All Questions
24
questions
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How high will this rocket be, when MECO occurs?
Find the altitude of the rocket at the time of engine cut-off.
Rocket Mass = 369208 kg,
Rocket Area = 391 m2,
Fuel = 170697 L,
Fuel density = 21 kg/l,
Exhaust Speed = 1338 m/s,
Exhaust Area = 164 m2
3
votes
1
answer
154
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What is missing in the conversion of specific impulse from units of seconds to thrust/mass flow rate? [duplicate]
I was trying to get the Specific Impulse of the Saturn V engines, hoping for a value in N/kg/s, as I need to know the mass consumption rate per thrust value. Any and all sources give me the value in ...
1
vote
0
answers
71
views
What is the best place on the internet to learn basic physics needed for rocket engineering? [closed]
Does anyone know a site where everything is in one place and it teaches equations and pricipals from the basics?
- 11
6
votes
2
answers
793
views
Modeling a rocket using Tsiolkovsky's equation and ordinary differential equations
So I have this uni assignment to make a model out of ODEs, and my idea was to use rockets. After some research I found about Tsiolkovsky's equation and tried using it on a Falcon 9 (disconsidering ...
- 61
3
votes
5
answers
991
views
Why is hydrogen better than helium as remass?
I just watched a very good YouTube video on why nuclear engines might be useful, and it also goes into why Hall Effect thrusters are super good at squeezing obscene ISP out of things.
During the video,...
3
votes
1
answer
481
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Pendulum rocket fallacy - so why *do* skyrockets have sticks?
This question is inspired by two, linked questions.
Skyrockets (of the pyrotechnic/firework kind) have guide sticks, which are (according to internet sources) to enhance stability: "The guide ...
- 131
20
votes
4
answers
8k
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What is the "pendulum rocket fallacy" as it relates to analogizing a pencil balanced on a finger to maintaining attitude of a hovering rocket?
I've received comments that explain to me that the analogy between rocket attitude control during a hovering maneuver and the act of balancing pencil on the end of a finger is a helpful and good one; ...
- 149k
4
votes
2
answers
758
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Design of starship fins
How much can the falling speed of starship approximately be reduced by the bellyflop fall with fins? Are we talking about numbers around 5% or 50% here?
Wouldn't it make sense to put holes where the ...
- 143
5
votes
1
answer
802
views
Contracting rocket engine nozzles
The efficiency of rocket engine nozzles depends greatly on their expansion ratio an how well the ambient pressure matches the rocket nozzles exit pressure. An optimal expansion ratio means that there ...
- 1,222
1
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0
answers
439
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Can Chemical Engineer work on something related to space?
I am an undergraduate student (scientific section) living in Qatar. I have a big interest in astronomy and astrophysics and have participated in the IOAA (International Olympiad on Astronomy and ...
- 11
4
votes
3
answers
3k
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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 ...
- 79
13
votes
6
answers
3k
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Why does this formula say rocket efficiency depends on velocity?
Wikipedia gives the following equation for the efficiency $\eta_p$ of an engine here:
$$\eta_p= \frac {2\, (\frac {v} {v_e})} {1 + ( \frac {v} {v_e} )^2 }$$
where $v$ is the rocket speed and $v_e$ ...
- 2,035
9
votes
5
answers
5k
views
Why do space rockets not start from an angle? Why go straight up? [duplicate]
I know that they used to have this idea, back in the day, of a "space gun" to fire somebody into space, and I understand why that was not safe or practical/feasible.
However, once they had come up ...
- 107
2
votes
1
answer
2k
views
How did NASA calculate 22 million "rocket horsepower" for the SLS Booster?
This answer to Does NASA really report the power of rockets in horsepower? cites NASA news item Space Launch System Booster Aimed and Ready to Fire which says
"What's impressive about this test is ...
- 149k
3
votes
2
answers
2k
views
At a height of 100 km, what speed do you need to be going to escape Earth's gravity?
I understand that the escape velocity of Earth is 11 km/s. However, Earth's gravitational sphere of influence is not infinite, so it is possible to go slower than that and still escape the sphere of ...
- 33
2
votes
3
answers
981
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Stability of rocket during flight; why does the lift force change direction when the center of pressure moves?
I am currently learning about fins and the role they play in the stability of a rocket during flight. I came across a relatively minor problem.
Here is one of the resources I'm looking at: http://www....
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4
votes
2
answers
457
views
Could a fat rocket be used on Mars?
Since Mars' atmosphere is around 2% the density of Earth's then could a much wider rocket achieve orbit?
Could the rocket be in the shape of a capsule or an optimal shape for reentry on Earth?
- 1
0
votes
2
answers
725
views
Why are exhaust nozzles in space shaped the way they are? [duplicate]
Why are nozzles in space shaped like a cone and not like a tube ensuring all the exhaust is directed strait?
- 1
2
votes
0
answers
66
views
How to make a orbital launch tube work?
Normal rockets would not work in a pressurized tube, but could a stage be made for the diagonal launch tube to save fuel and weight? Can the bottom stage be nuclear powered?
Unlike the piston launch ...
- 1
1
vote
3
answers
1k
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How does a rocket in space go faster than its own rocket engine gas velocity?
How can a rocket in space go several times faster than its own engine's gas velocity? Doesnt this break Newton's 3rd law? Gas velocity, 12,800kph, rocket speed 40,000kph?
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8
votes
2
answers
878
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Is engine thrust noticeably increased near the ground?
I know next to nothing about rocketry and space flight.
I assume that the majority of the force generated by a rocket's engine is simply the result of throwing gasses out of the bottom very fast, and ...
- 181
1
vote
1
answer
687
views
Chamber pressure for Merlin vs Raptor
So, I've been doing some digging, and I found that the chamber pressure for the raptor engine is more than 4 times that of Merlin (~4,000 psi to ~980 psi). How would SpaceX manage to pressurize the ...
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8
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3
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14k
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What does the exhaust plume of a rocket look like in vacuum?
There are plenty of photos of rocket tests and launches in atmosphere, and in these the exhaust plume tends to be a long thin flame.
Is this true for when rocket engines operate in a vacuum? My guess ...
- 83
9
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3
answers
4k
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Oberth effect for Earth vehicles
I don't understand this and must ask a probably very stoopid question here:
The Oberth effect says that a rocket is much more efficient when (and in the orbital direction of) a payload when it ...
- 27k