The launch of the Falcon 9 rocket and Dragon capsule had been
slated for 4:58 p.m. EDT (2058 GMT). But an hour before liftoff,
engineers reported that the rocket's first stage was leaking helium,
prompting a postponement.
The next opportunity for the Falcon 9 to fly is 3:25 p.m. (1925 GMT)
on Friday if the problem can be resolved, NASA said in a statement.
The flight, the third of 12 under the firm's 1.6 billion contract
with NASA, already had been delayed several times for technical
issues, including a potential contamination concern with the rocket
and damage to an Air Force ground tracking radar needed to monitor
the Falcon's flight.
Another postponement loomed over the weekend after one of two
computers that control key space stations systems, including the
solar wing panels and a moveable base for the robot arm, failed. A
spacewalk is needed to replace the unit, which is located in the
station's external framework.
NASA managers decided on Sunday to let SpaceX proceed with launch
and scheduled the repair spacewalk for later in the month.
In addition to delivering cargo to the space station, SpaceX plans
to use the Falcon's launch to test technology it has been developing
to recover and reuse its rockets.
The Falcon 9's first stage holds extra fuel and four landing legs.
After it separates from the upper stage and Dragon capsule, the
rocket is expected to reignite its engines to slow its descent and
position itself for a vertical touchdown on the ocean before
toppling over on its side.
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"This is a really difficult maneuver," SpaceX Vice President Hans
Koenigsmann told reporters during a news conference on Sunday.
Overall, the company considers the test has less than a 40 percent
chance of success.
Eventually, SpaceX hopes to fly its Falcon rockets back to land for
refurbishment and reuse.
SpaceX is one of two firms hired by NASA to fly cargo to the station
after the space shuttles were retired in 2011. So far, SpaceX has
made one test flight and two cargo runs to the station, a project of
Orbital Sciences Corp, which holds a separate $1.9 billion NASA
contract, has made one test flight and is preparing for its second
resupply mission in June.
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