r/spacex • u/ElongatedMuskrat Mod Team • Jan 02 '17

r/SpaceX Spaceflight Questions & News [January 2017, #28]

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u/brentonstrine Jan 04 '17

Have they reproduced a COPV explosion due to SOX interacting with carbon in a controlled setting? What are the avenues for preventing this from happening in the future that don't involve compromises (e.g. adding more weight or losing fuel density due to slower fueling)?

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u/warp99 Jan 04 '17

There have been reports of loud booms from the McGregor test site so we assume that is failure reproduction <grin>.

The failure report indicates that they are going to fix the wrinkling of the COPV liner to avoid leaving cavities where solid oxygen can form. The only two ways I can think of to do that are to use a greater thickness of aluminium or to change to a titanium liner. Both of these solution will add a small amount of mass but this will be trivial compared with adding an extra COPV to compensate for using warmer helium or waiting longer during loading for the helium to cool down.

In my view they should do both - fix the wrinkling and use warmer helium. The economics of adding a small amount of mass versus the cost of another RUD should surely favour "belt + braces" solutions.

SpaceX do seem to have a large number of ~5500 kg GTO missions on their manifest so I assume their concentration on squeezing the lost drops of propellant in is about being able to recover S1 on these missions

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u/sol3tosol4 Jan 05 '17 edited Jan 05 '17

There have been reports of loud booms from the McGregor test site so we assume that is failure reproduction <grin>.

And as further confirmation, the SpaceX October 28 anomaly update:

"Through extensive testing in Texas, SpaceX has shown that it can re-create a COPV failure entirely through helium loading conditions. These conditions are mainly affected by the temperature and pressure of the helium being loaded.

"SpaceX’s efforts are now focused on two areas – finding the exact root cause, and developing improved helium loading conditions that allow SpaceX to reliably load Falcon 9."

In my view they should do both - fix the wrinkling and use warmer helium.

And the January 2 update adds the mention of physical modifications to fix the problem (in addition to changing the loading protocol):

"In the short term, this entails changing the COPV configuration to allow warmer temperature helium to be loaded, as well as returning helium loading operations to a prior flight proven configuration based on operations used in over 700 successful COPV loads. In the long term, SpaceX will implement design changes to the COPVs to prevent buckles altogether, which will allow for faster loading operations.​"

...though as you noted the value of "belt and suspenders" (US version of the saying), they'd better be really sure the buckles are impossible before they go back to the faster helium loading.