Monday, November 17, 2014

Space Suit and Habitat Atmospheres

See also updates 11-20-14 and 11-26-14 at end.

Spacesuits are usually designed for pure oxygen “atmospheres“ supplied as breathing gas.  This is especially important to full pressure suit designs,  as lower pressures can be used with pure oxygen,  which eases the joint restriction design problem.  However,  long-term breathing of pure oxygen is detrimental to human health.  Plus,  it is a very serious fire hazard:  flammability and explosiveness are greatly amplified in pure oxygen at full atmospheric pressure. 

All of that taken together means that the habitation for astronauts (be it a ship,  a space station,  or a base on another planet) needs a suitable diluent gas.  Such atmospheres are thus inherently two (or more) gas systems.  We evolved in an atmosphere of 20.946 volume percent oxygen,  about 78% nitrogen,  and around 1% argon,  plus some other trace gases. 

Although sea level pressure is “the standard”,  there are many human communities living at altitudes where pressures are substantially lower.  Many large populations live near 10,000 feet elevation,  some near 15,000 feet,  and a very few approaching 20,000 feet.  Air pressure,  and oxygen partial pressure,  are both substantially lower at altitude. 


The pilots of aircraft are required to use supplemental oxygen when flying above certain altitudes.  The exact standards vary,  but the US Navy uses 5000 feet as the altitude above which oxygen must be used.  Most other authorities use 10,000 feet as the “trigger” for mandating oxygen.  Below those altitudes,  pilots seem to be fully functional.  Therefore,  atmospheric oxygen concentrations resembling those in the 5000-10,000 feet altitude range make pretty good criteria for the minimum life support requirements of any space suit design.  See also Figure 1.  These data were also used in “Fundamental Design Criteria for Alternative Spacesuit Approaches”,  posted this site 1-21-11.  


 Figure 1 -- Life Support Experiences

Suit Criteria

The Earth’s atmosphere has very variable humidity.  Dry air composition is 20.946 volume percent oxygen.  Water vapor acts to “displace” dry air,  so there is a slightly-lower oxygen partial pressure to breathe on very humid days versus very dry days,  at any altitude.  At human body temperature,  the steam tables show the partial pressure of saturated water vapor to be just about 47.06 mm mercury. 

Respiration depends upon the partial pressure of oxygen in the air we breathe,  not the volume percent.  This is because so many biochemical processes are driven by osmotic pressure differences. 

These two effects (water vapor displacement and partial pressure-driven osmosis) taken together say that the actual oxygen requirement,  when designing space suit and habitat atmospheres,  is the partial pressure of oxygen in the near-equilibrium saturated environment of the lungs.  This same water vapor displacement effect must be taken into account in selecting the pressure of the pure dry oxygen in the suit.  (There are other displacement effects,  but all are far less significant than this water vapor effect.)

The other factor to consider is leakage from the suit.  Suit pressures can be increased to compensate for losses that might (or might not) occur.  The “usual” factor seems to be 1.10 for leakage effects.  The suit oxygen pressure selection approach is shown in Figure 2,  Figure 3 presents the actual data.  This applies to any type of suit,  not just the full pressure suits that have been standard. 

Suit designs that supply pure oxygen at compression pressures between 147 mm mercury (10,000 feet) and 167 mm mercury (5000 feet) would thus seem to be quite adequate.  196 mm mercury corresponds to full sea level oxygen.  Those figures include the water vapor displacement effectbut not the increase for leak compensation.  Using a factor of 1.10 as leak compensation,  the design suit pressures become 216 mm mercury for sea level-based,  187 mm mercury for 5000 ft-based,  and 161 mm mercury for 10,000 foot-based designs.  

Figure 2 – Selecting Pressure in a Pure Oxygen Suit


 Figure 3 – Pressures in a Pure Oxygen Suit of Any Type.

Getting from Suit to Habitat Atmosphere

Since we evolved to breathe them,  oxygen,  nitrogen,  and argon make pretty good choices for the gases in the atmosphere of any astronaut habitat.  This is important because interplanetary missions will require living in such habitats for years at a time.  Oxygen-nitrogen is a basic two-gas system.  We might add substantial argon as an additional diluent for reducing the risk of fire. 

The problem going from a two-gas system in the habitat to pure oxygen in the suit is a requirement to “blow off” the nitrogen (and any third diluent gas) dissolved in the blood,  without risking “the bends”.  This is “pre-breathe” time,  and it is quite significant with the atmospheres used in the ISS and associated spacesuits.  There is a tested criterion for this:  if habitat partial pressure of nitrogen ≤ 1.20 suit pure oxygen pressure,  then no pre-breathe is needed. 

So,  once a design suit pressure has been selected,  this factor of 1.2 should be used to determine the maximum partial pressure of nitrogen in the habitat atmosphere.  Suit and habitat share the same in-lung wet partial pressure of oxygen.  The in-lung wet and habitat dry atmospheres share the same total pressure.  If this a multiple-gas atmosphere in the habitat,  then we know its total pressure as the sum of the wet O2 and N2 (and Argon,  if any) partial pressures,  and can figure the volume percentage of oxygen in the dry mix as its partial pressure divided by the total.  That process logic is a part of Figure 4,  with the numbers as a function of suit pressure in Figure 5. 

As a two-gas system,  all the suit pressure designs under these criteria share the same habitat atmosphere oxygen percentage:  45%.  That sounds like a high fire risk,  unless low total pressure mitigates it.  These total pressures are much lower than standard atmospheric:  ranging from only 6.86 psia for the 15,000 foot-based design up to only 9.19 psia for the sea-level-based design. 

These total pressure and oxygen percent data and the oxygen partial pressure can be used to evaluate fire risks.  I have no ready criteria for this myself.  It can be tested experimentally in test chambers right here on Earth,  however.  Adding argon lowers the percentage oxygen (but not its partial pressure),  and raises habitat total pressure.  


 Figure 4 – Scaling Up from Suit to Habitat to Avoid Pre-Breathe Requirements

Figure 5 – Basic Two-Gas Habitat Atmospheres as a Function of Design Suit Pressure

Three-Gas System for Reducing Fire Risks?

I do not know of a pre-breathe criterion factor for argon.  One might assume the same 1.2 factor over suit oxygen pressure applies,  so that one can add substantial argon to the mix,  at a partial pressure equal to that of the nitrogen. 

On the other hand,  monatomic argon has a molecular weight near 39,  versus diatomic nitrogen’s molecular weight of 28.  If osmotic rates depend directly upon molecular weight,  then argon should be slower than nitrogen to dissolve into,  and out of,  the blood.  Then perhaps the pre-breathe criterion for argon should be nearer 0.86 than nitrogen’s 1.20.  We just don’t know.  But,  that assumption lowers the argon content,  which is in the safer direction.  Results are in Figure 6.

Figure 6 – Three-Gas Atmospheres as a Function of Design Suit Pressure

Results:

#1. Go with the Navy oxygen mask criterion of 5000 feet as slightly more conservative than the 10,000 foot criterion.   Your suit (whatever its design) is then at-minimum pure O2 at 3.28 psia.  Factored up for leaks,  this is 3.61 psia.  Even full pressure suits can be somewhat supple at pressures this low. 

#2. For a two-gas habitat atmosphere,  use a pre-breathe factor of 1.20 for nitrogen as well-supported.  Use the in-lung wet suit oxygen partial pressure as the in-lung wet habitat partial pressure of oxygen.  Results are given in figure 5 for all the suit designs.  For the recommended 5000 foot-based suit design and the two-gas system,  your habitat atmosphere is 45.45% O2 and 54.55% N2,  at 6.13 psia,  with zero pre-breathe time required to don the spacesuitThe 45% O2 is rather alarming as a fire hazard.  It is at best unclear whether the low pressure of 6.13 psia could mitigate this risk.  At worst,  this is simply too severe a fire hazard. 

#3. For a 3-gas habitat atmosphere,  we use all the same design factors,  plus we set the argon pre-breathe factor at about 0.86.  Results are given for all the suit designs in Figure 6.  For the 5000 foot-based design,  we are looking at a habitat atmosphere that is 32.68 volume % O2,  39.22% N2,  and 28.10% Ar,  at a total pressure of 8.16 psia,  again with zero pre-breathe time required to don the spacesuit.  Adding the third gas greatly reduced the objectionable high volume percent oxygen.  But it is unclear whether this is enough reduction. 

#4. It is entirely possible that more argon could be used,  once a pre-breathe limit factor has been established for it.  That would act to lower oxygen percentage and raise habitat total pressure,  but would not affect the suit design. 

#5. It might also be possible to add a fourth gas (preferably an inert one,  and one not linked to the biology of life as CO2 is).    This would also lower oxygen percentage and increase habitat total pressure,  without changing the suit design.  One candidate might be helium,  which has been used in deep sea diving.  It takes longer to decompress than nitrogen in that application,  which means its pre-breathe factor is lower than nitrogen’s,  in spite of the low molecular weight. 

#6. Note that in the tables given in Figures 5 and 6,  that oxygen percentages are constant,  regardless of the suit design pressure.  Raising suit pressure will not cut oxygen percentage in the habitat,  without violating the pre-breathe factors that make EVA’s into practical operations. 

Speculation:

Assume as a wild guess that the pre-breathe factor for helium is 0.5Assume also that the pre-breathe factor for argon is closer to that of nitrogen,  for about 1.0.  Under those conditions,  a hand calculation for the 5000 foot-based suit design gives a habitat atmosphere of 27.03% O2,  32.43% N2,  27.03% Ar,  and 13.51%% He,  at 9.68 psia.  Earth-normal oxygen percentage is nearly 21%,  so surely this 4-gas atmosphere would be far less risky in terms of fire. 

Recommendations:

Determine reliable pre-breathe factors for argon and helium.

Identify other candidate gases that could be added to the mix,  and determine the pre-breathe factors for them. 

Final Note:

The atmosphere we evolved with (20.946% O2 78% N2,  and 1% argon) at 14.7 sea level psia could be a habitat atmosphere as safe as here at home,  in terms of fire risk and any long-term medical risks.  The nitrogen pre-breathe factor of 1.2 says the spacesuit pure oxygen pressure would have to be about 9.55 psi in order to avoid pre-breathe time donning the suit. 

That’s impossibly high,  even for a full pressure suit.  Our astronauts have severe mobility restrictions at about half that pressure currently.  The ISS uses near Earth-normal air,  and hours of pre-breathe time,  to use a suit at about 4.85 psi.    


Something has to change,  or these EVA-practicality issues will stymie us.  

Update 11-20-14:

The preceding calculations and graphs were made under the assumption that we wanted a minimal suit pressure,  and that we calculated habit atmospheres to match the wet in-lung oxygen partial pressure of the suit  Only 3 and 4-gas atmospheres were considered (oxygen,  nitrogen,  and argon,  plus maybe helium).

For this update,  I looked at setting habitat atmospheric oxygen to something very near Earth-normal oxygen 20.946 volume % for fire protection,  and added two more noble gases to the mix,  resulting in a 6-gas mixture.  All the inert gases added to inert nitrogen are chemically-inert noble gases.  In order,  the diluents are nitrogen,  argon,  helium,  neon,  and krypton.  There are more noble gases available (xenon and radon),  but these are becoming radioactive items,  and are to be avoided. 

I used the same pre-breathe factor of 1.2 on the nitrogen that has been proven.  The other factors are speculative.  I used a factor of 1.0 for the argon,  and 0.5 for helium and the other noble gases.  This is an arbitrary selection,  but should be in the ballpark (so something like this mix will work.)  The last noble gas (krypton) I allowed to fall a tiny bit short of its max pre-breathe factor to balance the mix at 100%. 

I did not use exactly the Earth-normal oxygen percentage,  because I could not quite achieve mathematical closure with a 6-gas mix.  But since the next noble gases are radioactive,  I did not use them.  Instead I picked an oxygen percentage very close to a nominal 21 volume percent,  which should present exactly the same fire hazard as Earth-normal air.  My number was exactly 21.28% oxygen. 

I forced the wet in-lung oxygen partial pressure of the mix to match that from sea level Earth-normal air at 149.33 mm mercury.  Removing the water vapor but retaining the mixture total pressure gives this dry habitat atmosphere:

                Gas        Pp,  mm Hg         vol%
                O2          159.34                   21.28  compare to 20.946% for sea-level Earth-normal air
                N2          191.21                   25.54
                Ar           159.34                   21.28
                He          79.67                    10.64
                Ne          79.67                     10.64
                Kr            74.55                     10.62
                Dry tot  748.80                   100.

The habitat atmosphere works out to 0.9853 atm = 14.48 psia,  very close to Earth-normal air.  The difference is 5 diluent gases at significant concentrations,  instead of just one.  None of the 5 will have large concentrations (or osmotic pressures) in the blood.  Thus,  there should be little or no risk of “the bends” going straight from this atmosphere to the corresponding suit,  assuming my pre-breathe factors are anywhere close to right.  But,  it will take experiment to find out what the real factors are. 

In the wet-lung environment,  water vapor pressure displaces part of this dry atmosphere,  lowering the partial pressures.  I assume equilibrium water vapor pressure at body temperature.  Those adjusted data look like this:

                Gas                                        Pp, mmHg
                O2                                          149.33  same as sea-level Earth-normal air in the wet lungs
                N2                                          179.20
                Ar                                           149.33
                He                                            74.67
                Ne                                          74.67
                Kr                                            74.55
                Water vapor                       47.06
                Total                                      748.80  = 0.9853 atm = 14.48 psia

We want the pure-oxygen suit to match wet in-lung oxygen partial pressures,  so that tissue oxygenation and resistance to hypoxia issues is the same,  in the suit as in the habitat.  Because the suit is a 1-gas system,  you just add the water vapor partial pressure to the wet in-lung oxygen partial pressure to determine total suit pressure. 

                149.33 + 47.06 = 196.39 mm Hg = 0.2584 atm = 3.798 psia  

Even if you add a factor 1.10 increase to counter leakage,  the suit pressure is still only 216.03 mm Hg = 0.2842 atm = 4.177 psia.  That is far lower than current practice on the ISS. 

Conclusions:

#1. It is quite feasible to have habitat atmosphere at very nearly Earth-normal pressure and Earth-normal oxygen percentages,  and yet avoid high nitrogen concentrations,  by going to a multi-gas mixture.

#2. It is very likely feasible to do this in a way that avoids the long pre-breathe times associated with the high nitrogen concentration in Earth-normal air.

#3. If you do it as a multi-gas system,  there is no need for a high-pressure space suit,  just to lower (but not eliminate) the pre-breathe times using Earth-normal air. 

#4. The lowered suit pressure requirement makes full pressure suits more supple,  and makes mechanical counterpressure suits immediately feasible with compression levels already easily achieved.

Final Note: 

My pre-breathe factors for all but nitrogen are probably only ballpark,  but certainly not exactly correct.  The research to quantify these factors correctly can be done on the ground.  Thus there is no excuse not to research this,  the payoff is simply too attractive. 

Update 11-26-14:

Once again,  my pre-breathe limit factors for all but nitrogen are guesses requiring experiment before application!  I have heard that the US Navy knows the pre-breathe factors for at least some of the noble gases that I proposed using here,  and has experience with actual use of multiple diluent gases,  exactly as proposed here.  The pre-breathe factor of 1.2 for nitrogen is in fact a US Navy value.

While not conclusive as presented here,  this does make my analysis seem at least ballpark correct.

Use the Navy's factors,  and this becomes possible as a 4-, 5-,  or at most 6-gas system.  You will be at no more at risk of fire than here on Earth with 21% by volume oxygen,  and you can use a lower-pressure,  more-supple pressure suit in the vicinity of at most 4 psia (for a sea-level-equivalent oxygenation design plus leak margin).

And,  best of all,  you need no long pre-breathe times to avoid the bends.  That is completely unlike current practice on the ISS.

Or even better than a supple full pressure suit,  you can use a really supple mechanical counterpressure suit at the same low pressure.  Such a low-pressure suit is technologically feasible right now,  and has been since 1968,  in one form or another.  3 to 4 psia compression has been well demonstrated as feasible in that approach,  with two disparate technologies.  

There is simply no excuse not to try all of this out.  The payoff,  in terms of basic astronaut mobility,  and in terms of effective human exploration capability,  is just too great.  Not to mention enabling feasible and practical designs for habitats and bases on other celestial bodies of all kinds.  And,  enabling far more effective assembly and repair operations by humans in space!

Any space agency,  public or private,  that is really interested in manned travel beyond cis-lunar space should be looking very seriously at the issues and possibilities raised here.

As for the rest of us,  we can safely conclude that agencies not looking very seriously at these same issues and possibilities,  are simply not yet serious about manned travel beyond cis-lunar space.

Monday, November 3, 2014

A Really Nice Airliner

On Wednesday 10-29-14,  I had the privilege of working on EAA’s Ford tri-motor NC8407 (built in 1929),  as part of a team of volunteers,  doing a 100-hour inspection.  This was at the McGregor,  Texas,  airport,  and I did this just after completing the annual inspection on my own plane (a Cessna 170B,  N2794D,  see "Super Red-Letter Event",  posted 1-18-14 on this site). 

On Saturday 11-1-14,  I got to take a ride in that same Ford tri-motor.  It was a really nice ride,  and very comfortable.  The seat pitch allowed one to stretch one’s legs,  something ignored by airlines today.  We flew around the Waco,  Texas,  area for about 20 minutes,  at about 90 mph,  at around 3000 feet.  Very comfortable.  

The pilots that morning were Jeff Skiles and Ashley Messenger.  Yes,  it was THE Jeff Skiles,  Capt. Sullenberger’s copilot during the “Miracle on the Hudson” water landing.  I got to talk extensively with both of them. 


I found a good image of this aircraft overall,  and a unique image of the engine gauges on the outboard engine.  You read them by looking out the window at them.  Enjoy

EAA Ford Tri-Motor NC8407


3-Gauge Instrument Cluster on No. 1 (Left) Engine

Saturday, November 1, 2014

Two Commercial Spaceflight Disasters in One Week

Two commercial launch failures within days is a lot for a fledgling industry to take.  Especially with political critics that are quite undeserved.  One of these failures relates to commercial manned flights,  that being Virgin Galactic's SpaceShip Two.  The other relates to unmanned cargo and satellite launch,  that being Orbital Sciences' Antares rocket and Cygnus cargo spacecraft.  

Update 11-3-14:  with a rocket-powered vehicle,  the first suspect is always the engine when there is a problem.  That appears to be the case with the Orbital Sciences launch failure.  

But with the Virgin Atlantic spaceplane,  preliminary NTSB comments reported this morning indicate there was a problem with the re-entry feathering system,  not the engine.  This one is going to be very interesting when the report is done.  

In any event,  enjoy the rocket technology discussions that follow.

Update 11-5-14:  Published news releases as of today indicate that Orbital thinks their launch disaster was caused by a turbopump failure.  They also no longer intend to use those engines.  The best new information about the Spaceship Two disaster suggests that the two pilots were literally ejected into the air as the cabin broke up around them,  at about Mach 1,  near 50,000 feet.  These reports indicate they were so ejected without pressure suits or supplemental oxygen.  One managed to deploy his parachute and lived,  the other didn't and died.  

Hybrid vs Solid Rocket Technology

Hybrid rockets “done right” have safety advantages over solid propellant rockets,  if the fuel is just that:  fuel,  without any oxidizer in its formulation.  That can be a rubber,  a plastic,  or even a wax,  and it can have solid powders dispersed in it,  just not oxidizer powders. 

That kind of hybrid ceases combustion when you stop the liquid oxidizer flow.  That makes the vehicle abortable,  since you can shut off the engine,  as with liquid rockets.  Solids burn like dynamite sticks:  once lit,  they burn to completion,  no choice.

Solid propellants are typically a rubber or rubber-like binder loaded with particulate solids,  solids that include the solid oxidizer as powder.  Solid oxidizers are typically ammonium perchlorate or ammonium nitrate these days.  There are some others. 

Solid propellants,  even those that are seriously fuel-rich,  all burn with two physical effects controlling their burn rate.  The prime factor is an inherent burn rate of exposed surface that depends upon chamber pressure per a power function with an exponent under 1,  usually well under 1.  The secondary factor is often called “erosive burning”,  and shows up as a burn rate enhancement (added term) in the presence of hot gas scrubbing along the exposed surface at high speed. 

All exposed solid surface quickly produces massflow,  because there is very rapid surface flame spread from lit areas to unlit areas.  The most common problem encountered with solid rockets is the presence of cracks or voids in the propellant charge,  because these very quickly (in milliseconds) add large quantities of burning surface,  producing massive increases in motor massflow.

This very quickly drives the chamber pressure too high,  overpressuring the case,  and causing a violent explosion.  It typically happens without warning symptoms,  and very quickly (on a few milliseconds time scale).  This is due to the very nonlinear mathematics of what determines the chamber pressure,  which is a balance between pressure-driven surface massflow generation,  and pressure-driven nozzle massflow capability.

The second most common failure in solid motors is a case insulation failure,  leading to a burn-through,  followed quickly (usually just under a second) by the case exploding.  The third most common failure is a type of combustion instability wherein the oscillations cause higher average pressures from an enhanced burn rate,  due to the erosive-burning effect.  These can lead to over-pressurization explosions on a time scale of a few seconds,  but not always.

That kind of combustion instability has an unstable positive feedback of combustion energy released from tiny combustion eddies directly into the oscillations.  It occurs when some natural gas vibration mode in the geometry is close to the small-scale combustion eddy frequencies.

A very distant fourth most common failure is a piece of propellant or other debris coming loose inside the motor,  and getting blown into the nozzle,  where it obstructs the throat,  causing the motor to virtually-instantaneously explode like a pipe bomb. 

The most common problem in the hybrids is a kind of combustion instability that causes very rough operation and vibrations,  but usually without the unstable feedback of the solid.  This is inherent due to the gross unmixedness resulting from generating the fuel from only the erosive-burning effect of the hot port flow (oxidizer plus fuel from upstream plus still-combusting fuel and oxidizer). 

There are localized fuel-rich and fuel-lean pockets of gas.  As fuel and oxidizer suddenly combine in the very turbulent mixing,  these pockets explode.  The bigger the “exploding vortices”,  the stronger the thrust and pressure oscillations.  But because there is no feedback into a chamber-pressure burn rate effect,  the instability doesn’t grow catastrophically out-of-control within seconds,  the way it does in solids. 

The other two fatal hybrid failure modes are the same as solids:  case insulation failure leading to burn-through,  and debris blocking the throat.  Update 11-3-14:  hybrids with no oxidizer in their fuel grains are pretty much immune to the effects of grain cracks or voids.  There is no pressure effect burn rate in these freshly-exposed spaces,  and the massflow scrubbing effect just doesn't reach there hardly at all.  Fuel burnout "tailoff" characteristics can be affected somewhat,  though.  

Historically,  hybrids have suffered design impracticality from very low effective burn rates (more properly,  “regression rates”).  The historical “fixes” for this are (1) multiport grain designs that reduce the effective thickness to be burned,  and (2) adding low amounts of oxidizer powder to the fuel grain formulation. 

In recent years,  a third option has become available:  fuel formulations that liquefy (literally melt) before they pyrolyze into combustion.  That third option is the best.  The multiport option leads to low volumetric efficiency.  Adding solid oxidizer is absolutely the worst,  by far.

Adding oxidizer,  even in amounts too low to sustain combustion with the liquid oxidizer shut off,  converts the hybrid “fuel” into a fuel-rich conventional solid propellant.  That negates the very most important safety advantage of being a hybrid.  Now there is fast surface flamespread,  drive by the inherent burn rate vs pressure effect of a solid,  into cracks and voids.  This restores the same vulnerability to motor explosion as any other solid.  

If you add too much solid oxidizer,  you cannot stop the motor by cutting off the liquid oxidizer.  This negates the other advantage of a hybrid,  abortability. 

A Word About Liquid Rockets

Liquids have three of the very same failure modes that afflict solids and hybrids:  burn-through,  debris blocking nozzle throats,  and combustion instability.  The failure of regenerative cooling (not insulation) is what causes the burn-through.   Combustion instability in liquids takes many forms,  all being related to ignition of mixing eddies that are rich or lean in fuel. 

The unique problem with liquids is turbopump failures,  since nearly all liquid systems have them. (Update 11-3-14:  some hybrids can also have pumped liquid oxidizers,  others are pressure-fed.)  These components are very highly stressed,  and exposed to very extreme conditions of heat and cold simultaneously.  It is not surprising that they fail.  When they do,  there is almost always some kind of explosion. 

Another failure mode known since the V-2 missile of World War 2 is starting at too high a propellant flow rate.  This will literally blow the engine apart,  virtually instantaneously.  It does take a very finite time to spool turbomachinery up from low thrust settings to high thrust settings.  Further,  there are serious limitations on just what the minimum thrust of any particular engine design can be. 

SpaceShip Two’s Loss 10-31-14:

The available data-to-date are spotty at best.  We will have to wait for the NTSB investigation to complete,  before the truth and all the facts come out.  That can take over a year. 

The news photos I have seen indicates that SpaceShip Two dropped from White Knight Two successfully,  and then successfully ignited its rocket engine.  Then there was an explosion. Update 11-3-14:  not an explosion,  a mid-air breakup,  according to very preliminary comments made by the NTSB.  

Photos of the wreckage tell me that the engine compartment was violently destroyed,  also blowing away the tail booms of Spaceship Two.  Without the tails,  the fuselage and its stub wings just become a tumbling ballistic projectile to the desert floor. 

The tail booms,  and that which is recognizable as fuselage wreckage,  appear to have crashed in different places on the desert.  I did recognize the fuselage aft pressure bulkhead in some photos of the wreckage.  There was nothing left aft of it.  Update 11-3-14:  more published photos from more view angles show that there was nothing left on either side of this bulkhead.  

Some accounts I have seen claim CNN as a source for the assertion that the engine shut down,  and then exploded upon a restart attempt.  I do not know anything about that,  myself. 

Nothing I have found among open sources on the internet would indicate that solid oxidizer was a part of the original HTPB fuel grain formulation,  or the new plastic grain formulation on the lost flight.  That’s not to say there wasn’t any,  but nothing released publicly indicates it. 

Everything I saw says fuel-only grain plus liquid nitrous oxide (N2O).  The only change seemed to be the switch from HTPB rubber to a plastic for the binder.  That occurred when Virgin took the motor design in-house,  away from Sierra Nevada,  who had done the HTPB version.

That leaves motor case burn-throughs or debris plugging the nozzle,  from the failure modes listed above.  There is also the possibility that the restart attempt was transiently just too violent an event,  and simply split the motor case open. 

Whatever happened,  the event was violent enough to suddenly “disperse” the entire engine compartment from the aft fuselage,  since the fuselage debris in the desert terminates at the aft pressure bulkhead.  Update 11-3-14:  with a midair breakup,  it was broadside air pressures that broke up and dispersed everything.  It doesn't take an internal explosion to do that,  just a loss of attitude control.  

This same violent event was enough to separate both articulated tail booms from the aircraft.  They can be quite clearly seen about a vehicle length away on each side in the news still photo that was taken a split second after the explosion. 

Pieces of the motor case are going to be hard to find in all of that desert.  It may be impossible to find enough to reassemble it,  to determine if there was a burn-through. 

If there was some kind of mixing baffle inside the motor to help with the low-grade instability of hybrids due to poor mixing,  then it might have come loose and blocked the nozzle.  It might be vulnerable during an ignition transient.  If it can be found,  extreme distortion of the part might suggest this possibility.

Finding out whether restart attempts might be too violent will require motor restart testing on the ground.  Virgin and Scaled Composites certainly have a lot to investigate.  I would suggest doing any such restart tests in a revetment of some kind,  as a ground crew safety measure. 

Update 11-3-14:  With the NTSB focusing up the the feathering system causing a mid-air breakup,  the engine issue revises to confirming that it was operating correctly.  

Orbital Sciences Antares/Cygnus Loss

I have seen news video footage of this loss enough times to know that something was wrong from liftoff.   The engine plumes of kerosene-liquid oxygen engines are very brilliant,  enough to cause camera “image bloom” all the time.  Yet in this launch,  that “apparent fireball” was just too bright. 

A few vehicle lengths off the launch pad I saw the vehicle slowing to a stop,  followed by the first explosion.  That first explosion would have been the range safety self-destruct charge ripping apart the first stage.  The rest of it blew up as multiple explosions upon impact very near the launch pad.

I do not know,  but I suspect either a turbopump or chamber failure leading to a loss of incandescent gas around the engine at vehicle rear.  After a few seconds overheating,  the engine blew apart,  killing thrust,  and precipitating self-destruct.  These are refurbished 40+ year-old Russian-made engines! 

Orbital Sciences is using these Russian-made engines as the only thing available to them in the right size range.  These were originally built in Russia over 4 decades ago,  and were stored most of those years in a barn of some kind in Siberia.  Aerojet Rocketdyne refurbished these for Orbital Sciences.

This says more about corporate (and government) policies regarding offshoring overseas critical US capabilities,  than it does anything about the engines themselves.  If “we” had not frittered-away this country’s rocket engine manufacturing capabilities,  Orbital would not have been forced to use refurbished 40+ year old foreign made units.  Period.  Somebody needs their butt thoroughly kicked over this issue!

From what I can find on the internet,  one of these same engines blew up in a ground test a while back.  I could not locate anything explaining that test failure,  but then,  I am no internet expert.  However,  that’s enough to cast some doubt on this engine.

Conclusions:

Orbital has to get to the bottom of this.  They will need Aerojet’s help.  The rest of us need to give them the “wiggle room” to get that job done.  Critics stirring up trouble in the halls of congress are not needed,  and can go stuff their unhelpful “suggestions” where the sun doesn’t shine!

Same goes for Virgin’s fatal problem with SpaceShip Two:  they need “wiggle room” and time to get to the bottom of what happened. 

I can only wish both outfits well,  and may God speed their investigations.  I would gladly help either or both of them.


GW

Monday, October 20, 2014

Ethanol From Cellulose Goes Into Industrial Production

This from Biofuels Digest for 10-20-2014:


In Kansas, Abengoa Bioenergy officially opened the world's largest cellulosic biorefinery in Hugoton on Friday, surrounded by dignitaries such as US Energy Secretary Ernest Moniz, Kansas Governor Sam Brownback, Kansas senior Senator Pat Roberts, former Interior Secretary Ken Salazar, former Energy Secretary Bill Richardson among many others.

The second generation cellulosic ethanol plant in Hugoton, Kansas, located about 90 miles southwest of Dodge City finished construction in mid-August and began producing cellulosic ethanol at the end of September with the capacity to produce up to 25 million gallons per year.

In today's Digest, we have the complete story - including remarks by US Energy Secretary Ernest Moniz, US Senator Pat Roberts, Kansas Governor Sam Brownback, Abengoa CEO Manuel Sánchez Ortega and Abengoa Bioenergy chief Javier Garoz - and more - plus the full background on the refinery and industry reaction, at biofuelsdigest.com.



At last,  non-food ethanol is arriving.  We now have a way to eat the corn,  and make fuel out of the cobs and stalks,  and it scales up to industrial operations.  When this catches on in a big way,  there will be no more "food versus fuel" as the excuse for not employing this technology to the max.

There's a lot more cellulose to convert out there than there is grain.  That'll take the resource-limitation off of ethanol production rates.  Which leaves only bureaucratic recalcitrance from those agencies in the pockets of big oil,  and from congress itself.

As it says in my other ethanol-related postings,  you can use this stuff in very stiff gasohol blends in totally factory-stock cars,  of any age.  It acts to extend catalytic converter life,  by keeping the soot buildup down.  Engines and engine oil run cleaner,  and last longer.  All from reduced flame soot.

Which also is why mileage is the same as plain gasoline up to about E-40:  the reduced-soot flame is also a more efficient combustion process.  That is what my doctoral dissertation was about.

E-10 is currently "unleaded regular",  E-15 is available in a few places for newer cars,  just not widely available.  I routinely use E-30 to E-35 in all my 4-stroke equipment of any age,  and have for 8 years.  If there were a problem in cars or 4-stroke lawn equipment,  I'd have found it by now.

The 2-stroke and boat motor communities need to catch up and get on board with this,  by making the change to ethanol-compatible materials.  The automotive and 4-stroke folks did this years ago,  and my experimentation confirms it.  The airplane folks also need to make this change:  leaded avgas won't be around forever.

The EPA is simply wrong to restrict its use to E-10 or E-15 for "fear of damage to emission controls",  and to restrict its use as E-15 to newer cars.  They listened too closely to the lobbies and not to the actual science and experimentation.

See also on this site not far below:

11-2-13:  "An Update on Ethanol Fuel Use"

11-3-13:  "Aviation Alternative Fuel Compatibility Issues"


Update 12-18-14:

This press release is from “Biofuels Digest” for Thursday 12-18-14.  One should note that Brazil is the world capital of sugar cane ethanol production.  This announcement is for cellulosic ethanol production at a price that sells in Brazil,  where the “easy” ethanol from sugar cane sugar has been “king” since the 1980’s.  Remarkable!  The end of the food-versus-fuel objection is now in sight. 


In Brazil, Iogen and Raí­zen announced they have begun production of cellulosic ethanol on schedule at Raízen`s newly expanded Costa Pinto sugar cane mill in Piracicaba, São Paulo, Brazil.

"We finished construction on schedule, and said we expected a Q4 startup, and we're on time," said Ziyad Rahme, SVP and General Manager for Iogen Energy. "We've had a short one-month ramp up, and started production and are making ethanol. Raizen right now have made 200,000 liters available and are selling cellulosic ethanol in Brazil. That's also very exciting."

Friday, September 5, 2014

Mars "Thighbone"?

Depending upon where you look on the internet,  this NASA photo has created quite a stir.  It was taken by the latest Curiosity rover on Mars.  The object in photo center looks very much like a thigh bone,  based on our Earthly experiences with human and animal skeletons. 

NASA say this is just an oddly-shaped eroded rock.  Maybe so.  But,  it is a striking-enough image to warrant further investigation.  Such investigation is certainly something that Curiosity can do.  So,  it should be done.   You all should contact NASA and demand that it be done.  It’s your tax dollars. 

If I was present on-site,  I would look at sampling that “thighbone” to confirm or deny exactly what it is made of.  And,  I would scratch around in that dirt looking for more such weirdly-shaped artifacts.  In the interests of science,  such an effort is certainly with the effort. 


For one thing,  the dark holes evident in the photo suggest that there are subsurface cavities under the rocks whose outlines we can see in the dirt.  Cavities?  Really?  How did they get there?  Those are awfully good questions!  They deserve answers.  



Update 9-6-14:

This same article and picture appeared as a letter-to-the-editor in the Waco "Tribune-Herald" Saturday 9-6-14.

Update 9-13-14:

As best I can tell from the news releases,  Curiosity did not stop and poke around at this site.  The press releases say it has arrived at Mount Sharp,  its intended target.  Too bad,  this was a very interesting site.


Friday, August 22, 2014

Extremism in Any Form is Evil

Update:  8-28-2014:  A version of this made the op ed page of the Waco,  Texas,  "Tribune Herald" Thursday 8-20-14.
______________________________________________

The beheading of American journalist James Foley by the Muslim extremist organization we call ISIS has brought to a head a very serious question:  what do we do about evident evil operating in our midst?  Mr. Foley’s murder is not the only crime  committed by these people:  thousands have already died at their hands in Syria and Iraq.         

ISIS is an example of religious extremism in operation “at full tilt”.  These are people who believe that God has told them to kill those who think differently from them,  in any way.  They believe so strongly in this,  that they are willing to commit any atrocity,  no matter how evil,  “in the name of God”. 

My reading of the Bible and multiple other religious texts leads me to believe two things:  (1) these scriptures are complicated and self-contradictory enough to support any interpretation one wants to promulgate,  simply by taking things out of context,  and more importantly (2) if that little voice inside you says “kill for God”,  that ain’t God you are listening to.  It’s Satan (or whatever name in any religion for the personification of evil). 

We are now faced with the rapid spread of a very evil idea across much of the middle east and Africa,  plus some other places,  including here at home.   Since before the 9-11 attacks,  we have been trying to fight this evil idea with military force,  and with police work.  In all the decades since,  we have not succeeded. 

We have also completely failed to recognize that it is not exclusively Muslim extremism that threatens us!  There have been Christian extremists willing to kill doctors and bomb clinics over here,  for many years now.  “Killing for God”!  That’s really Satan’s work. 

You must remember that all religions can be corrupted by the evil of extremism. 

Governments around the world have completely failed to stand up to this evil in any effective way.  You don’t fight a bad idea with weapons,  you fight it with a better idea. 

And that means that you demonstrate publicly and frequently why your idea is good,  while simultaneously demonstrating publicly and frequently why their idea is bad.  Our government is so hog-tied with “political correctness” that it has not ever done this,  and to this day it cannot,  “for fear of offending someone”. 

Not offending the bad guys?  That’s utter bullshit!

Folks,  the only folks who should be offended by such a message are the evil extremists themselves!  I really don’t care if I offend them,  they are Satan’s minions!  Death is too good for them,  but very expedient for the rest of us.

What all of us really have to do is get the truth out there,  to prevent the further spread of this evil religious-extremist idea,  no matter the religious label it bears. 

And spread it has,  especially among the uneducated and the downtrodden,  which is something I can understand.  Why educated persons would fall for an extremist creed is something I do not personally understand,  but the available data says that they do:  the Fort Hood shooter Nidal Hasan for one,  who held a doctoral degree in the mental health field. 

Since governments around the world,  especially ours,  are paralyzed by political correctness and completely ineffective,  this counter-message has to come from the grassroots.  I don’t care what religion we are talking about,  if there is a preacher of whatever stripe promoting violence and hostility from his pulpit,  then remove him!  Cast him out as the servant of Satan that he is.  Period. 

The rest of you,  testify to your neighbors,  especially those of other religions,  about how God does not demand that we kill unbelievers.  Right now,  it is crucially important that the good majority of Muslims speak out in exactly this way,  for it is Muslim extremists who are killing the most people right now.  But,  that does not let the rest of us off the hook!

It’ll take at least 2 or 3 generations to rid the world of this evil,  but we can do it,  all of us,  together.  Doesn’t matter what your faith is. 

The hell of it is,  political extremism is just as evil.  Examples include the Nazis,  the Fascists,  and the Communists,  just in the 20th century.  I see political extremism on the rise all around us,  right here in the US,  and it will eventually be just as deadly as religious extremism,  to the continued existence of a free people. 


Think about that,  before you forward your next political-email hit-piece.  

Saturday, August 16, 2014

The Realities of Air Launch to Low Earth Orbit

Air launch to LEO works better if you take into account the three top items in their order of importance:  (1) staging speed,  (2) path angle at staging,  and (3) staging altitude.  These three items are not even close to equal importance,  speed is simply everything (an unfortunate technological fact-of-life).  You get do-able second stage mass ratios starting about Mach 5 to 6,  and reasonable second-stage mass ratios at about Mach 10,  for two-stage vehicles. 

Speed at staging figures directly into the delta-vee requirements associated with the rocket equation for the second stage.  Path angle at staging gets you to a second stage trajectory that needs no lift (and no drag-due-to-lift) for a simple non-lifting ballistic trajectory to orbit.  Altitude at staging gets you some extra energy in the flight vehicle energy-management equations,  but is the weakest of the three effects,  by far. 

An all-rocket first stage airplane can do this job,  but it is of enormous size,  with some very serious structural issues having to do with landing gear loads that start to resemble a water balloon resting on nails.  That’s a common sense thing,  as well as a structural design thing.  On the other hand,  you can save weight by using airbreathing propulsion to the greatest extent possible in that first stage.  “Greatest extent” simply means the widest-possible range of speeds.  That’s just common sense.

Scramjet is neither ready-for-prime-time technologically,  nor a wide speed-range type of propulsion just yet (X-51 flew in scramjet at Mach 5 +/- 0.1).  It takes over at about Mach 4 ,  minimum,  so going for Mach 10 capability,  you cover only a delta-Mach of 6.  If your scramjet system really only gets you to Mach 7 or 8 as currently seems practical,  well,  the delta-Mach drops to 3 or 4.  That’s a lot more likely outcome for the next few decades.

The fastest turbines that ever were (those powering the SR-71),  were good only to about Mach 3.6-ish,  which is woefully short of an adequate staging speed.  So such a first stage would require rockets as well,  and also some protection for the engines against overheated inlet air,  at speeds above Mach 3.6-ish,  which the SR-71 never had.  If the turbine-powered stage can take off on only-turbine power,  then the airbreathing delta-Mach is about 3.6-ish at maximum,  since turbine supplies static (Mach 0) thrust. 

Plain ramjet technology has been well-proven in flight for many decades now,  and can be arranged to work from Mach 1.8-ish to Mach 6 quite easily.  That's a delta-Mach of 4.2-ish.  That figure is at least as good as the more realistic scramjet concepts,  and better than any of the turbine concepts.  So,  of the choices,  it’s quite simply the best,  especially when you look at technological readiness-for-application.  That’s just basic common sense plus the facts of technological readiness. 

If one were to do a combined rocket-ramjet propulsion airplane for a first stage,  we would take off on rocket at Mach 0 and accelerate to about Mach 1.8,  then transition to ramjet and climb-and-accelerate to Mach 6 as high as is feasible,  then go back on rocket power,  pull up sharply,  and accelerate exoatmospheric to speeds that would have been near Mach 10 in the air.  And,  with ramjet,  there’s less susceptibility to overheated inlet air (no turbomachinery to damage).

That switching back and forth between rocket and ramjet requires either combined-cycle or parallel-burn (with separate engines).  Combined cycle is quite simply not technologically ready for prime time,  and has always very seriously compromised the performance of both propulsion cycles,  because of the incompatible engine geometries.  So parallel-burn with separate engines really is the way to go!  Basic common sense.   

The hardest part of the design is packaging the rocket engines somewhere in the airframe,  because the ramjet will essentially fill the fuselage (a hard technological fact-of-life).  But the rocket thrust chambers are actually quite small,  and will fit inside the aft portions of the wing strakes or fillets.  Plus,  there is now aerospike nozzle technology to eliminate drag-inducing huge engine bells.  The next hardest part of the design will be inlet and combustor heat protection-as-reusable devices,  not one-shot ablatives as in missile work. 

This could have been done at least 2 decades ago.  It was not. 


GW