it is only hard for the SSME since it wasn't designed for it. It is head started which means the start box is small, the initial conditions are very critical. Also it depends on ground GSE for start and purges
How much energy/m^2 does a tile on the Space Shuttle have to dissipate? Wouldn't it be possible to construct a metallic heat shield cooled by some material say wax being molten during reentry? I mean a phase transition should take a lot of energy off the metallic heat shield.
How much energy/m^2 does a tile on the Space Shuttle have to dissipate?
Wouldn't it be possible to construct a metallic heat shield cooled by some material say wax being molten during reentry? I mean a phase transition should take a lot of energy off the metallic heat shield.
How essential is choked flow through the throat? Would a de Laval nozzle still have an effect if the flow were not choked? My guess is yes, but it would be less effective.
Quote from: Spacenick on 03/02/2009 05:17 pmWouldn't it be possible to construct a metallic heat shield cooled by some material say wax being molten during reentry? I mean a phase transition should take a lot of energy off the metallic heat shield.You are really just talking about an ablative heat shield using a novel material The key point with the Shuttles TPS is that it is not an ablator and you can dust it off and fly it again (on paper!). It is simply unfortunate that such a great heatshield is so susceptible to phsyical damage.
Quote from: kneecaps on 03/02/2009 07:16 pmQuote from: Spacenick on 03/02/2009 05:17 pmWouldn't it be possible to construct a metallic heat shield cooled by some material say wax being molten during reentry? I mean a phase transition should take a lot of energy off the metallic heat shield.You are really just talking about an ablative heat shield using a novel material The key point with the Shuttles TPS is that it is not an ablator and you can dust it off and fly it again (on paper!). It is simply unfortunate that such a great heatshield is so susceptible to phsyical damage. I'm pretty sure he was talking about a system where the metal was on the "outside" and the interior of the metal shell was packed with wax. The wax would melt during re-entry, but a couple of hours later on the ground the wax would have re-solidified, and thus his idea was for a re-usable heat shield. Not to say it has any chance of being practical: at a latent heat of fusion of 200 J per gram, you would need 35,000kg of parafin to melt in order to absorb the quoted 7 giga-joules per meter squared for every square meter of heat shield. Plus wax expands in volume quite a bit when it melts.
It wouldn't BE a deLaval nozzle if it weren't "choked".
- How essential is choked flow through the throat?
How essential is it that the fluid is compressible? Would it work with a liquid?
- How essential is it that the gas is hot? My guess is very important, though I wonder what the reference point is.
What if you left off the nozzle? My guess is you would still have thrust just less and your gas would be very hot.
What if you left off both the throat and the nozzle?
What if you kept the nozzle but left off the throat?
Maybe someone could expand how the real concepts for metallic actively cooled heat shields looked like?
Quote- How essential is choked flow through the throat?Choked means Mach 1. If it doesn't get to Mach 1, it won't be supersonic in the divergent section. Low thrust, very low Isp.
QuoteHow essential is it that the fluid is compressible? Would it work with a liquid?Force is rate of change of momentum, right? M-dot v in this case. So for high thrust you need to maximize each one. A liquid is going to be denser and more viscous, requiring more energy to get both a higher m-dot and higher v. Low thrust, very low Isp.
Quote- How essential is it that the gas is hot? My guess is very important, though I wonder what the reference point is.It needs to be energetic - so it can become speedy. When it's nearly static near the injector face or unburned solid propellant, it's REALLY hot. Adiabatically, in the nozzle, it's also REALLY hot - if you say stick your finger in the flow. If, instead, you put your finger on the edge of the flow in a big enough nozzle, it might FEEL cold because so much of the static enthalpy has become velocity (this is not wind chill factor).
QuoteWhat if you left off both the throat and the nozzle?Remember the scene in Hot Shots where the aircraft tech is roasting weinies or marshmallows at the nozzle of the fighter?
QuoteWhat if you kept the nozzle but left off the throat?No, it would still choke at the throat, unless the mass flow were so low that it didn't need to accelerate to sonic to get out of the combustion chamber. Flow in the nozzle would be indeterminate (subsonic or supersonic) without more information like chamber pressure and ambient pressure.
Huzel & Huang; Sutton; J.D. Anderson are your friends.
QuoteQuoteHow essential is it that the fluid is compressible? Would it work with a liquid?Force is rate of change of momentum, right? M-dot v in this case. So for high thrust you need to maximize each one. A liquid is going to be denser and more viscous, requiring more energy to get both a higher m-dot and higher v. Low thrust, very low Isp.I'm imagining attaching a garden hose to a de Laval nozzle and turning on the tap. I'd expect water to come out at a higher velocity than without the nozzle. I'd also be worried about my hose or nozzle bursting. I'd expect the same thrust as without the nozzle, just with a meaner jet. I wouldn't expect a hot water tap to produce better results than a cold water tap.
QuoteQuote- How essential is it that the gas is hot? My guess is very important, though I wonder what the reference point is.It needs to be energetic - so it can become speedy. When it's nearly static near the injector face or unburned solid propellant, it's REALLY hot. Adiabatically, in the nozzle, it's also REALLY hot - if you say stick your finger in the flow. If, instead, you put your finger on the edge of the flow in a big enough nozzle, it might FEEL cold because so much of the static enthalpy has become velocity (this is not wind chill factor).So a leaf blower would produce the same 'thrust' with a nozzle as without it? And a hair dryer slightly more with a nozzle than without it?
QuoteQuoteWhat if you kept the nozzle but left off the throat?No, it would still choke at the throat, unless the mass flow were so low that it didn't need to accelerate to sonic to get out of the combustion chamber. Flow in the nozzle would be indeterminate (subsonic or supersonic) without more information like chamber pressure and ambient pressure.Let me see if I understand.1) Suppose we have a fixed pressure at the inlet and a (lower) fixed pressure at the outlet. Is it the case that for every positive pressure differential the flow through a de Laval nozzle would choke in steady state?2) And the only way it could not choke would be if instead you specified mass flow at the inlet and that mass flow were sufficiently low to prevent choking at the throat? And even then it would depend on the other conditions.
Read Anderson.
Ignore the equations if you're not good at math. The explanations and pictures are really good.
I found that what you find at 75šE is the major Indic Ocean perturbation, but it's a negative perturbation, meaning (and I checked this several times through different sources) it exerts less gravitational pull.