Talk:Relativistic rocket

message: I will present a credible theoretical design for a relatavistic , or semi-relatavistic
rocket here. For now I will use algebra & geometry based newtonian physics to describe such a rocket . A calculas based version of this description may also be presented here in a future improved version of  this article.* Improvements to the article may be made by other editors here if the nature  of their work is good, and correct. Let all editors feel free to correct
what ever spelling errors, spacing errors, or puntuation errors may be found in this article.
Tmayes1965
 
Please excuse my clumsy editing. This is my first contribution here, and I don't know much about the markup and conventions. I was trying to find the tag for attaching a signature with time and date, but I'll just type them in. 
: 1) Please kill "relatavistic", "relavistic". relativistic please.
: 2) 2nd paragraph contains two conflicting definitions of "relativistic rocket"
I have now fixed this contradiction.*tim
: 3) Punctuation is messed up. Please put a space after commas and periods, not before.
: 4) "wickipedia"?! "cruising velocity"?!!
Article begun by OneRock on 7/23/04. 
Somewhere, I have a numerical Fortran solution (or did I write that in Basic) of the general-relativistic rocket problem on a 5 1/4 floppy, which I can no longer access. It ran quite well on my old TRS-80 with no hard drive. I don't think I have the will to solve it again, but I am curious whether anyone else has such a program. 
In case you want to duplicate my work, here's what it involves: 
First, you must postulate the existence of a propulsion mechanism with specific parameters. My imaginary rocket was propelled by a laser which converts matter and antimatter to a light beam with 100% efficiency. (Onerock 19:40, 28 Jul 2004 (UTC)
replies: text: I've read as much as I can :)  Anyway, there was a science fiction story many years back about a space faring race that created highways by collapsing suitable stars into black holes, turning all the resulting energy into laser beams that were bent into loops by the created blackholes.  The idea was that to travel through space one simply dipped a mirror into these beams and got an immediate thrust.  The beam also cleared the path of any debris.  The reason I'm posting this is the fact that your calculations assume that the reaction mass-energy is carried with the ship, but in fact beaming the energy out makes the limit somewhat less useful. njh 05:30, 31 December 2005 (UTC)
thread_title:  Relativistic Rocket Problem 

message: I've put a bunch of formulas at User:Wwoods/Relativistic rocket formulas. I collected or worked them out several years ago, so I don't have the derivations at hand, but for most of them it shouldn't be to hard to verify them. —wwoods 22:36, 10 February 2006 (UTC)
replies: text: You give some data for a rocket accelerating at constant rate, but it is more relevant, especiall to this article, to correctly apply the rocket equation that takes into account the depletion of propellant during thrust. DonPMitchell (talk) 00:13, 5 July 2008 (UTC)
thread_title:  Relativistic rocket formulas 

message: A long series of paragraphs have been added to this article by the above user, describing the design of a theoretical relativistic rocket. While there are a number of useful points on design considerations that would need to be taken into account, as it stands the additions are much more a prescription for the design on an individual rocket. Sentences such as "It would have a rotating crew habitat" or "There would be an array of high energy lasers, particle beams and some missiles mounted on the starship" are nothing more than crystal ball gazing. Would it make more sense to try and selectively eliminate passages that refer to non-critical design features, move the whole section to a new article on this ""beam core" pion rocket" or just wipe the entire section and try to rebuild a few useful points of consideration, such as the need for sheilding at the bow of the craft? Icelight 01:18, 7 June 2006 (UTC)
thread_title:  Additions by Tmayes1965 

message: I reverted these additions:
:It should be noted that any electrical source can be used to have an effective exhaust velocity of nearly c using a linear acelerator.
This is not true because you have to include the energy source's fuel ...
:The implication of this is that even a c exhaust velocity needs a fuel ratio of 99.9997%; effectively making a 50 ton spaceship require 2 million tons of fuel to have 0.5c final velocity. Being able to decelerate also would mean 4x the fuel mass.
The calculation is obviously flawed.
Icek 05:46, 28 December 2006 (UTC)
thread_title:  Additions by 71.124.2.194 

message: It may be worth noting that the only onboard fuel that would be required would the amount necessary to get to a noticeably relativistic velocity.  After that point, the radiation energy from the forward direction (from stars or even from cosmic background radiation) would be blue-shifted to the point where it would be providing all the energy needed for further acceleration.  68.39.154.196 (talk) 15:18, 4 October 2008 (UTC)
replies: text: This article is really bad. Apparently none of the editors understand the difference between rocket fuel and rocket propellant. Confusing the two is rampant here. Fuel is the energy source; propellant is the "stuff" (atoms, electrons, photons) which a rocket expels in order to gain momentum. It also does, imho, a really bad job of separating the useful physical properties (of the various parts of the system) from parameters used (mostly in comparisons by hobbyists, I'd guess) to compare properties. Ve & Isp for instance. I understand that the clowns who established the field used these and that they are so entrenched in the field's literature that they need to be discussed, but I also think that most kids, after taking high school physics, are NOT familiar with them while they are quiet familiar with the concepts of mass, velocity, acceleration, and momentum. I suggest that the introductory discussion confine itself to concepts which most readers will be familiar with before jumping to other, and unnecessary, concepts.67.140.181.214 (talk) 18:39, 22 March 2018 (UTC)
thread_title:  Fuel 

message: Where do the values in the table about specific impulse come from? In particular, I can find no research article in which it was calculated that electron-positron annihilation with a "hemispherical absorbing shield" results in a 0.25c specific impulse. Also note that the values for eta and I_sp/c as reported in the table have apparently no connection with the formula for I_sp given in terms of eta, as given in the article just before the table appears. [For example, the table says that for the pion engine, eta is 0.56. However, if you plug eta = 0.56 into the equation given for I_sp, you would get I_sp = 0.898c. What is going on? If the I_sp is reduced due to "energy losses," this needs to be explicitly and clearly stated.]
Please give references for the data in the table.
Also, at the moment Reference (1) is nothing but a broken link.
Nullinfinity (talk) 22:49, 23 June 2009 (UTC)
thread_title:  Table on specific impulse needs references 

message: I_sp is defined as:
I_sp = g0 * v_e
Where g0 is acceleration due to gravity at earth's surface. This doesn't significantly affect the derivation, but either each I_sp has to be replaced with a v_e or every v_e needs to be multiplied by g0.  — Preceding unsigned comment added by 129.22.124.89 (talk) 00:25, 5 July 2014 (UTC)
thread_title:  Specific Impulse 

message: This article's lead claims:"Achieving relativistic velocities is difficult, requiring advanced forms of spacecraft propulsion that have not yet been adequately developed." Plainly speaking: this is false. First, we need to carefully frame the issue. While "atom smashers" are able to accelerate massive objects (H, Pb, & Xe (LHC); H, Al, Au, Cu, U (RHIC)) to near light speed (protons were accelerated to 0.99999999c at the LHC) with a GREAT deal of difficulty there is no recorded event in which any macroscopic object has been accelerated to near light speed. Nor is the attainment of such velocity possible with any known or reasonably straightforward improvements of known technology; that is it is not "difficult" it is (currently) impossible. Claiming is is "difficult" is false and misleading because in fact it may never be accomplished. (This is using the reasonable constraints that a rocket vehicle carries its own fuel (energy) and propellant.) "have not yet been adequately developed" is another misleading, but factually correct statement. In fact, there are very good {evidence based) reasons to believe attaining relativistic velocities with rockets in the kilogram to kilotonne range is not possible; no evidence contradicts this. I am changing this profoundly misleading sentence to:"There is no known technology capable of accelerating a rocket to relativistic velocities. Relativistic rockets require enormous advances in spacecraft propulsion, energy storage, and engine efficiency which may or may not ever be possible."71.31.150.130 (talk) 15:40, 25 January 2018 (UTC)
replies: text: I agree with the edit. An extra book source would be welcome. - DVdm (talk) 15:51, 25 January 2018 (UTC)
replies: text: This is not quite accurate. There are many theoretically possible designs that would allow such engines, and there has been some research into photonic thrusters, which (due to their 'exhaust' velocity literally being the speed of light), can absolutely be used to accelerate to relativistic speeds assuming a large enough energy supply. Current photonic thrusters have been able to exert forces on the order of millinewtons with power inputs of a few kilowatts and so it is entirely feasible that with enough resources this idea could be scaled up to practical sizes. 131.227.33.141 (talk) 18:39, 7 March 2018 (UTC)
thread_title:  Difficult