Author Topic: Fairing reuse  (Read 590305 times)

Offline Jim

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Re: Fairing reuse
« Reply #740 on: 03/29/2017 05:46 PM »

I've often wondered if you could get by with an inflatable design,

Not viable.  See elsewhere in the forum as to why.

Offline whitelancer64

Re: Fairing reuse
« Reply #741 on: 03/29/2017 06:00 PM »
TBH I've never really understood need for the very rigid, heavy fairings that LV's use.

I've often wondered if you could get by with an inflatable design, soft of like those emergency half circular shelters, but with two edge to edge and both on end.

 Seriously? For max Q, we're talking around mach 1 and airliner cruising altitude. That's a pretty tough gig. I don't see too many inflatable supersonic aircraft going about.
The difference between launch and cruise.  During launch dynamic pressure is quoted in pounds per sq foot because the rise in terms of psi (IE 1/144 smaller) is pretty small. I could see the need for a rigid fairing if there is a real fear of impact damage to the outside of the payload or if the fairing has inside ties to the payload to keep in place. 

The former is a real threat but the latter is not done AFAIK, even for payloads that require "vertical launch" due to the fragility of some of their components.

A lot of common practice in this industry seems to have evolved during the development of ICBMs.

I'd also point out that Joseph Kittinger and Felix Baumgarntner have gone supersonic in free fall inside nothing but a flexible sack (or "pressure suit" as I like to call it   :)  ).

Rigid nose cones assured the aerodynamics and their weight was acceptable. But LV's don't sit in silos for decades with staff walking around them periodically for inspection that might damage their payloads by dropping tools on them. The best way to protect a payload is inside a vehicle assembly building, followed by a transfer to the pad and a launch ASAP.

The two issues I can see are the very high noise levels and maintaining a controlled environment, which means making it pressure tight to slightly above atmospheric pressure.

Very little in this industry is original so I'd love to find some NASA report from the 1960's that looked at this and explains why it's unrealistic but so far all I've found is a brief discussion from 2015.

Fairings do several things to protect the payload. They protect against environmental hazards, as well as thermal, aerodynamic, noise, and EM stresses. Environmental and thermal is very important during the sit on the pad, which could be for several days in varying weather conditions, but could also be helpful during launch, if there's flight through a cloud, or a bird strike. Aerodynamic and noise during launch - as noted, Max Q is almost always supersonic and still well within the stratosphere. If there's an airplane with inflatable leading wing edges that can go supersonic, I'd love to know about it. EM conditions can vary during launch and on the pad, but the most extreme would be a lightning strike - the EM forces must be diverted so the payload isn't harmed.

Inflatable is just not going to cut it for any of these functions.
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Offline SLC

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Re: Fairing reuse
« Reply #742 on: 03/29/2017 11:21 PM »
TBH I've never really understood need for the very rigid, heavy fairings that LV's use.

I've often wondered if you could get by with an inflatable design, soft of like those emergency half circular shelters, but with two edge to edge and both on end.

 Seriously? For max Q, we're talking around mach 1 and airliner cruising altitude. That's a pretty tough gig. I don't see too many inflatable supersonic aircraft going about.
The difference between launch and cruise.  During launch dynamic pressure is quoted in pounds per sq foot because the rise in terms of psi (IE 1/144 smaller) is pretty small. I could see the need for a rigid fairing if there is a real fear of impact damage to the outside of the payload or if the fairing has inside ties to the payload to keep in place. 

The former is a real threat but the latter is not done AFAIK, even for payloads that require "vertical launch" due to the fragility of some of their components.

A lot of common practice in this industry seems to have evolved during the development of ICBMs.

I'd also point out that Joseph Kittinger and Felix Baumgarntner have gone supersonic in free fall inside nothing but a flexible sack (or "pressure suit" as I like to call it   :)  ).

Rigid nose cones assured the aerodynamics and their weight was acceptable. But LV's don't sit in silos for decades with staff walking around them periodically for inspection that might damage their payloads by dropping tools on them. The best way to protect a payload is inside a vehicle assembly building, followed by a transfer to the pad and a launch ASAP.

The two issues I can see are the very high noise levels and maintaining a controlled environment, which means making it pressure tight to slightly above atmospheric pressure.

Very little in this industry is original so I'd love to find some NASA report from the 1960's that looked at this and explains why it's unrealistic but so far all I've found is a brief discussion from 2015.

Fairings do several things to protect the payload. They protect against environmental hazards, as well as thermal, aerodynamic, noise, and EM stresses. Environmental and thermal is very important during the sit on the pad, which could be for several days in varying weather conditions, but could also be helpful during launch, if there's flight through a cloud, or a bird strike. Aerodynamic and noise during launch - as noted, Max Q is almost always supersonic and still well within the stratosphere. If there's an airplane with inflatable leading wing edges that can go supersonic, I'd love to know about it. EM conditions can vary during launch and on the pad, but the most extreme would be a lightning strike - the EM forces must be diverted so the payload isn't harmed.

Inflatable is just not going to cut it for any of these functions.
Then again, NASA seems quite serious about HIAD inflatable heat-shields for atmospheric entry - see the two references quoted in the Wikipedia NASA HIAD paragraph here:

http://en.wikipedia.org/wiki/Atmospheric_entry#NASA_HIAD

If a re-entry heat-shield can be made inflatable, why not a fairing?

Offline Jim

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Re: Fairing reuse
« Reply #743 on: 03/30/2017 12:16 AM »

If a re-entry heat-shield can be made inflatable, why not a fairing?

It isn't a whole heat heat, it is only the parameter and it is not protecting anything in the interior.

Offline Jim

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Re: Fairing reuse
« Reply #744 on: 03/30/2017 12:30 AM »

Random max q number of 1000 psf.

typical fairing frontal area 200 sq ft.

so, what inflatable tube of 50 ft or so can support 100 tons.

Now add in a slight angle of attack which:
a.  increases the frontal area
b.  induces bending forces.
c. while still maintaining a dynamic envelope of a few inches.

Offline Robotbeat

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Re: Fairing reuse
« Reply #745 on: 03/30/2017 02:40 AM »
I think you could build an inflatable fairing if you pumped it to a high enough pressure, but why? It's dumb. Separation is actually more complicated. The payload now has to handle higher than Earth pressure. It's now a pad hazard as it could pop. It probably is worse acoustically as well.

I think you could definitely build an inflatable tube to hold 50-100 tons. But it's a terrible idea.
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Offline LouScheffer

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Re: Fairing reuse
« Reply #746 on: 03/30/2017 04:40 AM »

Random max q number of 1000 psf.

typical fairing frontal area 200 sq ft.

so, what inflatable tube of 50 ft or so can support 100 tons.

Atlas balloon tank.

Offline guckyfan

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Re: Fairing reuse
« Reply #747 on: 03/30/2017 10:39 AM »
Atlas ballon tank is not inflatable.

Online Johnnyhinbos

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Re: Fairing reuse
« Reply #748 on: 03/30/2017 11:02 AM »
Ok, I'm not jumping on the inflatable fairing bandwagon, but I do want to point out that perhaps when posters refer to an inflatable fairing they aren't referring to an outer shell that encapsulates the payload and the entire volume is pumped up to desired pressure for rigidity, but rather an inflatable fairing would be, say, two parts just like a traditional SpaceX fairing, but each half has an outer and an inner wall so that only the fairing itself is pressurized. It would still have the same bulkhead fittings for HVAC etc, the same vents to allow the payload to equalize to ambient pressure, etc.

The perceived benefits would be weight, possible cost, and possibly the halves would be easier to recover.

Boosting this hollow shell to required stiffness pressure isn't that hard, requires much less gas, and stiffness increases with height (though no doubt a pressure relief valve is required to prevent overpressure events.)

Materiel science and tech have come a long way and I'd say this concept is definitely solvable if desired.

But again, just making a point. Not stating my personal opinion.
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Offline Lar

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Re: Fairing reuse
« Reply #749 on: 03/30/2017 11:15 AM »
SpaceX optimize for cost. Not PMF, not anything else. Cost.

I'm not seeing how an inflatable fairing, even if it could be made to work, makes recovery easier, or costs so much less that it can be discarded without concern like the blisterpack on your next phone charger cable[1]... Even if you could figure out how to discard (separate) cleanly.

I mean, I see paths to solving many of these problems. But no reason to do so. Rigid fairings are going to fly better once separated anyway.

1 - there are movements afoot to get rid of blisterpacks in favor of reusable packaging but you know what I mean.
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Offline Kaputnik

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Re: Fairing reuse
« Reply #750 on: 03/30/2017 11:20 AM »
This inflatable fairing thing is like beating a dead horse.
Single skin: too much pressure on the payload
Double skin: you lose all the weight advantages

There must be realistic methods of reducing fairing weight. E.g. a weaker fairing connected to a load bearing pathway through the payload (trade payload mass for fairing mass). Or a single piece fairing with a higher risk jettison manoeuvre. Or reduced fairing size to cater for smaller payload, trading higher manufacturing costs and multiple configurations for slight weight loss.
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Offline Lar

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Re: Fairing reuse
« Reply #751 on: 03/30/2017 12:03 PM »
This inflatable fairing thing is like beating a dead horse.
Single skin: too much pressure on the payload
Double skin: you lose all the weight advantages

There must be realistic methods of reducing fairing weight. E.g. a weaker fairing connected to a load bearing pathway through the payload (trade payload mass for fairing mass). Or a single piece fairing with a higher risk jettison manoeuvre. Or reduced fairing size to cater for smaller payload, trading higher manufacturing costs and multiple configurations for slight weight loss.

I'm sure there are.  Let ULA pursue them. SpaceX optimizes for cost. Not weight. It so happens that a high PMF often reduces cost, but it's not the goal per se...
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Offline Jim

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Re: Fairing reuse
« Reply #752 on: 03/30/2017 01:35 PM »

Random max q number of 1000 psf.

typical fairing frontal area 200 sq ft.

so, what inflatable tube of 50 ft or so can support 100 tons.

Atlas balloon tank.

That is at 30 to 40 psi and did not separate

Offline john smith 19

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Re: Fairing reuse
« Reply #753 on: 03/30/2017 02:29 PM »
I'm sure there are.  Let ULA pursue them. SpaceX optimizes for cost. Not weight. It so happens that a high PMF often reduces cost, but it's not the goal per se...
That's a fair point .

Turning the question on its head how much mass does making the opening mechanism reclosable add to the current design. In fact what does a current PLF for the F9 weigh? I'm guessing several tonnes.
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Offline Jim

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Re: Fairing reuse
« Reply #754 on: 03/30/2017 02:36 PM »

There must be realistic methods of reducing fairing weight. E.g. a weaker fairing connected to a load bearing pathway through the payload (trade payload mass for fairing mass).

That isn't realistic.  Fairing mass is not a one to one ratio with payload mass.

Offline meekGee

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Re: Fairing reuse
« Reply #755 on: 03/30/2017 04:28 PM »
This inflatable fairing thing is like beating a dead horse.
Single skin: too much pressure on the payload
Double skin: you lose all the weight advantages

There must be realistic methods of reducing fairing weight. E.g. a weaker fairing connected to a load bearing pathway through the payload (trade payload mass for fairing mass). Or a single piece fairing with a higher risk jettison manoeuvre. Or reduced fairing size to cater for smaller payload, trading higher manufacturing costs and multiple configurations for slight weight loss.
The central pillar is exactly what I was thinking for the fairings of the comsats deployers, since you already have the dispenser spine in place.

You could even take it a step further, with radial support, and remove most of the structural demand on the fairing.
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Offline MikeAtkinson

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Re: Fairing reuse
« Reply #756 on: 03/30/2017 04:36 PM »
This inflatable fairing thing is like beating a dead horse.
Single skin: too much pressure on the payload
Double skin: you lose all the weight advantages

There must be realistic methods of reducing fairing weight. E.g. a weaker fairing connected to a load bearing pathway through the payload (trade payload mass for fairing mass). Or a single piece fairing with a higher risk jettison manoeuvre. Or reduced fairing size to cater for smaller payload, trading higher manufacturing costs and multiple configurations for slight weight loss.
The central pillar is exactly what I was thinking for the fairings of the comsats deployers, since you already have the dispenser spine in place.

You could even take it a step further, with radial support, and remove most of the structural demand on the fairing.

But that central pillar would then go all the way to orbit, wouldn't it? So might not end up being a net win, even for LEO, unlikely to be a net win for GTO.

Offline meekGee

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Re: Fairing reuse
« Reply #757 on: 03/30/2017 04:42 PM »
This inflatable fairing thing is like beating a dead horse.
Single skin: too much pressure on the payload
Double skin: you lose all the weight advantages

There must be realistic methods of reducing fairing weight. E.g. a weaker fairing connected to a load bearing pathway through the payload (trade payload mass for fairing mass). Or a single piece fairing with a higher risk jettison manoeuvre. Or reduced fairing size to cater for smaller payload, trading higher manufacturing costs and multiple configurations for slight weight loss.
The central pillar is exactly what I was thinking for the fairings of the comsats deployers, since you already have the dispenser spine in place.

You could even take it a step further, with radial support, and remove most of the structural demand on the fairing.

But that central pillar would then go all the way to orbit, wouldn't it? So might not end up being a net win, even for LEO, unlikely to be a net win for GTO.
It already does, and is already holding 10 tons of cantilevered satellites off of it, at high g.

Designing it to give support for the fairing would not add significant weight IMO, but would not only save fairing weight, but make it much easier to manufacture.

With less constraints, maybe also easier to recover and reuse.
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Offline Kaputnik

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Re: Fairing reuse
« Reply #758 on: 03/30/2017 04:49 PM »

There must be realistic methods of reducing fairing weight. E.g. a weaker fairing connected to a load bearing pathway through the payload (trade payload mass for fairing mass).

That isn't realistic.  Fairing mass is not a one to one ratio with payload mass.

I meant 'realistic compared to inflatable PLFs'. I'm not saying it's a good idea compared to what already happens.

If someone did think it was a good idea to pass fairing loads through the payload (or, more specifically, the dispenser), then you have to think of a way to reliably decouple that load for jettison, and also swallow the additional manufacturing and qualifying for a complete second PLF system (because not all payloads are going to be able to do this).
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Offline ChrisC

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Re: Fairing reuse
« Reply #759 on: 03/30/2017 04:59 PM »
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