Dossier de clotude du projet Leia (fusee experimentale)

1. LEIA
Closing Document
CLES-FACIL 2008
http://cles-facil.insa-lyon.fr
cles-facil@insa-lyon.fr

2. Table of Contents
Project Goals................................................................................................4
1.1 Cansat.................................................................................................4
1.2 Recuperation System..........................................................................5
1.3 In-Rocket Measurements....................................................................5
1.4 Integration of the New Motor..............................................................5
Developed Solutions....................................................................................6
1.5 Cansat.................................................................................................6
1.5.1 Structure..........................................................................................6
1.5.2 Ejection............................................................................................7
1.5.3 Original Parachute System...............................................................7
1.5.4 Radio Link........................................................................................8
1.5.5 Control.............................................................................................9
1.5.6 Recuperation....................................................................................9
1.6Recuperation system.........................................................................10
1.6.1 Ejection Mechanism.......................................................................10
1.6.2 Double Parachute System..............................................................11
1.6.3 Timer..............................................................................................11
1.7 Measure in the rocket.......................................................................12
1.7.1 Accelerometer................................................................................12
1.7.2 Pressure Sensor.............................................................................12
1.7.3 Camera..........................................................................................13
1.8 Integration of the new motor............................................................13
Results and analyses..................................................................................15
1.9 Cansat...............................................................................................15
1.10 Recuperation System......................................................................16
1.11 Measurements in the Rocket..........................................................16
1.12 Integration of the New Motor..........................................................17
1.13 Unexpected Result..........................................................................17
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3. Project Members
Gabriel Arnold-
Nicolas Praly
Dulac
Project Lead
President
Florent Gabriel Arnold-
Nicolas Praly Bouchoux Dulac
Mechanics Lead Electronics Software Lead
Lead
Séverine Belloir
Michal Ruzek Bertrand
Sylvain Tanguy Mathieu Mandrin
Rafic Meziani Riedinger Fernando
Jérôme Bégel André Machado Mattioli
Jean-Mathieu Raphael Antoine Damien Malric
Cousin Philippe Roudot
With help of:
Sylvain Rouard
Marc Dal-Molin Spas Balinov
Former Project
President (2007) President (2006)
Lead
3/18

4. Project Goals
This year the project’s goal was to realize a reusable cansat launcher.
The rocket supposed to be built in such a way that it could be launched at
least two times during the launch campaign. As a launch vehicle, its
payload was supposed to be a cansat with an approximate weight of 600g.
The rocket was also supposed to integrate various sensors to better
understand the flight path (accelerometer, altimeter) and help in its
recuperation (GPS, radio link).
This year the rocket was launched with a new motor never used by the
club before. One of the objectives of the year was also to properly
integrate this ne motor in the rocket.
1.1 Cansat
The CANSAT (Can- Satellite)
is an international
competition to promote
space-oriented research
and engineering activities
at the student level. Cansat
competitions are very
active in Japan and in the
United States, but a cansat
was launched for the first
time in France only last year
in our INESS project (please
refer to the closing document of CLES FACIL 2007).
The objective is to embark a module of the size of a soda can in an
experimental rocket and eject it at the flight’s appex. The final objective is
to bring the CANSAT towards a target on the ground by controlling its
trajectory.
In our case, we chose, as last year, to conceive a cansat able to control a
parafoil with an automatic pilot. The difference between the “traditional”
cansats and ours is the decision that our ejected module would not be the
same size as a soda can. This choice is justified by the fact that our
cansat will carry in addition to the standard payload, a Kiwi transmitter, 2
servomotors, and a camera, the sum of which require substantial
additional volume. However we remain in the ‘special category’ range of
less than 1kg.
Our previous cansat had an extremely unstable flight, so in hopes of
bettering the stability of our flight this year, we chose to go with a 2 stage
deployment of the parafoil : once the cansat is ejected from the rocket, a
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5. first parachute opens. After a few seconds the first parachute releases
itself and acts as a drag chute for the parafoil.
1.2 Recuperation System
This year we choose to enhance our traditional recuperation system.
Since one of our objectives was to launch the rocket twice during the
week, we needed to assure ourselves that the landing would cause as little
damage as possible. However, since the launch campaign takes place on
a military base, we have a constrained space in which we can operate.
Therefore, we cannot simply use a bigger parachute, as the slower
descent speed could cause us to land too far off course (in a mine field for
example). As a compromise, we decided on a dual parachute system for
the rocket.
The first parachute deploys after the cansat is ejected. This would be a
smaller chute like we used in previous years. The second one would open
near the ground (approximately 200 m). We also ameliorated our
parachute door opening mechanism to replace the rubber band with a
steel spring.
In the hope of speeding up the recuperation process, the rocket would
have a GPS receiver and a telemetry system that would allow the ground
station to know the rocket’s position at all times.
1.3 In-Rocket Measurements
This year we also wanted to
integrate an accelerometer and a
pressure sensor in the rocket to
know the evolution of acceleration
and the culminating altitude. We
also decided to transmit the data
in real time via the Kiwi
transmitter (more on the Kiwi
later). Since last year there was
also a camera in the rocket, we
decided to keep this feature.
1.4 Integration of the New Motor
There is a significant difference between the new Pro 54 motor and the old
Chamoix motor. First of all, the Chamoix has a threaded rod at the top of
the motor, so the mechanical integration is simple. Secondly, the Pro 54 is
much longer and thinner than the Chamoix.
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6. Rocket
s kin
Thrus t Pro 54 Retaining
Free zone Retaining tab
ring s leeve
Developed Solutions
1.5 Cansat
1.5.1 Structure
The CANSAT is a 105 x 115 x 220 mm box (≈2,3 L). It contains:
• 2 servo motors
• a parafoil stored inside a shell
• a system to deploy the parafoil
• a micro-controller
• a GPS
• an accelerometer
• a magnetometer
• a Li-Poly (non-rechargeable) battery
• an FSK modulator
• a Kiwi radio transmitter (custom transmitter provided by the CNES)
• a video camera
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7. 1.5.2 Ejection
As described in the previous part, the cansat is ejected at the apex of the
flight parabola. Since we see the cansat as a payload (and not a part of
the rocket as we did last year), we had to design a generic payload
ejection system. We based our work on our traditional parachute ejection
system and used it to open a side of the rocket’s fuselage through which
we could eject the cansat. In order to eject the cansat properly we put in
place four large elastic bands to push the cansat out of the rocket.
Pictures on next page:
The new ejection system will be described more completely in the recuperation
system part.
1.5.3 Original Parachute System
Last year we had trouble controlling the cansat once ejected from the
rocket. One of our hypotheses was that the parafoil opened while the
speed of the cansat was too high. In order to solve the problem we chose
to use a first parachute to slow the cansat before opening the parafoil.
When the cansat is ejected from the rocket the parachute opens. After five
second the first parachute is liberated, acting as a drag chute for the
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8. parafoil. This way, the parafoil deploys while the speed of the cansat is
approximately 10m/s.
In order to liberate the parachute we designed a small system to absorb
the opening shock of the first parachute and then liberate the first
parachute after 5 seconds.
1.5.4 Radio Link
Due to the dense vegetation on the camp of La Courtine (where the launch
campaign takes place), both rocket and cansat are not necessarily
recovered, so we cannot rely on onboard memory for data storage. To be
sure to get at least essential data from the rocket we used a radio link.
Last year this system allowed us to quickly recover the cansat thanks to
GPS data that had been transmitted. This year we included GPS devices in
both the rocket and the cansat, in the hope of being able to recover them
easily.
Aside from the GPS coordinates, some other parameters were also
transmitted, such as altitude data for the rocket and acceleration for the
cansat.
Planète Science and the CNES lent us an FM radio transmitter called the
Kiwi. It has a TX power of 300mW and uses space-reserved frequency
bands (137MHz – 139MHz).
In order to be able to transmit digital data, we needed a frequency
modulator. At first we developed a modulator built around a DDS-chip,
allowing a transmission speed of 480 bytes/sec. Unfortunately, just before
the launch, it appeared that the modulator was not working as expected,
most likely due to soldering problems of the SMD DDS chip. At the last
minute we had to build another modulator using an analog IC FSK
modulator: the XR2206.
The reception and demodulation process was done by the CNES. They
have an awesome, fully equipped truck with everything we could possibly
need for the reception of our telemetry. It has a 3-meter extensible mast
with a high-gain antenna, which should normally have received our signal
perfectly…
Like every year, we had to develop our own ground station software. The
radio link is set up in such a way that it is actually transparent for us at a
software level. It is effectively a 9600baud unidirectional serial link. We
chose to use Python with wxPython & PySerial to decode the data stream
and display it in a simple window. We highly recommend the use of
PySerial for working on serial data links, as development was very rapid
and the PySerial library quite robust and intuitive.
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9. 1.5.5 Control
This year’s control algorithm was built on top of our previous design.
Originally we were using multiple GPS coordinates to derive our velocity
(both for direction and speed). The problem with this approach was the
fact that our GPS was a 1Hz model; this meant that to have the 3 points
necessary to properly derive our velocity we ended up with a measured
velocity that was 1-2 seconds behind our actual velocity.
This year we decided to take a new approach: we integrated a 2-axis
magnetometer based on a MEMS IC. With this sensor we were able to get
our heading in real-time (ground speed being an information that is not
very interesting to us), thus allowing us to react much faster to sudden
velocity changes, and therefore have a much more stable flight. The GPS
receiver was still used for absolute positioning and ideal heading
calculations. We also integrated a 3-axis accelerometer (also a MEMS IC)
simply to gather additional data. All data was sent back every second
over our Kiwi radio link.
The control loop ran on the onboard microcontroller (AtMega 128) and was
composed of these 5 major steps:
1. Gather all TWI sensor data (Magnetometer, Accelerometer).
2. Gather GPS data (UART).
3. Calculate ideal heading (based on current GPS coordinate and target
GPS coordinate).
4. Calculate angle between ideal and current heading. This is the
necessary correction.
5. Apply necessary correction on the servomotors for one second (until
next iteration).
This control system has absolutely no flight model, and is a simple closed-
loop directional control. We either pull left or right on the parafoil for a set
amount of time t (t < 1s), and the next iteration will correct the remaining
offset. We have a threshold in place so that if our heading is almost
correct, we will not turn.
Aside from the addition of the magnetometer, the control system is
identical to last year’s. We considered adding a 2nd level of control that
would stabilize an unstable flight, but we are still not decided as to the
necessary actions to take to stabilize ourselves, nor are we completely
sure of what our stability problems really are.
1.5.6 Recuperation
The cansat, due to its control system, would already transmit its GPS
coordinates to us. Recuperation is therefore quite simple, as we already
know approximately where it landed.
9/18

10. 1.6 Recuperation system
1.6.1 Ejection Mechanism
To not reinvent the wheel, we
used our old ejection system with
a slight evolution. The previous
version used elastics to keep the
latch in place. As we had to
change the elastics quite often
due to wear during our tests, we
designed a system with a spring.
Otherwise, the system functions
identically to the old model.
When the ejection door is latched
shut, the system is in the same
configuration as the picture.
When the parachute or the cansat
must be ejected, the motor is
turned on, thus turning the cam
and lifting the latch.
10/18

11. 1.6.2 Double Parachute System
As is explained in the project goals (p. 3-4), we used a
dual parachute this year to reduce the landing shock
while still staying within our authorized operating zone.
The first parachute opens just after the cansat is ejected
(right after the flight’s apex). The rocket’s airspeed with
this first parachute is approximately 15m/s.
To save place in the rocket we had to put the second
parachute in the same compartment as the first one. To
avoid opening the second parachute inadvertently, we
put it in a bag that is kept shut until we wish to deploy it.
You can see a description of our deployment system to
the left. The first parachute is attached to a string (the
red string in the diagram). When the rocket is at 200m
over the ground this string is cut by a system using an
electrical heating wire. When the string is cut, the first
parachute (which is also attached to the second
parachute’s bag) pulls on the bag. When the parachute
pulls the bag away, the second parachute comes out
and deploys.
As we don’t want to lose the first parachute and the bag.
They are attached to the second parachute. With the
two parachutes open, the speed of the rocket is around
5m/s.
Note: the system is not exactly identical to the one
represented on the picture but it follows the same
general principle.
1.6.3 Timer
The timer system is responsible for deploying the parachute and the
cansat at the correct points in the flight (the times are based on
calculations). The timer is based on an NE555 and can be set with a
potentiometer.
A push button switch with a a weighted lever is triggered at liftoff with the
force of the acceleration. This switch starts the timer by sending a rising
edge to the 555. After a set time, the 555 triggers with a leading edge a
flip-flop that closes the door motor's power supply circuit. With the intent
of conserving power (in case we take time to locate the rocket, or want to
relaunch it without replacing batteries), a second 555 is triggered when
the motor starts, and takes care of cutting the power supply to the motor
after a couple seconds.
11/18

12. 1.7 Measure in the rocket
1.7.1 Accelerometer
A 3-axis MEMS IC accelerometer was installed in the nosecone of the
rocket. The intended purpose was to measure the new motor’s
acceleration curve and perhaps get some attitude information during the
later stages of the flight. The accelerometer was set on a +-20G scale to
avoid saturation.
1.7.2 Pressure Sensor
Before the GPS era, one of the easiest ways to know the rocket’s altitude
was to use a pressure sensor. Knowing the relationship between the
pressure and the height – which is a quite linear function at low altitudes –
you could determine not only the altitude of your rocket, but also its
approximate vertical speed.
Even nowadays there are very few digital pressure sensors. So it’s a great
way to use some OP-amps, differential amps, filters and DACs.
The sensor we used (MPX5100) is an absolute pressure sensor that does
not need any amplifier, so it was directly connected to the microcontroller
DAC.
But due to a lack of time (and importance to the project) it was calibrated
at the last second, and we didn’t expect great results.
12/18

13. 1.7.3 Camera
2 small camcorders (FlyCamOne V.2) were taken onboard the rocket and the
CANSAT. They’re lightweight camcorders usually used by RC planes, obviously
optimized for such a use and consequently able to start recording by themselves
after a delay you can define. They store compressed movies on a standard SD
card you can easily read using any computer.
Only the cam in the rocket worked ; the CANSATs one stopped recording at the
very moment of the launch, probably due to the proximity of the Start/Stop
button with the structure.
However the quality of the movie is far from regular camcorders movies quality.
This may be caused by the size of the cam, using bad quality optical components.
We’d not recommend using such cameras on a rocket flight, it would need
suitable cams that can quickly adapt their contrast to the light sources
encountered in the sky.
1.8 Integration of the new motor
In order to integrate the motor we use a system with a thrust ring, a carbon tube,
a threaded retaining ring and a threaded ring. As we can see the alignment of the
motor with the rocket is made with the thrust ring and the threaded ring. In order
to make easier the integration of the motor there were strip of foam along the
carbon tube. The mass of all the system is under 750g.
13/18

14. 14/18

15. Results and analyses
1.9 Cansat
The cansat was well ejected from the rocket. The first parachute deployed
correctly, but due to the shock the parafoil seem to have also deployed itself
prematurely as we can see in the following picture:
First
Parafoil
parachute
CANSAT
The MEMS sensors ended up being extremely sensitive to the onboard radio, and
were rendered inoperable. With the hope of at least getting some interesting
data we chose to remove the flight control algorithm, and created a
predetermined set of commands. The reason is that our previous cansat had a
completely unstable flight (somersaults, 360s etc.) and we wanted first and
foremost to verify that we had at least conquered that problem with our new
mechanical structure. We therefore chose to have the cansat fly straight for a
dozen seconds, then turn right, then left, then straight again, then repeat. We
hoped we could therefore correlate the actions with the GPS coordinates and
verify that we were indeed having an effect on the flight path of the cansat.
Even after numerous integration tests and a full flight simulation that was
successful, our telemetry system failed catastrophically. We think the cansat’s
antenna may have been to blame (small home-made helical ¼ band that couldn’t
transmit far), but there is no conclusive evidence as to what happened. We
know the system worked up the FSK modulator, so something in the actual radio
link or demodulation is to blame. Due to this failure we have absolutely no
sensor data from the whole flight, which was a great disappointment for us. We
have opted to move to a POTS radio data link for our future projects, since the
KIWI demodulation truck’s system is not set up by default to handle multiple
frequencies in parallel and the overall size of the KIWI makes integration
sometimes difficult.
The experience nevertheless had positive results: we succeeded in stabilizing the
cansat’s flight. We also validated the rocket’s ejection mechanism. The rocket’s
current design allows us to integrate any cansat with the following constraints:
less than 105 x 115 x 300 mm and a mass of less than 1kg.
15/18

16. 1.10 Recuperation System
The recuperation system didn’t work because the parachute bay doors didn’t
open. However when we found the rocket, the string holding the first parachute
in place was nearly cut due to the heat wire.
Since we have not had such a problem in at least 20 years, we aren’t sure of the
causes. We know the timer was properly triggered, so we are left with the
following hypotheses about the door:
• As we can see on some pictures, the cansat’s door was already open and
may have blocked the parachute’s door.
• The timer had some problem to provide sufficient power to the motor.
Even with new batteries, the power may not have been sufficient to
unlatch the door.
• As the cansat’s door was open in mid flight, there was too much pressure
on the parachute bay doors from within the rocket. This, coupled with the
potential power problems, may have been enough for the door not to
unlatch.
As we can see on the pictures, the bottom half of the rocket resisted quite well to
the crash landing, which will allow us to reuse the bottom part to build another
rocket.
1.11 Measurements in the Rocket
We actually have no measurement results at all since both the rocket and cansat
radio links failed. With our inability to get the onboard memory to function
correctly, all measurements are unfortunately lost.
The problem with the radio link seems to be with the CNES radio receivers not
receiving a strong enough signal from our transmitters to be able to demodulate
it.
Several problems may have occurred:
 Most probably, batteries were not powerful enough to supply the radio
transmitter, which consumes a lot of power. Indeed, tons of tests were
made before the launch, and the batteries – lithium-ion camera cells –
were not changed before the flight. Using a transmitter near the receiver
lead us to think everything is OK, while the signal couldn’t be received
when we were too far away from the receiver.
 The cansat antenna, which should normally have been 50cm long, was
shortened to a pigtail antenna, making it less efficient. Nevertheless, with
a 300mW TX power, this should not have been a real issue.
 The CNES radio RX equipment was not prepared for receiving our 2 radio
transmitters in parallel. It seems that one of the receivers had a sensitivity
problem, which could explain why it didn’t receive the rocket’s radio
signal. At least one radio link could have been received if we had chosen
16/18

17. to discard the other one, but at the time of the launch we didn’t realize
this.
Both rocket and cansat were able to be recovered even without any GPS data.
Our rocket was recovered by a Japanese team (many thanks to them!) while they
were searching for their own rocket, and the cansat was recovered thanks to a
triangulation process done by Planète Sciences’ volunteers, and visual data.
1.12 Integration of the New Motor
The system was a success. As we can see on the video the motor is
integrated and blocked in the rocket in less than 15s without using any
tools.
1.13 Unexpected Result
As we can see on the video the rocket acted like a glider during the descent. The
only explanation we can come up with is that the cansat bay’s door was acting
like a wing and caused the rocket to glide.
17/18

18. Conclusion
The launch of Leia was not a total success, however we were able to
validate some important aspects of the project:
• The system to eject the cansat laterally from the rocket worked as
planned.
• The use of a first parachute in the cansat permitted us to stabilize
the cansat’s flight.
• The system designed to contain the new engine worked very well,
and was easy to use by the pyrotechnician.
In conclusion, we can say that even if the project did not work entirely as
hoped, we have discovered good solutions to recurring problems which will
allow the club to concentrate all its effort on the cansat and its control for
the 2008-2009 year.
The CLES-FACIL team right before launch.
18/18