SpaceX and its salty nuts

To say that rockets are complex things is almost ridiculous, an observation that is so patently obvious that the phrase “rocket scientist” has passed into common cultural usage to mean, someone who works with very complicated things.


Then one wonders why Space Exploration Technologies’ (SpaceX) rocket scientists made such a basic mistake with the 570kg (1,254lb) to low Earth orbit (LEO) Falcon 1 launcher that led to its disastrous maiden fight on 31 March this year. Reading the 25 July update by SpaceX founder Elon Musk on his company’s website it would seem that his engineers designed a fuel system using two incompatible metals that build up a high electrochemical potential between them when the environmental conditions are damp and salty. That’s the conclusion of spaceflight commentator Dr Jeffrey Bell, and as an engineer (and recovering powerpoint user) myself I find that theory very plausible. Certainly the Falcon 1 accident report found that the likely cause of the failed ascent was an aluminium nut on its fuel system corroding and leaking fuel, which led to a fire during ascent, which led to an engine shutdown at T+34s. 


One explanation for that design mishap is that the launch was moved from the original site at the US Vandenberg air force base to the Kwajalein Atoll. The vehicle was simply not designed for a Pacific ocean Atoll environment. But in engineering that is no defence.


The Atoll is the Ronald Reagan Ballistic Missile Defense Test site. It’s been a US Army missile firing range for decades. According to a contact of Bell’s “standard operating procedure [at the Kwajalien Atoll] was that all parts had to be electrolytically compatible and even then, all bolts got…a Teflon grease…put on them and all moving interfaces, bearings, slides, got coated in lithium grease.”


One wonders why SpaceX did not follow the Army procedures – I’m assuming this contact is a test range serviceman, or woman. And as corrosion begins on the surface it is slightly worrying that, as Bell puts it, “the fuel pipe joints corroded away but nobody noticed.”


Kwajalein is to be the launch site for SpaceX’s rockets for seven out of the next ten launches, with the location of an 11th contract yet to be announced. One of those seven is the maiden flight of the company’s larger 9,300kg to LEO Falcon 9 rocket, to be launched in the first quarter of 2008.


In his 25 July update Musk gives a number of changes to tackle the corrosion problem and discusses further additions to the launch sequence. That would all appear to be welcome but as any engineer knows the more complex a system is, the more things can go wrong. And with the decision to massively increase the number of parameters tracked by sensors during the count down “by an order of magnitude greater than in the past” SpaceX is just asking for anomalous readings and further launch delays; which in themselves can be a danger in a corrosive salty environment.


SpaceX and its vehicles have a great potential to change the face of the launch business. Interestingly Lockheed’s International Launch Services has already decided to drop out of the 1.5t, and less, to LEO market. That company has clearly taken into account the environment in which it’s working. SpaceX should, literally, do the same. After all such a decision is common sense not rocket science.

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