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I've read in @geoff's answer that SpaceX is doing some experimentation that may lead to fairing recovery capability. In fact I remember hearing Elon Musk mentioning a few years ago that it was being seriously looked at.

Originally I hadn't given them much consideration, and in the back of my head I probably thought of them as big fiberglass shells that kept the wind off of the payload. However within the first minute of each launch there's always the mention of max-Q, and in some un-manned launch cases thrust is reduced during max-Q specifically to decrease stresses in the rocket's frame - thrust is pushing up on the frame while aerodynamic drag on the noise is simultaneously pushing down on it. And the "nose" which experiences this stress is actually the fairing, something that has to separate into pieces and reliably clear the area shortly thereafter.

So I am wondering, what goes into the manufacture of a 21st century fairing that might make it expensive enough to recover and refurbish, and to then convince a customer your going to protect their payload with a used fairing? Expensive high strength alloys? Expensive manufacturing techniques? Integrated sensors and actuators?

The "Skybox" and the "Atlantis" - selected for their SXSE sounding names. 21st century fairings are much more than passive rooftop boxes to "keep the wind off of the customer's stuff."

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    $\begingroup$ I can not remember in which cases thrust is reduced around max-Q to limit structural stresses in the rocket body, allowing some weight reduction. A comment or an edit is appreciated. $\endgroup$
    – uhoh
    Commented Feb 2, 2017 at 17:58
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    $\begingroup$ You may be thinking of the way the Shuttle reduced thrust in the "thrust bucket" around max-Q, but of course the Shuttle no longer flies and wasn't unmanned anyway. $\endgroup$
    – Nathan Tuggy
    Commented Feb 2, 2017 at 19:30
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    $\begingroup$ They don't have to be "so" valuable. They just need to be a little more valuable than it would cost to recover and refurbish them. $\endgroup$
    – Mark Adler
    Commented Feb 2, 2017 at 22:06
  • $\begingroup$ @MarkAdler Improved wording most welcome! I may have used a bit of SE license. I struggled with several variants; "valuable enough", "sufficiently valuable", settled for something that at at least got the job done. "Why might fairing recovery be economically viable?" just doesn't have the same pizzaz, nor flag the fairing itself as my central focus (rather than economic theory of cost-effectiveness). $\endgroup$
    – uhoh
    Commented Feb 2, 2017 at 22:39
  • $\begingroup$ I've asked this follow-up question. $\endgroup$
    – uhoh
    Commented Feb 3, 2017 at 1:54

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It is not so much that in the 21st century it is hard or expensive to make a fairing.

Rather they are just REALLY REALLY big. 13 meters by 4.6 meters.

Falcon 9 Fairing dimensions That is about 40 feet long, and 14 feet wide. The common description is that a school bus would fit in it. (Sort of like the Space Shuttle cargo bay size).

These need to be very light, as every gram/pound of mass, is a reduction in chargeable payload, but they need to be strong, since they are the aerodynamic shell around a very fragile payload as it accelerates from a dead stop at sea level to Mach 25 (I do not know what speed they are at, when they ditch the fairing, but orbital is Mach 25 or so) in orbit.

Thus the aero loads on it can be quite high. The size is quite large. The need to manage weight is quite critical.

All these items conspire to make it cost enough to matter, that recovering it, if possible to do cheaply enough, is a good idea.

In terms of actual construction it is mostly carbon fibre reinforced where needed.

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    $\begingroup$ +1, light plus strong = expensive. The fairing is usually ejected when the vehicle reaches the free molecular flow regime, I think. $\endgroup$
    – Organic Marble
    Commented Feb 2, 2017 at 18:52
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    $\begingroup$ ISTR it's when the mean free path is bigger than the vehicle. This paper gives mean free path vs altitude. science.widener.edu/~svanbram/chem332/pdf/menfpath.pdf $\endgroup$
    – Organic Marble
    Commented Feb 2, 2017 at 21:15
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    $\begingroup$ @ITBear no that's wrong. Speed of sound scales as the average molecular velocity, which scales as the square root of temperature. The effect of pressure is relatively small in comparison, until it's so low that effective sound propagation stops. $\endgroup$
    – uhoh
    Commented Feb 2, 2017 at 23:28
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    $\begingroup$ @OrganicMarble Good news! Instead of using the simple scale height there, I found some tabulated data from the 1976 standard atmosphere. ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19770009539.pdf On page 56 they show the density at 110 km of about 9.7E-08 of standard. MFP scales inversely with pressure, so 70 nanometers at standard atmosphere becomes 72 centimeters, not the 3cm from the simplified model, and the MFP is almost doubling every 5km, so you are basically right, within a few km. $\endgroup$
    – uhoh
    Commented Feb 3, 2017 at 13:52
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    $\begingroup$ I'd just like to add that from the launch vehicle manuals I've read the time the fairing is jettisoned is determined so that the free molecular aerothermal flux remains below 1135 W/m^2 $\endgroup$
    – awksp
    Commented Dec 10, 2017 at 1:33
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The fairings are large structures, made in a way that's difficult to automate. The structure consists of an aluminium honeycomb core with carbon fibre inner and outer panels laminated onto it. Carbon fibre is a labor-intensive material. Then there's the quality assurance that makes everything rocket-related expensive.

Roof boxes, OTOH are injection moulded plastic so the entire shell goes from plastic granules to finished product in 10 seconds. And they are made by the million so it's cost-effective to automate the process.

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It's also possible that they don't want the negative publicity of these farings floating on the surface of the ocean downrange and being either navigational hazards, or a target for environmental concerns. I'd guess they're light enough that they wouldn't burn up and probably would just float after hitting the water.

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    $\begingroup$ Hmmm.... aluminum honeycomb and carbon fiber - wow they might float! I never thought of that. Considering they are "the size of a bus" and there are two of them, and they would probably sit quite low in the water and be harder to spot visually (and perhaps radar) until fairly close, they might be candidates for some kind of navigation hazard. $\endgroup$
    – uhoh
    Commented Feb 7, 2017 at 3:07
  • $\begingroup$ So I've asked this. $\endgroup$
    – uhoh
    Commented Feb 7, 2017 at 3:29
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    $\begingroup$ It seems that finding these on beaches isn't too uncommon collectspace.com/ubb/Forum14/HTML/001305.html $\endgroup$
    – Tyler
    Commented Apr 11, 2017 at 19:45

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