[SS-Propellant] Launch of the Propellant Development phase of SS2S

[Mateica Vlad]

Rich Nakka <richnakka at rogers.com> wrote:Welcome to the SS2S Propellant Development Team (PDT) e-mail discussion group
!  <>

Team members: 
<>* Richard Nakka 
* Randy Dormans 
* Matthew McFarland 
* Chris Richards
* José Miraglia (please confirm whether or not  you received the earlier test message)
* Vlad Mateica
* Antoon Vyverman (Antoon, have you signed up to the list? I am cc’ing you for now)  <>
---
What is on our agenda?  <>

First, the big news is that test firing of the ¼ scale motor  (BEM) will be taking place soon, tentatively at the beginning of December. With sorbitol based propellant (KNSB) being used, it can be expected that the motor thrust curve will experience the odd behaviour that has been seen in the past with KNSB motor. That is, the “triangular” thrust curve, rather than the predicted “flat” curve that BATES should provide.  <>

For those of you not familiar with this phenomenon (which I’ll refer to as “flushing” coined by,  C.Knight ), I recommend reading the test report of the Kappa-SB motor:
http://members.aol.com/kappadx/ksb002.html#Analysis

Note that the use of primer coating and  pyrogen ignition does not eliminate this behaviour.
<>Also check out C.Knight’s hypothesized explanation for this phenom:
http://www.nakka-rocketry.net/knsbchar.html  <>

Tony Vyverman has written an excellent article that also hyhpothesises certain causes such as partially-delayed igntion:
http://sugarshot.org/downloads/evaluation_of_kno3.pdf <>It is important that we avoid this type of behaviour for the SS2S motor, for two important reasons: 
1) We need full thrust off the pad to get the rocket stable quickly to avoid any deviation from the desired flight path.

2)  The low average chamber pressure resulting from a “triangular” thrust significantly cuts into the delivered specific impulse, which we cannot afford. The sims for the flight are based on an average 130 sec. Isp.
 <>Suggestions are needed on how we can modify the KNSB propellant, or the motor design to achieve this goal.  <>

Miraglia has suggested the use of a sorbitol/sucrose (SB/SU) mixture. This is an interesting option. Although this may not eliminate the flushing problem (see Tony’s report) it may nevertheless help, or such a formulation could provide other advantages. For example, sucrose has a greater density, which means more propellant mass for a given motor  volume.  A 1 or 2 % performance gain might be realized, based on my calcs.  <>

My own feeling of late is that flushing might be a result of the grain segments being too close together, causing a sort of self-extinquishing. Perhaps we can do  static testing to see if greater spacing helps. Also consider instead of flat faces on segments, have end surfaces sloped (shallow cone). A really interesting suggestion put forth by Tony is the use of KNSU on segment ends. This would also boost thrust off the pad, due to KNSU’s greater burn rate. Instead of KNSU, perhaps KNSB doped with  Iron oxide ? Thoughts?  <>

Additives such as carbon or iron oxide to act as opacifier  can also be considered/tested.  <>

Erosive burning behaviour of  KNSB should be investigated. Perhaps someone can come up with a test proposal. 
Consider small modifications to the formulation to improve Isp (e.g. 66/34 instead of 65/35)?  GUIPEP runs can be done to get an idea if this is worthwhile. Runs can also be done on KN/SB/SU formulations.
<>If the propellant formulation is changed in any way, testing will need to be performed to characterize burnrate & c-star, as well as other qualities such as hygroscopicity and safety with regard to overheating during casting.  <>

Much of the testing can be done using small, scaled down motors.  Vlad has volunteered to do some static testing. Randy, could you do some testing as well? I can do propellant characterization tests, such as strand burner. I may also be able to do limited static testing, say, with the A-100M motor. 

<>The next major SS2S motor test will be the “short-stack” motor. Before this, we need to come up with a means of casting large propellant grains. The short-stack is slated to have 2 segments, each with a mass of about 34 kg (75 lbs), which is identical to the full-size motor. Also, curing the grains under pressure to ensure positive bonding to the casting tube will need to be investigated and testing done. <>So there is no shortage of work for the PDT, and no shortage of ideas that need to be put forth. 
And  please respond to the ss-propellant list, not to me personally, to keep this a group project.


Richard Nakka


 


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Hi!

I will make some static testing with the A-100 motor as soon as I will get my test stand operational and put my hands on some sorbitol(I should receive about 800grams). Richard told me that the SB/SU mixture when is moltem it becomes like water witch is a verry good thing. I hope that when the KNO3 is added the mixturewill still be fluyd enough to cast it into the molds. We could make a multiple grain configuration to the bates. We could make the first bates with a star shape grain to have a maximum burning area, and we could make the ends conical. After that we could use the normal round grain. 

I made some simulation in GUIPEP and have some good results with a combination of 65grams KNO3+ 22,75 grams sugar+12,25grams sorbitol I ended up with impuls of about 164(the highest of all) 

Vlad



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