For every Southern boy fourteen years old, not once but whenever he wants it, there is the instant when it’s still not yet two o’clock on that July afternoon in 1863, the brigades are in position … and it’s all in the balance, it hasn’t happened yet … and that moment doesn’t need even a fourteen-year-old boy to think This time. Maybe this time …

— From “Intruder in the Dust” by William Faulkner

One hundred forty years ago today, General George Pickett and his gallant men made their tragic charge up Cemetary Ridge, thousands of men died uselessly (half of his division), and the Confederate cause began to unravel.

The fall of Vicksburg to Grant the next day would sunder the South, and these two events in early July, in Pennsylvania and Mississippi, would lead inexorably to the defeat of the rebellion.

Mark Steyn, who’s been observing from across the border in New Hampshire for years, says that Howard Dean (sadly, for those Bushophiles who’d love to see him as an opponent) won’t survive the south.

The Chicken Littles at the WaPo are wringing their hands (in glee, since they’ll think it will hurt Bush’s approval ratings) over the June unemployment numbers, which increased to 6.4% (a number that used to be considered relatively low during previous downturns).

Isn’t it just terrible for all of those recent college graduates, new on the job market, to see unemployment spiking just as they’re seeking work?

(And yes, lest anyone ask, that is indeed sarcasm at the WaPo’s ignorance of the seasonality of last month’s number.)

The Chicken Littles at the WaPo are wringing their hands (in glee, since they’ll think it will hurt Bush’s approval ratings) over the June unemployment numbers, which increased to 6.4% (a number that used to be considered relatively low during previous downturns).

Isn’t it just terrible for all of those recent college graduates, new on the job market, to see unemployment spiking just as they’re seeking work?

(And yes, lest anyone ask, that is indeed sarcasm at the WaPo’s ignorance of the seasonality of last month’s number.)

The Chicken Littles at the WaPo are wringing their hands (in glee, since they’ll think it will hurt Bush’s approval ratings) over the June unemployment numbers, which increased to 6.4% (a number that used to be considered relatively low during previous downturns).

Isn’t it just terrible for all of those recent college graduates, new on the job market, to see unemployment spiking just as they’re seeking work?

(And yes, lest anyone ask, that is indeed sarcasm at the WaPo’s ignorance of the seasonality of last month’s number.)

Evan Coyne Maloney talks about the democratizing effects of open-source media.

My Fox column is up, but it’s basically the same 4th of July piece as the post a couple down, on rockets and freedom.

This is interesting (and possibly dismaying for solar sail fans). Thomas Gold says that they won’t work, at least not the way people have had in mind.

Basically, he contends that none of the analyses of their performance has taken into account thermodynamics–that they only consider the momentum change of the photon. The sails are built to be as reflective as possible to minimize heating of the fragile sail fabric. But according to Gold, if no heat is absorbed (i.e., no temperature change in the photon), the Carnot’s Rule says that no energy can be extracted.

It’s been too long since my thermo courses to know if he’s right or not, but he’s not obviously wrong. Considering that people have been thinking about this for decades, I find it a little surprising that the physics remains unsettled. We’ll find out when the first demo sails are flown shortly, and we’ll see if the performance matches predictions.

[Update at 11:26 AM PDT]

There’s been a lot of discussion in the comments section, but considering the source (Henry Spencer, over at sci.space.*), I’ll consider this the last word for now.

A *moving* perfect mirror *does* reduce the “temperature” of photons reflected from it — by Doppler shift! Where does the energy lost in Doppler shift go? Into added kinetic energy of the mirror.

(If the mirror is held stationary — relative to the observer who is measuring the details — by some means, then there can be no Doppler shift. But there is also no work done on the mirror, since work is thrust times *distance*, and hence there is no added kinetic energy.)

Yes, Doppler shift at ordinary velocities is pretty damn small. But so is the acceleration produced by light pressure.

Gold appears to be unaware that the physics of light pressure are well understood and have been demonstrated many times — in the laboratory, in precision tracking of spacecraft, and in attitude control of spacecraft. A particularly glaring example is Radarsat 1, which is in a dawn-dusk sun-synchronous orbit (i.e. essentially continuous sunlight) and flies with an essentially constant attitude. Its designers overlooked solar-sail effects on its big solar arrays and radar antenna, which are slightly tilted with respect to the Sun for engineering reasons. Turns out that nearly 2/3 of Radarsat’s stationkeeping fuel goes to fight light-pressure drag — it’s trying to sail down into the atmosphere. See “Radarsat Time Rate of Mean Semi-Major Axis Due to Drag”, by Said R. Marandi, in the AAS/GSFC 13th International Symposium on Space-Flight Dynamics, 1998.

Note that the experts consulted for the article were a thermodynamicist and an astronomer, neither of them a physicist. (Citing the Crookes radiometer is just plain embarrassing — it turns by thermal effects, not by light pressure.)

Well, certainly in theory both thermodynamicists and astronomers are supposed to have a good grounding in physics (and arguably, the former is a specialized form of physicist), but other than that bit of ad hominem, I’ve nothing to dispute.

[One more a few minutes later]

OK, Geoff Landis has also weighed in.

Unfortunately, Gold has apparently forgotten to account for a well-known physical effect: the Doppler shift.

It’s worth saying that the photon pressure on a spacecraft is not theoretical; its effect on spacecraft is measurable, and it has been observed and measured to great precision routinely in space. Photon pressure– the solar sail effect– has already been used for an operational space mission; it was for spacecraft attitude control on the Pioneer Venus-Mercury mission.

The Crookes radiometer does not operate on photon pressure, and the explanation for how it operates has been known for over a century.

The energy transfer to a solar sail can be accounted for from the Doppler shift of reflected photons; even when the reflectivity is 100%, a photon looses [sic] energy when reflecting from a moving sail. This effect exactly corresponds to the energy increase of the sail. No sophisticated physics is needed to analyze this effect, it is a problem suitable for a homework assignment for a college undergraduate.

When the sail is moving, then the reflected photons are Doppler shifted, and leave the sail with lower energy than they arrived. This loss of energy exactly equals the energy imparted to the sail, a fact which can be trivially verified by using Newton’s laws, the Doppler formula, and the Einstein equation for photon momentum p=E/c.

If the sail is not moving, there is no Doppler shift. However, note that since energy is proportional to momentum squared, the derivative of energy with respect to momentum is zero for a non-moving sail. Thus, when the sail is stationary, it can reflect photons with perfect efficiency and still gain momentum at no energy cost.

For completeness, note that if the sail is moving *toward* the light source, then the phtons [sic] are Doppler shifted to *higher* energy by the reflection. This implies that the sail must lose energy– which is correct; when the sail moves toward the light source, it slows down.

As we celebrate the 227th anniversary of our country’s formal declaration of independence this coming Friday, it’s always useful to review how we’ve evolved since then as a nation.

While I’d be the last to urge anyone to forego the barbecue and beer, and other festivities that have become de rigeur in recent years, I also believe that the event is one to be commemorated, as well as simply celebrated. Which is to say, that I urge all to take a few moments, as sadly too few do, and print out and read (or hopefully reread) Thomas Jefferson’s work of genius, and reflect on why so many died then, and since, to preserve the idea that we have certain “inalienable rights.”

In light of current events, it’s also useful to remind ourselves that “…whenever any Form of Government becomes destructive of these ends, it is the Right of the People to alter or to abolish it, and to institute new Government, laying its foundation on such principles and organizing its powers in such form, as to them shall seem most likely to effect their Safety and Happiness…”

Along those lines (I’ll explain why in a moment), there is another activity in which we partake on this date that is both a celebration and a commemoration. As dusk approaches, we settle in to watch a display of pyrotechnics that are at once not just awesome and beautiful, but a stark reminder of the price that must often be paid for freedom, in blood and treasure. In fact, it is memorialized in the words of our national anthem, by Francis Scott Key.

Of course, the rockets that we enjoy in our celebration are closely related to some of the weapons of war by which we won our liberation then, and in fact, for decades, and even today, still represent the ultimate weapon when tipped with nuclear warheads. Fortunately, yet more rockets are being developed that may finally render such devices relatively impotent.

But rockets have peaceful uses as well, and not just for fireworks displays. For decades, many young people (including yours truly, back when I was a young person) have built and flown model rockets, often as a prelude to a later career in aerospace engineering. Today, the sport has evolved to the point at which amateurs are about to actually launch payloads into space. The most common propellant for solid-propulsion model rockets is ammonium perchlorate composite propellant (APCP).

Sadly, the misnamed “War on Terrorism” (“terrorism” is a tactic, not an enemy–we are actually at war with radical Islam and Arab nationalism) is about to claim this hobby as another victim. The newly-formed Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATFE–formerly the Bureau of Alcohol, Tobacco and Firearms) managed to slip something called the “Safe Explosives Act” into the broader Homeland Security Act signed by President Bush last fall. In it, APCP became a controlled substance, and rocket motors containing more than 62.5 grams of it (only a couple ounces) were essentially reclassified as explosive devices.

This is a misclassification over which the rocketry community has been fighting the agency since APCP first mistakenly appeared on the list of explosives back in the ’70s, and they’ve never been able to get them to remove it, despite pressure from sympathetic legislators. For example, in a letter to the ATFE director, Senator Mike Enzi (R-WY) wrote:”Congress defined an explosive as any chemical mixture or device whose primary or common purpose is to function by explosion. I am told that the ATF claims that the primary or common purpose of a rocket propellant (i.e., ammonium perchlorate composite propellant) is to explode. A rocket propellant is not designed or intended to explode.”

The agency continues to refuse to budge, however. An attempt has been ongoing to get a regulatory exemption for the hobbyists through legislation. Such legislation (Senate bill S724) has been approved by the Senate Judiciary Committee, but it continues to place undue restrictions on model rocketry in terms of allowable propellant loading, and it only exempts APCP, leaving open the possibility that ATFE could restrict other (perhaps safer and more effective) propellant types in the future by placing them on its explosives list.

The Justice Department, predictably, is fighting such a change, but their stated fears of home-made anti-aircraft and anti-tank weapons, and their misunderstanding of the difference between detonable and non-detonable APCP are, frankly, laughable to anyone who actually understands the technology.

When it comes to decisions with potential implications for public safety, it’s natural for a bureaucrat to want to err on the side of caution, but there are often unintended consequences (e.g., my point that it might actually make it more difficult to develop safer propellants). There are no risk-free choices, and in a free society, we must often make compromises of security versus freedom. In a sense, that’s what the “War on Terror” is all about–how to maintain the proper balance. If our freedoms become too restricted as a result, then it can truly be said that the “terrorists win.”

Ignoring the fact that the hobby of building model rockets has created at least a couple generations of rocket engineers, some argue that still, it is “just a hobby,” and can’t justify the possibly increased risk to the public welfare of reducing restrictions. Given the political response, perhaps it’s been a mistake for the hobbyists to paint their endeavors as harmless and educational, because other than the obligatory “pursuit of happiness,” there’s no apparent constitutional right to entertainment and hobbies.

Ironically, if they were to return to their roots, and proudly proclaim their projects as weapons, then perhaps they could find a sympathetic court under the Second Amendment.

In any event, as we watch the rockets fly on Friday, we should reflect and be thankful that we haven’t yet lost the freedom to view the fireworks with which we celebrate all of our freedoms.

As we celebrate the 227th anniversary of our country’s formal declaration of independence this coming Friday, it’s always useful to review how we’ve evolved since then as a nation.

While I’d be the last to urge anyone to forego the barbecue and beer, and other festivities that have become de rigeur in recent years, I also believe that the event is one to be commemorated, as well as simply celebrated. Which is to say, that I urge all to take a few moments, as sadly too few do, and print out and read (or hopefully reread) Thomas Jefferson’s work of genius, and reflect on why so many died then, and since, to preserve the idea that we have certain “inalienable rights.”

In light of current events, it’s also useful to remind ourselves that “…whenever any Form of Government becomes destructive of these ends, it is the Right of the People to alter or to abolish it, and to institute new Government, laying its foundation on such principles and organizing its powers in such form, as to them shall seem most likely to effect their Safety and Happiness…”

Along those lines (I’ll explain why in a moment), there is another activity in which we partake on this date that is both a celebration and a commemoration. As dusk approaches, we settle in to watch a display of pyrotechnics that are at once not just awesome and beautiful, but a stark reminder of the price that must often be paid for freedom, in blood and treasure. In fact, it is memorialized in the words of our national anthem, by Francis Scott Key.

Of course, the rockets that we enjoy in our celebration are closely related to some of the weapons of war by which we won our liberation then, and in fact, for decades, and even today, still represent the ultimate weapon when tipped with nuclear warheads. Fortunately, yet more rockets are being developed that may finally render such devices relatively impotent.

But rockets have peaceful uses as well, and not just for fireworks displays. For decades, many young people (including yours truly, back when I was a young person) have built and flown model rockets, often as a prelude to a later career in aerospace engineering. Today, the sport has evolved to the point at which amateurs are about to actually launch payloads into space. The most common propellant for solid-propulsion model rockets is ammonium perchlorate composite propellant (APCP).

Sadly, the misnamed “War on Terrorism” (“terrorism” is a tactic, not an enemy–we are actually at war with radical Islam and Arab nationalism) is about to claim this hobby as another victim. The newly-formed Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATFE–formerly the Bureau of Alcohol, Tobacco and Firearms) managed to slip something called the “Safe Explosives Act” into the broader Homeland Security Act signed by President Bush last fall. In it, APCP became a controlled substance, and rocket motors containing more than 62.5 grams of it (only a couple ounces) were essentially reclassified as explosive devices.

This is a misclassification over which the rocketry community has been fighting the agency since APCP first mistakenly appeared on the list of explosives back in the ’70s, and they’ve never been able to get them to remove it, despite pressure from sympathetic legislators. For example, in a letter to the ATFE director, Senator Mike Enzi (R-WY) wrote:”Congress defined an explosive as any chemical mixture or device whose primary or common purpose is to function by explosion. I am told that the ATF claims that the primary or common purpose of a rocket propellant (i.e., ammonium perchlorate composite propellant) is to explode. A rocket propellant is not designed or intended to explode.”

The agency continues to refuse to budge, however. An attempt has been ongoing to get a regulatory exemption for the hobbyists through legislation. Such legislation (Senate bill S724) has been approved by the Senate Judiciary Committee, but it continues to place undue restrictions on model rocketry in terms of allowable propellant loading, and it only exempts APCP, leaving open the possibility that ATFE could restrict other (perhaps safer and more effective) propellant types in the future by placing them on its explosives list.

The Justice Department, predictably, is fighting such a change, but their stated fears of home-made anti-aircraft and anti-tank weapons, and their misunderstanding of the difference between detonable and non-detonable APCP are, frankly, laughable to anyone who actually understands the technology.

When it comes to decisions with potential implications for public safety, it’s natural for a bureaucrat to want to err on the side of caution, but there are often unintended consequences (e.g., my point that it might actually make it more difficult to develop safer propellants). There are no risk-free choices, and in a free society, we must often make compromises of security versus freedom. In a sense, that’s what the “War on Terror” is all about–how to maintain the proper balance. If our freedoms become too restricted as a result, then it can truly be said that the “terrorists win.”

Ignoring the fact that the hobby of building model rockets has created at least a couple generations of rocket engineers, some argue that still, it is “just a hobby,” and can’t justify the possibly increased risk to the public welfare of reducing restrictions. Given the political response, perhaps it’s been a mistake for the hobbyists to paint their endeavors as harmless and educational, because other than the obligatory “pursuit of happiness,” there’s no apparent constitutional right to entertainment and hobbies.

Ironically, if they were to return to their roots, and proudly proclaim their projects as weapons, then perhaps they could find a sympathetic court under the Second Amendment.

In any event, as we watch the rockets fly on Friday, we should reflect and be thankful that we haven’t yet lost the freedom to view the fireworks with which we celebrate all of our freedoms.