Catch up on stories from the past week (and beyond) at the Slashdot story archive

 



Forgot your password?
typodupeerror
Check out the new SourceForge HTML5 internet speed test! No Flash necessary and runs on all devices. Also, Slashdot's Facebook page has a chat bot now. Message it for stories and more. ×

Comment Re: No Dragon 2 Soft Landing Yet (Score 1) 125

He's first going to have to learn how to launch that fast. That's one area where SpaceX hasn't had much success - getting its launch turnaround times down. Hopefully they will in the future. Also, since an explosion takes them out for half a year or more (regardless of turnaround times), they better up their reliability by an order of magnitude or more, since each increase in launch rate means more possible rockets that can fail. And of course they want the ITS booster to have a service life of 1000x launches, which means an immensely high reliability.

Anyway, SpaceX's big goal is to have their satellite service give them a nearly unlimited demand for launches in the coming decade, as well as a correspondingly huge income from global sales of satellite net / communications services - and to funnel those profits into ITS. Time will tell... but there's certainly no shortage of ambition.

Comment Re:Not Happening Anytime Soon (Score 1) 125

That's the biggest concern I have. People tire of ongoing expenses. ISS seemed neat at first; now everyone hates it. Why would a moon base fare differently?

Long-term presences in space need to very quickly cut ties with earth, on order of greatest resource dependencies down to smallest resource dependencies. Aka, first things like oxygen, propellant, etc, then to industrial chemicals, of increasingly smaller quantities, with increasingly diversified manufacturing facilities, with very complex/low volume chemical feedstocks and manufacturing processes coming last. Cutting all ties is a process that would take centuries. But you can start with the low hanging fruit, bit by bit, and keep stockpiles of everything needed for maintenance that you can't produce locally.

Unfortunately, running counter to this is expansion. Because if you double the size of your operations, you also double your resource demands. So you need to improve resource independence at a faster rate than you grow.

Part of the problem with the moon is that it's just not a great place for ISRU. Volatiles are rare. We've never even sampled any moon that aren't depleted in volatiles, although there's some data to suggest that various volatiles might be scattered in permanently shaded areas (all of them, in the same place? That's a good question). Surface mineral diversity is limited - primarily light, non-volatile elements. Oxygen is at least widely abundant, but locked up tightly. And while the moon offers short transit times, it's surprisingly not that advantageous concerning delta-V. You can't aerocapture there, landing is fully powered (no parachute deceleration), and to get there you have to already be on such a high apogee orbit that it's not much more energy to go into a Mars transfer. Gravity is less and night is two days long. There are a couple "maybe" peaks of eternal light, but that doesn't mean that they're colocated with volatiles; the last I looked into it it looked like the closest suggested find of water was dozens of kilometers away from the nearest such peak, which would be quite the commute (and thus low throughput / high wear).

The moon is certainly the "cautious" option; emergency returns / resupplies are easy there, and communication fast. Its main value appears to be a testing ground for systems while minimizing risk. But it's not a very appealing place from a settlement perspective.

Of course, I prefer Venus to Mars, but that's neither here nor there ;) I'd like to see a parallel program for both, as the same sort of booster and transfer stage can be used for both, so it's only habitat / ascent stage development costs that are doubled. And once you get past the differences in feedstock sources, production industrial processes converge (Venus advantaged by the higher power availability and easier ability to get rid of heat - excepting in the case of cryogenics, where Mars holds the advantage)

Comment Re:Younger astronauts (Score 1) 125

One, there would be howls of protest. Two, you're not taking that argument to its logical end. You should only send pygmy women by that logic.

Women do consume less resources (by a good margin on average) and take up less space, but if I recall correctly are more vulnerable to radiation-related disease. So it's a tossup depending on what factors are constraining your mission architecture.

Comment Re:Rockets are too expensive (Score 1) 125

I have read the book, and it's an absurd degree of wishful thinking. Just ignoring the huge number of things that they just gloss over or omit outright, the materials technology they're talking about is about two orders of magnitude away from what we actually have, and might even be physically impossible. Measurements of individual carbon nanotubes (let alone bundles, let alone bulk fibres) don't approach the strengths being talked about there. Colossal carbon tube does better on an individual tube basis, but again, we're nowhere even close to the materials tech required. And for what? For a massive, very low throughput, tiny safety margin, most-failure-modes-unaccounted-for, low-power-efficiency means of access to space? Colour me unimpressed.

If you want something better, I recommend looking into Lofstrom loops (launch loops). Current materials tech, high efficiency, high throughput per unit mass, no orbit restrictions, and works even on tidally locked bodies.

Comment Re:Rockets are too expensive (Score 1) 125

Quite true. The materials technology required is about two orders of magnitude away from actual materials technology, for starters. And among the countless other problems with space elevators, they're not actually all that efficient. Laser power beaming over those distances works out to single-digit transfer efficiencies, and microwave power beaming even less (microwave power beaming to space can be efficient, but only if the receiving antenna is huge). And no, you can't regularly hang things or run power wires up a space elevator - the mass of the cable has to be vanishingly small.

Active-suspended structures, such as Lofstrom loops, are a much better choice. Power transfer efficiency can be greater than 50% and current materials technology should be sufficient. They can also be designed to shoot payloads into any orbit (unlike space elevators), and work independent of the properties of the body in question, as well as having far greater throughput per unit mass. There's really no reason to choose a space elevator over a Lofstrom loop.

Comment Re:Too good to be true. (Score 2) 177

It doesn't work like that. Radiative heating/cooling works via exchange of IR. You're not just giving it up; everything you're radiating at is proportionally radiating back at you. So you cool the most when you're radiatively exchanging with something that's very cold. Aka, you want to be radiatively exchanging with the cosmic microwave background, not with low-altitude clouds. That's the whole point of radiating at low absorption frequencies in the atmosphere: so that you're exchanging with space, not with atmospheric air.

Comment Re:"Police found Purinton 80 miles away at Applebe (Score 1) 969

1) The Founding Fathers, almost all of whom were British subjects, saw firsthand what happens when only the government has firearms. They can use those weapons to quell public outcry over anything, claiming the people were "rioting" or were "a threat to peace and order" because the people can't effectively fight back. If you read The Federalist Papers, Hamilton, Madison and Jay all say the same basic thing: citizens who have weapons are more fully able to defend themselves from the government.

That may sound odd to Europeans

It also sounds odd to the current U.S. Supreme Court, which affirmed in D.C. vs Heller the right to bear arms for self-defense. A later court finding (People v. Aguilar) summarized the majority opinion:

In District of Columbia v. Heller, 554 U.S. 570 (2008), the Supreme Court undertook its first-ever "in-depth examination" of the second amendment's meaning Id. at 635. After a lengthy historical discussion, the Court ultimately concluded that the second amendment "guarantee[s] the individual right to possess and carry weapons in case of confrontation" (id. at 592); that "central to" this right is "the inherent right of self-defense" (id. at 628); that "the home" is "where the need for defense of self, family, and property is most acute" (id. at 628); and that, "above all other interests," the second amendment elevates "the right of law-abiding, responsible citizens to use arms in defense of hearth and home" (id. at 635). Based on this understanding, the Court held that a District of Columbia law banning handgun possession in the home violated the second amendment. Id. at 635.

So at this point they've basically decided it's a self-defense thing. The idea that the Second Amendment is to facilitate armed insurrection to overthrow a tyrannical government (a.k.a. the so-called "Second Amendment solution") has no current legal basis. The dissenting opinion went with the "well-regulated militia" idea:

The Second Amendment was adopted to protect the right of the people of each of the several States to maintain a well-regulated militia. It was a response to concerns raised during the ratification of the Constitution that the power of Congress to disarm the state militias and create a national standing army posed an intolerable threat to the sovereignty of the several States. Neither the text of the Amendment nor the arguments advanced by its proponents evidenced the slightest interest in limiting any legislature's authority to regulate private civilian uses of firearms. Specifically, there is no indication that the Framers of the Amendment intended to enshrine the common-law right of self-defense in the Constitution.

Here are the first six drafts of the Second Amendment and the final version:

  • The right of the people to keep and bear arms shall not be infringed; a well armed and well regulated militia being the best security of a free country but no person religiously scrupulous of bearing arms shall be compelled to render military service in person.
  • A well regulated militia, composed of the body of the people, being the best security of a free State, the right of the people to keep and bear arms shall not be infringed; but no person religiously scrupulous shall be compelled to bear arms.
  • A well regulated militia, composed of the body of the people, being the best security of a free state, the right of the people to keep and bear arms shall not be infringed; but no one religiously scrupulous of bearing arms shall be compelled to render military service in person.
  • A well regulated militia, composed of the body of the people, being the best security of a free state, the right of the people to keep and bear arms, shall not be infringed, but no one religiously scrupulous of bearing arms shall be compelled to render military service in person.
  • A well regulated militia, being the best security of a free state, the right of the people to keep and bear arms, shall not be infringed.
  • A well regulated militia being the security of a free state, the right of the people to keep and bear arms shall not be infringed.
  • A well regulated militia being necessary to the security of a free State, the right of the People to keep and bear arms shall not be infringed.

If they had C-SPAN back then, we would have more insight into what motivated these careful rephrasings, comma deletions, etc. At least some are known to have been introduced by Senate scribes inadvertently modifying punctuation, and introducing subtle changes in meaning. (Thank God somebody removed that "religiously scrupulous" crap.) But the Second Amendment is just badly written. we're forced to read through the Federalist Papers and other contemporary writings to figure out what these guys were thinking when they wrote it.

Two things you need to keep in mind when you read all this stuff. First of all, these were being defined as restrictions on the federal government, and only the federal government. The courts affirmed this model during the first half of the 19th century. Northern and Southern states had very different appetites for democracy in general, for obvious reasons, so the Constitution followed an "If you like your authoritarianism, you can keep it" model. The federal government was not allowed to restrict speech in any way, but if your state wanted to violate those same individual liberties, go right ahead. In most Southern states, speaking ill of slavery was a hanging offense.

Second, we have to seriously reexamine this attitude we have toward the Constitution. The older it gets, the more revered it becomes, and at this point, most Americans think of it as an appendix to the Bible. People are seriously arguing that the Bill of Rights are ordained by God. Back when it was written, things were more casual. Everyone agreed their founding document sucked, then simply crumpled it up and wrote another one. No one was in a mood to do this a third time, so the Constitution has a nice section describing how to modify it. (And nowhere does it say "and if things don't work out, start shootin'.") There seems no reason to think that they intended the document to be unalterable by future generations centuries afterward- that would be absurd. But modifying the Constitution at this point is politically impossible and will remain so. We have worshipped the document so much that we no longer control it- which is exactly what its authors tried to prevent.

Comment Re:Only? (Score 1) 146

Productivity is calculated by dividing the units of output completed by hours of input. So yes Productivity is based on working time.

You're obviously not a Project Manager nor work for a corporation because your example is pure bullshit. The simple fact is if you knocked on someone's door they would tell you in a polite way to fuck off while they finish their work. Because if they stop work on their project in order to help you they would fall behind. So your example is pure bullshit.

Comment Re: Fake News (Score 1) 272

1. That was just an old theory, and not a widely accepted one.

2. Given what we've just seen, it demonstrably isn't.

That doesn't mean that there aren't compounds formed at great pressure that can remain stable at moderate pressures and represent very dense energy sources - there surely are. Metastability is a very real thing. But apparently not in the case of metallic hydrogen at ~STP.

Assuming that this actually even was metallic hydrogen; even that is somewhat in dispute.

Slashdot Top Deals

Live within your income, even if you have to borrow to do so. -- Josh Billings

Working...