【Author/Observer Net Columnist, Liusunyan】
On June 26, Northrop Grumman conducted the "Demonstration Motor-1" (DM-1) ground test of its "Booster Obsolescence and Life Extension" (BOLE) booster. This was the second-largest solid rocket engine ignition experiment in human history, planned to ignite for 140 seconds at the Promontory Production and Test Site in Utah, USA.
Northrop Grumman set up 763 measurement points on the BOLE booster to monitor engine performance and installed a carbon dioxide extinguishing system to ensure safety after shutdown, preventing residual propellant from igniting the test stand. However, despite extensive preparations, an anomaly occurred near shutdown.
According to the test results, 101 seconds after ignition, the throat area on the top of the BOLE booster was burned through, releasing flames. Almost simultaneously, when the ground reported "110 seconds of ignition," the nozzle of the BOLE broke and flew off, while the engine continued to burn until all the solid propellant was consumed.
The moment the BOLE nozzle collapsed
BOLE is intended to replace the current five-segment reusable solid rocket motor (RSRMV) used in the Space Launch System (SLS). The RSRMV itself is inherited from the Space Shuttle's Reusable Solid Rocket Motor (RSRM), using relatively old steel casings and TP-H1148 polybutadiene acrylonitrile solid propellant.
Currently, the SLS still uses solid rocket boosters from the Space Shuttle era, but it does not plan to recover these casings; the remaining casings will support the rocket's eighth flight mission. BOLE will be added to the SLS starting with the ninth mission to form the Block 2 version of the rocket.
To achieve this goal, BOLE uses advanced T1100 carbon fiber casings and hydroxyl-terminated polybutadiene solid propellant, producing over 1800 tons of ground thrust, increasing specific impulse by 3.9% and total impulse by 11%, which can increase the SLS' lunar orbit payload capacity to more than 46 tons.
Segments of the BOLE booster in the factory
Although BOLE is planned to use high-performance T1100 carbon fiber casings, the casing of the "Demonstration Motor-1" used slightly inferior IM7/T300 carbon fiber, which will be replaced with T1100 later. The front and rear heads of the BOLE booster still use steel structures because NASA wants to maintain some margin. BOLE optimized the grain shape to reduce the maximum dynamic pressure of the rocket and improved aerodynamic conditions, redesigned the separation mechanism, and modified the direction of booster separation.
In addition, BOLE uses electro-hydraulic servo systems instead of the hydraulic servos of RSRMV to reduce weight and complexity. The larger thrust increased the nozzle diameter of BOLE from 3.9 meters of RSRMV to 4.4 meters, and Northrop Grumman developed a nozzle made of brown glass phenolic composite material for this purpose.
This test was one of two ground tests for BOLE. Northrop Grumman specifically reduced the temperature of the solid propellant to 15 degrees Celsius to evaluate its response under environmental conditions. Subsequent tests will also assess BOLE's performance under cold and hot environments.
The separation direction of BOLE will be more similar to "Titan-4"
Jim Carlbauer, Vice President of Northrop Grumman's propulsion systems, said: "The test today pushed the limits of large solid rocket engine design to meet strict performance requirements. Although the engine performed well under harsh combustion conditions, we observed an anomaly as the two-minute combustion was about to end. As a completely new design and the largest segmented solid rocket booster ever built, this test provided us with valuable data to continuously iterate and improve our future designs."
The first segment of BOLE booster launched in the first half of 2024
However, this was not the first anomaly for this type of solid rocket engine.
On May 29, 2019, Northrop Grumman conducted a ground test of the Castor-600 solid rocket engine, which was part of the mid-sized configuration of the OmegA launch vehicle competing for the "National Security Space Launch" program. At the end of the test, the nozzle also ruptured and fell off. The reason was different between the ground test and actual flight environment. When the solid rocket engine approached shutdown, the thrust dropped rapidly, and the nozzle pressure also decreased accordingly. As the Castor-600 engine approached shutdown, the nozzle pressure quickly dropped below one atmosphere, causing external atmospheric pressure to crush the nozzle inward.
In actual flight, since the rocket had already reached tens of kilometers in altitude at shutdown, the thin external air pressure was not enough to burst the nozzle, so it was not a major issue. However, Northrop Grumman made improvements based on the situation. In the 2020 test of the second-stage Castor-300 engine, the nozzle did not have any problems, proving the rationality of the improvement plan.
Ground ignition test of OmegA's first stage Castor-600
After the 2019 OmegA rocket's first stage Castor-600 test, the nozzle ruptured
Successful 2020 OmegA rocket second stage Castor-300 test
In 2021, NASA awarded the BOLE contract to Northrop Grumman. Since both the Omega-I/H common core stage (CBS) and BOLE use composite casings, their technologies come from NASA's "Fiber-Wound Casing" (FWC) developed in the 1980s. Technologies such as the new flexible sealing system, high nozzle efficiency contour, composite nozzles, and electro-hydraulic actuation systems developed for the OmegA rocket can be directly applied to BOLE, reducing development risks.
However, in 2022, the OmegA rocket was abandoned by Northrop Grumman, but BOLE was not greatly affected and continued to proceed based on the technology developed for OmegA, so BOLE can also be seen as a larger version of the OmegA CBS.
FWC at the ground test site
The OmegA's electro-hydraulic actuator uses a modular design, and BOLE has a larger hydraulic cylinder
However, during this test, BOLE experienced nozzle burn-through, leakage, and rupture, which is different from the direct rupture of Castor-600 due to ground environment reasons a few years ago.
Northrop Grumman recently also had an anomaly with a solid rocket engine nozzle, which occurred during the second certification flight (Cert-2) of the United Launch Alliance's Vulcan-Centaur rocket in October 2024.
The Vulcan-Centaur rocket uses Northrop Grumman's GEM-63XLT solid rocket boosters. However, within 37 seconds of the start of the Cert-2 mission, the nozzle of one of the GEM-63XLT boosters completely ruptured and fell off. Although the problem was compensated by extending the working time of the first stage by 8 seconds, this anomaly delayed the process of the rocket obtaining military space launch certification.
The problem came from a manufacturing defect in the insulation layer of the GEM-63XLT solid rocket engine, leading to the detachment of the rear head of the solid rocket. United Launch Alliance and Northrop Grumman retrieved the problematic booster, identified the manufacturing defect, and corrected the issue in the ignition test in February 2025.
Currently, there are some reports that the damage to the tail section of BOLE is quite severe. If the Space Launch System rocket experiences such a problem during the power segment of the Orion spacecraft, it would directly trigger the flight termination system.
Nozzle of GEM-63XLT that fell off during the Cert-2 mission
However, although this problem is significant, it will not affect the U.S. plan to return to the moon. The main reason is that the production volume of the Space Launch System is too low. Boeing can only maintain a delivery rate of one Space Launch System every two years. Therefore, the first Block 1B version rocket for the Artemis-4 mission will not be ready until after 2028, and after completing eight Block 1/1B versions, it will be as late as 2040. Currently, the second Space Launch System launch for the Artemis-2 crewed lunar orbit mission is scheduled for February 2026, and the progress is in line with expectations.
Another point to note is that although Russell Watt, the director of the Office of Management and Budget under Trump, who is an environmental conspiracy theorist, proposed a budget plan to completely cancel the Space Launch System and the lunar orbit space station "Lunar Gateway," if this project were to be canceled, it would be equivalent to a political suicide worth millions of dollars in several districts like Alabama. Therefore, it seems unlikely that this project will be canceled.
The plan to return to the moon is not in a hurry to use BOLE, but another accident during the Safety Production Month could be more serious.
Earlier on June 18, Central Daylight Time in the United States, at 23:01:55, the Starship No. 36 (later called SN-36) at SpaceX's "Star City" research base in Boca Chica was suddenly destroyed by a massive explosion, destroying the already fueled SN-36 and igniting a fire at the launch site.
Subsequently, we can see that there were more than one explosion, which can be considered as the largest ground accident in the development history of the Starship-Super Heavy heavy-lift rocket.
Since the Starship spacecraft will serve as the foundation and key part of the Human Landing System (HLS) for the Artemis-3 mission, any delay in the Starship spacecraft may affect the schedule for returning to the moon. Moreover, the spacecraft has already experienced more than half a year of delays.
Explosion of the Starship SN-36 at the梅西试验场
At the time of the explosion, SN-36 had already completed the fueling for static firing and was possibly preparing to pressurize the pressurization bottles. According to some videos released by NSF, SN-36 first experienced a collapse at the top of the payload compartment, with a large amount of gas being expelled. Then, the regenerative cooling thermal protection device at the bottom of the payload compartment disintegrated, and the methane tank of SN-36 exploded within 1 second, with the liquid oxygen tank at the bottom still intact at the time of the explosion.
Thirteen seconds after the methane tank exploded, the liquid oxygen tank also exploded, completely destroying the entire spacecraft. A long carbon fiber pressure vessel could be seen flying into the air. About 30 seconds after the explosion of the liquid oxygen tank, a smaller fireball appeared on the left side, which might have been caused by the ignition of ground facilities. The fire burned for more than an hour before being extinguished.
This explosion was likely caused by a failure in the gas bottle located at the head of SN-36, which had many ambient temperature gas bottles. Musk later stated that it was a failure of a nitrogen high-pressure gas bottle under ambient temperature conditions and referred to it as a "small problem."
Fire scene at the梅西试验场 after the explosion
Although it looks like a quality issue, according to some subsequent footage, it may have been a problem with the new technology.
Among the debris found, multiple Luxfer G-Stor™ GO carbon fiber-wrapped gas bottles were discovered, and the inner bladder seemed to be nylon. Compared to traditional III-type composite gas bottles that use aluminum alloy or titanium alloy as the inner bladder, IV-type gas bottles with composite inner bladders can reduce the mass by more than half.
For the currently overweight "Starship-Super Heavy" heavy-lift rocket, weight reduction is urgently needed, but stainless steel tanks are difficult to reduce. Therefore, SpaceX decided to put this gas bottle into flight directly, and given their habits, they probably gave less margin than usual. In a more positive light, it can be said that they are sufficiently confident, but whether this so-called "boldness" led to the destruction of SN-36 is just a possibility, and it cannot be concluded yet.
A composite gas bottle that was photographed, with a neat crack, seems to indicate that it might be the culprit
The SN-36 spacecraft that exploded was the fourth v2 status "Starship" spacecraft. Compared to the v1 status, the v2 increased the amount of propellant that the spacecraft could carry, added a new payload compartment for deploying Starlink v3 satellites, and redesigned the head tank used for landing ignition (called the Header Tank). Compared to the v1 version, which had almost no usable payload capacity, the v2 version may have a payload capacity of 50 tons for deploying Starlink satellites. In addition, the v2 version of the "Starship" will be used to verify recovery-related technologies and is an important test and transition toward the v3 version of the "Starship" for lunar landing and on-orbit refueling.
However, the development of the v2 status "Starship" spacecraft has been very problematic, delaying it by more than half a year. Its first spacecraft, SN-33, as part of IFT-7, was launched in January 2025, but began experiencing faults 7 minutes and 39 seconds into the flight and completely lost data 8 minutes and 26 seconds into the flight.
The debris eventually fell in the skies over the Caribbean Islands, Puerto Rico, and the British Virgin Islands, but the falling point exceeded the safe range limit and caused air traffic disruptions for over an hour, resulting in a flight stoppage for inspection. The cause of the anomaly was that the vibration intensity generated during the flight of SN-33 far exceeded expectations, leading to methane leakage exceeding the capability of the fire suppression equipment, ultimately causing a fire in the engine compartment of SN-33.
During the IFT-8 test, the SN-34 spacecraft flew for 8 minutes and 4 seconds when one of the sea-level "Raptor 2" engines exploded, quickly destroying the surrounding two sea-level and one vacuum "Raptor 2" engines, directly causing the SN-34 spacecraft to start rolling and eventually being destroyed by the flight termination system.
Although SN-34 had similar issues to SN-33 at a similar time, the resonance problem in SN-33 had been resolved in SN-34. The problem with SN-34 was caused by a leak in the "Raptor 2" engine joint leading to propellant mixing and an explosion. The related issues have been resolved by modifying the joint prestress, adding nitrogen purging, and optimizing propellant management.
Potentially leaked internal pictures of the Starship SN-34, but some say it is AI-generated
However, the two complete failures brought some concerns. Internal sources at SpaceX indicated that the v2 design of the "Starship" had fundamental problems, requiring the scrapping of the already completed SN-35 spacecraft and rebuilding the tail section of SN-36. However, Musk strongly opposed scrapping SN-35, so engineers proposed alternative methods, including adjusting the speed of the "Raptor" engines to reduce resonance. Additionally, some engineers stated that the current Messi test site was unable to conduct full-scale testing of the "Starship," and the v3 version of the "Starship" with nine engines was even more impossible to conduct full-scale testing.
Finally, the SN-35 spacecraft was launched as part of IFT-9. This time, there was no explosion during the ascent phase, but there seemed to be a slight leak in the tail section of the spacecraft, and the vacuum Raptor engine might have had some erosion. After entering the glide phase, the tail section of SN-35 started to emit a lot of gas and soon lost attitude control, eventually tumbling into the atmosphere above the Indian Ocean and turning into a meteor.
The loss of control of SN-35 was due to propellant leakage, but the exact cause of the leakage has not yet been determined. Some reports suggest that one possible cause was that IFT-9 blocked part of the thermal separation ring interface to direct the "Super Heavy" booster, which may have increased the pressure on the tail section of SN-35 during separation and caused pipe leakage.
Possible minor leakage of SN-35
The development of the "Starship-Super Heavy" heavy-lift rocket has been delayed by nearly a year due to four anomalies in the "Starship" v2. Although SpaceX considered the impact of the explosion of the "Starship" spacecraft at the Messi test site and had a plan to repair and resume operations within two months.
On the evening of June 28, the support frame used to lift the "Starship" spacecraft had been lowered to the bottom of the orbital launch pad-A, indicating that SpaceX is trying to build a temporary test stand using the main launch pad to conduct static firing tests of the "Starship" spacecraft.
Other issues include whether to use the remaining two v2 "Starship" spacecraft to complete IFT-10 and IFT-11 tests, conducting multi-orbit gliding and tower connection tests, or directly moving to the v3 "Starship" SN-39 equipped with "Raptor 3." There is currently no conclusion.
On the night of June 27, the OLM-A support frame was lowered to near the ground
As Musk went to Washington to establish his government, the management of the "Star City" construction site seems to have encountered problems. Recently, an engineer on Reddit revealed that employees at "Star City" were stealing heat-resistant tiles to sell for money and even engaging in what was described as "playful" behavior of using the "Starship" spacecraft for toilet purposes. Such four different types of anomalies are certainly not normal for a company that possesses the world's strongest rocket technology.
Therefore, I believe that the shortcoming of the U.S. moon landing plan has already shifted from the "Space Launch System" to the "Starship-Super Heavy." Given that it is now mid-2025, and the "Artemis-3" moon landing is scheduled for 2027, it is necessary to verify orbital gliding, landing, on-orbit refueling, rapid reuse, large-scale turnover, and landing drills before then. If everything goes smoothly in the future, the problems won't be too big, but if something unexpected happens, it could be problematic. Also, the recent decline in Musk's influence may bring additional non-technical uncertainties, which should be noted.
This article is exclusive content from Observer Net. The content of the article is solely the personal opinion of the author and does not represent the views of the platform. Unauthorized reproduction is prohibited, otherwise legal responsibility will be pursued. Follow Observer Net WeChat account guanchacn to read interesting articles every day.
Original: https://www.toutiao.com/article/7521541737056043570/
Statement: This article represents the personal views of the author. Please express your opinion by clicking on the 【top/down】 buttons below.