NASA on Friday begins a critical two-day-long test of its giant Space Launch
System (SLS) rocket complete with a mock countdown, as the agency gears up to
return humans to the Moon.
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Known as the "wet dress rehearsal," it is the final major test
before the Artemis-1 mission this summer: an uncrewed lunar flight that will
eventually be followed by boots on the ground, likely no sooner than
2026.
"It is our last design verification prior to our launch," senior
NASA official Tom Whitmeyer said in a call with reporters this week.
Data collected from the test will be used to finalize a date for Artemis-1
-- NASA had said May could be the first window, but later now seems likely.
It is called a "wet" dress rehearsal because super-cooled liquid
hydrogen and liquid oxygen will be loaded into SLS from ground systems, just as
they would be in a real launch.
The 322 feet (98 meters) tall rocket -- expected to be the most powerful in
history at the time it is operational -- was rolled out to Launch Complex 39B
at the Kennedy Space Center in Florida around two weeks ago.
The test begins at 5:00 pm Eastern Time (2100 GMT) with a "call to
stations," as members of the launch control team arrive at their firing
rooms and start a countdown of more than 45 hours.
With the SLS rocket and Orion crew capsule fixed on top powered on, teams
will proceed to load 700,000 gallons (3.2 million liters) of propellant, and
practice procedures such as pauses in countdown and other checks.
They won't actually ignite the rocket's RS-25 engines, which were tested
previously. Instead they will halt the countdown about 10 seconds before
liftoff, in order to simulate a "scrub," when launch is aborted due
to technical or weather related issues.
The fuel will be drained, and a few days later SLS and Orion will be rolled
back to the vehicle assembly building to carry out checks on how everything
went.
Test milestones will be posted on NASA's blog for the Artemis mission, but
the agency won't let the public listen to live internal audio, as it did in the
past for Space Shuttle missions.
Whitmeyer explained this was because certain key information, including
timing sequences, could assist other countries looking to develop long range
missiles.
"We're really, really super sensitive to cryogenic launch vehicles that
are of this size and capability, (and) are very analogous to ballistic type
capabilities that our countries are very interested in," he said, but
added that the agency could re-evaluate the position in future.
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