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Sunday, October 30, 2011

Happy Halloween!

Have been offline last few weeks, and will be offline most of next week, so posting this a few hours before the 31st. Have a happy and safe Halloween, and a blessed Samhain to those who celebrate it.

Oh, and yes, this is a real pumpkin.

Fawkes News


You've probably already heard that the hacker collective Anonymous is promising to hack and shut down the Fox News website on Guy Fawkes Day, in response to what they perceive as unfair and unbalanced coverage of the Occupy Wall Street protests.

I'm not going to address the politics of this, interesting though they are. I'm also not going to address whether I think what Anonymous is planning is "right or wrong"; that is for the history books to decide. If you follow this blog at all, you know that I have very little patience for Fox News, and corporate news media generally. My issue with them is mostly their execrable science reporting. I also don't typically agree with the political bias of Fox News, but I staunchly defend their right to hold and express their political opinions, however erroneous. I also don't agree with a lot of the tactics or motives of Anonymous. So these are my own biases, but the politics of Fox News or Anonymous are not my real interest at the moment.

What I'm more interested in are the tactics behind the announcement Anonymous made. From a purely tactical standpoint it seems very weird to me that Anonymous would go to the great lengths it has to pre-announce the target and date of the attack.

To date, Anonymous has succeeded in about 50% of their attacks, which is respectable. But that indicates that while their hackers are very competent, they're not infallible. So if a massive crippling cyber-attack on the Fox News website were indeed being planned, it would seem to be in the best interests of Anonymous to stack the deck as much in favor of success as possible. A little stealth goes a long way. That the already paranoid Fox will now step-up their already substantial internet security is given.

Also given is that by pre-announcing the date and form of the attack, if Anonymous fails, everyone will know that, and Fox will make hay out of it. Without pre-announcing, the situation for Anonymous would be win-win; if the attack works, they get the credit, and if it doesn't, nobody is the wiser. But they've gone to a fair amount of trouble to ensure that this isn't the case. If Anonymous fails in their attack, they will do so famously, and their political capital goes way down.

Also, by pre-announcing the hack, they've ensured that many more people will visit the Fox News website that day, increasing Fox's advertising revenue. It occurred to me based on this that perhaps Fox WAS "Anonymous", and the whole thing was just a gimmick to get more traffic on the Fox News website. But Fox News doesn't seem to be covering it at all. And if the point of pre-announcing was to intimidate, it doesn't seem to be having much effect.

So, I'm left with only a couple of possibilities. One is that Anonymous is in fact planning a major cyberattack on Fox News for the 5th of November, and are so incredibly confident of their success that they're deliberately taunting the Fox cyber-security people. Which could be the case. The other possibility I can see, which would be rather more clever if it happened to work, is that Anonymous is counting on enough people going to the Fox News website that day to crash their servers. But that would probably require a rather larger ad campaign than what Anonymous has put forward so far.

So, we'll see what we see.

Friday, October 21, 2011

Celestial Navigation 101: Lesson 5, Objects in Motion (Introduction)

So far, we have looked at celestial objects as if they were more or less motionless in the sky. But with the exception of Polaris, nothing could be farther from the truth. The earth rotates on its own axis, causing the entire sky to appear to spin around it once every day. The earth revolves around the sun in an elliptical orbit once each year, and the other planets also revolve around the sun. The moon revolves around the earth, moving easterly relative to the stars. The stars themselves move relative to the earth and to one another. From our perspective this motion of the stars is minor, but not so minor that we can ignore it for our navigation.

I'll be on the water the next few days; when I'm back in front of a real computer we'll tackle the problem of how to determine the geographic position of a body in motion on a different body in motion.

Justice for All (who can afford it)

If you're still wondering what the 99% are yelling about, this would be it.

Wednesday, October 19, 2011

Ex-Meridians for USCG exams

This post is about celestial navigation, however it is most emphatically NOT part of the "Celestial Navigation 101" series. This topic is beyond the scope of even what we normally teach as "advanced celestial navigation". However, esoteric though it is, it shows up on USCG licensing exams for 1600 ton Mate Oceans and above. So this post is mostly intended for Oceans license candidates in the US Merchant Marine; however, it may have some interest for those working with celestial navigation generally. It happens that at work today I stumbled across a very simple way to solve ex-meridian problems, and so I thought I'd pass that along here.

We have not yet discussed Local Apparent Noon sights in the CelNav 101 series, so let me start with a very brief description of this. Local Apparent Noon, or LAN, is the moment when the sun crosses your longitude line. At that moment it is the highest it is going to be all day. Measure the altitude of the sun with a sextant at that moment, and then, comparing that altitude to the known Declination (latitude) of the sun, you can determine your own latitude. I'm going to explain this in more detail in the CelNav 101 series, but that's the gist of it.

The advantage of LAN is that it is a very easy sight to take with a sextant, and it is very easy to compute. That, however, is its only benefit. The fact that the Line of Position derived from it happens to be a latitude line is irrelevant, because it is as inherently flawed as any other LoP derived from a sextant sight. The real reason we teach LAN at all is that it is a good confidence-builder for fledgling navigators. Once the student masters basic sight-reduction, they never again have a need for LAN, because any celestial object at any time can give them just as much information as the sun can only one time each day.

The technique used to derive latitude from LAN can also, theoretically, be applied to any other celestial body when it crosses your meridian. There's no reason to do so, but it's possible.

These days we confidently rely on twilight sights of stars and planets to confirm our GPS only once each day. However, once upon a time, before the invention of GPS, the "noon sight" was a routine part of the navigator's daily work. If the navigator failed to obtain their noon sight, either due to cloud cover or simply not getting up on deck in time, this was a significant loss of navigational data. So methods were developed to allow the navigator to take a sight a few minutes after the sun had crossed the meridian, and still be able to derive a reasonable latitude from it. This is what is meant by an ex-meridian sight. Centuries ago, when computing a sight reduction required that spherical trigonometric calculations be solved long-hand, ANY celestial line of position which did not require that was an obvious benefit. Since the invention of logarithmic tables (and later calculators and computers) to perform the trig for us, this has not been the case. If a navigator happens to miss their noon sight, they simply take a sight of the sun at whatever time is convenient and reduce that into a line of position which is every bit as useful as an LAN derived latitude. Put another way, no modern navigator worthy of the name would ever use an ex-meridian sight, because a simple sunline is easier and far more accurate.

Except, of course, for USCG license candidates, who are expected to.

There is another CelNav technique on USCG exams which is basically useless and can be done more easily and accurately with another technique which is also required on the same exam. It's called an Amplitude, and is basically a means of computing the azimuth to an object without getting into the spherical trig necessary to compute an azimuth. But with sight-reduction tables or calculators, azimuths are simple, and we have to be able to use them anyway. So the easy way to avoid dealing with amplitudes on a USCG exam is to simply work amplitude questions as azimuth problems.

It turns out that you can do exactly the same thing with ex-meridian sights. Simply compute it as a normal sight-reduction. Because the sights are necessarily either nearly north or nearly south, the intercept can be applied directly to the Assumed Latitude or DR Latitude to derive the latitude of the ex-meridian. That's all.

Here's an actual example from the USCG database. In it they're asking to compute your latitude from the meridian transit of the star Dubhe, in the Big Dipper.

-- On 8 May 1981, in DR position LAT 30°26.0'N, LONG 46°55.1'W, you take an ex-meridian observation of Dubhe. The chronometer time of the sight is 11h 10m 54s, and the chronometer error is 01m 18s slow. The sextant altitude (hs) is 58°35.0'. The index error is 1.5' on the arc, and your height of eye is 44 feet. What is the latitude at meridian transit?

a) 30°12.5'N
b) 30°19.8'N
c) 30°27.6'N
d) 30°35.8'N

30°19.8'N (answer b) is correct. However, if I simply do this as a standard sight reduction (cheating and using a StarPilot calculator, but the result is the same regardless), I get 6.2' Away from 358° T, from my DR latitude of 30° 26.0'N. Since my ex-meridian sight is always going to be essentially north or south of me, I simply subtracted my intercept from my AP (actually DR in this case) and get 30° 19.8'.

In this case it works out to be exactly right, but even worst case it can't possibly be enough off to lead me to pick any of the other answers.

So if you are taking a USCG Oceans Master or Mate exam, you can effectively NOT study the Amplitude or Ex-Meridian methods and still do fine on those questions, so long as you know how to compute a simple sight-reduction. Incidentally, you can also use your sight-reduction method to determine great-circle courses and distances.

At some point soon we'll do a comparison of the two or three leading methods of computing a standard sight-reduction.

Saturday, October 15, 2011

Strait of Magellan safely circumnavigates the sun

I'm working on the water tomorrow (Sunday) and so won't be able to post. But it's 2320 on the 15th now, so I'm actually jumping the gun by 40 minutes or so, in order to get to bed.

That said, Strait of Magellan is one year old today. Believe it or not.

Friday, October 14, 2011

Fortuna Rota

In an earlier post about outmigration, I suggested that a classic Stanford torus space station design could be landed onto the surface of Enceladus in such a way that it would spin like a top, generating artificial gravity for its inhabitants.

A few of you have requested that I elaborate a bit on this idea, but I really don't have a lot to elaborate with. The research for a Stanford torus in space has been done exhaustively. In order to effectively mimic earth's gravity, a Stanford torus is a 1.8 km diameter ring turning at one revolution per minute. A torus this size could provide sustainable habitat for some 10,000 people.

Enceladus has a surface gravity of 0.011% of earth's, meaning something as small as a human would be essentially weightless, but gyroscope nearly 2 kilometers in diameter would presumably have enough mass to keep it "on the ground". The surface of Enceladus is fairly featureless ice, so creating a more or less frictionless stylus for the torus to pivot on should be manageable.

Enceladus has relatively vast resources of fairly accessible seawater and heat energy, although we don't yet know what the source of that energy is. So, that's my idea about putting a torus colony on Enceladus.

Discuss.

;)

Celestial Navigation 101: Lesson 4, Sextant Sights

Continuing with the basic introduction to celestial navigation, we now look at how we're going to actually use the sextant to determine the angle of the celestial object above the horizon. I've made a number of illustrations in MS Paint to illustrate what you will see through the sextant telescope. This was fairly simple. I have not, however, created corresponding illustrations of the sextant itself, either as a whole, or illustrating reading the limb or micrometer drum. I did attempt to render such illustrations in Paint, but doing so proved beyond my skill level. Hopefully their absence will not prove a stumbling block.

For this lesson I will assume that we are using a sextant with a traditional split-horizon mirror, but the principles are the same with a whole-horizon mirror also.

When you begin a round of sextant sights, you must first determine the amount of intrinsic error the alignment of the index mirror will instill into your sights. For a good metal sextant you might perform this step once every several days; for a plastic sextant you'll want to do this before and after every set of sights.

Set your sextant index arm to 0° 00.0'. Then look at the horizon. You will see something like this:


Now, adjust the index arm until the two images come together like this:


Now look at your index arm, and micrometer drum if your sextant has one. Unless your sextant is perfectly aligned, you will now read some number larger than 0° 00.0', either "on" the sextant arc between 0° and 90° or 120° or whatever number your sextant goes to, or else "off" the sextant arc beyond zero in the other direction. Which side this Instrument Error is on, you are going to correct your Height Shot (Hs) of the celestial object in the opposite direction. Think of it being like a jacket; if it's on, take it off, and if it's off, put it on. This opposite value of the Instrument Error is called the Instrument Correction, or IC. Write this number down, you'll be using it in all of your calculations later.

Now, move the index arm out toward the middle of the arc, somewhere around 40° is fine. Now looking at the horizon, on the index side of the mirror we see only sky:


Now, the sun has set and civil twilight has ended. We have precomputed that the star Capella bears about 043° True at an altitude of about 52° above the horizon. We dial 52° into the sextant index arm and aim the sextant toward the northeast horizon. And, by the miracles of astronomy and arithmetic, we find in our sextant telescope this:


Which is pretty darned impressive, considering.

You now, using the micrometer drum, bring Capella down until it just barely touches the horizon:


And to ensure that you are holding your sextant exactly vertical, you rock it back and forth so that the image of Capella also rocks back and forth. You want to measure the angle at the exact moment (very exact, remember four seconds of time is one nautical mile) that Capella barely kisses the horizon in lowest portion of the rockering.


That's all there is to taking a star sight with a sextant. Bring the star down to the horizon, mark the time, write the time down in your notebook, read the angle you shot off of the sextant limb and micrometer drum and then write those down next to the time. That's it.

The sun is mostly the same, with two exceptions. First, we have to use filters so that staring at the sun through a telescope doesn't burn out our retinas. In this case, the filter has made the sun appear purple.


Using the micrometer drum, bring the sun down so that the very bottom of the disk of the sun, called the Lower Limb, just touches the horizon. I haven't drawn it, but rock the sun just like you did with Capella. Because the sun is very bright, you will usually get a "ghost" image of the sun on the side of the horizon mirror that is not a mirror. It's perfectly fine to utilize this image.


If the sun is reflecting brightly on the water, you may need to use a filter on the horizon as well. In this example, the filter for the sun is dark purple and the filter for the horizon is light green. This incidentally is fairly common.


In almost every single case, you will use the Lower Limb of the sun whenever you shoot it. However, when you shoot the moon, depending on its phase and position in the sky you will sometimes need to shoot the Lower Limb and at other times you will need to shoot the Upper Limb, like this:


In most cases, the visible disk of planets are so small in a sextant telescope that you can simply treat them as points of light like a star. If the visible disk of a planet is large enough that you can easily discern an upper and lower limb, align the horizon with the center of the planet. Pictured here is Jupiter, with three of the Galilean moons visible:


That is really, really, all there is to it. Oh, except that I forgot to mention that the celestial body you're shooting happens to be moving.

More on that, soon.

Monday, October 10, 2011

Puny Little Ants


"You let one ant stand up to us, and they all might stand up! Those 'puny little ants' outnumber us a hundred to one. And if they ever figure that out, there goes our way of life! It's not about food. It's about keeping those ants in line."

News flash, Mr Cain. The puny little ants have figured it out.

Friday, October 7, 2011

Faster than light


Last week CERN announced that they had observed neutrinos to be traveling faster than the speed of light in a vacuum. I seem to recall Fermilabs finding similar (although inconclusive) results a couple years ago.

I realize it may be asking too much of particle physicists to stoop so low as to ask for help from an astronomer. But it turns out that the astronomy community has been aware for quite some time that when a star goes supernova, the neutron stream from that reaches earth some significant amount of time (minutes or hours, not nanoseconds) earlier than the light from the same event does. It has been previously assumed that the neutrinos were somehow being released earlier than the light, which may still be true. But if instead the time lag is due wholly or partly to neutrinos traveling faster than the light, then the further away the supernova is, the greater the timelag should be. That should be a pretty easy lookup for somebody. I may look it up myself this weekend, but I'm at work and my lunch break is rather short.

Here's the CERN press release, for those who have only heard this from Fox News:

OPERA experiment reports anomaly in flight time of neutrinos from CERN to Gran Sasso
Geneva, 23 September 2011. The OPERA1 experiment, which observes a neutrino beam from CERN2 730 km away at Italy’s INFN Gran Sasso Laboratory, will present new results in a seminar at CERN this afternoon at 16:00 CEST. The seminar will be webcast at http://webcast.cern.ch. Journalists wishing to ask questions may do so via twitter using the hash tag #nuquestions, or via the usual CERN press office channels.

The OPERA result is based on the observation of over 15000 neutrino events measured at Gran Sasso, and appears to indicate that the neutrinos travel at a velocity 20 parts per million above the speed of light, nature’s cosmic speed limit. Given the potential far-reaching consequences of such a result, independent measurements are needed before the effect can either be refuted or firmly established. This is why the OPERA collaboration has decided to open the result to broader scrutiny. The collaboration’s result is available on the preprint server arxiv.org: http://arxiv.org/abs/1109.4897.

The OPERA measurement is at odds with well-established laws of nature, though science frequently progresses by overthrowing the established paradigms. For this reason, many searches have been made for deviations from Einstein’s theory of relativity, so far not finding any such evidence. The strong constraints arising from these observations makes an interpretation of the OPERA measurement in terms of modification of Einstein’s theory unlikely, and give further strong reason to seek new independent measurements.

“This result comes as a complete surprise,” said OPERA spokesperson, Antonio Ereditato of the University of Bern. “After many months of studies and cross checks we have not found any instrumental effect that could explain the result of the measurement. While OPERA researchers will continue their studies, we are also looking forward to independent measurements to fully assess the nature of this observation.”

“When an experiment finds an apparently unbelievable result and can find no artefact of the measurement to account for it, it’s normal procedure to invite broader scrutiny, and this is exactly what the OPERA collaboration is doing, it’s good scientific practice,” said CERN Research Director Sergio Bertolucci. “If this measurement is confirmed, it might change our view of physics, but we need to be sure that there are no other, more mundane, explanations. That will require independent measurements.”

In order to perform this study, the OPERA Collaboration teamed up with experts in metrology from CERN and other institutions to perform a series of high precision measurements of the distance between the source and the detector, and of the neutrinos’ time of flight. The distance between the origin of the neutrino beam and OPERA was measured with an uncertainty of 20 cm over the 730 km travel path. The neutrinos’ time of flight was determined with an accuracy of less than 10 nanoseconds by using sophisticated instruments including advanced GPS systems and atomic clocks. The time response of all elements of the CNGS beam line and of the OPERA detector has also been measured with great precision.

"We have established synchronization between CERN and Gran Sasso that gives us nanosecond accuracy, and we’ve measured the distance between the two sites to 20 centimetres,” said Dario Autiero, the CNRS researcher who will give this afternoon’s seminar. “Although our measurements have low systematic uncertainty and high statistical accuracy, and we place great confidence in our results, we’re looking forward to comparing them with those from other experiments."

“The potential impact on science is too large to draw immediate conclusions or attempt physics interpretations. My first reaction is that the neutrino is still surprising us with its mysteries.” said Ereditato. “Today’s seminar is intended to invite scrutiny from the broader particle physics community.”

The OPERA experiment was inaugurated in 2006, with the main goal of studying the rare transformation (oscillation) of muon neutrinos into tau neutrinos. One first such event was observed in 2010, proving the unique ability of the experiment in the detection of the elusive signal of tau neutrinos.

Monday, October 3, 2011

Tiger, tiger, burning steadily


The above is a raw, unprocessed photo from the Cassini flyby of Enceladus on Saturday. No data yet on the actual surface temperatures or energy outputs from the Tiger Stripes, but it is clear from this and other photos from this series that whatever the energy source is, it has not diminished significantly.

Curiouser, and curiouser.

Sunday, October 2, 2011

SpaceX Falcon 9 fully reusable rocket system


$50,000 per launch, with a payload of significantly more than 5,000 kg. That's, oh, let's see, carry the five...$10 per kilogram. Total weight of myself, my clothes and a well-stuffed carry-on probably 100 kg. That's $1000 to get into orbit, before considerations of administrative costs and profit margins. That's comparable to a round-trip commercial flight from Seattle to Tokyo.

There seems to be an over-reliance on the use of retrorockets for landings. This makes sense for landing the capsule itself on worlds other than earth (which seems to be the intent). It seems counterintuitive to me for the first stage booster, when a parachute would presumably require less space than the fuel needed for the retrorockets. But SpaceX has lots of experience already with parachute recovery, so I'm assuming the retrorockets are actually a better solution.

But Elon Musk seems very focused on using this technology for large-scale outmigration to the moon, Mars and beyond.

100 kilograms into space for $1000. If this works, and it very well may, this is a complete game-changer.

SPACE.COM--

The private spaceflight firm SpaceX will try to build the world's first completely reusable rocket and spaceship, a space travel method that could open the gates of Mars for humanity, the company's millionaire CEO Elon Musk announced Thursday (Sept. 29).

A fully reusable rocket would dramatically decrease the cost of lofting cargo and humans to space, making the exploration and colonization of other worlds such as Mars more feasible, Musk said in a speech at the National Press Club in Washington, D.C.

Musk did not guarantee success, acknowledging the daunting task his SpaceX team has taken on. SpaceX released a video animation of its proposed reusable rocket and space capsule system to illustrate how it would work.

"We will see if this works," Musk said. "And if it does work, it'll be pretty huge."

The hunt for an economic and reusable method for space travel has been a goal of many companies and government agencies from the Space Age's inception.

The only reusable manned spaceships built to date have been NASA's winged space shuttles, which were retired this year. The shuttles used reusable orbiters and solid rocket boosters for 30 years, but the system was not completely reusable.

Each of NASA's 135 shuttle missions also used a disposable 15-story external fuel tank. The tank was jettisoned once a shuttle reached orbit and ultimately burned up during re-entry.

Going to Mars?

Musk has said repeatedly over the years that he founded SpaceX in 2002 with the primary goal of helping humanity establish a lasting presence beyond Earth. Such expansion is necessary to ensure our species' survival, according to Musk, since a catastrophic asteroid strike or other calamity could one day wipe out life on our home planet.

Mars is a prime candidate for human settlement, and Musk has said he hopes SpaceX can send astronauts to the Red Planet within 10 or 20 years.

Colonizing Mars — or any other world — would require ferrying thousands of people and millions of tons of cargo through space. That's just not feasible with today's launch costs, Musk has said.

But a fully reusable rocket could change the equation dramatically. Musk illustrated the point by citing SpaceX's Falcon 9, which costs between $50 million to $60 million per launch in its current configuration.

"But the cost of the fuel and oxygen and so forth is only about $200,000," Musk said."So obviously, if we can reuse the rocket, say, a thousand times, then that would make the capital cost of the rocket for launch only about $50,000."

In its video new animation, SpaceX officials detail how their new launch vehicle, which is based on the Falcon 9 rocket, would work.

After separating in orbit, the two stages of the rocket would come back to Earth and land at the launch pad. The stages would not glide back using wings like the space shuttle; rather, they'd descend vertically, eventually settling down on four legs.

They could then be refueled, reintegrated and relaunched.

In the video, the Falcon 9 launches SpaceX's Dragon capsule to the International Space Station. NASA has contracted the company to make cargo flights to the orbiting lab.

Falcon 9 lofted Dragon to Earth orbit for the first time last December, and SpaceX had been planning to launch a demonstration mission docking Dragon to the station in January 2012. SpaceX officials announced late today (Sept. 30) that the firm could be ready to launch the next Dragon test flight by Dec. 19, but that target is still awaiting review by the U.S. Air Force and NASA.

Whenever that demo launches, if all goes well, Dragon's next flight would be an operational cargo mission to the space station, SpaceX officials have said.

Dragon is also designed to be reusable, and SpaceX is modifying it to carry crew as well as supplies. The company hopes NASA eventually uses Dragon to launch its astronauts to low-Earth orbit. The country has lacked this capability since NASA's space shuttle fleet retired in July and currently depends on Russian Soyuz vehicles to provide this taxi service.

Musk did not say when he hopes the reusable rocket would be operational, or how much its development would cost. But SpaceX is going to give the enterprise its best shot.

"We have a design that on paper — doing the calculations, doing the simulations — it does work," Musk said. "Now we need to make sure those simulations and reality agree because generally, when they don't, reality wins."