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A disclaimer: There is a lot of real Science involved.

Imagine a world which is exactly a copy of Earth (at least in terms of power as a species and technology). There is a company that aims to make space travel extremely cheap so that Earth could actually import stuff from asteroids passing by (just to give you a financial estimate). For reasons of abstraction, a method of converting electrical energy directly into kinetic linear motion (unlike a motor, which is rotational) has already been discovered.

My question is about the feasibility of making a "spaceship" whose only operational cost is in energy (everything else is, like in real life, considerably cheaper). There are two facets to this problem that I could see:

  1. Can we claim back most (in the order of 95%) of the energy of the ship that is falling back to Earth as part of Law of Conservation of Energy, assuming that Second Law of Thermodynamics (100% efficiency is not possible) still applies?

  2. Even then, energy is lost through air resistance. Is there an theoretical substance which could be mass produced (it maybe be slightly expensive), could work in rough conditions and still provide zero (or near zero) air resistance regardless of speed of the spaceship? The shape of the ship till be as aerodynamic as possible.

This part may help, but it is not necessary to look into: It may be possible that the ship is fired from a spaceport using electricity and a falling ship could be caught by the spaceport to convert its kinetic energy into electricity using, say super-capacitors to store the energy (because they charge really fast).

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    $\begingroup$ Space elevator can save you. $\endgroup$ – Alexander Mar 29 '18 at 20:32
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    $\begingroup$ We actually have "a method of converting electrical energy directly into kinetic linear motion"; it's called a linear motor, and is used in various applications such as coilguns and rapid transit systems. As for the "theoritical substance which could [...] provide zero (or near zero) air resistance", you understand that "air resistance" has nothing to do with friction and is strictly a function of the shape and speed of the airfoil? $\endgroup$ – AlexP Mar 29 '18 at 20:32
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    $\begingroup$ I have a feeling this is more of a physics question than a world building one, read up on what energy is before you go there though, your use of the term energy is way too broad. $\endgroup$ – V. Sim Mar 29 '18 at 20:34
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    $\begingroup$ There are a bunch of (more or less wacky looking) non-rocket launch platforms that might fit. $\endgroup$ – user25818 Mar 29 '18 at 20:56
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    $\begingroup$ After thinking a lot about this, I've decided to vote to close. You're asking 3 questions when you're only supposed to be asking 1 and the questions are very opinion based. I could have picked "Primarily Opinion-Based" but I elected to choose "too broad." Frankly, it doesn't matter which. (a) There are nowhere near enough conditions to allow for one right answer. It's OK to fish for ideas so long as one best answer can be determined. As written, no answer is any better than any other. (b) Ask one question. $\endgroup$ – JBH Mar 30 '18 at 0:38
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NASA is working on an EM drive that uses the pressure of microwaves to move forward. If that works at all, it won't produce a lot of thrust.

What you describe is like the hand waved Star Trek "Impulse Engines." If you posit that then your drive works. If you don't want to hand wave it that much, you are out of luck.

In order to convert your downward motion into energy, you would have to have something to act against.

  1. A wind turbine mounted on the ship would do it but would only capture a small fraction of the energy you are talking about.
  2. Impact with the ground transfers all the energy of the drop (less wind resistance). However, you would need a way to convert it into a form that is more useful than terrain excavation. The longer the "impact" takes the easier it is to handle the energy. So landing on a long ramp or rails would make the energy easier to handle.

As far as wind resistance is concerned, regardless of shape, the faster you go the more wind resistance you face. So, to minimize wind resistance, go slow. Attaching to rails is one way to slow yourself down and regain a great deal of the energy.

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  • $\begingroup$ ShadoCat, This addresses the two "facets" (posed as questions), but does not answer the question: "My question is about the feasability of making a spaceship whose only operational cost is in energy." $\endgroup$ – JBH Mar 30 '18 at 0:41
  • $\begingroup$ @JBH, that's the problem with asking more than one question in a post. You never know which one will get answered. In any case, I edited my answer to answer the feasibility question. $\endgroup$ – ShadoCat Mar 30 '18 at 0:46
  • $\begingroup$ Thanks. I'm frankly having trouble saving this question. You did a good job. $\endgroup$ – JBH Mar 30 '18 at 0:47
  • $\begingroup$ @JBH The two facets of the problem are non-problems. Vide my comment above on the question. $\endgroup$ – a4android Mar 30 '18 at 1:38
  • $\begingroup$ Well done. You've thought through the aspects of the questions and provided appropriate answers. Plus one. $\endgroup$ – a4android Mar 30 '18 at 1:40
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What you need is an orbital ring. A solid ring of matter that is stationary to the earth, magnetically levitated above an orbiting wire. With cables from it to the ground. https://www.youtube.com/watch?v=LMbI6sk-62E

Using these and magnetic acceleration, you can launch payloads for a reasonable amount of electricity, and regain most of that energy when they return. If you are mining asteroids, this could be net positive in electricity.

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By far and large the largest factor that determines the expense of a spaceship is if it is manned or not.

If it is manned, this severely limits your options. The largest expense is that of safety and redundancy. To ensure the safety of the crew, multiple systems require rigorous testing, research must be conducted in risk analysis with no tolerance for any failure. Keep in mind the cost of a launch platform of any kind is a small cost compared to the dozens, if not hundreds, of failures and tests that preceded it.

Add that to of course the weight penalty of life support, communications and control systems, training, health, food, water, waste disposal, insurance and crew amenities - you can easily see why the Space Shuttle became the behemoth it did, and although mostly successful, the program was often considered much too expensive for what it achieved.

Alternatively unmanned ships could be launched with relatively small payloads, on launch vehicles that it would not matter too much if they fail. Space X is an example where the re-use of launch vehicles could reduce launch costs by a third, where the heavy rocket was actually a trio of the same launch vehicle design, however if manned they have reiterated they would need to develop a completely different design for reasons above.

If you want to have costs even less than this, you need to think outside the box and look at methods of launch other than rockets.

  1. Forget about 'space elevators' and 'orbiting rings' - the energy, material and construction costs for these mega-structures are well north of any savings you would get from the use of these structures. (A cable from the Lagrange point to earth will need to be 1km thick steel to not snap - think about that for a moment)

  2. Mass drivers are an option, essentially making the spacecraft a bullet, but this is definitely not an option if it is to be manned.

  3. You could accelerate a solar sail craft using lasers from the ground, however this is not tested at all yet.

  4. Space planes are an option but no-one has perfected them - combined with high altitude launches this could be possible and more realistic. However, fuel is a large cost associated with this option, and I know in your question you mentioned conserving energy. The weight penalty for duel propulsion and fuel is a major negative to this route.

  5. One option you could consider if you do not want on-board propellant: orbital airships. Using staged airships, it may be possible to slowly but surely lift a light buoyancy craft to the upper atmosphere, then use solar power to slowly accelerate it to orbital velocity, over several days, weeks or even months. JP Aerospace I believe is working on this concept, and although prototypes have been made they haven't got there yet. However, I could easily envisage this to be an ultra-low cost way to orbit with reusable cheap craft. Re-entry would be easier because of its lightweight nature and size.

Getting up to space cheaply is a hot topic at the moment, it's a holy grail and everyone is trying to look at ways to do it. Long gone are the old Nasa days of dumping large amounts of funding, fuel and labour into a program to get something up there.

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Here is a pseudo science is solution that comes from 1960 scifi*

Your ships use a magnetic drive to take off and labs on the earth, only able to land on landing pads that can produce a powerful em field. As the ship lands their kinetic energy is converted into stored energy on the em landing field.

Really powerful drives don't need a landing pad that boosts the planets em field, but can land anywhere.

*cannot remember who the author is, or the book name. It was from a penny book.

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