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Rockets versus space elevators.  Space elevators versus rockets.  From listening to altspace conversations on the subject, one could be forgiven for thinking that these are the only two ways to achieve orbit and beyond.  But the reality is much more interesting.  Follow me below the fold for more.

After SpaceX just completed their first successful Falcon 9 flight, the old conversations started back up -- "Now we need to move beyond rockets to space elevators, the logical next step"  However, space elevators are hardly the only non-rocket game in town.  In this diary, we shall explore some of the possibilities.

First, let us explore the "rocket-like" vehicles and those that still require significant rocket stages for more than just a kick or OMS stage.  By comparison, a conventional rocket is:

Tech readiness: 9/9
Development/Research cost: high
Launch cost per unit payload: very high

Aircraft-assisted launch

There are a variety of methods with which an aircraft can launch a spacecraft.  This is actually a fairly mature tech; the Pegasus rocket is launched in this way.  Use of an aircraft gets the rocket past the atmosphere, reducing its drag and allowing its engine(s) to be optimized for space.  It provides it a small amount of orbital velocity.  And perhaps most importantly, it lets you launch your craft from virtually anywhere, which reduces legal liability and red tape and facilitates equatorial launches.  A rocket can be:

  1. Carried under the wing of a conventional craft.  This limits rocket size to whatever will A) not unbalance or overly strain the craft, B) not drag along the ground, and C) fall within the aircraft's carrying capacity.
  1. Internal stowage in a conventional craft.  Experiments have been done in this regard.  A parachute pulls the rocket out of an open cargo bay, it falls, drops the chute, then fires.  The rocket size is limited to A) what will fit inside the craft, and B) fall within the aircraft's carrying capacity.
  1. Carried under the body of a custom-designed twin-fuselage aircraft.  This is the approach of the suborbital "SpaceShipOne".  The rocket is limited to A) what will not drag along the ground, and B) what falls within the aircraft's carrying capacity.
  1. Mid-air refueling.  As proposed by "Black Horse" and "Black Colt".  A pure rocket or hybrid rocket/airbreathing craft takes off with minimal fuel, docks midair with a fueling tanker to transfer fuel and/or oxidizer, then fires rockets to orbit.  The advantages of this approach versus just taking off fully loaded is that A) an airbreathing craft (airplane) carries your fuel to altitude for you, and B) you can use much lighter landing gear and structural supports if you don't have to bear the full weight of the vehicle on the ground.
  1. Tow launch.  Like mid-air refuelling, but the rocket is towed to altitude by the fueling tanker, then refuelled.  The advantage of this approach is that it eliminates the need for a midair docking.

There's one big problem to aircraft-assisted launch: namely, the carrying capacity of aircraft.  The pegasus rocket uses four stages and can only get a tiny payload to space.  SpaceShipOne is merely suborbital, and nowhere close to orbit.  You need a very favorable combination of stages, a low payload, a high ISP, and an extremely large aircraft to make aircraft-assisted launch work.

Tech readiness: 9/9
Development/Research cost: high
Launch cost per unit payload: high


Conventional ramjet operation does not work at extreme speeds.  As the airflow inside a ramjet reaches supersonic velocies, internal shockwaves make sustaining a combustion front impossible.  A scramjet burns its fuel at supersonic velocities, using one of a range of techiques (for example, using a small amount of a hypergolic fuel such as silane to maintain combustion).  While scramjets bear very poor lift to drag ratios, the incredible ISP advantage they offer from airbreathing operation makes them intriguing.  A popular variety of scramjet is the "waverider", in which the "engine" has only one side; the other side is virtual, formed by the shockwave of the spacecraft itself.

Scramjets cannot operate at very low speeds and cannot achieve orbit on their own.  Various scramjet hybrids or stages have been proposed.

Tech readiness: 2/9
Development/Research cost: very high
Launch cost per unit payload: medium-high

Skylon (SABRE)

The SABRE engine concept is a successor to the (less likely plausible) LACE concept.  In LACE, incoming air is chilled by the liquid hydrogen fuel in order to liquefy the oxygen component.  This oxygen is then burned with the liquid hydrogen fuel in a rocket engine.

The problem with LACE is that it requires a tremendous amount of liquid hydrogen be brought onboard in order to cool the air, and more to overcome the extra vehicle drag.  SABRE, by contrast, is a "rocket engine/precooled air turboramjet".  In each engine, small turbine/compressor accelerates the vehicle to ramjet speeds, where a ram takes over compression.  At higher speeds, the liquid hydrogen fuel is used to cool, but not liquefy, the incoming air.  This should allow the engine to near the maximum theoretical velocity for a ramjet -- Mach 5.5 -- as well as operating at high altitudes.  

SABRE is to be used on an innovative launch vehicle called Skylon.  The large mass of hydrogen and low mass of oxidizer gives the vehicle a high surface area to mass ratio, which simplifies reentry heat shielding requirements. The very high ISP of atmospheric operation allows the vehicle to be an SSTO; combined with horizontal takeoff and landing, its turnaround time and maintenance should be low.  For the development process, probably the best example to look to is the SR-71 Blackbird; Skylon is 2x larger, 1.5x the speed under turbojet power, 3x the takeoff weight, and 1.3x the cruising weight.

Tech readiness: 3/9
Development/Research cost: very high
Launch cost per unit payload: medium-high

From here, we'll get into the less rocketlike launch mechanisms.  First, ballistic launch mechanisms.  Note that all ballistic launch mechanisms need a kick stage to circularize their orbits (if not outright reach orbital velocity), and most are unsuitable for launching living payloads.


Straight out of Jules Verne, this technology is surprisingly well-developed, and much of the story of it traces back to one man: Gerald Bull.  Bull was a researcher with a knack for two things: brilliant artillery innovations and ticking off his superiors.  Many of his innovations are still used in top-of-the-line artillery systems, such as giving shells a small rocket engine that fills in their low-pressure wake with its exhaust to reduce drag.  Bull managed to get a project going called HARP, in which they connected multiple naval guns end-to-end, smoothed out the bores (in favor of self-expanding fins on the projectile), perfected sabot launch, and demonstrated that not only could they provide a good chunk of a projectile's delta-V, but that they could do it without damaging sensitive electronics systems.

Unfortuantely for Bull, despite getting projectiles up to half of orbital velocity, his funding was soon cut.  He continued his artillery research as a private corporation, but served six months in jail for exporting weapons to South Africa -- something that he had previously been permitted to do.  Bitter, he left the US and decided to sell his services to the highest bidder (anyone but the Russians).  He found a buyer in Saddam Hussein, and commissioned the Babylon Supergun project; Hussein's fee for funding the project was assistance with his missile program, which Bull provided.  This work in particular likely led to Bull's assassination in 1990, by individuals largely suspected to be tied to the Mossad.

A related program for a supergun traces back to World War II.  The Germans created a special cannon: the V3.  It used multiple successive charges and incredibly precise timing to continue boosting the projectile -- a difficult technique called "blast acceleration" later tested by HARP.  It proved an ineffective weapon, as it was very easy to target.

Tech readiness: 4/9
Development/Research cost: medium
Launch cost per unit payload: medium

Ram accelerator

A ram accelerator takes an entirely different approach to the problem of the force on a projectile dropping as it goes down the barrel.  Instead of repeatedly boosting back pressure, they make the shell of
the projectile shaped like the core of a ramjet and fire it down a tube of fuel-air mixture.  Thus, the core accelerates tremendously as it travels, with the thrust always behind it.  Mixtures with progressively higher speeds of sound are used, separated by thin membranes, down the length of the barrel; this helps the ram keep the flame behind it burning properly, as ramjets perform poorly at hypersonic speeds.

Tech readiness: 4/9
Development/Research cost: medium
Launch cost per unit payload: medium

Light gas gun

A light gas gun is a conventional gun which deals with the problem of maximum acceleration of a projectile due to its speed of sound in a different manner: rather than having the exhaust of an explosive accelerate a projectile, the explosive compresses a large ram, which presses a light gas like hydrogen against the projectile.  The much higher speed of sound allows for higher barrel exit velocities.

Tech readiness: 4/9
Development/Research cost: medium
Launch cost per unit payload: medium


The Slingatron is a concept that proposes to use a spiral-shaped tube with the payload beginning in the center, which is shaken around in a cylindrical motion to spin the projectile along the walls of the tube until it emerges out of the spiral with high velocity.

Tech readiness: 1/9
Development/Research cost: high
Launch cost per unit payload: medium-low


A railgun uses two charge-carrying rails with opposite polarity over a long track.  These create strong magnetic fields.  The projectile forms a conductive path between them, developing its own magnetic field tangential to that of the tracks.  This propels the projectile down the track.

The primary downside to railguns is heavy wear on the rails at high velocity.

Tech readiness: 4/9
Development/Research cost: medium
Launch cost per unit payload: medium-low to medium


A coilgun addresses the wear problem with railguns: there are no rails to wear.  Coilguns are comprised of a series of electromagnetic coils which are activated in sequence such as to attract a projectile on approach and repel it upon departure.

The primary disadvantage to coilguns for spacecraft launch is high-speed switching.  The coil needs to be brought from no current or an inverted flow to a full flow in the desired direction in a tiny fraction of a second, with split-second timing.  

Tech readiness: 3/9
Development/Research cost: medium
Launch cost per unit payload: medium-low

Now, off to the old altspace favorite: structures in tension!

Space elevator

Ah, the space elevator -- the old sci-fi fallback!  What could be more romantic than a giant technological beanstalk to the stars?  Part of it (climbers) is simple enough that college students can compete on designs, furthering interest.  Travel is low-G and, unlike ballistic launch, does not suffer from extreme atmospheric drag.

Unfortunately, space elevators have a number of huge problems.  The first one is tensile strengh.  Technically, you can make a space elevator with any tensile strength.  But to make one practical, you need a tensile strength of at least 100GPa, and preferably 120GPa or more, with the density of graphite.  Single-walled carbon nanotubes have been theorized to be that high with that density, but the strongest ones ever measured are barely over 60GPa.  And these are individual tubes; the strength of bulk fabrics is far lower than that of its component fibers.  The tubes form ropes held together weakly by pi bonding and van der waals force.  These are themselves strung together to form fabrics.  Achieving 10GPa at the density of graphite on a fabric that long would be quite the feat.  100GPa may ultimately prove to be be physically impossible.

Even if you can achieve this, the safety margins in space elevators are appallingly low, with countless threats to their integrity.  The transit time in the radiation belt is high.  And recent simulations show that space elevators may likely be dynamically unstable.  While space elevators are electrically powered, which is quite efficient, they have to transmit that power from the surface to the climbers.  Small-receiver power beaming is grossly inefficient over the distances involved -- single-digit percent.  Sadly, I cannot endorse this beautiful concept.  The one thing I can say in their favor is that, contrary to popular perception, a falling space elevator poses no threat to anyone.  By their very nature, they must have extremely low mass per unit length.  A space elevator tether falling on you won't hurt any more than a nylon stocking falling on you.

Tech readiness: 1/9, possibly 0/9
Development/Research cost: very high
Launch cost per unit payload: medium-low

Skyhooks and Rotavators

A skyhook is basically an undersized space elevator.  By virtue of not having to reach all the way to earth, their tensile strength requirements are reduced.  Unfortunately, so is their utility.  One must fly up to the base of the skyhook, achieve its relative velocity (often a good chunk of orbital velocity), then climb it.  And, since the skyhook isn't tethered to the ground, it must re-boost itself back to its original position.

A rotavator is a skyhook which rotates around its axis.  This allows it to have a lower tip speed at the base.  It still needs reboost, but some designs allow for returning payloads to provide the reboost.  Rotavators require precise timing in their operations.

Both skyhooks and rotavators may suffer from the same dynamic instabilities affecting zero-gravity zero-atmosphere high-tension tethers that affect a space elevator.

Tech readiness: 2/9 at best
Development/Research cost: high
Launch cost per unit payload: medium

We will now discuss kinetically-suspended launch structures.  They provides the potential for use as both a space launch track and a large energy storage system.  Because of this, unlike a space elevator, there are much lower power losses during the acceleration of a vehicle, allowing for the cheapest possible access to orbit.

Space fountain

The best way to understand the space fountain, and all kinetically-suspended structures, is to picture it this way.  Imagine you've got a falling plate overhead and you've got a basketball.  You throw the basketball upwards at the plate before it hits you.  The ball bounces off the plate with greater velocity and the plate flies back upwards.  It starts to fall again.  But you throw the basketball again.  If your aim is flawless, you can keep the plate roughly suspended in the air.

Now, imagine that your basketball was automatically routed back upwards toward the plate -- instead of you throwing it, it simply took a loop.  Imagine that your system was lossless.  Your plate will hover without any additional energy input.

Now let's make it practical.  Instead of basketballs, you use a continuous stream of particles in a near-vacuum.  At the top is a magnet that redirects them back downward, reversing their velocity and accelerating them back to Earth.  At the bottom is another magnet, as well as a cyclotron that re-accelerates the particles to compensate for any system losses (which there always will be).  You now have a tower suspended in air with no unusual tensile strength requirements -- just a relatively low constant input energy.  This is a space fountain.

Like most kinetically-suspended structures, it provides the potential for use as both a space launch track and a large energy storage system.  Because of this, unlike a space elevator, there are virtually no power losses during the acceleration to orbit.

Tech readiness: 2/9
Development/Research cost: high
Launch cost per unit payload: low to medium, depending on how orbital velocity is reached in space.

Launch loop

The "Launch Loop" is a particularly interesting kinetically-suspended structure.  A long loop of iron at the equator spins rapidly inside an evacuated tube.  Its centrifigual force supports it to reach up to near space, while weighted cables shape it into a track for acceleration to orbital velocity.  The evacuated tube ends in space, where it is no longer needed.  The tube is kept separated from the loop by magnetic levitation.  Craft are launched atop the tube/track by magnetic acceleration against the spinning ribbon (approximately 50% efficient).

Unlike the space fountain, the Launch Loop naturally provides a long track for steady acceleration to orbit.  Like all kinetically-suspended structures, it stores a great amount of energy; however, its length gives it an additional use (power transition).

I personally find the Launch Loop proposal the most promising for dramatic launch cost reductions.  Loftstrom's calculations suggest that a $30B loop could launch 6 million tons to Low Earth Orbit per year at a stunningly low cost of only $3/kg.  No exotic materials required.

Tech readiness: 2/9
Development/Research cost: high
Launch cost per unit payload: low


Are these the only non-rocket ways to get to space?  Hardly!  But they're a nice starter.  Who knows how we'll utimately move beyond our planet, but there certainly are plenty of possibilities.

I'll leave you now with Carl Sagan and Stephen Hawking singing A Glorious Dawn":

Originally posted to Rei on Sat Jun 05, 2010 at 12:46 PM PDT.

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Comment Preferences

    •  Re (15+ / 0-)

      This is my first space diary; if there is interest, I may write more in the future.

      Out of curiosity, how does one leave a custom tip jar?  I've seen other diaries do this.

      •  Tip jars are automatic (2+ / 0-)
        Recommended by:
        JeffW, leftykook

        Space elevators are a mega disaster waiting to happen. There's a lot of mass tied up in such a beastie and if it starts to fall nothing's going to stop it.

        •  Mass (8+ / 0-)

          That's actually a misconception, popularized by science fiction.  While the elevator may have significant total mass, this is spread over many tens of millions of meters.  Anything above a break will raise up instead of falling down; only the lower end will fall.  The further you get from GEO, the less mass there is per unit length.  So the net result is that a space elevator has to be incredibly light per unit length.  It's not something that's going to cause significant damage upon failure.  Now, the climbers, on the other hand... that'd be like having a rocket capsule land on you.

          The real problem is that it may well be physically impossible, both from a stability perspective and a materials perspective.  And due to the problem of long-distance power transmission, it's very inefficient.  The kinetically-suspended structures provide for much more efficient, more stable, and technologically feasible routes to space.

          •  And Maybe Absolutely Necessary (2+ / 0-)
            Recommended by:
            G2geek, palantir

            The kinetically-suspended structures provide for much more efficient, more stable, and technologically feasible routes to space

            We cannot have hundreds of launches per year regularly dumping exhaust pollution into the upper atmosphere if we want to have a sustainable space-development program. We must hatch up some sort of cockamamie (but viable) scheme for dealing with the pollution issue, and the kinetic devices offer a way to reduce our in-atmosphere rocketry.

            I'm pretty confident we can develop systems that involve docking with a moving target, a KC-10 refueling a C-5 involves two aircraft that weigh a half a million pounds each flying twenty feet apart for 30-40 minutes, and they do it regularly. (The pilots sweat bullets)

            "Ronald Reagan is DEAD! His policies live on but we're doing something about THAT!"

            by leftykook on Sat Jun 05, 2010 at 01:40:20 PM PDT

            [ Parent ]

          •  Benford wrote one of the pioneering stories (3+ / 0-)
            Recommended by:
            HeyMikey, G2geek, Bill White

            ...back in the '80's, and even tho it's "scifi", Benford was a highly educated fellow who did actual sciency stuff when he wasn't scribbling stories... The point I'm trying to make is that he spent a lot of time and effort working out the framework of the engineering involved, he didn't just pick some ideas out of his butt and build a story around them....

            An interesting, maybe eerie fact about this subject is that Clarke and Benford independently wrote their stories and their publishers released the books within days of each's like the meme popped up simultaneously in different writers at almost the same moment....weird!

            "Ronald Reagan is DEAD! His policies live on but we're doing something about THAT!"

            by leftykook on Sat Jun 05, 2010 at 02:08:27 PM PDT

            [ Parent ]

            •  Indeed (2+ / 0-)
              Recommended by:
              G2geek, leftykook

              Back then, a lot of the problems with space elevators hadn't been thoroughly studied.  Ignoring the materials issues, some of the significant stability problems have only arisen in the past few years.  Nowadays there are papers being written suggesting things like having the climbers regularly reverse their velocity and things like that to try to dampen the oscillations (making the energy consumption and transit time problems worse, and they're still not sure it'll address all of the oscillation modes).  But authors in the past can hardly be faulted for not knowing these things.

              You could certainly design a space elevator in a book that is heavy enough to cause problems on collapse.  But such an elevator would have an implausibly high total system mass.  The 730k kg 130GPa, 20,000kg payload "Edwards" elevator is only 7 grams per meter on average, and more like 4 or 5 near near the surface.  If it took, say, an average 1kg per meter to cause a problem, with the same parameters, your elevator would have to weigh 100,000,000kg, and more at the surface.  If you have a different taper factor (due to more realistic materials, for example), to get that density near the surface, the actual total mass would have to be 2x to dozens or even hundreds of times that.  And 1kg per meter of cable (under a pound per foot) wouldn't be all that devastating -- if you wanted a real disaster, you'd need hundreds or thousands of kilograms per meter.  So you're looking at many trillions or quadrillions of kilograms of total space elevator mass.

              In short, it's not impossible to cause a space elevator catastrophe, but it'd involve an elevator far more massive than anyone is seriously proposing to build.

              Either way, a space elevator does not appear to be, technologically, a good idea.

              •  I wonder about my assumptions about cost.... (2+ / 0-)
                Recommended by:
                G2geek, Rei

                ...what if the 20,000 KG-load elevator turned out to be relatively cheap; if it were cheap enough you just build more of them!

                I mean, the mission-planners for the ISS would probably crap themselves from delight if we told them we were gonna send up 20,000 KG of stuff every week....

                (I wonder if you could "drop off" loads someplace other than the very top of the Stalk...wouldn't an object released from the cable at less that full height actually be going too slow for the speed needed for the actual orbital altitude?)

                (And you could release stuff from the upper end of the cable end weight when the earth's pointed the way you want and it would have a certain speed right out of the box!)

                "Ronald Reagan is DEAD! His policies live on but we're doing something about THAT!"

                by leftykook on Sat Jun 05, 2010 at 04:40:47 PM PDT

                [ Parent ]

                •  Elevators, etc (1+ / 0-)
                  Recommended by:

                  Yes, if you drop something off at below GEO, it ends up in an elliptical orbit.  Drop it off low enough and that orbit intercepts the atmosphere and decays rapidly.  Drop it off higher than GEO and it's also an elliptical orbit.  Higher still and it escapes.

                  Of course, it's all relative.  If you have the budget to justify a 20k kg elevator, then you also have the budget to justify orders of magnitude greater throughput via other mechanisms, such as launch loops.  

                  Not like building any space elevator is realistic under our current understanding.  Earth-based space elevators require practically impossible materials and low safety factors to achieve any remotely reasonable taper factor and total mass, are unstable, have numerous risk factors, long transit times, low throughput compared to system mass, and very low efficiency (and thus much higher prices than other systems).

                  •  I've been pretty impressed by... (1+ / 0-)
                    Recommended by:

                    ...Bolos and Loops that are spun in orbit, then are lowered into the atmosphere where a spacecraft latches onto the end of it...

                    There were several Fact articles in Analog about ten years ago that were pretty much analogs of your diary, discussing other means of getting vehicles into orbit, they discussed the loop and bolo ideas at some length....

                    They also haad a discussion of using The Biggest Friggin' Laser in the World along with Star Wars aiming technology to provide power for a steam-powered rocket, you have a rocket that only carries water as reaction mass and a big heating plate/target that you point the laser at...

                    "Ronald Reagan is DEAD! His policies live on but we're doing something about THAT!"

                    by leftykook on Sat Jun 05, 2010 at 07:22:07 PM PDT

                    [ Parent ]

                    •  I assume you're referring to rotavators. (0+ / 0-)

                      I covered those in this diary.

                      Our experiments thusfar with space tethers really haven't gone very well.  There have been big problems with induced currents and with propagating oscillations (there's nothing to damp them).

                      I mulled over taking time to include laser-based propulsion (there are a number of different methods), but I decided I didn't want the diary to get too long.

            •  weird stuff (2+ / 0-)
              Recommended by:
              Rei, leftykook

              Given one or more pieces of information "X" that are picked up by a large number of human minds at roughly the same time (e.g. a news story or peer-reviewed paper read by many readers).  

              Now take the background information "Y" that each reader brings to bear on the new pieces of information, and produce a synthesis: a new idea "Z".  

              Consider various subsets of readers, whose background information we can sort into categories, Y1, Y2, Y3, and so on:  X plus each of these will lead to new ideas accordingly, Z1, Z2, Z3, and so on.

              Now let's take similarly trained writers with similar background that we'll call Y2.

              These writers will tend to hit on idea Z2 at roughly the same time.

              Now we take a subset of those trained writers, and notice that they are working out the implications of idea Z2 and seeking to publish.  

              Eventually some further subset of those writers publish, and if one assumes a similar degree of "inertia" each one has to overcome in order to get a work in print, the result is that their publications come out at roughly the same time.

              Another example is that both Graham Bell and Elisha Gray developed a working telephone at about the same time, and submitted their patent applications within a few hours of each other.  

              And given the way humans perceive meaning, the closer the timing between two or more similar publications (or patents), the more meaningful the coincidence.  

              Neat, eh?

              •  Wow, Geek.... (1+ / 0-)
                Recommended by:

                I actually understood all of that!

                Didn't some annoying Frenchman figure out calculus at the same time as Newton(?)

                "Ronald Reagan is DEAD! His policies live on but we're doing something about THAT!"

                by leftykook on Sat Jun 05, 2010 at 07:31:00 PM PDT

                [ Parent ]

                •  cool; it's actually pretty simple. (2+ / 0-)
                  Recommended by:
                  Rei, leftykook

                  Think of mice who run a maze of similar length to get to some cheese.  They all arrive at the cheese at roughly the same time.  

                  I don't know the history of the calculus so I don't know about whether there were two or more people who invented it at the same time. But if so, it would be another case in point.  

          •  Climbers: parachutes? (1+ / 0-)
            Recommended by:

            Or pop-out wings, for a space-shuttle-style re-entry?

            "The true strength of our nation comes not from the might of our arms or the scale of our wealth, but from the enduring power of our ideals." - Barack Obama

            by HeyMikey on Sat Jun 05, 2010 at 03:45:38 PM PDT

            [ Parent ]

      •  Very nice diary (1+ / 0-)
        Recommended by:
      •  When you preview your diay (2+ / 0-)
        Recommended by:
        WI Deadhead, Rei

        two sets of "post a comment" prompts will pop up on the bottom of your preview. Hit the first one and post the comment in your diary preview before you publish the diary.

      •  Yes, write more. (2+ / 0-)
        Recommended by:
        Dragon5616, Trotskyrepublican

        Enjoyable diary. You write well.

        (Yeah I disagree, somewhat...still wanna see what else you have to write about....)

        "Ronald Reagan is DEAD! His policies live on but we're doing something about THAT!"

        by leftykook on Sat Jun 05, 2010 at 02:01:21 PM PDT

        [ Parent ]

      •  custom tip jar (1+ / 0-)
        Recommended by:
        WI Deadhead

        here is a diary on how too

        you cant fool all of the people all of the time unless they watch fox news

        by eeff on Sat Jun 05, 2010 at 02:25:38 PM PDT

        [ Parent ]

      •  Isp (0+ / 0-)

        is specific impulse, the amount of momentum change you can get per unit mass of fuel, for those (like me) who didn't know.

  •  What? (3+ / 0-)
    Recommended by:
    WI Deadhead, se portland, Rei
    No maglev launch tracks? The future ain't what it was...

    Float like a manhole cover, sting like a sash weight! Clean Coal Is A Clinker!

    by JeffW on Sat Jun 05, 2010 at 01:00:14 PM PDT

    •  Maglev (4+ / 0-)
      Recommended by:
      WI Deadhead, G2geek, JeffW, palantir

      Indeed, this wasn't intended to be an exhaustive list; that would have taken way too long  ;)  Maglev launch proposals that I've read like "Maglifter" generally don't provide a very significant boost.  In Maglifter's case, it was only about a 600mph boost.  It's not impossible to do more, mind you, but there are difficulties.

      •  Combined with the Loop... (3+ / 0-)
        Recommended by:
        G2geek, Rei, Dragon5616'd have a significant 2-stage system. The only downside is that you need lots of baseload power, i.e., nuclear fission at the start. It could make use of powersats in the future, however, and indeed could be the road to building them.

        Float like a manhole cover, sting like a sash weight! Clean Coal Is A Clinker!

        by JeffW on Sat Jun 05, 2010 at 01:13:27 PM PDT

        [ Parent ]

        •  Yep -- but any power you provide from electricity (3+ / 0-)
          Recommended by:
          G2geek, JeffW, Dragon5616

          is a good thing, since electricity can be both clean and cheap.  It's always going to take a lot of energy to reach 7800m/s and hundreds of kilometers in altitude (minimum).  But the use of electricity, and especially the efficient use of electricity, is the best you can do.

  •  Excellent lay-friendly explanations of tech stuff (5+ / 0-)

    Thanks. This obviously took some real time and effort.
    Thanks also for clearly outlining why space elevators should probably stay in airport rack paperback novels. Ive lost track how many times Ive seen someone ask "golly gee willikers, why not?' about this concept. Which isnt really much less fanciful than 'Warp Factor 9, Mr Sulu'.

  •  I'm very skeptical about Beanstalks (1+ / 0-)
    Recommended by:

    Contrary to your assertion to the contrary, I believe a space elevator would be incredibly dangerous in a world full of terrorists and Arrogant Suits that run Deep-Sea drilling rigs...("Arrogant Suits" hmmmm....sounds like a good name for a Hard-Core band)

    The cable would wrap nearly around the earth, and anything that fell to earth in an accident would be moving very fast when it hit....Suppose it was cut in two at the halfway point there would be thousands of miles of cable falling and parts of it would be zipping along at an extremely high rate of speed.  If yer talking about a little dinky thing big enuf for one climbing car it might not be so bad, but the economy of building such a thing would probably demand a very massive system with many climbing cars and a total mass of millions of tonnes, imagine a climbing car the size of a ten-story office building augering in from a thousand miles up the cable....

    A Bolo or Rotorvator would likely be easier to build and less dangerous.  The bigger the thing is, the slower the end dipping into the atmosphere would be moving, relative to the surface of the Earth, and the longer the window of hooking up would last....

    Paradoxically, it would be apparently easier to build an elevator on the Moon, since the material strength requirements would be substantially lower. (Betcha 50 cents that if they ever do build an elevator, the prototype and pilot project will be built on the Moon, less political drama, less technically challenging, almost a dry run for building the big one.)  

    "Ronald Reagan is DEAD! His policies live on but we're doing something about THAT!"

    by leftykook on Sat Jun 05, 2010 at 01:29:51 PM PDT

    •  Lunar elevator (2+ / 0-)
      Recommended by:
      G2geek, leftykook

      building a lunar elevator requires a much longer cable but the material requirements are less stringent.

      To give an idea of what the density of the falling elevator ribbon would be, the Edwards elevator, with a payload of 20,000 kg, would have a mass of 730,000kg over a length of 100,000,000 meters, or 7 grams per meter on average (less near the surface of the Earth).  Incredibly light, but with relevant surface area for climber grip -- meaning a very low terminal velocity.  Any additional "whipping" strain would simply sever the tether, since there's such a low safety factor on it.  

      The problems are technological, however.  There just aren't any materials out there that can come even remotely close to its needs, and a long, undampened cable subject to various perturbations is not dynamically stable.  As well as a ton of other problems, which have varying degrees of solutions (some easy, some extremely hard) -- micrometeoroids, small space debris, large objects in space, weather on the atmospheric side of the tether (wind, lightning, rain, etc), corrosion of the tether, atmospheric discharge of Lorentz currents, heat dissipation, and so forth.  So it's at best extremely difficult to build.  At worst, it's physically impossible under our laws of physics.  And it's rather inefficient, too, due to the power beaming requirements.

      •  20,000 KG is NOTHING..... (2+ / 0-)
        Recommended by:
        G2geek, Rei

        ...a four engine cargo jet carries about 20,000 KG, a Space Elevator needs to be a heck of a lot bigger than that to be reasonably viable....The SciFi stories by Clarke and Benford from twenty years ago had a lot of the nuts and bolts and back of the envelope calculations figgered out about the basic numbers, both of those stories had the climber cars taking days to reach GEO, are we gonna build a space elevator that can lift 20,000 KG every 12 days or so?  And costs multiple billions to build?

        (They also had some figgering on keeping the whole thing in balance, cars need to be going up while others are going down, etc....)

        Hey, how long WOULD a lunar elevator have to be?  How far away from the moon is the synchronous point with a rotation period of 28 days per turn?  Never thought of that!

        "Ronald Reagan is DEAD! His policies live on but we're doing something about THAT!"

        by leftykook on Sat Jun 05, 2010 at 01:53:17 PM PDT

        [ Parent ]

        •  Indeed, that's part of the problem. (3+ / 0-)
          Recommended by:
          HeyMikey, G2geek, leftykook

          With a (miraculous) 130GPa tether with almost no safety factor, it takes a massive 730,000kg tether to haul up 20,000kg.  With 100GPa, it's 1,800,000.  At the maximum strength and density for collossal carbon tubes, it's 4,280,000 kg.  For the best SWNTs, it's 3,300,000 kg.  For the best things we could actually make a bulk cable out of today, it's no more than 50,000,000,000 kg.  All to haul 20,000kg loads, slowly, and not very efficiently.  Space elevators just really aren't a very good solution to get off Earth, a romantic as they are.

          Lunar elevators tend to go to either L1 or L2 -- a minimum of 56k km or 67k km, respectively.  Mercurian and venusian elevators are even harder than on Earth due to the very slow rotation rate.  Of the inner planets, only Mars has an easier elevator than on Earth.  Some small moons and asteroids may be realistic places for space elevators, mind you.

  •  ballistic launch (3+ / 0-)
    Recommended by:
    JeffW, Rei, Dragon5616

    The Russian played with this, but decided that you couldn't get a big enough load into space. But, I have been thinking that, with the miniaturization of chips, you COULD put a highly sophisticated satilite into orbit for a very reasonable price using ballistic launches today.

    On a side note, I am a bit disappointed that you didn't even consider the 'Ralph Kramden' method of deployment. Recent advancements in steroids would at least make this an avenue of future research. :)

    I appreciate your diaries Rei, they are always inspiring to me. :)

    Four out five sock puppets agree

    by se portland on Sat Jun 05, 2010 at 01:36:22 PM PDT

    •  Ralph Kramden Launch Mechanism (6+ / 0-)

      The problem with that method is that it's vaporware.  You keep thinking it'll be ready soon, but the completion date is always "One of these days..."   ;)

      Indeed, HARP showed what was considered an avenue of significant doubt -- that sophisticated electronics can survive the forces of ballistic launch, and that you could even ignite a rocket after being fired at those accelerations.  They hardened the electronics against launch forces by embedding them in a solid block of plastic.

  •  Cool--thanks! (2+ / 0-)
    Recommended by:
    HeyMikey, G2geek

    But Launch Loop needs another attempt at explanation; I'm not fathoming what it looks like or how it works.

    "The human capacity for goodness makes democracy possible, but it's precisely the human capacity for evil that makes democracy utterly necessary." Gary Dorrien

    by ogre on Sat Jun 05, 2010 at 02:26:58 PM PDT

      •  Thanks. (1+ / 0-)
        Recommended by:

        Off to educate myself.

        I'm the non-engineer in my family. Tech writer, yes. Engineer, no.

        "The human capacity for goodness makes democracy possible, but it's precisely the human capacity for evil that makes democracy utterly necessary." Gary Dorrien

        by ogre on Sat Jun 05, 2010 at 03:29:32 PM PDT

        [ Parent ]

        •  I think probably the best argument (3+ / 0-)
          Recommended by:
          ogre, HeyMikey, G2geek

          for the launch loop comes from the summary:

          The published cost estimates for a working launch loop are significantly lower than a space elevator and additionally the proposed system has a greater launch capacity, lower payload costs and similar or greater payload masses. Unlike the space elevator no new materials need to be developed.

          Imagine a day when we can have $3/kg to space, powered by clean electricity.  That's the goal here.  :)  $1,500 tickets to orbit.  $8,000 tickets to Mars.

      •  why stabilization cables? (1+ / 0-)
        Recommended by:

        The diagram looks like it will use one or two thousand kilometers of stabilization cables. Compared to the mass of pairs of 100 km cables, might fans mounted on the loop that leech power from the rotor be more efficient?

        •  There's almost no atmosphere at the top. (2+ / 0-)
          Recommended by:
          G2geek, HiBob

          Also, the cables weigh down the track into a proper shape.

          •  Where to build the launch loop? (0+ / 0-)

            Best place is along the equator, right? Or close to the equator, and parallel to it?


            1. Across northern Brazil, possibly into Colombia and Ecuador.
            1. Across Africa from Ethiopia to Sierra Leone.
            1. Across Indonesia (spanning the Java Sea).
            1. Spanning the entire Atlantic, roughly (a) from Natal, Brazil to Boma, D.R.C., or (b) from the Brazil-French Guyana border to southern Liberia.
            1. Using any major land mass as one end, and extending out into the open ocean -- into the Pacific from Ecuador or Papua New Guinea or Indonesia; into the Indian Ocean from Indonesia, Somalia, or Kenya; into the Atlantic from the equatorial African coast.
            1. Entirely in the open ocean, maybe starting at an island or passing over a few islands.

            Many of the land locations are politically unstable and corrupt. Building over open ocean avoids those problems and probably makes transport to & from simpler, both for construction and for cargo once operational.

            Building over Ecuador-Colombia-Brazil would allow some of the western support stations to be built on the Andes, but (a) not many, and (b) transport of construction materials would probably be more difficult than to open ocean, and (c) probably not a good idea to put world's biggest construction project across Amazon rainforest.

            Spanning the Atlantic: (a) would allow spacebound cargo to be shipped by both land and sea; (b) would allow launch loop to double as earth transport when not in use for space launches. Unload your truck onto the launch loop in Liberia, unload it at the other end onto another truck in Brazil. The trip is cheaper than ship or air, faster than ship, burns less fossil fuel than either. Imagine how that could transform the economics of the whole project, and be a badly needed economic asset for West Africa.

            "The true strength of our nation comes not from the might of our arms or the scale of our wealth, but from the enduring power of our ideals." - Barack Obama

            by HeyMikey on Sun Jun 06, 2010 at 09:08:53 AM PDT

            [ Parent ]

            •  Or, if not too far north-- (0+ / 0-)

              Western Mexico to Hawaii (a little long) or western Mexico to Miami.

              "The true strength of our nation comes not from the might of our arms or the scale of our wealth, but from the enduring power of our ideals." - Barack Obama

              by HeyMikey on Sun Jun 06, 2010 at 09:22:14 AM PDT

              [ Parent ]

            •  There's one location that has generally become (1+ / 0-)
              Recommended by:

              Seen as optimal for space megastructures: the far eastern equatorial Pacific.  Reasons include:

              1. Weather: Low wind, little lightning, no hurricanes, etc.
              1. Terrain: Oceangoing structures mean no terrain obstacles, the ability to easily move the structure, easy to transport goods there in bulk, etc.
              1. Geopolitics: No taxation, no political instability, no concerns during failure, etc.
              1. Orbital mechanics: the greatest boost to orbit from the planet's rotation is at the equator.

              While space elevators become more complicated at other latitudes, however, launch loops do not.  And there are some interesting arguments  for building one over land -- namely, that you can also use it for long-distance power transmission and energy storage.

  •  Here's an interesting one...balloons! (2+ / 0-)
    Recommended by:
    G2geek, Trotskyrepublican

    (or airships, really).

    JP Aerospace

    Can't assess the technical viability or likelihood of success myself, but does look interesting (and to me at least, plausible).

    Although the general look of the program suggests that they are likely horribly underfunded...

    •  I didn't list that one on purpose. (4+ / 0-)
      Recommended by:
      PeterHug, G2geek, HiBob, Trotskyrepublican

      I started becoming skeptical of their claims when I tried to simulate it myself, and then I later found that other people had come to the same conclusion.  Even in the extremely thin upper atmosphere, the drag of such a large blimp is tremendous.

      •  The impression I get is that they accomodate that (2+ / 0-)
        Recommended by:
        G2geek, Trotskyrepublican

        by never going fast.

        I could imagine a scheme that uses airships to lift fuel to their interim station (~150,000 feet) that then would fuel something looking like Black Horse to get from there to orbit.

        Dunno.  But it would be really need for them to be able to try their concept for real.

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