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Author: Richard Nakka
In the duration since the previous test firing that occurred
at the end of July, much work had been done to resolve
the propellant disbonding issue that plagued earlier grain
casting attempts. A satisfactory solution was eventually
developed. This involved curing of the propellant under
clamping pressure, in conjunction with a casting tube
manufactured from high-temperature, absorbent gasket material.
For this fourth firing, it was only necessary to cast
six grain segments for reloading of the 1st phase motor
casing. . The 2nd phase had not been fired in the previous
test, due to an inadvertent failure to arm the ignition
system. The grain segments for this test were made to
a slightly larger diameter than previous, to achieve a
close fit within the casing. This was done as it was decided
not to line the 1st phase casing with thermal insulation,
as had been done for the preceding test, due to the difficulty
that was encountered in removing the degraded insulation
material after firing the motor. The insulation had been
epoxy-bonded to the casing. Removal required a great deal
of peeling and scraping after soaking in solvent for several
days. Other tasks that needed to be done in preparation
for the fourth firing, besides propellant casting, were
casting of a replacement pyrogen grain, and casting of
the RNX delay plug inside the mid-bulkhead
The date for this fourth firing
had been originally projected to occur in mid-September,
but eventually slipped a week. By then, preparations had
come together nicely and by the 22nd, everything was set
for the test firing to take place the following day. Weather
had been a factor during the last test, when rain made
for complications and delays during setup of the test
equipment. Although the forecast had suggested rain might
once again show its unwelcome face, the forecasted probability
was low enough that postponement of the test wasn't justified.
As such, early Saturday morning
Tarun Tuli, Daniel Faber and I headed to the test site,
a two hour drive to the Columbiad Commercial Test Range.
This time the drive there was mercifully uneventful. We
arrived just after noon hour. After resting for a short
while, we proceeded to begin setting up for the test firing.
Richard Graf, of Columbiad Launch Services, gave us a
welcome hand in setting up the test stand, instrumentation
shelter and with mounting the rocket motor in the stand.
Preparations went very smoothly, without any noteworthy
glitches. The only snag was a malfunctioning FRS radio,
one of three brought along for communication. The rain
held off, in fact, the sun broke through the clouds as
we neared completion of the preparations.
After setting up the equipment,
the rocket motor was assembled, the tandem load cells
mounted in the stand and confirmed to be functioning,
the two pressure transducers were mounted on the motor,
and the eight thermocouples attached at their assigned
locations to the motor casing and nozzle. Following this,
it was time to fish out the final checklist that had been
prepared in order to help ensure all final preparations
would go smoothly and without oversight. This involved
doing a confirmation that both ignition systems were fully
functional, that data acquisition was activated, as well
as confirmation that the video recording cameras were
adjusted and turned on. I did a last minute walk around
of the motor to get visual confirmation that nothing obvious
had been overlooked or was askew. Following this, the
others left the vicinity and took up positions at the
firing safety area, while I stayed behind to do the final
connections of the igniters to the ignition boxes.
Following the checklist procedure,
electrical continuity to both igniters was confirmed,
and then both ARM switches were thrown from the SAFE position
to the ARM position. I alerted the others over the FRS
radio that both systems were being armed, and subsequently
hurried to the safety area to join the others. I had taken
on the duty of announcing the countdown and, using a stopwatch,
tracking the time following burnout of the first phase.
The second phase was to be fired 18 seconds later. Tarun
was once again assigned the task of pressing the firing
button for both phases. After confirming that all participants
were ready, and that Tarun had turned the key to arm the
firing button, I announced the countdown.
Five - 4 - 3 - 2 - 1 - fire!
Immediately the motor roared to life, firing with an exceptionally
loud shriek and sending a large white smoke plume well
beyond the treetops, high into the cool autumn air. The
thrusting of the motor continued forcefully for about
three seconds, then tailed off as the propellant was consumed.
Black smoke could then be seen issuing from the nozzle
from the burning delay plug and hot residue inside the
motor. I pressed the "start" button on my stopwatch
as soon as burnout occurred. When the stopwatch read "13"
seconds of elapsed time, I began the second countdown:
5 - 4 -3 - 2 - 1 - fire! At this cue, Tarun pressed the
second ignition button. After a brief moment, the motor
once again awakened, roaring to life in much the same
manner as it had moments earlier. The intensity of the
sound was much the same, as was the burning duration,
but in my mind, the three seconds seemed eternally longer,
knowing that these were the critical seconds that had
doomed the first two BEM firings. As the thrust tailed
off and came to an end, accompanied by a weird, brief
whistling sound, relief and awe silenced us all for but
a moment. Then the cheers and hand-clapping of victory
replaced the sudden silence, followed by hand-shakes all
around.
The data acquisition systems
for the thermocouples, load cells and pressure transducers
once again worked well. Good data was collected which
will be analyzed in detail in the days to come. A brief
look at the data showed that the motor overpressurized
to some extent, during the first phase firing, reaching
a peak pressure of approximately 1700 psi (12 MPa). Initial
thinking is that erosive burning once again factored into
the performance of this somewhat temperamental propellant.
Thermocouple data looked reasonable for the first phase
burn, with the nozzle throat reaching a peak temperature
of 450oC. (850oF.). However, the temperature data exhibited
aberrant behaviour during the rapid temperature rise of
the second firing. Both of these issues will have to be
scrutinized carefully in the days and weeks to come.
A post-firing teardown of the
motor showed it to be in excellent condition. Debris from
the second phase grain inhibitor was found nested in the
mid-bulkhead throat. This was likely the cause of the
unusual whistling sound that was heard. Examination of
the video showed a plume of black smoke that erupted briefly
during the second burn, which was undoubtedly a sizeable
fragment of ejected inhibitor material.
It was highly rewarding to see
it all come together and culminate as well as it did.
A tremendous amount had been learned over the course of
the three prior BEM firings, as well as some valuable
lessons in planning and preparedness. This allowed for
many improvements to be incorporated. Undoubtedly, this
will help us improve the odds of success for upcoming
phases of the Sugar Shot to Space project. As it stands,
this successful demonstration of the “two-phase”,
re-startable rocket motor concept is a milestone in our
quest for reaching space.
Photos
Preparations
- Casting
setup with provision for clamping the propellant during
cure
- 6
newly cast propellant segments for 1st phase motor
- A
pair of freshly cast pyrogen grains
Setting up for the test
- Unpacking
our gear at the test range
- Tarun
checking out the laptops used for data acquisition
- Daniel
and Tarun adjusting the motor mounts
- Mounting
the thermocouples is a three man job
- Daniel
in the thick of things
- Motor
just moments before firing
Fire!
- Motor
under full 1st phase thrust
- After
1st phase burnout, black smoke issues from nozzle
- Motor
under full 2nd phase thrust
- Motor
smoulders after burnout
- Close
up of motor smouldering after burnout
- Nozzle
close up
- Thumbs
up!
Post-firing teardown
- Large
fragment of propellant inhibitor nested in mid-bulkhead
throat
- Extruded
o-ring residue at nozzle joint
- Heat
affected paint tells the story
- Motor
components were in pristine condition after cleaning
Video
Panorama
view of motor firing (hi-res, 4.8 meg, wmv format)
Panorama
view of motor firing (medium-res, 1.9 meg, wmv format)
Close-up
view of motor firing (hi-res, 6.1 meg, wmv format)
Close-up
view of motor firing (medium-res, 2.4 meg, wmv format)
Close-up
view of motor firing (lo-res, 840k, wmv format)
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Project
Description
