31
votes
How realistic is the 1 kg/km² solar sail in "Death's End"?
A solar sail with an areal density of $1~\mathrm{kg}/\mathrm{km}^2 = 1~\mathrm{mg}/\mathrm{m}^2 =0.001~\mathrm{g}/\mathrm{m}^2$ is impossible by known materials science because graphene has an areal ...
- 1,950
30
votes
Accepted
Teleporting an object into geosynchronous orbit
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 ...
- 178k
24
votes
Collecting antimatter from Van Allen radiation belts
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 ...
- 58.5k
20
votes
How realistic is the 1 kg/km² solar sail in "Death's End"?
There is a extensive summary report on possible improvements of solar sail materials:
"Ultra-Thin Solar Sails for Interstellar Travel - Phase I Final Report"
December 1999, Dean Spieth, Dr. ...
- 14.9k
17
votes
Accepted
Would a nuclear propelled spaceship still need a storm shelter?
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 ...
16
votes
Accepted
Why aren't linear aerospike engines in common use?
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 ...
- 54.9k
14
votes
Accepted
What kind of engine does this Isp = 1600 refer to? Is it cubesat-friendly?
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 ...
- 54.9k
14
votes
Accepted
What would be the specific impulse of a continuous nuclear fusion drive?
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 ...
- 19.3k
14
votes
Accepted
Is the propulsion for the Scorpion nuclear-thermal-electric ship concept viable and credible?
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 ...
13
votes
Accepted
Could cosmic rays be produced by alien propulsion systems?
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 ...
- 14.9k
13
votes
Accepted
Which theoretical propulsion system has the highest specific impulse?
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,...
- 54.9k
13
votes
Is there an elegant method to stop an asteroid's spin?
I found at least 1 paper proposing enclosing the asteroid in a bag filled with gas.
https://www.researchgate.net/publication/273913280_SHEPHERD_A_Concept_for_Gentle_Asteroid_Retrieval_with_a_Gas-...
- 1,788
13
votes
Is there an elegant method to stop an asteroid's spin?
Look at how satellites are commonly de-spinned, and apply it on a larger scale.
A commonly done method is the Yo-yo de-spin where you have long ropes with weights, and extending them slowy from the ...
- 231
11
votes
What will be the best way to convert nuclear fusion energy into thrust for a rocket?
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 ...
- 58.5k
11
votes
Which theoretical propulsion system has the highest specific impulse?
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 ...
10
votes
Accepted
Continuous staging?
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 ...
9
votes
Why aren't linear aerospike engines in common use?
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 ...
- 541
9
votes
Accepted
EmDrive compared to flashlight in space
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 ...
- 4,548
9
votes
Could the helical engine work?
tl;dr:
The problem is that this idea relies on a fundamental misunderstanding of Special Relativity.
$$+$$
Newton's second law of $F = ma$ doesn't work, exactly, in Special Relativity.
$$+$$
But ...
- 149k
8
votes
Could fuel be "hosed" (pumped) from the ground to a launcher?
There exist one way for this to work
As pointed out by others before, a hose is heavy to carry along. However, if the propellant station had the same altitude and velocity as the rocket, it may be ...
8
votes
Accepted
What is our ability to capture or reflect photons with a wavelength of $2.5×10^{-12}$ meters?
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 ...
- 1,184
8
votes
How does the Sabre engine's pre-cooler achieve such high performance?
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 ...
- 19.3k
8
votes
How efficient and fast would seven Caplan thrusters be at pushing the Sun and would it be worth building more than one?
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 ...
7
votes
Could fuel be "hosed" (pumped) from the ground to a launcher?
You'll lose more energy hauling that hose up than you could possibly save by pumping fuel in. A hose full of fuel is going to be heavy, not to mention you'll have quite a time keeping it out of the ...
- 11.5k
7
votes
Inertialess Drive?
NASA's already testing the EmDrive, at the NASA/JSC Advanced Propulsion Physics Laboratory.
To have no doubt that the device works, we'd need to see the test results replicated consistently by ...
- 126k
7
votes
What is our ability to capture or reflect photons with a wavelength of $2.5×10^{-12}$ meters?
The wavelength you mention corresponds to about 510 KeV. As hdhondt says, conventional optics, such as a parabolic mirror, don't work at this range. Wolter telescopes use grazing incidence ...
- 2,611
7
votes
Teleporting an object into geosynchronous orbit
As Organic Marble indicates, you'd have insufficient orbital velocity.
However, even if you haven't increased the orbital velocity with your teleport, you have increased the orbital energy by ...
- 1,023
7
votes
Accepted
Does a feasible high thrust high specific impulse engine exist using current non space technology?
How about NERVA?
NERVA (Nuclear Engine for Rocket Vehicle Application) was a nuclear-thermal engine. A reactor heated hydrogen propellant and exhausted it out the nozzle.
The engine was extensively ...
- 178k
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