If you have a chance, talk to Dr John Rusek at Purdue and CEO/founder of
Swift Enterprises. We worked together at the rocket lab at Edwards AFB,
AFRL during the 80's..
John's a very talented, experienced and down to earth rocket guy and just
plain fun person to work with and talk rockets. We formulated modified
Asphalt solid rocket propellants that rivaled composited HTPB formulations
of which I shared here on aR a few years ago. Currently I've been
collaborating with him on an experimental high energy ingredient that
models indicate a 10-15% boost in ISP which can be used in solid,liquid and
hybrid systems.
Ken
Ken
On Tue, Nov 30, 2021 at 8:47 AM Jim Rosson <jmrosson@xxxxxxx> wrote:
James:
Glad I can help. If you get near Purdue University in Indiana, hit the
library. They have had active 'rocket' programs since 60's and have most
of old AIAA/JANNIF in stacks.
IME - Arrhenius equation extrapolation of service life is reasonably
accurate for PU binders, even when thermal cycled. Temp cycling was
handled by simulating both extreme temperatures. Usually find actual
measured values between the two curves?
What changes the service life results is when cycling of temperature
creates stresses that exceed the bond strength of polymer to filler or
composite mixture to the liner; creating extra surface area that changes a
rocket motor into a bomb upon ignition. The challenge I found in small
hobby size motors is always the polymer to filler bond.
Been out of the game awhile, but DOT used to require certified HTPB
propellants to have 10 year service life. This data point is not
officially monitored by DOT. And never seen DOT ask for test data on a new
product? :)
Out of curiosity, cut apart some 8-10 year old motor grains from my
earliest AMW development motors for destructive analysis. Did Instron pull
testing on dog bone samples. Results align with your inspection and were
as expected? I used combination of perchlorate and nitrate oxidizers for
color generation. In early days tested several different wetting agents to
improve filler bonding, and had some old data on what worked best. Got
best results with combination of amine and ethyl-silane. Age samples
showed a much larger gap between good and once marginal - now bad; bonding
agents. Testing showed any propellant exposed to moisture showed lower
strength due weak bond on 'wet' nitrates. The large diameter perchlorate
showed slight adhesion degradation due moisture, with filler dropping out
of matrix during testing. All of the samples properly stored in a moisture
barrier bag with desiccant; only showed slight PU degradation resulting in
crack formation during pull, despite a higher strength due loss of
plasticizer. One strange result? It seemed like the moisture reduced the
plasticizer leech out, as' wet' sample PU was not as strong as dry
samples? None of grains show evidence of liner debonding, even the 5.5" OD
grain.
Also put some of these same aged motor grains on test stand. The nice
part was despite a stiffer PU; the burn time and thrust curves were within
10-15% of the original test data averages (typically with a slightly faster
burn rate). I have since flown several 15+yr old hobby motors and have yet
to have a failure with anything stored in 0-110°F storage.
Cheers!
On November 30, 2021 at 7:33 AM J P <james.padfield@xxxxxxxxx> wrote:
Jim, many thanks for that advice!
Unfortunately, where I work now doesn't have good access to a library.
The university I used to work at *may*have access to some of the old
AIAA/JANNAF, and I get back there occasionally since I still work on a few
projects with them, and get asked to give guest lectures sometimes. So I
may be able to find something there. I'll also look into the other missile
systems you mention.
Yes, the tactical missile motor compositions that use RDX or HMX are
closer to my PBX compositions, however my understanding from the literature
that I have read is that the predominant mechanisms of ageing are (i)
plasticiser loss, and/or (ii) oxidation of the PU binder (most likely, IMO,
probably a combination of both). Ageing of the nitramines isn't usually a
factor in ageing of the composition (as I understand - I may be completely
wrong!). In fact we just pulled some bombs loaded in PBXN-109 (RDX, Al,
HTPB-IPDI, DOA), after 15 years in the magazines, and the RDX doesn't
appear to have aged at all. The mech props of the PU though have changed -
it has become significantly stiffer, less flexible. More or less what we
expected, but it is nice to actually get our hands on the samples and
confirm it!
Annex C to AOP-46 has an interesting discussion that uses the Arrhenius
equation to relate accelerated ageing studies to long-term storage life,
which (if this kind of thing interests you) you may find useful, if you
weren't already aware of it. It's only really applicable to constant
temperature ageing/storage though, applying it when the temperatures are
cycled is a little trickier...
Thanks again,
James
On Mon, 29 Nov 2021 at 17:57, Jim Rosson <jmrosson@xxxxxxx> wrote:
James:
You want solid propellant service life data? I might be able to help:
See if you get your hands on a copy of text book: Volume 170 of Progress
in Astronautics and Aeronautics, title Tactical Missile Propulsion.
Chapter 5 has treatise on service life predictions .vs actual.
Can also find articles in old AIAA/JANNAF journals from many
rocket/missile programs service life studies. Most of these antique
publications are not online, even if you are member of organization; so
might need to visit a decent science tech college library to find them.
Look for dedicated studies on Polaris, Minuteman, Titan, and Shuttle SRB
solid booster motors. These studies usually detail the polymer blend,
oxidizers, and additives.
The amateur community focus is on "safer" HTPB polymer system, and leave
the DOT 1.1 materials to experts. Regardless, Tactical missiles often use
HMX/RDX modifiers that might be more interesting to you? Couple current
missile programs like Aim-9 Sidewinder and AIM-120 AMRAAM; have published
service life studies. Couple of vehicles in the Nike missile project
<https://en.wikipedia.org/wiki/Project_Nike> had several service life
studies published. There are also some NATO member and other international
service life reports on non-US missile systems. These are all hiding in
same old AIAA/JANNAF periodicals. Some of newer declassified articles
published since 2000 can be found online.
Another source of solid propellant service life data is gas generators
used in automotive airbags, and aircraft exit slide inflation. They used
different oxidizers to lower flame temperatures, but they use polymer
binders that can be useful comparison. Have to hunt around the
automotive/aircraft tech journals for the papers, but they have published
extensive measured .vs. predicted service life studies at command of US
federal gubermint and NHTSA/FMVSS regulations.
Cheers!
Jim