Cheap Steel Fairings for small payload Falcon 9 missions

[RedKraken]

Why does SpaceX use expensive fairings for small payloads ?

I'm talking about any GTO mission around 3 tonnes or less.

Or any LEO mission at all  since the adaptor is rated about 10 tonnes, when the vehicle is capable of 23-24 tonnes.

Falc9 has so much margin on these missions. 

Why use a super-light, expensive, 6 month lead-time fairing when you could use a very cheap, expendable steel fairing?

I must be missing something important.

 

Some fairing info : https://www.reddit.com/r/spacex/comments/7llf74/anatomy_of_a_falcon_9_fairing/

 

The current composite fairing weighs in at about 2 tonnes.

 

Steel is about 5 times the density of composite (8000 kg/m3 versus 1600)

A cheap 10 tonne fairing in steel would penalise less than 10% of its payload (GTO or LEO) on small payload missions.

And you could throw it away without incurring a significant loss.

(Doesn't work for larger payloads because the deltav margins are too fine.)

The booster does all of the hard work, and does not care if it is lifting 550t or 560t off the pad.

The upper stage is 115t (normal fairing) or 123t(proposed heavy fairing), but only carries the fairing for 30 seconds in a 300 second burn.

I'm sure spacex must have looked at cheap, heavy fairings but decided against them.

What is the reason?

[Xd the great]

How about aerodynamic stress?

Perhaps their metallurgy team is too busy on starship?

[RedKraken]

I don't think it could be structural stress.

The fairing can be as strong (and heavy) as you need.... even a 20t fairing wouldn't put a big dent in the small payload performance.

Although after 25t i expect you would have to start reenforce the stages like FH...or redesign from scratch...not worth it.

You could be right about the teams/personnel.

Starship has all of the priority now.

[Starman4308]

Based on a 2-ton estimate for fairing mass, and a cost of carbon fiber from this article, I estimate the bulk material of the fairing to be roughly $300,000.

What I've heard is that each fairing costs $5 million a pop.

 

Wherever the remaining $4.7 million is coming from, it's not from the bulk material, but rather in things like:

Ensuring no contaminants will get onto valuable payloads

Telemetry sensors

Fairing separation machinery

Testing fairing separation machinery to death, so that $500 million satellites don't fail because of a fairing issue.

 

As such, I strongly doubt they would save any money whatsoever by making a second, steel-based fairing manufacturing line.

[StrandedonEarth]

A big part

2 hours ago, RedKraken said:

Why use a super-light, expensive, 6 month lead-time fairing when you could use a very cheap, expendable steel fairing?

I must be missing something important.

One important service the fairing provides is acoustic mitigation and protection. A cheap cone of steel would probably be pretty loud, and they don't have the engineering resources to spare to make it quiet, especially for an edge case. Why add another item to produce in their manufacturing space, when they don't have to?

[RedKraken]

4 hours ago, Starman4308 said:

I strongly doubt they would save any money whatsoever by making a second, steel-based fairing manufacturing line.

I'm thinking you are right....

2 hours ago, StrandedonEarth said:

acoustic mitigation and protection

I had not considered this.

[Jaelommiss]

I'm not sure how much they would actually end up saving. R&D is expensive, opening a new production line is expensive, hiring new employees to work on that line is expensive, renting or building an additional factory (assuming there's not sufficient space in their current facilities) is expensive. Saving 40% of their fairing costs on some flights probably wouldn't recoup the costs that are required up front in a reasonable time frame. The new employees that this would require is an expense that will eat into any savings.

More importantly than all of that, designing and implementing a new fairing introduces a potential point of failure in a mature and reliable product.

[p1t1o]

Carbon fibre is light. 2 tons of it is a lot. Besides the starting materials (which are...soot and plastic) the manufacturing processes are quite involved. It has to be baked in vacuum, for a start.

When a 5kg carbon fibre tour-de-France bike can cost 20k, 5 mill for a 2000kg fairing sounds reasonable.

I'd wager that a steel fairing would not be strong enough, and a heavy fairing, taking advantage of leftover lift capacity, might have disadvantages not immediately obvious. Eg: steel strength falls rapidly with temperature increase or a heavy steel fairing might be cheaper to build but more expensive to handle (being ten times heavier), it could easily be a health+safety thing that cannot be predicted simply from the bulk properties of the material.

The least likely explanation is that they are wasting money on an expensive fairing with a cheap option right there. Id wager there is something that makes a steel fairing more expensive in the long run, or the CF one cheaper, above and beyond their respective retail prices.

Edited January 25, 2019 by p1t1o

[RedKraken]

On 1/25/2019 at 2:45 AM, Jaelommiss said:

Saving 40% of their fairing costs on some flights probably wouldn't recoup the costs that are required up front in a reasonable time frame

Yes. Not enough savings to justify new line.

The cost savings might look like 2-3 million on 8 (out of 24) launches per year. 

~20 million savings per year....just isnt enough.

Starman3408 nailed it.

I would be interested to know what a steel equivalent of the composite fairing would weigh (guess 300%?), and how much quicker (easier) it could be produced.

It may not be useful for spacex.

But other agencies might be interested.

Edited January 25, 2019 by RedKraken

[kerbiloid]

Spoiler

Make it even cheaper.

Cast'em from iron

 

[magnemoe]

7 hours ago, RedKraken said:

Yes. Not enough savings to justify new line.

The cost savings might look like 2-3 million on 8 (out of 24) launches per year. 

~20 million savings per year....just isnt enough.

Starman3408 nailed it.

I would be interested to know what a steel equivalent of the composite fairing would weigh (guess 300%?), and how much quicker (easier) it could be produced.

It may not be useful for spacex.

But other agencies might be interested.

Yes, same reason they have not made an smaller diameter and shorter fairing who would also be cheaper. 

[Starman4308]

On 1/25/2019 at 6:14 AM, p1t1o said:

Carbon fibre is light. 2 tons of it is a lot. Besides the starting materials (which are...soot and plastic) the manufacturing processes are quite involved. It has to be baked in vacuum, for a start.

When a 5kg carbon fibre tour-de-France bike can cost 20k, 5 mill for a 2000kg fairing sounds reasonable.

I'd wager that a steel fairing would not be strong enough, and a heavy fairing, taking advantage of leftover lift capacity, might have disadvantages not immediately obvious. Eg: steel strength falls rapidly with temperature increase or a heavy steel fairing might be cheaper to build but more expensive to handle (being ten times heavier), it could easily be a health+safety thing that cannot be predicted simply from the bulk properties of the material.

The least likely explanation is that they are wasting money on an expensive fairing with a cheap option right there. Id wager there is something that makes a steel fairing more expensive in the long run, or the CF one cheaper, above and beyond their respective retail prices.

If you look at the article I linked, that $300,000 figure I quoted includes shaping.

My guess is that Tour de France bikes cost $20k due to the complex shapes involved, and possibly because the manufacturer can charge $20k. Meanwhile, a Falcon 9 fairing is a relatively simple shape, likely meaning easier manufacturing... and I'm not even sure it's carbon fiber, it might be some other type of composite.

EDIT: Added three extra zeros initiallly.

Edited January 29, 2019 by Starman4308

[DerekL1963]

On 1/23/2019 at 3:19 PM, RedKraken said:

I'm sure spacex must have looked at cheap, heavy fairings but decided against them.

What is the reason?

Among other things, they'd have to modify the fairing mountings to take the higher weight/stress.  And they'd have to develop new separation mechanisms to ensure the heavier fairing separated cleanly.  And they'd have to go through and recalculate how the weight changes the vibration levels.  And...  well, you get the picture.  It's not nearly so simple as just swapping out the material the fairing is constructed from.