Questions tagged [specific-impulse]

Questions about specific impulse (Isp), which is a comparative measure of efficiency of rocket, jet engines and used propellants, measured either in seconds of thrust per unit weight of propellants, or effective exhaust velocity (thrust per unit mass of propellants) as a measure of launcher system's specific energy efficiency.

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How can I find the predicted approximate altitude of a rocket based on simply the propellant, specific impulse, and propellant mass?(solid propellant) [duplicate]

I am getting all the inputs I outlined above, including burn-time which I could not mention above(character limit), from a small scale motor test. I know there are specific specific impulses for each ...
Anish Kommireddy's user avatar
3 votes
1 answer
147 views

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 ...
confused_aspirant's user avatar
1 vote
0 answers
76 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. ...
Infinite_Maelstrom's user avatar
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How is the rocket equation affected by changing the number of engines or boosters? [duplicate]

Specific impulse is not affected by the number of boosters or engines on a rocket, correct? Let's say I take a rocket with two SRBs and add to more for the first stage. The specific impulse of the ...
Put1demerde's user avatar
0 votes
1 answer
120 views

NTR performance of hydrazine compared to ammonia?

Methane, ammonia and water are sometimes suggested as alternatives to hydrogen for a nuclear thermal rocket. While they have a lower specific impulse, they offer much better density, thrust, and ...
SE - stop firing the good guys's user avatar
1 vote
2 answers
320 views

Calculating propellant mass from total impulse

I have a simple question about how to calculate the total propellant mass used by a satellite in space. From Simulink, I have a graph of thrust VS time, so I could integrate this to calculate the ...
Sato Yusei's user avatar
3 votes
1 answer
142 views

Equations evaluating engine performance

What kind of equation would best evaluate a rocket engine's performance in foreign atmospheres such as Mars? Does it matter that specific impulse does not consider air resistance? Should I focus on ...
boarbytes's user avatar
17 votes
3 answers
6k views

What is the best chemical rocket fuel from a purely specific impulse standpoint?

A variety of different rocket programs use a variety of different fuel types. Researching this, the main fuel combinations I saw were: RP-1 / LOX (SpaceX's Falcon rockets, early stage Atlas and Saturn ...
Vivek's user avatar
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1 answer
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Do engines in the middle of an engine cluster get impulse benefits?

Presumably the rocket engines in the center of an engine cluster would be surrounded by lower-pressure exhaust from the outer engines so essentially the "atmospheric pressure" around the ...
WarpPrime's user avatar
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3 votes
1 answer
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Is this a plot of Isp vs propellant mass fraction for a SSTO vehicle?

Whilst trying to find some information on SSTO designs, I came across this chart: It was used in an ancient forum thread by as part of an SSTO discussion, but the poster didn't cite the paper they'd ...
Starfish Prime's user avatar
3 votes
1 answer
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Specific impulse of a rocket engine

Keeping other things (fuel, oxidizer, their ratio, mass flow rates, throat diameter, other hardware like pump, injector nozzles & impinging pattern etc.) same, if I changed only the geometry (...
Niranjan's user avatar
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2 answers
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Understanding g₀ to calculate delta-v

I am trying to calculate the exact delta-v from various existing upper stages with a given payload in a vaccum and in orbit, say LEO. I understand that according to the Tsiolkovsky rocket equation: $$\...
Joe's user avatar
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2 answers
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What is the Isp of gunpowder likely to be? Could this table be right? Can it even be determined?

There are some unsourced refutations of the value for the Isp of gunpowder in the table shown below can be found under What kind of engine does this Isp = 1600 refer to? Is it cubesat-friendly? Alas ...
uhoh's user avatar
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What equation is being used- chamber pressure v.s. mass flow rate? (Cold-gas thruster)

I am doing a project on cold gas thrusters and have seen a couple of graphs relating chamber pressure against mass flow rate. I can't seem to find the equation that relates these two parameters to ...
spacegirl98's user avatar
4 votes
1 answer
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Can kerolox or SRB soot particles grow too large too quickly; not accelerated in expanding exhaust leading to a loss of mass-specific impulse?

In this answer to Is methyl silane CH6Si ever considered as fuel in rocketry? I argue that there's no huge loss in mass-specific impulse (Isp) when producing sand (and by extension soot) in the ...
uhoh's user avatar
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Engine thrust gain with altitude [duplicate]

As you climb at launch, atmospheric pressure falls, causing thrust to rise. The thrust gain I'm talking about here is due to the increased ratio of nozzle pressure to atmospheric pressure. I'm going ...
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4 votes
2 answers
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Specific impulse and delta-v in Tsiolkovsky's rocket equation

According to Tsiolkovsky's rocket equation, it is possible to calculate the delta-v of a multistage rocket if you know the characteristics of each stage of the rocket. In my case, the only ...
Miguel's user avatar
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1 answer
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Highest Isp achieved with nitrous oxide as oxidizer

What is the highest Isp achieved on orbital rocket for an engine that used nitrous oxide as oxidizer? Both hybrid and liquid engines can be considered. Not considering nitrous oxide monopropellant ...
Kozuch's user avatar
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Trying to calculate Starship's ability to escape earth gravitational potential

The Wikipedia had the spectrum of SpaceX Raptor's specific impulse to be 330s at sea level and 380 in vacuum. Using an updated effective exhaust velocity at sea level to = 3280 m/s and in the vacuum ...
ShoutOutAndCalculate's user avatar
3 votes
1 answer
468 views

Rocket engine with lowest Isp to reach orbit

Which engine with the lowest possible specific impulse has reached orbit propelling a given rocket? There is a page at Wikipedia that compares orbital engines but some engines are missing Isp value ...
Kozuch's user avatar
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What is the effect of calorific value of fuel on the specific impulse of a rocket engine?

What is the effect of calorific value of a fuel on the specific impulse of a rocket engine? Other things remaining the same, and if it is possible to use both, will the same fuel provide the same ...
Niranjan's user avatar
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4 votes
5 answers
2k views

Why is specific impulse equivalent to effective exhaust velocity?

I am very comfortable with specific impulse in seconds. I know how to calculate it, I know what it is, I know what happens to a rocket when you double in or cut it in half. But it feels like the ...
TheEnvironmentalist's user avatar
8 votes
3 answers
6k views

Which theoretical propulsion system has the highest specific impulse?

I know that NERVA physically demonstrated 811 seconds, and the theoretical range for Orion was around 10,000. After stipulating that we can't really know for sure until it's built, given plausible ...
Chris B. Behrens's user avatar
2 votes
1 answer
176 views

What are the practical limits of a rocket that receives propellant from the surface?

The Orion spacecraft was supposed to be propelled by igniting nuclear bombs behind it. Its proponents successfully demonstrated the concept using conventional explosives, on a small scale, for a few ...
keepitwiel's user avatar
5 votes
3 answers
2k 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 ...
user avatar
6 votes
1 answer
605 views

Do lower pressure pressure-fed rockets get more Delta-V?

I was playing around with the math for getting a pressure-fed rocket to orbit and came across something that I haven't seen addressed anywhere. In a pressure-fed rocket, the chamber pressure of the ...
Orion DeYoe's user avatar
11 votes
1 answer
3k views

Have there been rocket engines designed for diesel? What ISP theoretically possible?

Have there been rocket engines or even test engines that have used diesel as a fuel? If so, what oxidizer had they used and what ISP did they achieve? If not, is it possible to say what ISP is at ...
R. Hall's user avatar
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How much pressure would the raptor engines experience when Starship does an atmosphere entry burn at Mars?

The Starship second stage has 3 sea level engines and 3 vacuum engines. When doing the atmosphere entry burn to mars, how many Bars will the raptor engines experience? I'm thinking that because of the ...
moshevi's user avatar
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8 votes
1 answer
339 views

How many Raptor engines will Starship use for TMI and Mars landing?

The Starship second stage has 3 sea level engines and 3 vacuum engines. I don't imagine that all 6 will be used for trans Mars injection, as it isn't very efficient. And for the Mars landing which ...
moshevi's user avatar
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1 answer
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Why might krypton have a lower utilization fraction than xenon for ion propulsion, and what can be done to improve it?

A comment below Why will Starlink satellites use krypton instead of xenon for electric propulsion? links to the 2011 preprint A Performance Comparison of Xenon and KryptonPropellant on an SPT-100 Hall ...
uhoh's user avatar
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4 answers
236 views

Relating Rocket Propellant Selection to Specific Impulse

Is it possible to directly relate a fuel/oxidizer selection to specific impulse at vacuum? I have tried a few different methods, but cannot seem to directly relate the two.
Din Djarin's user avatar
7 votes
0 answers
186 views

What performance can be expected from chemical rockets under Venusian atmospheric conditions?

Is it feasible to use either solid or bipropellant liquid rocket engines to lift off from the surface of Venus? "Reference datum" air pressure on Venus is around 9.3 MPa; even on the top of, say, ...
Russell Borogove's user avatar
6 votes
3 answers
4k views

What is the theoretical max specific impulse of rotating detonation engines in space flight?

I am curious if a rotating detonation engine were made stable, how much more efficient it would be than a standard rocket engine. With a methane or hydrogen and LOX mixture, what is the theoretical ...
David's user avatar
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1 vote
1 answer
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A question about $I_{s}=\frac{F}{\dot{w}}=\frac{c}{g}$ with an example

I'm new to rocket propulsion elements and I'm reading Rocket Propulsion Elements by George P. Sutton, 4th Edition. In the second chapter, it introduced me the following expression, $$I_{s}=\frac{F}{\...
M. Çağlar TUFAN's user avatar
6 votes
2 answers
2k views

Does chamber pressure have the same impact on ISP for different types of engines?

From this answer I understand that higher chamber pressure means higher ISP - but is this always the case for similar engines? For example: I noticed that a lot of upper-stage engines have pretty low ...
irakliy's user avatar
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25 votes
3 answers
5k views

What is the story behind specific impulse being expressed in seconds?

I've heard a couple of explanations but none of them quite make sense. One was that the German rocket engineers used metric and the American rocket engineers used the English system and seconds were ...
Andre Duval's user avatar
2 votes
1 answer
118 views

Reactionless Electrodynamic Propulsion in LEO

Put simply, the earth has a large magnetic field ranging in intensity between .25 and .65 Gauss. Would it not be possible to use the earth's magnetic field as a stator and electromagnets within a ...
Justin Braun's user avatar
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2 votes
2 answers
281 views

How to use specific impulse for multiple stages

I am given a scenario where I need to create a program to give the initial launch mass of a spacecraft that can vary between 4 and 20 stages. I am given that the "specific impulse for all stages is ...
Scotch Jones's user avatar
0 votes
1 answer
140 views

Would Sabre make a good first stage engine for a hypothetical 2-stage design?

Sabre is usually described in the context of the Skylon SSTO design but, would it make more sense to use such engines for the first stage of a two stage design? Basically, would the air breathing ...
InkWiring's user avatar
2 votes
4 answers
678 views

When would the density Isp product be an important performance metric of a propellant?

The quote NASA is testing hydroxylammonium nitrate in space which is expected to perform 50% better than standard propellants and can be allowed to freeze (hydrazine must be kept liquid). LMP-103S ...
uhoh's user avatar
  • 148k
7 votes
1 answer
254 views

Does central Merlin have a different specific impulse?

On a Falcon 9 booster, does the central engine experience unique variations of its ISP due to its plume bordering the eight other plumes? If there is any influence, how does the ambient relative ...
jkztd's user avatar
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7 votes
1 answer
290 views

Apollo SM RCS specific impulse?

What is the specific impulse of the RCS thrusters on the Apollo Service Module? This document cites 281 seconds for the LM's RCS thrusters, but I cannot find similar specs for the SM.
space_voyager's user avatar
3 votes
1 answer
1k views

What are Mass Rate(∆v)/∆v, Mass Rate(Isp)/Isp and time of burn(MR)/MR graphs?

I have some problems about Tsiolkovsky's Rocket Equation and some graphs. Firstly, I didn't get what I can do with Rocket Equation formulas as seen below, Also, what these three graphs try to mean? ...
M. Çağlar TUFAN's user avatar
4 votes
1 answer
1k views

Why doesn't the Merlin 1-D use higher LOX to RP-1 mixture ratios?

So I've been screwing around with CEARUN, which is the chemical equilibrium with applications program created by NASA. I've been using it to calculate theoretical Isps for rocket engines using RP-1 ...
chuckstables's user avatar
6 votes
4 answers
725 views

If specific impulse is directly related to exhaust velocity, would a ion post-accelerator improve the Isp of a propulsion system?

I understand that ion- and hall thrusters resemble a particle accelerator, and that led me to wonder if a post-accelerator (particle accelerator) used to boost the velocity of the ions would improve ...
Nick van der Kroon's user avatar
10 votes
3 answers
3k views

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. ...
DrSheldon's user avatar
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5 votes
1 answer
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What would be the specific impulse of a continuous nuclear fusion drive?

Let's assume problems of running sustained nuclear fusion are overcome (be it by making the mechanism highly energy-positive, or just supplying all the energy deficit externally, like beamed power.) ...
SF.'s user avatar
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13 votes
2 answers
873 views

When does $I_{sp}$ become more of a concern than thrust?

In an orbital launch from Earth, the priority in the initial phase of the launch is high thrust, so as to actually get off the ground, and minimise losses due to "gravity drag" and air resistance. ...
Steve Linton's user avatar
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6 votes
1 answer
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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 ...
Ingolifs's user avatar
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11 votes
3 answers
1k views

Which chemical propellant combination has the highest theoretical isp?

That is disregarding practical factors like making a bomb rather than a rocket in the case of using acetylene+ozone. I know that the highest isp achieved was 542 with lithium, hydrogen, and fluorine. ...
Péter Simon's user avatar