Re-Entering Space Junk Threats

Update 5-10-2025:

A close version of this article appeared as an opinion column in the Waco "Tribune-Herald" newspaper on Saturday,  10 May 2025.  I happen to be on their board of contributors.

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News stories have it that sometime this week Kosmos 482 will be entering the Earth’s atmosphere uncontrolled,  after 53 years of being lost in a decaying orbit.  This is the Venus atmospheric entry craft for a Russian probe to Venus launched in 1972.  It failed to leave Earth orbit.  Most of it came apart and reentered years ago,  but this entry capsule did not.

This thing could come down anywhere on Earth between 51 degrees north latitude and 51 degrees south latitude!  It weighs about 1100 lb (or 500 kg).   It is an entry craft design,  so the claims that it will likely burn up in the atmosphere are hogwash!  It was specifically designed to survive that! 

Update 5-10-2025:  Kosmos 482 fell to Earth today,  Saturday,  10 May 2025.  Most reports do not know where,  although Roscosmos in Russia says it fell in the Indian Ocean. 

It has a landing parachute designed for Venus’s thicker atmosphere,  but after 53 years in space,  that might not work,  and certainly the controls to deploy it might not work.  Which means you will most likely have around a half-a-ton object,  coming down to hit at a few hundred miles per hour,  and all in one big piece!  The odds are roughly 2 against 1 that it will hit ocean.  That’s mostly empty water,  but there are people living on islands out there!  There are also ships and planes at risk crossing the ocean,  not to mention the many risks on or over land.

There’s more space flights in recent years,  so we have seen more space junk coming back.  There was a half-ton chunk of metal fell on a village in Africa,  and a Florida house struck by a chunk of steel weighing several pounds.  Some of this debris has been identified,  some not.  Most of it came from things not designed to be re-entry craft,  yet they still hit the surface,  at least as several pieces.  The point is,  there’s now enough of it,  and it is large and heavy enough,  to be a significant risk!

Up to now,  the pronouncements have been (1) it’ll most likely fall in the ocean (true) and (2) it will mostly burn up in the atmosphere before striking the ground (not true). 

This one (Kosmos 482) is an entry vehicle.  Kosmos 954 that fell in Canada back in 1978 was a Russian spy satellite not designed for re-entry,  that had a nuclear reactor aboard.  It made a radioactive mess to clean up in multiple Canadian lakes and a swath of arctic land hundreds of miles in extent!  Reactors are designed for high core temperatures:  the claim that it “would burn up on entry” was patently false,  even then. 

The US space station Skylab fell on western Australia a couple of years later.  The Space Shuttle was supposed to re-boost it,  but ended up not even making its very first test flight until a couple of years after that crash.  Skylab was converted from the thin propellant tankage of a Saturn-5 third stage.  It weighed about 85 or 90 tons at entry and it did break up,  but not very many of the pieces burned up!  The Australians claimed to have picked up some 75 tons of Skylab debris,  including a 1-ton film vault that was almost entirely intact.  So much for the “these things burn up on entry” theory!

The loss of Shuttle Columbia halfway through re-entry over Texas in 2002,  rained down tons of debris for hundreds of miles,  showing just exactly how ridiculous that oft-repeated claim is. 

And this risk has been known for decades!  John Glenn’s Mercury capsule was sent to orbit by an Atlas booster that was essentially a lightweight stainless steel balloon,  relying on some inflation pressure just to hold its shape.   That shell broke up during entry,  yes,  but a piece of the internal propellant piping washed up on an African beach only a few years later.  This piece of debris was identified by the serial number stamped on it,  it was in that good a shape!    This was 6 decades ago that “they” knew this could happen!

There’s a lot of debris up there in orbit that sooner or later we will have to contrive a means to go get,  for disposal.  I think everybody understands that.  But when you find yourself in a deep hole,  the first thing to do is stop digging!  We do not need to be launching more things into orbit that inherently become debris that will collide (creating more debris) or fall back.

We need to modify the international space treaty to preclude launching satellites that have no means to de-orbit themselves in a controlled fashion over the remotest part of the Pacific.  We need to preclude the jettisoning of anything at all,  not even paint flecks,  once orbital-class speeds have been achieved.  We need to very strongly discourage fielding any future launch and space vehicles that are not fully reusable,  or that do not offer safe stage disposal capability. 

That’s the real lesson here,  and it has been staring us in the face for many years now,  unaddressed!  Will it take deaths on the ground from falling debris to prompt addressing it?  How negligent is that?

Photo of one piece of Kosmos 954 debris,  in the Canadian Arctic

Vehicle Assembly and Refueling Facility in LEO

Described herein is a concept (only) for a facility in low Earth orbit for the assembly and fueling of interplanetary vehicles requiring hyperbolic departure (and arrival),  in particular those associated with space-tug assisted departures and arrivals.  Such a facility need not be a 1-to-2-decade long international project to build,  if it is docked together out of modules that fit within the payload spaces of the current launcher fleet!  That should be easily achievable for a “clean sheet of paper” design like this!

For lunar missions,  the departure from LEO is not hyperbolic,  although it is elliptic at very-near-escape perigee speeds!  Depending upon the choice of the extended departure (and arrival) ellipse,  the LEO departure velocity requirement for a lunar mission can be reduced to near-zero,  with the space tug assuming most or all of that velocity requirement just getting the craft onto the ellipse. 

No calculations have been made,  these results are concept only,  as is perfectly reasonable at this early stage!  The basic design concept has two core sections,  one made of pressurized modules docked together,  and the other a truss core to which a multitude of propellant tanks are attached. 

Attached to one end is the Power and Propulsion Section,  where solar electricity is made,  stored,  and distributed.   This section includes propulsion sufficient to address the needs for countering orbital decay,  conducting debris avoidance,  and performing end-of-life safe disposal. 

The pressurized-core section is the Vehicle Assembly and Refueling Section,  where interplanetary vehicles are assembled from modules,  mated to space tug vehicles as appropriate,  and fueled-up from the propellant depot section for the relevant missions.  Many remote-operated arms similar to those used at the International Space Station (ISS),  and previously on the old Space Shuttle,  are installed to make vehicle assembly and handling operations as safe and easy,  as is possible.  This is a manned microgravity facility,  probably manned by rotating crews,  as is the ISS.

The truss core section has multiple propellant tanks attached to it,  with the propellant feed lines and electric power lines housed inside the truss.  This is the Propellant Depot Section,  presumed to be kept supplied by unspecified tanker flights up from Earth.  It would have both cryogenics and storables,  to supply a variety of on-orbit needs.  Its capacity is also easily expandable. 

The concept for the Vehicle Assembly and Fueling Section is sketched in Figure 1.  The concept for the Power and Propulsion Section is sketched in Figure 2.  The concept for the Propellant Depot Section is sketched in Figure 3.  All figures are at the end of this article.

This kind of a facility would be easiest to keep supplied,  if located in a low-inclination eastward Earth orbit.  That presumes vehicle modules,  propellants,  and supplies are shipped up from the surface.  It would clearly be useful in any event,  but it is an essential enabling item for making use of reusable space tugs for elliptic departure and arrivals,  as described elsewhere in Reference 1. 

Vehicle Assembly and Fueling Section

As the sketches in the first figure indicate,  this facility is built up from many cylindrical modules docked together,  and each is to be small enough to fit in the payload spaces of the existing launcher fleet.  Some of these are oriented along the section axis,  and the others are perpendicular to it,  but all are in one plane.  These could be either hard-shell modules,  or inflatables with hard structural cores,  or a mix of both types.  That choice remains unspecified,  at this time.

The modules along the core axis provide much crew living space,  lots of storage space for life support and other supplies,  airlocks for space-walk activities,  plus any equipment for Earth observations (potentially replacing those functions after the ISS is decommissioned).  These modules would be equipped with external cradle mounts,  to help hold the vehicles being assembled,  thus freeing up the arms for other tasks that are part of the assembly process.  Some of the hatches should be closed,  when the modules are not in use by the crew. 

The modules perpendicular to the core provide the spaces for the arm operators to work.  The arms are affixed to the module ends.  These modules need large windows,  by which the arm operators can see their workpieces in order to work.  Assembly work areas are disposed along this section,  on two opposite sides.  It should be able to handle a busy traffic load,  if arranged in this way.

Per Reference 2,  I am suggesting that this section’s internal atmosphere follow the “Rule of 43”,  that being a two-gas oxygen-nitrogen system,  at 43 volume percent oxygen,  and 43% of a standard atmosphere total pressure.   This is very close to the best atmosphere that I found (which was 43% oxygen,  43.5% of an atmosphere total pressure),  and it is easier to remember!  It has the same oxygen concentration (as mass per unit volume) as sea level Earthly air at 70 F,  so the “predicted fire burn rate danger” from the usual Arrhenius overall-chemical rate equation,  is no worse than that down here on Earth,  at sea level on a warm day. 

Further,  the “pre-breathe criterion” allows no pre-breathe requirement be imposed for donning pure-oxygen space suits,  of helmet pressures down to as low as only 3.002 psia (155.2 mm Hg)!  That criterion says the ratio of nitrogen partial pressure to suit oxygen helmet pressure,  may not exceed 1.2, in order to avoid the nitrogen blow-off time otherwise required.  (The absolute minimum tolerable suit pressure for functional cognitive capability is 2.675 psia (138.3 mm Hg),  before applying a 10% leak-down factor.  The cognition margin is very slightly negative once leaked down.) 

As a further bonus,  the proposed oxygen partial pressure is the same as that at about 2500 m altitude,  so there should be no long-term hypoxia risks,  or even any reproductive health risks for female crew,  based on centuries of human experiences living up to that altitude,  but not above it.

Power and Propulsion Section

Most likely,  the “best” propulsion choice for this application is a hypergolic storable bi-propellant system,  pressure-fed for the greatest engine simplicity and reliability.  Tanks would be bladdered,  with inert gas (helium) expulsion at effectively the feed pressure to the engines.  Propellants would likely be nitrogen tetroxide (NTO) oxidizer and monomethyl hydrazine (MMH) fuel,  although the other hydrazines could also serve,  which include plain hydrazine,  unsymmetrical dimethyl hydrazine (UDMH),  and Aerozine-50 (a 50-50 blend of plain hydrazine and UDMH).  These tanks would need a thin layer of insulation topped with a very reflective aluminum foil,  plus electric tank heaters to prevent freezing while shadowed.

There is a core module to this section that connects to the rest of the station on one end,  and the engines and their propellant tanks on the other.  It would have multiple “fins” mounted to the sides,  some being waste heat radiators,  the others being solar photovoltaic panels.  There would be controls,  batteries,  and distribution switching equipment inside,  plus a docking module for capsules bringing crew and supplies.  This core module is pressurized for easy access,  but the hatch into it should be closed,  when crew are not working in there.

Propellant Depot Section

This section has a modular truss core containing the multiple types of propellant feed lines,  and the necessary power lines.  The propellant tanks are mounted to its periphery,  as sketched in the third figure.  There are basically two types of propellant tanks,  those equipped to store and deliver cryogenics,  and those equipped to store and deliver storables.  Each propellant species must have its own line fittings,  not interchangeable,  so as to prevent incorrect hookups (which would most likely be disastrous).   There are no pressurized modules in this section. 

For the storables (which includes rocket-grade kerosene RP-1),  the bladder in the tank provides the means to transfer propellant,  driven by inert gas pressure that everts the bladder,  as indicated in the third figure.  These tanks will also need some insulation topped by reflective foil,  and some in-tank heaters,  much like the tanks on the Power and Propulsion Section.  The difference is that the inert gas pressure can be lower,  just enough to drive the transfer,  and not at all far above the level to prevent “hot room temperature” boiloff.

The cryogenics are different,  in that there are no feasible bladder materials that could survive eversion at cryogenic temperatures.  These have to be metal tanks with no bladders,  although they do need a layer of insulation topped by reflective aluminum foil,  plus cryocooler equipment. 

In zero gee,  the propellant will initially be free-floating globules,  eventually settling into a thick film coating the entire inner surface of the tank with a vapor void up the core,  but with no pressure other than enough inert gas pressure to stop boiloff.  The slightest touch causes the thick film to break up into free-floating globules again.  Up to now,  the only way to control this behavior into a stable pool from which a pump can draw suction,  was to use thrusters to accelerate the vehicle.  You can’t do that with tanks on a space station whose orbit you do not want to change.

I had previously come up with the spinning tank concept to fling the propellant to the outer wall by centrifugal force.  From there,  a pump could draw suction from openings along the tank sides instead of one end.  This was conceptualized as the vehicle docking with the tank,  in turn undocked from the station.  The docked vehicle and tank would move away to a safe distance and then spin-up in “rifle-bullet” mode,  to fling tank contents to the outer walls.  Then pumped transfer could take place,  followed by de-spin,  then redocking the tank with the station,  and finally undocking the vehicle from the station’s tank.  While this would work,  it does involve multiple docking operations,  and spin-up/de-spin of some massive objects.  But it was better than trying to store spinning tanks on the station.  This concept was described in Reference 3. 

I have since revised the concept to just spinning the propellant inside the stationary tank,  by means of moving vanes inside the tank.  The suction pickups remain on the outer periphery.  If you use a pair of counter-rotating vane sets inside the tank,  separated by a perforated baffle,  you can avoid gyroscopic forces being applied to the station. This concept is shown in the third figure. 

There are no dock/undock operations associated with a propellant transfer by this means.  The vanes can be spun by a coaxial counter-rotating shaft assembly,  entering one end of the tank through a gland seal,  with the drive motor left accessible for repairs and replacements.  You just spin up for the transfer.  Otherwise,  nothing moves.  This is also the least mass to spin up,  reducing the energy requirements for spin-up/de-spin,  and eliminating any and all thruster operations. 

I put the oxygen (LOX) tanks closest to the Vehicle Assembly and Fueling Section,  because that is the largest species volume being used,  and that shorter length minimizes the power line losses for the motors powering the liquid spin.  As the third figure shows,  I put the cryogenic fuels hydrogen (LH2) and methane (LCH4) adjacent to the oxygen,  because their volumes are also large,  to reduce transmission line losses a bit further.  I separated the NTO from the MMH with the storable RP1,  in order to minimize the possibility of spilled hypergolics coming into contact,  even in vacuum.  That is a crucial safety consideration!

The truss can be extended further,  with additional tanks installed,  either for other propellant species,  or for additional capacity,  or both.  This is because there is no other section to the station beyond the Propellant Depot Section.

I think this “spin the propellant inside stationary tanks” concept may be easier to develop and implement than the alternative “each tank is its own syringe” concept,  because (1) the rotating-shaft gland seal technology already exists,  even for cryogenics,  (2) the required piston seal concepts and associated leakage recovery concepts for the “syringe” do not yet exist for cryogenic fluids,  and (3) the tank-and-equipment masses and dimensions would be lower:  vanes and motor vs a syringe piston and its driving equipment.  The hardware has to ride up to LEO inside existing payload spaces,  after all!

Conclusions

#1.  A combined vehicle assembly facility and propellant depot in LEO could enable all sorts of interplanetary missions very effectively,  and even missions to lunar orbit,  plus replace the Earth-observation functions that will likely cease for a while when the ISS is decommissioned. 

#2.  This type of LEO facility is an enabling item to put an effective space tug operation into effect,  that uses elliptic departures and elliptic arrivals,  to reduce the velocity requirements of interplanetary (and lunar) vehicles.

#3.  This kind of fueling operation could use “spin-the-fluid-in-a-stationary-tank” to reduce the overall energy requirements of propellant transfer,  eliminate any need for the use of ullage thrusters,  and also eliminate many dock/undock operations.

#4.  All the other technologies required to build this thing already exist. 

References (use date and title in the archive tool on the left,  to access quickly):

#1.  G. W. Johnson,  “Tug-Assisted Arrivals and Departures”,  posted to “exrocketman” 1 December 2024. 

#2.  G. W. Johnson,  “Refining Proposed Suit and Habitat Atmospheres”,  posted to “exrocketman” 2 January 2022.

#3.  G. W. Johnson,  “A Concept for an On-Orbit Propellant Depot”,  posted to “exrocketman” 1 February 2022.

Figures:

Figure 1 – Concept Sketches For the Vehicle Assembly and Fueling Section

Figure 2 – Concept Sketches For the Power and Propulsion Section

Figure 3 – Concept Sketches For the Propellant Depot Section

Update 5-4-2025: 

Conversations with a friend led me to understand that what I have in mind for the vane-equipped tank may not be readily apparent to the reader.  Please see the sketch in Figure A below,  as you read the following more detailed descriptions.

There are just two sets of vanes inside the tank,  mounted on shafting that causes them to counter-rotate.  Their tips spin circumferentially,  but in opposite directions (which avoids applying gyroscopic forces to the depot station).  There is a perforated baffle between the two sets of vanes so that the two volumes of fluid which are affected by the vanes,  also rotate circumferentially,  independently in each section. 

Yet the baffle is perforated,  so that the radially-measured levels of the fluid,  flung out to the tank wall,  are equal in the two sections.  It is one shaft,  with a gland seal at one tank head,  and an internally-mounted  bearing at the other.  There is a gear box near the middle that makes the shafting turn in opposite directions in the two sections.  There are probably 4+ vanes in each section,  mounted to the shafts.  If you forgo “instant” response,  these vane and shaft assemblies can be fairly lightweight construction.

The propellant pickup is along one side of the tank,  not one or the other end head,  since the centrifugal forces will fling the propellant to the outer cylindrical wall,  forming a big hollow cylindrical "form" in each of the two sections,  as wetted to the local outer wall.  These propellants are moving in opposite directions circumferentially in the two sections,  induced to do so by the spinning vanes.  But that circumferential motion does not really affect the suction drains along the tank cylindrical wall! 

You spin the vanes to withdraw propellants,  but you need no spin to pump propellant into the tank.  I put the drive motor outside the propellant tank for its safety (remembering the in-tank stirring-fan device that caused the explosion on Apollo-13),  and for easy maintenance and repair.  Cryogenic gland seal technology already exists,  in rocket engine turbopumps.  The vane shaft motor and the propellant withdrawal line are on the end that attaches to the core structure of the orbital propellant depot space station.  All the power lines and fluid delivery piping is inside that core.

This is a heavier solution than ullage thrusters,  so this is definitely only for a propellant depot in orbit (where you do not want to disturb the orbit with ullage thrust),  not the vehicles it is supposed to supply with propellants on orbit. 

However,  per the not-to-scale concept sketch in Figure B below,  it might be "just the thing" for the "payload" propellant tanks of a dedicated tanker vehicle sent up to supply this depot station.  Those will be rather small compared to the rest of the upper stage delivery craft,  in turn small compared to its launch booster.  The sketch is not to scale,  in order to provide clarity about which tanks are vane-equipped,  and which are not.  Ultimately,  this tanker needs to be a fully-recoverable vehicle. 

Figure A – Concept Details for Cryogenic Vane-Ullage Propellant Tank

Figure B – Concept Sketch for Dedicated Tanker Vehicle 

How Tariffs Really Work?

My wife found a version of this on Facebook and told me about it.  I went searching on the internet,  and found this jpg file version,  which I could actually use.  It was so funny I cannot resist posting it! 

Note the Canadian maple leaf on the fan.  Considering all the crud Trump and his minions have done regarding Canada,  I am not surprised someone drew this cartoon.  Pretty soon that maple leaf could be any of the symbols for every country in the world!

But with a looming recession and high inflation,  it is definitely gallows humor!  Trump has done this in less than 90 days:  taking a decent economy and crashing it.  If you don’t believe that,  then explain to me why the values of your 401(k)’s have crashed!

Bad Data Leads to Bad Decisions

Robert F. Kennedy,  Jr.,  our Health and Human Services Secretary,  has stopped our government from recommending fluoridation of drinking water,  based on false theories that it might do harm. 

Fluoridating water at the concentrations we have historically used,  prevents a significant portion of tooth decay,  without any known harm.  You use just enough to be effective.  The data shows this to be true.    

The water fluoridation risk is really all about yellow or brown stains on your teeth with too much fluoridation,  versus enhanced rates of tooth decay with too little.  There are no other scientifically-known side effects except those stains!  

Kennedy is entitled to his own opinion,  but he is NOT ENTITLED to his own “facts”!   There really is such a thing as “absolute scientific fact”! 

Using too much of anything can do harm,  as also can using too little!  A case in point is life-sustaining oxygen itself:  too little causes death!  No one denies that!   But,  too much also causes harm,  up to and including death!  You really do need an adequate amount!  And the range of adequate values is known!

Earth’s air has volume 20.94% oxygen,  corresponding to about 0.21 atmosphere partial pressure,  out of 1.0 atmosphere total at sea level.  We do fine up to 40% oxygen in hospital oxygen masks,  but anything above that 0.21 atmosphere is an enhanced fire danger.  People do just fine very long-term from there all the way up to 8,000-9000 foot elevations,  where the oxygen partial pressure is about 0.15 atmosphere. 

Long-term,  that suggests that 0.155 to 0.21 atmosphere partial pressure of oxygen is quite safe.  Short-term,   both lower and higher values are known to be safe from flying experiences using vented pure oxygen masks.  Those range from about 0.14 to about 0.8 atmosphere partial pressure of oxygen.  Too little is too little,  and too much is too much.  So you stay in the range known to be adequate.

So also it is with fluoridation of water.  Kennedy cannot make good decisions based on bad information!  No one else can,  either.  He’s also wrong about vaccines,  and for the same reason:  false beliefs!

I vote with science,  which has proven to be self-correcting,  even when what was thought to be true has instead proven to be wrong.  Politicians who spout false narratives like Kennedy CANNOT claim that!!!

The Truth About AI is Finally Coming Out!

Found this image on LinkedIn.  It’s too good (and too true) not to post. 

It is my opinion that “they” are already starting to automate-away all the white collar jobs.  But “they” are doing it without paying any attention to the “garbage-in,  garbage-out” law that is inherent with any computers.  And with absolutely no regard to the evident fact that AI has no capacity for factuality or truth. 

“They” are the vast majority of the super-rich individuals and the giant companies they own.  Their only concern is more wealth and power,  at everybody else’s expense.  They own the politicians who enable them to oppress you,  by rigging the laws against you!  “They” are the oligopoly!

In point of fact,  it is also my opinion that the term “artificial intelligence” is an oxymoron!  There is no intelligence or understanding,  there is only stylistic imitation.  Even a real parrot is more intelligent and actually understands something.  AI does not!

If “they” can figure out how to build robot plumbers,  electricians,  carpenters,  truck drivers,  welders,  and such,  “they” will automate away all the blue collar jobs,  too! 

Between the white collar jobs and the blue collar jobs,  that’s the end of the American middle class!  Welcome back to abject economic slavery,  folks!  If “they” don’t just outright kill you instead!  Or deport you to some overseas prison that will kill you for them. 

This is NOT going to end well for the vast majority of the American people! 

Ballistic Coefficient Study for Earth Entry

It has been suggested that inflatable or extendible heat shields can be used to lower the entry ballistic coefficient,  and thereby lower entry heating,  perhaps to the point of not needing heat protection on a stage or other item returning from low Earth orbit. 

To that end,  I used my spreadsheet version of the old H. Julian Allen and A. J. Eggers 1950’s-vintage entry model,  at fixed entry speed and angle below horizontal,  with a constant entry interface altitude.  I kept the object mass and hypersonic drag coefficient constant,  and used a fixed nose radius to heat shield diameter ratio. 

All I varied was the diameter (and nose radius right with it).  This produced a set of ballistic coefficients β = M/(C_D*A) that decreased dramatically from a near-Apollo value of 300 kg/m²,  down to very low values at very large diameters.  See Figure 1 below for the scope investigated and inputs used (all figures are located at end of this article).

The trajectory model uses a simple scale-height type exponential model of density with altitude.  It presumes a constant angle below horizontal in a 2-D Cartesian modeling set up.  It presumes the drag coefficient (and thus the ballistic coefficient) is constant with speed.  It corresponds to a certain velocity-altitude trend that is doubly exponential.  This is only approximate,  but it really is in the ballpark!  End-of-hypersonics for a blunt object is usually local Mach 3,  which for Earth,  is just about 1 km/s,  but I arbitrarily took this down to 0.7 km/s (about Mach 2.1),  which is well into the range where ribbon chutes can be deployed.

The results I obtained for each of the four ballistic coefficient cases are given in Figures 2 through 5 below.  I expected to see the end of hypersonics altitudes increase,  and the peak stagnation heating rates decrease,  as the ballistic coefficients reduced,  and they did.  I also expected to see peak deceleration gees increase as ballistic coefficients decreased,  but that is not what I got:  peak gees stayed just about the same for all 4 cases.

I then ran stagnation surface temperatures at those peak heating rates,  for a low emissivity and a high-emissivity case.  I did the analysis in US Customary after converting the heating rates,  then converted the temperatures back to metric.  These show a strong decrease as ballistic coefficients get very low,  but are still problematic for anything but high-temperature steels and exotic alloys!   They are reported in Figure 6 below.

I also ran the average pressure exerted upon the heat shield at that observed constant 6.3 gee peak deceleration.  This is nothing but mass times gees times the acceleration of gravity,  then divided by the heat shield blockage area.  These are not as problematic as the stagnation point temperatures,  by far.  They are also reported in Figure 6.

Whether the inflatable or extendible heat shield concepts are survivable,  I leave to others. 

Figure 1 – Inputs Used for Entry Ballistic Coefficient Study

Figure 2 – Entry Trajectory Results for the Highest Ballistic Coefficient

Figure 3 – Entry Trajectory Results for a Lower Ballistic Coefficient

Figure 4 – Entry Trajectory Results for the Next-to-Lowest Ballistic Coefficient

Figure 5 – Entry Trajectory Results for the Lowest Ballistic Coefficient

Update 4-12-2025:  Oops,  found an error converting to degrees C in my data.  Revised Figure 6 replaces the original.  

Figure 6 – Temperature and Pressure Results for the Ballistic Coefficient Study

Update 4-12-2025:

I went ahead and estimated the attached-flow heating rates as stagnation divided by 3,  and the wake zone heating rates as stagnation divided by 10.  This is only an educated guess,  but it is rough ballpark correct. 

From these I computed surface temperatures that equilibriate the convective heating with thermal re-radiation to surroundings at 300 K Earth temperatures.  There is no ablation,  no transpiration cooling,  and no conduction into an interior heat sink.  These temperatures are shown in Figure 7.  Bear in mind that they are very approximate! 

Figure 7 – Temperature Trends Around the Entering Structure

The pictures I’ve seen of inflatable and extendible heat shield concepts seem to fall in the range of 2 to 3 for shield/capsule diameter ratio.  2.5 diameter ratio is about an area ratio near 6.  Factor 6 below typical capsule ballistic coefficients (near 300 kg/m²) would be about 50 kg/m².  Bigger diameter ratio may be too fragile to serve,  since I have not seen any concept images with ratios any bigger than about 3.

At a rather low ballistic coefficient of about 50 kg/m²,  assuming a dark and emissive surface,  we are looking at surface temperatures near 1100 C at stagnation,  near 790 C for attached-flow regions near the rim of the shield,  and near 500 C for all the surfaces immersed on the wake zone behind the heat shield.  If the surfaces are not highly-emissive,  those temperatures will be significantly higher yet!  That is what the plot indicates.

The table just below gives some typical “max service temperatures” for a variety of possible materials of construction.  It would seem that there are no flexible materials one could use to construct inflatable or extendible heat shields for Earth entry from low orbit,  which would not be damaged or destroyed by only one use. 

Carbon cloth might work,  but would suffer both serious oxidation damage,  and heat-induced embrittlement,  preventing any re-use.  It might actually suffer burn-through holes,  if too thin or too-lightweight a weave.

TV Commercial Content Is Out of Control!

As of Wednesday 9 April 2025,  I just timed the commercial content of a local 5:00 PM news broadcast as just about 10.5 minutes out of a 30 minute slot.  And I just timed the commercial content of a national broadcast news program as 10 minutes out of a 30 minute slot starting at 5:30 PM.  That corresponds to 36.7% commercial local,  and 33.3% commercial nationally. 

In both cases,  the majority of the commercial content was in the second half of the 30 minute time slot,  which really means during that second half of the news program,  there was actually more commercial time than there was news time!

These stations are supposedly licensed by the FCC to broadcast “in the public interest”.  Commercials in a news program are not in the public interest,  they clearly are in the profit interest of the advertisers.  It is only the news content that is actually in the public interest!  That is obvious even to the casual observer,  no matter how the lawyers might spin it!

In the 1950’s and 1960’s,  a typical hour-long prime-time program had 51 or 52 minutes of content,  and 8 or 9 minutes of commercials.  That corresponds to 13-15% commercials.  (Most programs were only a half-hour long back then,  but at about that same percentage commercials.)  You can time the DVD’s of those old programs for yourself! 

In the 1980’s,  this had changed to around 42 to 44 minutes of program,  and 16-18 minutes of commercials in an hour time slot in prime time.  That is 27-30% commercials,  about double the commercial percentage of 2+ decades earlier! 

Now,  4 decades since the 80’s,  it is even higher at 33-37%,  right there in prime time news broadcasts!  Outside prime time,  it appears to be even higher commercial content!  When flipping channels,  it often seems like there’s more commercials than content.

As a case in point,  on Thursday 4-10-2025,  I scrolled through all 36 channels that I can pick up with a rabbit-ears antenna,  between 2:10 and 2:15 PM.  Two of those are shopping channels (all commercials),  and one is a weather update (no commercials).  Those 3 don’t count.  The rest all show content with commercials.  As I scrolled through,  I counted 13 out of that 33 as showing commercials,  not content.  That’s an empirical estimate of 39.4% commercials in non-prime time!

So,  how does so much commercial time actually qualify as “broadcasting in the public interest”? 

Is there no law or regulation limiting this commercial content?  If not,  there should be! 

And I suspect there once upon a time there was at least a regulation,  which was quietly done away with,  long ago.  It was eliminated simply so that the advertisers could make more money!  Probably at the behest of the politicians those advertisers bought.