Princeton University attempt at a suborbital space shot?

Discussion in 'High Power Rocketry (HPR)' started by RGClark, Apr 21, 2018.

  1. Sep 12, 2018 #121

    RGClark

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    Just saw on USC's Rocket Propulsion Lab mailing list that they intend to make an attempt at the 100 km altitude for suborbital space Sept. 29, 2018. So with Virginia Tech and TU Wien, at least three teams plan to make an attempt by the end of this month.

    Bob Clark
     
  2. Sep 13, 2018 #122

    plugger

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    I'm a bit confused by the TU Wien project publicity. They definitely talk about the Hound being 100km capable but the project page title on their website is "42km - The Hound" and includes the quote "Our simulations suggest that – dependant on the actual reload type – the rocket will reach altitudes greater than 42 km above ground and fly velocities exceeding Mach 3."

    I don't think it's realistic to expect a COTS CTI 98mm to 75mm two stage solid to reach 100km.
     
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  3. Sep 13, 2018 #123

    RGClark

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    It is similar to the Princeton attempt in using COTs motors. The Princeton team showed their OpenRocket simulations suggestion 100 km is technically feasible. The issue is whether they can get their upper stage to fire reliably.
    Like the Princeton team they don’t use airframes to save weight, just using a fin can for each stage.

    Bob Clark
     
  4. Sep 13, 2018 #124

    eggplant

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    That's part of the problem.
     
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  5. Sep 13, 2018 #125

    grouch

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    So these guys are just sim ninjas?
     
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  6. Sep 13, 2018 #126

    Reinhard

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    Upper stage ignition will be one of the biggest "ifs", but the topic was not completely without consideration. ;-)

    There was no complete test, for a variety of reasons. But some component testing was done. One hope was that an easily ignitable propellant might have a better chance than Loki Red. At least for Blue Thunder, this doesn't appear to be the case. It was not possible to ignite an uncontained grain with an ematch at an absolute pressure of 100mBar. Estes A10 will ignite, but not reliably so (~50 % success). At higher pressures (upper stage ignition is not planned at 100mBar) ignition gets more reliable but not enough tests were made to quantify that. If an A10 ignites, it will generate enough gas and heat to ignite a nearby BT grain, but probably not enough to overpressure a M motor. It is also not a very fast method, without sharp transits, so there should hopefully be some heat transfer before the nozzle plug will be expelled. The nozzle plug is 3d printed mostly from flexible filament. Basically a rubber plug in the convergent section of the nozzle. There is a secondary plug in the divergent part, to protect the primary plug from the stage separation charge.
    There are a bunch of things, that could be done better, but some of these options carry significant costs or regulatory burdens. I guess it would be better to throw something like BKNO3 at the problem, but this wasn't practical for us.

    The initial plan back than (around 2014) was to build a rocket that can exceed 40km. It wasn't hard to convince the other team members, that 42 is a much better number. ;) Simulations indicated early on, that more is possible with the basic concept. For most of the time, this wasn't publicly announced. Earlier released simulation plots contained significant ballast to keep the "official" altitude low. Personally, I would have preferred to stay with the 42km+ story on the outside, but I'm probably a lousy PR person.
    From a mass fraction/performance perspective, I don't think the goal is completely unrealistic. But there are countless things that can go wrong during flight, especially if the envelope gets pushed and related experience is rare.
    Historically speaking, these kinds of projects are not very successful. They are interesting though and I finally have a good excuse to attend BALLS :).

    Sorry for hijacking the wrong thread. I should start a new one, but currently I don't have too much time.

    Reinhard
     
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  7. Sep 14, 2018 #127

    plugger

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    Not really. From The Hound web page:

    So they're not using the Loki 54mm baby M, but a 75mm CTI M. Most likely a M2245 given the 6GXL casing, but possibly a M1545.

    Here's their sim graph that clearly indicates ~47km for simulated apogee.

    [​IMG]

    I reckon it'd be pretty hard to more than double their projected max altitude from ~150k' to ~330k'.
     
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  8. Sep 14, 2018 #128

    plugger

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    And that's what Curt did for his flight that went over 200k', which was a 4" booster to 4" sustainer. Below is a link to a picture of that rocket.

    http://www.traphx.com/wp-content/gallery/phx4/PHX4.jpg
    According to tfish his motors were a N5800 booster and N1100 sustainer. The sustainer is ~4,000Ns more powerful than the largest Ns motor The Hound could accommodate and is a "better fit" from a sustainer staging perspective as it's a 12.5 second long burn motor. I don't think there's much margin for optimisation above what Curt can do. Hence my scepticism regarding the TU Wien stack truly being 100km capable.
     
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  9. Sep 14, 2018 #129

    Andrew_ASC

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    Massless sim components sure would inflate apogee values.
     
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  10. Sep 14, 2018 #130

    plugger

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    Thanks for chiming in Reinhard, it's always good to hear from the source so to speak. First off, good luck on your flight! I hope y'all are able to both stage successfully and recover!
    I'm with you that simulations indicate more is possible but I think you'd run into all sorts of issues if you tried to squeeze too much more out of the stack. Looking at your simulation graph for The Hound it appears that you're planning on lighting the sustainer at ~230m/s or ~750f/s. That's from my understanding right about where you want to be from a staging velocity perspective, or just a touch low. If you attempt to squeeze more coast time before sustainer ignition you might start to run into some other issues.
    Regardless, GOOD LUCK!
     
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  11. Sep 14, 2018 #131

    RGClark

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    They posted the results of their OpenRocket sim on their Facebook page:

    https://m.facebook.com/245686032125543/posts/2286071868086939/

    that shows it reaching 100 km.

    However, I would prefer they posted the full OpenRocket sim so we can see the breakdown of weights of the rocket.


    Bob Clark
     
  12. Sep 14, 2018 #132

    plugger

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    Thanks for sharing that Bob, I hadn't looked at the comments in that post. I must say I'm even more confused now. Looking at the post you'll notice the "staging logic" for lack of a better term is roughly identical to the sim plot above.
    [​IMG]
    So by my reading it appears their motor choices and sustainer ignition times are virtually identical and yet they've more than doubled their apogee figure. The only way they could have "gotten there" from my perspective is elimination of weight and possibly length. Still, that's a lot of altitude gained by mass optimisation.
     
  13. Sep 14, 2018 #133

    RGClark

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    How do professional solid rocket companies ensure high altitude ignition for their solid rocket orbital stages?

    Bob Clark
     
  14. Sep 14, 2018 #134

    ksaves2

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    I think BKNO3 perhaps and Zirconium but Zr can be very dangerous and sensitive to static electricity when used in the ZPP form. https://en.wikipedia.org/wiki/Pyrotechnic_initiator
    There's always "augmented" thermite but that can be as hairy as ZPP. I've heard of fliers making BKNO3 pellets and using it successfully and augmented thermite. None of which I'll
    discuss details on the open forum. "Augmented" thermite is doctored so it has a lower heat of activation so it's easier to get it started. I was lucky I didn't hurt myself with the thermite
    when I was experimenting with it (Would go off with an ematch at least in powder form). I've never progressed to staging so I abandoned further testing and never used it to light anything. Will Pyrodex work at altitude or no? Just wondering as
    that would be the simplest remedy if it would work. Another thing would be an initiator to start some loose coarse propellant chips. In that case, would need a means to keep the chips in
    a "bunch" to keep the G forces from breaking the ignition pack apart. Also maybe HEI (head end ignition) might simplify the electronics/igniter setup? Excuse me if I missed some details in the
    earlier parts of this thread.

    Oh, for fun I put a single 38mm cored grain on the ground and put a bit of 4f in there and an ematch. Stood back, pushed the button and just saw a flash and nothing else. Inspected the grain, made sure it was cool, put a bit of augmented
    thermite in and an ematch. Pushed the button and the grain caught and burned. That was the limit of my testing. Doing it enclosed at high G's and at high altitude I know is another story. Kurt
     
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  15. Sep 14, 2018 #135

    Nytrunner

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    Short answer: Experience, Money, and Years of Qualification testing

    Not as short answer: Giant igniter elements at the head of their propellant column. Sometimes specific grain geometries to allow more surface area during initiation (see the Thiokol 11pt star for shuttle boosters). There is a forum member that works for such a company and shared a photo of the installation of one such igniter element. Initiator and core are designed to function together to get the right heat flux and pressure conditions for that motor. These designs are then validated through extensive test and qual programs.
     
  16. Sep 14, 2018 #136

    markkoelsch

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    I understand the issues getting enough heat flux with reduced air pressure etc in the core. I see the idea of a plug in the nozzle. How does this not cause a Cato, or does it fail at a fairly low pressure?

    Has anyone thought about possibly filling the nozzle with a low density foam ( maybe a Urethane) to hold the igniter in place, and keep the vast bulk of the air in the core? Possibly just in the divergent nozzle?
     
  17. Sep 14, 2018 #137

    Nytrunner

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    That's the kicker. How to tune the plug or burst disk Juuuuust right so that it allows just enough pressure for the motor to catch, but fails before problems happen.
     
  18. Sep 14, 2018 #138

    KC3KNM

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    I’m still quite ignorant to motor design, but I think it’d be fairly simple to test a plug design. If you take a motor casing and nozzle you plan to use and build a forward closure with a fitting for an air line, it’d be possible to test plugs to see if you could get any real consistency as well as fine tune to the pressure you’re after. Not sure if that’s a viable idea or not, though. I’m sure there’s plenty of variables such as temperature and external pressure that will effect this, but it could at least get someone in the ballpark.
     
  19. Sep 14, 2018 #139

    Nytrunner

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    I agree such a setup has potential if they had the time to design and iterate it. Sort of like a custom HEI closure cap but with the inlet and a pressure transducer

    A hitch I see is: what is the necessary successful ignition pressure? Making some assumptions based on the highest thrust reload for that hardware could get them a "safe" pressure that will blow the plug/disc and not reach case limits. That's the easy part of the effort. Here's one for the motor formulators out there, if the motor reaches such a pressure and then the plug lets go, would there then be a chuff or some other startup issue? If so, then it'll become a lot harder to dial it in.
     
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  20. Sep 15, 2018 #140

    grouch

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    What about a burst disk that is between the two top grains? Something that would hold the pressure long enough to light the top grain then easily burn though? Maybe an acrylic type disc?
     
  21. Sep 15, 2018 #141

    Nytrunner

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    That's out if they're attempting to use commercial motors. Although in the realm of research, that could be an avenue. May require more testing than a student team can afford.
     
  22. Sep 20, 2018 at 2:48 AM #142

    RGClark

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    Last edited: Sep 20, 2018 at 2:54 AM
  23. Sep 20, 2018 at 3:20 AM #143

    blackjack2564

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    High temp wax plug [ canning paraffin] & BKNO3 pellets.
    Holds enough pressure & will release instantly, no damage.
    Vast amount of hot gas to ignite all. Matters not if in vacuum or -100degrees. Functions same at all altitudes & space. [heat transfer wise]
     
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  24. Sep 20, 2018 at 9:08 AM #144

    egp

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    The Virginia Tech team is on their way to Gerlach with a two stage minimum diameter rocket. Custom 8-inch single-grain P-class motors. Good luck to them. Wish I was there to observe, advise and assist. IMG_0310.jpg
     
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  25. Sep 20, 2018 at 2:38 PM #145

    eggplant

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    Were these motors static fired?
     
  26. Sep 20, 2018 at 6:38 PM #146

    RGClark

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    Is that also at Balls 27?

    Bob Clark
     
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  27. Sep 20, 2018 at 7:45 PM #147

    boatgeek

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    By the time the paraffin plug blows, is the burning motor generating enough hot gas that the internal pressure doesn't drop much? The words "release instantly" make me think about chuffing. I'm probably having a "that's all well and good in practice, but it will never work in theory!" moment though. :)
     
  28. Sep 21, 2018 at 11:57 AM #148

    egp

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    Yes. They are planning to fly on Saturday.
     
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  29. Sep 21, 2018 at 2:50 PM #149

    RGClark

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    Cool! It's going to be exciting!

    Semper Altius!
     
  30. Sep 23, 2018 at 10:51 PM #150

    RGClark

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    Just saw that the TU Wien team had the same problem as the Princeton team in that the upper stage failed to ignite:

    https://twitter.com/tuspaceteam/status/1043898974174756864

    Perhaps these student teams should get advice from the professional launch companies about how to ensure high altitude ignition for solid motors.

    Bob Clark
     

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