( CNN ) -- The space shuttle Discovery is on pace for a Sunday launch after NASA engineers repaired a leaky gas venting system , officials said Saturday . Space shuttle Discovery readies for launch , which now appears on pace for Sunday . The leak had canceled a planned launch on Wednesday . NASA hopes the seven-member crew can take off around 7:40 p.m. Sunday on a mission to the international space station , where they will deliver supplies needed to expand the station 's crew to six people . `` The vehicle is looking real good ... , '' lead shuttle flight director Mike Moses said . `` Basically , I think I can sum this up by just saying we 're good to go tomorrow and we 're looking forward to getting the count going . '' A leak in a hydrogen gas vent line forced Wednesday 's delay . Repairs went smoothly , Moses said . The line funnels flammable hydrogen away from the launch pad during takeoff . The shuttle crew will be delivering the final parts needed for an expanded solar energy power system that will allow the station to double its crew to six people . The crew also will be dropping off Japanese astronaut Koichi Wakata , who will replace NASA 's Sandy Magnus on the space station . The shuttle also will carry a replacement for a failed unit in a system that converts urine to drinkable water , NASA said . Watch an explanation of why Wednesday 's launch was scrubbed » . Kathy Winters , the mission 's chief weather officer , said Sunday appears to offer only a 20 percent chance of weather that would scrub the launch . The crew , led by commander Lee Archambault , is expected to board Discovery at Kennedy Space Center at Cape Canaveral , Florida , at about 4:30 p.m. Sunday . Officials said the crew has been training and resting for the mission since Wednesday . Earlier this week , Magnus , station commander Michael Fincke and Russian engineer Yury Lonchakov had to take shelter in their Soyuz spacecraft -- a lifeboat of sorts -- when a piece of debris from an earlier mission hurtled uncomfortably close to the station . The debris , moving about 20,000 mph , came within three miles of the station but caused no damage . Wednesday 's launch postponement was the latest in a series of delays for Discovery as it tries to make the 28th shuttle mission to the space station . The launch had been delayed previously to allow time to check a `` flow-control valve in the shuttle 's main engines , '' NASA said last week . That resulted from damage being found in a valve on the shuttle Endeavour during its November 2008 flight . Three valves were cleared and installed on Discovery , it said . CNN 's Kim Segal and John Zarella contributed to this report .
NEW : Repairs to leaky hydrogen gas vent line went well , NASA says . NASA hopes launch , scrubbed this week , will happen Sunday evening . Shuttle launch postponed Wednesday because of leak in a venting system . Shuttle to deliver supplies to the International Space Station .