Back   in   October   2016,   two   students   from   DHBW Stuttgart   reached   out   to   us   because   they   needed help   with   a   graduation   project.   The   goal   was   to build   a   water   rocket   which   collects   data   from   the environment    such    as    particulate    matter,    carbon dioxide,    atmospheric    humidity    and    much    more. During     our     first     meeting     in     a     restaurant     we decided   to   help   them   and   made   the   first   steps   in developing   a   concept   for   the   project.   But   we   didn‘t want    to    build    just    a    water    rocket    and    put    the electronics   in   it   -   we   wanted   to   go   a   step   further and develop something new:

THE CONCEPT

The   plan   was   to   place   a   mechanism   on   top   of   a modified    „ Ueberflieger    Mini    Evo “     Water    Rocket, which   should   eject   the   upper   part   of   the   rocket (including   the   electronics)   right   after   reaching   the apogee.   This   enables   the   sensors   to   collect   much more   data   than   on   a   regular   flight   without   probe ejection     since     the     probe     has     a     pretty     large parachute.

The   separation   of   the   probe   and   the   water   rocket should   be   realized   with   a   tommy   timer,   just   like our   regular   parachute   mechanisms   work.   This   was really   challenging   because   the   rubber   band   had   to be    deflected    two    times    at    the    probe.    The    timer itself   is   placed   at   the   ejection   mechanism,   not   at the probe. 

During     the     construction     we     faced     numerous problems.    The    probe    had    to    have    a    sufficient spring   in   order   to   separate   it   from   the   rocket.   But at   the   same   time,   the   mechanism   had   to   be   strong enough   to   prevent   the   probe   to   be   ejected   before reaching    the    apogee.    The    connection    between probe    and    rocket    was    planned    to    consist    of    a shrunken   bottle   (in   hot   water),   but   unfortunately   it turned    out    that    the    rubber    bands    pressed    the probe   so   strong   against   the   connection   that   the spring    wasn‘t    able    to    eject    the    probe    anymore. After   some   prototyping,   we   were   able   to   solve   the problem   with   a   new   connection   which   has   a   stop point,   so   the   probe   and   the   rocket   were   not   able   to stick together anymore.

On   March   26th,   we   were   finally   ready   to   launch   the rocket   with   the   probe.   The   day   started   with   the assembly     of     the     last     components     and     some ground   tests.   In   the   early   afternoon,   we   set   out   to launch   the   rocket.   But   that   didn‘t   turned   out   well: Due   to   a   damage   on   one   of   the   bottles,   the   upper segment   of   the   rocket   exploded   at   14   bar   /   200   psi. Luckily,   the   damage   was   not   as   bad   as   expected. Only    the    ejection    mechanism    had    to    be    rebuilt. And   so   we   were   able   to   start   a   second   attempt   of launching the rocket in the evening…