Huturoa aerospace accident

The M53 Test Campaign Incident, popularly known as the Huturoa Aerospace Accident is an accident that happened in the Empire of Fegeland at the Huturoa Space Center (HSC) on December 2, 2052, when a prototype M53 missile was launched. It caused the partial destruction of the Huturoa Space Center, the University of Huturoa and many minor damage to other infrastructure and the environment. The accident killed 67 people, most of them at the University of Huturoa, and more than 150 wounded to varying degrees. It is due to a structural defect of the first stage of the M53.

Circumstances

The M53 missile

The M53 missile is a long-range ballistic missile. It was developed as a replacement for the aging M52 missile, which had become incompatible with some of the CFS convention technologies. Its construction and development is the result of a national defense contract between the Fegeland Air Force and FAITO Aerospace. The M53 consists of 3 stages: a first liftoff stage, a second orbital injection stage, and a third stage for the tactical strike, carrying several offensive charges.

Structural analysis of the first stage

The first stage is identical to the first stage of the M52, with the exception of improved propulsion to cope with the significant increase in mass between the M52 and the M53 (in particular the M52 had only two stages). The propulsion is provided by a FTX-8 Vector engine developed by FAITO Aerospace, with a power of 800 kN at ambient pressure. This engine allows increased maneuverability thanks to its significant gimbal range (+ 15 ° to -15 ° in each direction). The main structure of the stage contains a liquid fuel tank and an oxydizer tank (Ox) located above the previous one. These tanks are cylindrically shaped, but their ends are hemispherical to withstand the important internal pressure stresses caused by the fuel. The rigidity of the structure is ensured by the sides of the tanks. This leaves a zone of weakness at the junction of the two tanks, where their hemispherical parts does not strengthen the outer side.

In order to reinforce this part, the first stage of the M52 has S255NL steel longitudinal spars placed between the two tanks, along the outer side. These longitudinal spars provide the compressive strength of the inter-tank junction (avoiding the problems of buckling of the outer side encountered for example on the M40 and M41), but their bending strength is much lower. This was not a problem on the M52, which had a less powerful engine and especially less steerable. But with the new Vector motor, the stresses exerted on these spars during thrusts with a high gimbal were at the limit of their resistance.

Their replacement would have required the development of a new and more resistant stage, which was refused for budgetary reasons, the program being financed 75% by the Ministry of Defense via the FAF, and 25% by private funding from FAITO Aerospace. The Ministry refused to extend the requested budget, as the program has already suffered several budget overruns. It was thus decided to reuse the M52 stage on the M53, and the problem of the spars was forgotten.

Weather conditions

On launch day (December 2, 2052), a large tropical storm was raging on the Feguan Sea, moving north under the influence of the algizan anticyclone. The storm reached Huturoa around 5am, but, with moderate winds remaining, it was decided to maintain the launch, which had already been postponed three times due to delays and technical problems. The winds in the center of the storm reached 250 km/h in gusts, against 80 km/h in the periphery. Weather forecasts by the Space Center predicted that the storm would depart west of Huturoa towards the NMC. Contrary to forecasts, the storm continued its course towards the North, becoming even stronger in contact with the warm waters of the Huturoa lagoon, and hit Huturoa hard at around 7am when the launching procedure had already begun. Extremely powerful bursts were recorded at the Space Center, with winds reaching 257 km/h.

Accident

Events

The launch, initially planned for 8:43 AM was advanced to 7:19AM due to the income of a tropical storm over the Hahuai'ian archipelago and Huturoa island. Launching sequence proceeded as planned, and the XRC-M53 'Atea' lifted off from the Pad 4 at 7:21 AM. The rocked behaved as expected during the first minutes of flight. But at MT+3:45 the onboard computer reported lateral winds over 70 m/s, and started a trajectory correction. At MT+3:57, the rocket was still in the high wind zone, being laterally pushed at 42 m/s. At MT+4:09 the computer reported a gust over 80 m/s. The rocket tilt brutally increased to +43°. As a result, the computer proceeded to a correction, pushing the engine to it's gimbal limit.

At MT+4:11 the engine reached the gimbal limit while the tilt was still increasing dangerously. At MT+4:16 the computer required 100% throttle to perform the trajectory correction. This resulted in an extreme effort on the truss structure. At MT+4:26, an alarm indicating the loss of control of the upper control surface was triggered.

At this time, the rocket was reaching an altitude of 5500m and was still above the HSC installations. Suddenly, at MT+4:27, a fire alarm was triggered. The control screens showed that a large and intense flame was coming out of the middle of the first stage. As the flame was growing rapidly, ground witnesses reported that "the upper side of the rocket was burning". Fire particles were seen falling from the rocket. Ground control at HSC lost control a few seconds later. At MT+4:45, the rocket seemed to broke in two parts, the truss structure of the first stage melted by the flame. This was immediately followed by the explosion of the lower part of the first stage. Ground witnesses reported "a great boom and a big light in the sky". The detonation were heard all around Huturoa island. The upper first stage part, the second stage and the third stage broke into several parts.

Many burning debris then started to fall on the trajectory of the rocket. The oxidizer tank of the first stage crashed into a fuel preparation facility of the HSC, setting fire to the whole facility and nearby fuel cisterns. Burning parts of the second stage crashed into the free lands around the space center. But even worse, several large parts of the third stage crashed in the nearby city of Kahelau. Some of them crashed into the streets, but 3 hit houses and one crashed into the Huturoa Institute of Technology.

Mechanical weakness leading to the accident

The first stage of the XRC-M53 is a M52 first stage reinforced by steel spars in the truss structure separating the Ox. and Lq. fuel tanks. The engine have been upgraded to a more powerful version able to lift the additional mass added by the M53's thrid stage. To add maneuverability, 4 control surfaces have been added at the bottom of the first stage. Although the structure of this first stage was initially designed to endure lateral accelerations up to 20 m/s² and a max. bending moment of 65KN, it was known that the new engine was able to reach a little bit more due to it's max thrust of 800KN and max gimbal angle of 15° (resulting in a bending moment around 69KN). Therefore, due to financial restrictions, no changes were made. Engineers assumed that the first stage would never have to face such a bending moment in real conditions. In laymans terms, the rocket wasn't designed to resist to the lateral force generated by the engine at max thrust and max gimbal angle.

Kerbal and material losses

67 died into the accident, 11 technicians and engineers in the fuel facility, 5 into their houses, and 51 in the Institute. More than 150 were injured , some severely.