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Questions tagged [efficiency]

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20 votes
3 answers
4k views

Why is the aperture door of the Hubble Space Telescope so weirdly shaped?

Why is the door not rounder? I understand it's main purpose is to block sunlight from entering the telescope. Especially the right side (in the provided image) seems to waste material. But also the ...
9 votes
0 answers
242 views

What rocket uses the largest percentage of Fuel/Oxidizer before liftoff?

inspired by this question: How much propellant is used up until liftoff? which asks how much propellant (fuel/oxidizer) a typical rocket uses before liftoff. What has been or is the most non-typical ...
13 votes
2 answers
23k views

Is the concept of the Epstein Drive based on actual theorized scientific research which is considered plausable?

I've always found it interesting when we see real life taking its cues from fictional arts, especially when it comes to Science Fiction technology. There are plenty of examples of classic books, TV ...
3 votes
1 answer
482 views

Which are more efficient: oxidizer-rich or fuel rich rocket engines?

Several internet articles claim that the high Isp of the Soviet RD-180 engine (as used in the Atlas III and V launch vehicles) was (at least partially) due to the fact the RD-180 ran oxidizer-rich, ...
5 votes
3 answers
332 views

What is the reason for a LACE rocket to dump fuel?

The concept of LACE sounds awesome, especially the part "fuel is hard to come by in the atmosphere but there's some oxidizer available". The inefficiency due to the heat exchange ...
1 vote
0 answers
80 views

Is using a variable Isp (constant power & acceleration) more efficient than a constant Isp when launching?

So after I wrote a particularly poorly received answer about variable specific impulse, based on discussion I read here, I realise I may have misinterpreted what was being discussed in that thread. ...
4 votes
1 answer
421 views

Disadvantage of interstage trusses on Soyuz launch vehicle?

Brian Tompsett gave a detailed explanation of the advantages of the trussing in his answer to the question Why do the Russians use these fence-like interstage fairings? The gap between Stage II and ...
11 votes
1 answer
2k views

What's the typical temperature of a reactor core in a nuclear thermal rocket?

I am curious of the typical temperature of a nuclear fission reactor in a NTR and I heard that increasing temperature could increase Isp but couldn't find any useful data online. Please provide viable ...
5 votes
2 answers
2k views

What is wrong with hydrazine as a monopropellant?

While answering a question about if N2O was a practical monopropellant, I found that hydrazine was considerably more efficient. So, why do people want to replace it with N2O, if hydrazine is more ...
1 vote
1 answer
192 views

What is the point of having a central rocket engine when it receives performance losses?

Recently I asked this question about center engine performance and received an excellent answer from @OrganicMarble. The first sentence of the answer is If anything, the flow field interactions hurt ...
4 votes
2 answers
572 views

How to compute each of these link budget terms?

The terms in Equation are all in decibels (dB), which is logarithmically scaled. In Equation, $P_{rx}$ is the received peak power, $P_{tx}$ is the transmitted peak power, $G_{tx}$ is the transmitter ...
40 votes
6 answers
9k views

How much has fuel efficiency increased in rockets since the Apollo missions?

I have been talking with a friend of mine and the subject turned to modern rockets versus Apollo era rockets and fuel efficiency. My friend stated that today’s rockets use half the fuel of the rockets ...
4 votes
3 answers
3k views

What (if anything) limits the efficiency of a rocket engine?

Humans have developed lots of rockets. I observe that in most cases to increase the payload capacity we just increase the amount of fuel. Is it not possible to exponentially increase the efficiency ...
3 votes
1 answer
599 views

ISP losses associated with exhaust vane TVC

What is the impact of exhaust vanes, such as those in the A4 and Redstone rockets, on exhaust velocity and overall ISP? As well as this, what is the relationship between ISP losses and the width of ...
2 votes
2 answers
132 views

Efficiency in Space Capsule Docking Process

I'm watching the first operational Crew Dragon Capsule proceed through the regimented, and VERY careful International Space Station (ISS) docking process, which was turned on after pausing another ...
3 votes
2 answers
1k views

How much more cost efficent are SRB's over the main engine?

Why use SRBs instead of a simpler rocket design that dispenses with SRB's and instead has a bigger main engine? The Saturn V escaped earth's gravity just fine without boosters. Since then though SRBs ...
2 votes
2 answers
334 views

Is it more efficient to burn all needed fuel in an Oberth manoeuvre at once or burn a fraction of the fuel for each orbit?

I was looking into Parker Solar Probes trajectory and was wondering what would be the most optimal way to utilize a retrograde thrust at perihelion to reduce the number of needed gravity assists. I ...
17 votes
1 answer
1k views

How much propellant is used up until liftoff?

How much of the total propellant mass (fuel+oxidizer) of the first stage/boosters is usually burnt between ignition and liftoff?
2 votes
1 answer
312 views

Does "Air Launch to Orbit" makes the best use of Earth's Rotation?

Usually, all artificial satellites are launched in the prograde direction, since this minimizes the amount of propellant required to reach orbit by taking advantage of the Earth's rotation. Further, ...
5 votes
2 answers
446 views

Launch capabilities of GSLV Mark III

What are the parameters of determining the launch capabilities of a rocket? Also, How does ISRO's GSLV Mark III fare against rockets like N-1, Proton, R-7 etc?
1 vote
0 answers
206 views

Orbit to Orbit Transport Stage

Would it be faster or cheaper to have a lander, SSTO, and/or SpaceX Mars rocket to rendezvous connect with a more efficient engine or "transport stage" or another lander, SSTO? When the spacecraft ...
0 votes
1 answer
165 views

Coupling satellites already in orbit reduce drag and debris?

How would 2 or more satellites be joined to reduce atmospheric drag? Could a 3rd satellite tow and join 2 or more satellites that are in similar orbits to prevent Kessler syndrome? At the very least ...
-2 votes
3 answers
326 views

Can more thrust come from launching parallel to water?

Would having the exhaust of a rocket or air breathing engine in an early stage in close proximity to water on a horizontal launch provide more thrust? Could a rocket launch off water horizontally in ...
0 votes
1 answer
109 views

What types of engines are able to go from Earth orbit to Martian orbit? [closed]

What engine is the most efficient in fuel and/or time to go from Earth orbit to Mars orbit and back again that are not capable of launching from the ground?