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I checked the links.  They all work.  Both links to the user manual lead to the same updated document.  That update is a dated paragraph added to the spin rate discussion near the end.  It refers to the recent NASA data.

I know Terraformer posted a link to the NASA document reporting their 2020-vintage gee-acclimatization studies,  because I found it and scanned the document.  But I have so far been unable to find that link again,  to take a closer look. 

GW

If one does a baton spin design,  you put your workstations and your gym gear in the modules at the ends of the stick,  where gee is near 1 by the design of the vehicle.  You put your sleeping quarters near the center where gee is near zero,  because you get no benefit resisting gravity while sleeping prone (prone is first cousin to zero gee,  according to the experiments).   Put your other recreational and support stations in the intermediate modules where you have intermediate gee.  That would be for a 6-module stick in a one or two-stick straight baton design.

You end up spending a full work shift and part of an off-duty shift at 1 gee,  working,  or working out.  The rest of the waking hours are spent at partial gee (near 0.5),  so you average 0.75 to 0.80 gee for your waking hours.  Sleeping at low-to-no-gee doesn't hurt,  so it doesn't count against that average.

Why is this so difficult for so many to understand?

GW

For any given level of spin gravity,  there is a fixed spin radius matching that gee,  at some rpm.  It's usually quite large,  leading to "battlestar galactica" designs if you approach it with classical rifle-bullet spin mode.  This would be appropriate if you needed to transport many hundreds to several thousand people at a time.  But until you actually do have that need,  nobody is going to want to pay for building such a giant ship. 

Using a centrifuge wheel (or multiple wheels) inside an otherwise smaller ship allows you to reduce the size and mass of the ship,  at the "price" of a very odd shape that can never penetrate an atmosphere.  Wheel thickness has to exceed a min dimension on the order of 2-3 meters,  in order for the spaces inside the wheel not to feel too claustrophobic.  But if you do an even number of wheels,  rotating in opposite directions,  you can avoid all the gyroscopic force effects that make ship pointing difficult.  This might be appropriate for transporting a few hundred to several hundred at a time. 

There is an intermediate between the rifle bullet spin and internal centrifuge wheel approaches just described:  "frisbee"-type spin.  If your ship is shaped like a frisbee instead of a long cylinder,  you can do rifle-bullet whole-ship spin ,  but with a reduced contained volume,  and consequently less mass.  It would still be appropriate to housing a few hundred people at a time.

Both of those approaches (and the intermediate) would be appropriate for transporting large amounts of settlers,  once you have a real colony planted:  multiple hundreds at a time.  But there is no need for that many people at a time during the exploration and experimental base phases, on Mars or anywhere else.   Those crews are just smaller:  a handful,  to at most a few dozen.

Baton spin allows you to build a much smaller-mass ship capable of carrying only a few people at a time,  with only one large dimension in order to provide the right-sized spin radius.  This is most likely a string of modules docked together in a long "stick",  that performs as a rigid object,  able to resist the bending forces that occur during spin up and spin down.  This approach produces designs that you can afford to build which carry the right-size smaller crews appropriate to the exploration and experimental base phases.  And if you need more space for a slightly-larger crew,  make your long baton stick out of two (or more) sticks of these docked modules mounted side-by-side.  There is also the option of a "cross",  generalized as 3 or more arms extending radially (but equally spaced around),  from a common spin center.

All of these are spin gravity designs that could be built.  Each is appropriate to a greatly-different carried-population size range.  You just pick the appropriate approach for the size of populations that you need to transport. Uniquely,  the baton spin approach also offers the fastest and cheapest way to build a spinning space station in LEO,  where the min partial-gee level can be determined experimentally,  and where max tolerable spin rate can also be determined experimentally. 

Don't confuse rigid baton spin with the long-proposed cable-connected spin concepts.  We already know how to spin up rigid objects.  The cable-connected approach presents vast unaddressed development difficulties during the spin up and spin down transients,  precisely because the cables cannot resist bending moments.  You cannot push on a string!  Of the two,  rigid baton spin thus presents far less needed development effort,  in order to become a reliable approach.

GW

Launch and booster recovery went well.  No vent fire this time after catch.  Contact with ship lost just before end of ascent burn.  One after another of the vacuum engines dropped out,  along with the 3 sea level engines,  right up to lost contact showing 1 vacuum engine still burning,  but speed and altitude indications not changing.  I noticed the methane-remaining indication looked low compared to the oxygen.

Loss of ship not confirmed as I type this,  but it really looks like it was lost,  and the SpaceX commentators said so. 

Update moments later:  loss of ship confirmed. 

GW

Salt contamination does stop the growth of a lot of grasses, shrubs, and trees,  as well as most crops.  Copious rainfall does wash it clean,  at the risk of contaminating groundwater further down.  That is usually not too serious.  Dilution effect accounts for that.

You don't have to be a believer or a disbeliever in anthropogenic climate change to recognize that a very serious change is going on,  in a direction of warming that also makes storms more severe,  and even strengthens cold snaps.  Doesn't matter what causes it,  the real question is what can we do about it?

When I was young in high school,  the average Arctic sea ice pack thickness was around 20-30 feet,  too much for a sub to surface through it,  they had to look for a lead where it was thin (5 feet or under).  Atmospheric CO2 was 304 ppm,  per the measurements made in Hawaii that make up the Keeling curve. 

Today,  subs can surface anywhere they want (and the pressure hulls are not a lot stronger),  because the ice pack is only about 5 feet thick.  In summer,  the Arctic Ocean is ice free on the Siberian side.  According to the Keeling curve data,  atmospheric CO2 is now above 400 ppm,  a 33% increase over about 60 years.  There have not been that many more volcanoes erupting now than there were back then,  but there has been a large increase in smokestack and tailpipe emissions that include copious CO2.

Disbelievers will say there is no connection,  believers will say there is and that the Keeling data prove it.  I dunno for sure,  but I do know that a bell jar full of CO2 gets hotter out in the sun than a bell jar of air,  so the infrared absorption effect of CO2 is quite real.

Believe what you want.  Data is less likely to lie to you,  though.

GW

Kbd512 is right.  And Eucalyptus trees really do explode in forest fires,  ask the Australians.

While there are folks worried about salt damage to the ecology,  I notice in the news videos that the firefighters are using some seawater.  Salt damage is preferable to total incineration,  let's get some perspective here!

The sea water is being dropped from the Canadair 415 amphibious water-bomber aircraft,  scooped out of the Pacific just offshore from the fires,  because time is of the essence in firefighting.  The other water bombers are converted jetliners,  which cannot do that,  they have to be loaded at an airport on land.  Takes longer.

GW

Earth entry gee exposures vary with speed at entry interface.  From LEO,  it is about 3-4 gees peak.  Astronauts exposed to that are affected by microgravity diseases,  up to about a year's exposure,  but that works for them.  Most rocket vehicle burns are that or less,  by design.  But,  coming back from the moon at a snit under escape it was 11 gee peak.  The astronauts who were exposed to that were fully Earth-fit,  since the total mission time on Apollo moon missions was only 2 weeks. We have experience with that. 

We have no experience whatsoever to asses the health effects of long-term exposures to Mars gravity (0.382 gee) or lunar gravity (0.165 gee).  So we do not know how weakened by this they will be,  other than it is bounded by 0-gee weightless exposures,  and our entire evolutionary history at 1 gee here on Earth.  That would suggest 3-4 gees is OK,  because it is OK for the weightless exposures long-term. 

BUT (and this is a huge BUT !!!) we have zero experience to suggest our weightless-exposed astronauts could withstand anything higher than 3-4 gee,  because NO ONE ever came back from LEO after long-term weightlessness at anything higher than 3-4 gee!

Could a person exposed to weightlessness (or reduced gravity) long term,  survive direct free entries at Earth coming back from the moon or Mars?  WE DO NOT KNOW,  THERE IS SIMPLY NO APPLICABLE EXPERIENCE!  The moon is likely near 11 gees again,  like Apollo,  from Mars is likely higher still,  above 12 gee.

Getting onto Mars is not so much the problem,  direct entries there fall in the 1-4 gee range with most proposed designs,  higher as you try to fly faster.  It is the necessary rocket braking after coming out of hypersonics at very low altitude,  in larger vehicles,  that is the risk.  That's around 4 gees if you come out of hypersonics at about 4-5 km altitude,  but gets very rapidly larger as you come out lower still!

The real bugaboo is gees coming back to Earth from the moon or Mars,  after extended stays out there.  If you don't stop in LEO before attempting atmospheric entry,  you could kill your crew/passengers/whatever.

GW

Before Nixon killed Apollo in the midst of the landings (we had already built hardware to support through Apollo-22),  NASA's formal plans called for a manned Mars mission during the 1983 opposition.  This was to be flown weightless,  and without solar particle radiation shielding.  Knowing what we know today,  that crew would likely have died on the way. 

After Nixon's order killed Apollo AND ALL MANNED FLIGHT OUTSIDE LEO,  NASA cancelled its Mars mission plans,  which had by then slipped to the 1989 opposition.  They also killed the NERVA nuclear engine program,  on the rationale that "if we aren't going to go,  who needs the engine?"  (They had already killed the nuclear pulse propulsion project they got from USAF,  in favor of NERVA.)

There were no space stations up to this point,  other than Almaz.  Our MOL never flew a manned mission,  before it was totally shut down.  It was not until Skylab in 1973 (and the Salyut stations),  that we began to experiment with exercise and drugs to counter the previously-expected muscle atrophy and bone density loss. 

That knowledge has expanded across the decades of ISS.  We now know there are many unanticipated effects of 0-gee,  that some are irreversible after about a year,  and we have no countermeasures for most of them.  The single-minded determination to find countermeasures to the ill effects of long-term weightlessness has proven to be a dead end. 

The awkward single-mindedness shows in that we NEVER built any spinning stations to explore the effects of low but non-zero gee.  There should already have been several years worth of experience with that,  which is what it takes to uncover the real truth,  based on our experiences with 0-gee. 

There is now no longer the time to get that research done "right",  because in the next very few years,  some outfit is going to send a crew there anyway.  Probably in weightless flight,  and with inadequate radiation shielding,  and based upon error-ridden remote sensing as to where to land,  and with in-situ resource utilization gear that probably will not work right.  The decision will be made not on facts and evidence,  but on geopolitical crap.

It does seem to me like rather high odds that those outfits (whoever they turn out to be) will get crews (plural) killed,  learning what not to do,  which is the hard way to do that. And that is why I said what I said about "finding out the hard way".

GW

There are a lot of different things that impact what an appropriate exploration vessel might be.  Some of these will drive the design very hard.  Overall driving factors considered here are reusability,  spin gravity,  radiation protection,  meteoroid protection,  and “exploration” as opposed to “settlement”. 

That last implies smaller crews,  and I am entirely unsure that 38 is a “small crew for exploration”!  I think it might be significantly less.  A little excess capacity is needed for future growth,  so that the design has a long service life,  but way too much excess capacity is simply not affordable.  No one will buy such a thing until numbers of people that large are actually really needing to travel across space.  That simply does NOT happen in exploration! 

Exploration designs for crew transports can be used during the experimental base phase as well.  But settlement designs could initially transport dozens-to-hundreds,  and some years later hundreds-to-thousands,  after the settlement grows a lot bigger. 

I think 38 falls in the “dozens-to-hundreds” class,  and is therefore an early settlement-type design,  NOT an exploration/experimental base design.  Those are more likely a “single-handful-to-at-most-a-couple-of-dozen”.

Whether you pick 3 or 4 rpm as the max tolerable spin rate for spin gravity,  it does not matter very much.  Both produce huge spin radii,  when you force them to provide near 1 full gee of spin gravity.  Less gee is immoral and unethical,  precisely because we have experience and results only at 1 and 0 gee,  NOTHING in between, and we already know 0-gee is a very serious risk past just a bit over only a year’s exposure.  At 4 rpm and 1 gee,  it is 56 m radius.  At 3 rpm and 1 gee,  it is about 100 m.

Crew size drives the habitable volume,  yes.  But that has to be tempered with the need to be able to reconfigure some of that volume to meet changing needs as time goes by.  The volume-per-person figure for months-to-years in space does NOT look like the volume inside an airliner,  which is 12-14 hours at most.  Sleeping quarters volume can be that small,  but each person needs a lot more space during waking hours to go do things.  You need space in which to congregate,  and space in which to be alone. 

The real volume-per-person allowance looks more like Skylab and ISS,  at something like 300-500 cubic meters per person,  as a minimum figure.  For voyages of multiple years,  something closing upon 1000 cubic meters per person may actually be more realistic. 

So,  what is the right crew size for an exploration mission?  Well,  it varies!  I was looking at 3 crews of 3,  plus a commander,  for a total of 10 (I’m unsure entirely where the 38 figure came from).  Under some circumstances,  you have 3 crews for each of 3 8-hour shifts around the clock,  when that sort of thing is necessary.  Otherwise,  for surface exploration purposes,  I was looking at (at least) 3 landers,  each intended for a crew of 3,  but with seats up to 6. 

You only send 1 lander down at a time,  and only for a short stay camping-out in the lander:  days-to-a-couple of weeks.  That way you have at least 2 landers on-orbit with you at all times.  Even if 1 on-orbit lander fails,  you still have 1 left with which to mount a surface rescue attempt,  should the lander on the surface also fail.  No other exploration choice offers that capability,  only on-orbit basing!  I consider it immoral and unethical not to provide such capability,  if it can be done.

So,  crew of 10,  and at least 500 cubic meters per person for years in space,  is a habitable volume of at least 5000 cubic meters.  If that were a sphere,  it would still only be about 10.6 m inside diameter.   At 1000 cubic meters per person,  this is still only be about 6.2 m inside diameter!  Neither is anywhere remotely close to a disk or wheel of 56-100 m spin radius dimension!  That makes baton spin your ONLY feasible option for a small exploration crew,  right there!

Just for the sake of argument,  let us assume we can dock together a set of cylindrical modules,  each around 5 m diameter and 20 m long,  with about 400 cubic meters available inside as habitable volume.  If I use a stick of 6 of these end-to-end,  that is about 120 m long,  for a 60 m radius,  so we can use just under 4 rpm and get 1 gee near the ends in baton spin.  The summed volume is around 2400 cubic meters,  which at 500 per person,  says a crew of 4.8 could live for some years in there.  That’s not enough!  I needed 10 crew,  5000 cubic meters.

Second attempt:  go to fatter,  longer modules,  and use more of them.  Try 8 m dia by 30 m long,  and call it 900 cubic meters inside.  We would need at least 6 of them.  The stick of 6 is 180 m long,  for a spin radius of 90 m in baton spin.  At 1 gee near the ends,  we only need to spin at about 3.1 or 3.2  rpm!  There,  that would work,  and provide plenty of reconfigurable volume for a crew of 10. 

Work stations would be in the two end modules at highest spin gravity gee.  Recreation and food prep would be in the two intermediate modules at around half a gee.  Sleeping would be in the two center modules,  fairly near zero gee.  Prone sleeping in gravity is a close cousin to weightlessness anyway,  medically speaking.  Excluding the sleep cycle,  the two waking shifts average about 0.75 gee,  with one full shift at a full 1 gee.  That should be adequately therapeutic against microgravity diseases,  as best we know anything about it.

Put the engines on one end,  and the electricity-making equipment on the other,  so it still balances out pretty near the center as center of gravity.  The propellant tanks mount clustered around the periphery alongside the habitation modules,  to serve as radiation shadow shields,  augmenting the construction of the habitation modules themselves as radiation shielding.  Those modules would have about half-to-a-full-meter thickness of layers of fabric,  woven from artificial fibers (low molecular weight). 

That fabric wrapping serves as both thermal insulation and as the solar particle radiation shield,  and it will even reduce cosmic rays a little.  And if you intersperse some metal foil layers at intervals in your layers of fabric,  the same structure can serve yet a third purpose:  meteoroid shield.   This would be true whether the modules were inflatables or hard-shell.   The thickness helps contain the secondary showers from cosmic ray particles striking the metal foils.

Even at a crew of 38,  you are looking at a habitable volume in the neighborhood of 19,000 cubic meters.  If spherical,  the radius would be only about 16.3 m.  This is still a long way from the fixed spin radius requirement in the 56-99 m range.  But,  if you consider 2 counter-rotating disks each 2 m thick,  their radii would be near 77 m,  which is definitely in the ballpark for looking at that approach.  If the disks were each 3 m thick,  their radii would be 63 m.  If 4 m thick,  the radii become 55 m.  And that last choice would be just about right,  for a ship design with two counter-rotating centrifuge disks inside it.

In contrast,  look at two centrifuge disks for the 5000 cubic meters and a crew of 10 that is closer to a real exploration design.  If each disk is 2 m thick,  disk radius is near only 40 m.  That is just too small.  If we go to only 1 centrifuge disk 2m thick,  that radius grows to a feasible 56 m,  but we incur all sorts of dynamic coupling of gyroscopic effects into our vehicle,  while the individual spaces are still only 2 m wide (just over a man-height).  That would be fairly claustrophobic!  The centrifuge disk design is just not a feasible or practical design approach at that smaller crew size!

See how crew size interplays so very strongly with the more-or-less fixed min spin radius for a 1-gee centrifuge?  This interplay very strongly limits what you can do with your space transport design!  You are simply NOT free to just arbitrarily choose a design approach!

GW

Thanks Kbd512.  I just fixed that fault. 

GW

This one was posted on-line for the forums before I put it up on "exrocketman".  The two differ only in some minor wordsmithing here and there. 

GW

I sent them the how-to to put the hex back into the Avcoat tiles they want to bond onto the capsule substrate.  Initially I thought they were casting tiles to near net shape,  but it turned out they cast big blocks of Avcoat,  and then "machined" the various tiles out of those blocks. 

You could still put the hex back in,  either way,  using a plastics industry extrusion press.  Cut hex to fit the mold of the big blocks (there has to be one).  Extrude the Avcoat through all the cells in that chunk of hex all at once,  which precludes any voids,  and eliminates all the variation in hand-gunning expertise,  plus all the hand-gunning labor.  Then line the box mold with some Avcoat,  and drop the loaded hex core into it.  Anything you cut from that cured block will have hex reinforcement in it. 

The problem is who has Avcoat and who does not.  I suspect Lockheed-Martin and Boeing have it,  but nobody in "new space" is allowed to use it.  Lawyers make a lot of money making sure these things happen that way. 

Avcoat is an epoxy novolac resin loaded with microballoons to lower its density in a controllable manner.  You can adjust the ablation rate somewhat by varying the finished density.  This also varies finished heat shield weight:  lower density is lower weight but higher ablation rate (it's a tradeoff you must make for the mission).  But Avcoat ablative as defined during Apollo always without exception was hand-gunned into the hex cells of a fiberglass hex honeycomb previously bonded to the capsule substrate.  That produced a monolithic hex-reinforced heat shield integrally bonded to the capsule.  But on Orion,  there are almost 400,000 such cells to fill.

There is nothing wrong with wanting to do this as pre-made tiles bonded separately to the capsule substrate.  The integrity of the bonds and the integrity of the between-tile gap fillers is not in question on Artemis.  But,  they cast the big blocks of Avcoat without any fiberglass hex reinforcement,  and then expected it to perform the same,  without any prior flight test experience to show that it would work. 

It was no skin off Lockheed's nose when it did not work,  they got paid anyway,  as was (and still is) typical for "old space".  It was the upper echelons of NASA management that made that mistake,  now compounded by building both Artemis-1 and Artemis-2 in that very same way,  BEFORE flying Artemis-1 to verify it would work (which it did not).  This mistake was further compounded by adding the skip re-entry.  The original pre-Artemis Orion flight test used the Apollo hand-gunned approach identical to Apollo,  and did not fly a skip re-entry.  Too many variables from test to test.  That's a lesson they either forgot or never learned,  over time and personnel changes.

GW