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:
  1. Reduce cost-to-Earth-orbit by a factor of 100 or so. Everything else depends on this.


  2. Find a place where we could build a self-sustaining colony.


  3. 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.



Overview section
Arguments in Favor section
Analogies section
Commentators section
Factors That Don't Matter section
Future section





Overview

Levels of exploration:
  1. Observation (telescopes).
  2. "Space" (out of atmosphere; 100 km altitude).
    X-15 did this in 1963; commercial space companies have done this in 2011/2012.
  3. Earth orbit.
    Requires about 50x as much energy as getting to "space / out of atmosphere".
  4. Unmanned vehicles (Sputnik, Mariner, Pioneer, Voyager, Mars rovers, etc).
  5. Manned exploration (NASA's Mercury, Gemini, Apollo, Skylab, Shuttle, ISS; Russian Soyuz, Mir).
  6. Research station (scientists and explorers).
  7. Colony (includes families, various occupations).
  8. 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 space fountain, or a space elevator, or a launch loop.

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:



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.












Analogies

People like to use analogies to justify the Manned Space Program, so let's examine a few.



Columbus:
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, and found:
  1. Some atmosphere, maybe not breathable, but at least not toxic/fatal. Say 5% oxygen, the rest nitrogen and carbon dioxide.
  2. Temperatures cold, maybe average 30F, but at least not insanely, fatally cold.
  3. A bit of magnetosphere, to give partial protection from solar radiation.
  4. 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:
  1. Zero atmosphere.
  2. Coldest temperatures, and widest extremes, of any body we've seen yet.
  3. No magnetosphere.
  4. 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 ?




Mount Everest:
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, exercise limited. 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.



Antarctica:
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.




Commentators



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:

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.







Dreaming:
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 enough, it 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. 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: The first five are good reasons. The last isn't and we're not going to do the others the indecency of considering it.

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:






Future



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:

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 short-term missions.

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. (But: 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) that 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 1/2013:
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 ?

Dear sweetie,
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 2/2013:
From me:
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 ?

From Lars0:
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.

http://en.wikipedia.org/wiki/Rocket_equation

http://en.wikipedia.org/wiki/Liquid_rocket_propellants

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. http://en.wikibooks.org/wiki/Space_Transport_and_Engineering_Methods

From me:
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 ?

From HydraulicDruid:
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).

From me:
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 ?

From Lars0:
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!

From me:
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.

From skpkzk2:
Of note would be the mass driver propulsion concept. 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?"

Dilbert1
Dilbert2



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 Amazon):
[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.

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.

From question_all_the_thi on reddit:
The calculations used to determine if you are able to receive a signal are called a link budget.

If you plug in the numbers, you'll find that to receive commercial transmissions from the earth at the distance of the nearest stars, you would need huge antennas, maybe something the size of the solar system.

Not to mention that the earth, at that distance, would be seen as very close to the sun, so any transmission from the earth would be swamped by the much stronger radio emissions from the sun.

The Straight Dope on this



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.

Maddie Stone's "Aliens Are Probably Everywhere, Just Not Anywhere Near Humans"
WaitButWhy's "The Fermi Paradox"



Terraforming:
Some people think we just need to get to Mars and start terraforming it, and all will be wonderful. But: 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 (on Amazon):
"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. ..."

From Crushnaut on reddit:
Getting oxygen and CO2 into a Martian atmosphere, in the grand scheme of things, isn't really difficult. They are already present on the planet. The problem is if the concentration of CO2 is too high it would be poisonous to animal life. If the oxygen levels are too high then you have a highly reactive atmosphere which would have a tendency to combust most combustibles (including animals). In order to get pressures that would be suitable for animal life with only CO2 and oxygen you run into one of these problems or both.

The trick is finding a filler gas. Earth's atmosphere is roughly 3/4 nitrogen. Finding a source of nitrogen for Mars might be the most difficult part in terraforming of Mars. Nitrogen isn't the only choice though, argon could be used too, or another inert gas. Nitrogen has the advantage in that it would be needed to support a robust ecology.

...

> If we didn't use filler air, we could
> just plant crops on the entire planet, correct?

It depends on the level of nitrates that are present in the Martian soil. That is not something we currently know. Without them it would be like trying to start a farm in pure sand. Even with nitrates, creating dirt/soil on mars might be difficult. Soil on Earth is an extremely complex ecosystem. Getting this ecosystem started could take a very long time and prove to be extremely difficult.

There is also reason to believe that higher CO2 levels would not be beneficial to plants and may actually slow down their growth.

This also negates the fact that a lot of our crops rely on animals to perform some sort of task for them, whether it be worms which aerate soil, bees which act as pollinators, large herbivores which distribute seeds, or bacteria which fix nitrogen.

With enough genetic modifications, perhaps we could overcome some of these difficulties, but it would be a difficult task.




Space Elevator
From internet_sage on reddit 2/2014:
It was a bullsh*t pipe dream a decade ago, and it's still a bullsh*t pipe dream.

It doesn't even matter if we have the materials to build one (we don't). It comes down to four major problems:

1) Having a counterweight/docking platform in GSO. This would need to handle the weight of the cable + elevator. (Ballpark. Lots of other forces to consider. It's not trivial.) The best suggestion I've ever seen is using an asteroid. As soon as someone goes and parks a couple of asteroids with enough mass to serve this function in GSO, you have my full and undivided attention. Until that happens, f*ck off. From an engineering and physics standpoint, this is a non-negotiable part of a space elevator.

2) Some sort of cable you could do this with. You need to secure 22,000 miles / 36,000 km of cable from damage, or you need it to be so huge that anything impacting it won't cause structural failure. Everything from planes to micro-meteorites need to be considered. Ever catch how the ISS is moved to avoid 2 cm pieces of space junk? You can't move the cable of a space elevator like that. Either it has to somehow be impervious to 5,000 mph pieces of junk and 400 mph planes, or it has to have some active defense that can destroy those things before they impact it. Again, I'll consider this slightly plausible when this has been adequately addressed.

3) Getting the cable into space. GSO is 22,000 mi / 36,000 km up in the air. You either need a cable this long (not likely, since even a tiny-diameter cable this long would be far larger than most rockets can carry) or you need an orbital cable-splicing station. Wake me up when someone puts an orbital cable-splicing station in GSO and starts splicing cables.

4) The pockets to do this. We can barely afford to keep the space station running. While there's an asteroid-mining corporation, they're nowhere near even planning their first mission. Maybe once they bring one back and make a trillion dollars they'll have the capital to invest in a risky project like this. Maybe. But any given government? No way. Any corporation? They're just barely figuring out how to make private rocket launches profitable. Any space elevator would be a multi-decade investment. Nobody is willing to bet billions or trillions on something this risky with that much of a delay before any profits are seen.
(Actually, the counterweight has to be somewhere well above GSO; even the center of mass of the cable-and-counterweight has to be slightly above GSO.)

space elevator



Wikipedia's "Mars"
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?"
Kevin Bonsor's "How Terraforming Mars Will Work"
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 ? cartoon



The Discovery Channel just announced plans for a new miniseries. It's hosting a race to land an unmanned spacecraft on the moon. So technically-savvy individuals can compete to see who can get their spacecraft to the moon first. It will be televised live. The show aims to prove that people who are bright and determined and work hard can accomplish anything we already accomplished 50 years ago.
-- Jimmy Kimmel Live, 4/2014





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