Why does the JWST’s secondary mirror need to be supported by a tripod?

Question

Obviously not because of gravity or to make it stable enough in wind, but then why?

I imagine that the [diffraction spike pattern](https://en.wikipedia.org/wiki/Diffraction_spike#/media/File:Comparison_strut_diffraction_spikes.svg) caused by a single supporting element would be preferable to that caused by 3 of them, so there must be a good reason.

Edit: perhaps more important than the diffraction spike pattern, a single supporting element would mean less weight we need to get into space, which is expensive.

In: 2

Answer 1

> Edit: perhaps more important than the diffraction spike pattern, a single supporting element would mean less weight we need to get into space, which is expensive.

The opposite would be true. It’s like deciding whether to use a truss or a single beam to build a bridge. A single beam with the same strength will weigh more than a truss.