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58

The problem is what Konstantin Tsiolkovsky discovered 100 years ago: as speed increases, the mass required (in fuel) increases exponentially. This relation, specifically, is $$ \Delta v=v_e\ln\left(\frac{m_i}{m_f}\right) $$ where $v_e$ is the exhaust velocity, $m_i$ the initial mass and $m_f$ the final mass. The above can be rearranged to get $$ ...


20

TL;DR: This answer arrives at roughly the same conclusion as Kyle Kanos', i.e. in addition to payload considerations, the difficulty lies in stuffing a small rocket with a mass of fuel exceeding to the mass of the rocket itself. This answer, however, is more rigorous in how the $\Delta v$ budget is treated. Developing a relationship between rocket and ...


9

The primary factor that determines the ability of an aircraft to takeoff is having a speed exceeding that of the liftoff speed: that is the minimum (air) speed of the aircraft to generate sufficient lift by its wings to counteract the gravitational pull from the earth. Large passenger planes at takeoff often change the wing configuration (lowers flaps etc) ...


5

Probably possible, rockets have been built that used kerosene and even Hydrogen peroxide. Liquid natural gas stores a lot of energy per volume, but hydrogen is very light and so offers a huge amount of energy per kg. And in trying to accelerate your rocket vertically upward at several 'g' it's kg that matter. Note: data from ...


4

The principle of relativity says that we can analyze a physical situation from any reference frame, as long as it moves with some constant speed relative to a known inertial frame. Thus, the ion drive does not find it more difficult to accelerate the ship when the ship is "going fast" because the ion drive cannot physically distinguish going fast from going ...


4

I think you are really asking "how can light deliver an impulse to the sail". The answer is that although light has no mass it does carry momentum. When light is reflected off the sail, conservation of momentum requires that the sail changes momentum by twice the momentum of the light. The extra kinetic energy of the sail comes from the red shift of the ...


3

Because most payloads are quite heavy. I am not sure what kind of payloads you had in mind, I am no expert on this, but I think that most launches contain satellites, which might be heavier then you think, for instance the satellite in this BBC Documentary weighs 6000 kg. And according to Wikipedia, miniaturized satellites weigh less than 500 kg (so heavier ...


3

I am an engineering student making an ionocraft as my master's project, these are my 2 cents: Initially, there is the problem of space charge saturation: simply put, there is an upper limit to the amount of ions that can coexist in a given space. This has been shown and modelled in papers concerning high voltage coronas. Another way to see this is as a ...


2

Well, the structure of spacetime (i.e. special relativity) imposes an overall speed limit of the speed of light, $c = 299792458\frac{\mathrm{m}}{\mathrm{s}}$. So whatever maximum speed you do get up to, it's going to be less than that. You've done the calculation to show that, non-relativistically, the ship would pass the speed of light in less than a year; ...


2

The acceleration you're describing is known as a gravity assist. You can get an idea of the maximum acceleration possible by working in your rest frame i.e. the frame in which you're stationary and the planet is approaching you at a speed $v$. If you can arrange to do a half loop round the planet and exit in the opposite direction then you'd leave the ...


2

A problem I can see with this layout is that it generates a point (at the last upward curvature) for the plane to lift off. In general planes need different runway lengths depending on weight and type of the plane, as well as on external influences like wind. I therefore assume(!) that a typical flat layout is suited for a wider range of aircraft, and also ...


2

Delta-V is effectively just a change of speed so it has dimensions of $LT^{-1}$ e.g. metres per second. Suppose you have a rocket with mass $m$ that can generate a thrust (i.e. a force) $F$, then by Newton's first law the acceleration is simply: $$ a = \frac{F}{m} $$ Acceleration is $dv/dt$, so you get the change in velocity simply by integrating the ...


2

Disposal in outer space The objective of this option is to remove the radioactive waste from the Earth, for all time, by ejecting it into outer space. The waste would be packaged so that it would be likely to remain intact under most conceivable accident scenarios. A rocket or space shuttle would be used to launch the packaged waste into space. There ...


2

The distance to the asteroid belt is roughly 1.5 AU (1 AU $\sim$ 150 million km). To reach that distance in 1 year (one way trip), we'd need to travel at $$ \frac{1.5\cdot150\,{\rm million\,km}}{1\,{\rm year}} \simeq 26,000\,{\rm km/h}\simeq7\,{\rm km/s} $$ The shuttle that took Curiosity to Mars did the 563 million km trip in about 8 months, leading to ...


2

Although your terms are not precise, I have a feeling that what you are describing is a Rubens' Tube. Yes, the combustion reflects the standing wave as shown below (from Wikipedia): Recall that sound is made up of pressure waves and so a standing sound wave means there is larger pressure at some points and lower pressure at others. At the high pressure ...


1

Dyson fans are NOT efficient (despite claiming otherwise). They emit about 1 gram of high-speed air for every 10 grams of air accelerated. Sounds efficient, right? No! The Dyson fan is analogous to throwing a 1kg dart at 10 m/s toward at a 9kg target sitting on ice. The resulting dart+target has a velocity of 1 m/s (momentum conservation). However, the ...


1

Think about the recoil of a gun. The gun shoots some mass (the projectile) with very high momentum into negative direction. Because of the balance of momentum the gun gets a momentum into positive direction. The jet engine does the same with highly accelerated gas which has also mass and therefore also a high momentum at high speed.


1

A hamburger's enthalpy of combustion equals TNT's enthalpy of detonation. Energy proposes, power disposes. Consider a 100 W bulb running for an hour vs. the same total energy handled within a microsecond, 100 W vs. 360 GW. A Space Scuttle detonation would have transpired over minutes (mixing plus propagation time) vs. nuclear microseconds. Now, coupling ...


1

In space the exhaust gases will never cool. They will get more and more diffuse, but the temperature will remain the same. We measure the temperature of a gas by measuring the speed profile of the particles (molecules, atoms or whatever) and comparing the measured speed profile with the Maxwell-Boltzmann distribution. In an atmosphere the particles in the ...


1

In principle you can shoot anything into space. Economically, it will never be affordable, but how about energetically. The earth escape velocity is about $v_e=11.2 km/s$. This means, that per unit mass, to get something to outer space, you need at least the following amount of energy $$ \frac{E_{kinetic}}{m}=\frac{1}{2}v_e^2 = 63 \frac{MJ}{kg} $$ Now it ...


1

By conservation of momentum. When the thruster expels high velocity gas in one direction, that gas has momentum. Since there is no external force acting on the system, the total momentum of the system (thruster and expelled gas) cannot change. Thus, the thruster must acquire an opposing momentum such that the total momentum is unchanged. See the Wiki ...


1

If you give your disk enough ideal properties, such as being infinitely thin and conducting heat perfectly, so that there is no temperature difference between both sides, so that its own radiation has no net effect on its movement, and being able to reflect and absorb radiation perfectly no matter what the wavelength, then methinks it will be the ...


1

Specific impulse and Δv describe different quantities. Specific impulse describes the efficiency of rocket engines by telling you how much thrust (force) you are going to obtain by burning particular type of fuel at a particular rate: \begin{equation} F_{thrust} = I_{sp} g \frac{dm}{dt} \end{equation} Δv on the other hand describes the required change in ...


1

Nice thought experiment! The most optimistic scenario would be that all of the incident radiation on the front of the ship were light (that way there is no energy stuck in the form of rest-mass), and that it was all (somehow) captured (e.g. 100% efficient solar-panels). It's easy (see: energy-momentum relation) to show that converting all of that energy to ...


1

Vertical take-off/landing aircrafts already exist, the Harrier is probably the most notable example. The Air-Elf however is not an aircraft, it is an image on a web page. It does not seem that any actual engineering has gone into it. The wings should supposedly work by the cyclogyro principle, note that the Wikipedia article seems rather biased towards the ...


1

It looks to me that in principle it could work, but there are practical issues: the wings are small, meaning it would take a lot of power, thus heavy engine, high fuel consumption, etc. stability and balance. I see no tail or delta or canard to stabilize its airspeed. Hardly any control surfaces besides the stubby wing. There is a tendency to be really ...


1

The problem I've encountered is that ion thrusters produce low thrust, nothing like one gravity. This means it would take much longer time to reach even nearby star systems. This is a quote from Wikipedia: "Electric thrusters tend to produce low thrust, which results in low acceleration. Using $g=9.81\,\frac{m}{s^2}$; $F = m\cdot a$ or $a = \frac{F}{m}$. ...


1

It is not sound propagation but rather momentum diffusion that makes a fish swim. The rate at which momentum diffuses is determined by the kinematic viscosity, which for water is about $10^{-6} m^2/s$. It takes minutes for momentum to diffuse in water over distances of centimeters, while the time scale over which a fish wiggles is tenths of a second. So, ...


1

Yes the fish will swim normally. Most people who have fish in an aquarium would agree. Would those fish lose the ability to swim if I lowered plate glass onto the water surface to make a totally encapulated swimming space? No. Another way to look at it: If you had a totally encased mixing bowl, which was totally filled with water, and manufactured so as ...



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