA Robotic Camera/Sprint - which was supposed to demonstrate a free-flying camera that could be remotely controlled by an astronaut on board the Shuttle to inspect the exterior of the International Space Station for possible damage.

The concept had attracted particular interest from NASA after the collision of an unmanned Progress resupply freighter into the Mir space station in June 1997, which forced the evacuation and depressurisation of one of its scientific research modules. Had a free-flying camera of AERCam/Sprint's capabilities been available, it might have been possible to investigate and acquire high-quality photographs of the damage, without risking human lives on a spacewalk. ''They're [Mir's crew] limited on the views they can get right now because of where the [station's] windows are located,'' project manager Cliff Hess said before Columbia's launch. ''That's exactly what AERCam is meant for: to give you some other view that you can't get otherwise.''

Future applications could include sophisticated sensors to 'sniff out coolant leaks or mechanical arms to hold spacewalkers' tools. ''One thing you could do is maybe go out periodically and do a scan of the [International Space Station's] solar arrays, to look maybe for meteoroids that may have hit it,'' speculated Hess. ''You could automate something like this free-flyer to do a scan somewhat like a crop-duster.'' Multiple AERCams could be mounted on the station's exterior to carry out routine inspections.

''I think it's very useful,'' said Steve Lindsey, who tested AERCam for its first outing. ''There are other applications for it, [such as] moving large masses from one part of the station or another. It's a really neat project. The potential of this technology is limitless.'' The focus of all this attention looked innocuous enough: a 36-cm-diameter, 16-kg aluminium sphere, coated with soft Nomex felt. This, and onboard control mechanisms that constrain its speed to no more than a few centimetres per second, allow it to be employed safely in close proximity to spacewalking astronauts. If its velocity somehow doubled that, explained Hess, AERCam would automatically shut itself down.

''We don't want anything to inadvertently hit a person or any part of [the Shuttle],'' added Kregel before the flight. ''The likelihood of damage is very minimal, but our plan is to not let that happen. If it is really out of control, we would just [fly Columbia] out of the way.'' The free-flyer was designed to move itself using a system of 12 tiny cold-gas thrusters, operated by Lindsey via a joystick, antenna and two laptop computers from the aft flight deck.

Housed in the airlock, the original plan called for Scott to hand-release it for a half-hour joyride. If time permitted, Lindsey hoped to 'fly' it up to 50 m 'above' Columbia, take a series of video images, then guide it back into Scott's gloved hands. Two miniature colour television cameras, with 6-mm and 12-mm lenses, would provide stunning views for the crew and Mission Control. ''It's unlike anything I've ever flown before,'' said Lindsey before the mission. ''In some ways, the closest thing you could compare it to is flying a radio-controlled airplane.''

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