Reasoning about the Manned Space Program
I try to present facts and logic and solutions rather than just opinions.
|Please send any reasoned disagreements to me.
If your facts and logic are convincing, I'll change my mind !
Our space-program priorities should be:
- Reduce cost-to-Earth-orbit by a factor of 100 or so. Everything else depends on this.
- Find a place where we could build a self-sustaining colony.
- Develop a new propulsion technology for use in space. Carrying chemical rocket fuel around
imposes huge penalties on every mission. In fact, we really need faster-than-light (FTL) travel
if we're going to go anywhere useful, but who knows if we'll ever get that ?
Halt NASA's Manned Space Program
until we accomplish these things.
Arguments in Favor section
Factors That Don't Matter section
Levels of exploration:
- Observation (telescopes).
- "Space" (out of atmosphere; 100 km altitude).
X-15 did this in 1963; commercial space companies have done this in 2011/2012.
- Earth orbit.
Requires about 50x as much energy as getting to "space / out of atmosphere".
- Unmanned vehicles (Sputnik, Mariner, Pioneer, Voyager, Mars rovers, etc).
- Manned exploration (NASA's Mercury, Gemini, Apollo, Skylab, Shuttle, ISS; Russian Soyuz, Mir).
- Research station (scientists and explorers).
- Colony (includes families, various occupations).
- Self-sustaining colony.
Programs and dependencies:
As far as I can tell, nothing much has changed in the "Foundation" area in the last 40 years:
no new propulsion or fuels or materials to change the basics of space exploration.
Maybe we should work on something like a
, or a
, or a
As far as I can tell, everything we've learned about realistic destinations has
been fairly bad: we haven't found a good destination to establish a colony.
Arguments in Favor
The stated justifications for the Manned Space Program are:
- We need to discover the wonderful riches out there in space.
But we've explored "near" space (Earth orbit and the Moon) pretty
well, and there isn't much of interest there. Hostile
territory, few resources (but availability of water/oxygen/metals on Moon and Mars is unclear;
Homesteading the planets),
no atmosphere, little gravity, dangerous radiation, etc. Why keep going there again
and again ? If we had discovered a decent atmosphere and
protection from radiation, the situation would be different; we'd have a
reason to keep going back. But we haven't. Space is a desert !
Keep using robot craft to look for a reasonable environment, but don't
pour men and huge resources into it unless something worthwhile is found.
"Medium" space (the other planets) holds the prospect of better resources, but daunting distances,
and harsher conditions on-planet (higher pressures, toxic atmospheres, less solar power, etc).
Unmanned missions to other planets make sense;
lots we don't know about them, and the benefits could be big.
And I'll bet we could find volunteers for a one-way (suicide)
manned mission to Mars, if we had the political stomach for it.
But what we know about Mars suggests it also is very like a desert;
not much useful there [3/2007: that's changed a bit, with reports of lots of water-ice on Mars].
Little atmosphere, less gravity (38% as much as Earth), less solar energy (40% as much as Earth gets), few resources (unclear),
no protection from solar radiation (no magnetosphere), etc.
And the distances are a problem.
"Far" space (outside the solar system) is out of reach,
unless we come up with faster-than-light travel.
- We can make great new things in space (ball bearings, crystals, vaccines, etc).
They've been saying this for 40 years, SkyLab and ISS were supposed to demonstrate this, and it hasn't panned out.
Paying $10k to put a pound of stuff in Earth orbit ($25k to the Moon)
makes most things economically infeasible. No private company has looked at
space research or manufacturing and said "wow, looks good, let's invest in that". NASA should stop
burning fuel and money doing visually impressive stunts, and put all efforts
into getting the cost to orbit down to $10/pound (maybe via a
space elevator ?). Then start
up the manned program again.
From Lawrence Krauss's "To the Moon, Newt!":
What would we manufacture on the moon that we could not do on Earth for a fraction of the cost?
It is true that there may be significant terrestrially-rare isotopes such as helium-3 in
the lunar soil, and some have argued that this would be useful for fusion power here on Earth.
But since we don't yet know how to produce fusion power on Earth, it seems a little premature
to rush out on a trillion-dollar adventure to gather up potential fuel.
Perhaps we could put mirrors on the moon to beam sunlight to Earth for power. But given that
currently 10,000 times the total energy used by humanity on a daily basis falls on the Earth from the sun,
it is not clear that we need to go to the moon to harness more of it.
... It took more than $100 billion to manufacture a white elephant in near-Earth orbit called the
International Space Station, a large, smelly metal can that to date has produced no science,
no manufacturing, and tourism that only billionaires could afford. ...
- We need to learn the effects of space on the human body.
We need a space program to find out the effects of
a space program on the human body ? Doesn't make sense.
Especially when we are far from finding a useful place to send humans to.
- We get all kinds of great spinoffs from the space program.
There have been some neat little
but we probably could have developed them a lot more cheaply if we'd just
decided to develop them.
We got even more great spinoffs from World War II:
RADAR, jet engines, computers, atomic energy, etc.
By the same logic, maybe we should have another world war to get some more spinoffs ?
In fact, military weapon development in general is a great creator of spinoffs;
it always pushes for the best possible materials, energies, and technologies.
If it's spinoffs we want, put the money into the military ?
Many of the claimed NASA spinoffs did not come from the space program.
Some people claim transistors (invented by Bell Labs, unrelated to space),
integrated circuits (military and private industry pushed them, as well as NASA),
satellites (military and telecommunications industry),
computers, Teflon (invented by Dupont in 1938), GPS (came from military space program ?),
DSP (came from military ?), and other things that
did not come from the space program.
Many of the "spinoffs" advocates deliberately blur the line between the "unmanned" and "manned"
parts of the space program. We certainly didn't need men in space to
get weather satellites or GPS or solar panels, for example.
Most of the "spinoffs" claims are VERY heavy on 1950's-era stuff; not much of any importance from ISS or Shuttle.
Could we have developed those spin-offs a lot more cheaply if we didn't spend a lot
of money burning fuel to lift metal into space ? Refurbishing the Shuttle before each
launch and launching it costs $300M to $500M each time; what part of that cost is "R&D" ?
For 120 flights, that's $36 to $60 Billion right there. Probably could have had a lot of
R&D for that money.
FAS's "NASA Technological Spinoff Fables"
- We need to have frontiers and be explorers.
We know very little about the oceans, the mind, how to live
sustainably and peacefully on Earth, how to communicate with intelligent animals,
how to conquer poverty and malnutrition and disease,
lots of things. There are plenty of "frontiers" to work on. We know less
about many of them than we do about "near" space.
From article by Charles Krauthammer in 2/17/2003 issue of "The Weekly Standard":
Saying we should address problems on Earth before going to space is
"a perennial excuse for going nowhere, for dreaming nothing".
And he says the "romance" of going to space "is reason enough" for a manned
program for bases on the Moon and Mars.
But there is plenty of "romance" to be had here on Earth.
Does "romance" have to involve burning lots of fuel and going a long distance
and planting the flag somewhere ? That's a NASCAR-type attitude: loud noises and
lots of beer.
The answer to the "we can't afford to turn inward" slur:
We can explore "outward" and push out frontiers and advance the human race without sending humans into space.
There are many frontiers.
And I challenge the notion that humans are necessarily explorers.
Sure, there have been some famous episodes of exploration in history,
such as the opening of the New World (N and S America). But I would
say most of history has not been characterized by rampant exploration.
In fact, if you wanted to pick one activity most characteristic of human
life throughout history, it probably would be agriculture or war,
not exploration. Few people are explorers, either physically or mentally.
Early humans migrated because of pressures from climate or resources or competition.
Later explorers were motivated mainly by religion or nationalism, or seeking money or fame.
Few were motivated by just curiosity.
Many people bring up Columbus' discovery of the New World as an analogy to space exploration.
We'll deal with that in the Analogies section of this page.
From interview of Graham Hawks in 11/2011 issue of Wired magazine:
Q: Does it bother you that we spend so much on space exploration when our oceans remain mostly uncharted ?
A: By my calculations, in the unclaimed part of this planet, beneath the ocean, at all depths,
there are seven moon's worth of material - I'm talking about physical minerals, food, space - to fuel humanity.
And it's on the order of maybe 10,000-to-1 times less expensive to get there than to the moon.
Everyone has got their head screwed on backward if they don't go to the oceans instead of space.
- We need to spread off the earth in case we blow it up or it gets
wiped out by an asteroid.
Yes, it would be nice to have a second planet. But looking
for one can be done with unmanned probes, and there's no
feasible place near enough for a manned mission any time soon.
We'd make more progress toward this goal by financing research into
suspended animation, deep-space ramjets, space-sails, space elevators, etc rather than in
blowing the money on sending manned rockets to nearby rocks again and again.
And all of the "needing" or "wanting" in the world won't make a feasible planet suddenly appear.
We've scoped out the most likely places within reach (Moon, Mars, Venus) and they don't look good.
- We get "national prestige" by having a space program.
I'd rather we got "national prestige" from good government (balanced budget, small national debt, justice),
good quality of life (healthcare, education, fighting poverty and hunger),
responsible environmental practices, peace. Blasting men into space
is way down the list.
- We need to stop the Chinese from getting a monopoly on space.
Hmmm, just like the USA got a monopoly on the Moon by being the only country to land there ?
Is that why USA "owns" all of the wonderful resources of the Moon today ?
- We need to inspire innovation by having a space program. (Neil deGrasse Tyson)
How about inspiring innovation by funding R&D into other areas that have better prospects
of paying off ? Clean energy, education, infrastructure, health, sanitation.
By the way, I was a computer programmer, so I'm no
anti-science Luddite. But the Manned Space Program just
doesn't make sense. Except as a government-run jobs program.
Also by the way, I wrote much of this before the 2nd space shuttle
blew up. And even if the shuttle didn't cost $500 million
per launch and explode once every 65 flights, it still
should be stopped: it has no rational purpose.
People like to use analogies to justify the Manned Space Program, so let's
examine a few.
A typical gambit: What if Columbus had said "oh, crossing the ocean looks too hard, let's not bother" ?
But here's a Columbus analogy that matches the space situation better:
Suppose Columbus and his band of merry men sailed the ocean blue in 1492 and found the New World.
And found it was like Antarctica is today: 98% covered with ice a mile thick,
with average summer temperature of maybe 20F and average winter temperature of maybe -20F.
Do you think Cristoforo would have said:
Okay, guys, let's not get discouraged. Off-hand, I don't see any of the
cities of gold or Fountains of Youth we expected, but I'm still sure they must be here somewhere.
We just need to hold onto the dream, step up to the challenge, extend the limits of the possible,
plan for success, keep thinking positively. After all, we're an adventurous, exploring species; we
need to push the frontiers. The New World is our destiny ! Let's go back and tell the Queen she should give
me a medal and lots of money, and send lots more ships over here.
No, more likely he'd have said:
Well, crap. Look at this place. It's a wasteland !
What do we do now ? Sure, we could establish a tiny colony, and the guys in it could search
for gold or something, but I'm not optimistic. We'd have to supply them with every bit
of their food, liquor, firewood, clothing, tools from Europe. And if anything serious went wrong,
if they got scurvy, or the food spoiled, or bears attacked, or a blizzard buried the firewood,
or one of the re-supply ships sank, they'd all die. They'd starve, or freeze, or starve and then freeze.
The heck with this place. Back to Europe !
And he'd be right. If you get to a new place and it turns out to be pretty worthless, you
don't ramp up a huge effort to invest a lot more there.
And here's a Moon-landing analogy that matches the Columbus/NewWorld situation better:
Suppose Neil Armstrong had stepped down onto the Moon, not
flubbed his one line,
- Some atmosphere, maybe not breathable, but at least not toxic/fatal. Say 5% oxygen, the rest nitrogen and carbon dioxide.
- Temperatures cold, maybe average 30F, but at least not insanely, fatally cold.
- A bit of magnetosphere, to give partial protection from solar radiation.
- A little stuff growing, maybe fungi and lichens and algae, maybe even a little grass.
If Neil had found those conditions, we'd have a colony on the Moon today.
No doubt about it.
But instead, he found:
- Zero atmosphere.
- Coldest temperatures, and widest extremes, of any body we've seen yet.
- No magnetosphere.
- Nothing growing and no prospect of ever growing anything there.
This explains why the analogy of space exploration to Columbus' expeditions doesn't work.
Columbus found something good; Neil didn't.
The Moon looks like a great place to live, right ?
Planning to establish manned bases on the Moon or Mars would be like
planning to establish a permanent manned outpost on the peak of Mount Everest.
All three outposts would be exciting to the "dreamers", right ? A challenge,
pushing back the frontiers, an avenue to do some science, good visuals, etc.
Of course, in all three places, we'd have to haul every bit of oxygen, food and energy needed
up a long, expensive supply route.
In all three places, the hostile environment
would be trying to kill all humans, all the time. Cold, dryness, lack of oxygen, cosmic radiation, etc.
All three places would offer a miserable daily experience, huddling inside a dome or two,
living dormitory-style, every bit of space and air and energy and food at a premium,
Similar to the research stations in Antarctica (except air is not a problem there,
and supplies come via large ships).
In all three places (Moon, Mars, peak of Everest), we have a fair idea of the situation: we've looked for
important resources, and come up empty. So the amount of new science that could
be done is limited. For example, any scientific investigation of biology there
would be limited to spores and fungi and bacteria and such. Little or no chance of growing
anything, finding any more complicated life, etc.
Establishing manned bases on the Moon or Mars would be much harder than establishing our research bases in Antarctica.
The residents in Antarctica didn't have to bring their own atmosphere, gravity and radiation-shielding with them.
They're at the end of a supply line a couple of thousand miles long, not hundreds of thousands of miles or
tens of millions of miles long. And that supply line is at the same altitude the whole way (sea level),
so it doesn't have to spend huge amounts of energy going up and down gravity-wells. And the supply vessels also
don't have to carry their own atmosphere, gravity and radiation-shielding with them.
We still haven't established a self-sustaining "colony" (one that grew its own food and made its own fuel, for example) in Antarctica.
Maybe we should do that before trying one in space.
[But someone pointed out that Antarctica has no sunlight in winter.
Maybe a test-colony near top of Mt Everest would be a better test.]
From "After Apollo" by Martin Elvis 4/2012:
Imagine that the United States had ignored the territories acquired in the Louisiana Purchase.
At first, this was a hostile territory and much of it was considered a desert.
Ignoring the American West might have left the Native Americans better off, but the United States
would be radically reduced. Other European nations were then actively exploring the territory,
as other nations are today exploring space. In the hostile territory of space there is, fortunately,
no indigenous population to abuse, and we already know that the resources are there.
Yes, but: "the resources" of space are far, far away, through uniquely hostile territory.
And we are still (physically) the same humans that we were in the 1800's; we need gravity, air, protection from radiation.
We've scoped out space quite a bit, and the physics and economics of it are appalling.
And no, other nations are taking baby-steps in space, not really "actively exploring" it.
They've learned from the USA's explorations, and what they've learned is: no good reason to
mount some major space-station or colonizing activity.
Mars looks like a great place to live, right ?
How about Titan ?
Maybe Ganymede will be better ?
Venus is lovely this time of year.
From article by Charles Krauthammer in 2/17/2003 issue of "The Weekly Standard":
The space station and shuttle are "an enormous risk for very little payoff",
and "the entire shuttle/station idea was a wrong turn" and "it does not serve as
a waystation and landing base on the way to the Moon and Mars"
and "No one even pretends that it is doing serious science".
More about the Shuttle:
A Rocket To Nowhere
About a base on the moon:
article by Gregg Easterbrook
Lawrence Krauss's "To the Moon, Newt!"
From James Surowiecki in The New Yorker 1/26/2004:
... there is no economic case for space exploration. If the goal is to increase employment
or spur technological innovation, then the dollars invested in NASA would be better spent elsewhere ...
... Many of the innovations we credit to the space program - such as
Teflon and Velcro - were actually invented outside it.
Others originated in space research, but the return the government
got on its R&D investment was fairly slim. To
invent somethig like the CAT scan, to use one of Bush's examples of
NASA innovations, it would be a lot cheaper and wiser simply
to invest in medical research, rather than in moon shots. ...
When John F. Kennedy announced his moon program, in 1961, the
budget deficit was about 3 percent of the total budget. ...
This year, the budget deficit is about 17 percent of the
budget - when you exclude Social Security, 36 percent. ...
you have to wonder where we're going to get the money.
Bush's plan [to go to Mars] sidesteps the budget question by proposing that all
the spending be backloaded. ... The President gets the credit for the big, bold idea,
and his successors get the bill. ...
From John Derbyshire on Space on National Review Online:
... There is no longer much pretense that shuttle flights in particular, or manned space flight in general,
has any practical value. You will still occasionally hear people repeating the old NASA lines about the joys
of microgravity manufacturing and insights into osteoporesis, but if you repeat these tales to a materials scientist
or a physiologist, you will get peals of laughter in return. To seek a cure for osteoporesis by spending $500 million
to put seven persons and 2000 tons of equipment into earth orbit ...
... There is nothing - nothing, no thing, not one darned cotton-picking thing you can
name - of either military, or commercial, or scientific, or national importance to be done in space,
that could not be done twenty times better and at one thousandth the cost, by machines rather than human beings. ...
From "Columbia's Last Flight" by William Langewiesche 11/2003:
... this mission was a yawn - a low-priority "science" flight forced onto NASA by Congress and postponed
for two years because of a more pressing schedule of construction deliveries to the International Space Station.
The truth is, it had finally been launched as much to clear the books as to add to human knowledge, and it
had gone nowhere except into low Earth orbit, around the globe every ninety minutes for sixteen days,
carrying the first Israeli astronaut, and performing a string of experiments, many of which, like the
shuttle program itself, seemed to suffer from something of a make-work character - the examination of dust
in the Middle East (by the Israeli, of course); the ever-popular ozone study; experiments designed by schoolchildren
in six countries to observe the effect of weightlessness on spiders, silkworms, and other creatures;
an exercise in "astroculture" involving the extraction of essential oils from rose and rice flowers,
which was said to hold promise for new perfumes; and so forth. No doubt some good science was done too - particularly
pertaining to space flight itself - though none of it was so urgent that it could not have been performed
later, under better circumstances, in the under-booked International Space Station. The astronauts aboard
the shuttle were smart and accomplished people, and they were deeply committed to human space flight and
exploration. They were also team players, by intense selection, and nothing if not wise to the game.
From orbit one of them had radioed, "The science we're doing here is great, and it's fantastic. It's leading-edge."
Others had dutifully reported that the planet seems beautiful, fragile, and borderless when seen from such altitudes,
and they had expressed their hopes in English and Hebrew for world peace. It was Miracle Whip on Wonder Bread,
standard NASA fare. On the ground so little attention was being paid that even the RADARs that could have been
directed upward to track the Columbia's re-entry into the atmosphere - from Vandenberg Air Force Base,
or White Sands Missile Range - were sleeping. As a result, no RADAR record of the breakup exists - only of the metal
rain that drifted down over East Texas, and eventually came into the view of air-traffic control.
Paraphrased from interview of Lawrence Krauss on Skeptics' Guide to the Universe 12/2011, episode number 334:
- There is no reason to "mourn" the end of the Shuttle program.
It was a $200 billion boondoggle, useless. End of manned space program is no loss; more worrisome
is that the unmanned program is dying too. Most of manned space program for last 30 years has been a waste.
ISS was opposed by every major scientific organization; has no scientific value.
- Repairing the Hubble space telescope was one of the few "scientific" contributions of the Shuttle program.
But for the cost of a few Shuttle missions, we could have built a complete new telescope and launched it.
- The postulated industrial/manufacturing uses of the ISS or a Moon base are nonsense; costs are far too high.
- For the cost of a single manned round-trip to Mars, we could send 1000 or 10000 rovers to Mars.
And robots are getting better and better.
- Private companies exploring beyond Earth orbit isn't going to work; it's just too expensive, takes too long,
and there's no business purpose for it.
- In a manned mission, 99% of the cost is expended just to get the humans there and back.
Only 1% is left over for actually doing anything at the destination.
- Chris Kraft (spelling ?) estimates the cost of a manned round-trip to Mars is about
10x the cost of a one-way manned trip to Mars PLUS robotic one-way trips to
keep resupplying them for the rest of their lives. The round-trip gets better if you can manufacture fuel on Mars.
But the additional radiation of a round-trip might be lethal. Lots of unknowns.
From Paul Lutus on reddit 2/2012:
> Do you miss the space shuttle?
No. In spite of the fact that I designed parts of it, I think it was a disaster.
It should have been retired -- it cost far too much and was unsafe.
From "After Apollo" by Martin Elvis 4/2012:
... Today it costs US$10,000 to US$20,000 per kilogram, just to get to low Earth orbit (LEO).
It is a rare industry that can make a profit with cargo rates this high.
This price has barely changed since Apollo, in constant dollars. ...
From Lawrence Krauss 10/2012:
Why the space station? ... no one talks about why we keep the stupid thing up there.
More than $100 billion has been invested to produce a smelly tin can that periodically
threatens to break down, and in which almost no significant scientific discoveries have been made.
Why are we still wedded to this project, other than the claim that it fosters international
science cooperation? For that misty goal, the space station pales in comparison to the Large Hadron Collider,
which cost one-tenth as much, involves far more countries, and actually does real science.
Many of the advocates of manned space exploration and colonization seem caught up
in a dream
, in defiance of reality. They've probably read too much Science Fiction
(which I love, but it's not reality). They seem to feel that if they could just
get all of us to share the same dream, and dream it hard
will come true. But that's not the way life works most of the time.
We know enough about the reality of what's in space, and the "numbers"
of space travel (money and time and distance and mass and radiation), to know that
this dream is physically impossible (until some amazing breakthroughs are made in propulsion,
and maybe also terraforming, and medicine).
Many people have been seduced by "Star Trek" or other TV shows. They think traveling or living in space will
be clean and comfortable and gee-whiz and interesting. But I think it will be more like living
in a WWII-era diesel submarine: extremely limited quarters, smelly, dangerous, little exercise, limited resources, boring most of
the time, and you're dead if anything serious goes wrong.
From bluecoffee on reddit 1/2013:
Despite being a huge space nerd for many years, I've gradually come round to monkeys in deep space being a Really Stupid Idea
For the next few decades at least.
- First off, the wonderful, magical thing about the Earth is that - unlike the Moon or Mars or deep space in general - it has
a damn great magnetic field around it and a thick atmosphere. This serves two purposes: it deflects galactic cosmic rays (GCRs)
and it deflects solar flares and their associated solar proton events (SPEs).
- So problem #1 with leaving the Earth's magnetosphere is that you're exposed to a constant barrage of GCRs.
They stay at a pretty constant level, and that constant level is .3-.7Sv/year (Sv being the sievert,
the SI unit of effective dose) depending on where we are in the solar cycle. Now as far as chronic doses
like this go, each sievert you absorb corresponds to a (linearly increasing) ~5.5% chance of getting cancer.
What I'm saying is that if you stick a colony in deep space without shielding, everyone will get cancer
and die inside 20 years. Things are a little better on Mars, where the weak-but-present atmosphere
and having your backside shielded by the planet dissipates some of the dose, but it's still sitting
at .1-.3, which is still utterly lethal in 30-40 years. Even with shielding, you better hope your
colonists are doing all their work inside else it'll knock a fair chunk of them out anyway.
- Problem #2 is the aforementioned SPEs. These are occasional events, and vary hugely in magnitude, but a
medium-sized one can dump 2Sv in an hour. For the big ones, it's an order of magnitude higher. With an
acute dose of 2Sv, you don't have a 11% chance of getting cancer, you have a 100% chance of bleeding out
of every orifice by the end of the week. More, these things can arrive at Earth within 15 mins of leaving the Sun,
which means that in a space colony no-one could venture more than 15, 30, 60 minutes (depending on how far from the Sun you are)
from the nearest shelter. On a Moon or Mars colony, you can of course travel as much as you want during the night,
but if your rover breaks down 8 hours out you are In For It.
- Of course that's all without shielding. What about with shielding? Well, there are two kinds:
- Active shielding ! Active shielding systems propose to emulate the Earth's magnetosphere with damn great
superconducting magnets. Because SPEs and GCRs move at significant fractions of the speed of light though,
they need to be truly vast and ridiculously intense, leaving them out of the question for the near future.
Maybe, someday, we'll have the power supplies and materials to do this sh*t, but it ain't happening any time soon.
"But with another Apollo program, we'd solve it!" I hear you say. No, we wouldn't.
Things like "really f**king good superconductors" and "awesome energy supplies!" are things that'd be hella
valuable everywhere else on Earth, so if they were only a few billion dollars away we'd have them already.
- Passive shielding ! Passive shielding works on the principle of putting a lot of nuclei between you
and the radiation source. The obvious thing to use is stuff up the periodic table like lead, but unfortunately
when a relativistic particle runs into a huge nuclei, the huge nuclei absorbs the relativistic particle ... and spits
out a couple more. The latter bunch aren't as relativistic, but they'll still chew holes in your brain.
Heavy-nuclei shielding actually makes things worse. Instead, you have to use small nuclei - hydrogen ideally - which
work to gradually slow the particle down through many many collisions. This means the best passive shielding material
ever is stuff like polyethylene, but regolith will do too. Estimates vary on how much shielding you need, but they
all hang around "a couple of tonnes per square meter", and the more the better. Obviously this is easy enough to find
on planets and asteroids, but it pretty much rules out classic-SF space stations.
Something else I should mention: as bad as deep space radiation is, there are a couple of places in the solar system
where it's worse. The first place is close to the Sun. Your warning for SPEs drops, and the dosage goes through the roof.
Those solar arrays orbiting just above the heliosphere? Maybe we'll build them one day, but no human is going
to get to see them up close. Hell, silicon will have a hard enough time down there. The other bad places are
in Jovian orbit. While Jupiter does have a spectacular magnetic field, and it does indeed deflect GCRs and SPEs,
Jupiter unfortunately spews out its own barrage of radiation, and that fantastic magnetosphere then traps it all
and rains it down upon the moons.
(There's one exception - Callisto
- that's far enough in to be protected by the magnetosphere
but not so far as to get eviscerated by the radiation belts. It only gets ~40mSv/year, which while ten times
the Earth background, is kinda-safe-enough for it to be one of the few Non-Stupid places to live in the solar system.
Unfortunately it's also f**king miles from Earth. Similarly, some of the other outer-planet moons are decent targets.)
So, conclusions: traditional space stations are out. Traditional colony ships are out too, but they're daft
anyway. If you want to do Mars, Moon or asteroid colonies with regular ole' humans, the base is going to be
several meters underground and you better manage their time on the surface damned well. More, your workers will
likely refuse point-blank to go more than an hour from a shelter, what with the risk of sudden death and all.
Where does that leave us? With what we've always known, that humans are woefully ill-designed for space exploration.
The entire radiation thing aside, we're a kilo or so of (pretty wasteful) computational matrix stuck in 70kg of meat
that needs >10,000kg of life support in order to have any hope of functioning off of this planet.
When considering the mass budget, if you think them's good economics then you're plain crazy.
Fortunately, for every worthwhile thing space offers us as a species, there're some damn good alternatives.
Anyone who's a fan of space colonization has a few justifications in mind:
- Living space
The first five are good reasons. The last isn't and we're not going to do the others the indecency of considering it.
- Energy, minerals and living space are proposed as justifications because we look around us and see
they're in deathly short supply. Thing is, if you can build a colony on Mars to reduce population pressures,
you can build one in the 70% of the Earth still yet to be occupied. If you can build solar panels in space
to supply energy to Earth, you can build them in the deserts here. Sure, they won't be as efficient but
the transmission losses will be a damn sight smaller and you won't have to drag all the material up
there in the first place. Minerals? We're sitting on a twelve-thousand kilometer ball of rock for chrissake.
It's a bit quicker to dig a new hole than it is to re-orbit an asteroid, and again 70% of the Earth has
yet to have holes dug in it. Sometimes people will talk about how automated factories will make space solar
and asteroid mining economical. But if it were to make those things economical, then surely we could pave
the Sahara with photovoltaics for next-to-nothing.
- Knowledge. No question about it, we can't find this one on Earth. We want to learn about the solar system,
we have to go out there. Except, we don't. People say "oh a robot is great but if you want to do complex science
or engineering then you need a human on the ground" well yeah, right now you do. But 20 years from now?
Then I'd put even money on those people being wrong. It's a long way off sure and requires a lot of major leaps,
but those leaps are dwarfed by the revolutions that'd be needed to make human scientific expedition a more
cost-effective option. More, the research needed to make human-equivalent robotic exploration feasible - learning
algorithms, complex reactive behaviours, etc - has trillions of dollars behind it, enough to dwarf even the wildest
dreams of a second Apollo program.
- Security. When people talk about how delicate Earth is, they're not worried about every living
thing on Earth being wiped out, but about society being so disrupted by an asteroid strike/nukes/grb/whatever
that the warring remnants finish the job. So the value in an off-world base isn't so much in being off-world as
it is in it being self-sufficient and divorced from anything going on at home. But if we can build a
self-sufficient community off-world, we can certainly build one here. Except what about making sure it
doesn't get wiped out by the initial blast? Well, there're two options: first, your off-world city will
have to be meters underground anyway, so you may as well build it underground here. Secondly, may I draw
your attention to the exceptional energy-absorbing properties of liquid water. Nuclear blasts are good for
all of a few hundred meters in it, and if you're worried about asteroid-induced tsunamis then hell just build
one in the Atlantic and the other in the Pacific. Build your colony underwater and not only will it dodge
whatever rain of hellfire is consuming the rest of the world, but when things go t*ts up for the colony
(which is far more likely than the end of the world) you'll actually be able to reach out and help them.
Anyway, there's my argument. Don't send anyone to their death in the next few decades,
send ever-improving robots instead and get the rest without leaving the gravity well
. I'm aware this position
is in opposition to a lot of very smart people who know a lot more than I do, but I suspect many of them
are heavily invested in actualizing their dreams. You don't really go into the space industry for any other reason.
The romantic notion I mentioned? I dismissed it out of hand because it can't be rationally argued with,
not because it isn't a powerful justification.
Note that none of the above forbids a human-manned Moon or Mars base if you bury it deep enough,
it's just liable to end up in the same position as the ISS: cool, but a boondoggle. Anything worth doing
you do with specially-designed robots instead. As to full colonies - maybe humans (or our offspring) will
eventually be able to thrive off Earth, but it isn't going to happen until we've got flavour-of-the-week "singularity"
technologies like compact fusion reactors or super-advanced genetic engineering or mind uploading or strong AI.
When you pull those things into an argument, though, you may as well be debating about how leprechauns will
help us live on the Moon, so I'm choosing to ignore them. My personal (unfounded) opinion is that Mars is
unlikely to ever see a "baseline" human, and the asteroid belt almost certainly won't.
As an aside, if I had Elon Musk's money and arrogance, I'd probably still have similar ambitions.
'First man on Mars' is about as lasting a legacy as you could hope to have.
> What about Bigelow Aerospace ?
Bigelow is constructing habitats for low Earth orbit. While that's of course outside the atmosphere,
it's still shrouded in 90,000km of magnetosphere that serves to deflect the overwhelming majority
of charged particles. Even then though, ISS levels sit at .15Sv/year, which is about a ~1% rate of
cancer incidence per annum, cumulative. That's fine for six-month rotations, but colonies?
You gotta be kidding. Moreover, put those habitats outside the magnetosphere, and the inhabitants will cook in the first SPE to turn up.
A problem with using manned missions to explore new places: it's extremely difficult
to fully sterilize a manned capsule and prevent contamination of the destination.
The humans are carrying bacteria etc inside and outside their bodies.
Food and waste also carry contaminants.
Johan Volkert's "6 Reasons Space Travel Will Always Suck"
Factors That Don't Matter
Things that are not valid arguments for or against the Manned Space Program:
- Risk / danger.
It doesn't bother me at all that space travel is dangerous; the
astronauts knew that when they signed up. That's not a reason for or against the
manned space program.
It doesn't matter whether the Chinese or a private company or anyone else starts up
a manned space program. Let them waste their money. But I don't want my government
to waste my money on such a program. (An estimated $150 billion spent
on Shuttle and Space Station from 1971 to 2005; for what result ? Conservative estimates
of a Mars mission are in the same neighborhood, another $150 billion; for what result ?
Yes, these numbers are smaller than, say, the cost of the war in Iraq, but
that's not a justification for spending them.)
And if someone else makes it to the Moon, they won't "own" the Moon or space.
Does the USA "own" the Moon by virtue of having landed there first ?
Do the Russians "own" Earth orbit ?
(Among many other things; see
A few of the many "first" of the Russian Space Industry.)
Often the most profitable company in a sector is not the first, the one that
spent all the money to prove a technology and make all the mistakes,
but the second or third one into that market. If it turns out to be a viable market.
Countries such as Japan and China are ramping up space programs because of national
prestige issues, not because they've detected some amazing valuable resource in space
that NASA failed to find.
- Cost (which is different from cost/benefit).
Big, ambitious, leading-edge projects are costly; no way around it.
I'd support a manned space program if the likely benefits were equally huge.
But they're not; we've scoped out Earth orbit and Moon and Mars a fair amount,
and it looks like there's not much benefit in any of them. That's too bad; would
have been nice if we'd found some viable place. We should keep looking a bit more,
with unmanned missions.
- Low Cost (compared to other USA federal budget items).
It doesn't matter if NASA's budget is "only" 1% of the total budget, or 0.1% of the total, or if we're
wasting the equivalent of NASA's budget every month in Afghanistan, or whatever.
If there is no good reason to do manned missions to the Moon or Mars, don't do them.
That's separate from whether we should be at war in Afghanistan, etc.
Should we waste money on NASA's manned missions (or anything else) just because we waste even more money somewhere else ?
- Military implications, including past military involvement with the space program.
Any advanced technology or new terrain will be of interest to the military.
The only way to avoid this would be to stop all development of all kinds, in space
and medicine and materials and computing and all other technologies.
- We waste money on lots of things (such as military), so it's okay to waste some on the manned space program.
We have limited resources and many important things that need funding: healthcare, education, infrastructure (bridges, tunnels,
schools, water systems, sewer systems), renewable energy, new drugs, etc. We should direct resources (money, people, mindshare) to
the best uses of them.
- The money we'd free up by cancelling the manned space program isn't enough
to "fix every problem on Earth" or "eradicate poverty" or "eradicate hunger".
No one believes that taking the money from NASA (or the entire USA federal budget, for that matter)
would "end poverty", or "eradicate hunger". Or that we shouldn't do anything in space until
we've "fixed everything on Earth". Those are straw-man arguments created by manned spaceflight backers.
I say: we've scoped out space, found not much of use there, so there's no reason to continue manned flights.
Keep the unmanned program going. Put the money saved into something more promising, such as renewable energy tech,
infrastructure repair (bridges, schools, etc), fixing USA healthcare, etc.
We have lots of areas where money invested promises far greater benefits than NASA's manned flight program does.
The Onion's "NASA Continues Search For Planet Capable Of Supporting NASA"
What we need to find on a planet or moon, to support sustained manned presence:
- Gravity. Human bodies do not react well to sustained zero gravity; animals and plants affected too.
- Atmosphere. For protection from UV, protection from micro-meteorites, for breathing, for manufacturing.
- Magnetosphere. For protection from cosmic and solar radiation.
- Water. For human consumption, for growing food, for manufacturing.
- Oxygen. For human consumption.
- Raw materials to make fuel. Need energy for transportation, living, manufacturing.
- Platform to grow food. Soil, nitrogen, other elements ?
- Raw materials for manufacturing.
- Reasonable temperatures. We can compensate for extreme temperatures, but that
will increase costs of everything else.
Perhaps every one of these can be worked around, by bringing things from Earth or
by living on the planet/moon only for short periods of time, and by not growing food or
doing manufacturing. But transportation from
Earth is very expensive and very slow, and costs and distances preclude
Distance rules out anywhere but the moon, Venus, and Mars (for quite a while, at least).
Temperature seems to rule out Venus (average temp +900 F), maybe Mars (average surface temp -81 F),
and maybe the moon (range -387 F to +253 F). For comparison, Antarctica (where we have yet to establish a self-sustaining
colony) has mean annual temperature of interior of -70 F, coastal temperature monthly means of -18 F to +27 F.
Lunar day/night cycle of two weeks prohibits plant-growing using natural sunlight.
Heard on a podcast: plants are very sensitive to circadian cycles, which is one reason that certain plants
tend to grow in certain latitudes on Earth; even slightly different day-length such
as on Mars would be enough to reduce crop yields. Similar problem if trying to grow plants aboard
ship while traveling to Mars. Gravity change would affect plant growth too.
Mike Malaska's "Earth's toughest life could survive on Mars"
Gravity rules out the moon.
Atmosphere rules out the moon and Mars.
Magnetosphere rules out the moon and Mars (not sure about Venus).
Water and oxygen on moon, and oxygen on Mars, are still open issues.
Temperature and lack of water rules out Venus.
So nowhere reasonably close is looking feasible.
The Mars Society makes a case for going to
Mars, sending an unmanned vehicle first, manufacturing rocket fuel on Mars, sending
a refueled vehicle back to Earth to fetch men, then back to Mars. I don't believe
their cost numbers, I think they minimize the gravity and radiation effects of the
long manned voyages, there are a lot of moving parts (opportunities for failure) in their plan,
and I think they exaggerate the joys of living on the surface of Mars
(astronaut kicking back on the Moon).
Private companies and the "commercialization of space":
Private companies have made it to "space", but that achievement is
deceptive. They've made it (briefly) to sub-orbital
space (out of the atmosphere); it takes about 50 times
more energy to make it to stable Earth orbit. [5/2012: SpaceX has made it to the ISS.]
They did it by replicating old NASA
technology (X-15, rocket fuel); no radical new designs or new propulsion technology.
[But: Ad Astra is working on a plasma rocket (VASIMR) for use in space.
And Reaction Engines Limited is working on a hybrid engine (SABRE
could be used for surface-to-orbit.]
And they're all chasing mostly government money (contracts for launching
and servicing satellites, and servicing the ISS); no one has found a
compelling commercial/economic reason for going to space beyond Earth orbit,
or for manufacturing in Earth orbit.
They're certainly not planning space stations or colonies.
Too much is being made of the fact that private companies can do it for lower cost than NASA.
Partly, that's because NASA is a government agency, forced by Congress to spread facilities all over
the USA, bound by government contracting rules, given multiple goals and requirements, budget being yanked up or down
from year to year, projects being started and then killed halfway through. Partly, it's because
NASA was still flying a 1970's-designed Shuttle until 2011.
Just updating to the newest materials and computers and such brings costs down.
And learning from NASA's past successes and mistakes also brings costs down.
From interview of NDGT on CBC Mar 24 2012:
"[Commercial space companies] will have nothing to do with advancing the frontier, contrary to what many people describe."
From Jeffrey Marlow interview of James Logsdon
Wired: Private space companies are clearly changing the economics of launching payloads to orbit,
but the path is less clear when it comes to true exploration. Do you think private spaceflight
will play a key role in our exploration of the universe?
Logsdon: I think they will follow, not lead, and that's how most exploration has worked throughout history.
The government funds the pioneering expeditions, and they find gold or spices or fertile land or whatever,
and then commerce follows. There's not much profit motive in that first manned mission to Mars.
I'm not sure there's any profit motivation in sending humans to Mars, period.
Wired: Companies like SpaceX are all about lowering the cost of launch, and companies like Virgin Galactic
are interested in space tourism. Recently, the Planetary Resources company proposed a different
type of private involvement in space, and that is resource acquisition. What do you make of that approach?
Logsdon: There is no doubt that asteroids are resource rich bodies. There's plenty of doubt about
whether anybody can do anything about it. Planetary Resources says that's what they're after,
but it's a bit of a shell game in my opinion. If you listen to them closely, they say their only goal
is being able to extract valuable resources from asteroids, and that's what everybody hooks onto.
But then they say, that's decades away, and what we're really doing now is planning to launch,
hopefully with government sponsorship, little telescopes to find the asteroids.
At this first stage, it's very shrewd marketing of hardware to government, basically.
Wired: When do you think we will see humans on Mars?
Logsdon: Sometime between 2035-2050, or never.
From NPR's "Wait, Wait, Don't Tell Me" 5/4/2013:
What will the first postcard from a space tourist say ?
Haven't stopped throwing up for 3 days.
You were right: we should have just burned the money.
Near-Earth asteroid mining:
Doesn't sound feasible to me. The orbits of these asteroids are unpredictable, it would take plenty of
energy to rendezvous with and then divert one of them, most of them probably are carbonaceous or silicate, any water on them probably
would be sparse.
But the venture is fine with me as long as it doesn't use any taxpayer money.
Had this conversation on reddit
Trying to calculate how to capture an asteroid; need help
NASA's "NEO Earth Close Approaches"
shows a few asteroids come by Earth
with relative velocity of "only" 3 KM/second or so; average is more like 12 KM/second.
Diameter ranges from 4 to 1000 meters.
Density of water-ice is about 917 KG/meter³;
typical density of many kinds of rock is around 180 lb/cuft,
or about 2900 KG/meter³. Volume of a sphere is 4/3πr³. So:
a 4-meter-diameter ice asteroid masses about 31,000 KG;
a 4-meter-diameter rock asteroid masses about 97,000 KG;
a 1000-meter-diameter ice asteroid masses about 480,000,000,000 KG;
a 1000-meter-diameter rock asteroid masses about 1,500,000,000,000 KG.
Am I right so far ?
Then I get lost trying to calculate rockets and thrust. Shuttle solid-rocket booster (SRB) is 150 feet long and 12 feet in diameter,
weighs about 600,000 KG, provides up to 15 MN thrust, burns for about 2 minutes. I think 1 MN = adding 1 km/s to a 1000 KG object.
Maybe that's wrong, is it 1,000,000 KG object ? Is it "against 1 g", or does it still apply in free-fall ?
Anyway, question is: if somehow you could get an SRB up to the asteroid, could it change velocity of a 1000-meter
diameter asteroid by 1 km/second ? Then scale up and down from there; what size rocket to change velocity on smaller
asteroids ? What velocity change needed to "capture" (put into Earth orbit) an asteroid moving past at
12 km/sec relative velocity ?
MN = Mega Newton, which is a force.
The equation for change in velocity by a rocket is as follows:
Delta V = Isp * g * ln ( wet mass / dry mass)
Delta V is the change in Velocity.
Isp is how we measure a rockets efficiency.
g is earth surface gravity. (In fact, Isp = Exhaust velocity / g, which is the actual orgin of isp.)
The wet mass is mass of spacecraft plus fuel.
The dry mass is mass of spacecraft after the burn.
The SRB has an isp of 269 in vacuum, a fueled mass of 590,000 kg and dry mass of 86,000 kg.
dV = 269 * 9.81 * ln ( (590,000 + asteroid mass) / (86,000 + asteroid mass) = ~0.9 mm/s
for the 1000 m rocky asteroid. I didn't check your math.
Wikipedia has some good articles on the rocket equation (there are multiple), and even a great list of rocket propellants and their isp.
If you want real books I can also recommend further reading.
Also Dani is guaranteed to plug his book in progress, which covers a lot of that as well.
Okay, thanks for the info. I tried reading some of that Wikipedia stuff before posting, but got lost in it.
Sounds like it would take a million SRB's to change velocity of that 1000 m rocky asteroid by 1 KM/sec ?
Yeah, about a million and a half: each SRB has 503487kg of propellant. With an I_sp of 269,
you need a mass ratio of e^(1000/(9.81*296)) = 1.46ish to change velocity by 1 km/s, so each SRB can
"push" about 1008353 kg (excluding the 86183 kg mass of a spent SRB) of asteroid. In other words,
you'd need ~1488000 SRBs to move the asteroid.
To change the velocity of such a large object, you'd be better off looking at a propulsion system with a higher I_sp
like an ion drive
With an I_sp of 4000, "only" 2% of the asteroid's mass is needed for 1 km/s delta-v. Admittedly,
that's still thirty million tonnes of xenon, but it's more plausible than a million SRBs!
More interesting reading: The Keck Institute did an
Asteroid Retrieval Feasibility Study (pdf)
for a 7-metre-wide asteroid which might be informative! (for the version that isn't technical-jargon-filled, try
New Scientist's article about it
But an ion drive would generally have lower thrust than a chemical rocket, right ?
So you'd have to thrust (the big asteroid) for a thousand years, maybe with a thousand ion drives,
or something ? Not to mention solar panels or something to power the ion drives ?
That is correct. Ion drives present other challenges due to the required mass to keep them running.
Also, with a Isp about 15 times higher, you still need about 1/15 of the propellant calculated earlier!
That New Scientist article is light on details, but says maybe it would take 6 to 10 years to take
a 7-meter diameter asteroid that's passing Earth and put it into lunar orbit.
Of note would be the
It's basically an ion drive but it can accelerate a much wider variety of propellants.
That 2% of asteroid mass could therefore come from the asteroid itself.
Good explanation of the complexities of capturing an asteroid:
Phil Plait's "NASA May Be Towing An Asteroid to a Planet Near You"
Chris Gayomali's "Is the asteroid zipping past Earth this week really worth $195 billion?"
Search for Extra-Terrestrial Intelligence (SETI):
It seems unlikely that aliens would use signals limited to the speed of light (radio, lasers, etc)
to communicate across deep-space distances. Star systems are multiple light-years apart, minimum. Even a signal
from Earth to Mars would take 15 minutes one-way if the two planets were on opposite sides of the sun at the time.
What would colonies 50 light-years away have to say to each other if a one-way signal took 50 years to get there ?
And wouldn't such a signal be very narrowly focused, tight-beam, directional, to maximize signal reception ?
No, I'd guess that either aliens aren't communicating across deep space, or they're doing it some way we haven't invented yet.
Re: "humans have been broadcasting radio and television signals since the 1920's":
They're being broadcast from inside an electrically active atmosphere and a magnetosphere
(including radiation belts), and from inside the hail of radiation from the sun,
and broadcast omnidirectionally. So the residual power you might detect if you were on, say, Pluto,
would be TINY and the noise would be HUGE. Have to use scientific notation to show how tiny the signal strength would be,
and how tiny the signal-to-noise ratio would be.
And someone would have to be listening in the right direction and on the right frequency to gather even that tiny signal.
No chance of anyone much outside the solar system "hearing" us.
Multiple TV and radio stations broadcast on
the same frequency; they don't interfere with each other because they're hundreds of miles apart
and separated by the curvature of the Earth.
But to someone off-planet, the signals would interfere with each other.
As the Earth rotates and orbits, any strong directional signal emitted from the surface sweeps across
the heavens. So any faraway alien trying to detect that signal would have only a fleeting
chance to detect it. [Same would be true of a transmitter on an alien planet. Unless the
signal direction is constantly adjusted to point at the target, and that target is Earth,
receivers on Earth would have only a brief instant to try to detect it. Unless the signal was
incredibly powerful and not very directional.]
From "Is Anyone There ?" by Isaac Asimov
[On contacting extra-terrestrial intelligent life: Microwaves probably best way to do it.]
Right now (approx 1964), mankind on earth is producing power at the rate of 4 billion kilowatts.
Even if all of this were poured into a microwave beacon and sent out into space it would not suffice.
The beacon would spread and grow dilute, even though it were made as coherent as possible,
and by the time even the nearest intelligent beings had been reached, it would
have grown too feeble to detect. To produce beacons strong enough to detect would
require a civilization capable of wielding far more energy than we do.
The Straight Dope on this
If our energy output keeps growing at today's 3 to 4 percent a year, in another 3200 years,
we'll match the output of the sun, and could then announce our
own existence with beams that will stretch through the length and breadth
of our galaxy.
I accept the probability calculation that
Extra-Terrestrial Intelligent Life (ETIL) probably
exists, given so many planets per star, so many stars per galaxy, so many galaxies
in the universe, chance of life on
each planet, chance of life being intelligent, etc.
But, by a similar calculation (so much space between habitable planets, so much time to cross
that space even at the speed of light, finite lifetime of any civilization, chance
of compatible technologies, chance that FTL communication exists, etc),
the probability of us ever contacting
ETIL is almost zero. It's very unlikely that ETIL exists near enough,
in both space and time, for us to have any contact with it. Sorry.
At least the SETI effort has been cheap ($3-5 million per year ?) and privately-funded (since 1994). But don't expect anything from it.
Some people think we just need to get to Mars and start terraforming it, and all will be
- "Just getting to" Mars with any volume of people, equipment and supplies will
require a huge investment, with prospect of any benefit hundreds or thousands of years in the future.
- We don't know how to do terraforming; we've never done it. It's not as
easy as just sprinkling some seeds and bacteria. It probably will take decades or centuries of trial and error
and experimentation. It may require capturing and crashing asteroids, or some other major mass-transfer.
- It's totally unclear that bodies with gravity far less than Earth's gravity can be
terraformed. Any atmosphere you create will just leak off into space. That (and lack of magnetosphere) is why Mars (11% of mass of Earth,
38% of surface gravity of Earth) has
atmospheric pressure about 1/200th that of Earth, and why the Moon has zero atmosphere. Without a significant
atmosphere, temperatures will remain extreme. No atmosphere and bad temperatures = bad for plants, animals, and humans.
- How do you take a body with no magnetosphere and give it one ?
Earth's magnetosphere and atmosphere protect us from solar radiation.
No radiation protection means plants, animals, and humans will have to live
in bunkers or underground.
From Kevin Bonsor's "How Terraforming Mars Will Work"
"Terraforming Mars will be a huge undertaking, if it is ever done at all.
Initial stages of terraforming Mars could take several decades or centuries.
Terraforming the entire planet into an Earth-like habitat would have to be done
over several millennia. Some have even suggested that such a project would last thousands of millennia."
From "Life Everywhere" by David Darling 2001
"Understanding why some planets turn out Earth-like while others don't isn't just a question of pinning down one or two isolated
factors. The climate, the makeup of the atmosphere, the amount of heat coming from the central star,
the size of the planet, what's happening on and below the ground - all these are linked together.
The terrestrial life-support machine runs on interlocked cycles: the hydrological cycle, the carbon cycle and the
recycling of carbon dioxide which is part of it, the nitrogen cycle, the steady slip-sliding of the oceanic crust [plate tectonics].
Even clouds exert a regulatory effect. ..."
Wikipedia's "Colonization of Mars"
Wikipedia's "Terraforming of Mars"
NASA Science's "The Solar Wind at Mars"
Robert Lamb's "Is it possible to terraform Mars?"
Michael Chorost's "Our Guts May Hate Mars"
Resources for Science Fiction Writers' "Space Math"
Stephen R. Schmitt's "Relativistic Star Ship Calculator"
Was the moon landing a fake ?
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