External Pulse Propulsion Versus Rocketry When You Can Say No To Gravity

[Bamax]

Scifi scenario; A gravity absorption metal that is liquid at room temperature is invented which causes all in the vicinity around the vessel carrying the liquid to ignore Earth's gravity.

The grav-absorbent liquid metal can absorb several hours worth of gravity before becoming 'full' at which point it won't absorb any more gravity because it will turn solid and change it's properties to a more dense metal similar to lead. Of course you may carry some spare fluid but you do not want your entire cargo hold to be full of grav-absorbent liquid do you?

And yes you can turn it on or off... at least until it becomes 'full' and therefore useless for gravity absorbtion.

In such a case space travel would be transformed... in that many current and even theoretical space propulsion systems would go farther for less propellant spent.


External Pulse Propulsion: Most think of nuclear project orion, but when you can say no to gravity you don't need nukes anymore... at least not for leaving earth via EPP.

Thermobaric (fuel/air) bombs that use air surrounding them to create a big blast wave would be sufficient to propel a gravity blocking EPP spaceship out of lower atmosphere.

Concerned about your launch site? Don't be. Use chemical rocket engines to boost to a safe height where you can flip over and use your rear mounted EPP pusher plate with the your fuel/air bombs.

Once the air thins out fuel/air bombs won't give as much thrust, but due to inertia you would coast into space anyway.

Once in space you could switch to higher yield bombs for better efficiency.

Arguably a step up from nukes would be pure fusion bombs that skip the fission step and just do fusion. But they are very much scifi because IRL they would only be easy with small amounts of antimatter reacting with a fuel source... which we know requires better production and storage approaching scifi levels.

Still it is a step up because without fission it is far cleaner with regards to deadly radiation... plus it leaves no electromagnetic pulse in it's wake either. So no burning out satelites or leaving lots of radioactive particles in orbit.


I figured out with this engine design, you can indeed make any scifi shape you want take off a planet, and land again with relative ease.

Since EPP is so efficient, the only thing you would have to worry about refueling on occasion is the chemical rockets used for clearing the launch area or landing.


ISRU in space can be done with ice which is fairly common if you know where to look (comets, moon polar areas where the sun hardly hits, and some planets). Can yield hydrogen and oxygen. Which is rocket fuel once separated and burned together.


For bomb refueling you would visit spacestations that stored them or inhabited planets that produced them.

In space EPP beats chemical rocketry for efficiency, but combining the two technologies and adding a grav-absorber allows for the classic go anywhere scifi spaceship.

Only it makes quite the entrance or exit to say the least on Earth worlds.

Boom boom.

Such tech also means classic atmospheric fighter jets would think twice about attacking such a ship because:

1. It floats.

2. It only has to turn around and pop off a fuel/air bomb to get away. Use your imagination as to what happens to any incoming missiles on it's tail.

And if it's nukes... it laughs at that too. That is just extra get away boost, assuming it's own blast waves don't wipe out the incoming nuclear missiles before they can even detonate a blast wave of their own.

[Cthulhu]

Perhaps you mean a material that can negate gravity?

[Keklas Rekobah]

Ah, yes ... Cavorite!

I read about it in the mid-1960s, more than 60 years after The First Men in the Moon was originally published.

Great story ... ground-breaking for its time.

[TerrifyingKitten]

Given that the entirety of rocket science is built around overcoming gravity, if you can prevent it from affecting your ship you do not even need fuel air bombs. Even the slightest force would produce instance acceleration.

You'd still have to accelerate the mass of the ship, but no longer would you have to worry about up/down. Think of the space shuttle astronauts manipulating satellites in the cargo bay. Those weigh several tons, but they pushed them by hand.

And once you started your ship moving you could stop providing thrust, except for air resistance, there would be nothing to stop it from leaving the atmo.

There would be a very tricky situation when you first started absorbing gravity. If you only negate a fraction of the gravity on the ship then you'd still have to have some thrust to overcome the rest, and that might be for the best. Because if you negated ALL the gravity there is nothing holding your ship in place except friction. One stiff breeze and and it WILL leave ground. And once it leaves ground (breaking the friction that holds it to our rotational frame of reference) it will zoom (assuming Earth) West at high speed (the Earth will rotate out from under it - 1,000 MPH at the equator). Also, Earth orbit the sun at about 66,000 MPH in a "circle" and you'd no longer be gravitationally tied to that orbital path, so your ship will get left behind as the Earth "turns the corner" on the orbit.

How much gravity are you absorbing? If you absorb the sun's gravity too then you won't even be held to the gravity well of our solar system and all those angular momentum rules above will apply there too. The sun is moving around the galaxy at roughly 500,000 MPH so your ship will tangent off that direction (the ecliptic plane of our solar system is tilted up to about 60 degrees from horizontal in our orbital plane around Sagittarius A - although it weaves through a +/- range along the orbital path relative to the plane of the galaxy).

So your gravity absorbent material is a super material. Wed be a solar system based species in a matter of years and a multi-solar species in decades. I'd use an Ion propulsion system.

Look up DS1/Dawn Mission for Ion propulsion.
Look up sol galactic motion for the path of our solar system.
Look up earth solar trajectory or how earth moves for the path of Earth around our sun.

Now if you could negate mass instead of gravity, then you'd be famous forever. And that may be easier give that gravity isn't really a force, it is the name given to the shape of spacetime. Negating mass means that you don't care about gravity wells any more. As soon as you begin to even reduce your mass (without affecting your momentum) you will begin to move very very fast (in what appears as a random direction - do not start this test first thing in the morning or you'll plow into the ground with much force! Do have a space suit on when you do this.),

Negating mass would be achieved by some interaction with the Higgs Field. No idea what that would look like IRL, but in a fiction setting I'd have some set of coils made of unobtanium that took a tremendous amount of power to operate. But it doesn't matter how much your generator or batteries weigh, your coils would emit a field of their own over some volume of space. With a large enough set of coils you could move a whole planet. With a Dyson sphere around the sun you might be able to power coils large enough to fly your whole solar system around the galaxy. Assuming that the Higgs Field inside the volume your generated field remains intact.

Look up Higgs Field or Higgs Boson or curved spacetime vs gravity for theories of the nature of gravity.


I'd love a sports car sized device using the mechanism you describe. Fuel up with liquid metal, drive around like a maniac for a few hours visit the outer planets, then come back and drop off a slab for thawing and tank up again!

[Bamax]

Mass has inertia, so removing gravity won't be an issue.

Think about it. Birds fly. Planes fly, yet they don't have major problems landing. The air is tends to move a lot, it does not stand still, so a gentle breeze would take some time to get big hulking floating spaceship going fast.

I do agree being able to toggle how much gravity is absorbed is a good idea.

But with my originally posted design, it does not grant thrust. It just makes thrust and inertia more efficient than it should be on a planet.

Things like like spin launch would work even better here.

[Cthulhu]

This video simply screams "investor scam", just like that ridiculous inertia energy storage prototype. Nothing concrete, just pretty music, people hugging each other in joy or staring at screens with an utterly silly expression, bleh... should've hired better actors.
The forces generated by the full-sized facility will destroy any payload, except for a rugged military KKV, perhaps.

[Bamax]

This video simply screams "investor scam", just like that ridiculous inertia energy storage prototype. Nothing concrete, just pretty music, people hugging each other in joy or staring at screens with an utterly silly expression, bleh... should've hired better actors.
The forces generated by the full-sized facility will destroy any payload, except for a rugged military KKV, perhaps.

Yeah.... the forces are a big isssue.

I think trying the same thing and shape with magnetic coils would be better.

Using magnets to accelerate a rocket to the required launch velocity.


Actually may work better since you have less stability issues than with catapult version.

Scott said it will have to deal with instability issues since the arm will weigh much less once ot releases the rocket.

With magnet coils lining the inner wall permeter of a giant standing disc launch facility, the stability problem is less of an issue.... because less moving parts are involved.

You trade instability of moving parts for massive amounts of waste heat, which can be solved with generous amounts of coolant or putting your facility near a water source.


It would be a massve drain on the electrical grid, but it would change space travel as we know it.

[Cthulhu]

Pretty much anything accelerating too abruptly will be crushed by the forces, that's why space rockets accelerate continuously, and not too rapidly. Theoretically, you could build a cannon big enough to shoot a payload directly into space, practically, though, nothing useful will survive that. In science-fiction, this can be mitigated by some wondrous inertial dampeners, yet we don't have anything like that, unfortunately.

The best possibility of "ground-assisted" launches would be either laser-pumped vehicles or very long (300) km magnetic catapults.

[Bamax]

Pretty much anything accelerating too abruptly will be crushed by the forces, that's why space rockets accelerate continuously, and not too rapidly. Theoretically, you could build a cannon big enough to shoot a payload directly into space, practically, though, nothing useful will survive that. In science-fiction, this can be mitigated by some wondrous inertial dampeners, yet we don't have anything like that, unfortunately.

The best possibility of "ground-assisted" launches would be either laser-pumped vehicles or very long (300) km magnetic catapults.

The laser ones have instability issuss at range since laser beams widen out and lose efficiency.

Plus the air also thins, so you will need rocketry once up high enough.

[Cthulhu]

The laser ones have instability issuss at range since laser beams widen out and lose efficiency.

Plus the air also thins, so you will need rocketry once up high enough.

The first problem is a general one, since lasers are not yet powerful enough anyway, and they cannot fire for such a prolonged time. In the future, lasers may become good enough to make this viable. The bigger issue might be the one of accurately targeting the vessel.

The second point can be solved by ablating a "sacrificial" layer off the vessel itself, or by adding a conventional rocket engine for the final flight stage.

[Cthulhu]

I've found something rather interesting. Apparently, an unintended "space cannon" test was actually conducted. The projectile blasted off at the speed of light, was accelerated so much that it probably disintegrated because of the explosion and air friction.