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The Falcon 9 fairing costs millions of dollars. It is 5.2 meters wide while the rocket itself is only 3.7 meters wide. There is no aerodynamic reason that the fairing has to be so big, since Dragon has the same width as the booster. For small spacecraft like TESS, a much shorter (and therefore lighter) fairing with half the cross-sectional area (for less dynamic pressure) would obviously suffice: TESS in fairing

Why doesn't SpaceX use smaller fairings for smaller payloads?

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  • $\begingroup$ Related: space.stackexchange.com/questions/23621/… $\endgroup$ – Everyday Astronaut Apr 16 '18 at 20:35
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    $\begingroup$ I suspect this is mostly a business decision. I'd guess that developing fairings to custom suit needs is more expensive than taking a small performance while being able to assembly line/copy paste a bunch of fairings. This saves engineering time, allows focused improvements, and every new fairing could have unexpected sidefects that would need to be tested. Atmospheric forces and effects at supersonic speeds can do strange and hard to simulate. $\endgroup$ – Dragongeek Apr 16 '18 at 20:53
  • $\begingroup$ Designing and tooling a much smaller and lighter fairing would probably cost more in R&D than the cost of the kerosene it would save to use on this launch. $\endgroup$ – Russell Borogove Apr 16 '18 at 21:47
  • $\begingroup$ @RussellBorogove if Kerosene is in fact the only issue. There is a potential payload delta-v limitation due to drag. I'm not sure if that's the cause of the narrow 40-second launch window (Why is TESS' launch window open for only 40 seconds per day?) for this complicated orbit or not, but for a deep space mission with a small payload, a giant oversized fairing could be a limiting factor. $\endgroup$ – uhoh Apr 17 '18 at 4:04
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    $\begingroup$ Maybe that is the smaller fairing. $\endgroup$ – A. I. Breveleri Apr 17 '18 at 15:56
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One of the keys to SpaceX's cost advantage is standardization on common parts. One example is the Merlin engine, which is used on both the first and second stages of the Falcon 9 and Falcon Heavy (though a slightly different vacum optimized version on the second stages).

This is also done for fairings. Fairings are very expensive to make (around $6M). Designing the largest possible fairing to work for any possible missions will cost less than designing customized fairings for specific missions. And design time can impact launch cadence.

And building one type of large fairing for each launch probably costs less than building smaller types for various missions, even if smaller fairings require less material. Some reasons are because there are required processes, such as assembly, testing, loading, etc that are safer/more consistent and easier to optimize if they apply to the same size/design of fairing each time.

But even if the build cost is actually lower for smaller fairings, SpaceX intends to recover and re-use fairings. Again recovery benefits from a standardized design/size, not just for the recovery process (which needs space for parachutes/steering jets/etc), but for re-use. Having a small, a medium and a large fairing would mean not re-using each as often and require a higher inventory of each (what happens when you have back to back small fairing launches and not enough time to refurb/test the first fairing?). Re-using a large \$6M fairing twice as often as a small $3M fairing means the large fairing will cost less per launch.

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    $\begingroup$ Good answer why they aren't using a smaller fairing on this launch. Why it's this size largely comes down to EELV. The US Aif Force designed some standards to make their lives simple and they largely permeated the entire launch industry. en.wikipedia.org/wiki/Evolved_Expendable_Launch_Vehicle $\endgroup$ – Evan Steinbrenner Apr 16 '18 at 21:35
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    $\begingroup$ The cost of assembling a fairing is less of an issue than the cost of testing and qualifying a new fairing design. $\endgroup$ – Hobbes Apr 17 '18 at 11:10
  • $\begingroup$ @Hobbes I don't buy that. Sure, R&D for everything in a rocket is costly, but a fairing is still much more of a dumb, sturdy shell than the intricacies of a rocket engine with hundreds of individual details that could fail. The reason it's so expensive are the materials, but you'd think the engineers have a pretty good idea of how the material properties scale to different size. Likewise, the ærodynamic properties can be modelled pretty well with CFD simulations, especially if you have lots of reference data from one size already. I reckon it's really the reusability aspect that dominates. $\endgroup$ – leftaroundabout Apr 17 '18 at 13:16
  • $\begingroup$ @leftaroundabout coming from aircraft, I reckon Hobbes is correct. $\endgroup$ – fectin Apr 18 '18 at 0:20
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    $\begingroup$ @leftaroundabout "a pretty good idea about how the properties scale" is not the same as actually having tested those properties. I have a pretty good idea about the nature of life, the universe, and everything - but i haven't tested any of it. $\endgroup$ – Knetic Apr 18 '18 at 6:00

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