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Questions tagged [thrust]

Force produced by pushing against a reaction mass in space à la Newton's third law: "For every action there is an equal and opposite reaction." The thrust of a rocket engine is the forward force produced by expelling the exhaust mass (reaction mass) in the backwards direction.

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2answers
1k views

How are rockets gimballed to produce a gravity turn for the space shuttle?

I'm trying to simulate a gravity turn using a gimbaled thruster. I'm using the dynamical system described in a previous post of mine to execute a gravity turn by changing the angle $\phi_T$ between ...
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1answer
468 views

What does it mean when the Voyagers "switch thrusters"?

The Gizmodo article NASA fights to keep the Voyager probes running after four decades says: As another example of the probes' need to adapt to circumstances to keep going, Voyager 2 has fired up ...
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Why is there a hole in solid rocket engines?

I would like to find out why there is a straight hole down the middle in all solid rocket engine motors. I thought it only makes sense in hybrid engines where pure oxygen needs to be blown down the ...
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618 views

Are side boosters sometimes angled even if they are symmetrically arranged?

When more than one side booster is added to a first stage to increase thrust and they are distributed uniformly around the core (as opposed to those shown in links below) thrust does not seem to need ...
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2answers
705 views

What is a non-propulsive vent?

I just hear the term "non-propulsive vent". Is it a thing, a vent that does not cause propulsion? Or is it an event, where a vent of some unwanted gas has occurred which did not result in a ...
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113 views

How should mass specific impulse calculated for relativistic exhaust?

This answer says: 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 ...
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2answers
842 views

Shear forces between Shuttle, tank, and boosters - what pushes what?

This is the question that I should have asked here. The space shuttle and the two solid rocket boosters (SRBs) are mechanically attached to the giant tank. SRB's, shuttle, and tank all experience ...
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230 views

Falcon 9 Merlin 1d thrust calculated through every moment of flight

I am currently trying to recreate the launch of falcon 9 in unity. For the calculations I need the thrust of the first stage (only doing it for one stage for now). How to calculate it depending on the ...
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1answer
265 views

Has an object ever been put in orbit where the first stage was always at maximum thrust?

Variable thrust through changing the number of engines burning, or through propellant throttling, or other means is often/usually done to reduce maximum aerodynamic stresses on the rocket as well as ...
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4answers
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Why do pressure-fed systems have to be pressurized with helium or nitrogen?

This is something I just don't understand. The way I see it, propellant can be pressurized all on its own in the tank. Just pump a lot of the stuff in there and make sure the tank is strong enough. ...
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498 views

Upper stage structural loads on ascent?

In another question, this came up: For example, if a Falcon 9 launches 20 tons of fuel to dock in LEO, how can the same upper stage be used to launch 40 tons of fuel to the same orbit? Doesn't it ...
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1answer
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How did the Space Shuttle maintain thrust/weight balance

As a seasoned KSP player, I am aware of how important it is during ascent to have center of thrust and center of mass perfectly aligned. If you don't, your rocket will deviate from its course and ...
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How far would the STS get without the SRBs

This is a very stupid hypothetical - sorry! Would the Space Shuttle Orbiter plus external tank have been able to leave the pad just using the SSMEs (i.e. without the solid rocket boosters ~80% of its ...
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1answer
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Merlin 1D Engine Throttling

How does the SpaceX Merlin engine control the mass flow rate to throttle its thrust? Do the pintle injectors move? Does the mass flow rate to the gas generator change?
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1answer
873 views

Ways to obtain thrust curves of different grain geometries

Different grain geometries in solid-fuel rockets produce various thrust curves: I can imagine it's not too difficult to obtain a thrust curve of a specific grain geometry with a measurement while ...
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What are the various ways that rockets measure the instantaneous thrust of each engine?

@DavidHammen's answer to Engine failure: how to detect? mentions thruster sensors. This intrigued me and so I thought I'd ask about how this is done. Thrust is a critical parameter to know in real ...
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Relationship between part dimensions and performance of ion electrospray thruster

I got the relationship between power, thrust and specific impulse for an ion electrospray thruster as follows: $$P/T= 1/2 \times g_o \times I_{\mathrm{sp}}$$ Where: $P$ = power required (in Watts), $...
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How much of the exhaust speed is due to combustion and how much is due to the injection?

The thrust $F$ of a rocket engine is given by $$F=\dot{m}v$$ where $\dot{m}$ is the mass flow and $v$ is the exhaust speed. Now the first factor, $\dot{m}$, is almost entirely due to the turbo pumps (...
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1answer
370 views

Microwave drive for cubesats

Theory: how is this? I was doing a lot of research about the EmDrive thruster, i find 50% papers says that it work and other 50% saying that the "thrust" is a product of the interaction with ...
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1answer
128 views

Could New Horizons' thrusters' ISP be as low as 157 sec?

A discussion below How much of a deep space spacecraft's structural mass is useless dead weight after launch? Any plans to shed it in the future? has lead to https://nssdc.gsfc.nasa.gov/nmc/...
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Are there any other examples of right-angle exhaust diverters in spacecraft?

The Scott Manley video The Only Pilot to Shoot Down A Spacecraft - A Space Ace talks about the ASM-135 ASAT and its successful test launched from an F-15. He shows images from the page The F-15 ASAT ...
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1answer
486 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 ...
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Why does the Indian PSLV rocket have tiny boosters?

I have noticed that the Indian rocket PSLV has tiny strap-on boosters attached to it on the sides at the bottom. Why would these be used instead of just using a larger first stage? Why is there an ...
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Limiting factors of liquid rocket engine thrust

What are the limitations for the 1st stage liquid fueled rocket engines that are currently in widespread use, what are the factors that limit their total thrust? Why can't you just inject more and ...
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Why do nuclear rockets (e.g. NERVA) have such poor Thrust-to-Weight ratios?

Nuclear fission releases far more energy per kilogram of fuel than conventional hydrocarbon sources. However, proposed nuclear rocket engines like NERVA (https://en.wikipedia.org/wiki/NERVA), while ...
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Where does the thrust act in a rocket engine and how is it transferred to rocket structure?

A rocket engine is basically a device that generates a high pressure inside the chamber and the pressure difference creates a force. A nozzle helps in effectively accelerating the flow and increases ...
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How much thrust to launch a regulation size FIFA soccerball into orbit

How much thrust is necessary to launch a regulation size FIFA soccer ball into orbit around the Earth? Let us assume a size 5 which weighs between 420g and 450g. Remember, we will need thrust to ...
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1answer
653 views

why do under-expanded engines have less than ideal thrust?

I've been looking into rocket propulsion a bit and got stumped on something. I read that the thrust generated by an engine can be determined by the following: $$ F = \frac{w}{g}v_{e}+A_{e}(P_{e}-P_{a})...
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Can we thrust a rocket from earth using electric power?

I wanted to know if we can thrust a rocket from earth using electric power? If yes, how and has anyone tried to do that?
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What is the lowest first stage thrust for a launch reaching orbit?

What is the lowest thrust for a first stage rocket for a rocket that reached Earth orbit?
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737 views

Optimal thrust vs isp for variable isp rockets (VASIMR) when taking off/orbiting

This question was initially inspired through playing Kerbal Space Program, however I am seeking a more general answer. I've been playing the excellent Near Future Propulsion mod for KSP, using ...
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373 views

With pressure-fed engines, is any measurable thrust generated by venting the pressurant out the engine bell after flameout?

A pressure-fed rocket engine supplies fuel and oxidiser to the combustion chamber by pressurising the fuel and oxidiser tanks with an inert gas (typically helium or nitrogen). Presumably, when a ...
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Why is a 1.5:1 TWR desirable for a reusable launcher?

According to a Teslerati article linked from another QA: The most critical component for the booster, according to Musk, is that there is “a lot of force pushing up.” He states that to launch ...
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1answer
434 views

Some exercise questions about Tsiolkovsky's Rocket Equation and Thrust Equation

I have found 6 of the question's answers, but I don't know they are correct. The last question about time of the burn I get negative result -0.42 seconds. Time could not be a negative value, so I ...
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1answer
459 views

Under-expanded nozzle at sea level - is it a problem?

I'm designing a solid rocket motor with a fixed pressure in the combustion chamber $p_{cc} = 70~bar$. When it comes to the choice of the right nozzle, I have to consider the proper expansion ratio, in ...
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Was the Titan SRM thrust vs time curve engineered to allow for acceleration switches to initiate staging sequence events?

This answer describes the timing between the Titan III Stage 0 (SRM's) and Stage 1 events. The Titan first stage ignited just prior to SRM separation: Titan Stage I ignition occurs at approximately ...