27 thoughts on ““Super” Planets”

  1. Kerbal Space Program demonstrates how much easier it is to launch from planets with 1/100 the mass of the Earth.

  2. I saw this story too. More fuel for the Science of Superman! There is some really interesting science behind the story of Superman. In the original story Krypton was very much like a Super Earth. It’s higher gravity and the Kryptonian’s adaptation to it were the source of super strength. This idea SHOULD have been a good argument against Kryptonian’s being a space faring species rather than the stupid Eradicator idea…

    Nonetheless a super big rocket isn’t a problem if you use powerful ground lasers to superheat water for fuel, combined with the traditional upper stage(s). But it would have put a dent in the progress of space travel vis-a-vis other technologies. A path we (fortunately) were blessed not to have to travel.

    An interesting parallel to Vernor Vinge’s faster than speed-of-light travel “zones” from his “A Fire Upon the Deep” series of books. The lower your gravity the quicker to space? Also having a nearby moon as a motivator?

    1. “In the original story Krypton was very much like a Super Earth. It’s higher gravity and the Kryptonian’s adaptation to it…” should have produced something much more like Hal Clement’s Mesklinites than the highly humanoid Superman and the other Kryptonians of that fictitious universe. The square-cube-law arguments against humanoid giants also apply against humanoids evolving on high-gravity worlds.

      1. I suppose (since this is all speculative anyway) if the Super Earth were only say at 1.5g up to possibly 2g I wouldn’t necessarily rule out humanoids, but they’d probably look different from Cro-Magnons in bone structure at least. But the Kent’s were eking out only a modest living in Kansas and couldn’t afford a whole body x-ray taken of Clark in the 30’s! Few could! (snicker).

        Then there is the question of atmospheric density. How that would effect lung development, etc. Assuming again nearly the same proportions of gases in the atmosphere, etc. Poor Clark was (mis)diagnosed as asthmatic as a child… 🙂

  3. Not just staging, but also refueling in a suitable low-orbit, and possibly using higher-Isp propulsion (SEP, beamed propulsion, etc) for getting from that low-orbit out to wherever it is you’re going.


  4. Another possibility is nuclear pulse propulsion, which would involve detonating a series of atom bombs behind a vehicle to hurl it through space. […] However, such a nuclear-powered spacecraft would pose not only technical challenges but political ones as well, he said.

    It’s fascinating how it’s always assumed that “they” are just like “us”, and share the same stupidities and prejudices.

  5. Gravity prohibits the ability to scale?

    I clicked over to the article and didn’t find anything saying that a planet’s mass could reach a point in which known methods of powering rockets (i.e. chemical reactions of common elements in the Universe) would be insufficient to life the rocket. Instead, the argument is it would cost more to do so. Why must that be true? Wouldn’t a planet with greater mass suggest a greater supply of materials to build a rocket and fuel it?

    I realize that greater mass means various elements will be found in other locations (heavier elements would be trapped deeper in the core and lighter elements more abundant on the surface). The article glosses over this to make a general statement on a subject absent based on simple relative size. Let’s keep in mind that if it is all relative, then larger sizes doesn’t inherently rule out proportional scaling.

    1. Something I haven’t done any research on, but perhaps many of the materials and mfg. methods we take for granted on Earth would be different on a Super Earth? I’d love to pour through the equivalent of a McMaster on a Super Earth. What are the tensile strength of materials used for construction of rockets? What are they alloys of? Maybe the holes you cast in various structural members aren’t as big? Maybe the alloy compositions are different? Maybe carbon composites came before aluminum and steel? That’s assuming the relative abundances of various minerals are roughly the same on a Super Earth as on Earth. This is truly fun speculation.

        1. The rail tracks would be wider apart because the hips on the beasts of burden would be wider, which would all be handy since the rockets are bigger.

          1. Are you invoking that trope that on account of rail transport, the size of the SRB was limited by a geometric factor from the width of a horse’s, um, “hips”?

          2. First, I humbled by the appreciation of others to my quip.

            Paul, nope. I wasn’t going there, because why would anyone still use SRBs? Especially why would anyone mix solid fuel with liquid fuel, so that you lose whatever benefit solid gives to on demand launch capability, and then carry the extra weight without cross-feed top-off capability of liquid stages? Have we not learned anything in this last year?

          3. It had been conjectured that the width of standard gauge railway tracks goes back to roads with wagon ruts, the spacing of which was determined by the back-leg stance of a horse.

            The “loading gauge” or “structural gauge” of a railroad network sets the maximum width of a railcar load, and this dimension does not have to fit between the spacing of the rails, but it is not much bigger than the spacing between the rails because there comes a point where the railcar is top heavy and risks tipping over on curves or from crosswinds.

            James Burke’s “Connections” also got a mention, where he delighted in establishing a bizarre set of “connections” between, don’t know, beer making in Henry VIII’s England and the atom bomb. In the spirit of James Burke, and he may have made that “connection” for all I know, the width of a horse’s backside established the width of the wagon ruts that in turn became railway “standard gauge” that in turn influenced the “loading gauge” that established the maximum size of an SRB segment shipped by rail that in turn constrained the performance of the Space Shuttle.

            Give me some space people, I am not a silly person, I am well aware that the External Tank, the largest item in the Space Shuttle launch “stack”, was made in a place called Michaud in Louisiana, from which said item could be shipped by barge all the way to the Kennedy Space Center, no railway line loading gauge need apply. I am not hinting that one should revert to the Space Shuttle’s use of solid rocket propulsion.

            It is just that it was speculated upon that one of the high-gravity planets would have stouter horses as well as bigger rockets, and I was asking if the author of that remark was suggesting that the purported connection between a horse’s backside and the SRB would “scale” in that high-gravity world.

  6. I’ve sometimes wondered if aviation on Earth would have started if the surface gravity was 20% stronger and/or the atmospheric pressure at the surface was significantly lower.
    Obviously not impossible to aviate under those circumstances with our current technology but getting started would have been MUCH more difficult.

  7. I’ve had a similar idea myself, that our Earth lies within a goldilocks zone of gravity and atmosphere within which chemical rockets can achieve spaceflight easily. Gravity and Atmosphere.

    Atmosphere? Think about it. An atmosphere not too thick to ruin rocket propulsion, but thick enough to use atmospheric heating to burn off orbital velocity and use parachutes for final landing.

    Getting up to orbit is just part of the spaceflight equation. Unless you are on a one way trip, what about getting back down to your planets surface? The delta V needed for a pure rocket solution to a 1 G planet is more than 15 km per second! An atmosphere is awfully convenient for reducing that delta V requirement by half.

    The origin of all that thought was years ago. I was thinking about travel to Mars in contradiction to all those JPL naysayers, who were decrying how difficult Mars is to land on and how much easier it would be if Mars were airless like the Moon.

    It occurred to me that Mars is actually a great planet for rocket flight for all the reasons I’ve just mentioned (in addition to the lower gravity of Mars). True enough, parachutes are useless for any spacecraft of larger size, but the near vacuum level pressure at the surface of Mars improves rocket engine ISP.

    And for all those JPL people who were worried about retro rocket function in a supersonic airflow if landing on Mars, well Falcon 9 booster recovery has convincingly demonstrated what a false fear that was!

  8. Staging has its limits if the source of energy is chemical. To orbit Jupiter at the top of the atmosphere requires 138,000 feet/sec velocity. not velocity change, which would be significantly more. But to do even this with a LOX/LH2 rocket with a specific impulse of 460 sec and a mass ratio per stage of 3, one would need a 22 stage rocket, with a small kick stage on top. An infinitely staged rocket (one with only payload and propellant, no intermediate structure) would require 11,207 pounds of propellant per pound of payload. The Shuttle needed only 15.96 pounds of propellant per pound of orbited mass (the Orbiter plus its payload).

    This is a perfectly sound article. I’ve been working on an analysis for quite some time to use variable gravity, planetary/radius, and/atmospheric profile, to determine at what point single stage to orbit becomes impossible using chemical propulsion. Earth is so close to the edge that I can’t as yet call it. Venus is impossible, mostly because of its atmosphere. The Moon…well, we’ve done it 6 times, so it’s proven. Mars…a snap. But the Earth teeters on the edge.

  9. We have the examples of Venus and Earth, having nearly the same surface gravity, with widely different atmospheric density.

    The lower-gravity on Mars is matched to a much thinner atmosphere. But Titan is smaller and has an atmosphere of about Earth thickness? Is it because of the extreme cold at that solar distance?

    Is there a lower bound on a surface gravity, making space launch easier, where that world would not have much of an atmosphere to support creatures breathing the air or having atmospheric pressure maintain gas partial pressures in their bloodstreams?

    1. You could say that alien beings might be able to function on an airless world, but if humans travel to another star system (say, by generation ships or in hibernation), a thick atmosphere would obviate the need for pressure suits, and a breathable atmosphere would be golden.

    2. The rate of escape of gases from an atmosphere is affected by several things. One is the molecular weight of the gases, another is the temperature at the exobase (the altitude at which the mean free path becomes comparable to the scale height), and another is whether the body is shielded from the solar wind or other plasma flows that can strip off ions.

      Titan’s exobase has a temperature of something like 160K, vs. about 1000K for Earth’s. This greatly helps retain gases. Even so, Titan is losing hydrogen, and over the lifespan of the solar system has lost a mass of atmosphere (to H2 escape, and simultaneous deposition of hydrocarbons produced from broken-down methane) estimated to be comparable to the current mass of the moon’s atmosphere.

      The temperature of the exobase is of course affected by the rate of energy input, but also by how effective the upper atmosphere is at radiating heat. That depends on what the gases are. Carbon monoxide, for example, will radiate much more effectively than, say, helium.

  10. I read Hugh Ross’ book Improbable Planet: How Earth Became Humanity’s Home and he presents what I consider to be a pretty compelling argument against life forming on any other planet…what happened here to enable the evolution of intelligent life, much less any form of life, was so rare that it never happened anywhere else in the universe. I know, the universe is a big place, but his arguments cover such a broad scope that by the end of the book I was convinced Earth is unique in this respect. Has anyone else read the book, what are your thoughts?


  11. The moon has 1/80th Earth mass and 1/6th the gravity.
    Neptune has 17 times Earth mass and escape velocity of
    23.5 km per second. And 11 m/s/s vs Earth 9.8 m/s/s.

    It seems it would matter what density of planet which was 10 times Earth mass.
    It could be a lot denser, and it could be 1/2 density and still be rocky.
    A large atmosphere would mean crew could need very high pressure, though large atmosphere could have floating cities and could use motherships for assisted rocket launches.
    A much denser planet might have much faster spin.
    A planet 10 times Earth mass could a moon or moons.
    It seems that generally it would be harder to leave and if have large atmosphere, they may not even know stars or planets exist.

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