Problem: Some power tools used to bolt station pieces together in orbit might not work properly.

Consequence: NASA doesn't know whether bolts and fasteners are too tight or too loose.

Shattered or stray bolts, or larger pieces, could pop off and hit the station or spacewalkers.

Consequence: A hose, fittings or connectors on the toilet could burst, spewing stored urine into the station. The floating urine droplets could blind crew members or impair their sight. Urine is one of many potential contaminants that NASA strives to keep contained because of the potential danger to the crew.

Problem: Main oxygen generator on station repeatedly failed between December and March.

Consequence: Crew attempting to repair important spare parts to revive a broken generator. Other key parts don't exist in orbit or on Earth.

Problem: The 95-minute limit for emergency shuttle departures from station can't be met on future outpost assembly missions.

Consequence: The station and shuttle could be destroyed, killing everyone aboard, if astronauts can't close evacuate quickly. This includes getting all crew members aboard the orbiter, undocking, closing the payload bay doors and preparing to de-orbit to get the crew safely back to Earth. The longer that takes, the more risk to the crew, the visiting shuttle and the station. Key parts might have to be thrown overboard if an emergency crops up during future construction flights because there would not be time to safely stow them.

Problem: Sensors designed to continuously measure toxic substances in station air and water don't work.

Consequence: Flight surgeons must rely on air and water samples returned to Earth every six months rather than real-time readings that would warn them about sudden toxic contamination.

Problem: Shuttle thrusters could accidentally fire when orbiter is docked to outpost.

Consequence: Force of thrusters could cause the outpost to tumble out of control or break apart.

Problem: Safety requirements waived for sharp edges and hot spots on station exterior.

Consequence: Sharp edges could rip pressurized spacesuits worn by astronauts, instantly killing them. Touching or grabbing super-hot metal parts could burn through spacesuit gloves.

Problem: Critical exercise equipment is in disrepair.

Consequence: Crew might have to abandon the station if astronauts cannot stay fit enough to endure return to normal gravity or avoid injury during rehabilitation. Last crew made makeshift repairs to a treadmill, but there are questions about how long those repairs will hold up.