Social Media in Space with Chris Hadfield

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About This Episode

Are you one of the millions of people who watched Chris Hadfield sing David Bowie’s Space Oddity while floating in the International Space Station? Now you can learn what it’s like to be an astronaut in the age of social media when Neil deGrasse Tyson interviews Canadian astronaut and former ISS Commander Hadfield. But that’s not all: frequent StarTalk guest Astro Mike Massimino, the first person to Tweet from space, joins Neil and co-host Eugene Mirman in studio to discuss his two Space Shuttle missions to repair the Hubble Telescope. Explore the different routes Chris and Mike took to get into space: one became a test pilot, the other studied engineering. But both used social media to share what they were doing in orbit with the rest of us down here on Earth. You’ll also find out why national distinctions mean less on the International Space Station than they do at home. Finally, the conversation turns to the Mars Curiosity Rover, and Bill Nye extols the value and the adventure that come with the human exploration of space.

NOTE: All-Access subscribers can listen to this entire episode commercial-free here: Social Media in Space with Chris Hadfield.

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  • Thinking out Loud: Zero G vs. Microgravity

    This interview was featured on a recent episode of StarTalk on the National Geographic Channel. In that episode, a brief flurry ensued regarding Zero G and NASA’s use of an alternate term, microgravity. That flurry got me to thinking.

    Keep in mind: this is literally me thinking out loud. I have done zero research on these thoughts.

    Am I remembering correctly that most (or all) satellites, including the ISS, have boosters to maintain their orbits? If so, does that not imply that there is, in fact, gravity (or some other force) acting on these satellites? So, mathematically, yes, it is possible to fire a cannonball from the surface of the earth so that it stays in orbit and achieves Zero G. However, because of some physical irregularity (shifting of the center of gravity, perhaps?), it is impossible to achieve Zero G in practice and, thus, the use of the term microgravity.


    • Firing boosters would be “acceleration,” not “gravity.” See my comment about how “microgravity” exists in every object.

      • Bruce Kamiat

        Another factor is drag. Friction with even the tenuous atmosphere that extends to those altitudes does slow the craft, so they need an occasional boost to maintain their momentum.

        • Agreed. They need to fire boosters occasionally to maintain orbital speeds, and they need to fire their vernier thrusters from time to time to keep their instruments pointed in the right direction. But neither type of rocket firing has anything to do with microgravity.

  • During the one part of the show, no one seemed to recall why NASA talks about “microgravity” when something is in orbit. Has everyone forgotten that there is gravity in EVERY object? So, while an astronaut is in orbit, he may be in a balance of forces between his velocity and gravity from the earth, but it is NOT “zero gravity.” He is still being drawn to the space ship by the space ship’s gravity, and the space ship is still being drawn to the astronaut by the astronaut’s gravity.

  • Dave K

    During this episode, I was surprised at the intensity in the zero-gravity vs micro-gravity remarks which included the question “what is the difference”. Here, for better or worse, is one attempt to explain the distinction.

    In short: a Zero-g environment does NOT exist. However Micro-g and “other-g” environments do exist. The perception of relative “g-induced” motion is associated, not with gravitational forces, but with gravitational tides. Since gravitational tides are present everywhere in the physical universe, zero-g environments are precluded.

    To understand this, first consider the classic Newtonian theory, in which gravity is represented as a 3D vector field whereby every point in space is associated with a strength and a direction of the gravitational force.

    A true “zero-g” environment is categorized as an environment (volume) throughout which the gravitation force field is *uniform* (not zero). A uniform field, in which all the gravitational forces are aligned in the same direction and have the same magnitude at all times will accelerate all objects identically, irrespective of their individual masses. This is what is meant by the concept of a “zero-g” environment.

    As an example, consider a blob of water in this hypothetical uniform field (and isolated from extraneous effects such as air currents, etc). In a zero-g environment, the effects of surface tension (and mutual gravitational attraction of the water molecules) will shape the blob into a perfect sphere. The shape will be unaffected by gravity because the uniform gravitational field accelerates every particle in the water identically the same. In a true zero-g environment, this sphere will be truly spherical with a precision of shape measured as individual atoms on the surface.

    However, to realize this condition, the gradients of the gravity field must be zero (i.e. the definition of uniform). In practice, this is an idealization that can not be realized.

    For the physical universe, the gravitational field in all regions of space exhibits a non-zero gradient. There are idealized theoretical constructs which produce a uniform gravity field (e.g. inside of a spherical shell), however, in the real world, no matter where you go, there be non-zero gravitational field gradients. At a minimum, the observer and the object being observed (two ingredients necessary for a physically real situation) have a mutual gravitation which can not everywhere be canceled.

    The non-zero gradient in a gravitational field produces an effect known as “tides”. In near Earth orbit, for example inside the space station, Earth generally has the largest tidal influence (short of holding a large exceptionally dense object very near to the water blob). The tidal effect means molecules of water on the Earth side of the blob molecules will feel a slightly stronger gravitational pull and will try to move into a faster lower Earth orbit compared with the center. Molecules on the far side of the blob will feel less of a pull and try to move into a slower (higher orbit). This will stretch the otherwise spherical blob into an elongated prolate ellipsoid shape. I.e. in the physical reality of an Earth orbital environment, the blob of water will be “stretched” a bit such that it is no longer spherical.

    The effect of this stretching is quite small – on the order of parts per several million for near Earth orbit. Therefore, one might say the blob is a “micro-deformed” sphere instead of a true sphere. Hence by association, one might say that the near-Earth environment is a “Micro-g” environment instead of “Zero-g” one.

    Now consider other locations in the universe and consider travling outward from Earth. As one leaves Earth orbit, after a short while Solar tides will begin to dominate. However, eventually, Micro-g environments will give way to “Nano-g” and then “Pico-g” ones. However, ultimately one then begins to get closer to some other star and star tides will increase again. Ultimately, somewhere in intergalactic space between galactic superclusters, tides will be very small indeed. However, they will still not be zero, and hence the environment will still be “Non-Zero-g” and be only an approximation to the theoretically ideal concept of zero-g.

    In the general relativistic formulation, gravitation is replaced by a theory of the curvature of space-time. The curvature of space-time within a local environment is a function of the mass and energy density within that region. To have a true zero-g environment would require a region of zero curvature, and therefore a region containing no mass nor energy. However, this is not the case for the physical universe. As a simple counter example, consider the cosmic microwave background radiation which permeates all of space and time. This energy albeit small, is everywhere. Thus, every local environment has some space-time curvature, and hence there are no zero-g environments in the universe.

  • Bob Kerman

    Movie soundtracks eh? Maybe The Wrath of Khan soundtrack?

  • Jess Ho

    Hi, StarTalk team!

    Is it possible for someone to go about requesting an autograph from Dr. Tyson? Would it be at all possible for me to send in one of Dr. Tyson’s books or a photograph to some address for a signature? I’ve followed his work for several years now, and have been catching up on StarTalks for a couple months, but have been unable to meet him in person yet.


  • Krzysztof Kotarba

    In eastern europe we do not trust people who do not drink… I’m not talking about heavy drinking but even casual social drinking.

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