If you would like to see more articles like this please support our coverage of the space program by becoming a Spaceflight Now Member . If everyone who enjoys our website helps fund it, we can expand and improve our coverage further.

Astronauts Peggy Whitson and Jack Fischer put on spacesuits Friday and headed outside the International Space Station for several repair and maintenance tasks, but the duo only completed part of their originally planned work after a leaky cooling umbilical delayed the start of their spacewalk.

Mission control in Houston marked the official start of the spacewalk at 9:08 a.m. EDT (1308 GMT).

NASA pushed back the start of the spacewalk after a troublesome servicing and cooling umbilical forced forced the duo to use their spacesuit’s internal electrical supply during final spacewalk preps and depressurization of the airlock.

The umbilical was not part of the spacesuit, NASA said, but a piece of support equipment inside the space station. It provides power, cooling and communications capability to the spacesuit before the astronauts exit the space station, according to Rob Navias, the NASA TV commentator for Friday’s excursion.

Teams noticed a small water leak in the umbilical early Friday.

Friday’s spacewalk was the ninth of Whitson’s career, and the first for Fischer, who gleefully remarked on the occasion.

“Oh my gosh, this is beautiful,” Fischer said as the station sailed 250 miles over the Atlantic Ocean east of Puerto Rico.

“Isn’t it?” Whitson replied.

“The biggest slice of awesome pie I’ve ever seen,” Fischer said.

“No awesome sauce?” Whitson said, referring to one of Fischer’s favorite sayings.

“How about a ginormous fondu pot bubbling over with piping hot awesome sauce?” Fischer joked.

Mission control radioed the astronauts that Friday’s spacewalk would be limited to run around four hours, not the six-and-a-half hour duration originally planned, due to the problem.

NASA expected the shortened spacewalk meant Whitson and Fischer would probably only have time to complete one of the jobs planned Friday — the replacement of a large avionics box that routes telemetry and power to experiments and spare parts mounted on a depot outside the space station.

In the end, the pair accomplished most of the spacewalk’s planned objectives.

Their first job was to remove and replace an ExPRESS Carrier Avionics box located on the starboard-side S3 truss of the space station. A replacement unit was delivered to the outpost aboard an Orbital ATK Cygnus supply ship last month.

Whitson and Fischer made quick work of the avionics box swapout, and mission control gave the astronauts the green light to secure a piece of separated insulation on the space station’s Japanese robotic arm and work on a data connector for the Alpha Magnetic Spectrometer, a particle detector and cosmic physics experiment outside the station.

Fischer repaired the Japanese robotic arm’s thermal insulation, while Whitson installed a terminator cap on the AMS instrument, a massive experiment attached to the station truss designed to study dark matter and antimatter.

The terminator cap will enable a telemetry path from AMS, allowing engineers to investigate the performance of cooling pumps inside the instrument that may need to be repaired or replaced on a future spacewalk.

Fischer also got the go-ahead to fasten micrometeoroid and orbital debris shielding to Pressurized Mating Adapter No. 3, which was recently relocated from the Tranquility module to the Harmony module, where it will receive a new docking mechanism next year for future link-ups with commercial crew spaceships developed by Boeing and SpaceX.

The astronauts did not have time to complete other jobs in Friday’s spacewalk plan.

The pair planned to set up a new high-definition video camera and a pair of wireless antennas outside the research complex, but those tasks will be deferred to another spacewalk.

Whitson and Fischer returned to the station airlock and began pressurizing it at 1:21 p.m. EDT (1721 GMT), wrapping up a 4-hour, 13-minute spacewalk.

Friday’s excursion was the 200th spacewalk in support of space station assembly and maintenance since December 1998, and the fifth this year.

Email the author.

Follow Stephen Clark on Twitter: @StephenClark1.