29

I'm afraid you are incorrect. An object on the equator of Earth has a velocity of ~460 m/s. A satellite in geosynchronous orbit has a velocity of ~3000 m/s. You may be confused by the fact that both objects complete an "orbit" in 24 hours. But consider the fact that the satellite travels a significantly greater distance in that time.


22

Does it have any additional thrusters? Not to thrust towards its targets. For that, it's 100% ion thruster propelled. It does also have a set of 12 MR-103G variable thrust (0.9 N maximum) RCS (Reaction Control System) hydrazine monopropellant thrusters that launched with only 46 kg of propellants (read: total thrust of its RCS doesn't provide the spacecraft ...


21

Original Answer Given Alcubierre's math, and White's calculations, it's a viable avenue of research to pursue. Whether or not it is practical as FTL, and given the expected maximum apparent speed of about 10 times the speed of light (White), and that the math says it should be able to be done, an attempt to implement a prototype series should be of immense ...


17

The total antimatter in the van Allen belts is estimated to be 160 nanograms. Annihilating that with matter would produce a whopping 8 kW-hr of energy. A quarter of a gallon of gasoline has that much energy. The star ship would be better off getting a quick spurt from a gas station pump before heading out.


16

It's a violation of Newton's 3rd law of motion? This is a fairly complete answer to the question in the absence of any deeper argument by the proponents of the device, but I'll get to those in a minute. Firstly, it's important to recognize that our universe follows a set of predictable and consistent laws. This might have been controversial in the 1700s. One ...


16

The basic idea here is to turn to have the shield you have towards the Sun. That does actually work, because the radiation from the Sun is directed, with a few exceptions: First, inside a planetary magnetosphere, charged particles are bent, and form radiation belts, for example the Van Allen belts. There, shielding is a bit more difficult. Secondly, that is ...


15

This is a repository community-wiki post with references to current work on Alcubierre drive at NASA (Harold White) and in other places. Harold White. Warp Field Mechanics 101 (2011). http://hdl.handle.net/2060/20110015936 Harold White. Warp Field Mechanics 102 Energy Optimization (2013). http://hdl.handle.net/2060/20130011213 (See also YouTube videos: http:...


15

Money. Most engine designs we're now using are an evolution of the space race era in one form or another, from the times when financing research in rocket engine / nozzle design wasn't such an issue. Linear spike fundamentally changes rocket design, for one engine support structure, and would as such require a revolution in engineering if someone expects it ...


14

Aerospikes are notoriously difficult to cool efficiently. With a bell nozzle, you have a minor part of rapidly expanding(+cooling) exhaust touching the broad, actively cooled nozzle - that means little conductive heat transfer, lower temperature gradient, lots of area for coolant plumbing on the outside (or within) the bell, and outer area radiating a lot ...


14

The easiest way is just to think in terms of energy. Using numbers from wikipedia, the mass of a deuterium nucleus is 2.014 daltons, that of a tritium nucleus is 3.016, helium 4 is 4.0026 and a neutron is 1.0087 Thus the net energy production is about 0.019 or very roughly 1/250 of the mass of the products, and in the perfect engine you describe, all of ...


13

I can't give a precise answer to your primary question besides "Extremely unlikely", but here are some facts on cosmic rays that might help coming to a conclusive answer: Current models are able to describe the distribution of energies and ion masses rather well. What we do not know precisely is the source of this radiation. There are plenty possible ...


13

The specific entry of the table appears to be the HIPARC-R hydrogen arcjet thruster developed by Space Travel Institute of University of Stuttgart. The concept of Arcjets is to use the propellant as conductor between two electrodes, creating intense electric arc, and exciting the propellant into superheated plasma. This allows to infuse it with more energy ...


13

With respect to specific impulse and nothing else? Simple, the photon drive, $c\over g_0$ or $3.057×10^7$ seconds (almost a year). It's pretty damn simple though - any kind of directional light source, like a halogen bulb with a reflector works just fine, you can also go with photons in other spectra - hard gamma from antimatter acceleration (providing you ...


12

Dawn and Deep Space 1 both use the NSTAR ion engine - I got my stats from a mix of sources so there may be small differences between the engines used on the two spacecraft, but they seem to be pretty similar. Dawn has 3 redundant NSTAR thrusters (not intended to be used together); DS1 has 1. Thruster mass is 8.2kg, power processing unit and control unit ...


12

As with any hypothetical design, one is limited to consider if it's making some "unreasonable" assumptions. First, one may compare the claimed performance to existing technology. Nuclear rockets were abandoned early, but the completed prototypes give some lower bound for what's possible (NERVA, RD-0410). Thrust: 2000 kN (NERVA 247 kN, RD-0410 35 ...


11

Baryonic matter by necessity occupies spacetime, but since the theoretical Alcubierre drive warps spacetime, there wouldn't actually be any travel through it and no additional interaction with baryonic matter would occur due to it. Miguel Alcubierre's proposal for warp drive does call for exotic matter to create a distortion in spacetime, when perceived as ...


11

Exploding thermonuclear bombs behind a big, thick plate, with the payload on giant shock absorbers behind that, referred to as Project Orion, is practical today, and has been for decades. There is no other practical way to generate net energy from fusion, and there won't be for decades.


11

Optimising for Isp only is problematic, as it's simply: $$I_{sp} = \frac{v_e}{g}$$ Which is the same as optimising for exhaust velocity. With no constraints on thrust, particle accelerations can achieve velocities arbitrarily close to the speed of light (The LHC is 3 m/s close). That's an Isp 30.6 million seconds, which can't be directly used in the usual ...


10

If gravity was repulsive between the Earth and the asteroid, this could at least make sense in principle. In that case, getting close is like pushing on a spring, and with a carefully managed trajectory, you might be able to finish the trajectory on the surface, with zero gravity. But gravity isn't like a pushing spring, it's like a pulling spring. That ...


10

It uses lots of ridiculously fine tubing - about 50km in a unit with walls thinner than a human hair. Each unit consists of about 20-30 modules, each consisting of thousands of closely arranged parallel tubes arranged in a single revolution spiral. Helium, chilled by the liquid hydrogen fuel (at below 20K) enters the spiral at the inside edge of the spiral ...


10

Conceptually, staging is getting rid of hardware we no longer need. Keeping useless hardware attached to the rocket is expensive, since added mass reduces acceleration. Ideally, we would want to get rid of hardware as soon as it gets useless, instead of piling it up to a "batch", which is essentially what the question boils down to. Rockets are very simple*...


9

Edit: second attempt, my initial post was completely incorrect. My intuition tells me you'll run into a limit on the exhaust velocity with a system like this. My initial thought, "The exhaust speed of a rocket is limited by the speed of sound" is incorrect, so where could the limit be? So let's see where we end up if we use the highest pressure possible ...


9

We can compute the power required to maintain speed as: $$ P=\frac{C_D}2\rho A v^3 $$ Assuming the hypersonic drag coefficient is around $1$ and that the atmospheric density is $1\%$ of Earth's, we get: $$ \frac P A=\frac 1 2\times 0.01225~\text{kg}/\text{m}^3\times\left(5.0~\text{km}/\text{s}\right)^3 = 780~\text{MW}/\text{m}^2 $$ Even on Mars the ...


9

A photon drive (the flashlight example) doesn't use reaction mass, just the momentum of (massless) photons. So if it's supplied with power, e.g. from the sun, it can keep thrusting indefinitely. The most obvious example is a solar sail. However, photon drives have a thrust/power ratio of about 3.34 nN/W, which means that ~300 MW is required for 1 N of thrust....


8

Exotic matter is an area that is worth looking at. The geometry of warp drive (or equivalently, Krasnikov tubes) is not really as interesting for FTL travel as people believe: Something that usually gets overlooked is the causality of the matter-geometry dependency. You need the matter to be deployed first on a space-like region between a home and a ...


8

The Everyday Astronaut just released an hour long video investigating this question. Some of the main points are: Aerospikes are especially advantageous to single stage to orbit vehicles, and current space companies are not building those. There isn't really an advantage in SSTOs compared to multi stage rockets. The efficiency advantage of aerospikes isn'...


8

Electromagnetic radiation with frequencies above $10^{19}Hz$ are conventionally called Gamma Rays. Gamma rays will penetrate instead of reflect of most materials. Reflection is only possible at very shallow angles of incidence, and even then it works best for lower energies like X-rays, below $10^{19}Hz$. This method is used in the European X-Ray satellite ...


8

There is some information online. Summarising that, it seems to be a matter of incremental improvements. Compared to other heat exchangers, they use more smaller thinner-walled coolant pipes, have a clever geometry, etc. Wikipedia has some complementary information, including the reason for using a closed helium loop for the cooler, rather than directly ...


8

Quick summary of what a "Caplan" thruster is: A Dyson swarm collecting sunlight, shooting it back at the Sun to stir up mass as solar winds. Some system to collect that solar wind. Fusion reactors, using the helium from the collected solar wind. A fusion product jet of oxygen-14 pointed into space. A hydrogen jet pointed back at the Sun. Caplan's ...


7

Thrust is a reaction force, so yes this formula provides instantaneous thrust. I think what you're asking is how does thrust (force) translate into velocity. Force is a rate of change of momentum (i.e. F=ma). To get velocity you need to integrate that over time. If you think about it, you're given F and m, you solve for acceleration and then integrate over ...


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