Re: A noteworthy amatuer space shot.

[Pat Flannery]

Ken S. Tucker wrote:
> In the case of the Sugar Shot to Space team they have been planning
> and testing for over 3 years, using IMHO solid engineering and theory,
> and are learning by scaling up, so tough stuff like vibrations and
> resonance is to measured and analysed on test rockets.
>

I still think the fuel isp is too low to make this a workable concept.
Also, the very high fineness ratio of the rocket is great for low drag,
but is going to mean a very high weight for the motor casing when you
consider the internal pressure it's going to have to withstand during
ascent.
And trying to cast a motor grain that long and thin isn't going to be
easy either, particularly getting a central bore down it that's
dead-center in it. You are going to have to cast the whole works in one
pour, and hope there aren't any bubbles or gaps in it.
Trying to cast it in multiple pours will lead to discontinuities between
the pours due to shrinkage as the fuel cools... in fact, considering the
size of the intended motor grain, shrinkage on cooling with even a
single pour is going to be a major problem that could well cause the
fuel to debond from the casing or develop internal cracks.
Then there are the inherent problems of the fuel itself - like a lot of
early solid fuels, caramel candy isn't very flexible and can crack or
debond from the motor casing if the casing is bumped or flexed during
transport (or given the fineness ratio of this design, bends under its
own weight during erection on the pad) or exposed to temperature changes
between manufacture and firing, leading to uneven combustion and
unexpected pressure peaks that can rupture the motor.
I had one that suffered internal cracking on ignition due to too robust
of a black powder ignition system, and led to a planned three second
burn being reduced to one second of very high thrust. Luckily, the
casing was a iron plumbing pipe, as this was just to test the fuel and
ignition systems for it, and it didn't rupture.

Pat

[Ken S. Tucker]

On Aug 8, 7:23 pm, Pat Flannery > wrote:
> Ken S. Tucker wrote:
> > In the case of the Sugar Shot to Space team they have been planning
> > and testing for over 3 years, using IMHO solid engineering and theory,
> > and are learning by scaling up, so tough stuff like vibrations and
> > resonance is to measured and analysed on test rockets.
>
> I still think the fuel isp is too low to make this a workable concept.
> Also, the very high fineness ratio of the rocket is great for low drag,
> but is going to mean a very high weight for the motor casing when you
> consider the internal pressure it's going to have to withstand during
> ascent.
> And trying to cast a motor grain that long and thin isn't going to be
> easy either, particularly getting a central bore down it that's
> dead-center in it. You are going to have to cast the whole works in one
> pour, and hope there aren't any bubbles or gaps in it.
> Trying to cast it in multiple pours will lead to discontinuities between
> the pours due to shrinkage as the fuel cools... in fact, considering the
> size of the intended motor grain, shrinkage on cooling with even a
> single pour is going to be a major problem that could well cause the
> fuel to debond from the casing or develop internal cracks.
> Then there are the inherent problems of the fuel itself - like a lot of
> early solid fuels, caramel candy isn't very flexible and can crack or
> debond from the motor casing if the casing is bumped or flexed during
> transport (or given the fineness ratio of this design, bends under its
> own weight during erection on the pad) or exposed to temperature changes
> between manufacture and firing, leading to uneven combustion and
> unexpected pressure peaks that can rupture the motor.
> I had one that suffered internal cracking on ignition due to too robust
> of a black powder ignition system, and led to a planned three second
> burn being reduced to one second of very high thrust. Luckily, the
> casing was a iron plumbing pipe, as this was just to test the fuel and
> ignition systems for it, and it didn't rupture.
>
> Pat

Your objections above are certainly valid, however using advanced
technology such as the Bates Grain in Fig.4 simply explained here,
http://www.nakka-rocketry.net/th_grain.html
many problems you mention can be alleviated as proven by testing,
which are now successful.

Mr. Nakka and Rob came to our place, we had a frozen lake front
good for rocket testing, (see the pix of the fish, I painted that :-).
http://www.nakka-rocketry.net/ldx001.html

The test stand was placed on the dock and the firing took place to
test the inhibitor, evidentally suggesting the need for improvement,
because it exploded, following a brief successful impulse, but that's
what R&D is for.

Pat I'm glad you're critical cuz it makes me think!
Ken

[Pat Flannery]

Ken S. Tucker wrote:
>
> The test stand was placed on the dock and the firing took place to
> test the inhibitor, evidentally suggesting the need for improvement,
> because it exploded, following a brief successful impulse, but that's
> what R&D is for.
>
> Pat I'm glad you're critical cuz it makes me think!
>

Okay, I see this motor uses four propellant segments with a inhibitor
along their outside edges.
So far, so good.
But... when the engine casing is pressurized by the burning fuel, it is
bound to stretch a bit. The slight increase in diameter shouldn't be a
problem, as the inhibitor should be able to compensate for that as the
four fuel segments will be pushed outwards from the central bore towards
the inside wall of the casing.
But looking at the photos, it doesn't look like there is any sort of
inhibitor on the _end_ of the propellant segments.
So when the case stretches along its _length_ on initial pressurization,
slight gaps could be created between the ends of the individual segments
that the flame could infiltrate, causing them to greatly increase their
burning surface and leading to contact between the combustion gases and
the motor casing wall right from the start of the burn. As the burn
continues, the segments could come loose inside of the casing as they
shrink in length due to burning on their ends, and that can't be good
either.
On the Space Shuttle SRBs, a non-combustible putty is is placed between
the ends of the individual motor segments when they are mated to prevent
flame infiltration between them as they burn. It was this putty that
temporally sealed the gas leak on the Challenger SRB after the O-ring
failed on launch.
You might want to try the same concept on your individual rocket
segments when they are assembled, and have a close look at the interior
of the motor casing of the failed engine to see if anything unusual is
noted at the points where the four segments met, indicating flame got
between them after ignition. That would certainly be one solution to the
unexpected rise in casing pressure as the burn went on.
On the design I was working on, the inhibitor was going to be several
layers of fiberglass tape, as this would adhere to both itself and the
propellant grain and give it great structural strength to resist both
expansion and stretching during burning (I never contemplated using
multiple fuel grains in a single motor).
As far as igniting the engine goes, don't give into the temptation of
using a sparkplug screwed into the front bulkhead of the motor casing
with some propellant on it. I tried that, and the sparkplug blew out on
ignition, leaving a hole in the motor of larger diameter than the
exhaust nozzle...meaning a strap-down test with the exhaust nozzle
facing upwards turned into a launch of a rocket with flame coming out
both ends... and no stabilizing fins on it.
Luckily, this went over my house, rather than through it.
That system was replaced by a plastic soda straw full of black powder
stuck up the central bore, which led to the grain cracking and runaway
burn I described in the earlier posting.
On its only flight test - this time with fins - and sitting in a
disposable pie tin on top of a snowbank, the pie tin being the "blast
deflector", the same ignition system (and everyone standing way, way,
back in case it blew) was used. The screw-on upper iron end cap of the
plumbing pipe blew off and went several hundred feet into the air*,
while the rocket body itself was pushed down through the pie tin and
ended up a couple of feet deep in the snowbank.

*Apparently taking a lot of the fuel grain with it somehow, as it was
trailing smoke all the way.


Pat

[Ken S. Tucker]

On Aug 9, 9:25 am, Pat Flannery > wrote:
> Ken S. Tucker wrote:
>
> > The test stand was placed on the dock and the firing took place to
> > test the inhibitor, evidentally suggesting the need for improvement,
> > because it exploded, following a brief successful impulse, but that's
> > what R&D is for.
>
> > Pat I'm glad you're critical cuz it makes me think!
>
> Okay, I see this motor uses four propellant segments with a inhibitor
> along their outside edges.
> So far, so good.
> But... when the engine casing is pressurized by the burning fuel, it is
> bound to stretch a bit. The slight increase in diameter shouldn't be a
> problem, as the inhibitor should be able to compensate for that as the
> four fuel segments will be pushed outwards from the central bore towards
> the inside wall of the casing.
> But looking at the photos, it doesn't look like there is any sort of
> inhibitor on the _end_ of the propellant segments.
> So when the case stretches along its _length_ on initial pressurization,
> slight gaps could be created between the ends of the individual segments
> that the flame could infiltrate, causing them to greatly increase their
> burning surface and leading to contact between the combustion gases and
> the motor casing wall right from the start of the burn. As the burn
> continues, the segments could come loose inside of the casing as they
> shrink in length due to burning on their ends, and that can't be good
> either.

The purpose of the Bates grain is a neutral rate burn, see,
http://74.125.155.132/search?q=cache:kIrMac-Ahn0J:www.rockets4schools.org/education/HPR_Motor_Basics.pdf+%22bates+grain%22&cd=4&hl=en&ct=clnk
and it is 'supposed' to burn the segment ends, that's how it's
designed.

> On the Space Shuttle SRBs, a non-combustible putty is is placed between
> the ends of the individual motor segments when they are mated to prevent
> flame infiltration between them as they burn. It was this putty that
> temporally sealed the gas leak on the Challenger SRB after the O-ring
> failed on launch.
> You might want to try the same concept on your individual rocket
> segments when they are assembled, and have a close look at the interior
> of the motor casing of the failed engine to see if anything unusual is
> noted at the points where the four segments met, indicating flame got
> between them after ignition. That would certainly be one solution to the
> unexpected rise in casing pressure as the burn went on.
> On the design I was working on, the inhibitor was going to be several
> layers of fiberglass tape, as this would adhere to both itself and the
> propellant grain and give it great structural strength to resist both
> expansion and stretching during burning (I never contemplated using
> multiple fuel grains in a single motor).
> As far as igniting the engine goes, don't give into the temptation of
> using a sparkplug screwed into the front bulkhead of the motor casing
> with some propellant on it. I tried that, and the sparkplug blew out on
> ignition, leaving a hole in the motor of larger diameter than the
> exhaust nozzle...meaning a strap-down test with the exhaust nozzle
> facing upwards turned into a launch of a rocket with flame coming out
> both ends... and no stabilizing fins on it.
> Luckily, this went over my house, rather than through it.
> That system was replaced by a plastic soda straw full of black powder
> stuck up the central bore, which led to the grain cracking and runaway
> burn I described in the earlier posting.
> On its only flight test - this time with fins - and sitting in a
> disposable pie tin on top of a snowbank, the pie tin being the "blast
> deflector", the same ignition system (and everyone standing way, way,
> back in case it blew) was used. The screw-on upper iron end cap of the
> plumbing pipe blew off and went several hundred feet into the air*,
> while the rocket body itself was pushed down through the pie tin and
> ended up a couple of feet deep in the snowbank.

Nakka developed an excellent solution to ignition combined with a
Delayed Ejection Device here,
http://www.nakka-rocketry.net/skydart2.html
((I'm over credited in the article))
The DED is a sort of Fail-Safe should the electrical/electronic charge
expulsion system fail.

> *Apparently taking a lot of the fuel grain with it somehow, as it was
> trailing smoke all the way.
> Pat

Here is a cheap and very reliable igniter we developed,
http://www.nakka-rocketry.net/igniter.html#Ultra
specifically for sub-zero, high-g operations, highly versatile.
Ken

[Pat Flannery]

Ken S. Tucker wrote:
>
> Nakka developed an excellent solution to ignition combined with a
> Delayed Ejection Device here,
> http://www.nakka-rocketry.net/skydart2.html
> ((I'm over credited in the article))
> The DED is a sort of Fail-Safe should the electrical/electronic charge
> expulsion system fail.
>
>
>> *Apparently taking a lot of the fuel grain with it somehow, as it was
>> trailing smoke all the way.
>> Pat
>>
>
> Here is a cheap and very reliable igniter we developed,
> http://www.nakka-rocketry.net/igniter.html#Ultra
> specifically for sub-zero, high-g operations, highly versatile.
> Ken
>
It's apparent we come at design problems from two different
directions...I prefer the KISS approach, and my ignition system
consisted of the aforesaid soda straw and a length of waterproof cannon
fuse, except in the sparkplug debacle. ;-)
If I was going to develop a recovery system (the idea was to make the
rocket either tough enough to withstand a impact with no parachute, or
cheap enough just to be expended on each launch, although I did give
some thought to having it come down in deep water to brake its impact
and then release some sort of tethered float to pull it up by) it would
probably also have been based on cannon fuse, with one end being placed
in a small hole in the side or top of the rocket casing that would
ignite when the burn reached the outside of the fuel grain, or went
through a slightly thicker section of fuel at the top that would
continue to burn after the main fuel grain had been expended.
If the central bore was going to be anything other than cylindrical it
would have been star shaped, although as long as liftoff velocity was
sufficient to let the fins get a good grip on the air, I really didn't
have any particular need to keep a constant thrust during the burn, but
overbuilt the casing to handle the high thrust at the end of the burn.
In the case of the Lambda failure:
http://www.nakka-rocketry.net/ldx001.html, the thrust-pressure graph
shows something very odd going on...the graph lines go almost straight
up till casing failure and never start to level off towards a
sustained-thrust burn as the Bates grain was supposed to accomplish.
You obviously have a lot more experience at this than I ever did, but
if it were me, instead of trying to build a all-out flyable motor design
right from the get-go I'd do something along the lines of my
"fuel-tester" motor...a way overbuilt and reusable non-flying engine
that would be as strong as a cannon barrel that you could try out
different fuel mixtures, grain designs, and exit nozzle designs in
without fear of it rupturing, while measuring internal pressure and
thrust curves during a test.
These tests could be done fairly quickly and at fairly low cost; once
the burn was generating the desired thrust curves, burn time, and
internal pressure, then it would be time to build a fly-capable version
using a lightweight motor casing capable of handling the demonstrated
behavior of a particular fuel grain design, since the variables would
now be known quantities.

Pat


======================================= MODERATOR'S COMMENT:
JDL

[Ken S. Tucker]

On Aug 10, 9:42 pm, Pat Flannery > wrote:
> Ken S. Tucker wrote:
>
> > Nakka developed an excellent solution to ignition combined with a
> > Delayed Ejection Device here,
> >http://www.nakka-rocketry.net/skydart2.html
> > ((I'm over credited in the article))
> > The DED is a sort of Fail-Safe should the electrical/electronic charge
> > expulsion system fail.
>
> >> *Apparently taking a lot of the fuel grain with it somehow, as it was
> >> trailing smoke all the way.
> >> Pat
>
> > Here is a cheap and very reliable igniter we developed,
> >http://www.nakka-rocketry.net/igniter.html#Ultra
> > specifically for sub-zero, high-g operations, highly versatile.
> > Ken
>
> It's apparent we come at design problems from two different
> directions...I prefer the KISS approach, and my ignition system
> consisted of the aforesaid soda straw and a length of waterproof cannon
> fuse, except in the sparkplug debacle. ;-)
> If I was going to develop a recovery system (the idea was to make the
> rocket either tough enough to withstand a impact with no parachute, or
> cheap enough just to be expended on each launch, although I did give
> some thought to having it come down in deep water to brake its impact
> and then release some sort of tethered float to pull it up by) it would
> probably also have been based on cannon fuse, with one end being placed
> in a small hole in the side or top of the rocket casing that would
> ignite when the burn reached the outside of the fuel grain, or went
> through a slightly thicker section of fuel at the top that would
> continue to burn after the main fuel grain had been expended.
> If the central bore was going to be anything other than cylindrical it
> would have been star shaped, although as long as liftoff velocity was
> sufficient to let the fins get a good grip on the air, I really didn't
> have any particular need to keep a constant thrust during the burn, but
> overbuilt the casing to handle the high thrust at the end of the burn.
> In the case of the Lambda failure:http://www.nakka-rocketry.net/ldx001.html, the thrust-pressure graph
> shows something very odd going on...the graph lines go almost straight
> up till casing failure and never start to level off towards a
> sustained-thrust burn as the Bates grain was supposed to accomplish.
> You obviously have a lot more experience at this than I ever did, but
> if it were me, instead of trying to build a all-out flyable motor design
> right from the get-go I'd do something along the lines of my
> "fuel-tester" motor...a way overbuilt and reusable non-flying engine
> that would be as strong as a cannon barrel that you could try out
> different fuel mixtures, grain designs, and exit nozzle designs in
> without fear of it rupturing, while measuring internal pressure and
> thrust curves during a test.
> These tests could be done fairly quickly and at fairly low cost; once
> the burn was generating the desired thrust curves, burn time, and
> internal pressure, then it would be time to build a fly-capable version
> using a lightweight motor casing capable of handling the demonstrated
> behavior of a particular fuel grain design, since the variables would
> now be known quantities.
> Pat

In place of KISS, perfecting a rocket to fly into space, with
instrumentation and returning it safely to Earth, uses QUEST,
"Quality Underwrites an Eventually Successful Team".

Consider 10 critical events, and place a 90% probability that
each will be successful, then the mission success becomes,
(0.9)^10 ~ 30%.
Boost Event Quality to 99% and (0.99)^10 ~ 90% is the success
rate, still a bit low, but near acceptable, if you're willing to
accept
1 out of 10 will fail.
Next, imagine you are in the nosecone, how would you feel?
I think that's the ultimate pre-flight test and design construction
criteria in the Team.
Ken

[Pat Flannery]

Ken S. Tucker wrote:
> In place of KISS, perfecting a rocket to fly into space, with
> instrumentation and returning it safely to Earth, uses QUEST,
> "Quality Underwrites an Eventually Successful Team".
>
> Consider 10 critical events, and place a 90% probability that
> each will be successful, then the mission success becomes,
> (0.9)^10 ~ 30%.
> Boost Event Quality to 99% and (0.99)^10 ~ 90% is the success
> rate, still a bit low, but near acceptable, if you're willing to
> accept
> 1 out of 10 will fail.
> Next, imagine you are in the nosecone, how would you feel?
> I think that's the ultimate pre-flight test and design construction
> criteria in the Team.
>

But you are doing all-up testing where you can't estimate the
probability of success of any part of the system. If the casing on the
Lambda hadn't ruptured, what would the thrust and internal pressure have
been like during the rest of the burn?
It might have just been ready to level out when the casing ruptured, or
it might have kept right on going up till it hit double what it did when
the casing blew. Knowing that is going to make a very big difference in
how you design a follow-up motor, but you don't have any data on it, as
your data stops at casing rupture. On the next attempt you might make
the casing too light and it will rupture again, or overestimate what's
needed and end up with a motor that is heavier than what's needed and
cuts into overall vehicle performance.
And you are going to need every last bit of motor performance versus
weight you can squeeze out of it on the Sugershot if you really do want
it to go into space using that propellant composition.
Also, if you can fire a particular grain design repeatedly, and get the
same approximate operating values over and over again, you can be pretty
sure that you have that particular part of the design licked, and move
on to other components of the rocket.

Pat

[Ken S. Tucker]

Hi Pat and fella's

> On Aug 11, 4:28 pm, Pat Flannery > wrote:
> Ken S. Tucker wrote:
> > In place of KISS, perfecting a rocket to fly into space, with
> > instrumentation and returning it safely to Earth, uses QUEST,
> > "Quality Underwrites an Eventually Successful Team".
>
> > Consider 10 critical events, and place a 90% probability that
> > each will be successful, then the mission success becomes,
> > (0.9)10 ~ 30%.
> > Boost Event Quality to 99% and (0.99)10 ~ 90% is the success
> > rate, still a bit low, but near acceptable, if you're willing to
> > accept
> > 1 out of 10 will fail.
> > Next, imagine you are in the nosecone, how would you feel?
> > I think that's the ultimate pre-flight test and design construction
> > criteria in the Team.

In High School we evolved a group that became a rocketry club, circa
1970,
and we finally evolved a simple reusable solid rocket motor. We
discovered
the propellant Sucrose + Salt-peter on our own. In powdered form (SS1)
it
was quite unstable as a rocket fuel, but ok for pipe bombs, but when
melted
to SS2 it was a reliable propellant.
>From that, we evolved a simple standard motor, (Orion), about 12" long
with
a hardwood 1.5" nozzle, with a 0.25" throat and 1" plug in a 1.25" Al
tube,
with a prescription for the propellant, inhibitor and progressive burn
drill.
Once standardized, we were able to put the rocket into a 20 foot
circle at
400' lateral from a zenith (apogee) altitude of 1000', accounting for
wind.

We went on to create a successful 3' long 3" dia motor (Quasar) that
was
successful, but stressed our merger high school kids budget, and it
took an
effort to fuel it...lot's of cooking.

For me that effort provided a motivation (for a disinterested average
student)
to learn calculus for ballistics, chemistry for propellants,
engineering for the
fuselage pressure, aerodynamics for the fin design, electricity and
electronics
for ignition systems, group management and coordination during
procurement,
construction, and launch safety, documentation, and probability theory
where
each component is certified per standards.

> But you are doing all-up testing where you can't estimate the
> probability of success of any part of the system. If the casing on the
> Lambda hadn't ruptured, what would the thrust and internal pressure have
> been like during the rest of the burn?

You can't really estimate probability in an R&D experiment, what you
can
do is strip down post firing and compare that to predicted parameters,
and
the deviation from prediction is entered into the failure probability.
In the case of Challenger - in hindsight - we see a variation from
prediction
that predicts an increased probability of failure together with a lack
of
understanding that persists. IOW's NASA (IMO) still doesn't
understand
SRB's.

> It might have just been ready to level out when the casing ruptured, or
> it might have kept right on going up till it hit double what it did when
> the casing blew. Knowing that is going to make a very big difference in
> how you design a follow-up motor, but you don't have any data on it, as
> your data stops at casing rupture. On the next attempt you might make
> the casing too light and it will rupture again, or overestimate what's
> needed and end up with a motor that is heavier than what's needed and
> cuts into overall vehicle performance.
> And you are going to need every last bit of motor performance versus
> weight you can squeeze out of it on the Sugershot if you really do want
> it to go into space using that propellant composition.
> Also, if you can fire a particular grain design repeatedly, and get the
> same approximate operating values over and over again, you can be pretty
> sure that you have that particular part of the design licked, and move
> on to other components of the rocket.
> Pat

You got that Pat. The SS2S team is getting ready to fly.
~~~~ ====> to space......
Ken