The propellant for the Starship is liquid methane and liquid oxygen. I do not understand why does it not use liquid hydrogen as it has the highest specific impulse of any propellant known. Or is this information incorrect?

What improvements would you guys try in order for the Starship to hit the 4% mark Elon was talking about?

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π︎ Dec 07 2021
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Specific impulse was developed by aerospace engineers to feel superior over other engineers who use regular velocity.
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π€︎ u/sherlock_norris
π︎ Nov 29 2021
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Specific impulse dependency on equivalence ratio in rocket science

Iβm doing this homework assignment and Iβve used NASAs CEARUN rocket program to output 3 things. Flame temp, molecular weight of products, and specific impulse. Held constant is the chamber pressure and expansion ratio pe/pa=1.

The independent variable is the equivalence ratio, the fuel/air ratio compared to the stoichiometric ratio. What I donβt understand is why the specific impulse increases with the equivalence ratio? My combustion products are liquid oxygen and liquid hydrogen so increase the equivalence ratio decreases the molecular weight of my products and also decreases the flame temperature. I cannot find a good paper to explain this trend online. If anyone can help me understand why specific impulse increases with the equivalence ratio I would be very thankful.

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π€︎ u/Dfurrles
π︎ Dec 06 2021
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What's up with Specific Impulse? youtube.com/watch?v=7z-Unβ¦
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π€︎ u/Triabolical_
π︎ Sep 30 2021
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What determines an element/molecule specific impulse

I'm curious why metallic hydrogen is so good (1700 SI) compared to say methane mix used by SpaceX. Is it mostly a matter of the element or molecule used? And so why? What makes metallic hydrogen so good potentially?

Thanks.

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π︎ Oct 07 2021
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Moving a RigidBody to a specific rotation using only apply_torque_impulse

Hello, I've been using Godot for quite a while as a primarily 2D game engine. Recently, I've decided to dive into 3D.

Right now, I'm trying to move a RigidBody to a specific position and rotation using only apply_impulse() and apply_torque_impulse().

I've figured out moving the body to a specific position using apply_impulse():

``````func _physics_process(delta):
self.linear_velocity = (self.translation.distance_to(targetPosition)/magnetFriction * linear_velocity * delta)
apply_impulse(Vector3.ZERO, (targetPosition - self.translation) * delta * moveForce )
``````

(this solution is not perfect but works...)

My problem is that I can't figure out how to move an object to a specific rotation, in the same way, using only apply_torque_impulse().

My target angle is a Vector3, corresponding to an Euler angle.

First I naively thought I could just apply the difference between my current Euler angle and my target Euler angle :

``````func _physics_process(delta):
apply_torque_impulse(targetAngle - rotation)
``````

This ended in disaster as it turns out, you can't rotate on two axes at once without your angles going crazy.

Next, I tried to use Quaternions,

I figured out something that sort of works sometimes but will break at other times:

``````func _physics_process(delta):
var targetQuat = Quat(targetRotation)
var currentQuat = Quat(rotation)
var intermediateQuat = currentQuat.slerp(targetQuat, 1 * delta)
var intermediateEuler = intermediateQuat.get_euler()
var targetEuler = intermediateEuler - rotation

apply_torque_impulse(targetEuler * delta * 100)
``````

This solution is really unpredictable and unstable,

The problem is that I'm having a hard time properly understanding Quaternions and how to use them in my problem.

I would really appreciate some help on this seemingly basic problem.

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π€︎ u/CroissantDev
π︎ Oct 14 2021
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How do I calculate the specific impulse of a hydrogen peroxide & hydroquinone fuel & oxidizer mixture for a bombardier beetle-inspired bio-punk astronaut jetpack?
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π€︎ u/32624647
π︎ Aug 26 2021
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Family photo after 1 year - I have a problem, BUT also a specific use case for each one of them... but mainly I have problems with impulse control. (Thanks to this community for one of the greatest hobbys of all times!)
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π︎ May 19 2021
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Specific impulse for Blue Origin engines

Do you know the specific drive of the Blue Origin engines?

Searching the internet I found nothing. The strange thing is that the lack of this type of information affects almost exclusively the US

Current and upcoming rocket engines (Wikipedia)

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π€︎ u/Coerenza
π︎ May 07 2021
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What would be the best future engine to liftoff from earth to LEO? High thrust, high specific impulse and low pollution.

Nuclear fission rocket is worst idea. It is polluted

Ion rocket is unsuitable due to its low thrust that may not overcome air resistance.

Is traditional chemical rocket is the only choice to liftoff from earth?

No space elevator

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π€︎ u/Evantargaryen
π︎ May 05 2021
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Why is "seconds" used as unit of Isp (specific impulse)?

Isp is generally used for describing how efficiently a rocket engine consumes fuel.

https://www.grc.nasa.gov/www/k-12/airplane/specimp.html

So I've read this from NASA. My understanding of specific impulse is, it's the total impulse created by fuel weight carried under 1G ( total_impulse / (mass*g0) ),

or equivalent velocity created under 1G ( Veq / g0 ),

or the amount of thrust created under certain flow rate ( thrust / (mass_flow_rate*g0) )

I wasn't a good student in physics class, so I'm kind of confused by all these units now.

Are impulse and thrust the same? Or thrust is in newtons, while impulse is in newton-second?

If all above is correct, why is "seconds" used as unit for Isp, not something like N*s/kg ?

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π€︎ u/K-H-C
π︎ Jun 08 2021
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What is the RL10 of jet engines? Which jet engine has the highest specific impulse of jet engines?
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π€︎ u/FrancescoKay
π︎ Dec 26 2020
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Rockets: How is the unit for specific impulse βsecondsβ?

Iβm using imperial units.

So, Impulse_specific=Impulse_total/(m_propellant*g)

Impulse_total has units of lb*sec m_propellant has units of lb g has units of ft/sec^2

After doing dimensional analysis, Impulse_specific has units of s^(3)/(ft). The units of Impulse_specific should be s. What am I doing wrong in terms of unit analysis?

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π€︎ u/jefa536
π︎ Feb 16 2021
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How can i give an impulse only when you have in hand OR when you place it in an item frame a specific item? 1.16.5 [java]

How can i give an impulse only when you have in hand OR when you place it in an item frame a specific item? Like when i have a stick with a specific name, and only when i place it inside the item frame? 1.16.5

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π€︎ u/LC_Redcube
π︎ May 24 2021
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Someone explain how specific impulse is measure in a unit of time, please, and how the Tsiolkovsky rocket equation works without knowing thrust.
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π€︎ u/Drone_Better
π︎ Feb 07 2021
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Specific impulse is important, but it isnβt everything.
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π€︎ u/Teboski78
π︎ Jun 09 2020
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How an Australian University Student Beat NASA at Its Own Game - Through his Honours, Masters, and PhD, Paddy invented the Neumann Drive, a world record-breaking ion engine that can achieve more than 11,000 seconds of specific impulse beating NASA's best experimental efforts of 9,600 vice.com/en_au/read/how-aβ¦
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π€︎ u/mvea
π︎ Oct 08 2016
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Switching off anger with an electrode: Anger and aggression can be suppressed by targeting a specific region of the brain using weak direct current stimulation through the skull to modulate a neural circuit implicated in impulse control, finds a new fMRI study in the journal Cortex. psychologytoday.com/au/blβ¦
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π€︎ u/mvea
π︎ Jan 08 2019
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I made a video calculating the Specific Impulse of the drain valve! youtu.be/To0Uij3POkI
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π︎ Apr 02 2020
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What is the expected Specific Impulse range of fusion drives?

I have read it was around 100k to 150k!! Seems just monstruous even compared to metallic hydrogen specific impulse (in the thousand) ... I guess it depends a lot of actual implementation, but in a ball park? Are we talking of 10 thousands, 100 thousands, 500 thousands??

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π€︎ u/PocusFR
π︎ Sep 04 2020
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What is the RL10 of jet engines? Which jet engine has the highest specific impulse of jet engines?
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π€︎ u/FrancescoKay
π︎ Dec 26 2020
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Hello, Iβm not an expert on this stuff so I came here. Is it possible to artificially send the same nerve impulses or electrical currents to the brain externally in specific locations to simulate the five senses such as touching a table without actually physically touching the table?

^ |

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π€︎ u/Alelom
π︎ Aug 14 2020
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Hello rocket nerds. I've made a plot showing thrust and specific impulse of notable rocket engines. Enjoy!
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π€︎ u/R0B0_Ninja
π︎ Apr 12 2020
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Specific Impulse, But no change in Mass? Hover-Slam

Hi all,

I'm trying to use the formulas found here: https://www.desmos.com/calculator/ms0zpkjkvp for another project but wondered if there is a way of calculating Isp for a rocket that doesn't change mass (Electric).

My understanding is that Isp is how effective something is at using its fuel, so are electric powered things 0% efficient because the mass doesn't decrease or are they 100% because they can get all their thrust without reducing mass.

I'm trying to avoid re-arranging that equation if I can.

Thanks!

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π︎ Jun 01 2020
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Elon Musk on Twitter: Production Raptor goal is specific impulse of 382 seconds and thrust of 3 MN (~310 metric tons) at 300 bar twitter.com/elonmusk/statβ¦
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π€︎ u/Zucal
π︎ Sep 26 2016
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Just impulse bought a Ryzen 7 3800x, been wanting to build for years, I've got a rough outline and some specific questions pertaining to a compact build pls.

###Build Help:

What is your intended use for this build? The more details the better. Gaming mostly, also probably run a small home entertainment setup. I have a loft condo and I'm thinking I'd like to combine the TV/computer in to one. Please let me know if this is stupid.

If gaming, what kind of performance are you looking for? (Screen resolution, framerate, game settings)

I like playing CIV so lowering turn time would be nice, I think I'll be able to run basically anything else I want to play on the intended build. Probably stuff like Witcher, Far Cry, stereotypical shit.

What is your budget (ballpark is okay)?

I don't have a fucking clue. I think I'd like to keep it under \$1500 but I also just spent more on the CPU by a few hundo than what's recommended so here we are.

US

**Post a draft of your potential build here (specific parts please). This is a super fungible list.

PCPartPicker Part List

Type Item Price
CPU AMD Ryzen 7 3800X 3.9 GHz 8-Core Processor \$329.99 @ B&H
CPU Cooler be quiet! Dark Rock Pro 4 50.5 CFM CPU Cooler \$88.99 @ SuperBiiz
Motherboard ASRock X570M Pro4 Micro ATX AM4 Motherboard \$159.99 @ Newegg
Memory G.Skill Ripjaws V Series 32 GB (2 x 16 GB) DDR4-3200 Memory -
Storage Samsung 860 Evo 1 TB 2.5" Solid State Drive \$109.99 @ Amazon
Video Card Gigabyte GeForce RTX 2060 SUPER 8 GB WINDFORCE OC Video Card \$399.99 @ Newegg
Case Thermaltake Core V21 MicroATX Mini Tower Case \$64.00 @ Amazon
Power Supply EVGA 650 W 80+ Gold Certified Semi-modular ATX Power Supply \$84.99 @
... keep reading on reddit β‘

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π︎ Dec 02 2019
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Guys look at the specific impulse of Merlin and Raptor in Vacuum

Merlin Vacuum Specific Impulse: 311 seconds.

Raptor Vacuum Specific Impulse: 380 seconds.

380-311 = 69.

Elon has been trolling us all along.

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π€︎ u/Nizo_GTO
π︎ Sep 10 2019
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(ELI5)Specific Impulse for Rockets

Hey guys, Iβm writing a paper on different propulsion systems for rockets and had a question about the formula for Specific Impulse. Before saying anything else iβd like to clarify that iβm a freshman engineering student so iβm not too bright lol. But anyways, Iβm reading a journal where it compares Chemical, Nuclear Thermal and Electric propulsion and they all list their exhaust speeds. Is the exhaust speed equal to the thrust? or the mass flow rate of the propellant.

Again Iβm sorry if this sounds like a retarded question. Thank you all.

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π︎ May 03 2020
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I impulse buy so often that Amazon emailed me today to ask if there's a specific reason why I return things so often

I have a bad habit of thinking I need things and ordering them right away and when they come to my house I realise it's not as useful or necessary as I thought it would be and end up returning them... apparently often enough that Amazon became concerned π¬

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π€︎ u/HappyyItalian
π︎ Aug 07 2019
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π€︎ u/LolsDudee
π︎ Dec 27 2018
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What is specific impulse?

I know that it's a unit of the efficiency of an engine, but I'd like to know more details, such as how it's calculated, and a sense of scale.

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π€︎ u/young_fire
π︎ Feb 07 2019
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Laser Powered Plasma Thrusters Have High Specific Impulse And High Thrust - opening the solar system to manned exploration johnmccone.com/2019/03/15β¦
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π€︎ u/philmethod
π︎ Mar 15 2019
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TIL of fission-fragment rockets. They use the products of nuclear fission to generate thrust. It can, in theory, produce a very high specific impulse while being within the abilities of current technologies. en.wikipedia.org/wiki/Fisβ¦
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π︎ May 27 2020
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Realistic fusion exhaust velocity/specific impulse

I have been looking at project rho's fusion rocket segments, and there is a large range in which the different designs' performance falls in, going from barely above a gas core NTR, to over a million seconds. I am interested in what a realistic high end estimate (as in we have mastered fusion) for the specific impulse of a fusion drive. I'm also curious about the other specs as well, but I am most curious of the ISP. Thank you!

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π€︎ u/LifeByAnon
π︎ May 01 2020
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Switching off anger with an electrode: Anger and aggression can be suppressed by targeting a specific region of the brain using weak direct current stimulation through the skull to modulate a neural circuit implicated in impulse control, finds a new fMRI study in the journal Cortex. psychologytoday.com/au/blβ¦
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π€︎ u/mvea
π︎ Jan 08 2019
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im specifically saving fragments for first officer content but then I impulsively spend on music
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π€︎ u/Korw_9S
π︎ Jan 01 2022
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ELI5: What do the terms Delta-V and Specific Impulse (Isp) mean, and what do they count for when it comes to space travel? If I had a rocket in space what would these two things mean for me if I tried getting from the Earth to the Moon?
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π€︎ u/A_HECKIN_DOGGO
π︎ Oct 22 2019
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ELI5: Why do rockets use low specific impulse - high thrust engines to reach orbits? Why can't High specific impulse and low thrust engines be used for the same purpose in a bit longer time?

I believe it could lead to fuel savings as High specific impulse means better fuel efficiency. Please correct me if I am wrong.

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π€︎ u/arjitraj_
π︎ Apr 23 2019
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Need to find specific impulse of american dollar bills

because if they turn out to be more efficient than kerosene, loading a Falcon Heavy with stacks and stacks of them could be a cheaper alternative to SLS

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π€︎ u/hiyougami
π︎ Mar 13 2018
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ELI5: How does specific impulse measure rocket engine efficiency? Why is it in seconds?

I know there are other threads on this but none of them are answered well.

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π€︎ u/SlabGizor120
π︎ Oct 10 2018
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ELI5 what is the specific impulse of a rocket?
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π︎ Feb 26 2020
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