Top plate ejection system

 

This system consists of a cutter inside the eBox, a Spectra cord, a Kevlar
cord, two springs and the FFU top plate, (see Figure 39).
Before packing the parachute, the Spectra cord is guided through the cutter
and secured to the eBox by a clamp on the inside. The cord is two folded in
order to increase strength and provide a loop, just outside the eBox, where a
heat resistant, two folded, Kevlar cord loop can be connected. The two free
ends of the Kevlar cord are then guided outside, via a guide plate and a hole
in the frame to the top plate lock mechanism.
Page 71
RX910-SQUID_SED-v4-02February.doc
Figure 39– Principal sketch of the guidance of the rope holding the top plate.
When the parachute has been folded and packed inside the FFU the top plate
is put in place on the frame with the extended part going into the
Page 72
RX910-SQUID_SED-v4-02February.doc
corresponding wall cut-out. With the compression springs in and the Kevlar
cord guided through and attached to the locking mechanism the springs are
loaded by turning the lock rod until the plate is about 4mm below the wall top.
The top plate is then locked in place by guiding two M2 screw through the lock
rod and into the lock base and securing these with a bolt.
Figure 40 – FFU top plate ejection mechanism.
The aramid fibre rope is custom made out of a 1/8 inch tubular shock cord of
Kevlar, first taken apart into single strings and then braided using three strings
to form a ~1 mm braided Kevlar cord. The Spectra cord applied is a Tuf-line
Spectra cord specified to 150lbs. This rope setup has been tested to be able
to withstand at least 40 kg extra load while the system is fully locked and
loaded.
Top plate
securement cut out
Spring + Spring
lock Top plate lock hat x2
mechanism
Page 73
RX910-SQUID_SED-v4-02February.doc
Figure 41 – The braided aramid cord.
The two compression springs employed are made out of stainless steel, have
a spring constant of 11 N/mm and are capable of delivering a maximum force
of 124 N. These springs were used during the successful drop test (see the
SQUID Drop-test Campaign Report under Appendix H – Experiment test
reports) and have also proven to be able to completely separate the top plate
from the FFU during static ground tests which was the initial requirement.
The spring lock hats are secured to the top plate by three M3 screws. The
hats are manufactured out of aluminium with a base diameter of 24mm, the
cylinder outer diameter is 10mm and the hollow shell inside is 8mm in
diameter. Total height is 10.5mm and one side is milled down in order for the
hat to fit inside the walls (see Figure 42).
Figure 42 –Spring lock hat close up.
The top plate lock mechanism features a 16x27 mm aluminium base that is
attached to the top plate by four M3 screws. The base has two 13mm high
perpendicular walls with one large hole for the 4mm diameter lock rod and two
smaller for the M2 screws locking the rod in place. The lock rod is made of
brass and has a 13mm hexagonal section where keys are to be used to turn
Page 74
RX910-SQUID_SED-v4-02February.doc
the rod. The part of the rod with the hexagonal cross section has eight holes
in it for feed through of the M2 lock screws.
Figure 43 – Top plate lock and spring tensioning mechanism
As soon as the altimeter reaches the preset altitude a signal is sent to power
the thermal cutter. Following about 20 seconds after initiation the Spectra
rope will melt by the heat inside the cutter, approximately 150°C, releasing the
top plate which is then ejected by the pre-loaded springs.
The rope to the parachute will be secured to four points on the frame. The
FFU has to be descending with the top facing upwards as the satellite
transmitters are required to be facing this way therefore four attachment
points are required. .
Figure 44 – Ejection of the top plate.
In order to assure functionality of the deployment mechanism tests have been
done as listed in section 5.2.

This system consists of a cutter inside the eBox, a Spectra cord, a Kevlar cord, two springs and the FFU top plate. Before packing the parachute, the Spectra cord is guided through the cutter and secured to the eBox by a clamp on the inside. The cord is two folded in order to increase strength and provide a loop, just outside the eBox, where a heat resistant, two folded, Kevlar cord loop can be connected. The two free ends of the Kevlar cord are then guided outside, via a guide plate and a hole in the frame to the top plate lock mechanism. 

When the parachute has been folded and packed inside the FFU the top plate is put in place on the frame with the extended part going into the corresponding wall cut-out. With the compression springs in and the Kevlar cord guided through and attached to the locking mechanism the springs are loaded by turning the lock rod until the plate is about 4mm below the wall top. The top plate is then locked in place by guiding two M2 screw through the lock rod and into the lock base and securing these with a bolt. 

The aramid fibre rope is custom made out of a 1/8 inch tubular shock cord of Kevlar, first taken apart into single strings and then braided using three strings to form a ~1 mm braided Kevlar cord. The Spectra cord applied is a Tuf-line Spectra cord specified to 150lbs. This rope setup has been tested to be able to withstand at least 40 kg extra load while the system is fully locked and loaded.

The two compression springs employed are made out of stainless steel, have a spring constant of 11 N/mm and are capable of delivering a maximum force of 124 N. These springs were used during the successful drop test and have also proven to be able to completely separate the top plate from the FFU during static ground tests which was the initial requirement. The spring lock hats are secured to the top plate by three M3 screws. The hats are manufactured out of aluminium with a base diameter of 24mm, the cylinder outer diameter is 10mm and the hollow shell inside is 8mm in diameter. Total height is 10.5mm and one side is milled down in order for the hat to fit inside the walls. 

The top plate lock mechanism features a 16x27 mm aluminium base that is attached to the top plate by four M3 screws. The base has two 13mm high perpendicular walls with one large hole for the 4mm diameter lock rod and two smaller for the M2 screws locking the rod in place. The lock rod is made of brass and has a 13mm hexagonal section where keys are to be used to turn the rod. The part of the rod with the hexagonal cross section has eight holes in it for feed through of the M2 lock screws. 

As soon as the altimeter reaches the preset altitude a signal is sent to power the thermal cutter. Following about 20 seconds after initiation the Spectra rope will melt by the heat inside the cutter, approximately 150°C, releasing the top plate which is then ejected by the pre-loaded springs. The rope to the parachute will be secured to four points on the frame. The FFU has to be descending with the top facing upwards as the satellite transmitters are required to be facing this way therefore four attachment points are required.