# Questions tagged [astrodynamics]

The study of satellite orbits and space flight dynamics.

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### What are some best practices for coding a satellite orbit propagator and ground track plotter?

I've seen interesting projects like this and I've been doing a decent amount of orbit propagation (numerically integrating state vectors, accounting for perturbations, etc.) in python and animating ...
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### In the context of delta-V budgets, what does C3 = 0 mean? [duplicate]

Wikipedia has the following article on delta-V budgets, which I'm trying to understand. https://en.wikipedia.org/wiki/Delta-v_budget Several times the condition C3 = 0 is included in abbreviations and ...
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### Why is there no difference between a transfer orbit delta-V and a capture orbit delta-V for Earth?

I'm particularly interested in understanding this beautiful solar system delta-v map and concepts on its Wikipedia page. In contrast to other planets there is no Earth Transfer only an Earth Capture/...
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### How feasible is dragging a 1 km asteroid into Mars orbit? (For All Mankind Spoiler Alert)

In the final episode of Season 4, Dev Ayesha, Ed Baldwin and other protagonists hijack the space ship Ranger to drag the wayward Asteroid 2003LC "Goldilocks" into Mars orbit. In terms of the ...
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1 vote
36 views

### How to apply primer vector theory to trajectory optimization under perturbed two-body problem?

I am currently reading the book Primer Vector Theory and Applications by John E. Prussing (https://doi.org/10.1017/CBO9780511778025) to learn primer vector theory. However, all the derivation and ...
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### Integration of Varying Forces, Impulses in Simulators

I am a software dude working on a personal project for building a spacecraft simulation software. And I've been looking into numerical integration methods, and I am just confused on how to tackle the ...
223 views

### How to build an orbit propagator?

I am trying to build my own satellite orbit prapagator in MATLAB with RK4 integrator and force models added to the propagator to give the perturbed orbit in ECI frame. I am a bit confused and just ...
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### For using the acceleration due to drag formula, which coordinate frame should the satellite's position and velocity vectors be in?

I am working on simulating the space environment for a VLEO satellite. I am working on the atmosphere model where I am using density values from NRLMSISE00 model and plugging them into the drag ...
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155 views

### How is the equation for non-spherical gravitational accelerations derived?

I am referencing Vallado (4th edition) to understand the acceleration contributions on a spacecraft due to non-spherical gravitational effects. Generally, I understand this derivation, except for how ...
• 215
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### connecting two satellites [closed]

How strong would my bond have to be if I wanted to closely connect (30cm - 1m link) two satellites on the same orbit in LEO? (I can move the satellites however I want to have them close to each other) ...
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### What can one do as an individual to help support the development of skyhooks?

In my recent research on the potential of a SkyHook, I've found a startling gap: it seems like no one is actively pursuing this technology. Many, including myself, believe that this could be the ...
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1 vote
117 views

### Objects move clockwise instead of counter-clockwise

I'm trying to write an orbital simulation with patched conics. For my sources I'm using https://orbital-mechanics.space/ and Fundamentals of Astrodynamics (Second Edition). Both sources suggest to use ...
• 63
984 views

### Object slowest at periapsis - despite correct position calculation

I'm coding up a simulation of celestial bodies using patched conics. At the moment I'm stuck with calculating the velocity of the object in the perifocal frame. For the position I'm simply using the ...
• 63
1 vote
99 views

### Gibbs' method and position vectors' reference frame

As mentioned on this website https://www.studeersnel.nl/nl/document/technische-universiteit-delft/flight-orbital-mechanics-and-propulsion/chapter-05-preliminary-orbit-determination/4604099, we need to ...
42 views

### Hyperbolic manifolds in the spatial circular restricted three body problem and topology definition

I am approaching the study of hyperbolic manifolds originated from Lagrange point periodic orbits in the spatial Circular Restricted Three Body Problem. I can read in many papers that what we obtain ...
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### How do engineers measure satellite drag, and how do they track it over time?

I’ve been slowly getting myself familiar with astrodynamics and understanding satellite orbits. I’m familiarizing myself with the concept of drag experienced by the satellites. I am curious about how ...
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### Given historical TLE’s, how do I determine the path/orbit/LLA of a satellite for a given historical period?

Im trying to get the historical Lon/Lat/Alt of a starlink satellite. I'm using TLE's from space-track and Skyfield to calculate latitude, longitude and altitude of satellites for a given date range. ...
• 349
296 views

### Geofence - satellite contact time

I need to find the access/contact times for a satellite passing through a random geofence (polygon). Is there a python library or any code to integrate the geofence to the orbit of the satellite to ...
• 113
76 views

### What are exactly each of the coefficients in Modified Difference Arrays?

I am looking into the different types of SPK kernels. Type 1 are the so-called Modified Difference Arrays (MDA). The linked document mentions that its reference 163 contains a description of the ...
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593 views

### Are there any sources with high-confidence state vectors for GRAIL-A?

I have been experimenting with propagation of Moon-orbiting satellites. In particular, of GRAIL-A. In order to obtain state vectors to use as starting points for my propagation, and to compare the ...
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405 views

### Is there an accepted method to compare orbits?

I'm wondering if there is a universal or accepted way to compare orbits. For example, I have a spacecraft orbiting Earth and it is slowly increasing its altitude every time it passes a local midnight ...
375 views

### How to convert TLE data into state vectors in ITRF?

As shown in the question, Now I have a TLE observation data and CPF(Consolidated Prediction Format) data. According to CPF's documentation, CPF predictions are tabulated satellite state vectors ...
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### Interstellar travel by lightsail – what are the main factors of the trajectory uncertainties?

Lightsail (solar sail or sail accelerated by lasers) is a theorized as realistic way for interstellar travel. Breakthrough Starshot is the most prominent example. Let’s assume we have a thin enough ...
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1 vote
77 views

### Initial Value in Vary Command (GMAT)

What number should I give as an initial value in GMAT's Vary command? I have been trying to use default values but in some missions this default value does not lead to the convergence of target or ...
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### Space-track SGP4 on MATLAB

I am new to orbital calculations and online resources, so I was hoping someone would be willing to help me get started. I have downloaded the space-track Astrodynamic standard library and I am ...
1 vote
211 views

### How to propagate satellite to orbit intersection (relative node) in GMAT? [closed]

I am trying to propagate the spacecraft to the intersection points of two orbits (relative node) in GMAT. The analytical calculations of the true anomaly of that point is done using the formulas in ...
193 views

### Earth to Mars Transfer using GMAT

I saw a couple of people mention here that in order to change the epoch date from the given Mars transfer example on GMAT I would need to change and re-optimize initial conditions. How would I do that?...
206 views

### Relationship between osculating eccentricity and Brouwer-Lyddane short eccentricity

I was under the impression that the mean elements are given by taking the average over an orbital period of the satellite, i.e.: $e_{mean}(t) = \int_{t}^{t+T(t)}e_{osc}(t')dt'[0.367in]$ where $T(t)$ ...
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### How to plot a satellite's orbit around Earth in MATLAB?

Given orbit height, mass and initial velocity how should I plot a satellite's orbit in MATLAB? I was hoping to use verlet integration (I need to implement a solver) possibly the velocity-verlet. I ...
1 vote
292 views

### Ноw to configure mission sequence for propagate until desired date in GMAT?

In GMAT, I have a state of satellite for a date (for example, 24.04.2022). Now, I need to propagate its motion for some days forward, until selected date (say, 29.04.2022). I added Propagation into ...
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### Predicting Satellite Flyover Calculations by Hand

Recently I used transit-finder.com to get a really cool picture of the ISS transiting the sun. The prediction from the website was spot-on. Since then I'm absolutely fascinated by how the prediction ...
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### Conversion of velocity vectors between ICRF frames with different central objects

Following the very nice answers to this question, I am trying to implement an appropriate procedure for change of central body during orbit propagation. The very interesting thesis by Mana Vautier ...
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### Different/better ways to calculate the shadow region passage of the satellite and the effect of orbital elements, other than shadow cone technique?

The NASA Technical Publication Method for the calculation of spacecraft umbra and penumbra shadow terminator points; TP-3547 describes the following: A method for calculating orbital shadow ...
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### How a continuous thrust orbit transfer can be compared with Hohmann transfer?

Suppose that I have found the solution of an optimal continuous thrust planar orbit transfer from circular orbit A to orbit B by means of a numerical method. It's considered that the mission must be ...
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1 vote
39 views

### Is DTM2000 density model expecting adjusted or observed solar flux?

I know two models to calculate the atmosphere density during a satellite orbit propagation. The two models are NRLMSISE-00 and DTM-2000. To feed the models I'm using Space Weather Data provided by ...
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879 views

### How to propagate the orbit of a satellite analytically using Lagrange planetary equations/VOPs and compare them with numerically propagated solution?

I have propagated the orbit of a satellite from TLE elements numerically using RK4 method. But I'm bit confused when it comes to the propagation of satellite orbits using analytical approach. From ...
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### How can we determine the most appropriate central body for orbit propagation?

I have recently been experimenting with expanding my numerical propagator to satellites that orbit central bodies other than Earth. I started with the Moon (using GRGM1200B gravity model), and found ...
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537 views

### Why is the eccentricity vector used to describe near-circular orbits?

When dealing with near-circular orbits I've seen the usage of the eccentricity vector defined as $$(e_x,e_y) = (e\cos\omega, e\sin\omega)$$ I've seen this in Schaubs' "Analytical mechanics of ...
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### Mission maneuver to Enceladus, I have some results from JPL trajectory browser, what comes next?

I am working on a project titled 'Astrodynamic mission maneuver to Enceladus'. I have found the launch date using NASA trajectory Browser. Can you let me know how to proceed further?
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### How can I find the x, y position of apogee and perigee, if I only have the value of distance vector (position) and velocity vector?

I am currently working on a 2D space simulator where I have two bodies; one is still and other is an orbiting object, which I can also control like a rocket. I'm using the Newton's gravity: \$F = \...
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### James Webb Space Telescope Velocity Loss Formula or how fast will JWST be going on L+26

I was never great at math but now I wish I would have taken it more seriously. We have an office bet going and I need to come up with a formula to figure out the future velocity the JWST. I was able ...
145 views

### ISS propagation becomes much more accurate with reduced drag. Any ideas why?

I have currently been testing my implementation of a numerical propagator with the ISS. Without going into much details, the propagator considers Earth gravity (with the GGM03S model including zonal, ...
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### Please explain a way of calculation of Lagrange multiplier in algorithm of low thrust transfer

In David Vallado's book 'Fundamental of Astrodynamics and Applications', chapter 6.7. ("Continuous-Thrust Transfers") there is an algorithm #47: Low Thrust Transfer. In this algorithm a ...
2k views

### Why are uncertainties of orbital state vectors provided as covariance matrixes?

I have recently become interested in testing a numerical orbital propagator with ISS ephemerides, following @RyanC's suggestion in this answer. Ephemerides for the ISS seem to be publicly available in ...
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### "Hohmann-Like" and Chemical / Electric Thrust Comparison

Part of the work I have to do for my degree is to perform a "Hohmann-like" transfer between Earth and Mercury, of which I believe I have accomplished. I have attempted numerous times to ...
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### GMAT B-plane Transfer to Mercury

I have been fighting with GMAT for about 3 days now trying to get this transfer to converge so literally ANY assistance and advice would be greatly appreciated. I need to do a direct hohmann like ...
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442 views

### How to perform a Hohmann-like transfer to mercury on GMAT

I am trying to simulate a Hohmann-like transfer from Earth to Mercury and establish an orbit there on GMAT. I have the following values already: launch velocity (22.25 km/s) Launch burn (-7.53 km/s) ...
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### SPICE toolkit occultation finder doesn't work with spacecraft

I've to know if the sun is occulted by earth from my spacecraft which is in low earth orbit with these parameters (a:6700 km, e:0.0, i:5°, ...). I run the following method with search window start at ...
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1 vote
920 views

### What does it take to be an Astrodynamics Engineer?

Astrodynamics is really complicated and requires some incredible intuition for not just physics, but math and programming. Most job descriptions for Astrodynamics Engineer say something about a degree ...
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