H6a flight report

1.

Project overview: a short history [Top] [Contents]

The primary goals of the H6 project were:

1. the design, construction and testing of a technically and systematically full-fledged rocket,
2. the development and application of new technique with the goal to improve the performances and reliability of the rocket.

Looking back on the five years since the H5 flight, the NERO Haarlem department has certainly succeeded in designing and building a full-fledged rocket, using several newly developed techniques but that the project did not go according to the plans made at the start of the project. Lack of time due to the high project pressure, in conjunction with the organisation of the NLC, the re-organisation of the entire NERO society and other activities (e.g. the Bulletin), resulted in insufficient testing of the complete rocket system. That's also why a considerable de-scoping of the on-board instruments was necessary. Among other things the developed light-weight structures made it possible to realise one of the technical goals, viz. reaching an as high as possible velocity. The mass of the rocket could be limited to just 8.5 kg.

2.

Construction of the rocket [Top] [Contents]

The parachute system has two stages. At the highest point of the rocket trajectory a hatch in the side of the parachute compartment is ejected, clearing the way for the deployment of drogue parachute. The rocket will descend on this parachute with a velocity of about 30 m/s. At an altitude of about 600 meter, the main parachute is released and the descent velocity decreases to about 10 m/s. The pyros of the parachute system are initiated by the timer.

The electrical system consists of an autonomous programmable timer/pyro-actuator unit, a micro-controller, a status monitor, a modulator and a 2-meter transmitter. The system is powered by a NiCd battery. The electrical system is designed in such a way that different types of instruments, e.g. P/T sensor, accelerometer, vibration sensor, impact resistant module etc., can be accommodated. Because of lack of time we have decided not to fly these modules in the first flight and to concentrate on the most essential electronics only. The advantage of this decision was that the mechanical system (motor, structure, recovery system) could be qualified without risking the extensive instrumentation. This decision was made with the H5 flight in our thoughts.

The ground segment consists of a receiver, a de-modulator and a PC. With this system we realised a working downlink. The data which are transmitted to the ground station consists of status information for the operation of the timer, the pyro-actuators and the parachutes. The final phase of the construction, flight preparations ???.

During the final phase of the construction of the rocket, some important system tests were conducted. On Sunday 20 September, the complete rocket was assembled for the first time. At that moment, less than six days before the launch, the following items still had to be realised:

• the wiring of the rocket,
• assembly of the sensors and electrical modules,
• testing of the electrical system, including the downlink,
• implementation of the controller software,
• assembly of the battery pack, battery container and connector board,
• finishing of the fins, the substructure and the parachute compartment hatch,
• testing of the parachute system and the pyrotechnical devices (de-blocking device en pyro bolt),
• mounting of the antenna in the boat tail,
• painting of the rocket body,
• writing the integration and launch procedures, as far as possible,
• determination of the mass and calculation of the flight trajectory,
• setting the timers.

On Thursday morning 24 September, the electrical system and the controller without the radio frequency part, was tested for the first time. During the night between Friday and Saturday, the pyro system and the parachute system were tested. The system proved to malfunction and several parts had to be adapted. On Saturday afternoon, the complete electrical system including the downlink was tested for the first time, observed by the crowd who had come to witness the launch. After this, the final preparations for the launch could be continued. The activation moments for the parachute system were calculated and programmed into the timer. Because of an enormous effort of the complete team it was finally possible to finish the preparations for the launch at Saturday evening, 18:50, which was just 10 minutes before closure of the launch window.

3.

Flight and recovery [Top] [Contents]

At t=0, the motor was ignited and the rocket ascended immediately and stable. At the same moment, the ground segment software crashed because the 2-meter receiver proved unable to handle the lowered signal quality. With impressive presence of mind, Hugo de Jong was able to restart the system, thus enabling the tracking of the remainder of the flight.

Judged by the naked eye, the burn of the motor was nominal. After about 10 s, the rocket disappeared from sight. Using a portable 2-meter receiver it was possible to listen to the telemetry signal. After 35 s, a bang was heard, which meant that the pyro-system of the parachute hatch had worked.. A few seconds later, the ejection of the hatch and the deployment of the drogue parachute was confirmed by the ground station crew, who could see the relevant status information on the PC monitor.

After about 2 minutes, the rocket was spotted hanging on its main parachute at an altitude of about 600 m. The rocket produced a smoke trail, which implied that certain parts had caught fire. Even before touchdown, the rocket transmitter went off the air, which was the signal for the people with radio receivers to turn off their equipment. Three minutes after launch, the rocket landed about 700 m from the launch tower in a north by north eastern direction. The recovery went smooth and about 20 minutes later, the complete rocket was back at the public stand. The drogue parachute as well as the sleeve of the main parachute and the parachute hatch have not been recovered up till now.

4.

Flight analysis [Top] [Contents]

At first sight, the flight was nominal. However, in reality, some things went wrong. The following information was obtained from the telemetry data.

It should be noted here that as a result of an as yet unresolved error in the system, a mix-up of status bits in the data flow from the rocket had occurred. In order to be able to interpret the information, it was necessary to correct this error by using some software code. From the information it can be concluded that everything went according to plan, except for the fact that the timer/counter should not have stopped after 110 seconds, and that the transmitter stopped operating before the rocket had landed. Should the rocket have contained a complete set of instruments, this would have resulted in the loss of a considerable amount of data. Furthermore, it was found that of the two available tapes containing telemetry data, only one tape contained data of a high enough quality that the ground segment software didn't crash while analysing the data. Once again, this proves that it is very important to have a telemetry receiver (and recorder) available on the launch site.

A week and a half after the launch, the H6A team inspected the rocket in detail. Upon opening of the electronics compartment, it became quickly clear why the timer/counter had stopped operating after 110 seconds; the piston of the de-blocking device had been 'launched' right through the upper platform of the sub-structure and had damaged a part of the timer, including the count status monitor.

The failure of the de-blocking device can be  traced back to the mistakes that were made during the assembly of the two igniters in the night before the launch. The actual charge which had been put into the igniters was 100 mg per igniter, instead of the normal 20 mg per igniter. The de-blocking device thus operated during the flight with a five times more powerful charge than actually required. The crushable honeycomb in the device, which should have absorbed any excess energy, was obviously not designed to withstand this amount of energy.

From the analysis of the telemetry data and the reports of the observers in the field, it is clear that the H6A flight was nominal to a large extent.

It is possible to reconstruct the flight profile on the basis of the explosion caused by the ejection of the parachute compartment hatch being heard about 35 s after lift-off. Taking into account the programmed time of 25 s after lift-off, this means that this event took place at a distance of about 3400 m from the spectator area. Furthermore, the main parachute deployment was observed at the pre-programmed time of 110 s at an altitude of about 600 m. The rocket landed about 700 m from the tower and about 450 m from the original trajectory due to drift in the wind.

When these data are compared with the flight profile as calculated by the computer program Flight of Mark Veltena a few hours before the launch, it is clear that within the limits of accuracy, the flight was indeed nominal. During a nominal flight, the maximum altitude would have been at 3450 m and the point would have been reached 24 s after lift-off. The deployment of the main parachute would have occurred at an altitude of 600 m and the landing point would have been at a distance of 645 m from the launch tower. These values are true for a standard atmosphere and without wind influence.

The differences between the ideal (calculated) flight and the actual trajectory can easily be explained by the presence of a weak wind blowing from the South-East, which is perpendicular to the trajectory at launch. The rocket descended on its drogue parachute for 85 s and on its main parachute for 70 s.

For the reconstruction of the flight trajectory, use is made of the information of wind velocities and directions, which were provided to us by the military authorities. It is assumed that the rocket remained in its original trajectory during the ascent phase and that the rocket had a horizontal velocity equal to the wind velocity during the descent phase on the parachutes. The 'weathercocking' effect (the horizontally blowing wind makes the vertically ascending rocket cock its nose into the wind like a weather vane or weathercock) has been neglected (this could have rotated the trajectory only several degrees under the given conditions). For the reconstructed flight, the landing spot turns out to be about 200 m more to the North that estimated by the recovery team.

It can therefore be stated that the flight trajectory and the landing spot can be determined with a high enough accuracy by using the data available prior to the flight in order to guarantee that the rocket would land with the launch site perimeter.

The flight being characterised nominal has two meanings: (i) the performance of the TG-10 motor was nominal and (ii) the drag coefficient of the 'Von Karman' nose cone was roughly in agreement with the presumptions (NB. in the transonic range, the drag causes a deceleration of the rocket of about 50 m/s²) and (iii) the descend velocity of the rocket on its parachutes was in agreement with the ground test results.

5.

Conclusions [Top] [Contents]

The department Haarlem succeeded in building and launching a technically full-fledged rocket. The 'novelties', which were introduced with the H6A flight have proven to function well. This includes for example · the light-weight construction technique (substructure and body parts) · the downlink and ground segment · new timer design · controller for data acquisition · new parachutes · more robust fastening of printed circuit boards.

These are all design improvements over the H5 rocket, the predecessor of the H6A.

The goal to completely document the project was realised to a large extent, however, many improvements can still be made.

Concerning the intention to improve planning the development and construction phase of the project, it must be said that this was not realised. The amount of work that had to be completed during the final stages prior to the launch was even larger than for the H5 rocket and raised the stress levels considerably. This can only be partly contributed to the additional work load accompanying the organisation of the NLC-2 launch campaign.

Development and construction of the rocket

For too long, the concept of a fully instrumented rocket had been adhered to, although this was no longer realistic given the limited time available and the experiences from the past.

Certain critical elements, in particular the sub-structure, were insufficiently developed when they were incorporated in the H6B baseline design. This resulted in problems during the rocket assembly phase. Nevertheless, the production of the tubes for the rocket body went quite smoothly.

Insufficient test support equipment had been developed for the H6A. As a result, test set-ups had to be improvised under considerable schedule pressure.

Conduct of the launch campaign

The operational NLC teams were inadequately instructed for the flight of the H6A. This resulted in the loss of a lot of flight data, such as data concerning the parachute descent phase (no timing data available) and the registration of the landing spot of the H6A and of the drogue parachute.

Not a lot of parameters have been actually measured; the major part of the information is based on estimates.

Remarks regarding the flight

In the case of stronger winds, it would not have been possible to set the parachute timers such that recovery within the terrain perimeter was guaranteed. This is caused by the fact that the parachute system used is based on hardware timing settings. For instance, for the location of the landing spot it does not really matter whether the drogue parachute is deployed 10 s before or after the highest point of the trajectory. For the time at which the main parachute is deployed, a large margin needs to be incorporated.

On the basis of the available data concerning the profile of the wind, the landing spot could be determined with a high enough accuracy.

6.

Recommendations [Top] [Contents]

1. During the construction phase of the rocket, test support equipment needs to be developed and built as well. The status of the rocket within the launch tower needs to be verified in a simple and easy way, especially with regard to arming the pyrotechnical system..
2. The operational teams need to be instructed to carefully register the following items:
• sounds during the flight (sonic boom, parachute hatch ejection), preferably using microphones;
• monitoring the entire flight using film or video;
• stability during the powered and ballistic phase;
• behaviour of the rocket suspended on the parachute(s) (stability, oscillating frequency etc.);
• landing spot of the rocket and other parts (theodolites);
• altitude at which the parachute is deployed (goniometer);
• descent velocity of the rocket suspended on the parachute (goniometer/stopwatch);
• telemetry signals from several receiver stations (using different locations, antennae, recorder etc.).
3. Detailed procedures have to be written for the following actions:
• preparations and tests for the pyrotechnical systems integration;
• flight preparations (including programming timer and folding parachutes);
• countdown;
• calculations of flight times on the basis of the most up-to-date data (mass, weather);
• programming flight times in timer.

Actions which are carried out according to these procedures have to be checked by a second (more or less competent) person. For critical actions a check list (incorporating a signature requirement) needs to be used.