Shuttle Endeavour Retraces Orbit to Map Earth in 3-D

The space shuttle Endeavour retraced its orbital steps Saturday, following the same path taken 24 hours earlier to produce the most detailed radar maps ever made of Earth.

The 3-D images will reveal changes in terrain as small as half an inch and possibly help scientists predict earthquakes and volcanic eruptions.

Until Saturday, a shuttle had never repeated its orbital path from one day to the next. Endeavour’s pilots periodically fired their steering jets to put the shuttle on a course duplicating all 16 orbits of the previous day; the same thing was planned for today.

That’s three days of traveling over the same spot at the same time at the same altitude.

“It’s going to be ‘Groundhog Day.’ Remember that movie?” said Mike Sander, project manager at NASA’s Jet Propulsion Laboratory in Pasadena.

In the 1993 film, comic Bill Murray portrays a caustic TV weatherman who awakens to the same day--Groundhog Day--again and again.

Endeavour soared over western Canada, across the Great Lakes and out over the Chesapeake Bay on Saturday afternoon, just as it did Friday. The radar instruments surveyed the same swath of land from 127 miles up, but from a slightly different angle.

Sander said he was thrilled with the results: Endeavour came within 30 feet of where it was Friday over Pennsylvania and 300 feet over northern Canada. Before the flight, scientists were hoping to be within 800 feet.

Other repeat targets include Africa, the Middle East, Ukraine and Siberia.

Scientists will combine these radar carbon copies to create topographic maps of extraordinarily high resolution--accurate in elevation to six yards or less--that will enable them to detect minute surface changes. This will be especially useful in Africa, a continent for which few good topographic maps exist.

Endeavour’s six astronauts continued taking turns photographing the radar targets. They had snapped nearly 10,000 pictures as of Saturday and had film for 4,000 more; their 11-day flight is scheduled to end Tuesday.