The mission begins with the rockets pointing to the sky in a near vertical position. The payload is shrouded beneath a nose cone to protect it during the ascent through the atmosphere.
If suitable atmospheric conditions prevail, the launch sequence begins. A final check is made of all the operational equipment using the on-board telemetry system. The arm button is then activated to start the computer running. At T=0, the Terrier motor is fired.
As the rocket leaves the launch pad, it pulls away the fuel lines and an umbilical cord which has enabled the scientists and engineers to control the payload systems whilst on the ground. The computer now has to control the experiment for the next 10 minutes by itself. With an acceleration of 22 g (22 times the acceleration due to the Earth's gravity) the Terrier motor propels the system to 4000 km/h after just 6 s. This motor is then jettisoned and the Orion motor and its payload coast for 9 s. The Orion motor is then fired and boosts the payload in 26 s to a speed in excess of eight times that of sound (8300 km/h) and to an altitude of 56 km, approaching the edge of the atmosphere. Five seconds later the nose cone is blown off with compressed nitrogen. During the next 400 s, the rocket is manoeuvered to point downwards, in readiness to re-enter the atmosphere. This is achieved by using a cold gas thruster which provides pulses of compressed nitrogen to gently nudge the spent Orion motor and the experiment into the correct orientation.
As the rocket and the experiment re-enter the atmosphere, the altitude is monitored using a Pitot probe. When it descends to 35 km, hydrogen is supplied to the scramjet and the supersonic combustion experiment begins. Measurements of pressure and temperature in the combustor are transmitted back to three ground stations to be stored for later analysis. The flow of fuel is maintained for the next 5 s as the experiment descends to an altitude of 23 km. At this point the experiment is complete.
The first two HyShot flight experiments used a two-dimensional supersonic combustion ramjet with a back to back configuration. It included boundary layer bleeds on the intake and constant area combustors. The configuration was not designed to produce a net thrust, as the objectives of the experiments are to measure the pressures in the combustor and on the thrust surface and correlate these with the shock tunnel data. Hence, simplicity of the flow field was a high priority in the design of the experiment and this resulted in an 'engine' with poor performance. Developing an engine with net positive thrust is the subject of future flight trials.
Ground Experiments on the 'engine' that was flown were made in the T4 shock tunnel, located in UQ's Centre for Hypersonics (Smart et al., 2006; Frost et al., 2009). These experiments showed that supersonic combustion could be achieved at angles of attack up to four degrees. Experiments were also made at different yaw angles. Again, it was shown that four degrees of yaw could be tolerated. It is important that the engine operates at non-zero angles of attack because the HyShot payloads spin and cone on re-entry, providing a continuous change in angle of attack and yaw.
This is advantageous to the experiment because it provides additional data for the correlation purposes. These data can also clearly be used for testing computational analyses also. It is important that the design of the pressure sensors ensures sufficient response time so that these changes can be detected.
The Vertical Trajectory has one difficulty in that only small aerodynamic forces act on the motor and its payload during re-entry to the atmosphere. If the payload and the Orion motor are not pointing downwards before re-entering the atmosphere, this lack of air makes it difficult to turn the payload into the downwards direction before reaching the altitude at which the experiment begins. To alleviate this problem, the payload is rotated so that it is correctly oriented before it re-enters the atmosphere. This is quite a difficult maneuver to perform as the payload and its attached spent rocket motor are spinning at between 4 and 6 Hertz. This coupled with the fact that the system weighs close to 600 kg provides for a very large angular momentum vector, which must be rotated through approximately 160 degrees. The method chosen to perform this maneuver is called a "Bang-Bang" maneuver.
A Bang-Bang Manoeuver is one where an impulse is provided to a spinning object. This allows the object to nutate. After it has nutated through 180 degrees, another impulse is provided. This stops the nutation, but the whole system has changed its angular position. The HyShot system undergoes approximately 50 Bang-Bang manoeuvers to complete its re-orientation. The procedure to re-orient the payload has to be done without any intervention from the ground as only a telemetry downlink is provided. Hence, on-board sensors are provided to determine the orientation. These include two sun-sensors and a three-component magnetometer.
Grounding Testing of the payload is an important part of the HyShot Flight Program. With this testing, confidence is obtained in the computer programs and the equipment that has been specially manufactured for the flight. The ground test program includes testing the response times of transducers, the structural integrity of individual components, vibration testing, shock load testing, vacuum testing and source code evaluation. The source code and the algorithms which have been implemented were checked by using a three-axis gimbal system developed at The University of Queensland, especially for the HyShot Program and with "hardware-in-the-loop" experiments.
The gimbal that was constructed rotated a quarter scale model of the spent Orion motor and its payload at speeds up to 6 Hz. The orientation of the system was monitored using a three-axis magnetometer and two sun sensors, as is done in flight.
When the Terrier motor initially starts there are accelerations approaching 60 g experienced by all the components. This acceleration is only short lived and dies away to less than 30 g after half a second, but unless the equipment on board can withstand this initial shock, the experiment will fail in the first second of the flight. Hence, a vibration rig, which is essentially a stiff beam, was built to simulate this environment. Different pieces of equipment can be bolted to the vibration rig and tested to see if they can withstand the vibrations. Up to 30 kg at a time can be placed on the rig. This allows complete testing of much of the experimental structure at the one time.
Ground testing also includes aerodynamic testing to determine if the experiment will be stable as it re-enters the atmosphere. Testing was been done at QINETIQ's Farnborough facilities. Extensive tests were performed to determine the orientation that the experiment should have relative to the tail fins to ensure the greatest aerodynamic stability. This contribution provided valuable information which was fed back into the designs to optimise the chances of a successful mission.
The Electrical Layout of the payload is also an important issue which must be addressed for a successful mission. Components must be chosen which can operate under testing operating conditions. A large effort was made to make the circuitry as simple as possible. This leads to reduced costs and weight and a higher chance of success.
The Fuel System was also designed using the same philosophy. Two separate systems are used. One for the hydrogen supplied to the scramjet during the experiment and the other is used to supply the nitrogen to the cold gas thruster during the maneuver.