The big advantage of a solar sail is that you don't need any propellant. Sure, you will probably need to carry a power source with you, but you won't need to carry huge amounts of propellant (plus engine(s), plus extra power supplies for the engines, above and beyond what you need to provide life support and comm). Even a high specific impulse ion engine will need a lot of propellant to generate any significant delta-vee.
Solar sails are not necessarily a better choice than an ion engine (or some other high Isp engine), but they should not be discounted arbitrarily until the appropriate trade studies can be carried out for the mission under consideration. It's possible (even for very heavy spacecraft) that the mass of the sail + support structure could be smaller than the mass of engine + power-supply + propellant. It depends on the amount of delta-vee that is required. The delta-vee produced by a conventional rocket (or ion engine) is proportional to the mass of propellant used. The delta-vee produced by a sail is not. All else being equal, an increase in the amount of delta-vee required will cause your propellant mass to increase, while your sail mass stays the same. For a given delivered payload mass there is clearly a cross-over as delta-vee increases, at which point the sail becomes a better choice in terms of cost and resource usage.
As you mentioned, a hybrid system using the sail at the beginning and end of the journey, and a mass-expulsion system for intermediate maneuvers, may be an even better solution. Again, it depends on the mission.
Actually, a solar sail works by momentum transfer from reflected photons (i.e. sunlight), rather than the solar wind. In fact the force created by the solar wind on a solar sail is several orders of magnitude less than that produced by sunlight. That said, you are correct that there will be an inverse square decrease in solar radiation pressure as you move away from the sun.
As far as radiation shielding goes, yes, that will increase the mass of the spacecraft. However, all that is required to counteract this is to increase the area of the sail (ok, that's a big all:-).
Solar sails generate thrust from solar radiation pressure, and as you'll remember from basic physics
Force = pressure x area
Increase the area and your force goes up. Since Newton told us that
Force = mass x acceleration
we can deduce that
acceleration = (pressure x area)/mass
and thus for a given solar radiation pressure an increase in mass will require a proportional increase in area to achieve the same acceleration. That's why the performance of a solar sail material/configuration combination is typically characterized in terms of either an area/mass ratio, or as a "characteristic acceleration" - both are good figures-of-merit that indicate how a particular solar sail design compares to other sail designs without requiring any consideration of the payloads they are carrying.
So, solar sails will work for a manned mission. We just need a really big sail. But since we haven't flown any sails yet, we probably do need to test the idea out on some unmanned probes first. Hopefully the powers-that-be are working on that as we speak.
There is an old saying, "Don't contribute to malice what can be explained by incompetence."
Actually, that would be "attribute", not "contribute". The two have rather different meanings:
Contribute = to play a part in bringing about an end or result, or to give to a greater whole
Attribute = to explain by indicating a cause
In this case the use of the word "contribute" makes your sentence nonsensical: "Don't bring about (or supply) malice what can otherwise be explained by incompetence"???
Customers provide requirements. Designers (by defininition) do the actual design. A customer may say "hey, this widget sucks, I'd find it much easier to use that one", but that's just redefining (or clarifying) their requirements. It's up to the designer to figure out how to make it work within the context of the rest of the system.
The capitalists -- at least the ones who matter -- are the few people who get to wield the power that the capital endows. It is the banker, not the saver, who decides to loan a ton of money to his brother-in-law to build too much office property during a real estate boom.
So don't invest in a dodgy bank. Don't invest in a bank at all, if you can't find one you trust. Provide a low interest loan to a personal friend you do trust, to help them build their business. Form a neighborhood cooperative to pool investment resources and invest larger sums (thus providing greater control) in investments you all agree are good.
I expect you probably snickered appreciatively the first time you heard the line about, "Those men in Washington wouldn't be there if they didn't know what they were doing."
Actually, I'm sure the men in Wasington know what they're doing. I just doubt that what they are doing has much to do with justice or reason or with benefiting the nation, but rather with retaining power.
I have not noticed any abundance of wisdom among the investment set or their manager priests. Actually, they seem to lead us from one folly to another, rarely learning anything from experience
So don't follow them. You aren't forced to work for stupid managers. If you're smarter than everyone you're working for, go into business for yourself - you should drive them out of business in no time.
Actually, what I'm saying is that the trend you are talking about is a result of the divergenc in technological level between developed and third world nations. It's happened before. It'll happen again. There's nothing you can do about it that isn't going to damage civilization as a whole in the long run.
Argentina fell apart because it was a corrupt government with massive cronyism in state-run jobs.
Don't like the IMF's conditions, don't borrow from them. Same way you wouldn't take out a home loan if the bank was going to screw you over.
Capitalism. Feudalism. The two are not the same. So to argue that there is a trend going back to the 15th century, and that at the same time it is capitalism's fault, is nonsensical.
I say plenty of people because I've seen plenty of people do it. And you're right, it does make me feel good. It makes me feel good to know that there are some people out there willing to earn a living instead of taking one.
I grew up in a socialist country. I've seen the kind of stagnation and inefficiency a socialist form of government breeds. I don't want to live in a place like that again. If you and your buddies want to "manifest violence" on me because I believe that the fruits of my labor are my own, so be it. I won't submit to a "your money or your life" proposition. And once you've taken my life and used my money, how will you survive?
Just because someone is poor doesn't mean they don't work hard, and just because someone is wealthy doesn't mean they do.
Labor does not equal value. I can work really hard to make an apple pie, but if I'm an incompetent cook, the pie will be burnt (and knowing my cooking probably inedible) - I've just worked hard to make a worthless pie. It's not quantity of labor that counts, but quality.
the relative value of capital versus labor is not determined by some sort of meaningful market, it is determined by the capitalists
And the capitalists are everyone who saves and invests. Which includes anyone who puts money in a bank. Realistically, the value of labor is determined by what people are willing to pay for it. Michael Jordan made millions because millions of people tuned in to see his games, and buy his merchandise. If they didn't, no team could have made enough money to afford to pay the salary Jordan got, and he would have had to settle for less.Jordan must have made more money for his team than they paid him, otherwise there wouldn't have been any point in paying him so much - it'd just bankrupt the team.
I worked for a super-capitalist once. At the point where he went from being just really rich to being super-rich, the 300 or so employees of his company -- without whom he simply could never have made his mega-fortune -- went from living paycheck-to-paycheck to living paycheck-to-paycheck while working for a smug, self-satisfied jerk.
I doubt you or your fellow employees would have had jobs if not for that self-satisfied jerk. If you could have found a way to make a living without whatever it was that he contributed, then why didn't you do it. All 300 employees could have pooled their resources and started their own company without the jerk. If you couldn't do that, then perhaps the jerk making a mega-fortune was just fair compensation for his ability to provide work for 300 people.
There is no particular justice to this aggregation, it's just a side-effect of the system.
So say you. I would argue that there is justice in rewarding those more able to create wealth with, well, wealth. Who better to decide what to do with accumulated wealth than those talented enough to accumulate it in the first place. That said, I think there is some injustice in the system, in that some who are incapable of creating wealth are able to accumulate it - usually by using corrupt legislators.
Whenever I hear someone arguing that stealing all that wealth from the people who created it will just make the wealth-creators opt out, I have to wonder: How come the wealth-creators weren't opting out when the average chief executive earned 10% of what he does now?
Because that 10% was all that they could earn at the time. There's a difference between getting 0.1x because that's all that is available to earn, and getting 0.1x because you earned x and someone took 0.9x from you. One is a just reward, the other is an injust penalty. Why punish someone for doing well? Should we take away Michael Jordan's millions because basketball players 20 years ago made 10% (or less) of his income?
In your personal experience, are the CEOs of companies the most intelligent or talented or wise or useful people in those companies?
Having dealt personally with only a few CEOs, I don't have enough data to say. However, they must be doing something useful, otherwise there wouldn't be such intense competition to recruit them. If being a successful CEO was easy, CEOs would be a dime a dozen, and their salaries would be a lot lower.
Here's one stat (Banko Milanovic, economist at WTO): In 1988, the richest 5 percent of the people in the world had incomes that were 78 teims as big as those of the pporest 5 percent. By 1993, the top 5 percent had incomes 114 times as big as those of the bottom 5 percent.
Thank you for the numbers. It's nice to see someone actually presenting hard data. However, two data points do not a trend line make. Especially over a mere 5 year span - that doesn't really indicate any kind of long term trend, and may just be a fluctuation.
Having said that, your post motivated to actually get off my ass and do a quick tour around the internet to see what data I could find. Looks like there really has been a divergence between wealthy and poor nations. However, that divergence started at about the same time as the industrial revolution kicked off. The gap we are seeing is the gap between developed and undeveloped nations, which has grown as the developed nations became more developed and other nations stagnated. Prior to the industrial revolution, China was wealthier than the "western nations". That gap rapidly closed once the the machine age kicked off. Now China is well behind other more developed nations. I'm sure that this gap will continue to fluctuate.
If you make 35,000$ Canadian a year (I make double, and I'm 23 years old),
Not that you're bragging or anything:-)
you are richer than 98 percent of the world's population.
That's nice. It doesn't really comtribute to your point though - doesn't mean the gap's widening, just that there is a gap. I'm sure the average Roman was much wealthier than his "barbarian" counterparts. Ditto the average Egyptian or Greek during their respective times of pre-eminence. High-tech nations tend to be wealthier than their low-tech neighbors. Duh. The thing is, the nation that has the advantage tends to change over time. And in the long run, everyone tends to get wealthier.
Think of post communist Russia. From 2 million poor to 60 million post-communism. (Not that I'm in any way advertising communism.. just, they got a free-market, supposedly)
Right. Because they weren't going to experience any difficulties dismantling 70 years worth of centrally planned economy and instituting a "free market". No one said it'd be easy. Just that it was the right thing to do in the long run. The reason they abandoned their old system (and that China is gradually experimenting with less regulated markets) is that the planned economy didn't work, and a free (or at least as free as the US has) economy seems to work better.
Anyhow, thats just sad about saying doing work. Other people want to do work. It is you who do not see that there are mechanisms in place to keep the poor down, as manifested in how the wealthy perceive them. I understand that it is difficult to feel good about being in this system, but it is important to know what it does.
Then ignore the wealthy, and work for yourself. Don't expect a handout (jobs or money). If you want to make it in this world, you have to exert some effort. It's not enough to want, you have to do. There are plenty of people who were poor but aren't anymore, and others who are poor, but are determined to not stay that way. Somehow, those mechanisms you mentioned are not keeping them down. Maybe because they are self-reliant and independent. They know the world doesn't owe them a living, they have to earn it. What's sad is that there are people that believe otherwise.
Your argument regarding the fact that people who get this money (the poor) are being rewarded for being sloth is based on the assumption that motivation comes from wealth. Ie, that money/is/ a reward, and that the freeloaders (the poor, the stupid) are perfectly happy to live off the backs of others. While we don't have time to debate such an axiom, it is not the axiom under under which I base my viewpoints. I believe people's primary motivation in life is to attain a social status by way of participating and contributing to the society they live in.
This would be true in a world in which it is possible to stay alive without material wealth. But in the real world it takes wealth (in the form of food, shelter, and clothing) to stay alive. I believe that people's primary focus is (or should be) remaining alive. It is only once that primary focus is taken care of that we can worry about social status and contribution. So by stripping those who create wealth (the "stuff of life") of that wealth, and rewarding those who contribute nothing to the continuation of life by handing the wealth to them, you are in effect punishing those who value life, and rewarding the suicidal. That way lies death and destruction. Note that I'm not referring to the kind of finanicial wealth accumulated by playing games with corrupt politicians, but the kind of wealth (if you can call it that) generated by the average working stiff as they toil in the offices, factories, and farms of the world.
Many an economist and phycologist have promoted the goal to contibute to one's society as the primary motivator of humans.
A motivator, perhaps. But not the primary motivator unless a substantial portion of the population is suicidal.
I tend to agree.. while we equate money as reward in this society, the poor people I know are not as interested in money as they are to have the ability to have the resources required to begin contributing to their society.
"The Lord helps those who help themselves..." So do I (even though I'm not Xtian). I'm perfectly happy to hand over some of my time or money to people that I know personally, and that I know are truly making an effort to better themselves. I've have "issues" with blithely handing over my money to some anonymous organization (govt or church) that presumes to decide who my wealth should help, and how. I believe that I should be able to decide what becomes of any wealth that I create.
It is, in my opinion, only the widening gap in incomes and standards of living...
Ya know, this is a pet peeve of mine. We keep hearing about this increasing gap between the rich and poor. But we never see any real numbers to back it up. What is the rate of increase of that gap? Where are the statistics that show the gap, and trace its fluctuation over time? There was a pretty significant gap between the rich and poor in, say, Victorian England. You're telling me that the gap has worsened since then? Prove it. Because I have to tell you, my feeling (based purely on anecdotal evidence, because I haven't done the research either) is that the gap is actually decreasing as the developed world flattens into "the great middle class", and the third world gradually becomes developed.
It's frusterating to see wealthy people suggest that poor people are driven by the same things they are, and then/withhold/ that very value to the point where these poor people can't afford the things that they both value.. food, water, rent, and cultural opportunities such as socializing.
Maybe those poor people should get off their ass and work for a living then, rather than relying on handouts from the wealthy folks. Ok, that's probably a little harsh. But really, where is it written that I must hand over my wealth to someone who hasn't earned it somehow. Life isn't free. If the wealthy person wasn't around, the poor person would have to earn the right to stay alive somehow. Why should they be get unearned life just because someone else did some work?
Consider the disproportionate amount of people in this society that wish to contribute in a vain that is unsupported by big business (arts, culture, non-quantitative branches of medicine, etc, etc.. whatever the wealthy elite don't value.)
First of all, what makes you assume that the "wealthy elite" won't value it? Wealthy people buy art. Wealthy people buy music. Art and music couldn't exist without wealthy people providing the means for the artists to stay alive (by paying them for their work). Otherwise said artists would be staring at the rear end of an ox while they ploughed a field to grow some food and stay alive.
Reality is a pretty harsh place. Either you create some wealth (primary wealth like food or shelter, or secondary wealth like labor or art), or you die. Either way, you will have earned it.
The only other choice is to take unearned wealth from someone else through the use of force. Not only is that considered immoral by most people, but it's the road to death (which is probably why it's immoral - dead people don't have morals). Take unearned wealth, and the people you have stolen from will eventually be unable to live (maybe not this generation, but eventually). Once the wealth-creators are all dead, how will you stay alive?
It all really depends on what the purpose of your planetary science is.
If you are out to study the evolution of the solar system you're probably going to want to look at the planets we haven't really examined in any detail yet (i.e. the distant outer ones), or do some comet fly-bys. If you want to look for life, then Europa's probably you're best bet right now. If you want to understand the Earth's environment in the context of other planets then it's off to Venus or Mars (the "most" Earth-like planets). If you're hot for colonization, then you probably want to take a really close and detailed look at Mars. If space resources are your thing then near Earth asteroids are the place to be.
The big question that is missing from the survey is: how well does our present budget match up with our intended purpose (whatever that may be), and if there is a mismatch should we increase the budget or reduce the magnitude of our goals. Personally, I lean towards increasing the budget (which has been happening, but it's all been funneled into ISS), but I'd be interested to see the general public's response to that question (although NASA might not like the answer).
Look, if RMS wanted to make everything that is derived from or uses GNU tools have the word "GNU" at the from (to ensure "credit where credit is due"), he should have stuck that condition in the license. It's no good complaining, after the fact, that you went and released a bunch of tools into the wild for free public use with no strings attached (aside from that source code thing), and no one is giving anything in return for using them (credit being one form of compensation).
It's also seem a little less cynical id RMS applied this same standard to every other piece of software out there that relies on GNU tools. That way it'd look slightly less like he's just trying to grab a free ride on the popularity of Linux.
It didn't help that the Math Department used a different symbology from the Science Departments, either.
That lack of consistency is not uncommon. The Math guys use different symbols and terminology than the Science geeks, who in turn do things a slightly different way than the Engineers. Sometimes it's a wonder that the technical world advances at all...
I actually thought Harry Potter was a fantastic book.
That's nice. I thought it was an enjoyable book as far as it went. But I've read plenty of other books in the same category just as good, or better (e.g. some of the Heinlein juveniles, or the Hobbit, or The Princess Bride). I honestly don't understand why this particular series has become such a huge fad (and let's face it, a fad is pretty much what it is). But since it's a fad, it's popular by definition. Which means it wins a popularity contest like the Hugo Awards.
Sure it may not be as "serious" as other books, but lots of readers liked it, and that is all that matters right?
It's not about seriousness, or lack thereof. Neal Stephenson's "Snow Crash" isn't exactly "serious", and yet it is a great science fiction novel all the same. But you're right, lots of readers liked Potter, and so it won. Regardless of its quality. Lots of people like N'Sync too, but I wouldn't necessarily rate them up there with the likes of Beethoven.
how does Harry Potter win over George R. R. Martin's A Storm of Swords [amazon.com] and Robert J. Sawyer's Calculating God [amazon.com]?
It wins because the Hugo is a reader-voted award, and the readers voted for Harry Potter. I'll leave you to draw your own conclusions about the quality of modern SF fans.
And I would disagree with you. CS teaches principles. Much the same way an undergrad engineering degree teaches principles.
A student engineer learns the principles of, for example, designing a digital ASIC to control a motor. They are less likely to learn that the particular fab process their particular vendor uses has some quirk that requires special care with the layout of the polysilicon. Or that the bearing manufacturer's tolerances are somewhat variable, and so the motor should not be driven to its max rated rpm. That's what experience (and good mentoring early in the career) is for - accumulating all of those technical anecdotes. Why do you think employers value people with solid work experience?
The principles learned in school can be supplemented by taking an active interest in the field, taking part in student projects, and doing internships. Which is why some engineers enter the workplace with more knowledge than others. Same reason some CS people can program their way out of a paper bag, and others can't.
I imagine it would be pretty easy to add them on after the fact, but the people running the project likely have plenty of other problems to worry about besides replacing a system that already does an acceptable job (the current stationkeeping method).
As you say, the ISS has plenty of issues to worry about. Many of them are system integration issues (getting all sorts of parts from different contractors to work well together). Adding an unplanned-for component to the mix is a recipe for schedule and cost disaster. There're likely to be structural issues with mounting the XIPS engines, and all sorts of exciting issues with routing command lines and power supplies. Not something you want to do to a project that's already $4B in the hole.
At the station's current mass (~120 Mg), about 3 continuously-firing 165 mN XIPS thrusters, at a combined power requirement of 13.5 kW, would be required to keep ISS in its orbit. At its completed mass (~450 Mg) about 10 would be required, using a total of 45 kW.
In other words, you wouldn't need many of the motors, but they'd suck all of your power, so they're not a viable solution for ISS as designed.
Not only that, but a quick back-of-the-envelope calculation gives me ~2 tons/year of propellant to supply 10 XIPS thrusters. That's a lot of Xenon to ship to orbit. Not that chemical propellants would be any less massive if you were using them to keep the ISS fixed in place. They're projecting ~6 tons/year for the present system.
Perhaps a better choice would be something that doesn't use any propellant - like an electrodynamic tether (see e.g. this)
My guess is that because the xenon exhaust is being launched into a lower-energy orbit than the station it would combine with the rest of the atmosphere, and wouldn't cause a problem. The electric field from the motors might cause problems with experiments, but I don't know enough about either to say for sure.
A chemical rocket you just point away from anything you don't want to hit, and you're fine since the rocket makes a relatively well directed jet of hot gas. An ion engine produces more of a cloud than a jet, so surfaces well off the thrust line are in danger of contamination. Xenon is more than likely going to impinge on many of the ISS surfaces and experiments, simply because the plume goes everywhere.
The ISS budget doesn't affect the cost of other projects, just the supply of money available to fund them. NASA spacecraft do cost a lot more than their student-built brethren, which is what the original post was about.
ISS is expensive because it is a political football with no clear mission. It exists to put dollars into the aerospace industries of as many different states as possible. Its secondary goal is to involve the rest of the world (this is the "international" part) in the space game - probably partly so they don't do space stuff themselves and accidentally generate a ballistic missile capability. Somewhere further down the list of goals is stuff like a continued manned presence in space, and performing useful science.
I do agree that it's sad that ISS sucks money from other, more worthy projects.
You are correct that large-force short-duration burns are not the only way to perform stationkeeping. I suspect that there are 3 reasons that ion propulsion has not been mentioned for the ISS:
(1) Ion propulsion was not mature when the ISS was being designed, so it wasn't included in the station design.
(2) While XIPS engines are used for stationkeeping GEO based comm satellites, the perturbing forces on LEO based space station like ISS are likely to be much larger. While I haven't done the calculations, I'd bet that means you would need a lot of XIPS engines - each one sucking down 4.5kW of power. Power is probably at a premium on the ISS, since they still don't have a whole lot of solar array area up there (and increasing the solar array area is likely to increase the drag force you are trying to counteract with your XIPS).
(3) Ion engines tend to produce a much less focused thruster plume than a chemical thruster. If your are constantly firing lots of thrusters that have unfocused plumes, you're going to end up with a big cloud of Xenon all around the station. It's likely to interfere with experiments and observations, and , and generally get in the way.
Ok its flying along in space, so how does that justify need for cash? I'm confused. Was it manned? Are we paying the astronauts wife?
It's not manned, but it doesn't fly itself. That requires ground based controllers (the mission operations folks) plus some expensive time using the Deep Space Network dishes (as others have mentioned already). The mission ops center is not exactly free either. Throw in some project management people, PR folks, and the scientists that are actually doing the extended mission, and the bill starts to add up.
No one's saying "if you don't give us money, DS1 will stop flying". What they're saying is "if you don't give us money, we can't continue to operate DS1 and collect data from it, so it'll fly along doing nothing" (seems like kind of a waste, doens't it?).
Why does it take a million dollars for everything we do at Nasa?????? Why can kids build soda can satalites for 20$ and Nasa build soda can satalites for 20 million? whats the damn difference
While I have no particular wish to defend NASA, they are not entirely at fault here. There're two reasons that NASA spacecraft cost so much:
(1) They are far more complicated, ambitious, and longer-lived than their student-built counterparts. NASA spacecraft operate in extreme conditions, doing unprecedented work, for years at a time. They have to work, so they are designed to be robust, redundant, and fault-tolerant. Trust me, this doesn't come cheap - and NASA's got a lot better at making it cheap in the last few years. Student-built satellites typically don't do much (a couple of minor experiments), although there are some neat things on the way (Three-corner sat for example). More importantly, student sats don't have to last as long, they only go to LEO, and no one cares if they fail. That means cheaper parts, less redundancy, and a simpler design.
(2) NASA also has to contend with the whole government appropriations issue. The best way to get congressional support is to have your program spend a little money in a bunch of different states. Let's face it, a large, arbitrarily distributed project (split up for political rather than technical reasons) is likely to cost more than the same project carried out in one central location. Plus NASA has to carry out all sorts of PR functions, and otherwise impress Joe Q. Public so that their budget doesn't get axed completely.
Which is not to say that NASA couldn't do better. They've done some pretty stupid things at times, and taken some enormous risks. On other hand, they've also done some pretty amazing stuff. NASA's biggest problems are corrosive bureaucracy, unrealistic project management, and congress.
If you really want a national space program to be proud of, write your congress-person. Don't say "Give NASA more money". Just say "Get off NASA's back, and let it do its job without having to pay a political bribe to everyone on congress. Ask for results, not for some concession for your home state. This is a national space program".
Yet somehow they manage to get radio signals back from the moon. Seems like maybe all that crap you mentioned doesn't actually interfere with RF transmissions (including microwaves) as much as you seem to think it does.
Microwave power transmission conceptual designs typically consider RF frequencies not dissimilar to those used for space comm applications (power transmission has been proposed at ~2.5GHz). See this for more info.
FUD. What happened at TMI? Something went wrong with the reactor and then all of the safety measures worked perfectly. No one was hurt. No radiation was released. The only thing that went wrong at TMI was the senseless media frenzy.
Chernobyl is a totally different situation. It was caused by porrly trained people performing a dangerous procedure they weren't supposed to be doing in a plant with hopeless safety features. The Chernobyl was a poorly designed reactor. End of story. Nuclear safety in the US is taken very seriously, and the reactors are designed to be robust, and fault-tolerant.
Actually, solar cells for space applications are hovering around 26% effciency right. Of course, they're multi-junction GaAs, and somewhat more expensive than the old silicon ones. Depends on how much you're willing to spend, and also on what the trade-off is between $/hectare of land and $/m^2 of solar array.
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Solar sails are not necessarily a better choice than an ion engine (or some other high Isp engine), but they should not be discounted arbitrarily until the appropriate trade studies can be carried out for the mission under consideration. It's possible (even for very heavy spacecraft) that the mass of the sail + support structure could be smaller than the mass of engine + power-supply + propellant. It depends on the amount of delta-vee that is required. The delta-vee produced by a conventional rocket (or ion engine) is proportional to the mass of propellant used. The delta-vee produced by a sail is not. All else being equal, an increase in the amount of delta-vee required will cause your propellant mass to increase, while your sail mass stays the same. For a given delivered payload mass there is clearly a cross-over as delta-vee increases, at which point the sail becomes a better choice in terms of cost and resource usage.
As you mentioned, a hybrid system using the sail at the beginning and end of the journey, and a mass-expulsion system for intermediate maneuvers, may be an even better solution. Again, it depends on the mission.
As far as radiation shielding goes, yes, that will increase the mass of the spacecraft. However, all that is required to counteract this is to increase the area of the sail (ok, that's a big all :-).
Solar sails generate thrust from solar radiation pressure, and as you'll remember from basic physics
Force = pressure x area
Increase the area and your force goes up. Since Newton told us that
Force = mass x acceleration
we can deduce that
acceleration = (pressure x area)/mass
and thus for a given solar radiation pressure an increase in mass will require a proportional increase in area to achieve the same acceleration. That's why the performance of a solar sail material/configuration combination is typically characterized in terms of either an area/mass ratio, or as a "characteristic acceleration" - both are good figures-of-merit that indicate how a particular solar sail design compares to other sail designs without requiring any consideration of the payloads they are carrying.
So, solar sails will work for a manned mission. We just need a really big sail. But since we haven't flown any sails yet, we probably do need to test the idea out on some unmanned probes first. Hopefully the powers-that-be are working on that as we speak.
Actually, that would be "attribute", not "contribute". The two have rather different meanings:
Contribute = to play a part in bringing about an end or result, or to give to a greater whole
Attribute = to explain by indicating a cause
In this case the use of the word "contribute" makes your sentence nonsensical: "Don't bring about (or supply) malice what can otherwise be explained by incompetence"???
Customers provide requirements. Designers (by defininition) do the actual design. A customer may say "hey, this widget sucks, I'd find it much easier to use that one", but that's just redefining (or clarifying) their requirements. It's up to the designer to figure out how to make it work within the context of the rest of the system.
So don't invest in a dodgy bank. Don't invest in a bank at all, if you can't find one you trust. Provide a low interest loan to a personal friend you do trust, to help them build their business. Form a neighborhood cooperative to pool investment resources and invest larger sums (thus providing greater control) in investments you all agree are good.
I expect you probably snickered appreciatively the first time you heard the line about, "Those men in Washington wouldn't be there if they didn't know what they were doing."
Actually, I'm sure the men in Wasington know what they're doing. I just doubt that what they are doing has much to do with justice or reason or with benefiting the nation, but rather with retaining power.
I have not noticed any abundance of wisdom among the investment set or their manager priests. Actually, they seem to lead us from one folly to another, rarely learning anything from experience
So don't follow them. You aren't forced to work for stupid managers. If you're smarter than everyone you're working for, go into business for yourself - you should drive them out of business in no time.
Argentina fell apart because it was a corrupt government with massive cronyism in state-run jobs.
Don't like the IMF's conditions, don't borrow from them. Same way you wouldn't take out a home loan if the bank was going to screw you over.
Capitalism. Feudalism. The two are not the same. So to argue that there is a trend going back to the 15th century, and that at the same time it is capitalism's fault, is nonsensical.
I say plenty of people because I've seen plenty of people do it. And you're right, it does make me feel good. It makes me feel good to know that there are some people out there willing to earn a living instead of taking one.
I grew up in a socialist country. I've seen the kind of stagnation and inefficiency a socialist form of government breeds. I don't want to live in a place like that again. If you and your buddies want to "manifest violence" on me because I believe that the fruits of my labor are my own, so be it. I won't submit to a "your money or your life" proposition. And once you've taken my life and used my money, how will you survive?
Labor does not equal value. I can work really hard to make an apple pie, but if I'm an incompetent cook, the pie will be burnt (and knowing my cooking probably inedible) - I've just worked hard to make a worthless pie. It's not quantity of labor that counts, but quality.
the relative value of capital versus labor is not determined by some sort of meaningful market, it is determined by the capitalists
And the capitalists are everyone who saves and invests. Which includes anyone who puts money in a bank. Realistically, the value of labor is determined by what people are willing to pay for it. Michael Jordan made millions because millions of people tuned in to see his games, and buy his merchandise. If they didn't, no team could have made enough money to afford to pay the salary Jordan got, and he would have had to settle for less.Jordan must have made more money for his team than they paid him, otherwise there wouldn't have been any point in paying him so much - it'd just bankrupt the team.
I worked for a super-capitalist once. At the point where he went from being just really rich to being super-rich, the 300 or so employees of his company -- without whom he simply could never have made his mega-fortune -- went from living paycheck-to-paycheck to living paycheck-to-paycheck while working for a smug, self-satisfied jerk.
I doubt you or your fellow employees would have had jobs if not for that self-satisfied jerk. If you could have found a way to make a living without whatever it was that he contributed, then why didn't you do it. All 300 employees could have pooled their resources and started their own company without the jerk. If you couldn't do that, then perhaps the jerk making a mega-fortune was just fair compensation for his ability to provide work for 300 people.
There is no particular justice to this aggregation, it's just a side-effect of the system.
So say you. I would argue that there is justice in rewarding those more able to create wealth with, well, wealth. Who better to decide what to do with accumulated wealth than those talented enough to accumulate it in the first place. That said, I think there is some injustice in the system, in that some who are incapable of creating wealth are able to accumulate it - usually by using corrupt legislators.
Whenever I hear someone arguing that stealing all that wealth from the people who created it will just make the wealth-creators opt out, I have to wonder: How come the wealth-creators weren't opting out when the average chief executive earned 10% of what he does now?
Because that 10% was all that they could earn at the time. There's a difference between getting 0.1x because that's all that is available to earn, and getting 0.1x because you earned x and someone took 0.9x from you. One is a just reward, the other is an injust penalty. Why punish someone for doing well? Should we take away Michael Jordan's millions because basketball players 20 years ago made 10% (or less) of his income?
In your personal experience, are the CEOs of companies the most intelligent or talented or wise or useful people in those companies?
Having dealt personally with only a few CEOs, I don't have enough data to say. However, they must be doing something useful, otherwise there wouldn't be such intense competition to recruit them. If being a successful CEO was easy, CEOs would be a dime a dozen, and their salaries would be a lot lower.
Thank you for the numbers. It's nice to see someone actually presenting hard data. However, two data points do not a trend line make. Especially over a mere 5 year span - that doesn't really indicate any kind of long term trend, and may just be a fluctuation.
Having said that, your post motivated to actually get off my ass and do a quick tour around the internet to see what data I could find. Looks like there really has been a divergence between wealthy and poor nations. However, that divergence started at about the same time as the industrial revolution kicked off. The gap we are seeing is the gap between developed and undeveloped nations, which has grown as the developed nations became more developed and other nations stagnated. Prior to the industrial revolution, China was wealthier than the "western nations". That gap rapidly closed once the the machine age kicked off. Now China is well behind other more developed nations. I'm sure that this gap will continue to fluctuate.
If you make 35,000$ Canadian a year (I make double, and I'm 23 years old),
Not that you're bragging or anything :-)
you are richer than 98 percent of the world's population.
That's nice. It doesn't really comtribute to your point though - doesn't mean the gap's widening, just that there is a gap. I'm sure the average Roman was much wealthier than his "barbarian" counterparts. Ditto the average Egyptian or Greek during their respective times of pre-eminence. High-tech nations tend to be wealthier than their low-tech neighbors. Duh. The thing is, the nation that has the advantage tends to change over time. And in the long run, everyone tends to get wealthier.
Think of post communist Russia. From 2 million poor to 60 million post-communism. (Not that I'm in any way advertising communism .. just, they got a free-market, supposedly)
Right. Because they weren't going to experience any difficulties dismantling 70 years worth of centrally planned economy and instituting a "free market". No one said it'd be easy. Just that it was the right thing to do in the long run. The reason they abandoned their old system (and that China is gradually experimenting with less regulated markets) is that the planned economy didn't work, and a free (or at least as free as the US has) economy seems to work better.
Anyhow, thats just sad about saying doing work. Other people want to do work. It is you who do not see that there are mechanisms in place to keep the poor down, as manifested in how the wealthy perceive them. I understand that it is difficult to feel good about being in this system, but it is important to know what it does.
Then ignore the wealthy, and work for yourself. Don't expect a handout (jobs or money). If you want to make it in this world, you have to exert some effort. It's not enough to want, you have to do. There are plenty of people who were poor but aren't anymore, and others who are poor, but are determined to not stay that way. Somehow, those mechanisms you mentioned are not keeping them down. Maybe because they are self-reliant and independent. They know the world doesn't owe them a living, they have to earn it. What's sad is that there are people that believe otherwise.
This would be true in a world in which it is possible to stay alive without material wealth. But in the real world it takes wealth (in the form of food, shelter, and clothing) to stay alive. I believe that people's primary focus is (or should be) remaining alive. It is only once that primary focus is taken care of that we can worry about social status and contribution. So by stripping those who create wealth (the "stuff of life") of that wealth, and rewarding those who contribute nothing to the continuation of life by handing the wealth to them, you are in effect punishing those who value life, and rewarding the suicidal. That way lies death and destruction. Note that I'm not referring to the kind of finanicial wealth accumulated by playing games with corrupt politicians, but the kind of wealth (if you can call it that) generated by the average working stiff as they toil in the offices, factories, and farms of the world.
Many an economist and phycologist have promoted the goal to contibute to one's society as the primary motivator of humans.
A motivator, perhaps. But not the primary motivator unless a substantial portion of the population is suicidal.
I tend to agree .. while we equate money as reward in this society, the poor people I know are not as interested in money as they are to have the ability to have the resources required to begin contributing to their society.
"The Lord helps those who help themselves..."
So do I (even though I'm not Xtian). I'm perfectly happy to hand over some of my time or money to people that I know personally, and that I know are truly making an effort to better themselves. I've have "issues" with blithely handing over my money to some anonymous organization (govt or church) that presumes to decide who my wealth should help, and how. I believe that I should be able to decide what becomes of any wealth that I create.
It is, in my opinion, only the widening gap in incomes and standards of living...
Ya know, this is a pet peeve of mine. We keep hearing about this increasing gap between the rich and poor. But we never see any real numbers to back it up. What is the rate of increase of that gap? Where are the statistics that show the gap, and trace its fluctuation over time? There was a pretty significant gap between the rich and poor in, say, Victorian England. You're telling me that the gap has worsened since then? Prove it. Because I have to tell you, my feeling (based purely on anecdotal evidence, because I haven't done the research either) is that the gap is actually decreasing as the developed world flattens into "the great middle class", and the third world gradually becomes developed.
It's frusterating to see wealthy people suggest that poor people are driven by the same things they are, and then /withhold/ that very value to the point where these poor people can't afford the things that they both value .. food, water, rent, and cultural opportunities such as socializing.
Maybe those poor people should get off their ass and work for a living then, rather than relying on handouts from the wealthy folks. Ok, that's probably a little harsh. But really, where is it written that I must hand over my wealth to someone who hasn't earned it somehow. Life isn't free. If the wealthy person wasn't around, the poor person would have to earn the right to stay alive somehow. Why should they be get unearned life just because someone else did some work?
Consider the disproportionate amount of people in this society that wish to contribute in a vain that is unsupported by big business (arts, culture, non-quantitative branches of medicine, etc, etc .. whatever the wealthy elite don't value.)
First of all, what makes you assume that the "wealthy elite" won't value it? Wealthy people buy art. Wealthy people buy music. Art and music couldn't exist without wealthy people providing the means for the artists to stay alive (by paying them for their work). Otherwise said artists would be staring at the rear end of an ox while they ploughed a field to grow some food and stay alive.
Reality is a pretty harsh place. Either you create some wealth (primary wealth like food or shelter, or secondary wealth like labor or art), or you die. Either way, you will have earned it.
The only other choice is to take unearned wealth from someone else through the use of force. Not only is that considered immoral by most people, but it's the road to death (which is probably why it's immoral - dead people don't have morals). Take unearned wealth, and the people you have stolen from will eventually be unable to live (maybe not this generation, but eventually). Once the wealth-creators are all dead, how will you stay alive?
If you are out to study the evolution of the solar system you're probably going to want to look at the planets we haven't really examined in any detail yet (i.e. the distant outer ones), or do some comet fly-bys. If you want to look for life, then Europa's probably you're best bet right now. If you want to understand the Earth's environment in the context of other planets then it's off to Venus or Mars (the "most" Earth-like planets). If you're hot for colonization, then you probably want to take a really close and detailed look at Mars. If space resources are your thing then near Earth asteroids are the place to be.
The big question that is missing from the survey is: how well does our present budget match up with our intended purpose (whatever that may be), and if there is a mismatch should we increase the budget or reduce the magnitude of our goals. Personally, I lean towards increasing the budget (which has been happening, but it's all been funneled into ISS), but I'd be interested to see the general public's response to that question (although NASA might not like the answer).
It's also seem a little less cynical id RMS applied this same standard to every other piece of software out there that relies on GNU tools. That way it'd look slightly less like he's just trying to grab a free ride on the popularity of Linux.
That lack of consistency is not uncommon. The Math guys use different symbols and terminology than the Science geeks, who in turn do things a slightly different way than the Engineers. Sometimes it's a wonder that the technical world advances at all...
Actually, I believe it very closely resembled solid rocket propellant (some kind of aluminum mix similar to thermite as I recall).
That's nice. I thought it was an enjoyable book as far as it went. But I've read plenty of other books in the same category just as good, or better (e.g. some of the Heinlein juveniles, or the Hobbit, or The Princess Bride). I honestly don't understand why this particular series has become such a huge fad (and let's face it, a fad is pretty much what it is). But since it's a fad, it's popular by definition. Which means it wins a popularity contest like the Hugo Awards.
Sure it may not be as "serious" as other books, but lots of readers liked it, and that is all that matters right?
It's not about seriousness, or lack thereof. Neal Stephenson's "Snow Crash" isn't exactly "serious", and yet it is a great science fiction novel all the same. But you're right, lots of readers liked Potter, and so it won. Regardless of its quality. Lots of people like N'Sync too, but I wouldn't necessarily rate them up there with the likes of Beethoven.
It wins because the Hugo is a reader-voted award, and the readers voted for Harry Potter. I'll leave you to draw your own conclusions about the quality of modern SF fans.
Theodore Sturgeon, actually. Silverberg may have quoted Sturgeon, but I'm pretty sure Sturgeon originated the 90% crap law.
A student engineer learns the principles of, for example, designing a digital ASIC to control a motor. They are less likely to learn that the particular fab process their particular vendor uses has some quirk that requires special care with the layout of the polysilicon. Or that the bearing manufacturer's tolerances are somewhat variable, and so the motor should not be driven to its max rated rpm. That's what experience (and good mentoring early in the career) is for - accumulating all of those technical anecdotes. Why do you think employers value people with solid work experience?
The principles learned in school can be supplemented by taking an active interest in the field, taking part in student projects, and doing internships. Which is why some engineers enter the workplace with more knowledge than others. Same reason some CS people can program their way out of a paper bag, and others can't.
As you say, the ISS has plenty of issues to worry about. Many of them are system integration issues (getting all sorts of parts from different contractors to work well together). Adding an unplanned-for component to the mix is a recipe for schedule and cost disaster. There're likely to be structural issues with mounting the XIPS engines, and all sorts of exciting issues with routing command lines and power supplies. Not something you want to do to a project that's already $4B in the hole.
At the station's current mass (~120 Mg), about 3 continuously-firing 165 mN XIPS thrusters, at a combined power requirement of 13.5 kW, would be required to keep ISS in its orbit. At its completed mass (~450 Mg) about 10 would be required, using a total of 45 kW.
In other words, you wouldn't need many of the motors, but they'd suck all of your power, so they're not a viable solution for ISS as designed.
Not only that, but a quick back-of-the-envelope calculation gives me ~2 tons/year of propellant to supply 10 XIPS thrusters. That's a lot of Xenon to ship to orbit. Not that chemical propellants would be any less massive if you were using them to keep the ISS fixed in place. They're projecting ~6 tons/year for the present system.
Perhaps a better choice would be something that doesn't use any propellant - like an electrodynamic tether (see e.g. this)
My guess is that because the xenon exhaust is being launched into a lower-energy orbit than the station it would combine with the rest of the atmosphere, and wouldn't cause a problem. The electric field from the motors might cause problems with experiments, but I don't know enough about either to say for sure.
A chemical rocket you just point away from anything you don't want to hit, and you're fine since the rocket makes a relatively well directed jet of hot gas. An ion engine produces more of a cloud than a jet, so surfaces well off the thrust line are in danger of contamination. Xenon is more than likely going to impinge on many of the ISS surfaces and experiments, simply because the plume goes everywhere.
ISS is expensive because it is a political football with no clear mission. It exists to put dollars into the aerospace industries of as many different states as possible. Its secondary goal is to involve the rest of the world (this is the "international" part) in the space game - probably partly so they don't do space stuff themselves and accidentally generate a ballistic missile capability. Somewhere further down the list of goals is stuff like a continued manned presence in space, and performing useful science.
I do agree that it's sad that ISS sucks money from other, more worthy projects.
(1) Ion propulsion was not mature when the ISS was being designed, so it wasn't included in the station design.
(2) While XIPS engines are used for stationkeeping GEO based comm satellites, the perturbing forces on LEO based space station like ISS are likely to be much larger. While I haven't done the calculations, I'd bet that means you would need a lot of XIPS engines - each one sucking down 4.5kW of power. Power is probably at a premium on the ISS, since they still don't have a whole lot of solar array area up there (and increasing the solar array area is likely to increase the drag force you are trying to counteract with your XIPS).
(3) Ion engines tend to produce a much less focused thruster plume than a chemical thruster. If your are constantly firing lots of thrusters that have unfocused plumes, you're going to end up with a big cloud of Xenon all around the station. It's likely to interfere with experiments and observations, and , and generally get in the way.
It's not manned, but it doesn't fly itself. That requires ground based controllers (the mission operations folks) plus some expensive time using the Deep Space Network dishes (as others have mentioned already). The mission ops center is not exactly free either. Throw in some project management people, PR folks, and the scientists that are actually doing the extended mission, and the bill starts to add up.
No one's saying "if you don't give us money, DS1 will stop flying". What they're saying is "if you don't give us money, we can't continue to operate DS1 and collect data from it, so it'll fly along doing nothing" (seems like kind of a waste, doens't it?).
Why does it take a million dollars for everything we do at Nasa?????? Why can kids build soda can satalites for 20$ and Nasa build soda can satalites for 20 million? whats the damn difference
While I have no particular wish to defend NASA, they are not entirely at fault here. There're two reasons that NASA spacecraft cost so much:
(1) They are far more complicated, ambitious, and longer-lived than their student-built counterparts. NASA spacecraft operate in extreme conditions, doing unprecedented work, for years at a time. They have to work, so they are designed to be robust, redundant, and fault-tolerant. Trust me, this doesn't come cheap - and NASA's got a lot better at making it cheap in the last few years.
Student-built satellites typically don't do much (a couple of minor experiments), although there are some neat things on the way (Three-corner sat for example). More importantly, student sats don't have to last as long, they only go to LEO, and no one cares if they fail. That means cheaper parts, less redundancy, and a simpler design.
(2) NASA also has to contend with the whole government appropriations issue. The best way to get congressional support is to have your program spend a little money in a bunch of different states. Let's face it, a large, arbitrarily distributed project (split up for political rather than technical reasons) is likely to cost more than the same project carried out in one central location. Plus NASA has to carry out all sorts of PR functions, and otherwise impress Joe Q. Public so that their budget doesn't get axed completely.
Which is not to say that NASA couldn't do better. They've done some pretty stupid things at times, and taken some enormous risks. On other hand, they've also done some pretty amazing stuff. NASA's biggest problems are corrosive bureaucracy, unrealistic project management, and congress.
If you really want a national space program to be proud of, write your congress-person. Don't say "Give NASA more money". Just say "Get off NASA's back, and let it do its job without having to pay a political bribe to everyone on congress. Ask for results, not for some concession for your home state. This is a national space program".
Gracious admission of error. Are you sure you're a slashdotter? :-)
Microwave power transmission conceptual designs typically consider RF frequencies not dissimilar to those used for space comm applications (power transmission has been proposed at ~2.5GHz). See this for more info.
FUD. What happened at TMI? Something went wrong with the reactor and then all of the safety measures worked perfectly. No one was hurt. No radiation was released. The only thing that went wrong at TMI was the senseless media frenzy.
Chernobyl is a totally different situation. It was caused by porrly trained people performing a dangerous procedure they weren't supposed to be doing in a plant with hopeless safety features. The Chernobyl was a poorly designed reactor. End of story. Nuclear safety in the US is taken very seriously, and the reactors are designed to be robust, and fault-tolerant.
Actually, solar cells for space applications are hovering around 26% effciency right. Of course, they're multi-junction GaAs, and somewhat more expensive than the old silicon ones. Depends on how much you're willing to spend, and also on what the trade-off is between $/hectare of land and $/m^2 of solar array.