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Quaoar:

To answer your question:  can we dock-together a conical vehicle 12 m in diameter?  Not so very much. 

To build such a thing in LEO,  the assembly astronauts are going to need to turn small bolts,  screws,  and nuts.  They will need to do wiring and small plumbing.  This is just not possible with the clumsy,  stiff gas balloon suits we currently use. 

Lighting and temperatures are also an issue.  Things in shadow get super cold,  things in sunlight get really hot.  Stuff fails to fit up due to extreme thermal expansion.  It's already been an issue with ISS EVA's. 

It's fairly easy to fix the lighting and temperatures thing with a very lightweight space frame around the work zone,  covered with aluminized-plastic sheet tarps.  Hang the work lights on the frame inside,  and use the reverberatory radiation oven effect to bring all workpieces to near room temperatures,  while at the same time providing nice,  bright lighting from all directions to eliminate shadows. 

You solve the clumsy space suit problem with a mechanical-counterpressure suit.  You just probably won't be working at the ciurrent 0.33 atm pure O2 pressure standard.  You'll be nearer 0.20 to 0.25 atm O2 pressure,  something that we already know can be done with simple elastic fabrics,  and probably with the oriented-stiffness fabrics being investigated at MIT.  We also already know it's quite adequate as a breathing pressure. 

Once you can do screwing,  plumbing,  and wiring in zero gee (inside a space that relieves the hot/cold/lighting issues),  then bolting up a 12 m diameter craft from components and panels becomes possible.  What ticks me off is that absolutely no one seems to be working on this critical capability. 

We need these capabilities anyway to properly explore on the surface of Mars (and other places).  Given that we need them anyway,  why would anyone spend multiple 100's of $billions on a giant launch rocket with a 12 m dia shroud,  just to avoid tens to hundreds of $millions for these capabilities?

That kind of penny-wise,  pound-foolish thinking is what ticks me off so.

GW

Hi RobertDyck:

I honestly don't know about moderators or heavy water stuff.  None of that was in the ancient report I read long ago.  I don't remember regenerative cooling system details.  Hard to say what you saw,  because the photo didn't come through in your post just above. 

Way back then,  the design target was a 6000 s Isp orbit-orbit engine.  The radiator for 2000-6000 sec Isp was supposed to be be a 4000 R (2000 K) device,  crudely.  At that time,  no such thing existed,  and I have yet to hear of one,  so their weight estimates from the late 60's would be bogus. 

If the GCNTR could be made to run on water instead of LH2,  there might be better regenerative cooling capability,  plus the water could be stored as ice.  That melt-off process would be a good use of the excess waste heat for operating above 2000 s Isp,  instead of the radiator.  Melt more than you need for the burn at hand,  then let the cold of space re-freeze it before the next burn. 

GW

If you put a thorium fuel plant "somewhere",  you will need lots of power for it.  Why not use a thorium reactor for heat and power,  but modified to breed U-233?  Use the U-233 directly in your "liquid uranium" fuel.  That way you can use water or hydrogen in your GCNTR,  and need not worry about He-3.

I dunno about ellipsoidal versus toroidal fission fireball geometries in a GCNTR.  The one they were aiming at in the late 1960's had a nearly-spherical fireball inside a spherically-symmetric flow field.  It was a liquid hydrogen propellant design,  with LH2 injection all around the spherical chamber,  angle-biased aft.  Accordingly,  there was an extreme temperature gradient from the cold wall to the edge of the fissioning fireball. 

What I remember reading was that up to about 2000-2500 sec Isp,  regenerative cooling was thought to be adequate,  and no waste heat rejection scheme was needed.  Above that level,  they were looking at a high-temperature radiator scheme,  something that was likely to be very large and heavy.  This had a limit,  too:  thermal radiation-induced propellant transparency to the extreme thermal radiation from the fissioning fireball.  This was believed to occur somewhere between 6000 and 10,000 sec Isp power levels.  But nobody really knew for sure back then. 

This device never got beyond benchtop concept demonstrations of a couple of the most critical individual technology items,  at academic-institution grant funding levels,  which are very low,  actually.  One outfit demonstrated successful controlled fission in a uranium gas.  Another outfit demonstrated 1000:1 flow ratio of the hydrogen vs uranium,  with some sort of plasma flow device,  in that spherical geometry. 

That's as far as it got.  Everything gas core nuclear died in 1973-ish,  same time as ready-to-test-fly solid-core NERVA died,  by presidential executive order killing Apollo and restricting men to LEO only.  NASA's thinking was "who needs the rockets if we're not going to go?"  The money got spent instead on shuttle,  then a series of X-planes that never flew,  then ISS.  And here we are.

GW

Some of the original GCNTR stuff I saw was in a report written by a Maxwell Hunter at United Aircraft,  ca. 1960.  I ran across it about 1970.  The concept then was solid U-233 feed as a metal rod fed through some sort of gland nut. 

This liquid feed idea is quite intriguing,  as it would solve a number of practical problems with ideas like those Hunter wrote about. 

Ultimately,  some sort of GCNTR that could use water directly as the working fluid would be a very practical type of propulsion,  able to "refuel" almost anywhere,  as long as the nuclear fuel held out.  Water as ice seems to be in a lot of places.  All that is really required is gravity-settling to get the solids out,  once the ice has been melted. 

Although a GCNTR sheds radioactive reaction products in its exhaust,  the amount contaminating a local atmosphere is actually quite small for any given launch,  even here on Earth.  For complete nuclear burn-up,  the flow ratio of uranium to hydrogen in the old UA designs was about 1/1000.  And at Isp's above 2000 s,  the total plume mass is actually fairly small compared to the thrust you get.  Even at Earth launch mass ratios,  1/1000 of the tonnage expelled is a pretty small number.  Coal plant exhaust radioactivity is actually the larger problem,  and by far (that's 1/3 of the "natural" background in the US). 

GW

It's my understanding that Ceres has no atmosphere,  and a very low surface gravity.  For there to be geysers,  there has to be liquid water inside there somewhere. 

Liquid water requires sufficient water vapor partial pressure (or its equivalent) over the liquid surface to be stable,  a number dependent on the temperature of the liquid.  That comes right out of the standard steam tables we've used for two centuries now.  At 0 C that's 0.0060 atm.  At 37 C that's 0.062 atm.  No way around that set of physics.  If the water vapor partial pressure is too low,  the liquid is unstable and evaporates or boils away.  A violent boil down in a hole with a path to space would produce a geyser.

Without an atmosphere,  the water vapor is the atmosphere over any liquid surface.  That,  or solid cover held in place by gravity.  The overburden weight (weight,  not mass!!!!) per unit of interface area is the pressure exerted upon the liquid by the solid overburden.  This could be ice or it could be dirt,  or a mixture of both.  Disturb the ice or dirt,  and the liquid or ice below it evaporates away.  We've already seen this on Mars where the rovers dig and hit buried ice.

If there's liquid water inside Ceres,  anything that produces cracking or any other disturbance to the overburden then opens up a path to space.  The water will boil violently away into vacuum until (1) it is gone,  or (2) ice and debris plug the path to space.  The observed geysers testify to (1) the presence of liquid water,  and (2) some sort of overburden disturbance that opens up a path to space. 

Assuming that ice and debris plug the path to space.  If the plug is not stable over geologic time,  it would open and close repeatedly,  and perhaps at irregular intervals.  There's a mechanism for repeated geyser eruptions. 

The disturbance that sets this off could be as simple as surface impacts of other bodies.  Another possibility is some kind of an "earthquake".  (Not much of a word choice here.)

The presence of liquid water demands a heat source to keep it from freezing over geologic time.  There not being a big planet nearby,  unsteady gravitational stress seems an unlikely source of the heat.  That leaves (1) radioactive decay,  (2) something electromagnetic perhaps from the sun,  or (3) something we are not yet aware of.  All three are intriguing possibilities. 

If it were radioactive decay,  that heat source would have been far stronger in the geologic past.  That poses some problems with why Ceres is what it is today.  But,  who knows?

I hope the probe can help sort all this out.  I doubt they had things like this in mind when they designed it.

GW

Hi Void:

"Bowl shaped rocks in Antarctica" -- if you say so.  But,  how did it get there?  Can't be by wind,  the pebbles would have blown around.  The bowl-shaped artifact is clearly a lot larger,  cavity notwithstanding.  If it's stone,  it's a lot heavier than any of the pebbles. 

GW

Back to site selection:  earlier in this thread there were several good candidates proposed.  Since then,  we have been discussing more the issue of living off the land. 

Here's a concept:  why not visit more than one site while there?

I think there might be two ways to do this,  and the choice probably depends upon achieving ISPP capability at tons per day output rates. 

(1) base from orbit,  use landing propellants brought from Earth sufficient to support a baseline mission to 2 or 3 sites,  and augment the mission scope to many sites with ISPP propellants,  in so far as the technology succeeds.

(2) base on the surface,  but leave your return vehicle and its propellant in orbit (the Apollo lunar orbit rendezvous lesson),  and make as much lander propellant with ISPP as you can to support suborbital trips to other sites;  yet as a safety thing,  bring down sufficient propellant from Earth to make that ascent to orbit even if the ISPP fails. 

I think betting lives on the ISPP alone for ascent is a single point failure mode that would be very unwise to risk.  Remember,  there is nothing as expensive as a dead crew.  That leaves out all the minimalist ideas as unsafe.

Option (1) requires that you assemble the larger expedition in LEO,  but also ensures more sites get explored.  Option (2) requires a much smaller assembly in LEO,  perhaps even an SLS or two would do it,  but only ensures that one site gets visited if ISPP doesn't work at high-rate production. 

You get what you pay for.

Here's another concept:  if you were to go with option (1) orbit basing,  you could explore multiple sites the first few months,  and then shift to surface basing at the best site the remaining months,  and create a base there.  It is the "best site" evaluation that creates the highest probability of creating a "successful base". 

That hybrid approach gets the greatest return,  but also costs the most.  Yet it probably would be the best bang-for-the-buck.  You cannot optimize bang-for-the-buck at small investment sizes,  that just doesn't work. 

Again,  you get exactly what you pay for. 

I guess my point is that site selection ties in integrally with mission architecture,  and with technologies available,  in ways that are not initially apparent.  The selection can very quickly constrain you into not being able to accomplish what you really want to do. 

I think what we really want to do is finish the exploration at multiple sites with real ground truth,  try out our live-off-the-land technologies at the best site,  and establish an operating base at that that site.  We leave the base operating on automatic when we return to Earth.  That's the target for any second missions or commercial ventures. 

"If you build it,  they will come".  If you don't,  it's chicken-and-egg paralysis forever. 

I see no point to an Apollo style flag-and-footprints stunt on Mars. 

GW

Hmmmm.  There are several small changes between the two photos that look like the effects of wind blowing dust around.  Maybe wind moving very small rocks.  Perhaps frost vs no frost.  One can map feature-to-feature between the two photos down to the smallest pebble size.  I think the occasional pebble "color" change (bright vs dark) is dust blown off a dark rock,  or maybe frost,  but I could be wrong.

The oddball one is that bowl-shaped object.  Quite startling.  That's too big to be a stone blown by the wind (most of the rest of the loose pebbles would have moved,  and they did not).  If it was blown there by the wind,  it's no rock,  it has to be very lightweight.  If it is a rock (or similar density),  something had to carry it there. 

Could it be a piece of some kind of debris off the rover itself?  Perhaps the equivalent of dried mud dropping off one of the wheel hubs?  Something like that would have a shape like that. 

GW

I'd hazard the guess that Decimator is partly right ("hi" by the way,  Decimator).  For physical commodities that have to be shipped,  transformed to other physical form,  then shipped,  the costs of space travel will push that business toward airless low-gravity bodies.

Intellectual property can be transferred best electronically/by radio.  I see no reason that there could not be trade in intellectual property between Mars and Earth.  Or any bodies with significant gravity and atmosphere. 

I rather think the novelty price of pieces of Mars here on Earth with be a transient that wears off and goes away,  and rather quickly,  once there are people on Mars permanently.  Until then,  there likely will be a market for rocks and dirt from Mars.  But that won't last. 

What we are talking about here is the temporary initial versus the long-term stable trade economy a colony must be based on.  Simple resource extraction ain't it,  either.  That didn't work very well here 300-500 years ago.  Those former colonies where the economic model was simply resource extraction are largely third-world countries today.  Those former colonies where a real two-way (or even three+ way) trade got started,  are largely prosperous nations today.

The "gotcha" was then (and still is now) that when you first go there,  you have no idea what commodities are going to be the basis of the trade economy.  That's because you don't know what's really there,  or what you can really do with it,  until you go,  stay a while,  and try lots of things out.  Simple (and as hard) as that.

It takes a while,  maybe a century,  to get all that settled.  At least it did here,  300-500 years ago.

GW

I'm no medical person.  But I do know from my days as a scuba diver that 1 atm partial pressure of oxygen induces convulsions in about half the people exposed to it,  and 2 atm partial pressure O2 is lethal to all exposed to it.  I'm simply guessing that it's a partial-pressure / osmosis thing across the membranes in the lung alveoli.  These data are for sea level atmospheric pressure,  and some very lethal experiences trying to breathe pure oxygen when underwater,  plus some really bad experiences with compressed air hard hat divers between about 170 to 300 feet down. No one has ever lived for more than a few minutes on compressed air more than 300 feet down.  Convulsions and death are fairly fast at those conditions.     

The article cited would seem to indicate that 0.9 to 0.95 atm partial pressure O2 is mostly OK.  Assuming the Sci Am-cited experiments took place near sea level,  that would be 0.95 atm O2 plus 0.05 atm CO2 added to 1.00 atm atmospheric pressure. 

I didn't notice where the experiments were run.  But if near 500 feet where the atm is 0.9644 atm in pressure,  that would be 0.9162 atm O2 and 0.0482 atm CO2.  If done in Denver a mile up,  atmospheric is 0.8321 atm,  and at 95-5 split,  the O2 would be 0.7905 atm and the CO2 would be 0.0416 atm.  So the partial pressures depend upon where you run the experiments,  as well as what the gas volume percentages are. 

So the 0.95 atm partial pressure of O2 being a max safe value makes a lot of sense as a rule-of-thumb.  Composition (like having the 5% CO2) no doubt complicates the picture.  Just to be safe,  I'd guess nearer 0.9 atm than 0.95.  And even then not for chronic long-term exposures. 

The NASA spacesuit standard is near 0.33 atm pure O2,  for a partial pressure of O2 of 0.33 atm.  You only really need around 20 to 25% of an atmosphere's worth of O2 to be quite healthy in a spacesuit.  So,  we're talking partial pressures between around 0.2 to 0.33 atm inside the suit.  That would be fine indeed for long EVA's,  etc.  I'm not so sure about exposures over a very long tern,  say weeks-to-months,  even years.  That's a completely different issue than immediate brain damage from too rich an O2 partial pressure.  I know next-to-nothing about chronic exposure effects. 

You medical types need to offset those gas composition data by the vapor pressure of water at body temperature,  if you want to check osmotic diffusion numbers inside the lungs.  That process works on the difference in effective partial pressures of each constituent you check.  That water vapor offset gets you a better estimate of the oxygen partial pressure inside the actual wet lung alveoli spaces.  That water vapor pressure is right at 0.062 atm.  So an astronaut inside a suit with 0.33 atm pure O2 would have something closer to 0.268 atm partial pressure oxygen and 0.062 atm partial pressure water vapor,  inside his lungs.  That reduced PP of O2 in the lung is what actually drives osmosis of O2 across the membranes into the blood. 

Fortunately,  most rigs have a really good CO2 absorber,  so that gas remains a far smaller trace in the breathing gas than the water.  But,  if you deliberately put CO2 in the breathing gas mix,  then you sharply reduce the rate at which it can leave the blood across the lung membranes. 

That's because the driving pressure in the blood is low,  acting against an increasing "backpressure" resisting its diffusion back out into the breathing gas.  Plus,  at too high a concentration,  it upsets the body chemistry and kills you. 

I have no numbers for that,  but 4% CO2 in the polluted air was the usual "deathpoint" rule-of-thumb in submarine rescue accidents.  Air in that scenario also has a lot less than 21% oxygen,  so it's medically far more complicated than I really understand. 

GW

The last point I was trying to make in post #19 just above was that the NASA space program has been over-bureaucratized into helplessness,  with all its major projects turned into political footballs.  The big projects become congressional mandates instead of things that make sense,  and control over them goes to congress,  not the agency.  SLS is just one example of this,  but it's a biggie. 

Here's a quote from an email I got from the NSS.  They oppose this latest power grab over NASA by congress.

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National Space Society Opposes HR 3625

(Washington DC - January 13, 2014) The Washington DC-based National Space Society (NSS) strongly opposes the passage of House of Representatives bill HR 3625.

This bill would (a) require NASA to obtain legislative permission to cancel four of its most expensive human spaceflight and science programs, and (b) allow contractors for these programs to have immediate access to hundreds of millions of dollars in funds which currently are held in reserve to pay the government's obligations in the event of such termination. The four covered programs are the Space Launch System, the Orion crew capsule, the James Webb Space Telescope (JWST), and the International Space Station.

Ordinarily, government agencies like NASA have the right to terminate a project if it no longer appears necessary or cost effective, provided it pays "termination liability costs" which are sometimes provided for in such contracts.  It is unusual to require an act of Congress in order to stop a program.  As a practical matter, getting Congress to pass such an act would be extremely difficult.

Consequently, if HR 3625 is enacted, even after the responsible agency determined that a project was no longer useful, contractors would continue to get millions of dollars for unnecessary and unwanted programs until such a time as Congress passed a bill specifically calling for the cancellation of the project and allocating the funds required for program termination.

"The ability to cancel a program for convenience is essential to allow the government to deal with changing circumstances," said NSS Executive Vice President Paul Werbos. "Requiring explicit Congressional approval to terminate a program for convenience represents a significant shift in power between the Executive and Legislative branches of government that should not be taken lightly."

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If passed,  this would further prove my point,  a minor thing.  Here's the major thing:

If passed,  you can kiss goodbye the government ever sending astronauts to Mars.  These idiots in congress cannot keep up the roads and bridges they funded as the interstate highway program in the 50's and 60's.  They cannot even carry out reliably their basic constitutionally-mandated duties. 

These idiots want to micromanage NASA?

GW

If NASA were serious about this,  she wouldn't be the only fundee,  and budgets would be higher.  After all these years,  that suit should be flying,  at least experimentally.  Does that tell you something about their intentions for men on Mars?  When you consider that the suits we have are too heavy and restrictive,  and too vulnerable to dirt-induced damage,  to be used on Mars. 

As far as I can tell,  the MIT MCP suit pretty much as it is will protect humans against vacuum death.  But the compression it can achieve is below the 1/3 atm standard they have used for the gas balloon suits.  It's adequate to protect,  but inadequate to use with existing cabin atmospheres without a long decompression to blow off blood nitrogen. 

GW