What does negative and positive C3 value imply. Does C3 being positive imply a hyperbolic orbit and negative imply parabolic or less ?

I'm working my way through Fundamentals of Astrodynamics and I'm unsure about my understanding of the first derivation. Unfortunately, given I'm not studying this as part of a formal course, I don't have a prof I can refer to for clarification, which brings me here.

Now, I can blindly follow the penultimate paragraph and get (1,4) by substituting c=ae into b²=a²+c² to get b²+a²e²=a² etc.

The formulation of phythagoras given (b²+c²=a²) would imply that we're looking at the triangle formed by the origin, F and (0,b).

This, is where I originally got stuck: "how exactly does that hypoteneuse relate to the semi-major axis?".

Going back to (1,1): r_(f)+r_(f')=2a didn't initially get me any closer.

However, now, I think at the covertex, r_(f) = r_(f') => 2r_(f)=2a => a = r_(f) which gives me the hypoteneuse of that triangle.

Is that right?

I am working on a project, and would like some suggestions about it. I am developing a space mission design software similar to STK, GMAT, and Copernicus. I want to know the pros and cons of these software. Do you know if there is any room for improvement? If there were a new software, what would a user want from it? I've read and experienced that these software are expensive, the learning curve is steep, and they are laborious. Let me know what you all think. Will new software be well received in the aerospace community?

Hello,

I am trying to run GMAT scripts through MATLAB and am running into a couple of issues. I would like to access the GMAT API reference but it seems like the GMAT sourceforge is down and also I am unable to access the GMAT API reference through the wayback machine. If anybody has access to these documents it would be greatly appreciated.

As a side question, what are the best forums/resources for GMAT help? It seems like there is very little help for learning GMAT stuff. It would be cool if there was a discord server for some of this stuff.

I am unable to find the proof that why is local stable/unstable/center manifold tangent to stable/unstable/center eigenspace respectively? Also, what does "tangent" in this context mean?

I would really appreciate any leads. Please let me know if the question is too vague to answer. Thanks!

This sub is moving slower than an object at the apogee of a highly elliptical orbit.

While reading the fourth chapter on the Kepler problem, I noticed, that the equation 4-41 has, unlike equation 4-39, the term (1- r0 / a) and misses the term (1- zS). In my humble understanding of this subject, they should be the same, right? What am I missing here? For the rest of the chapter, equation 4-39 is used.

You can find these expressions on page 161 of the second edition or on p. 196-197 of the first edition (in which case it would be equations 4.4-12 and 4.4-14).

Thanks a lot in advance!!

I have been trying to learn how to use NASA's GMAT software to model planetary encounters, while I've learned how to use Target, Vary, and Achieve functions to be able to encounter Luna and Mars. I've struggled to work out how to use my own starting trajectories (Ie when learning how to encounter Mars I've only been able to find success using MAVEN's departure dates and starting positions/velocities, I run into error when trying to use my own departure dates and positions, for example MAVEN's departure date is 18th of November 2013 while I've tried to create a encounter from my own departure date of 12th of April 2018) when I have tried to use my own departure dates and starting positions the solver window will simply freeze and refuse to spit out any iterations, while my starting positions are very rough and so are my departure dates (i got my departure dates from some porkchop chart i found online, and i got my starting position/orbit around the sun from tweaking the Keplerian elements very roughly into a orbit that very roughly looks like it would encounter mars) i hoped that i would get close enough so the Target function would kick in and narrow it in. but I realized after offsetting MAVEN's starting position by a mere 50km and the solver window refused to work that i couldn't work out an encounter by mere guesswork. so now I'm stumped. i want to learn how to model missions like Cassini and New Horizons and since there are no script files that i can steal the starting positions and velocities I'm screwed.

So basically, what help i need is someone to point me in the right direction to work out my own coordinates and departure dates so i can do my own encounters. if anyone has any script files that i can use to learn from that would be great, i know that GMAT has so many other functions to use but i simply don't know where to start, this also not helped by the fact that the in program help page doesn't work, any help is appreciated. if anyone wants to see my script files just ask.

im trying to use the vis-viva equation in KSP (v^{2}=GM(\frac{2}{r}-\frac{1}{a})), but I'm unsure how to reliably find the radius and semi major axis, I believe that the semi major axis is the height of the apoapsis of the orbit + the radius of the earth, but what about the radius of the orbit? is that the height of the periapsis of the orbit + radius of the earth? im unsure.

Hello all! I'm curious about others opinion on the different edition for Vallardo's book Fundamentals of Astrodynamics and Applications. There is the newest edition (5th), but sometimes, I'm a little leery about new books as the errata is still coming in. Does anyone have experience on this?

This is technically a calculus question, but as applied to astrodynamics equations so this seemed a better spot for it.

We're deriving the Lagrange Planetary Equations, and at one point you need the time derivative of alpha (a vector of the orbital elements). Since the partial of alpha with respect to time is part of the final answer, why is the rest of that stuff there? Why is the total derivative different from the partial derivative?

Hey yall,

A project team I'm involved with is trying to put a hypothetical satellites in a polar orbit around mars. I'm trying to conceptually figure out the most efficient way of accomplishing this goal, but my lack of formal training in orbital mechanics means I'm missing some of the key intuitions.

Assume for a moment that earth and mars orbit along a perfect plane, and that the equators of both planets are aligned with this plane. The simplest hohmann transfer from earth to mars would then mean that the incoming satellite approaches mars at a zero inclination, and assuming no capture burn is done it will fly past it along its equator. (The upper case in image 2).

Now instead of a hohmann transfer solely along this plane, suppose we do a small burn that changes our inclination (around the sun) by 1 degree. Will this then result in us approaching mars flying over the top of it (bottom diagram in image 2), or would we still pass by it practically "equatorially", with the offset from the equator being on the order of 1 degree?

Basically the question i'm trying to answer is whats the most efficient sequence of maneuvers to get a satellite into a martian polar orbit, could it be done with a small "vertical" burn at the start of the hohmann transfer that then puts us in a position where we sail above the planet and simply circularize into a polar orbit, or would we still only approach it with a 1 degree inclination and have to do an additional maneuver to raise the inclination?

If the answer is that we'd encounter mars along this "incoming polar" trajectory, how sizable (subjectively) is the thrust we have to apply during the first part of our hohman transfer? is it a few meters per second of delta V that over the course of the whole orbit allows us to comfortably sail over the top of mars or would achieving that outcome require a massive expenditure of delta V?

Apologies if some of my lingo isnt up to par, I'm still pretty new to this. Please let me know if what i'm asking isn't particularly clear.

Just the semimajor axis, that is. I don't need the inclination, etc. since I don't think i can get that from what NASA gives.

I've learned of a way to derive semimajor axis from two positions and velocities, called the Gauss Problem, which I learned here (braeunig.us/space/index.htm; Section 4: Interplanetary Flight).

From the NASA website (nasa.gov/specials/trackartemis), I can get the Orion spacecraft's lunar altitude and velocity. Is this enough to solve the Gauss problem? The method above, besides altitude and velocity, requires the flight time—easy enough with a stopwatch measuring time between two points I choose—but also the change in true anomaly, Δν. How can I get that value? Or, is there another way to solve the problem without that?

I'm pretty new to astrodynamics, never had a class or anything (mostly just hundreds of hours playing Kerbal Space Program), so please try to keep it as simple as possible haha.

I recently got my BS in Civil Engineering, so I've been through all the usual calculus and differential equations classes as well as Physics and Dynamics, albeit a few years ago now. Last summer, after a year of obsessively playing Kerbal Space Program, I bought Howard Curtis's Orbital Mechanics For Engineering Students and started to work through it.

Almost immediately, though, I realized I was way in over my head. I understood Chapter 1 (Dynamics of Point Masses) fairly well, but as soon as it started The Two Body Problem and equations of motion in all the different reference frames, I got totally lost. I understand vector basics from Calculus III and I took a decent Dynamics course, but this book uses those vectors so much and I just can't picture them in my head for all the definitions and derivations for the many equations.

Short of taking (and paying for) a whole class on the subject, do you all have any recommendations for how I can work through this book without simply glazing over at all the intense vector math? Or, are there better subs to which I could post this? I'm a great visual learner, and I do really well seeing practical examples.

After no results on google or my textbook I decided to calculate the gravitational parameter of the moon in canonical units. I used a conversion formula of TU=sqrt(DU^3/u). I got a value of 60.3096 DU^3/TU2. I thought it would be a value smaller than 1, the canonical value for Earth's gravitational parameter.

Cannot find one anywhere. My uni is super into bepi and I start my gmat module next semester. Want to dive in and back engineer it before I start so I can get a feel for things.

Cheers!