![]() This hold has been extended one extra hour from the Wet Dress Rehearsal counts due to gaseous nitrogen changeover lessons learned. ![]() The critical transition from air to gaseous nitrogen purge will then follow at L-10 hours 45 minutes.Īfter this, a two-and-a-half-hour built-in-hold will then take place from L-9 hours 40 minutes to L-7 hours 10 minutes. The launch team will then bring the Ground Launch Sequencer online, a two-hour process beginning at L-11 hours 15 minutes. (Credit: Jack Beyer for NSF)Īll non-essential personnel will be required to leave LC-39B between L-12 and L-10 hours. Final ICPS power-up for flight will take place at L-18 hours 30 minutes. While this is taking place, final launch preparations for the four RS-25 engines will begin.Īt L-34 hours, teams will pick up the process of powering up the Core Stage, an operation that should last approximately 40 minutes.Īt L-31 hours, the Core Stage Composite Overwrap Pressure Vessels (COPVs) will be pressurized to flight levels, followed by charging of the Orion and Core Stage flight batteries. After verifying functionality and systems, the ICPS will be powered back down until later in the count. Simultaneously, teams will start bringing online the liquid oxygen and liquid hydrogen ground systems ahead of final fuel loading preparations.Īt Launch minus 42 hours (L-42 hours), the 30-minute process of powering up the Orion spacecraft will begin however, there is an option to perform this operation at the very start of the countdown instead.Īt L-38 hours 30 minutes, teams will bring their attention to the ICPS and its initial power-up. The tower will be topped off just before terminal count (which begins at T-10 minutes) in the traditional fashion of pumping water into it until water starts to cascade from an over-fill line - indicating the tank is full. The start of the count commences with a five-hour operation to fill the water tower at LC-39B for use as sound suppression during engine start and liftoff. The twin five-segment Solid Rocket Boosters (SRBs) and the European Service Module (ESM) had their propellants (Polybutadiene acrylonitrile-Ammonium perchlorate composite propellant for the SRBs and mixed oxides of nitrogen & monomethylhydrazine for the ESM) loaded before the SRB segments were shipped from Utah and before the ESM and the Orion capsule were brought to the Vehicle Assembly Building (VAB) for stacking. The 46-hour 40-minute countdown will see the Exploration Ground Systems (EGS) launch team take the SLS vehicle through final configurations for launch, including the all-important fueling process to give SLS the needed propellants for its four RS-25 Core Stage engines and its single RL10B-2 engine on the Interim Cryogenic Propulsion Stage (ICPS). The countdown is the first for launch operations at LC-39B since Ares I-X’s only mission on October 28, 2009, and marks the first in a series of three NASA-led missions to return humanity to the surface of the Moon for the first time since December 1972. The launch count comes after more than a decade of development, capped by successful Green Run and Wet Dress Rehearsal tests - both of which provided good lessons learned and changes in procedures for launch day. The launch countdown for the Space Launch System (SLS) rocket and the Artemis I mission is underway at the Kennedy Space Center in Florida ahead of a planned liftoff within a two-hour launch window that opens at 8:33 AM EDT (12:33 UTC) on Monday, August 29.
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