Primary payload customers have traditionally been cautious when allowing secondary payloads on the same launcher. For example, a secondary payload is not trusted to have its own chemical propulsion system since it would be explosive.

But how often have secondary payloads caused its primary payload to fail? What are some examples of this happening, or being a strongly suspected cause of failure?

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    $\begingroup$ To my knowledge it has never happened. But I don't have documentation for it, which is why I'm not putting it down as an answer. $\endgroup$ – Carlos N Jun 10 '18 at 9:38
  • $\begingroup$ i side with Carlos N, while i am yet see an instance where the secondary payload has caused contamination with the primary payload, i guess the guidelines are in place to reduce the risk and for striking up lower insurance figures for the payload and the launch. $\endgroup$ – Amongdastarz Nov 20 '18 at 9:26
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    $\begingroup$ There was an instance where a secondary payload interfered with a different secondary payload - two cubesats stuck together due to magnets on one of them. $\endgroup$ – SF. Apr 26 at 14:50

To my knowledge, there has never been an instance where a secondary payload has damaged a primary payload, at least that is proven and publicly known.

Oftentimes secondary payloads are of lower quality than primary payloads, and issues with the secondary payloads do have the potential to damage the primary payloads. The cost of these secondary payloads is significantly less than a primary payload. The customer who is paying the most isn't going to want any risk to their payload that costs hundreds of millions of dollars when there is a payload in the cost of maybe $10 million. There are a multitude of ways these can cause issues, one of the more common one shows up in the "Coupled Load Analysis", where the loads on the spacecraft are studied for any potential issues, usually in some kind of a simulation. This looks for resonance frequencies with the entire system, and can often spot problems that need to be resolved prior to a launch that aren't seen with a single satellite. The failed launch of resupplies in "The Martian" could have been prevented with a good coupled load analysis being performed prior to launch.

In effect, this is similar to the "Big boat rule", which simply states "Big Boats rule" when it comes to right of way issues. It isn't strictly required, but you aren't going to risk something that costs hundreds of millions or even billions for something that cost a million or less, no matter how small that risk might be.


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