Some future update mod ideas/wishlist
- Thread starter The Astronomer
- Start date
Alright I looked into the video of the raptor engine's ignition phase, I just want to say I am not convinced about your claims of the use of spark plugs.
You can see from the video that upon ignition, you can see a green flame. From my knowledge of ignition methods, it is using some kind of boron-based pryoforic agent, hence the green flame at the beginning. From what i know, you don't need a spark plug when you are already using a pyroforic ignition system.
You can see from the video that upon ignition, you can see a green flame. From my knowledge of ignition methods, it is using some kind of boron-based pryoforic agent, hence the green flame at the beginning. From what i know, you don't need a spark plug when you are already using a pyroforic ignition system.
Can work too, we're using the same thing for aircraft engines. I guess that the torch is basically an aircraft's fuel injector that power a rocket's fuel injector. The aircraft fuel injector atomizes the fuel to make ignition possible with a spark plug, and the open flame generated can be used to ignite the liquid fuel.
Hey this is actually a pretty good idea, that eliminates the need to bring pyroforic agents, so as long as you have fuel, you can ignite.
Hey this is actually a pretty good idea, that eliminates the need to bring pyroforic agents, so as long as you have fuel, you can ignite.
Last edited:
@Johnkurveen @Altaïr
Remember back when I said something about finding out a way to compensate for delta velocity change due to free stream pressure loss? Well I looked into it and did some math about it on paper.
On the first image, since free stream pressure only affects thrust directly, I converted the Isp in the delta velocity equation to thrust divided by mass flow rate multiplied with the gravity constant, then I converted the thrust value to its full thrust equation to reveal the pressure factor. So far out of all the values in the equation, Po or Free Stream pressure is so far the only factor that changes, the rest in the thrust equation are constant.
On the second image, I am trying to figure out how to compensate for a changing delta velocity value due to pressure loss over altitude, I tried logarithmic and exponential functions to deduce the nature of the pressure ratio graph. I then came up with the final function of f(x)=0.2*2^x which was rather faulty, but later I noticed that delta velocity is not an addition system, so using integration to combine or compensate specific impulses of two different thrust values is completely wrong.
As you can see in the finalized (circled) formula which states delta thrust and delta mass, for delta thrust we know that it is affected by pressure, but pressure is affected by altitude and altitude gain is dependent on mass, so for delta mass? For this I thought about applying the time factor of the flight which can then be used to deduce the altitude of rocket, which then can allow us to find out the pressure, but all this depends on the payload of the rocket.
Look at it this way, depending on the payload of the rocket and Newton's 2nd law of F=ma, a rocket with greater payload may reach a lower altitude in for example 50 seconds, than a rocket with less payload, this means that the local pressure of the heavier rocket will be greater than the lighter rocket.
These writings still didn't help me in visualizing what factors I need nor the changes involved, I drew an entire graph which compares altitude, pressure ratio, thrust, seconds of specific impulse and time which can be seen below.
So we move on the final image, you can see that I have compared Isp, thrust and pressure ratio on the y-axis against altitude on the x-axis, the time factor is also drawn into the x-axis but on top for better visualization. As you can see, I am using the RD-107 engine as an example, both thrust and Isp increases with decreasing rate against the pressure ratio that decreases with decreasing rate. Fuel consumption is stated as constant as mass flow rate never changes.
After I have drawn out all of the factors, I drew a line down to intersect all the lines of thrust, Isp, mass, pressure and altitude, and labelled the time line as time constant b or Tb. I then deduced these info to the two equations below, and noticed that with decreasing free stream pressure which leads to increasing thrust, the dry-wet mass ratio reduces as well, this means that each rocket has its own unique delta velocity gain, and in theory hydrogen rockets like the SLS will receive the least gain due to its smaller dry-wet mass ratio.
I am still yet to experiment on using the "area under the exponential curve" method to find the compensated dV value, and with so many factors I have to involve, I don't think it will be as easy as putting in an integration and x-function and be done with it. I think using a computer aided software to simulate this will make it much easier.
So what do you guys think?
P.S. if all of these mumbo jumbo sound like the ramblings of a drunk asshole, its because I am writing this at 3 in the morning.
Remember back when I said something about finding out a way to compensate for delta velocity change due to free stream pressure loss? Well I looked into it and did some math about it on paper.
On the first image, since free stream pressure only affects thrust directly, I converted the Isp in the delta velocity equation to thrust divided by mass flow rate multiplied with the gravity constant, then I converted the thrust value to its full thrust equation to reveal the pressure factor. So far out of all the values in the equation, Po or Free Stream pressure is so far the only factor that changes, the rest in the thrust equation are constant.
On the second image, I am trying to figure out how to compensate for a changing delta velocity value due to pressure loss over altitude, I tried logarithmic and exponential functions to deduce the nature of the pressure ratio graph. I then came up with the final function of f(x)=0.2*2^x which was rather faulty, but later I noticed that delta velocity is not an addition system, so using integration to combine or compensate specific impulses of two different thrust values is completely wrong.
As you can see in the finalized (circled) formula which states delta thrust and delta mass, for delta thrust we know that it is affected by pressure, but pressure is affected by altitude and altitude gain is dependent on mass, so for delta mass? For this I thought about applying the time factor of the flight which can then be used to deduce the altitude of rocket, which then can allow us to find out the pressure, but all this depends on the payload of the rocket.
Look at it this way, depending on the payload of the rocket and Newton's 2nd law of F=ma, a rocket with greater payload may reach a lower altitude in for example 50 seconds, than a rocket with less payload, this means that the local pressure of the heavier rocket will be greater than the lighter rocket.
These writings still didn't help me in visualizing what factors I need nor the changes involved, I drew an entire graph which compares altitude, pressure ratio, thrust, seconds of specific impulse and time which can be seen below.
So we move on the final image, you can see that I have compared Isp, thrust and pressure ratio on the y-axis against altitude on the x-axis, the time factor is also drawn into the x-axis but on top for better visualization. As you can see, I am using the RD-107 engine as an example, both thrust and Isp increases with decreasing rate against the pressure ratio that decreases with decreasing rate. Fuel consumption is stated as constant as mass flow rate never changes.
After I have drawn out all of the factors, I drew a line down to intersect all the lines of thrust, Isp, mass, pressure and altitude, and labelled the time line as time constant b or Tb. I then deduced these info to the two equations below, and noticed that with decreasing free stream pressure which leads to increasing thrust, the dry-wet mass ratio reduces as well, this means that each rocket has its own unique delta velocity gain, and in theory hydrogen rockets like the SLS will receive the least gain due to its smaller dry-wet mass ratio.
I am still yet to experiment on using the "area under the exponential curve" method to find the compensated dV value, and with so many factors I have to involve, I don't think it will be as easy as putting in an integration and x-function and be done with it. I think using a computer aided software to simulate this will make it much easier.
So what do you guys think?
P.S. if all of these mumbo jumbo sound like the ramblings of a drunk asshole, its because I am writing this at 3 in the morning.
Altaïr
Space Stig, Master of gravity
Staff member
Head Moderator
Team Kolibri
Modder
TEAM HAWK
Atlas
Deja Vu
Under Pressure
Forum Legend
Wow, looks interesting but that's a lot of text to understand at once!
You're trying to evaluate the loss due to the difference of pressure right?
What do you call "free stream pressure"? Is it the gas pressure at the end of the nozzle? I'm not used to english terms...
The method is interesting, but is it still relevant to talk about delta-V when the launcher is still in the atmosphere? The launcher already fights gravity and drag in those conditions, and looses delta-V because of this (and also because of the pressure difference as you stated it of course). But I understand what you're trying to achieve.
I suppose there's no way to calculate the delta-V loss formally indeed, this depends on too much things. I already tried to do that for relatively simple situations (no atmosphere, small altitude variations, so g can be considered constant...), but this is already a nightmare. I suppose numerical integration will be the only option for that.
You're trying to evaluate the loss due to the difference of pressure right?
What do you call "free stream pressure"? Is it the gas pressure at the end of the nozzle? I'm not used to english terms...
The method is interesting, but is it still relevant to talk about delta-V when the launcher is still in the atmosphere? The launcher already fights gravity and drag in those conditions, and looses delta-V because of this (and also because of the pressure difference as you stated it of course). But I understand what you're trying to achieve.
I suppose there's no way to calculate the delta-V loss formally indeed, this depends on too much things. I already tried to do that for relatively simple situations (no atmosphere, small altitude variations, so g can be considered constant...), but this is already a nightmare. I suppose numerical integration will be the only option for that.
Wow, looks interesting but that's a lot of text to understand at once!
You're trying to evaluate the loss due to the difference of pressure right?
What do you call "free stream pressure"? Is it the gas pressure at the end of the nozzle? I'm not used to english terms...
The method is interesting, but is it still relevant to talk about delta-V when the launcher is still in the atmosphere? The launcher already fights gravity and drag in those conditions, and looses delta-V because of this (and also because of the pressure difference as you stated it of course). But I understand what you're trying to achieve.
I suppose there's no way to calculate the delta-V loss formally indeed, this depends on too much things. I already tried to do that for relatively simple situations (no atmosphere, small altitude variations, so g can be considered constant...), but this is already a nightmare. I suppose numerical integration will be the only option for that.
You're trying to evaluate the loss due to the difference of pressure right?
What do you call "free stream pressure"? Is it the gas pressure at the end of the nozzle? I'm not used to english terms...
The method is interesting, but is it still relevant to talk about delta-V when the launcher is still in the atmosphere? The launcher already fights gravity and drag in those conditions, and looses delta-V because of this (and also because of the pressure difference as you stated it of course). But I understand what you're trying to achieve.
I suppose there's no way to calculate the delta-V loss formally indeed, this depends on too much things. I already tried to do that for relatively simple situations (no atmosphere, small altitude variations, so g can be considered constant...), but this is already a nightmare. I suppose numerical integration will be the only option for that.
But what do you mean by "relevant to talk about delta-V when the launcher is still in the atmosphere"? The delta V budget is spent throughout the entire burn time, so that means from surface to orbit no matter the atmospheric conditions, its just that calculating for atmospheric conditions compensation for delta V gain are far more complicated.
Horus Lupercal
Primarch - Warmaster
Professor
Swingin' on a Star
Deja Vu
Biker Mice from Mars
ET phone home
Floater
Copycat
Registered
He means that unless you have a standardised flight profile (same launch site altitude, same flight path etc) and the weather is identical at every launch, you're going to have to re-calculate the exact Dv required based upon those conditions everytime you hit go and the amount of variables that will affect the calculations is so horrifying that he just goes off a ballpark figure of roughly x amount of delta v to achieve orbit and then works out what he has left to achieve whatever task he's doing afterwards more exactly.
Not to say it's not worth doing, but you're going to need some computer action to help you out there especially if you're doing this in a real world setting.
Not to say it's not worth doing, but you're going to need some computer action to help you out there especially if you're doing this in a real world setting.
Wow, looks interesting but that's a lot of text to understand at once!
You're trying to evaluate the loss due to the difference of pressure right?
What do you call "free stream pressure"? Is it the gas pressure at the end of the nozzle? I'm not used to english terms...
The method is interesting, but is it still relevant to talk about delta-V when the launcher is still in the atmosphere? The launcher already fights gravity and drag in those conditions, and looses delta-V because of this (and also because of the pressure difference as you stated it of course). But I understand what you're trying to achieve.
I suppose there's no way to calculate the delta-V loss formally indeed, this depends on too much things. I already tried to do that for relatively simple situations (no atmosphere, small altitude variations, so g can be considered constant...), but this is already a nightmare. I suppose numerical integration will be the only option for that.
You're trying to evaluate the loss due to the difference of pressure right?
What do you call "free stream pressure"? Is it the gas pressure at the end of the nozzle? I'm not used to english terms...
The method is interesting, but is it still relevant to talk about delta-V when the launcher is still in the atmosphere? The launcher already fights gravity and drag in those conditions, and looses delta-V because of this (and also because of the pressure difference as you stated it of course). But I understand what you're trying to achieve.
I suppose there's no way to calculate the delta-V loss formally indeed, this depends on too much things. I already tried to do that for relatively simple situations (no atmosphere, small altitude variations, so g can be considered constant...), but this is already a nightmare. I suppose numerical integration will be the only option for that.
The problem with this is that the two values of the x and y axis must end up with a usable value, take for example a speed and time graph, finding the area for a speed-time graph will get us distance, and finding the area for an acceleration-time graph will get us speed. However for this scenario? Finding the area under a pressure-altitude graph won't get us anything officially usable. So due to this I have to ditch this method.
Another problem with the delta V formula is it cannot give you a range, but a specific value, which means finding out the gain or loss of delta V must be done per specific altitude and be plotted onto a graph in order to properly visualize the changes. So if you refer to the first image below, I have found the functions for pressure change for two altitude regimes; troposphere and post-tropopause, as each regime has their unique pressure, density and temperature change rates.
After I have found the two functions, I substituted them into the delta V equation for each of them. In the image below, you can see two equations with their free stream pressure replaced by the functions, one labelled "troposphere compensation"
and the other "Post-Tropopause compensation" respectively.
I would love to hear your opinion on this.
This little project of mine is to find out the stuff I need to find an altitude compensated delta velocity value. Yes it may look ludicrous, but it may actually help us understand which launch vehicle of specific fuel types are the most efficient under specific conditions. For example a 100 ton to LEO heavy lift rocket using highly efficient but low density hydrogen fuel may be less efficient overall, compared to a heavy lift rocket with the same capability but burning less efficient but high density fossil/alkane/hypergolic fuel.