Liberating humanity from the tyranny of Konstantin Tsiolkovsky

[Alonso Quixano]

Dear sirs and madams:

I recently wrote a paper that concerns itself with how, if two space-craft were to use each other as reaction mass, the need for propellant between them would increase quadratically with desired speed and not exponentially. Sadly, the journal to which I sent said paper rejected it.

Does anyone know which journal one should send this paper to? Also, while we're at it, peer review would be much appreciated.

Thank you all for your time in advance.

[Rakaydos]

This sounds like a decoupler cannon, or perhaps one of Dannys mass relay stations. Is that right?

[N_las]

Where do you calculate that the need for propellant would increase quadratically and not exponentially?

[K^2]

He means that the energy requirement increases quadratically, and consequently, the amount of fuel you need is also quadratic with velocity.

There isn't really anything new with this kind of idea. The advantage of a rocket is that you can have reasonable acceleration. Transfer to the Moon from low Earth orbit takes something like 3km/s. If you wish to accelerate a 25m rocket over its length to that speed, you need acceleration of 18,000G. Not only is this impossible to survive, there exist no materials allowing you to build a rocket that can survive that acceleration.

As pointed out above, the idea of using a long rail to accelerate the ship is well known. Ideally, you fix the rail onto something massive, like a moon. But for a single launch, you can just use the rail as a reaction system. But we are talking about hundreds of kilometers of rail for a typical launch. It's not something we are going to be able to do practically for a very long time.

But if you really want to try and submit this paper, to practice publishing if nothing else, try arXiv. They don't require peer review, and will accept almost anything. Of course, it also means that nobody is going to take it seriously that you have an arXiv publication. (Though, arXiv is used by a lot of serious scientists to allow free access to their work.)

[Red Iron Crown]

The paper completely ignores the Oberth effect, that rocket engines generate more power the faster they are travelling. The same amount of propellant can accelerate a spacecraft by the same amount no matter what its initial speed (ignoring relativistic effects).

Near as I can tell, the paper is describing using another spacecraft as reaction mass, which is fine if you happen to want spacecraft in an exactly opposite orbit and the spacecraft can handle the immense acceleration rates this would require. For any other case (most), some more conventional propulsion method is better.

Some things in the paper reveal a lack of understanding of reaction mass:

"The two crafts could ï¬Âre large masses (â€Âcan-

nonballsâ€Â) towards one another; both the act of propelling the cannonball and the act of catching

the other one would give a sideways boost to the crafts. In a way, the cannonballs would act as

force-carrying particles.

The main advantage of this method is that it’s essentially propellant-free, as there are plenty

of ways for the cannonballs to be launched solely with electricity."

The "cannonballs" are the propellant.

The paper also suggests that a reusable casing can completely contain a nuclear explosion and convert most of its energy into useful kinetic energy; I know of no material that could make such a casing in anything remotely practically sized.

The paper is almost completely lacking in calculations supporting its assertions; to be taken seriously by rocket scientists the workings will have to be shown.

[cpast]

But if you really want to try and submit this paper, to practice publishing if nothing else, try arXiv. They don't require peer review, and will accept almost anything. Of course, it also means that nobody is going to take it seriously that you have an arXiv publication. (Though, arXiv is used by a lot of serious scientists to allow free access to their work.)

Note (K^2 may well be aware of this, but others may not be): Last I checked, arXiv requires some first-time submitters (especially those who aren't affiliated with an academic institution) to be endorsed by someone who's submitted a few papers in the field before their first paper in the field is allowed to be posted.

[Z-Man]

The cannonball thing is the only thing with a remote chance of being practicable. Yes, the balls would be the propellant, but the key thing is that they would be recyclable; the other ship would catch them. Now you only need to find a way to launch them with 22km/s+. Easy! Compared to the other suggestions, I mean. Catching can happen at arbitrarily low relative velocities.

[Jesrad]

A tether is much more practical.

Apply a little rotation (the tether goes taut), rewind with as much force you can, and release when the tether is almost completely rewound and the tethered pair of objects are spinning madly.

With a high enough ratio of masses between the two you would impart most of the momentum to the smaller half. That would let you keep one half roughly in the same orbit while madly accelerating the other half.

Another bonus is that a conductive tether can also double as a generator or an electrodynamic thruster, in the vicinity of Earth or any planet with at least a little magnetic field.

[christok]

you need acceleration of 18,000G. Not only is this impossible to survive, there exist no materials allowing you to build a rocket that can survive that acceleration.

Incorrect. That acceleration is quite typical of gun-launched rockets for military applications.

[Jesrad]

Yup, we have solid-state electronics that survive up to 40 000 G acceleration.

However I haven't found much in termes of actual cargo, which would resist that.

[Tommygun]

Yup, we have solid-state electronics that survive up to 40 000 G acceleration.

But isn't that for just a few milliseconds?

[K^2]

Incorrect. That acceleration is quite typical of gun-launched rockets for military applications.

Are any of these 25m long? You can have individual components that survive this acceleration, but the structure isn't going to take this.

[Duxwing]

Are any of these 25m long? You can have individual components that survive this acceleration, but the structure isn't going to take this.

Why does the length matter?

-Duxwing

[christok]

Are any of these 25m long?

No, they're not. You said it's impossible for the material a rocket is made of to handle the acceleration and I pointed out that's wrong. I see no reason to limit discussion to rockets of precisely 25m. (The gun-barrel component of the spacecraft is itself already assumed capable of handling the same forces it would have to handle when firing attached to some base. Its strenght is therefore not a concern.)

In any case, a rocket of that length would be impractically fat if it had to withstand such acceleration.

Why does the length matter?

Square-cube law. The strength of the material is proportional to its area while the mass (and hence force) is proportional to its volume. You can make a rocket longer but as you do so the required increase in diameter grows much faster than the increase in length.

Ever wondered about all these stories about ants lifting X times their own weight, which is like a human lifting tonnes? Or how fleas can jump so high it's like a man jumping over a multi-storey building? They're all rubbish for the same reason. An ant or flea wouldn't be strong enough to stand if it were scaled up to human size.

[KerikBalm]

I'm curious what journal he tried sending that paper to.

There are some interesting ideas in that, but

#1) They are not new, and thus not really publishable

#2) The ideas are not rigoruously developed and sufficiently explained for publication even if they were new.

Publishing is a hard task, even for PhDs, a lucky undergrad might get in on a paper with lots of authors (and won't be first author, that's a near certainty), but in your case, you may have been too ambitious.

[magnemoe]

Incorrect. That acceleration is quite typical of gun-launched rockets for military applications.

Yes plenty of gun launched stuff including rocket assist and smart shells . Gun launched rockets comes in two types: one is a artillery shell with an small booster rocket to increase range, you still need an thick steel casing to survive the launch for all artillery shells,

The other type is guided or smart missiles used from tanks and is launched at far lower acceleration and speed, they mostly use the gun as a launch tube who is smart as you don't need extra launchers.

Yes you can build larger stuff just as sturdy however it will be heavy, An rail gun based launcher might make sense as launch cost is so high

[Borklund]

I'm not sure posting your paper on the discussion forum of a video game aimed at adolescent kids necessarily counts as peer review.

[K^2]

No, they're not. You said it's impossible for the material a rocket is made of to handle the acceleration and I pointed out that's wrong. I see no reason to limit discussion to rockets of precisely 25m.

The 25m was the length used to compute acceleration. If you reduce length, you increase required acceleration by the same factor, so the total stress on the structure remains constant. This is NOT the case of square/cubed law. This is a constant relationship. No matter what length you make the structure, you can't get materials that can withstand acceleration required for two rockets to accelerate off each other.

Yes, if instead of two rockets you have rocket and a long rail/barrel, it's a different discussion. But it's not what we're talking about.

[christok]

The 25m was the length used to compute acceleration. If you reduce length, you increase required acceleration by the same factor, so the total stress on the structure remains constant. This is NOT the case of square/cubed law. This is a constant relationship. No matter what length you make the structure, you can't get materials that can withstand acceleration required for two rockets to accelerate off each other.

Yes, if instead of two rockets you have rocket and a long rail/barrel, it's a different discussion. But it's not what we're talking about.

I've pointed out that real rockets can handle more than 18 000g. You claimed they don't count because they're not 25m long. What exactly are you claiming?

[KerikBalm]

http://forum.kerbalspaceprogram.com/threads/70047-Hammerthrows-anyone

Same concept, splitting a craft in two, using each craft as reaction mass for the other....

Much much lower accelerations though.

[magnemoe]

You are using rotation to get the speed, it would work far better with a long wire, its actually an real world idea to use this mostly for deploying satellites in higher orbits.

Put an long wire between transfer stage and satellite and then cut it, satellite get speed and is put in orbit, transfer stage deorbit.

[KerikBalm]

yea, but thats what I have in KSP, it kicks the PE of my orbiter up, and the PE of my lander down, and gives a little "free" dV.

I was also thinking this would be better with long cables. Suppose you have the craft 10km apart, attached to each other by a cable... they both start reeling it in, at a really high acceleration that they get to orbital + speed before impact (and they fire a small thruster to avoid impacting each other).

They would then meet again near their apoapsis - although this isn't true if they reach escape velocity, or if they encounter the moon.

I guess it could save some propellant. In the case of a cable and two craft both going to the moon (they'd have to manuever as they approach the moon differently) - a lot of propellant.

It would be nearly "propellantless", I don't know where this "quadratic" thing from the OP comes from, you just need a higher "exhaust velocity" for the other craft - a longer cable perhaps? - The earth would "recoil" ever so slightly. For destinations within earth orbit, its essentially the same as a space gun.

If your craft can withstand the required accelerations... why not just use a space gun?

Heck we can fantasize even more about using a space elevator or orbital ring, so that the muzzle of the space gun is outside the atmosphere.

In the end, this isn't a rocket idea, its a ballistic launcher idea, and the idea of ballistic launches from a stationary position is not new.

What is described in that paper is about as feasible as useing a spacegun to launch a capsule equipped with airbags to "land on" (survivably impact) the moon.

[K^2]

I've pointed out that real rockets can handle more than 18 000g. You claimed they don't count because they're not 25m long. What exactly are you claiming?

Simple math. Look at where I got 18,000g from. Take a real rocket that can survive higher acceleration, plug in that rocket's length equation, and watch how you still get acceleration that it cannot handle.

It's really not that complicated. You cannot accelerate two rockets off each other to required velocity without overloading the structure.

[christok]

Simple math. Look at where I got 18,000g from. Take a real rocket that can survive higher acceleration, plug in that rocket's length equation, and watch how you still get acceleration that it cannot handle.

It's really not that complicated. You cannot accelerate two rockets off each other to required velocity without overloading the structure.

So you're referring to the case where the two rockets are a matching "barrel and rod" (or some variant thereof) firing off each other and accelerating only for the time that the rod is inside the barrel. Fair enough in that case.

I only skimmed the article but I think it refers more to two separate structures with an explosion which does not rely on them being in contact, at least not for the entire time they are being accelerated.

[Alonso Quixano]

Many thanks to everyone who replied. I'm off to tilt at more windmills.