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NASA Revamps Historic 4-Million-kg Mars Antenna
coondoggie writes NASA is working on some difficult renovations to reinvigorate its 70-meter-wide 'Mars antenna.' The antenna, a key cog in NASA's Deep Space Network, needs about $1.25M worth of what NASA calls major, delicate surgery. The revamp calls for lifting the antenna — about 4 million kilograms of finely tuned scientific instruments — to a height of about 5 millimeters so workers can replace the steel runner, walls and supporting grout."
I work at a commercial communications satellite company and we have an old earth station with a 32 meter antenna that's rarely used today, but we still keep it as a backup. Actually, the cost of bringing it down is more than the scrap value, so it's mostly just standing there.
What nobody realized was that the antenna had been tracking a single geostationary satellite for decades, so it was moving very slightly around one position. Geostationary satellites aren't exactly stationary, but close, there's a slight movement around a central point.
The result was that, when they tried to point the antenna to a different satellite they found that the circular steel rail had been cold-rolled over the years so each wheel was sitting in a small valley in the rail. The azimuth motor didn't have enough torque to get off that valley and point the antenna to a different position, although there was no problem in tracking a satellite in the old position.
The solution was to jack up the whole antenna, cut off a section of rail and weld a new piece of rail beneath each wheel. The trickiest part was grinding the rail so that the new parts were perfectly aligned.