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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35
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4answers
11k views

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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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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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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2answers
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How is thrust transmitted from strap on boosters to the central core?

Strap on boosters of a lot of heavy launch vehicles seems to be attached with just a few "flimsy" struts. Here are few images for reference : Some of the possibilities: These support structures ...
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2answers
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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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1answer
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Is there any rule for rocket engine nozzle proximity from each other?

I wonder if there is any rule for how closely you can put engine nozzles to each other. Are there any vibration, heat, etc. constraints when you are assembling two or more engine bells together? ...
12
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2answers
3k views

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 ...
12
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4answers
9k views

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. ...
12
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1answer
447 views

Do the propellants ionize in chemical rockets?

When combustion takes place in a chemical rocket (LOX/LH2), do the gases ionize due to high temperatures? If they do, how do they get around the problem? Ionization is a waste of energy I believe, ...
11
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1answer
3k views

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 ...
11
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1answer
3k views

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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3answers
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Why do chemical rockets encompass a weird shape on this thrust vs. Isp graph?

Consider this graph of engine thrust versus specific impulse (from https://dawn.jpl.nasa.gov/mission/ion_prop.html): Most propulsion technologies encompass roughly rectangular regions on the graph. ...
10
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1answer
627 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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1answer
929 views

Rocket engine test bed structure

Rocket engine thrust will eventually "lift" a certain amount of weight, to a certain height. For Saturn V, they used 5# F1 engines, each of which produced a thrust sufficient to lift ...
9
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1answer
2k views

What was the first rocket to use gimbaled thrust?

A gimbaled thrust system was used on the Space Shuttle, which is easily recognized in the beginning of this launch video. Was this technology first used by jet fighters, or was it first invented for ...
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What is the correct thrust curve for a solid rocket with a simple circular hole, and why?

Going to wikipedia's article on solid-fuel rockets, I come across some graphs of thrust curves for certain bore-hole geometry. Right now I'm interested in the simplest bore-hole: a circular hole right ...
8
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1answer
310 views

What was Sutton talking about? How to “obtain small accelerations by taking advantage of difference in gravity as a function of altitude”?

Sutton and Biblarz's Rocket Propulsion elements says in Chapter 1, section 1.2 (editions 7, 8, 9, possibly earlier as well) that: Totally different methods of producing thrust are used in ...
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5answers
991 views

Earth Launch System with Water Propellant

Water based thrusters have been proposed (and possibly tested by now) for use in satellites and other in-space vehicles - see this NASA article. The idea is to perform electrolysis on the water to ...
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8answers
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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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2answers
1k views

How are thrust specifications for multi-nozzle engines given?

The Soviet R-7 ICBM used 5 RD-107/RD-108 engines in its first stage in a "Quincunx" formation. Each engine had four CD nozzles, and 1 propellant pump, common for all four nozzles. The thrust ...
7
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1answer
762 views

Why will SLS Block I bring less mass to LEO than the STS shuttle system did?

The Space Transportation System (STS) could bring a fully loaded shuttle orbiter of 109 tons to orbit (or maybe empty+payload 68+25=93 tons). The Space Launch System (SLS) Block I is based on STS, but ...
7
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1answer
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How did SpaceX achieve such a high Thrust to Weight ratio with the Merlin engine?

Were there specific breakthroughs which allowed SpaceX to get such an incredible thrust to weight ratio? The next closest American engine was almost twice as heavy (199 vs 82), and the next closest ...
7
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1answer
484 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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3answers
624 views

How well can hybrid motors be throttled?

Pretty self explanatory: down to what percentage can hybrid rocket engines be throttled to? And what fuel / oxidiser combinations allow for the greatest throttling? I'm planning on using hybrids for ...
7
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1answer
858 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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3answers
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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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Why are optimal launch TWRs so different in KSP than on earth?

In Kerbal Space Program (KSP), optimum thrust-to-weight ratio (TWR) is around 1.5-3. When looking at NASA, SpaceX, Blue Origin spacecraft, the launch TWR is around 1.25-1.3. Is it because the ...
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5answers
930 views

Can you reach the Sun by only thrusting horizontally?

Suppose you have a hypothetical spacecraft launched from Earth. When it escapes from Earth's gravity it will still be orbiting the sun at roughly the same velocity as the earth, approximately 30km/...
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2answers
811 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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1answer
717 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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0answers
169 views

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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137 views

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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3answers
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Could the Bloodhound Rocket Car be launched into orbit?

The Bloodhound SSC (Supersonic Car) currently being constructed to break the 1000 mph barrier is powered by a Hybrid Rocket (Solid fuel + HTP) and a Rolls-Royce EJ2000 Jet Engine: Considering the ...
5
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2answers
612 views

How much G force is applied when correcting an orbit around Earth?

How much g force is applied to a satellite to correct a decaying orbit if done each orbit? How long does it take to correct an orbit on the average? I understand there are variables as in which orbit ...
5
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1answer
538 views

Saturn 1 thrust mismatch

While reading about Saturn launch vehicle family, I read that Saturn 1 third stage used 2# RL 10 engines, producing a total thrust of 30K Pounds. But each RL 10, individually produced approx 25K ...
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3answers
968 views

Rocket specifications: specific impulse, thrust to weight ratio and burn time

In my somewhat unrealistic school project regarding space tourism to Mars we have to accelerate a 500 ton module (mass of propellant and engines not included) from LEO to an orbit around the sun at ...
5
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2answers
366 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 ...
5
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1answer
560 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 this and this) thrust does not seem to need to be angled. ...
5
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1answer
12k views

How to calculate rocket acceleration?

What are the equations used to calculate rocket thrust, acceleration, and weight? Obviously this depends on the type of fuel and engine and a lot of other factors, but I'm interested in a simplified ...
5
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2answers
215 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 ...
5
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1answer
255 views

Sea Launch, and other ocean-based launch pads: Stability?

A rocket launch generates a huge volume of gas which are then deflected in different directions. (source: Space News) Ejected gas have the potential to move the deflecting panels, so the platform ...
5
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1answer
207 views

Second stage thrust used to slow first stage

Is it possible to use a large lightweight sail deployed on the first stage shortly after separation from the second stage to receive exhaust thrust from the second stage engine, so as to slow the ...
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4answers
2k views

Payload capacity of a rocket

Why does a rocket have far more payload capacity when placing an object in LEO compared to when it's placing the object in farther orbits, like on the Moon? If a rocket has sufficient thrust to take ...
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1answer
3k views

How can a rocket approaching the Karman Line then return to earth faster than 53 m/s terminal velocity?

In the book, How to Make a Spaceship: A Band of Renegades, an Epic Race and the Birth of Private Spaceflight the opening chapter details the June 2004 attempt to take SpaceShipOne to the Karman Line. ...
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3answers
349 views

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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2answers
1k views

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 ...
4
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2answers
552 views

Calculating mass expelled from cold gas thrusters

Consider a cold gas thruster rated at 1 lbf per firing. The thruster is on-off: there is no throttling, so when it fires it's at a constant full thrust. Assume the gas is nitrogen, and that it has a ...
4
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2answers
686 views

Compressed gas thruster for an orbital launch vehicle?

Is it possible for a compressed gas thruster to be used to launch a spacecraft into orbit? Let's say, it's already moving at 250MPH(111.7 meters/second) relative to the planets surface. Planets ...
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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 ...
4
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2answers
286 views

single thrust vs. multiple thrust

Does using one 5000 pound thrust engine give the same amount of thrust as five 1000 pound thrust engines? I am asking in terms of effectiveness not efficiency. Do the two different configurations ...