sahil saxena

Hi sevenperforce, i had gone through the document, though very informative but it doesnt contain the values of Cm (moment) vs AoA graphs. Which i what i require i believe to understand how much, resistive torque/moment will I have to counter to get a change in orientation. Are there any softwares with which i could get hold of some counter moment generated values for a given stability margin. Also in the post-boost phase vehicle (without any boosters), say i use the rcs to change the orientation, I would require to trim to that orientation (equate all forces in that orientation to be able to hold that orientation), now as they say this will change the CoP, probably forward with increase in AoA, so how do i get CoP back for a sufficient stability margin. And why do we care about the CoP when the actual aerodynamic forces act on the aerodynamic center (a.c) Thanks in advance

oh, i hadn't realized that that was what it meant, amazing, thanks.

yes yes. my bad, i missed that detail and assumed everything accordingly. thankyou for the support, i really appreciate it. I will. i am going to try to do something with the shape of the missile taken as an airfoil, the shape of which would resemble the sideview of a sharpened pencil. Even if i can get some approximate calculations done, that would be useful to begin with. Does this sound do-able ? calculate lift etc..

torque applied to the rocket by any means would slightly change the AoA which would generate a lift in the opposite direction to the direction of applied torque, and that is how the extreme airflow rapidly dampens any torque, and lift generated in the opposite direction to the direction of the torque is only possible when the CoP is behind the CG, right ? But the above mentioned video says otherwise, I would kindly request you to view the video maybe once more, it clearly shows through the graph, that the CoP was always ahead of CG. i hope center of mass and CG can be used interchangeably. i shouldn't be discussing these things here, but i do not have a subscription to ARC journals, and hence cannot view the paper, throughout my search I have seen some very interesting abstracts on their journals. Thanks sevenperforce

Hi, was going through some material, and it was stated with the help of a graph for one of the rockets, that the CP of the rocket moves ahead of the CG drastically as it breaks the sound barrier and then continues to stay above the CG, and if this might happen for every rocket/missile in general, then the rocket is inherently unstable at higher speeds, so now i need to be more careful in applying the side thrust because it might easily over-shoot and then spin erratically, which means that i don't need to worry about any resistive corrective force which generates from the CP being behind the CG. Am i correct in assuming these points ? This video along with the animation, talks about a rocket and the graph indicating the CP moving ahead of CG. Thanks in advance.

i see. yes thankyou, i would like to know how they deal with the loss of velocity during the period of coast.

Thank you sevenperforce, I will start understanding it. for an ABM, after the first stage has given the required velocity through accelerating it, it then still produces a thrust, after the separation of first stage, I can only assume that that is for some form of maneuverability through thrust vectoring and essentially for MAINTAINING the achieved velocity from the first stage. So that very small thrust to keep it going, can that phase be called COASTING, because I don't know if an ABM after the first stage should coast without any propulsion at all. Thanks in advance.

Thank you sevenperforce, recently understood flow separation , and yes this seems like a possibility. sevenperforce, Referring to something you said earlier, I have been trying to understand, how much lift will a missile of certain dimension produce, is there a formula or some literature to figure that out, that way I would know how much more force is required to resist the resisting force. I have been trying to understand airfoil, but I am not able to relate the two. Thanks in advance.

sounds interesting, will try to look into it.:) Thankyou (excited to read one more paper, of which most i wont understand.)! So is it pure KSP, or the folks here have some previous experience in this area. To be honest, to know that my doubts have an answer is relieving, but I still am having a tough time, making a progress. Where do I start studying these topics, can i be pointed to resources that might help me ? Thanks.

to ALL, this was my first time, reaching out for help over the internet, on forums, and I must say this very specific forum was the only fruitful one, or maybe i did not make my question readable on other platforms. Thankyou everyone for your input.

Yes, just for aiming, its also clear to me that what i wanted the rcs to do (aim) is exactly possible, but in space, and not really while under the influence of atmosphere. I wonder how they might implement (if not already implemented) it, because it will also face the same problems that you have mentioned about right ? unless they plan on using this for the mid-course phase in space, which would then make sense. For answering the rest of my questions, thankyou very much. I guess i have cleared most of my doubts.

Hi nightside to be able to maneuver the interceptor to the missile target for a successful hit-to-kill intercept. I also realizes why its not feasible due to its low specific impulse. yes but the grid fins were not used while in space, or at low altitudes and low speeds because they dont have that much control authority, yes thrust vectoring was the primary source, but also cold gas thrusters during landing for small corrections, for which if thrust vectoring was used, it could be an overkill.

Thankyou sevenperforce, I totally see how you got the rank physics god, the explanation was damn intuitive, i now have a better perspective. I think I have heard of something that can perhaps move the Cg, Cp. So is it possible to make a rotation in the cylinder, using rcs or something and then also accordingly change the Cg, Cp so that, the rotation is held on to by making the orientation stable, because we repositioned the Cg, Cp to its stable position ? Also the cylinder mid air, resists change right, is it because say we are using rcs, because we gave a thrust and then turned the rcs off, maybe if we continuously keep the rcs on, will it even then not hold the changed orientation (obviously thats a waste of fuel and a ineffective way, but is it possible then?) I am final year undergraduate student of mechanical engineering, I am trying to present a concept of using cold gas thruster (I understand that they have very less specific impulse and a lot of fuel required to get anything done) on a anti-ballistic missile (use case under altitudes of 100 km, by which i mean i will have to counter the atmosphere), as basically a modification to the old proximity fuse triggered anti-ballistic missiles for a better chance of hitting the target missile. But then spaceX on its reusable first stage booster uses cold gas thruster to re-orient the booster for its descent, how come they got it to work ? the U.S multiple/single kill vehicle has very similar motion with the divert thrusters and all, can I also ask you, if you can guide me towards how to start calculating these forces. For eg. the kill vehicle is almost always maintaining constant height despite the directional thrusts acting on it, and how much force is required to displace it laterally from one point to other. Thanks in advance, I just realized I have asked way too many questions under one post, I would be fine with a delayed answer, but if you could answer all these questions i would really be grateful, as the internet has not been so kind to me.

Thankyou DDE, ok now i see them, lets hope the paper gets converted accurately. Thankyou

To all, https://youtu.be/KBMU6l6GsdM would it be possible to give me an idea into how to start calculating the forces acting on a body like this multiple kill vehicle, as in, it maintains a almost constant height, how much force, is required to stay in place, and how that is not being disturbed when side forces are acting on the body and the body has lateral displacement, An idea into maybe how to begin calculating such things maybe on something simpler, then i can climb the way up. Thanks again.

Thankyou DDE, yes i have seen this fantastic video of the multiple kill vehicle. This gives me some confident that i might be able to imply that the concept is possible (obviously it exists, but using maths, physics at my disposal). This is the first time I have turned to forums for help and the experience was overwhelming. Can i also request for some papers or sites mentioning Vympel 9M96 and its miniaturized engines down the mid-section, though I fail to see them in the image provided. That might help me get started with some calculations, instead of assuming everything on my own. Again thanks in advance.

Thankyou p1t10, This was very insightful. I understand the dynamics, kinematics and whatnot is extremely complicated up there specially at such speeds. But can this approach (given below) be even remotely be used to know if the concept that i wish to present will work: Assume the rocket standing stationary on the ground, then applying a force towards the top of the missile, create a torque, and given that we know the moment of inetia of the missile, we can calculate the angular acceleration by dividing the torque by moment of inertia. If i want an angular displacement of say pi/180 rad either side as and when required so that I can stay fixed on the target, we can then calculate the angular velocity and then by using the kinematics equations of motion in an angular aspect, as in s = u*t + 0.5*a*t^2 can be in angular terms written as theta = w*t + 0.5*alpha*t^2 we can find the time required, where i assume this time to be the time required to bring about an pi/180 radian change in orientation. So i wanted to know if we just consider stopping the missile mid air, know how much it weighs, recalculate the moment of inertia maybe, and then find the force required to possibly tilt it. I completely understand how silly and foolish this sounds, but I have no one else to guide me for this project. And f there is a chance that this methodology might work with many more assumptions, this would be quite convenient for me to work it out. thanks in advance.

Thankyou DDE, May i ask then how do anti ballistic missiles alter their trajectory (in the terminal phase) as and when required, and i believe they can travel at speeds upto 3km/sec. I was actually thinking of cold gas thrusters on the missiles to create a torque and have a better target lock on the missile target, but now obviously cold gas thrusters are not powerful enough so I was thinking of using any reaction control system. Can you guide me to some resources maybe, that could help me get a better understanding of these concepts, and how would i achieve "maneuvering a missile at 3km/sec in the terminal phase". Thanks in advance. Thankyou sevenperforce, an anti-ballistic missile for the terminal phase neutralization travels at speeds upto 3 km/sec, and the whole phase lasts only for a max of 120sec. Pardon me for my silly questions as i do not have a proper hold on the basic concepts of anything, but while it is accelerating, it is already moving "not in the lowest air-resistance orientation" because of the angle of attack, so i would think that the change of orientation, though, would face resistance but because it is accelerating it should hold the changed position. I am trying to somehow on a small scale replicate the concept of anti-ballistic missile (in the terminal phase) for my major project, i would really appreciate being pointed to some related resources, and maybe something to understand how the existing technology maneuvers mid air to be able to have a direct hit with the target missile. Thanks in advance.

Assume a rocket is standing on the ground with mass = 1000 kg, and near the top of rocket we apply a force of 100 N for say 1 sec,now assume that this is sufficient to tip rocket over/start tipping over. If the rocket is mid air and accelerating at 30 m/s^2, then likewise how much force would be required to tilt it pi/180 rad or change its trajectory by some degree, please neglect the change of mass due to consumption of fuel because the value calculated with this assumption is going to be a a value higher than required, so that is not an issue. Will the force required mid air be the same as the force required on the ground with no acceleration ?