h a l f b a k e r yIt's as much a hovercraft as a pancake is a waffle.
add, search, annotate, link, view, overview, recent, by name, random
news, help, about, links, report a problem
browse anonymously,
or get an account
and write.
register,
|
|
|
draughting rockets
Is the plasma from a rocket easier to travel through than the atmosphere? | |
I had the thought of firing a ball of plasma into orbit with a protected rocket inside but even my mind baulked at the number of scifi steps needed for it to be a reality.
I did come up with the question of whether a rocket traveling in behind another rocket has a less eanergetic trip ? due to the
first doing a lot of the work.
If this is feasible, the first rocket could be a drone of the second. Third could make a train of it, in the trains of the other two.
Launch one, get another one off by 10% less.
Wikipedia: Ayaks § Plasma sheath
https://en.wikipedi...Ayaks#Plasma_sheath
Mentioned in my anno [notexactly, Sep 23 2019]
Rocket engine nozzle
https://en.wikipedi...ocket_engine_nozzle
They look simple. They’re not. [Frankx, Sep 25 2019]
Wikipedia: Drag-reducing aerospike
https://en.wikipedi...-reducing_aerospike
Mentioned by [Frankx] [notexactly, Sep 26 2019]
[link]
|
| |
Most of the energy goes into hauling the vehicle's mass (most of which is fuel) out of the gravity well; an orbital launcher is on a near-vertical trajectory, and above 15km (where it gets very quickly) air resistance ceases to be significant. |
|
| |
//thought of firing a ball of plasma into orbit with a protected rocket inside but even my mind bulked// |
|
| |
The rocket could project its own preceding plasma... or at least a continuous collapsing super-heated volume of air at an optimal distance which would create a partial vacuum in front of the craft. |
|
| |
You would very quickly get your rocket out of the Earth's gravity
well if only you could get it to stay still while the Earth went
zooming off at 110 000 kph on its orbit around the Sun. Cosmic
equilibrium would be maintained in this case by the enormously
accelerated spinning of Newton in his grave. |
|
| |
// continuous collapsing super-heated volume of air // |
|
| |
Supercavitation for torpedoes (like the Shkval, widely known to exist, as used by the Kursk, widely known to have sunk) is Baked but in a launcher you must justify every extra gramme of mass - mass limits on torpedoes are rather less challenging. The idea was extensively researched in the 1950's and '60's - vide various published NASA studies. |
|
| |
The extra mass on your supercavitation system has the be less than the fuel saved in just punching through by brute force. |
|
| |
Bear in mind that such a system will need to be mounted at what rocket scientists refer to as "the pointy end". So either you work out a clever way of jettisoning it once you're out if the atmosphere, or it is designed to have negligible residual mass, or you lug the thing into orbit and add it to the ever-increasing cloud of junk up there. |
|
| |
Fair enough, only a small skin of air to worry about, relative to the jump.
Is the fuel burn linear or is that 15/200 a larger chuck of effort because of the air and fuel weight? |
|
| |
[pertinax] bulked fixed. I wonder what Newton's take on Quantum Mechanics would have been and his thoughts on how the fabric of space-time can help us climb the gravity well. |
|
| |
Of all the features of plasma, getting rid of mass fast seems the only one utilized. |
|
| |
// Is the fuel burn linear // |
|
| |
Not entirely, but the mass/velocity equation for a rocket (Tsilkowsky et. al., q.v) is a second order differential equation. |
|
| |
There is more pressure behind a rocket than there is in
front of it. That's what keeps it moving forward. |
|
| |
Yes, but at least it's not perpetual-motion over-unity lighter-than-air solid Bad Science; theoretically, the idea is not without merits, but in reality the extra mass penalty is too big. |
|
| |
Horrible thing, reality; that's why we carefully avoid it. |
|
| |
//we carefully avoid it// I think it's more the other way
around. |
|
| |
It's kind of a mutual thing, actually. |
|
| |
// //continuous collapsing super-heated volume of air// // |
|
| |
//Supercavitation for torpedoes (like the Shkval, widely known to exist, as used by the Kursk, widely known to have sunk) is Baked but in a launcher you must justify every extra gramme of mass - mass limits on torpedoes are rather less challenging. The idea was extensively researched in the 1950's and '60's - vide various published NASA studies.// |
|
| |
Can't find the specs any more, but apparently Russia has a jet which uses focused microwaves to super-cavitate air and create a partial vacuum while in the atmosphere.
You might have better luck at finding it than me. |
|
| |
//The extra mass on your supercavitation system has the be less than the fuel saved in just punching through by brute force.
Bear in mind that such a system will need to be mounted at what rocket scientists refer to as "the pointy end". So either you work out a clever way of jettisoning it once you're out if the atmosphere, or it is designed to have negligible residual mass, or you lug the thing into orbit and add it to the ever-increasing cloud of junk up there.// |
|
| |
hmmm, if the cavitation devices 'are' using focused microwaves like I read then perhaps beefing them up a bit and leaving them in LEO might be just the ticket for vaporizing garbage with orbits which are out of control while offsetting the cost of added weight.
Honestly though, if your rocket does not have to overcome atmospheric resistance then I think the extra weight vs. fuel thing goes away on its own. |
|
| |
//I think the extra weight vs. fuel thing goes away on its
own.// |
|
| |
For a big rocket, not really. Air resistance isn't a large factor
(especially as speed increases only as air density is falling
anyway). Extra mass, though, exponentiates in terms of fuel
requirements. |
|
| |
Interesting. Well obviously a dissipating gravity well at an optimal distance is the way to go then. |
|
| |
What sized aerodynamic flow does a fighter jet produce? |
|
| |
At least a Red Arrows five point, positive quadrant hyperbolic send off to 14,000m on the rockets trajectory axis wouldn't be a waste. It's still a, state of the art, visual display. |
|
| |
You're 'avin 'a larf, ain't yer ? Hawks are only little trainers ... 14000m is the edge of the envelope, if you want to go aerobatic at that altitude you'll need a Typhoon or an SU-27. |
|
| |
//Most of the energy goes into hauling the vehicle's mass (most of which is fuel) out of the gravity well//
So, logically, the answer is to fire a large source of gravity into orbit just ahead of the rocket, to neutralise the Earth's gravity - such as a very small black hole, or handy chunk of a white dwarf or neutron star |
|
| |
The sensible way is to use a graviton-polarity generator. |
|
| |
//graviton-polarity generator//
Does Radio-Shack still have those, or will I have to go
find one on e-bay? |
|
| |
//e-bay// Maybe there's an equivalent Higgs-bay out there. |
|
| |
//Typhoon or an SU-27// 14,000m was the guessed end of run but these planes could design a bigger splash/wash. To weave up the right functioned atmospheric wave; size, shape, and specs of a group of planes or even different planes would all come into play in sculpturing the air. |
|
| |
Why not use a vertically-launched rocket ? Oh, wait ... |
|
| |
Yo Dawg!
I heard you like rockets, so I put rockets on
your rocket so you can launch while you launch. |
|
| |
For a rocket, the best possible scenario would be every combustion reactant vectoring in the perfect direction to push the rocket forwards, well that's what the chamber and nozzle do. |
|
| |
Is there a complex pattern of air, a perfect patterned air environment, that will boost the rocket's engine in that first 15km stage? The denser under the rocket, lighter on top, right? |
|
| |
A thought, when does the reactant leave the rocket. When one throws a ball the, exact point the ball untouches the hand Newton's reaction is split. For a rocket is it in the reaction chamber? If the chaotic reacting, all directions vectoring plasma is treated as a solid then somewhere at the convergent section, before the nozzle, the plasma isn't touching the rocket anymore. |
|
| |
// There is more pressure behind a rocket than there is in front of it.
That's what keeps it moving forward. // |
|
| |
Are you saying that that implies that the first rocket would push the
second rocket backward, and keep it from making headway? Because
the rocket's trail is not at a higher pressure than the surrounding
atmosphere, once it's stopped expanding radially. Keep in mind that the
reason different rocket nozzles are used in atmosphere and in vacuum
is that the nozzle is sized such that it lets the propellant expand to the
same pressure as the surroundings (or as close as practical) before
leaving the nozzle. |
|
| |
// Can't find the specs any more, but apparently Russia has
a jet which uses focused microwaves to super-cavitate air
and create a partial vacuum while in the atmosphere.
You might have better luck at finding it than me. // |
|
| |
// For a rocket, the best possible senario // |
|
| |
Sp. 'scenario'. 'Senario' is apparently a masculine given name in Spanish. |
|
| |
// when does the reactant leave the rocket[?] // |
|
| |
The reaction force, as I understand it, is applied to the combustion
chamber and the nozzle. Of course, the combustion chamber pressure
is higher than the nozzle pressure, and both are higher than the
ambient pressure, so both parts have outward pressure in all
directions. It's just that the forward pressure is the biggest component
of that. |
|
| |
hmm... nuclear reactors are generally pretty heavy but, if you already have one in orbit, you could fire an x-aser along the rocket's trajectory. Though, like the Borg said... |
|
| |
Wonder how/if that would work for reentry : save a few million in ablatives. |
|
| |
What would be slowing you down, then? |
|
| |
Initially I was thinking that denser air is more solid for the expansion to grip/ push against in the first 15Km. The increase in parasitic drag would not increase as much as the potential gained from a combustion against a denser medium. A rocket would work better under water. |
|
| |
Can a better rocket combustion air interface be designed by combustion chamber texture or complex manifold shape? |
|
| |
Rocket nozzles are pretty much optimal for what
they do. They don’t create a pressure behind the
rocket to “push it along”, they convert pressure (in
the chamber) to velocity (in the bell). The shape
of the bell is optimised so the exhaust exits at
ambient pressure, but with high speed.
If you look for where in the rocket the “push” is
acting, it’s at the top of the combustion chamber.
Or maybe the throat. |
|
| |
And the plasma thing - it works in water because
water’s really dense. It’s probably not going to
help much in air.
But I do seem to remember that Trident achieved a
significant increase in range by sticking a 6-foot
pole on the front. Supersonic shock waves and
stuff. Aerospike (not the engine). |
|
| |
*ping* Oh no! Why are jet engine nozzles such a
different shape from (atmospheric) rocket engine
bells then? |
|
| |
Aargh! And where in a jet engine is the thrust
acting? On the back of the compression stage disk?
What about a ram jet, where then? |
|
| |
Don't panic, the endless series of questions is a normal development stage when trying to get out of the box. |
|
| |
// Trident achieved a significant increase in range by sticking a 6-foot
pole on the front. Supersonic shock waves and stuff. Aerospike (not the
engine). // |
|
| |
That reminds me of the thought I had the other day: You could launch five
whole Electron rockets (which are orbital launch vehicles themselves) to LEO on
a Falcon Heavy, unfaired, with four in a square and one in the center
sticking up to break the air. Its shockwave would, ideally, pass in front of
the other Electrons' nosecones, meaning they wouldn't be exposed to
supersonic flow at all. More importantly, that means you don't have to
worry about adverse shockwave interactions. |
|
| |