The success or failure of a rocket launch is typically judged by a single, definitive outcome.

Reaching orbit signifies success; falling short denotes failure.

For launch missions, this criterion is unquestionable. On April 3, the Tianlong-3 Yao-1 mission was aborted after 189.5 seconds, leaving the mission unfinished. Subsequently, Space Pioneer initiated a technical investigation, known as "zeroing," to identify the cause.

The root cause of the failure has now been determined. During flight, liquid oxygen was inadvertently directed toward the rocket's base, causing secondary combustion of the first-stage engine's turbine exhaust gases. This led to ablation and deformation of the base thermal protection skirt's connection structure, allowing high-temperature engine gases to infiltrate the first-stage tail compartment. This ignited a fire internally, resulting in abnormal flight behavior.

This marked a clear failure of the inaugural flight.

However, for a newly developed large liquid rocket, the 189.5 seconds of flight also unveiled several key achievements.

At 110 seconds, the rocket experienced maximum dynamic pressure, reaching its design threshold;

At 177.2 seconds, the first stage completed all programmed flight maneuvers;

At 182.2 seconds, the first and second stages separated as planned;

At 185.9 seconds, the second-stage engine ignited successfully.

In essence, prior to the mission's termination, Tianlong-3 had successfully navigated the maximum dynamic pressure zone, completed first-stage flight, stage separation, and second-stage ignition—a sequence of critical events. Technologies previously validated through calculations, simulations, and ground tests were, for the first time, subjected to the real-world flight environment of the complete rocket, generating operational data under actual conditions.

Following the completion of the zeroing process, the cause of the failure is now clear. Despite the incomplete mission, these 189.5 seconds of flight hold substantial value.

Pushing the Boundaries

Tianlong-3 stands at a towering 72 meters with a diameter of 3.8 meters, resulting in a slenderness ratio of approximately 19—a notably elongated design.

To enhance payload capacity, large liquid rockets require increased propellant. However, the rocket's diameter is constrained by factors such as engine layout, manufacturing capabilities, transportation logistics, and ground facility limitations. Increasing propellant load within a fixed diameter often necessitates extending the rocket's length.

Tianlong-3 achieves a 600-ton takeoff weight and a maximum low-Earth orbit payload capacity of 22 tons within a 3.8-meter diameter, pushing the slenderness ratio to about 19.

The Long March 12B serves as a comparative example. It stands roughly 72 meters tall but has a diameter of 4.37 meters, maintaining a slenderness ratio of around 16. Its development team has publicly stated that excessive slenderness imposes stricter wind load requirements, lower natural frequencies, and higher structural stiffness demands.

Thus, a slenderness ratio of 19 represents a trade-off to increase propellant load and payload capacity within the 3.8-meter diameter constraint, albeit at the expense of greater structural and control challenges.

The maximum dynamic pressure zone posed a critical test.

Yao-1 reached its design maximum dynamic pressure at 110 seconds, continued flying, and completed all first-stage flight sequences. Once in actual flight, aerodynamic loads, structural elasticity, and control responses began interacting simultaneously, subjecting the design models to real-world validation for the first time.

Between design and reality lies the true test.

Carl von Clausewitz once described war through the concept of "friction," where simple actions on paper become influenced by countless minor factors once executed in the real world.

The same principle applies to large rockets. As countless components integrate into a single vehicle, each system faces real aerodynamic, load, vibration, and thermal environments in their complete state for the first time during high-speed atmospheric transit.

Yao-1's passage through the maximum dynamic pressure zone also provided the first batch of real flight data for Tianlong-3's slender structure and stability control.

Flight as a Testimony

Tianlong-3 incorporated numerous innovative technical solutions. Although the mission was incomplete, multiple key technologies underwent real flight validation before the 189.5-second mark, yielding corresponding data.

Liquid nitrogen vaporization pressurization is one such example.

During liquid rocket flight, propellant continuously flows from tanks to engines, necessitating sustained tank pressure maintenance. Traditional methods typically use high-pressure helium for pressurization, but helium is costly and requires heavy, space-consuming high-pressure gas cylinders and piping.

Tianlong-3 opted to carry liquid nitrogen, which vaporizes into nitrogen gas during flight to pressurize both the liquid oxygen and kerosene tanks. This addresses the issues of excessive weight, cost, and complexity in large liquid rocket pressurization systems. For commercial rockets, such improvements are practical—a lighter, simpler system reduces subsequent manufacturing and mass production burdens.

The same principle applies to separation technology.

Traditional rockets rely heavily on pyrotechnics for unlocking and separation, offering crisp, reliable action but with significant shock, limiting pre-launch testing and reusability. Tianlong-3 adopted non-pyrotechnic separation technology to reduce separation shock, improve system detectability, and enable future reusability.

At 182.2 seconds, the first and second stages separated normally; 3.7 seconds later, the second-stage engine ignited successfully. This confirmed that the critical sequence of first-stage flight, stage separation, and second-stage ignition functioned as intended during actual flight.

The Long March 12B, which successfully debuted in June this year, similarly employs nine-engine clustering, single-layer common-bulkhead tanks, and pneumatic stage separation. The technical overlaps between these two 20-ton-class large liquid rockets indicate that these designs are being adopted across models to address high payload capacity, lightweighting, and cost reduction.

Gas-injected accumulators address a more subtle issue.

During flight, rocket structures vibrate, and propellant flow in piping generates pressure fluctuations. If these couple at certain frequencies, they can severely impact engine and onboard equipment operation.

Traditional bellows-type accumulators can buffer pressure fluctuations but are bulky and complex to manufacture. Tianlong-3 uses gas-injected accumulators to suppress longitudinal coupled vibration by dynamically adjusting piping system flexibility, saving onboard space and simplifying system structure.

The engines also warrant separate discussion.

Although Yao-1 ultimately saw four first-stage engines shut down sequentially, the zeroing results confirmed that this was not due to engine failures.

The Tianhuo-12 engine delivers 95 tons of sea-level thrust and 110 tons of vacuum thrust. With hundred-ton-class engines becoming more common, thrust alone is no longer sufficient—thrust-to-weight ratio has emerged as a key metric for engine lightweighting. Simply put, it measures how much thrust an engine generates relative to its own weight.

The Tianhuo-12 achieves a thrust-to-weight ratio of 163. Based on currently available public data, this ranks among the highest for domestic flown liquid oxygen-kerosene engines. For a hundred-ton-class engine, achieving high thrust while minimizing weight directly contributes to payload efficiency. Flight data from Yao-1 confirmed normal engine operation and stable system performance.

Additionally, Tianlong-3's common-bulkhead tanks feature unique characteristics. They employ a large-temperature-differential single-layer common-bulkhead design, with a 220°C temperature difference between the upper and lower sections, reducing tank weight by 10%.

A common-bulkhead tank shares a single structural base between two propellant tanks, improving structural efficiency by eliminating a layer. However, the significant temperature difference between liquid oxygen and kerosene increases thermal insulation and structural design challenges.

The value of Yao-1 lies in enabling these technologies to enter real flight environments as part of the complete rocket for the first time, experiencing acceleration, vibration, aerodynamic loads, propellant consumption, and operational changes while yielding a batch of real flight data irreplaceable by ground testing.

However, subsequent phases such as payload separation, extended second-stage operation, and final orbital insertion remain to be validated in future flights.

Systemic Challenges

The reliability of large rockets never results from simply combining normally functioning individual components.

Engines undergo repeated hot-fire tests, tanks undergo pressure and structural testing, and control systems undergo extensive simulation. However, once the complete rocket ascends, aerodynamics, heat, structure, propulsion, and control interact simultaneously, with previously studied systems beginning to influence one another.

Tianlong-3 Yao-1 illustrated this point. The zeroing process revealed not an issue with an individual component operating independently but coupling effects between different systems in the real flight environment. Particularly complex was the tail compartment flow field under nine-engine clustering conditions, which proved more intricate than ground tests could fully replicate.

Ground testing can approach real conditions but struggles to fully replicate the interactions between systems during actual flight. Maiden flights thus retain irreplaceable value—sometimes validating designs, other times revealing previously unrecognized boundaries.

Zeroing involves reconstructing this chain of events.

Space Pioneer first retraced telemetry data, conducting systematic reviews alongside product acceptance records, test launch data, and rocket flight status. They then used simulation calculations and fault tracing to locate the cause, followed by fault reproduction to verify the failure mode and mechanism. Subsequent verification tests focused on the improved technical state. Thermal test firings of the improved engines lasted approximately 200 seconds, covering and exceeding the normal first-stage flight duration, with the thermal protection structure remaining intact afterward.

Ultimately, the zeroing expert panel concluded that the problem was accurately located, the mechanism clear, fault reproduction completed, improvement measures effective, and lessons thoroughly learned, allowing zeroing to proceed.

The key here is "reproduction."

Proposing a logically sound explanation for an accident is not difficult. Aerospace zeroing requires the same physical processes to recur in testing, with test phenomena matching flight data, followed by validation of improvement measures.

It confronts the physical world and ultimately relies on testing for answers.

Moving Forward

In the months following Tianlong-3's maiden flight, China's large liquid rocket development has continued to advance rapidly.

In June, the Long March 12B completed its maiden flight, successfully validating 20-ton payload capacity, nine-engine clustering, pneumatic stage separation, and common-bulkhead tanks. In July, the Long March 10B achieved orbit on its maiden flight and completed China's first controlled recovery of a launch vehicle's first stage. In August, the Zhurong-3 Yao-2 achieved China's first controlled land-based recovery of a first stage using landing legs.

The industry has not paused, and Tianlong-3 must now meet higher standards.

As large commercial rockets proliferate, the novelty of individual technologies quickly gets overshadowed by new models. New structures, propulsion solutions, and separation methods must ultimately translate into reliable flight and stable delivery. Customers purchase definitive orbital transportation services, and technological innovation must ultimately serve this goal.

Tianlong-3 Yao-1 has undergone its first round of real flight evaluation. The extensive real flight data from 189.5 seconds forms the most valuable foundation for subsequent development; previously underestimated systemic coupling issues have undergone zeroing, reproduction, and improvement validation.

This is the significance of those 189.5 seconds.

There is no need to romanticize the maiden flight failure, nor should the value of those 189.5 seconds be erased.

For Tianlong-3, the meaning of zeroing ultimately rests on the next flight. Currently, Yao-2 has completed final assembly and testing, with a return to flight expected in the fourth quarter of this year.

Yao-1 remains frozen at 189.5 seconds.

Yao-2's mission is to carry these data forward and continue flying from there.