NASA and the SLS teams stand ready for the next series of launch attempts for the agency’s super heavy lift rocket which will facilitate humanity’s return to the Moon: this time to establish a permanent presence on our closest celestial neighbor.
The current no earlier than (NET) launch date for Artemis I is Wednesday, Nov. 16 within a 120-minute window that opens at 1:04:00 AM EST (06:04:00 UTC). A backup opportunity is confirmed on the Eastern Range for Nov. 19.
Should teams require additional time beyond Nov. 19, the Federal Aviation Administration (FAA) in the United States has stated that the next earliest possible airspace closure around KSC and the busy Atlantic flight corridors would be Friday, Nov. 25.
This is to account for the pre-Thanksgiving holiday travel season along the eastern seaboard of the United States, which the FAA does not wish to disrupt. Thanksgiving is traditionally the busiest period of air travel in the United States each year.
With a promising weather forecast predicting a 90% chance of acceptable conditions throughout the window, all eyes are largely on the late afternoon and evening hours of Tuesday, Nov. 15, when Launch Director Charlie Blackwell-Thompson and her team will begin fueling the SLS – a sequence that has given the team issues to work through in previous wet dress rehearsals (WDRs) and launch campaigns.
Nominal fueling milestone times for the Nov. 16 launch are all on Tuesday, Nov. 15:
3:24 PM EST (20:24 UTC) – Go for tanking
3:44 PM EST (20:44 UTC) – LH2 chilldown start
5:27 PM EST (22:27 UTC) – High-pressure bleed on RS-25 engines
The main focus will be on the liquid hydrogen (LH2) side of the propellant environment, where teams have struggled against leaks on the ground side while also working through feed pressure alterations.
While pumps are used to move liquid oxygen (LOX) from its storage sphere on the northwest corner of 39B into SLS, pressure is all that is used to move the more volatile LH2 from its storage sphere on the northeast corner of the pad.
After using the original pressure profile during the WDRs and first two launch attempts, all of which saw leaks on the LH2 ground side that exceeded the four percent ambient hydrogen concentration safety limits around the fuel lines on the LH2 Tail Service Mast Umbilical (TSMU), NASA tested a kinder, gentler fueling process in September.
To this, while there is a nominal prelaunch timeline for the team to follow, it would not be unexpected for the advertised timings to change during the countdown as Charlie Blackwell-Thompson and her team take the vehicle through the fueling process and respond to any issues that come up with this first-flight of a vehicle.
In the days leading up to the launch, workers at the Kennedy Space Center continued to assess the vehicle following Hurricane Nicole, noting a minor electrical signal issue with a data line on the LH2 TSMU that provides redundant readings.
The data line is not required for launch, but the team worked to restore the system to full capacity after it returned readings that were out-of-family but still within Launch Commit Criteria limits following Nicole’s passage.
RTV, an area of insulation 10 feet in length that peeled away from Orion during Hurricane Nicole, appears to be located below it’s hatch.
— Nathan Barker (@NASA_Nerd) November 14, 2022
Aside from the electrical line, a cable for Orion popped out of its cable tray on its associate Orion/ESM swing arm on the Mobile Launcher and was returned to the right position after the storm, while a rain curtain on one RS-25 engine had to be replaced.
Additionally, a piece of RTV sealing material on the outer Launch Abort System cover over Orion was liberated during Nicole. The missing piece is three meters (10 feet) long and five millimeters (0.2 inches) wide. After thoroughly reviewing data and transport mechanisms/paths, NASA officials cleared the issue for flight on Monday, Nov. 14.
The countdown began on Nov. 14 with Call To Stations at 1:24 AM EST (06:24 UTC) ahead of the clock starting to count backward to zero at 1:54 AM EST (06:54 UTC). The count is timed for liftoff at the opening of the two-hour launch window Wednesday morning and includes an extra hour of hold time than previous counts.
This extra time was inserted into the countdown hold at the T- six-hour 40-minute mark, which is now three and a half hours in duration. This added time is to account for the now-longer, nominal fueling process while still permitting teams time to work through and troubleshoot any issues that occur.
Overall, teams largely have the entirety of the 120-minute window available to them, with Charlie Blackwell-Thompson noting on Nov. 13 that as of that time there were 56 known cutouts in the window for collision avoidance with other spacecraft in orbit. Most of those cutouts are a few seconds in duration, with a few that are a couple of minutes long.
Launch teams will receive the final cutout list and timings on Tuesday, Nov. 15.
After resuming the count, fueling operations will continue for several hours, with the next standard, pre-planned hold point being 30 minutes in duration at the T-10 minute mark. This hold can be extended beyond 30 minutes if needed if teams are running behind schedule.
This is the last hold point for SLS before entering the terminal count. After this point, there are limited hold options available due to the complex sequencing for the final readiness of the vehicle for launch.
From T-10 minutes down to T-6 minutes, an issue requiring a hold would result in holding at T-6 minutes. The count can be held here for the duration of the window as this is just before the Core Stage pressurizes for flight.
From T-6 minutes to T-1 minute and 30 seconds, the count can be held at specific points for up to three minutes as the Core Stage has already pressurized for flight. Any hold longer than that in this timeframe would result in a recycle to T-10 minutes before trying again depending on the reason for the hold and the amount of launch window remaining.
An issue between T-1 minute 30 seconds and T-33 seconds would be an automatic cutoff and recycle to T-10 minutes, with evaluations on the issue and remaining window factoring into whether another attempt that same day would be possible.
After T-33 seconds, only a cutoff followed by a recycle to T-10 minutes and a mandatory scrub for the day is available. This is because the Ground Launch Sequencer hands off control of the countdown to the Automatic Launch Sequencer (ALS — SLS’s onboard flight computers) at this point, and the vehicle switches to flight mode.
To undo flight mode completely and reset everything, the SLS rocket has to be drained of its propellants, thus mandating a scrub for the day.
If everything goes to plan, the staggered start sequence of the four RS-25 engines will be commanded by the on-board flight computers at T-6.36 seconds, with each engine starting 120 milliseconds apart to ensure that acoustic energy levels around the vehicle, as well as engine start transients, stay within vehicle limits.
It will take each RS-25 approximately three seconds to arrive at 90% of rated thrust, at which point health checks will begin. If all engines and systems onboard the rocket are functioning nominally, the command to ignite the Solid Rocket Boosters (SRBs) and disconnect the T0 umbilicals will be sent as the countdown reaches zero.
Once ignited, the SRBs commit the vehicle to flight as there is nothing but its own mass holding it down to the launch pad. There are no hold-down bolts or mechanisms on the SLS.
After rising vertically for about seven seconds, SLS’s computers will command the engines and boosters to gimble their thrust vector control systems (TVCs) to roll, pitch, and yaw the vehicle onto the proper azimuth, or compass heading, needed to obtain the correct initial Earth parking orbit to set up for the trans-lunar injection (TLI) burn.
Because the Moon is constantly moving in its orbit, the launch site is moving due to Earth’s rotation, and the inclination between the two changes by the second, the exact compass heading SLS will fly is entirely dependent on the exact second it lifts off. The flight computers will automatically account for this and roll the vehicle onto the proper heading without input from controllers based on the actual day-of liftoff time.
For the Nov. 16 attempt, SLS has an overall azimuth range that begins at 70.1 degrees at the opening of the window at 1:04 AM EST (06:04 UTC), arcing more easterly to an 88.6-degree azimuth at window close at 3:04 AM EST (08:04 UTC).
At window open, the initial Earth parking orbit would be inclined 34.0 degrees to the equator while the initial inclination at window close would be 28.5 degrees.
As SLS and Orion accelerate toward space, the stack will reach max-q, the moment of maximum stress on the rocket, at T+1 minute and 10 seconds as the vehicle climbs through 12.9 km (42,500 feet) and accelerates through 447 meters per second (1,000 mph).
At approximately T+2 minutes and 12 seconds, the twin five-segment SRBs will separate from the Core Stage. Under a nominal mission profile, SLS will be traveling around 1,417 meters per second (3,170 mph) while being 48.1 km (158,000 feet) in altitude.
Approximately one minute later, with the vehicle now flying above the majority of Earth’s atmosphere, the aerodynamic elements protecting Orion can safely be jettisoned.
The three fairing panels surrounding the European Service Module (ESM) will separate at T+3 minutes and 13 seconds, followed by the Launch Abort System (LAS) at T+3 minutes and 19 seconds.
The timing of these events, especially those later in the mission, is approximated based on predicted vehicle performance. The changing trajectory options, based on when in the window that liftoff occurs, can also slightly affect the timing of staging events and burn times.
The core stage will continue to power the ascent for several more minutes, targeting an unstable 30 x 1805 km orbit. The 30 km perigee, while above the Earth’s surface, is well within the atmosphere. This trajectory ensures that the Core Stage safely reenters during its first orbit, breaking apart over a designated area of the Pacific Ocean. The 1805 km apogee gives the combined ICPS and Orion stack enough energy to, with two burns, reach the Moon.
After Main Engine Cutoff (MECO) at T+8 minutes and four seconds, the ICPS and Orion stack will separate from the core stage at T+8 minutes and 16 seconds. For ICPS and Orion to avoid the same fate as the core stage, the stack will coast up to apogee before performing the first of two ICPS burns. This perigee raise burn will increase the perigee to 185 km.
During this coast phase, Orion’s four solar arrays will deploy, beginning about 18 minutes and 20 seconds after liftoff. Solar array deployment takes approximately 12 minutes.
The ICPS, itself a slightly modified Delta Cryogenic Second Stage (DCSS) from United Launch Alliance’s Delta IV rocket family, is powered by a single RL-10-B-2 engine. That engine will begin the perigee raise burn at T+ 51 minutes and 22 seconds, and the engine will shut down 22 seconds later.
Following another coast phase for ICPS and Orion until perigee, the Trans-Lunar Injection (TLI) burn will occur. This maneuver raises the orbital apogee out to the Moon, allowing Orion to later insert itself into the desired Distant Retrograde Orbit. This second ICPS burn begins at T+1 hour and 37 minutes and lasts approximately 18 minutes.
Orion will separate from ICPS at T+ 2 hours, 6 minutes, and 10 seconds. Shortly after, and T+ 2 hours, 7 minutes, and 31 seconds, Orion’s thrusters will fire briefly to distance the spacecraft from ICPS.
With Orion delivered to its Trans-Lunar trajectory, ICPS conducts one final burn at T+ 3 and a half hours to safely dispose of itself into a heliocentric orbit.
Orion’s next maneuver will not occur until almost six hours later when the service module’s main engine ignites for a planned Outbound Trajectory Correction-1 burn. After a nominal liftoff, ascent, and a handful of on-orbit maneuvers, Orion will coast for a few days before Artemis I action resumes at the moon on flight day six.
(Lead photo: SLS stands at LC-39B before launch. Credit: Jack Beyer for NSF)
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