CAPE CANAVERAL -- NASA is drafting a plan to evacuate the International Space Station because the two-man crews are eating more than engineers predicted, prompting a critical food shortage weeks earlier than expected.

The Russians are packing seven extra containers of food into an automated space freighter set to blast off from Kazakhstan on Dec. 23 and, as long as the resupply ship reaches the station as planned, space agency officials say they do not expect to order the crew to return to Earth early.

However, if the ship is destroyed or delayed, temporary evacuation is likely.

Commander Leroy Chiao and Russian flight engineer Salizhan Sharipov will have to eat less to stretch their food supply. Their water situation is not much better.

"Everyone is confident the Progress ship will arrive (on Christmas Day)," said James Hartsfield, a spokesman at NASA's Johnson Space Center in Houston, where engineers are working on the evacuation plan.

The Progress cargo ships have a solid record and "we do not expect any issue with this one, but it's prudent to make all the preparations you need to make so you are ready if you have to be."

Supplies are tight aboard the space station because NASA's shuttles remain grounded, almost two years after the Columbia disintegrated trying to re-enter the atmosphere on Feb. 1, 2003. The station is relying on smaller Russian ships to deliver crew and cargo since then. The food and water dipped to near-critical levels just days ahead of the last two cargo ships.

The internal NASA reports call the shortage "critical" and attribute it in part to "higher consumption than planned." Station managers list the inability to keep the station staffed as one of the most serious risks facing the outpost, a problem driven by dwindling food, water and supplies.

The international partners agreed after the Columbia accident to cut the space station crew, from three people to two, to conserve food, water and other provisions.

Their agreement called for evacuation planning to begin about one month before food, water or breathable air supplies dip to 45 days' worth. The idea is for a crew to leave if the supply falls below 30 days. That would leave enough behind for astronauts to return to the station later.

"They have been working on a de-manning plan," Hartsfield said.

NASA and its partners knew food and water were tight when they decided to go ahead and launch the crew and the station hit the 45-day limit before the Christmas re-supply ship arrived. But at the time, engineers expected the food not to reach that critical level until Christmas.

However, astronauts are eating about 25 percent more food than expected. A series of repeated food audits, during which Chiao counted food containers in the station pantry and then engineers on the ground ran new calculations, has been going on since just after Thanksgiving.

Furthermore, the 45-day supply is an optimistic assessment because the engineering estimates are wrong. First, to make the food last 45 days, the astronauts will have to eat about 10 percent less -- but that's a cut back from the predicted food consumption.

Based on what crews actually ate in recent months, the men could be cutting back their munching by 30 percent or more.

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