Sunday, August 13, 2017

North Korea Has Come to a Head

Note:  this article appeared in a slightly shorter form as a guest column on the opinion page of the Waco "Tribune-Herald",  Sunday 8-13-17.

Update 8-19-17:  I have appended some very specific recommendations for what to do about this problem at the end of this article.

The North Korea atomic weapons crisis has come to a head.  Understanding this situation is a whole lot easier than many think.  Like a boil,  it must be lanced.

They now have the 4 elements needed to present a credible nuclear missile threat to the US and many other nations.  Those are a big-enough rocket,  a nuclear warhead small enough to ride that rocket,  a guidance system to get it near its target,  and a heat shield for the warhead to survive reentry. 

The recent high-arcing rocket tests demonstrate they have made sufficient progress on all four fronts.  The trajectory shows the capability of hitting the US if aimed differently,  the intelligence communities agree they have a bomb small enough to ride that particular rocket,  and the fact that these test flights have not gone astray shows that the guidance works.  “Something” from these rockets have been tracked to impact from these tests,  which very strongly suggests that the heat shield works. 

Whether this ICBM is actually reliable is beside the point,  same as it was with ours and Russia’s in the late 1950’s.  If they launched several,  at least a few would get to the target.  Now that he has a credible weapon,  Kim Jong Un is ready to play the age-old blackmail game.  This is a pattern known across millennia of history,  but most folks would recognize the name Adolf Hitler. 

The game is played thusly:  the aggressive one makes a threat to do something “unspeakable” unless he gets what he wants.  He must be willing to risk getting slapped down for it,  but throughout history,  most of those who are willing to make the threat,  have been willing to take that risk. 

Between the World Wars,  that “unspeakable” threat was to wage war at all,  based on the horrifying experiences of World War 1.  Since World War 2,  the “unspeakable” threat has been to wage nuclear war.  Notice how lots of conventional wars have been waged since then?  Only the technology deemed “unspeakable” has changed.  The game remains the same. 

Kim Jong Un may seem crazy to us,  but he is crazy like a fox.  It is not yet clear what he wants,  but he has already made the threat to nuke Guam.  His risk bet is that we won’t actually go to war over an island far from our shores.  That is why he has not yet threatened the lower 48 states. 

But as this escalates,  Hawaii and Alaska are at risk,  because of US military assets in both places,  plus our allies in the region.  Eventually,  he would attack the lower 48 as a final act of desperation.  We’ve seen this pattern many times before.

And escalate it will!  Just like with Hitler and the Nazis in 1930’s Europe.  This scenario has played out countless times over history.  Kim Jong Un is following a long-established pattern like it was a cooking recipe.  This is perfectly predictable. 

Of course,  there is no excuse not to pursue a diplomatic solution.  Basic humanity on our part demands it.  But,  don’t hold your breath for it to work!  It didn’t work with Hitler,  or his predecessors. 

What worked was raw naked force.  The only question is how much you have to use,  and that increases as time goes by.  This is very much like a boil:  the longer you let it fester,  the more it hurts when you lance it,  and more damage there is to heal afterwards.

It is very important that we not strike the first blow,  and that would be true,  even without any pronouncements from the Chinese as to whether they get involved or stay neutral.  It is also important that we not resort to half measures,  such as only striking test sites. 

This is the main lesson of World War 2:  you go “whole hawg or none”.  If North Korea strikes Guam or anywhere else,  we take out Kim Jong Un and his entire government.  Regime change or nothing.  Period. 

It would be nice if we could kill Kim Jong Un and all his government functionaries by destroying them in their big government complex in Pyongyang,  without killing all the civilians in the surrounding city.  Then there’s no need to send one tank or one soldier across the border,  or to commit genocide by nuking the city.

The size of that complex demands that we use a deep-penetrating “bunker-buster” projectile fitted with a small nuclear warhead,  exploded deep underground,  and turning the complex into a contained rubble pile in a pit,  too radioactive to enter.   For the most part,  the city and the people survive,  only Kim Jong Un and his government die.

But I haven’t ever heard that we actually have such a weapon!  North Korea has been festering since 1953,  so it’s not like we haven’t foreseen this problem coming.  This lack for so long a time makes me think we have spent an awful lot of money on the wrong weapons,  not the ones we really needed.

Think about THAT the next time you go vote.  Which is now too late to do anything about any of this.  

Meanwhile,  sleep tight!

Update 8-19-17:  Appended Specific Recommendations:

Specific Recommendations Regarding North Korea                                          

First,  privately among ourselves,  we must agree upon three things: 

(1) We will put an end to the regime if they launch any sort of weapon at any US territory or ally,  anywhere in the world. 

(2) We will accomplish this from a distance:  no invasion,  no occupation. 

(3) We would like to do this with minimal loss of civilian life on all sides,  but accomplishing an end to that ugly regime is higher priority than saving those lives.

Second,  we tell North Korea publicly that “we will put a permanent end to their regime if they launch any weapon toward any US territory or ally,  anywhere in the world”.  This should be calm,  quiet,  succinct,  and very much to the point.  No questions,  no discussion.  No bluster.  Just that fact.

Third,  we tell China very privately that we will put an end to the North Korean regime because they did not control the rogue regime that they created.  We tell them we will not invade or occupy,  because that is not in our interests.  It was in their interests to control what they created,  but they did not do their job. 

Our action will inevitably leave a failed state on their doorstep,  something neither of us wanted.  But because of them not doing their job,  it is only fair that they clean up the failed state mess that we leave for them.  No questions,  no discussion.  Not negotiable.  Best for them and for us.

Fourth,  among ourselves,  and probably in a deeply-classified information scenario,  we must address exactly how we will utterly destroy that regime from a standoff distance,  both “right now”,  and within the next year or so.  There will be no invasion (not even temporarily),  no occupation.  It is best to do this without even sending manned aircraft. 

We do this with standoff weapons,  and preferably not ICBM’s,  which could be mistaken for an attack on China.  Tactical (not strategic) weapon trajectories are an imperative here.

The goal is to suddenly destroy the entire governmental complex in Pyongyang,  in a completely-surprise attack,  at a time we choose,  not just an immediate knee-jerk response.  The hope is to catch Kim Jong Un and his top staff there,  and kill them all in the sudden utter destruction of that complex.  If we miss him,  then we target other installations where he might be,  in a similar fashion.  We keep up the strikes until we get him,  no matter how long it takes.  Then we quit.

A tactical missile with a nuclear warhead can do that job right now,  but with enormous civilian casualties and the destruction of much of the city.  That outcome would resemble Hiroshima and Nagasaki,  so it is imperative that they strike first,  no if’s,  and’s,  or but’s about that.  Such a weapon could be launched from Japan,  South Korea,  or a ship (or submarine) at sea close by.

However,  some sort of tactical missile might possibly be fitted with a deep-penetrating “bunker-buster” nuclear warhead.  It would likely be a larger tactical missile due to the weight of the Earth penetrator and the necessary speed at impact. 

Such a strike would excavate out a cavity under the foundations of the government complex,  shatter that complex into rubble,  and contain that radioactive rubble by its collapse into the excavation pit.  There would be some surface fallout,  but not nearly as much as the usual “city-busting” scenario.  In this underground nuclear scenario,  most of Pyongyang and its civilian population would survive in good shape.  That is the preferred scenario. 

The questions we must ask ourselves in this private,  classified discussion are two-fold. 

(1) Do we possess such a weapon?  If yes,  we’re “good-to-go” immediately.

(2) If not,  how soon could we have one?  And then get on with it as a “crash program”.  Speed is crucial.

Finally,  I would add that this crisis has been long foreseen.  If we have no such suitable weapon to end it with minimal civilian casualties,  why is that?  How do we fix that management lack?

(end update 8-19-17)

Update 8-23-17:  the same nuclear bunker-buster I suggested for decapitating the North Korean regime,  would work against the underground hardened nuclear production facilities in Iran.  That need would arise if  they choose to violate the agreement and start building bombs (a real risk).  I repeat: do we have such a weapon?  If not,  why not?

Update 9-19-17:  After thinking about it for a while,  I believe the real reason Kim Jong Un wants nuclear weapons is to extort the reunification of Korea on his terms.  The threat of nuclear attack "wherever" is the threat by which to ward off the counter-invasion that topples his regime.  I still say we do this by standoff strike,  not invasion.  We leave the failed state on China's doorstep to clean up.  It's only fair,  they created this abortion.

Previous Related Articles:

date,  search keywords
"article title"

4-8-17,  current events,  Mideast threats,  North Korean
rocket test
"The Time Has Come to Deal with Iran and North Korea"

4-6-09,  North Korean rocket test             
"Thoughts on the North Korean Rocket Test And Beyond"      

12-13-12,  current events, North Korean rocket test                   
"On the 12-12-12 North Korean Satellite Launch"

2-15-13,  Mideast threats, North Korean rocket test
"Third North Korean Nuclear Test"
4-5-13,  current events, North Korean rocket test          
"North Korean Threat Overblown, So Far"
9-12-15,  bad government, bad manners, current
events, idiocy in politics, Mideast threats            
"Iran Nuclear Deal Nonsense"

Tuesday, July 4, 2017

Heat Protection is the Key to Hypersonic Flight

The problem is not so much propulsion as it is heat protection.  The reason has to do with the enormous energies of high speed flight,  and with steady-state and transient heat transfer.  Any good rocket can push you to hypersonic speeds in the atmosphere.  But it is unlikely that you will survive very long there

The flow field around most supersonic and hypersonic objects looks somewhat like that in Figure 1.  There is a bow shock caused by the object parting the oncoming air stream.  Then,  the flow re-expands back to near streamline direction along the side of the object.  Then it over-expands around the aft edge,  having to experience another shock wave to straighten-out its direction parallel to free stream again.  This aft flow field usually also features a wake zone of one size or another,  as shown. 

The conditions along the lateral side of the object are not all that far from free stream,  in terms of static pressures,  flow velocities,  and air static temperatures.  One can compute skin heat transfer using those free-stream values as values at the edge of the local boundary layer,  and be “in the ballpark”.  That is what I do here,  for illustrative and conceptual purposes. 

 Figure 1 – Supersonic and Hypersonic Flow Fields About All But the Bluntest Objects

Once flow is supersonic,  the boundary layer behavior isn’t so simple any more.  There is a phenomenon that derives from the very high kinetic energies that one simply does not see in subsonic flow:  energy conservation.  The value of that kinetic energy shows up as the air total temperature Tt,  which is the upper bound for how hot things could be.  Air captured on board by any means will be very close to Tt,  if subsonic relative to the airframe after capture.  This includes any “cooling air” one might use!

In addition,  there is “viscous dissipation”,  which has the effect of raising the actual (thermodynamic) temperature of the air in a max shearing zone within that boundary layer,  to very high temperatures.  The peak of this temperature increase is called the recovery temperature TrThe difference between this recovery temperature and the local skin temperature Ts is what drives air friction heat transfer to the skin,  not the difference between the air static temperature and the skin temperature,  as is typical in subsonic flow.  See Figure 2.  The temperature rise from static to recovery is around 88 to 89% of the rise from static to total,  in turbulent flow,  which this almost always is.  

 Figure 2 – Viscous Dissipation and the Recovery Temperature

Most heat transfer calculations for this kind of flow regime take the basic form and sequence illustrated in Figure 3.  “How high and how fast” determines the conditions of flow,  ultimately.  Total and recovery temperatures may be computed from this,  and total temperature is conserved throughout the flow field around the object,  regardless of the shock and expansion processes.  The flow alongside the lateral skin is not far from free-stream to first order,  and that may be used to find out “what ballpark we are playing in”.  Better local edge-of-boundary layer estimates must come from far more sophisticated analyses,  such as computer fluid dynamics (CFD) codes. 

In Figure 3,  the process starts by determining recovery temperature.  The velocity,  density,  and viscosity at the edge of the boundary layer won’t be vastly different from free stream,  unless you are really hypersonic,  or really blunt (detached bow shock).  The various correlations account for this.

Using whatever dimension is appropriate for the selected heat transfer correlation,  one computes Reynolds number Re.  Low densities at high altitude lead to low values,  and vice versa.  High speeds lead to high values.  Different correlations have the density and viscosity (and thermal conductivity) evaluated in different ways and at different reference temperatures.  You simply follow the procedure for the correlation you selected.  Sometimes this is neither simple,  nor straightforward. 

The complexity of these correlations varies.  My favored lateral skin correlations use a T* for properties evaluation that is T* = mean film plus 22% of the stagnation rise above static.  My favored slower than reentry stagnation zone correlation evaluates fluid properties at total conditions behind a normal shock.  In the stagnation case,  Reynolds number is based on the pre-shock freestream velocity.

The next step is the correlation for Nusselt number Nu.  This nearly always takes the form of a power function of Re (plus some other nontrivial factors),  usually with an exponent in the vicinity of 0.8 or so.  Nusselt number is then converted to heat transfer coefficient h,  using the appropriate dimension and the appropriately-evaluated thermal conductivity of the air,  for the selected correlation. 
The heat transfer rate is then as given in Figure 3,  which shows the Tr – Ts temperature difference.  

One should note that because both density (which is in Re) and thermal conductivity k (which is in h) are low at high altitudes,  the computed values of h will be substantially smaller at high altitudes in the thin air.  High speeds act to raise h,  and to very dramatically raise Tr and Tt.  That last effect is truly exponential.

Having the heat transfer rate is only part of the problem.  One must also worry about transient vs steady-state effects.  If the skin is completely uncooled in any way,  it is then only a heat sink of finite capacity,  with the convective input from Q/Aconv = h (Tr - Ts).  One can use material masses and specific heats to estimate the heat that is sinkable as skin temperature rises.  The highest it can reach is Tr = Ts,  where it is fully “soaked out” to the recovery temperature.  That zeroes heat transfer to the skin. 

The time it takes to soak out can be very crudely estimated as 3 “time constants”,  where one “time constant” is the heat energy absorbed to soak-out all the way from initial Ts to Tr,  divided by the initial heat transfer rate when the skin is at the initial low Ts.  

 Figure 3 – How Lateral Skin Heat Transfer Is Computed

More complex steady-state situations must find the equilibriating Ts when there is convective input from air friction,  conductive/convective heat transfer into the interior of the object (something not illustrated here),  and re-radiation from the hot skin to the environment.  In high speed entry,  there is also a radiative input to the skin from the boundary layer itself,  which is an incandescent plasma at such speeds,  and this is very significant above about 10 km/s speeds. 

Not covered here in the first two estimates are heat transfer correlations for nose tips and leading edges.  Those heat transfer coefficients tend to be about an order of magnitude higher than the coefficients one would estimate for “typical” lateral skin.  Stagnation soak-out temperatures should really be nearer Ttot than Tr,  although those temperatures are really very little different.

Suffice it to say here that if one flies for hours instead of scant minutes or seconds with uncooled skins,  they will soak out rather close to the recovery temperature Tr or total temperature Ttot.  That brings up practical material temperature limits.  See Figures 4 and 5. 

For almost all organic composites,  the matrix degrades to structural uselessness by the time it reaches around 200 F.  The fiber might (or might not) be good for more,  but without a matrix,  it is useless.  For most aluminum alloys,  structural strength has degraded to under 25% of normal by the time it reaches about 300 F,  which is why no supersonic aircraft made of aluminum flies faster than Mach 2 to 2.3 in the stratosphere,  and slower still at sea level.  Dash speeds higher are limited to several seconds.

Carbon steels and titaniums respond to temperature very similarly,  it is a very serious mistake to think that titanium is a higher-temperature material than carbon steel!  Titanium is only lighter than steel.  And you “buy” that weight savings at the cost of far less formability potential with titanium.  Both materials are pretty-much structurally “junk” beyond about 750 F.  Various stainless alloys have max recommended use temperatures between 1200 and 1600 F.  Inconel is similar to the higher end at about 1500 F.  There are a very few “superalloys” that can be used to about 2000 F,  give or take 100 F.

Figure 4 compares steady-state recovery (max soak-out) and total temperatures to material limitations on a standard day at sea level.  Max speed for organic composites are barely over Mach 1,  and just under Mach 2 with aluminum.  Steel and titanium are only good to about Mach 2.5,  unless cooled in some way.  Stainless steels can get you to about Mach 3.5-to-4,  the superalloys not much higher.  

Figure 4 – Compare Tt and Tr to Material Limitations at Sea Level

Figure 5 makes the same comparison in the stratosphere on a standard day,  where the static air temperature is far colder.  You are good with organic composites to almost Mach 2,  and to about Mach 2.2 or 2.3 with aluminum.  Carbon steel and titanium will only take you to about Mach 3.5,  unless cooled in some way.  The various stainless alloys cover about Mach 4 to 4.5,  and the superalloys cover to just above Mach 5.  All of that is entirely uncooled soak-out.

 Figure 5 -- Compare Tt and Tr to Material Limitations in the Stratosphere

One should note that stratospheric temperatures are only -69.7 F from about 36,000 feet altitude to about 66,000 feet altitude.  Above 66,000 feet,  air temperatures rise again,  to values intermediate between these two figures!  That lowers the speed limitation some,  for altitudes above 66,000 feet.

This steady-state soak-out temperature comparison neatly explains why most ramjet missile designs (usually featuring shiny or white-painted bare alloy stainless steel skin) have been limited to about Mach 4 in the stratosphere,  and around Mach 3.3 or so at sea level.  Those limitations on speed are pretty close to the 1200 F isotherms of total or recovery temperature.  Without re-radiation cooling,  the skins soak out fairly quickly (the leading edges and nose tips extremely quickly).

To fly faster will require cooled skins,  or one-shot ablatives,  or else the briefest episodes (scant seconds) of transient flight.  The nose-tip and leading edge problem is even worse!  That means for long-duration / long-range flight,  the skin must be cooled,  or else coated with a thick,  heavy,  one-shot ablative.  There are two (and only two) ways to do cooling:  (1) backside heat removal,  and (2) re-radiation to the environment.  Or both!

Backside heat removal must address (1) conduction through the materials,  (2) some means of removing the heat from the backside of the materials,  and (3) some means of storing or disposing of all the collected heat (what usually gets forgotten).   Liquid backside cooling using the fuel comes to mind,  with the heat dumped in the fuel tank.  However,  there are two very severe limits:  (1) the liquid cooling materials and media may not exceed the boiling temperature at tolerable pressures,  and (2) the heat capacity of the fuel in the tank is very finite,  and decreasing rapidly as the vehicle burns off its fuel load. 

Re-radiation to the environment requires a very “black” (highly emissive) surface coating,  and is further limited by the temperature of the environment to which the heat is radiated.  These processes follow a form of the Stefan-Boltzmann Law,  to wit:  Q/A = σ εs (Ts4 – Te4),  where σ is the Stefan-Boltzmann constant,  and the εs is spectrally-averaged material emissivity at the corresponding temperature.  Subscript s refers to the hot radiating skin panels,  and subscript e refers to the environment. 

While deep space is ~4 K,  earth temperatures are nearer 300 K,  and that is what most atmospheric vehicles usually “see”.  The material absorptivity is its emissivity,  which is why that value is also used for the radiation received from the environment.  A truly “black” hot metal skin might have an emissivity near or above 0.8.  This could be achieved in some cases by a metallurgical coating or treatment,  in others by a suitable black paint (usually one of ceramic nature,  and very high in carbon content).

One More Limitation to Consider

Once the boundary layer air is hot enough,  it is no longer air,  it is becoming an ionized plasma.  The kinds of heat transfer calculations that I used here become increasingly inaccurate when that happens,  and other correlations developed for entry from space need to be used instead.  As a rough rule-of-thumb,  that limit is about 5000 F air temperature. 

If you look at Figure 4 (sea level),  you hit the “not-air anymore” limitation starting around Mach 7.  In figure 5 for coldest stratosphere,  that limit gets exceeded starting around Mach 8.  The only calculation methods that “work” reliably above these limits would be CFD codes,  and even then,  only if the correct models and correlations are built into the codes.  That last is not a given!  “Garbage-in,  garbage-out”.  That expression is no joke,  it is quite real. 

With Re-Radiation Cooling at Emissivity = 0.80

This applies only to lateral skins,  not leading edges,  because the heat transfer rates are an order of magnitude higher for leading edges.  That effect alone changes the energy balance enormously. 

But for lateral skins,  the speed limitation occurs when the re-radiation heat flow equals the convective input to the skin.  The complicating factor is that convective heat transfer is a strong function of altitude via the air density,  while re-radiation is entirely independent of altitude air density.  There are now more variables at work on the energy balance than just ambient air temperature. 

That means two charts depicting the “typical” effects are entirely inadequate.  We need a sense for how this changes with altitude air density.  What follows is a selection of equilibrium re-radiating temperature versus speed plots,  at various altitudes,  in a US 1962 Standard Day atmosphere model.  Material temperature capabilities are superposed,  as before.

Figure 6 -- Lateral Skin Radiational Equilibrium at Sea Level

 Figure 7 – Lateral Skin Radiational Equilibrium at 20,000 feet

 Figure 8 -- Lateral Skin Radiational Equilibrium at 37,000 feet

 Figure 9 – Lateral Skin Radiational Equilibrium at 66,000 feet

 Figure 10 – Lateral Skin Radiational Equilibrium at 80,000 feet

Figure 11 – Lateral Skin Radiational Equilibrium at 110,000 feet

Tough Design Problem

How exactly one achieves this re-radiation cooling is quite a difficult design problem.  The skin itself will be very hot,  in order to re-radiate effectively.  Not only will it be very structurally weak,  there will be heat leakage from it into the vehicle interior.  This is inherent,  but by careful design,  can be limited to rather small (1-2%) values compared to the energy incident and re-radiated from the outer surface. 

There must be a sufficient thickness of low density insulation between that skin and the interior,  one capable of surviving at the skin temperature.  This insulation must be some sort of mineral fiber wool.  There are no simple glasses that survive at the temperatures of interest for hypersonic flight. 

The mountings that hold the skin in place constitute metallic conduction paths into the interior.  These must be made of serpentine shape,  of length significantly greater than the insulation thickness,  in order to effectively limit heat leakage by the metallic conduction path. 

Finally,  there is the issue of sealing the structure against throughflow induced by the surface pressure distribution relative to the pressure in the interior.  Because it is much easier to design seals that survive cold,  than seals that survive incandescently-hot,  it seems likely that the surface skins must be vented,  with the pressure distribution resisted by colder structures deeper within the airframe. 

Two Sample Cases

The SR-71 and its variants featured a “black” titanium skin,  cooled by re-radiation,  but nothing else.  The leading edges (at least very locally) would approach the soak-out temperature limits shown in Figures 4 and 5 above.  Typical missions were flown at around 85,000 feet,  with speeds up to,  but not exceeding Mach 3.3.  In the very slightly-colder air at 66,000 feet,  that leading edge limit was Mach 3.5. 

As figure 10 shows,  the lateral skins had a higher speed limit nearer Mach 4.  So we can safely draw the rough conclusion that the SR-71 airframe was likely limited by leading-edge heating to about Mach 3.5 or so,  at something around 80,000 or 85,000 feet. 

The X-15 featured skins of Inconel-X that were radiationally very “black”.  About the max recommended material use temperature is 1500-1600 F.  Leading edges might tend toward the local soak-out limit at about Mach 4 to 4.5,  unless internally cooled by significant internal conduction toward the lateral surfaces of a solid piece,  which these were.  Thinner air “way up high” might help with that balance,  by reducing both the stagnation,  and lateral,  heating rates. 

As shown in figure 11,  the re-radiation equilibrium limitation near 110,000 feet is closer to Mach 10 for the lateral skins,  and higher still at higher altitudes,  as the other figures indicate by their trends.   The fastest flight had a white coating,  which effectively killed radiational cooling.  For that,  the soak-out speed limit is closer to Mach 4.5 to 5.5,  based upon figures 4 and 5. 

Again, we might very crudely conclude the X-15 was limited by its leading edges to something between Mach 5 and Mach 10.  The fastest flight actually flown reached Mach 6.7,  without any evident wing leading edge or nose damage,  excepting some shock impingement heating damage in the tail section.

My Conclusions:

Most of the outfits claiming they have vehicle designs that cruise steadily at Mach 8+ (high-hypersonic flight) have not done their thermal protection designs yet. 

That lack inherently means they do not have feasible vehicle designs at all,  since thermal protection is the enabling item for sustained high-hypersonic flight. 

“Hypersonic cruise” (meaning steady state cruise above Mach 4 or 5 for extended ranges) is therefore nothing but a buzz word,  without an advanced thermal protection system in place. 

The faster the cruise speed,  the more advanced this thermal protection must be,  and the more unlikely there will be a metallic solution.

Practical Definitions:

Blunt vehicles = hypersonic Mach 3+

Sharp vehicles = hypersonic Mach 5+

Formally,  “hypersonic” is when the bow shock position relative to the vehicle surface contour becomes insensitive to flight speed.

A Better Leading Edge Model

That is entirely out of scope here.  It might consist of one solid leading edge piece,  to be assumed isothermal.  It would have a very small percentage of its surface area calculated for stagnation heat transfer,  with the remainder calculated as lateral skin heat transfer,  except as modified for convexity into the flow near the leading edge.  There would be no conduction or convection into the interior.  All surfaces would re-radiate to cool.

The next best model is a finite-element approximation,  which allows for temperature variations and internal conduction,  within the leading edge piece.  Adding conduction and convection paths into the interior is the next level of modeling fidelity.  None of this is amenable to simple hand calculation. 

Supersonic Inlet Structures

These are an even more difficult problem,  as the inner surfaces are (1) blocked from viewing the external environment for radiational cooling,  and (2) are exposed to edge-of-boundary layer conditions that are very far indeed from freestream conditions. 

Monday, June 12, 2017

Shock Impingement Heating Is Very Dangerous

The X-15-A-2 was rebuilt from ship #2 after a crash.  In October 1967 Pete Knight flew this craft to Mach 6.7 as part of a flight envelope expansion project,  with a dummy scramjet pod attached to the ventral fin stub.  There was severe heating damage to the ventral fin stub from spike shock shed from the from dummy scramjet pod.  The pod separated in flight.  Inconel-X skins suffered about 7 times-normal heating rate due to shock wave impingement. 

The first photo shows the vehicle about to be dropped from its mothership B-52.  Note the white heat protection coating applied to vehicle,  and the dummy scramjet pod attached to ventral fin stub.  The white heat protection coating did not prove to be successful.  This version of the X-15 had two big drop tanks of rocket propellants.  

The second photo is actually 3 images combined to get 3 views of damaged ventral fin stub.  It shows clearly the damage to the ventral fin,  obviously of a meltback nature.  The material was simply overheated by shockwave impingement.  These skins were Inconel-X,  with a listed max useful temperature about 1500 F,  and with meltpoint well beyond 2500 F but far less than 3000 F.

The third image is another view of the damaged ventral fin,  with damage to the aft fuselage also visible.  The separated scramjet pod was also recovered,  and is shown. 

What this proves is that the “parallel nacelle” arrangement is a really bad idea when flight speeds exceed about Mach 5 or 6,  varying with the toughness of the materials involved.   If you let this situation go on long enough,  the impinging shock wave will cut away all the adjacent structure that it strikes.

That is the fundamental reason there have been no successful hypersonic vehicles using the “parallel nacelle” arrangement.  The SR-71 and similar aircraft simply did not fly fast enough to incur this kind of damage.  The X-15 did,  and any entry vehicle far exceeds the heating risks that the X-15 saw. 

Schematically,  this is illustrated in the sketch.  The areas at risk are subject to direct impingement,  meaning the shock wave is “headed directly toward” the surface at risk,  as if that surface is “in the way” of the wave.  For waves that propagate 90 degrees away from the “headed toward” direction,  the effects are very much less.  That is why fins do not damage the surface from which they extend.  There can be a little local heating,  but nothing at all like direct wave impingement.  

As to when the damage occurs,  that depends upon the material and upon the flight speed.  Even the turbine blade superalloys fail by melting under 3000 F,  and fail structurally at temperatures not much over 2000 F.  For a steady state exposure,  the energy balance is convective input to the material,  balanced by internal convective cooling,  or by external re-radiation of heat to environment,  or by a combination of both.  If neither cooling occurs,  the material soaks out to the recovery temperature.

The convective input is driven by the difference between the recovery temperature and the material temperature.  The re-radiation ability is driven by the infrared (and optical) emissivity of the material and its temperature.  In the case of the X-15 flight,  there was no internal cooling,  and the white coating had drastically reduced the material’s emissivity (the normal surface finish was nearly black).
At Mach 6.7 and 100,000 feet on a 1962 standard day,  the turbulent recovery temperature that drives convective input calculates as about 3250 F,  well beyond the melting point of any superalloy,  much less its maximum use temperature.  With re-radiative cooling suppressed by the white coating (and no internal cooling),  it should not be surprising in retrospect that the test nacelle bow shock did extensive damage to the fin stub and aft fuselage. 

The only real surprise is that this X-15 survived that particular flight at all.  The exposure was brief enough that these effects did not have the time to sever its tail section. 

Thursday, May 11, 2017

President Trump is Not Whom You Should Fear The Most

A lot of people are worried sick about what President Trump might do next.  Rest assured,  there are limits to the damage he can do.  But,  his term or terms in office will be quite interesting,  to say the least.  There is an old Chinese curse that is,  sadly,  applicable:  “may you live in interesting times”.

The office of President is specifically designed to limit the bad the President can do,  which also limits the good he or she can do.  All our Presidents do both good and bad while in office.  That’s just human nature.  The ones we consider "good" Presidents do more good than bad,  and vice versa.  It's never “either-or”.  

In Mr. Trump's case,  I fear he will do more bad than good,  not so much out of malicious intent,  but out of egregious ignorance compounded by unwarranted arrogance,  and a demonstrated inability to speak or value the truth.  But only time will tell. 

Age may not be the sole Constitutional qualification to be President that we need anymore.  Ignorance so egregious should be a disqualifier for the Presidency in the Constitution.  I’m not sure how you measure it to judge,  though.  Update 6-23-17:  readers please weigh in on how such ignorance might be measured,  using the comments feature.  

The President Is Not the Only Problem We Face

Meanwhile,  I am more concerned about the damage the Republicans will do while in control of all 3 branches.  They are demonstrably unfit to govern,  since for more than 3 decades now,  the entire party has been held hostage to an extremist minority within their midst.  As the popular vote indicates,  the Republicans are about half of American voters.  So minority within their party is a small minority indeed,  compared to all of us.

That minority has managed to either purge,  or forcibly convert the rest of the Republican party into voting with them,  via the "primarying" threat.  Because it’s an extremist minority view that controls,  everything the party has ever claimed about economics and public policy has proven to be a lie,  for many years now. 

This is an example of a minority takeover of a government,  via extortion and propaganda.  This a minority uninterested in doing things for the people,  or even in maintaining their freedom,  despite what is claimed.  It is all about obtaining and wielding power over others.

Prior examples:  the Nazis,  the Bolsheviks,  the Chinese communists,  Pol Pot in Cambodia,  etc.  And THAT is why I am concerned about our future as a democracy.  Mr. Trump's deficiencies are just incidental to THAT threat.  

So Where Is the Alternative?

The problem is that we have little in the way of an alternative that is not just as dangerous.  The Democrats also sold out many years ago to the same financial giants as the Republicans sold out to,  more than a century ago.  They went "rich elite",  and completely forgot about their core constituency,  the lower middle class working people who typically held factory jobs. 

Which neglect is exactly why that base revolted and elected Mr. Trump!

The fundamental trouble is with party agendas on both sides:  they have little to do with reality,  being extremized WITHOUT REGARD TO FACTS,  just to differentiate the parties.  Political agendas do not make good public policy.  They never have. 

An Unexpected Problem Confronts Us

Money is power.  The love of money and power corrupts everything it touches,  as any preacher can tell you.  The real problem:  the financial giants own both parties,  and controlled who actually ran for President in 2016. 

Mr. Trump was the only Republican a “corrupt elite politician” like Hillary Clinton could conceivably beat.  And she did,  in the popular vote!  On the other hand,  Mrs. Clinton was the only Democrat that an ignorant incompetent like Mr. Trump could possibly beat.  And he did,  in the electoral college!  PER THE PLAN!

Both party primaries were deliberately rigged for these two candidates to keep the "blood and circuses" interesting enough to prevent public perception of who was really pulling all the strings behind the scenes.  You didn't think Mr. Comey was incompetent enough to violate FBI investigation procedures by making those two public announcements (July and October) about Mrs. Clinton's email-mishandling,  did you?  And it WAS mishandling,  but she is not unique in that fault,  not by a long shot. 

Mr. Comey was forced to do those irregular election-swaying announcements by the financial giants to keep the race looking "even" for a longer time,  until the giants could get their man in at the last moment.  This was with Russian fake news (via Wikileaks,  Sputnik,  and RT) helping to sway voters' minds,  in addition to Mr. Comey’s October announcement. 

The collusion deserving investigation is less about Mr. Trump's campaign than it is those financial giants.  They wanted an incompetent they could influence or control to help give them everything they want.  They got him. 

Update 6-23-17:  It would appear the Russians actually did hack into the records of voter registration in multiple states,  and the records of multiple voting machine manufacturers.  There seems to be no evidence they actually succeeded in altering vote tallies,  but this was quite apparently not for lack of trying!

Update 7-28-17:  I consider both fake news election meddling,  and attempts at real election vote count tampering,  to be acts of war against the US,  committed by Russia.  These are every bit as damaging to us as an explosive bomb.  This does demand a punitive response.  I am glad to see that both the House and Senate largely think so,  as well.  Although,  I am not sure that only economic sanctions are the right response.  

Can We Fix This Problem?

You cannot expect a wholly-bought Congress to change this,  no matter which party is in power.  They work for who bought their jobs for them,  not us.  This has been true for decades now.  They would have to cooperate with a grassroots Constitutional amendment process,  too,  and they will not,  because of the money. 

Ballot-box solutions are thus pretty-well ruled out.  This evil takeover of our government will not go away without some sort of revolution,  I fear.  The giant corporations and banks control the entire federal government,  which means they control the armed forces.  And they know the rebellion is inevitably coming. 

Why else would EPA enforcement officers (and similar non-military career government workers) need body armor,  swat vehicles,  machine guns,  and most of the ammunition being produced?  They are to serve as adjunct troops to help put down the rebellion!

Compared to this picture,  an arrogant and ignorant incompetent like Mr. Trump is small change,  even with his finger on the nuclear trigger.  As serious and dangerous as that is (update 6-23-17).

Keep your guns and ammunition hidden.  You’re going to need them.  Just as the Second Amendment says. 


Update 6-23-17:  

There have already been a few calls for impeachment and removal of President Trump.  Right now that seems rather unlikely,  as his supporters still rabidly support him,  regardless of the damage that he does them on behalf of the radical-right wing of the GOP,  who also still support him.  This is showing up in the health care bills and the tax reform plan that takes money from his supporters,  and gives it to the super-rich instead.  And this is just getting started.  

There would be only three basic grounds for impeachment:  (1) egregious ignorance and incompetence,  leading to an inability to properly perform the duties of his office,  (2) obstruction of justice with regard to the various investigations of him and his campaign,  and (3) treason,  per the definitions in the Constitution.  

Update 7-28-17:  there is a connection between why Mr. Trump so viciously has turned on Jeff Sessions,  and why he is looking for ways to fire the special investigator Robert Mueller.  That connection is Mr. Trump's hidden tax returns and other hidden records of his financial dealings.  

I predict that when these are finally brought to light,  that two very disturbing things will be found:  (1) the majority of  Mr. Trump's income is coming from investors and customers in Russia,  and (2) Mr. Trump owes the best part of a billion dollars to Russian banks who financed his ventures when no other banks would touch him,  after his 6 bankruptcies of record.  These Russian banks are largely operated by Russian crime figures close to dictator Putin (they keep each other in power).  

That is an incredible vulnerability to coercion by a hostile foreign power!  It is simply not tolerable in an American president!  I am not surprised Mr. Trump is so vociferous about keeping his records unrevealed,  and why he is so determined to fire anybody who will not work to keep them concealed.  
The guilty dog is barking very,  very loudly here.  Loudest of all,  as a matter of fact. 

The first ground might actually come to pass,  sooner or later,  in spite of the fact that there is no precedent for doing this.  Whether this is a first-term or second term process depends upon how soon his supporters realize he has not,  and will not,  do anything substantive to help them,  which he promised to do during his campaign.  As rabid as they are,  they will resist to the last changing their minds about Mr. Trump. 

The second ground could happen in a first or second term,  should the GOP tire of the damage he does.  To turn away from supporting a GOP president willing to sign their legislation,  will require that they consider the good of the country above party advantage.  That is something we have not seen since Bill Clinton's first term.  I would not hold my breath waiting for it,  unless the Democrats take the House in 2018.  They would also need massive control of the Senate to convict. I think both are very unlikely.

The third ground is not something anybody is seriously talking about.  Yet.  The outcomes of the investigations may change that.  Those are months,  perhaps a couple of years,  away.  

The Constitution specifically defines "treason" to be either of two things:  (1) waging war against the United States,  or (2) providing aid and comfort to its enemies.  It requires two witnesses to the act,  or a confession in open court.  The charge is brought by the House (articles of impeachment),  and the court in which the case is tried is the Senate.  It takes a 2/3 majority to convict.

Mr. Trump's statements and actions (multiple examples exist) have clearly damaged our relations with NATO and all our other allies around the world.  This has been witnessed by millions.  It is something the Russians have tried to do without success since these alliances were formed right after WW2.  I doubt that there is any reasonable person in the US who does not consider Russia today to be an adversary.  The synonym for that is "enemy".  

I submit that damaging those alliances (NATO and the rest as separate counts),  when the Russians had not been able to accomplish that in 70+ years,  provided "aid and comfort" to the Russians, who qualify as an "enemy".  There are plenty of witnesses.  That satisfies the definition of treason in the Constitution.  

The only question is when will the House and Senate live up to their oaths of office,  and do what is right for the country instead of just maximizing party political advantage?  

THAT is the question you must ask yourself when you enter the voting booth in 2018,  2020,  and beyond.  You can vote counter to the financial giants who bought your politicians their jobs and rigged your elections.  If enough of you do,  we all can still take our country back without an insurrection.

Until our Representatives and Senators do live up to their oaths of office,  no impeachment is possible,  on any of the three possible grounds.  And the grounds of treason look to me to be most certain right now,  even without any investigation outcomes.

Saturday, April 15, 2017

Do We Fight Global Warming Or Not?

Note:  article was updated 4-23-17 in purple text below to include sources of traceable data.  

Note:  another update added below in blue text 4-25-17.

Note:  one slight edit adds an item in red text below 5-4-17.

This is an issue that has become politicized to the extreme,  which precludes rational action. What I present here has absolutely zero to do with ideologies or politics.  It is simple logic and common sense. 

There are two things to consider,  but only one available choice.  Whether humans cause global warming or not is not a matter of choice,  it is something decreed by nature,  which does not tell us which is true.  Our only choice is whether or not to act,  based on what we do know. 

What we know is this:  (1) there is a huge volume of ice on Earth located above sea level,  (2) if even some of it were to melt,  sea levels would rise sharply,  (3) added heat melts ice,  and (4) most of our critical institutions and a major fraction of our population live in the zone threatened with flooding. 

What portends here is a disaster far exceeding the temporary flooding of a city by a hurricane,  or the migration of millions out of Syria and Africa to escape war.  What could happen is the forced migration of billions,  and (nuclear) war over failing food resources.  So,  this decision is important to get “right”. 

Filling Out The Decision Matrix

One simple way to decide this is by a version of the trade study matrix,  a pretty standard tool.  However many choices you have is the number of columns (in this example 3),  however many versions of the unknown natural issue there might be is the number of rows (in this example 2).  That gives you a 6-hole pigeon-hole matrix to fill in with likely consequences. 

There are two rows because human emissions might,  or might not,  cause global warming.  You do not get to choose between them;  this is decided by nature,  not humans. 

There are three columns instead of two,  because if we decide to act,  there’s two ways this action might turn out.  There is only one,  if we choose not to act.  Acting versus not acting is the choice available to us.  If we act and it doesn’t work,  we’d better already be working on how to cope (the third column).

As for the consequences,  they need not be detailed,  and it is OK to exaggerate them for better contrast.  

If we choose to act,  we will spend lots of money to act,  and there will be monetary losses,  too.   These costs could range from significant (damaged economies) to catastrophic (going back to the stone age).  That variation doesn’t matter,  just fill in all four “choose to act” cells with “lose $$”.

If we choose not to act,  then the consequences depend upon what nature does not tell us:  whether or not human-caused global warming is real.  If not real,  there will be no meltdown,  no sea level rise,  no migrations,  no war,  and no money lost.  If real,  all those things will happen,  and both money and lives will be lost (at catastrophic levels). 

That fills in all 6 cells with consequences.  5 of the 6 involve lost money,  there is no avoiding that.  1 of the 6 involves life loss as well as loss of money;  that one is really bad.  1 of the 6 has no bad consequences in it at all. 

Now We Must Choose

You cannot choose which row you want (political ideologies notwithstanding).  You can only choose a column!  The standard way to use the matrix is to pick the outcome that you cannot abide,  and then cross out the entire column that contains it. 

In this example,  losing lives is to be avoided,  which rules out choosing not to act.  This valuing of lives over money is in accordance with the teachings of all 3 Abrahamic religions in the West.  Most of the Eastern religious traditions agree. 

That result says:  act,  and be prepared ahead of time to cope,  if your initial action fails. 

Did you notice that not once did I refer to any of the prognostications or temperature history data of the climate science community?  I didn’t need it to make this decision.  I need it only to help define the actions we might take to mitigate this threat:  reduce greenhouse gas emissions. 

And,  there is another independent science dataset that says the same thing:  observed ice melting behavior as the fossil fuel-guzzling population has exploded.  Getting the same answer by two independent means lends a lot of confidence to that answer. 

Update 4-23-17:  Sources of Real Data to Consider

There are ice core data that cover atmospheric composition during the ice ages and the warm periods in between.  This is based on the actual composition of the ancient air trapped in the bubbles in the ice.  The atmosphere is mixed well enough that this composition is not restricted to polar regions,  it is global.  These can be dated by the layers,  similar to tree ring dating.  Here is that data for atmospheric carbon dioxide over the last 400,000 years,  obtained right off a NASA website:

You can see the 4 dips to 180-200 ppm at the height of each of the 4 main glaciations of the ice age. We know when these glaciations occurred from the timing of the evidence in the rocks:  they show marks of glacier passage,  and the debris left behind on melting.   Note that it never got above about 280-290 ppm during the deglaciated warm intervals.  Ancient is to the left,  modern is to the right.  You can even see the little "wiggle" in the curve at about 260 ppm about 10,000 years ago that is the sudden cool-down they call the "Younger Dryas".  

From 180 ppm to 290 ppm encompasses atmospheric composition all the way between fully glaciated to fully warm.  Correlation does not establish causality,  that has to come from elsewhere (such as basic demonstrable physics).  So,  is something else going on?  Such as Milankovitch orbital cycles?

The thing we have that best models the cycling of the ice ages is Milankovitch orbital cycles.  This is not really a fully causal model,  except for the notion that more sunlight striking northern hemisphere land leads to warmer conditions globally.  It pretty much correlates with the advance and retreat of the ice;  not perfect,  but very,  very good.  It is limited;  for one thing,  the distribution of continents was different millions of years ago.  

The basic physics is simple:  ice melts if heated.  The Earth's "average" temperature is an energy balance between lots of visible and ultraviolet light coming from the sun,  and some heat of radioactive decay and original formation escaping from the interior,  versus the infrared heat re-radiated back out into space by the warmth of the Earth's surface.  And,  extra carbon dioxide in the atmosphere interferes with that re-radiation,  because it is less transparent to infrared than oxygen and nitrogen,  so the surface must warm further to radiate against the resistance of the carbon dioxide.

You can verify this effect for yourself without actually doing sophisticated measurements:  simply set two bell jars covering thermometers out in the sun at the same time.  One has air,  the other you fill with carbon dioxide (the extreme case).  Both thermometers rise.  But,  the carbon dioxide-filled jar's thermometer will read a lot higher than the air-filled jar's thermometer.  Both are "greenhouses",  but the carbon dioxide gas is far more potent as such than oxygen and nitrogen in the air.  

Another version of that very same chart I obtained from Wikipedia,  to which an inset was added showing atmospheric composition over only the last few centuries.  This makes the point that our unburying of carbon-containing fossil fuels and releasing it as exhaust gas carbon dioxide,  has had effects since the start of the Industrial Revolution,  and really sharp effects in the last 5 decades as our population explodes exponentially.  

If you look on much longer time scales,  there are other things going on as well.  On a time scale of 100 million years,  the astrophysicists tell us the sun has brightened by 4% or thereabouts.  On a 4.6 billion year time scale,  they tell us it has brightened by about 30%.  

Before about 380 million years ago,  there was no life on land.  Before 600 million years ago,  there was only single cell life in the ocean.  Before about 2.5 billion years ago,  there was no oxygen in the atmosphere.  And who knows what the surface air pressure was during those times (which also affects how good a "greenhouse" it makes)?

All we know is that there more carbon dioxide half a billion years ago than in "recent" times (only the couple of million years).  The sun was dimmer,  and yet the geology indicates ice-free conditions.  This chart was published a few years ago in the refereed journal "Science",  published by the American Association for the Advancement of Science.  It's based on atmospheric composition inferred from rock chemistry,  and it's pretty good back to the Cambrian,  570 million years ago.  Much before that,  it's inherently rather speculative,  which explains the scale change representing time.  These are indirect measures,  which explains the lack of scale tick marks on carbon dioxide concentrations,  which were roughly around 1000 to 2000 ppm during the Mesozoic.  

Update 4-25-17:

What the long-term carbon dioxide and temperature chart makes clear is twofold.  (1) Carbon dioxide fluctuations do not cause ice ages,  because there was little change in level during the Pleistocene Ice Ages,  and carbon dioxide levels were much higher during the earlier ice ages.  (2) Carbon dioxide in the air does indeed warm the planet,  as evidenced by ice-free intervals at high carbon dioxide earlier in Earth's history,  when the sun was significantly dimmer.  

Something else causes ice ages.  Many things,  this is poorly understood.  There have been many of these ice age events over geologic time:  the Pleistocene event we are most familiar with,  the Jurassic-Cretaceous event,  an event between the Carboniferous and the Permian,  another between the Ordovician and the Silurian,  and who-knows-what during Pre-Cambrian times.  

Climate-Modeling Science

The overwhelming majority of climate scientists agree that humans are causing major effects with greenhouse gas emissions.  They arrive at this conclusion with a combination of (1) computer modeling of climate,  and (2) various proxies for past temperature data earlier than historical measurements. 

There is inherently a lot of uncertainty in the computer modeling,  and a lot of inference in the proxies for past temperatures (unlike the ice core data for atmospheric composition).  There is potential for error,  disagreement,  and even fraud.  Many folks outside the community are uncomfortable with that,  and this is the weakness exploited by those who prefer to disbelieve that we are causing climate change. 

Ice Melting Behavior

Ice behavior is unambiguous.  The mountain glaciers have been generally receding since the 19th century.  Now there are enormous summer sea ice losses,  and thousands of summer meltwater lakes on Greenland,  that we have never seen before!  The co-timing of these symptoms with the increases in measured atmospheric carbon dioxide to unprecedented levels since 1958,  is quite damning.

There is a documentary film available in whole or in part on Youtube named “Chasing Ice”.  It was made by James Balog as part of his Extreme Ice Survey (EIS).  The award-winning film was first shown in 2013.  The time lapse photography of many glaciers' melt-back in the last 30 minutes of that film makes my point better than any words. 

Trade Study-Recommended Actions

The mitigation action to take first is to cut back carbon dioxide and methane emissions as fast as we can,  but without hurting or killing somebody for lack of energy, which limits how fast we can do this.  The coping action to take in case mitigation fails is twofold:  (1) start stockpiling foodstuffs,  and (2) to start moving critical institutions and assets to much higher ground.  

Any other “geo-engineering” activities we contemplate must be reversible,  because we simply do not know that they will do more good than harm.  If they do not work,  we have to be able to undo them. 

It is that simple. And it is that stark.  And,  it has absolutely nothing to do with politics or ideology.  Those who claim otherwise are lying to you.  Follow the money to see who and why. 

Previous Related Article on this Topic

There was one earlier article that I wrote on this topic,  which the current article updates and replaces.  That was “On Global Warming”,  dated 1-12-2010,  and sharing the same search keywords you can use to filter searches for this topic on this site:  "bad government",  “bad manners”,  “climate change”,  and “idiocy in politics”.  That older article was last updated in 2014 to show a simpler 4-cell version of the 6-cell trade study matrix presented here.   It now refers the reader to this article.