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2011-09-21

Sugar Shot Weekly Activity Report: September 12-18, 2011‏

Highlights of recent developments on the DoubleSShot project

Markus Bindhammer has provided two follow-up reports detailing his latest experiments with eutectic formulations. Mixtures of potassium nitrate, sodium nitrate and mannitol were studied as was potassium nitrate, sodium nitrate and sorbitol. The mannitol formulation was found to be non-hygroscopic at the humidity levels considered. These eutectic formulations are of particular interest due to the low viscosity of the melted product, which allows for simplified casting:
Eutectic sugar propellant research Part II
Eutectic sugar propellant research Part III

Rick Maschek has begun the process of cleaning, photographing, measuring and careful examination of the various recovered DSS BP motor components. Rick’s examination and measurements of the aft casing indicate that:
1) Rupture due to over-pressurization with initial failure occurring at the casing forward end. The casing ripped into several pieces.

2) Suffered permanent radial deformation due to high pressure (est. > 2000 psi).

This coming weekend, Rick will similarly examine the Forward Casing and Midbulkhead, currently in storage at the FAR site. Rick removed the nozzle from the aft section of the motor in order to examine its condition and that of the ablative liner. After removing the liner and giving it a scrubbing, the "star" shape of the burn pattern is striking.

Surprising is the degree of ablation, considering the burn time was only 1 second. The ablative liner on the MiniSShot nozzles consistently survived the 3-4 second burns very well, with much less erosion. The formulation was modified slightly for the DSS BP motor:
This small change would seemingly not account for the greater erosion, however, some testing will be needed to resolve this inconsistency. It is possible that the anomalous behavior of the motor could have played a role.


Alberto Gassol has begun updating the Showcase pages of the SS2S website and has added a DSS gallery page.

Hans reports that he has basically completed the investigation of when to release the drogue chute, with the follow-up task being to pair the pyros with the suitable avionics devices.

Rick Maschek has started to construct a dedicated "ignition controller" box for SS2S usage. This box will be specifically tailored to ignite dual-phase motors, having two pyro channels and two additional channels for triggering other events such as high-speed video cameras. Emphasis will be placed on high reliability. In the past, we've always relied on "borrowed" hardware to ignite our motors.


Highlights of recent developments on the eXSShot project

Markus Bindhammer has generously fulfilled his commitment to further endorse the SS2S program with a donation of $10,000 USD for funding in support of the eXSShot project. Rick Maschek reports that the funds have arrived into the SS2S bank account. Back in November of last year, Markus rocketed the DoubleSShot project forward at an accelerated pace with a $10,000 donation. This latest exciting development means that we can breathe a little easier knowing that once DSS wraps up to a successful conclusion, we will be on solid financial ground to keep the pace going unabated. A mere "thank you" to Markus would seem to be such an understatement.

Kommentare:

  1. dear mr. bindhammer,

    as i have just been browsing(and enjoying!) your blog and the sugarshot website i was wondering about how you calculated the DoubleSShot-motor-casing thickness.

    referring to http://www.sugarshot.org/downloads/DSS_Mass_Targets.pdf the weight of aft- an forward-casing together should be about 12kg and according to http://www.sugarshot.org/downloads/dss_technical_requirements.pdf they are about 3m long.

    if i do some humble calculus (simplified "Kesselformel") the weigth of a suitable steel(?)-tube is rather 24kg (doubled) ... and also the picture in http://sugarshot.org/gallery/ed107.jpg suggests that the thickness of the tube is rather 2mm (steel) or more -

    s = p*D/Sig_st*2

    s ... tube-wall-thickness
    p ... pressure (assumed max_working_pressure 120bar)
    d ... tube-diameter (assumed 168mm)
    Sig_st ...(UTS - tensible strength of welded_steel 520N/mm²)

    s = 1,94mm

    V = (r²*PI*h) - ((r-s)²*PI*h) = 3dm³

    V ... volume(steel)
    r ... radius
    PI ... const: 3,14
    h ... tube height (assumed 3m)

    m = V*ro_st

    m = 23,8kg

    m ... mass
    ro ... specific mass (steel: 7,85 kg/dm³)


    are my assumptions and calculations far off?

    best regards,
    manuel schleiffelder

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  2. Hi Manual,

    Your calculations are so far right.
    I was not involved in the dimensioning or construction of the motor casing. As far as I know was the max. combustion chamber pressure estimated wih 90 bar and the outer dia. of the casing was 6 inch. I do not know if the tube was welded and which steel was used, so I can not confirm the allowable stress value in Barlow's formula.

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  3. hello markus,

    after some more reading i understand that the final motor-casing will be made from something like fiberglass (at least the pictures from the miniSShot-launch suggest that) - therefore the difference in weight. sorry for the "premature" question *g*.

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  4. Hi Manual,

    Following message from SS2S program director Richard Nakka:

    Thanks for your interest in the SS2S project. With regard to the motor casing, we are using a commercially available fibreglass composite tubing. The mass of this tubing is 2.85 kg/m.
    The two motor sections together are about 3.5 m. length. Mass = 2.85 x 3.5 = 10 kg, so our mass target estimate is conservative.

    best wishes
    Richard Nakka

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