HEAT-2X was originally scheduled for launch in August/September 2014. Sadly, during the full up static test of the engine the cooling jacket ruptured, fuel flooded the test stand and engulfed the entire engine section in flames. The damage is beyond repair and HEAT-2X and its engine has been retired to the CS museum. In the following you can read about the plans, the potential flight and the sad demise of HEAT-2X.
Original plans and system design
On the outside it will look much like its predecessor, HEAT-1X, but it is built upon completely different technology, and is a far more advanced rocket. Most importantly, it is the first CS rocket potentially capable of flying above the Kármán line (100 km) in a suborbital trajectory to space!
HEAT-2X will carry the 80 kg heavy TDS80 spacecraft to an apogee of about 100 km, which is commonly referred to as the boundary to space. The HEAT-2X/TDS80 mission serves as a technology demonstrator for several key technologies that CS must master before reaching our ultimate goal of sending a man on a suborbital spaceflight.
The HEAT-2X rocket is powered by the liquid propellant engine TM65LE which provides about 45,000 N thrust at lift off. It runs on liquid oxygen (LOX) and 75% ethanol in water. The engine will burn for 100 seconds and consume 1,200 kg of propellant during flight!
The HEAT-2X vehicle is built almost entirely in aluminum to minimize its mass. It has a projected lift off mass of 1,753 kg, of which 1,200 kg is propellant. It measures 65 cm in diameter, and stands 10.7 meters tall when fitted with the TDS80 prototype spacecraft. The propellants are fed to the engine by using high pressure propellant tanks at an initial pressure of 24 bar. The main structure and components are shown in the figure below.
The vehicle consists of a great number of structural components. The most noteable are:
- TDS80 spacecraft: The spacecraft is equipped with its own radio and inertial navigation systems, such that vital data are constantly transmitted back to mission control. It is also equipped with a heat shield for suborbital reentry and parachute system, enabling it to make a soft landing. Please refer to the spacecraft section for more details.
- Booster recovery: Directly beneath the spacecraft sits the booster recovery ring. It contains a drogue and a parachute, enabling the booster to make a controlled landing at sea.
- Guidance and instrumentation ring: Electronics and instrumentation sits beneath the recovery section. This part houses radio systems for data and video feed to mission control, batteries, antennas, Autonomous Abort Unit, Guidance and Navigation Computer, and a few other electronic systems.
- Propellant tanks: Liquid oxygen and ethanol is stored in separate tanks, each with a volume of 1,000 liter. The propellant tanks are only filled to 65% of their volume, the remaining 35% is pressurized gas which provides the force necessary for feeding the propellants into the engine. The propellant tanks are welded from 6 mm aluminum sheets to provide structural strength to cope with the high pressure. The liquid oxygen tank is fitted with a chiller spiral which is flushed with liquid oxygen during fueling, to prevent excessive vaporization of the loaded liquid oxygen. During engine operation the liquid oxygen passes through the isolated central pipe that goes directly through the ethanol tank.
- Engine: The TM65LE engine is a regeneratively cooled bi-propellant rocket engine designed to operate at 12 bar. Please refer to the engine section for more details.
Though we strive to keep everything as simple as possible, the HEAT-2X is by far our most advanced rocket to date. The key technologies implemented in the HEAT-2X vehicle are:
- Guidance and Navigation Computer (GNC)
- Thrust Vector Control (TVC)
- Autonomous Abort Unit (AAU)
- Flight Termination System (FTS)
Guidance and Navigation Computer
The GNC is the control unit that constantly calculates flight information. It is equipped with an Analog Devices ADIS16448 inertial sensor. The sensor output is integrated over time, such that the GNC at all times knows the position and velocity vector of the vehicle. This is continuously compared to the predefined trajectory and the GNC uses this to calculate any necessary trajectory correction. If a correction is necessary, the correct response is calculated and passed on to the Thrust Vector Control system. The trajectory and corrections are updated at a frequency of about 200 Hz.
Thrust Vector Control
The TVC system is commanded by the GNC to carry out trajectory corrections. The main part of the TVC unit is a set of jet vanes positioned partially in the exhaust of the rocket engine. They are used to deflect part of the exhaust and thereby change the thrust vector and trajectory. This technology was successfully used for the first time by CS during the Sapphire flight on June 23rd 2013. The GNC and TVC system has been upgraded to also provide roll control on the HEAT-2X/TDS80 mission.
Autonomous Abort Unit (AAU) and Flight Termination System (FTS)
The AAU is a safety system designed to prevent the vehicle from leaving the closed off naval shooting terrain in an uncontrolled manner. It is a stand-alone system that monitors key flight parameters. If any of these parameters surpasses a predefined value, the AAU will command a mission abort. The consequence of a mission abort depends on the actual circumstances under which it occurs. It can be a premature engine cut off followed by a controlled parachute landing, or, in the most extreme case, it can be activation of the Flight Termination System which will bring the vehicle to complete destruction by detonation of the onboard explosive charges. This is naturally a last resort to ensure that safety range is not compromised.
The TM65LE engine is currently pending its first test fire and static performance test, this is scheduled for late May 2014. The following is an optimistic estimate, or rather the highest potential, of the HEAT-2X flight performance.
Velocity and altitude profiles of the TDS80 spacecraft are seen in the figures below. The profiles are naturally identical to those of the booster itself until separation which happens at apogee, 212 seconds into the flight. With an initial thrust of 45,000 N the initial acceleration will be 18.3 m/s2. Thrust will decline due to the expanding gas pocket in the propellant tanks, such that the acceleration reaches a minimum of 7.8 m/s2 at 35 sec, after which it will increase slightly again. Mach 1 is reached after 22.9 seconds at an altitude of 4.1 km. Shortly afterwards, at 28.7 seconds maximum Q is reached at 6.1 km. Burnout happens at 100 seconds into the flight, at an altitude of 56 km and a velocity of 3,960 km/h. From here the vehicle coasts to apogee at 118 km.
At apogee the booster and spacecraft separates. The spacecraft deploys a ballute to increase drag and position it in a heat-shield first position. The spacecraft free-falls in this configuration to an altitude of 3 km where it deploys a parachute and lands with a relatively high speed of 80 km/h. The booster will utilize a combination of a drogue and a parachute to land at sea as well.
The static test was conducted on August 16 2014. After two dry run rehearsals the previous days all procedures went very well and around 3 pm we were ready to fire the engine. At T-4 sec the pre-stage valves opened and pre-stage seemed nominal so the Engine Controller continued to open the main valves and go for main-stage at T-0.
As the main valves opened the engine went into main-stage but after just a little more than a second the cooling jacket of the engine ruptured and spilled the entire fuel load in a few seconds which engulfed the platform and engine in flames.
The entire engine section was significantly damaged by this fire and the engine has now been retired to the CS museum. Post-test inspections revealed that a couple of poor weld joins had ruptured due to the high pressure in the cooling jacket. This caused the cooling jacket to tear open and spill all of the fuel in a few seconds.