Tuesday, June 18, 2013

Bussard Ramjet and Scramjet- Is This a Fantasy?

Around 1960, physicist Robert W. Bussard came up with the idea of a new kind of rocket for space travel. Unlike other rockets such as Apollo 13 and newer shuttle models such as Challenger, Bussard's idea was a variation of a fusion rocket that was thought to be fully capable of interstellar space faring. In recent years, physicists have realized that shuttle designs were not an appropriate approach to space travel due to specific, complicated design flaws, where a cone shape is actually more practical for traveling through outer space. The space shuttle designs are far more complex yet give very little extra incentive to use since even minuscule oversights typically result in catastrophe, as was seen with other shuttle designs and cancelled shuttle take-offs, the rocket shape is far easier to build and more stable. Bussard could not have known this in 1960, as the first real flights did not take place until later years (landed on the moon in 1969 for example). But the Bussard ramjet still seems somewhat reasonable to build with current technology, well, at least for some of the smaller designs.
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The Ramjet basically consists of enormous electromagnetic fields in a scoop shape to capture hydrogen atoms in space for fuel-on-the-go in order to maintain near-light speed travel. The scoop, however, as seen in the pictures below and to the sides even further below, need to be fairly massive, or rather, the best and most realistic Ramjet design requires the scoop to be the size of Earth (in volume or 38.76×1020 ft3 ) in order to collect enough hydrogen atoms to maintain near light speed travel for a ship carrying more than a few people. Obviously, since hydrogen is so spread out in space, there would need to be a massive scoop to collect enough to maintain such incredible speeds. According to Einstein, in order to achieve light speed, an object would require both zero mass (be massless, basically) and have an infinite fuel supply since going light speed requires infinite energy. However, since the Ramjet would not being going light speed, some slack can be given but not a whole lot. The large Ramjet design could theoretically go 77% light speed since the scoop captures all atoms, thereby eliminating space-drag (but having any mass at all can cause infinite drag at light speed, and the ship itself has tremendous mass like the deltaV design ships of its era).
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Unfortunately, there isn't enough power or metal on the Earth to create an electrified scoop about 34,797 miles in circumference (56,000 km), so the idea itself was more or less impossible without already having an ability to go gather metals and resources from other exoplanets. Sadly, this makes creating the Ramjet a fantasy, even if the principles behind it are surprisingly sound.
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As the picture above illustrates, hydrogen atoms are "scooped" and funneled into the center. The scoop itself is not solid, but rather is more like a metal ring with a heap of electricity being channeled into it, which is meant to send out a powerful magnetic field into the cone-shaped scoop for harvesting more or less. Since magnetizing the hydrogen atoms themselves far enough out to help reduce the size of the scoop is out of the question, the scoop itself must be close to or beyond the volume of the Earth itself, and the magnetic fields will only serve to channel the atoms into the fusion chambers only after being caught. These atoms are pushed into a narrow channel just like water channeling, and the pressures builds as the speed of the atoms increase along with the shrinking size of the channel itself, until the atoms reach the fusion chamber and fuse by way of either a laser (many types of lasers) or by pressure, all of which produce a thermonuclear explosion, or in layman's terms, KABOOM! The magnetic field then directs the energy out as rocket exhaust opposite to the intended direction of travel, thereby accelerating the vessel, which is what actually propels the vessel.
Kind of neat but seems just far-fetched
It's a lovely concept, indeed. But the pictures fail to depict the mass of this ship. The "gas" that is collected can be used for antimatter-matter annihilation powered engines, thankfully, so the ship design actually packs a wallop, but the size of this ship is too large to ever come true. I said that the ship itself is about the size of Earth, this is actually because the scoop that sweeps up all of interstellar space's hydrogen needs to devour a constant amount of fuel. Interstellar space contains an average of 10−21 kg of mass per cubic meter of space (that is, 0.00000000000000000000220462262 lbs. per 35.3146667 cubic feet), primarily in the form of non-ionized and ionized hydrogen and some small portions of that being constituted by helium. As you can see by the really long decimal, that's really not a lot of hydrogen in space to power a ship traveling at 70,000,000 mph to 517,144,805 mph, where designs of these ramjets estimate between 10% to 77% light speed! This means that the ramjet's scoop must vacuum 1021 cubic meters of space (that is, 2,204,622,620,000,000,000,000 lbs. of hydrogen per 35.3146667 cubic feet / the volume of the Earth) to collect 2.20462262 pounds of hydrogen. But there are three other very, very minor problems may arise that could possibly hamper any realistic space traveling:
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1) Powering the electromagnetic scoop would require more power than the Earth has and represent a massive drain on ship's energy, forcing the ship to have a bigger scoop to compensate (ironic?)
2) The fusion reaction would be many megatons in force, possibly above or beyond 30-50 megatons (that is, the world's most powerful bombs exploding non-stop behind your buttocks), the ship's metal itself might explode into teeny-tiny pieces
3) Assuming the force of the propulsive explosion itself is even possible to contain at all, let alone for years or decades or centuries, the temperatures might not be, as the heat of these explosions would be well beyond 180,000,032 °F/100,000,000°C, which is 660% HOTTER THAN THE CORE OF THE SUN (estimated Sun's center is 26,999,540.33°F)
4) Lastly, at even minuscule percentages of the speed of light, dust in space and rocks would impact the ship with the force of thermonuclear bombs.
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So I suppose there are 6 issues total with this space ship design: Basic size, fuel consumption, powering the scoop, containing the forces of propulsion, heat, and interstellar objects like dust becomes nuclear bombs on the hull. In my mind, once this ship is built, I'd demand that they fire dozens of nukes at it before I took it for a test flight since at those speeds dust has the force of thermonuclear bombs on the hull. This seems totally unrealistic.
These very teeny-tiny minor problems just might possibly completely-absolutely-utterly hamper any realistic space traveling. Just saying.
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If you like this, read my much more optimistic article on Project Daedalus: Possibility or Hubris? at http://astronomy-by-kyle.blogspot.com/2012/05/project-daedalus-possibility-or-hubris.html
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Feel free to comment!

1 comment:

  1. Seems odd, there is a picture of the Laser Powered Interstellar Ramjet above and no description.
    The LPIR does not use a fusion engine , it could, but just a linear accelerator would work since all the energy generation is back in the Solar System.
    One thing , advanced civilizations may have mastered these kinds of technologies and they might be observable.

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