I've often wondered if you could get by with an inflatable design,
Quote from: Kaputnik on 03/29/2017 11:36 amQuote from: john smith 19 on 03/29/2017 06:41 amTBH 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.
Quote from: john smith 19 on 03/29/2017 06:41 amTBH 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.
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.
Quote from: john smith 19 on 03/29/2017 01:05 pmQuote from: Kaputnik on 03/29/2017 11:36 amQuote from: john smith 19 on 03/29/2017 06:41 amTBH 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.
If a re-entry heat-shield can be made inflatable, why not a fairing?
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.
This inflatable fairing thing is like beating a dead horse.Single skin: too much pressure on the payloadDouble skin: you lose all the weight advantagesThere 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.
Quote from: Jim on 03/30/2017 12:30 amRandom 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.
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...
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).
Quote from: Kaputnik on 03/30/2017 11:20 amThis inflatable fairing thing is like beating a dead horse.Single skin: too much pressure on the payloadDouble skin: you lose all the weight advantagesThere 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.
Quote from: meekGee on 03/30/2017 04:28 pmQuote from: Kaputnik on 03/30/2017 11:20 amThis inflatable fairing thing is like beating a dead horse.Single skin: too much pressure on the payloadDouble skin: you lose all the weight advantagesThere 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.
Quote from: Kaputnik on 03/30/2017 11:20 amThere 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.
At the historic Apollo 11 Pad 39A for the first reuse of a SpaceX booster (and first attempt at a fairing recovery). Go SpaceX and SES-10, go, go go!