The End of the Cassini Mission

Cassini Saturn Orbit Insertion.jpg

Yesterday morning, NASA’s Cassini spacecraft at Saturn was deorbited into the planet’s atmosphere in the Grand Finale of an epic 20-year mission. Cassini observed Venus, Earth, and Jupiter while it was in transit and has spent the past 13 years orbiting Saturn, taking constant observations of the planet and its moons. Even its fiery demise was not devoid of scientific value. As it made its final descent, Cassini was able to take the first direct measurements of the giant planet’s notoriously enigmatic atmosphere, reporting its finding back to Earth live to the very last second.

I’ve been with this mission not quite from the beginning, but absolutely since its arrival at Saturn. I remember being 14 years old and staying up until 3:00 in the morning of July 1, 2004 to watch the live stream of the original orbital insertion. And this was before YouTube, which feels hard to believe as I write it. If you’re too young to remember (something else that feels weird to write), internet video back then was sketchy at best, unusable at worst. Personally, I remember NASA TV’s online stream being unreliable well into this decade, but I’m happy to say they had worked the kinks out for yesterday morning as I watch the live stream of Cassini’s final act.

It may seem strange to end a mission that took 20 years and cost over $3 billion by crashing the spacecraft, but in fact, this is standard practice. Cassini was out of fuel, so it couldn’t be maneuvered anymore. NASA has strict rules about not contaminating other worlds that could possibly have life on them, even when it’s very unlikely. In fact, they are bound to this by the Outer Space Treaty. That means they don’t want Cassini flying around Saturn, out of fuel and out of control, where it could possibly crash into one of the moons, especially Enceladus, which is known to have liquid water and organic chemicals.

It’s theoretically possible that Saturn could have life in its atmosphere as well, but it’s much less likely, and the heat as Cassini burns up in the atmosphere should do a good job of sterilizing it…probably. Considering how much of the Space Shuttle Columbia made it through reentry, I’m not convinced, but it’s really the best option they have.

In any case, Cassini has been one of NASA’s great successes among its interplanetary missions. It has increased our knowledge of Saturn, its moons, and the entire Outer Solar System by leaps and bounds, all on the computer technology of the early 1990s. It’s sad to see it go, but it’s done a great job, and here’s hoping the next Outer Solar System missions, the Jupiter Icy Moons Explorer and the Europa Clipper, go just as well.

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What If? Rejects #7.2: Kisses

Previous post in this series: Thor’s Hammer

Next post in this series: Nuke it from Orbit!

Q: If you saved a whole life’s worth of kissing and used all of that suction on one single kiss, how much suction force would that single kiss have?

Randall’s response: No response.

My response: Um… I’m not entirely sure what this means, much less why. And how do you measure a kiss? Does duration count? Are we counting all kisses or just kisses on the lips?

Okay, Fermi problem time! We’ll have to make a few assumptions, but I think we can compute a “suction force.”

First, let’s say that we’re taking the average duration of an ordinary kiss for our one super-kiss instead of adding them one after the other. That sounds more in the spirit of the question. We’ll include kisses anywhere on the body, not just the mouth, but based on the wording, that is specifically kisses given, not received. Next, the question said “suction force”. There are two factors that go into the force exerted by a kiss: pressure and area of contact. An open-mouthed kiss will have both greater pressure and greater area of contact than a simple peck, so we’ll have to consider a wide range of both.

Now, how many kisses does the average person give over the course of their life? For that matter, how many kisses does the average person give per day? There’s going to be a big range there, too. For parents with babies, I’m sure it’s a lot. For tweens who are embarrassed by their parents, very few. Hormonal teenagers might not give that many, but they’ll probably rack up a lot of “suction force” when they do.

It will vary with the person, too. Does gender affect the number? Are husbands more likely to kiss their wives, or vice versa? Are mothers more likely to kiss their children than fathers? Are daughters of any age more likely to kiss their parents? Or alternatively, what about personality? Do extraverts give more kisses than introverts? What about nationality? If you’re in Europe, where kissing is a greeting, you might give several times as many kisses as here in America, where we like our personal space (although those are frequently air kisses, which probably shouldn’t count).

Let’s say the average human gives 100,000 kisses in their lifetime. That’s an average of 3.4 kisses per day over 80 years, which is probably good for an order of magnitude estimate. The majority of those will probably be closed-mouthed, so let’s say 10 square centimeters for the average area of contact. And let’s give them an average duration of 1 second. These are very rough numbers, but for a Fermi problem, they only need to be within a factor of 10, so they’re good enough.

Now, what about suction pressure? That’s a bit trickier and can also vary a lot. One important fact to keep in mind is that pressures in the human body rarely go above a couple of PSI, generally less than blood pressure. Any more than that, and you start to tear stuff that you don’t want torn. Since the large majority of kisses probably don’t put a lot of effort into suction, I’m going to lowball it. Let’s say 1 kPa, or about 1/7th of a PSI.

Let’s multiply these numbers together!

100,000 kisses x 0.001 m2 x 1 kPa x 1 s = 100,000 N*s

That’s 100,000 newton-seconds—that is, a suction force of 100,000 newtons (about 20,000 pounds) delivered for a period of 1 second.

Newton-seconds are a measure of momentum and, similarly, a measure of impulse (which happens to be how rocket engines are rated). 100,000 newton-seconds represents the momentum (note that this is different from kinetic energy) of a large car barreling down the highway at 100 miles per hour. It’s also the amount of impulse needed to launch a 10 kilogram satellite into space. Both of those are done by thrusting force, not suction force, and it neglects air resistance, but it gets the idea across. A lifetime of kissing represents a surprisingly large amount of suction. Use it wisely.

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Movie Review: Dunkirk

Dunkirk Film poster.jpg

France, 1940. A British army of 300,000 men is stranded on the beaches of Dunkirk. With the Luftwaffe bearing down on them and not enough naval forces to evacuate, England is desperate to bring just a tenth of them home to defend the homeland against the inevitable German invasion. The call goes out to send every civilian vessel that can cross the English Channel to bring the troops home, and many civilian sailors answer the call. The Royal Air Force sends what reinforcements they can, but they also have to maintain a reserve for when the Luftwaffe comes calling at the Battle of Britain.

Christopher Nolan’s newest film, Dunkirk, tells the harrowing tale of the evacuation of the British Army as only Christopher Nolan can. And I am happy to say that after the mess that was Interstellar, he is back in top form.

My rating 4.5 out of 5.

Dunkirk is a little tricky to follow, I admit, but it’s really masterfully done. It tells the story from three different perspectives over three different time periods in parallel: a week at the Mole (that is, the pier at the beach), where a trio of desperate soldiers are among the many trying to escape the Luftwaffe’s bombardment; a day on the sea, where an older Englishman and two boys take their private boat across the Channel to the beach; and an hour-long battle in the air between a pair of Spitfire pilots and a Luftwaffe bomber. As the movie progresses, all three stories converge in one dramatic moment.

I’m not usually a fan of war movies, but I really liked this film. Even though he’s hit-or-miss, I don’t think it’s an exaggeration to say that Christopher Nolan is one of the few true visionaries in this era of sequels and reboots. He manages to tell an engaging story while breaking all the usual rules. You don’t need linear time (this is one of the most non-linear movies I’ve ever seen). You hardly need any dialogue (there’s not much of it). And you don’t need to know the character’s names. (I honestly couldn’t tell you any of them with as little dialogue as there was, but unlike Rogue One, it didn’t detract from the story.) You can just experience the war as it happens, and it feels real enough.

And of course, I couldn’t talk about a Chris Nolan film without mentioning that he once again teamed up with Hans Zimmer for the music. Mr. Zimmer’s music is a constant presence, with almost every track, loud or soft, driven by the rhythm of the ticking clock, giving that much more of a sense of urgency to the story. It’s not as good as the Interstellar soundtrack, which I still consider possibly the best soundtrack of all time; and it’s perhaps not even as good as the Inception soundtrack, but it’s still some of his best work.

Dunkirk is an excellent film in terms of cinematography; it’s an important piece of history, and if you’re interested in either of those things, or you just like war movies, it’s well worth seeing.

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Movie Review: War for the Planet of the Apes

Caesar, with a rifle and Nova behind his back, on a horse with the film's logo and "Witness the End July 14" at the bottom.

The third installment in the latest Planet of the Apes series has come out, and the world has only gotten darker. By the time of War for the Planet of the Apes, Caesar, the genetically modified chimpanzee ruler of the apes, has been fighting a long war with the human survivors of the great plague that wiped out civilization. Now, a brutal human leader known only as the Colonel has found the apes’ hideout and is moving in for a final strike.

That’s how the story starts, but there’s a lot more to it—a complex plot, many references to other films, and thought-provoking questions raised about the difference between human and animal. Overall, I’d say it’s maybe not as good as the first film, Rise of the Planet of the Apes, but better than the second, Dawn of the Planet of the Apes, and well worth watching.

My rating: 4.5 out of 5.

Spoilers below.

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There’s a Solar Eclipse Tomorrow!

Image result for partial eclipse

In case you’ve been living under a rock, there is a total eclipse of the Sun tomorrow, and it’s going to cross the entire continental United States!

A solar eclipse is a once in a lifetime event. Any given location on Earth experiences a total eclipse on average once every 375 years, and they only visit the United States a few times per century. You do not want to miss this!

I’m not even going to bother explaining the science because it’s not about the science. It’s just awesome.

Eclipse Science

Personally, I’m currently sitting in Boise, Idaho for the Exoclipse astrophysics conference, and I’m getting up at 3:00 in the morning tomorrow to ride up to Weiser (pronounced “Wheezer”) to see it in person. It’s my first total eclipse, and that’s only because it’s the first one to hit the United States in my lifetime. (Although I did see the 1994 annular eclipse from my home in Ohio.)

The weather forecast for tomorrow is good along most of the eclipse path. So go out there, get to the path of totality, and go see it!

And if you can’t get to the path of totality, the Sun will still be at least 50% covered, so go see it anyway.

So get out your eclipse glasses. If you can’t get any eclipse glasses, you can use #14 welder’s glasses. If you can get those either, make a pinhole projector. Just don’t miss it!

But…if you absolutely can’t get out to see the solar eclipse tomorrow, don’t worry…There’s another one on April 8, 2024.

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What If? Rejects #7.1: Thor’s Hammer

Previous post in this series: Chainsaws

Next post in this series: Kisses

Q: In Thor, the main character is at one point spinning his hammer so fast that he creates a strong tornado. Would this be possible in real life?

Randall’s response: (Facepalm) “NO.” Also, a picture of a woman attempting to do this with a regular hammer.

My response: The main problem with this is not that you wouldn’t be able to generate wind by swinging a hammer around. You definitely could. (It wouldn’t be very efficient, but you could do it.) The main problem is that a hammer spinning in a circle is basically a propeller—or in other words, a fan. And fans don’t create tornadoes. They only create straight-line wind.

These giant fans are designed to create the winds of a Category 5 hurricane force for testing the integrity of building. The blades spin around incredibly fast, but the wind only moves in a straight line. Thor’s hammer doesn’t even have a tilted fan-blade shape, so it won’t even make a very good fan. It will still push air aside as it swings, so it will create some wind, but it won’t be a tornado.

Tornados are formed when the air is already rotating in a storm known as a mesocyclone. A mesocyclone is much larger than a tornado, large enough for its rotation to be driven by Earth’s rotation through the Coriolis force. Downdrafts in the storm drive the mesocyclone down to ground level and in the process compress it down to tornado size. This compression causes the mesocyclone to spin faster, reaching the hundreds of miles per hour of tornado-force winds.

Not only doesn’t Thor’s hammer not create rotating winds, but the problem is even worse than that. Instead of compressing a large cyclone down. Thor has to pour enough energy into a small vortex to make it grow into a full-size tornado. Even if that were possible, the sheer kinetic energy required and the subsequent heat generated would probably cause an explosion rather than a recognizable weather system. After all, a strong tornado can contain a kiloton of kinetic energy, and it would be difficult at best to transfer all of that energy from the hammer into the wind without destroying everything in the area with waste heat.

So no, swinging Thor’s hammer around at any speed will not create a tornado.

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Movie Review: Valerian and the City of a Thousand Planets

Valerian and the City of a Thousand Planets.jpg

Valerian and the City of a Thousand Planets is a French-made science fiction film based on the long-running French comics series, Valérian and Laureline. It was something a little different in the summer of superhero movies, post-apocalyptic fiction, and so forth, and even though it’s technically an adaptation, it’s refreshing change from the endless sequels and remakes.

Valerian has been regarded as a flop, but I actually liked it. Not only is it a refreshing change from the endless sequels, but it’s very optimistic in some ways, hearkening back to Star Trek and the “strange new worlds” sci-fi that we really don’t get enough of anymore. And even though Valerian is no Star Trek (it’s a typical action movie in space), it’s a fun movie to watch.

My rating: 4 out of 5.

Spoilers below.

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