NASA successfully test fires Space Launch System mega rocket
A view of the first Space Launch System hot fire test on Jan. 16, 2021. The second hot fire test occurred March 18 and saw the vehicle successfully complete a full-duration burn. Credit: NASA
The second time was the charm for NASA’s Space Launch System core stage as the agency successfully performed a full-duration firing of all four RS-25 engines at the base of the rocket, the final evaluation in vehicle’s Green Run test campaign.
The test took place at 4:37 p.m. EDT (20:37 UTC) March 18, 2021, at the B-2 Test Stand at NASA’s Stennis Space Center in Mississippi about two months after the first attempt ended with a computer-initiated shutdown of all four Aerojet Rocketdyne RS-25 engines just about a minute after ignition.
At 212 feet (65 meters) tall and 27 feet (8.5 meter) wide, the Space Launch System core stage is the backbone of NASA’s ambitions to send humans beyond low Earth orbit later this decade. Fully stacked with Orion, its launch abort system and an Interim Cryogenic Propulsion Stage, the full rocket stands about 321 feet (98 meters).
Inside the core stage are tanks for two propellants, liquid oxygen and liquid hydrogen. Together these will be consumed by the RS-25 engines to produce about 1.6 million pounds (about 7,440 kilonewtons) of thrust.
Add the twin five-segment solid rocket boosters and the full liftoff thrust of the SLS is expected to be some 8.4 million pounds (nearly 40,000 kilonewtons).
An infographic on the Space Launch System and how it compares to the space shuttle external tank. Credit: Derek Richardson / Spaceflight Insider / Orbital Velocity
For today’s Green Run hot fire test, the two hour window opened at 3 p.m. EDT (19:00 UTC). However, ignition of the four RS-25 engines didn’t come until 4:37 p.m. EDT (20:37 UTC). The reason for the postponement into the window is not known.
Overall, the test is designed to simulate the exact duration and flight profile the legacy shuttle engines are expected to perform on their 8-minute flight toward space. The engines ignited nominally followed by gimbal movement approximately one minute later.
From there, the engines were throttled down to simulate the vehicle entering the area of maximum aerodynamic pressure known as “Max-Q.” They were then throttled back up to rated performance. Just over 8 minutes into the burn, the engines were powered down to simulate MECO, or main engine cutoff.
While data is still being gathered after today’s full-duration test, it appeared visually to be successful, especially compared to the first attempt in mid-January, which was cut short after only about a minute after engine ignition.
Part of the test parameters associated with the hot fire included the gimbaling, or movement, of the four RS-25 engines as to direct their thrust in order to steer the giant SLS rocket during flight.
Each engine uses two actuators that generate the force to precisely control the pivoting of each engine contained within the thrust vector control system. These actuators are controlled by the core stage’s auxiliary power unit, or CAPU, which is an internal engine providing power for the vehicle’s systems, including the RS-25’s hydraulic system.
Video courtesy of Orbital Velocity
During the previously aborted test attempt on Jan. 16, which shut down just over one minute into the planned 8-minute firing, the CAPU’s hydraulic system associated with engine No. 2 exceeded the overly-conservative testing limits that were pre programmed before the test. This exceedance caused the onboard computers monitoring the test to shut down all four of the core stage engines in an abundance of caution in an attempt to protect the vehicle.
In addition to the anomaly experienced with engine No. 2, a faulty electrical harness in the No. 4 engine resulting in a false detection of a major component malfunction. The electrical harness was replaced before this test.
NASA recently completed stacking the twin solid-rocket boosters that are expected to fly on the first Space Launch System flight, Artemis 1, to send an uncrewed Orion spacecraft toward the Moon for a month-long flight.
The completion of SRB stacking has given NASA a timeline of about a year to launch the first SLS rocket. In order to meet this timeline, NASA will have to expedite the shipping process of the SLS core stage from its current home in Mississippi, to the launch site at Kennedy Space Center in Florida.
Publicly, NASA is still targeting no earlier than November 2021 for Artemis 1. However it is getting increasingly more likely the flight could take place within the first couple months of 2022.
Video courtesy of SciNews
Cullen Desforges
Having a life-long interest in crewed space flight, Desforges’ passion materialized on a family vacation in 1999 when he was able see the launch of Space Shuttle Discovery on STS-96. Since then, Desforges has been an enthusiast of space exploration efforts. He lived in Orlando, Florida for a year, during which time he had the opportunity to witness the flights of the historic CRS-4 and EFT-1 missions in person at Cape Canaveral. He earned his Private Pilot Certificate in 2017, holds a degree in Aviation Management, and currently works as an Operations Analyst in the aviation industry in Georgia.
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