27
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How come we don’t put a huge windmill-like machine in space?
As far as I understand you want the "windmill" to drive a dynamo. Have you ever tried turning a dynamo? It takes some force to do so, and that force is then (partially) turned into electricity. So the ...
- 12.5k
25
votes
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Does it take more energy to get to Venus or to Mars?
To flyby or impact Venus varies from 3.45 to 3.6 km/s from LEO for the optimal time every 19 months. Mars varies from 3.55 to 3.9 km/s for the optimal time every 26 months. So on average, getting to ...
- 58.5k
23
votes
Accepted
How much of the energy of a rocket ends up as a noise?
The maximum percentage wasted to noise is approximately 1%.
The acoustic efficiency, defined as the ratio of the sound power to
the rocket exhaust's mechanical power, for the majority of these data
...
- 178k
19
votes
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Splitting water quickly to turn a water rocket into a H/O rocket at launch: could it work?
You'll need a nuclear reactor for that because the process of dissociation of water into constituent hydrogen and oxygen consumes vast amounts of energy and for an ascent stage you'll also need a very ...
- 76.5k
16
votes
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Do any realistic rocket systems use different substances for propellant and fuel?
To beam the power to the rocket, especially when needing high acceleration, is not what I will expect to show up in the near future. However, separating the energy source from the propellant is the ...
15
votes
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Would it be possible to generate electricty in space with a satellite in orbit
No, it wouldn't work.
In order to drive the treadmill, momentum would have to be transferred from the satellites to the treadmill. The sats would slow down and eventually stop.
The "highway" itself ...
- 167k
15
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Why are Ion Thrusters so energy hungry?
A conventional thruster with two liquid propellants requires energy too. But it is chemical energy stored in the propellants. Ion thrusters use no chemical energy at all, all the energy of the ion ...
- 48.8k
15
votes
Icy Hot Astronauts
Common wisdom says that space is cold. I wouldn't go so far as to call that a misconception, but it's certainly a bit of a misunderstood fact.
See, space is not cold in the way your fridge or a block ...
- 3,585
14
votes
Does it take more energy to get to Venus or to Mars?
The second table here essentially answers your question. Venus transfer from Low Earth Orbit is 3.5 km/s, Mars transfer is 3.6.
This will allow you to impact either body (on Venus you will need to ...
- 19.3k
13
votes
Never reducing propellant for space propulsion
NO
As a rule of thumb: if you think you invented either a way to generate infinite energy or infinite propellant: you are wrong.
But [...]
No. Always.
Your craft will gain a velocity ...
- 12.6k
13
votes
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Why are RTGs so inefficient?
Here's a brief answer since some people are trying to close the question and prevent answers:
As @ikrase points out answers to the Physics SE question Why is the Peltier / Seebeck Effect's efficiency ...
- 149k
12
votes
Could thermal energy be collected by dragging a thermoconductive device against the outer atmosphere
No: The heat produced by atmospheric reentry isn't a happy side effect of returning to the earth, it's a byproduct of the fact that your satellite/orbiter has enough kinetic energy to be circling the ...
- 7,216
12
votes
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Solar panels on Mars?
Well, we don't really know how much energy a Mars base would need, but we can make some rough estimates. Bases like McMurdo and Mawson have power capacities of several hundred to several thousand ...
- 5,626
12
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Why are Ion Thrusters so energy hungry?
The thing to notice about this type of drive is that the ions encounter the positively charged accelerating grid first. The ions that provide the thrust to the rocket are positively charged as well, ...
- 286
12
votes
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What is the distribution of ∆V amongst different stages of rocket flight?
Considering fuel consumption or energy expenditure may be misleading, because of the huge change in mass over the flight as fuel is expended. 2/3 of the fuel is expended by the first stage, which only ...
- 167k
12
votes
How come we don’t put a huge windmill-like machine in space?
Consider the windmill as a system.
If there is no wind blowing on the windmill, there is no energy being
input into the system.
If you pull power out of the windmill, energy is being output from
the ...
- 178k
12
votes
How much of the energy of a rocket ends up as a noise?
Of the the 0.2% to 1% of energy that is generated as sound, most of the sound is generated well after the exhaust gases have fulfilled their purpose of thrust:
https://en.m.wikipedia.org/wiki/...
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10
votes
Dissipating large amounts of energy fast, in space
Don't convert it into heat in the first place, and then don't dissipate it fast.
MSL used an electromagnetic brake to slow the descent of the rover from the skycrane. It dissipated the energy into a ...
- 58.5k
10
votes
In the absolute vacuum of Space, will an electric dynamo still work?
Unless the lubrication system fails in the dynamo that is in vacuum, electrical generation will work. Magnetic fields are unaffected by air or the lack of, at least at the level under consideration.
...
- 1,870
9
votes
Why are Ion Thrusters so energy hungry?
There is a sense in which the wonderfully high ISP of ion thrusters is the cause of their energy hunger, independently of the detail of their operation.
It works like this: we need a certain amount ...
9
votes
Accepted
What is the relation between the rocket equation and work, energy and power?
If you're in vacuum, the power represented by the kinetic energy of the thrust is the thrust force times the exhaust velocity (g times Isp) over two:
$$P={g I_{sp}T\over 2}$$
One SSME in vacuum ...
- 58.5k
9
votes
Accepted
"Free energy" moving the space elevator possible?
Yes, but E' > E is dubious, at least in case of Earth. The point of reversal lies exactly at the GEO altitude, where the elevator moves at speed proper for that ...
- 54.9k
9
votes
Rocket Turbopump Energy Balance
Where does that pressurization energy go?
Into the flow and then into the vehicle, exactly as you would expect!
I am assuming (like you) that the most immediate effect of a nuclear turbo-pump like ...
- 2,473
8
votes
Do any realistic rocket systems use different substances for propellant and fuel?
Kevin Parkin has been the lead researcher into Microwave Thermal Thrusters, which was his PhD thesis at CalTech. He continues to work on the technology. From an interview with NextBigFuture:
We are ...
- 21.3k
8
votes
Is wind-power a viable backup power source for Mars One?
Yes, to an extent. A few key facts:
While the atmosphere has 1% of the pressure of Earth's, it consists primarily of carbon dioxide (MW = 44) much more than nitrogen (MW = 28). Thus the effective ...
- 121k
7
votes
Splitting water quickly to turn a water rocket into a H/O rocket at launch: could it work?
First we'll see how much energy you would need for the electrolysis:
Water has a molecular weight of 18.01528 g/mol, so 1 kg of water is 55.55 mol. You need 286 kJ/mol of energy to split water. 55x286=...
- 126k
7
votes
What are the energy-to-mass ratios of some fuels/oxidizers, when including the oxidizer?
First we have to go back to the chemical equations, and this time, include the standard enthalpy of combustion.
Hydrogen: 2 H$_2$ + O$_2$ → 2 H$_2$O + 572 kJ/mol
Methane: CH$_4$ + 2 O$_2$ → CO$_2$ + ...
- 4,566
7
votes
Rocket explosion compared to kT of TNT; has one ever knocked something over at a distance?
National Geographic reports that the 2014 Antares explosion carrying a Cygnus v4 for the Cygnus CRS Orb-3 mission "knocked two spectators off the bed of their pickup truck and another off her dock. ...
- 6,906
6
votes
Splitting water quickly to turn a water rocket into a H/O rocket at launch: could it work?
A key physics limit is the conservation of energy. If you split water into hydrogen and oxygen, then let them "burn" to combine back into water, you cannot possibly gain energy from the process. The ...
- 1,939
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