The summer is half over, but the winner for my top read has already been determined. Orbital: A Novel, by Samantha Harvey, has enraptured me. It is a story about one day in the lives of a crew of six astronauts in low Earth orbit. We orbit with them, experience sixteen sunrises and sunsets, perform weightless tasks, but mostly, follow their inner monologues, which I would describe as meditations on nature and space.
The novel is a love letter to Earth and a prayer that we will learn to inhabit it with grace. Harvey describes the daytime view of Earth as "... the humanless simplicity of land and sea. The way the planet seems to breathe, an animal unto itself. It's the planet's indifferent turning in indifferent space and the perfection of the sphere which transcends all language."
Summer is a wonderful time to read this book. One thing I've always enjoyed about physics is how it opens up amazing conversations during late evening strolls, when the stars come out. At such times, with the Sun blocked out, we see the vastness beyond our atmosphere, and feel so very small. This sense of awe overcomes us. Orbital gives us this same feeling, but from a privileged vantage point some 400 km above our planet.
Many students have asked me if I would like to travel to space, and I tell them there's no point thinking about it because my wife wouldn't let me. The truth is that while I would love to see Earth with my own eyes from low Earth orbit, I do not think my body would enjoy the experience of weightlessness. Most amusement park rides are no-go zones for me now, which totally sucks, because they were a delight before I turned thirty.
It is not possible to experience weightlessness for a significant amount of time in our day-to-day lives, because along with Earth's gravitational force, we are always subjected to some other contact force (like the push of a chair onto our butt, say). An orbit is a perpetual state of falling; astronauts are falling along with the capsule they inhabit. The reason satellites don't fall down to Earth's surface is because they have a sufficient lateral speed (many km/s). A circular orbit maintains its constant speed because there is no atmosphere to slow it down, so round and round it goes.
Okay, quick tangent... Here's a fun little question that just came to me: Standing on the surface of the Moon, with its negligible atmosphere, how hard would I need to throw a rock for it to complete a full orbit and hit me in the back of my head? A quick application of Newton's second law leads to the result: v = sqrt(GM/R), where M and R are the Moon's mass and radius, respectively (G is the universal gravitational constant). Plugging values in, we get a speed of 1,680 m/s (over 6,000 km/h). I can't throw that fast, and in any case, would prefer not to get hit in the back of my head by a rock moving that fast.
Let's get back to the feeling of weightlessness. When you jump off of a diving board, you feel weightless from the moment your feet leave the board up until your body enters the water; a few brief seconds of weightlessness. I cannot fathom enduring that 'organs floating in the ether of my rib-cage' feeling for days, weeks, and even months, without a break, as astronauts do.
There really is no way to simulate weightlessness on Earth. Even skydiving does not replicate the sensation, because we quickly reach terminal velocity, where the upward drag force matches the downward weight force. Yes, we are falling, but we feel our weight. As far as your innards are concerned, it's like lying flat on your bed, only it is the air giving the steady upward push.
A compromise between the brevity of diving into a pool and, say, a 90-minute complete circling of Earth in a spacecraft, is a zero-g airplane, which cuts off its engine for about 22 seconds, during which its thrill-seeking passengers float around the cabin. It then repeats the parabolic maneuver many more times until someone pukes.
I guess I will have to be satisfied with musing about space. For this earthbound physics teacher, reading Orbital will have to suffice.
Wishing you a summer of blue skies and starry nights.
2 comments:
So, listening to Science Friday podcast about space elevator this morning got my attention, Started doing some research online and found your blog through article in Scientific American. Not a great student, engineer, or physicist, but very curious. Looking for a Professor Proton level explanation rather than a Sheldon Cooper answer. I grew up in the time of Carl Sagen's Cosmos series. Hoping you might want to answer some probably stupid questions about a space elevator.
Most of the available information on space elevators seems to be very high level about it being possible. I have not been able to find anything that describes the mechanics of how it would be built a the level of someone physically working on the project.
My big problem is understanding the mechanics of inserting a cable through the Karman Line interface at a point between the ground station and the geosync station. Do you simply tie the end of the cable to an outrageously large rocket, point it at the other end, and fire it to travel in a straight line between the two? Do you unravel it from the geo station moving it towards the ground station with a big weight tied to the end, and it just gently enters the atmosphere and falls to the ground? All my experiences with space involve launching to escape the atmosphere and enter earth orbit, so that can't be how it would be done because the cable would wrap around the earth. All the returns involve de-orbiting which involves high heat generating events.
So, would a cable hanging down from space generate the heat we see when a vehicle de-orbits?
And, since we would now basically have a huge straw between the earth's atmosphere and the vacuum of deep space, what prevents atmosphere being sucked into space?
I am a big Carl Sagan fan too. These are not 'stupid questions'... Regarding the placement of the cable, your second description where cable is slowly unspooled down from a mother satellite around GEO is the current leading proposal. Regarding the 'straw'... The space elevator poses numerous engineering challenges, but sucking atmosphere into space isn't one of them ;)
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