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34 votes

Does the Voyager team use a wrapper (Fortran(77?) to Python) to transmit current commands?

In 2015, the last original Voyager engineer still on the project, retired. NASA specified that his replacement would have to know FORTRAN. The software was updated regularly after launch: The ...
Hobbes's user avatar
  • 128k
18 votes
Accepted

What computer programs does ITAR say I can or can not write, or share, or use in the US?

With the exception of model rockets made of paper, wood, or breakable plastic, that are passively stabilized, that have low thrust and low delta V, and that do not have guidance software, launch ...
David Hammen's user avatar
  • 74.9k
15 votes

Does the Voyager team use a wrapper (Fortran(77?) to Python) to transmit current commands?

The Voyager spacecraft are still being patched as of 2023. The uplink is only 16 bits/second, just enough to send (simple) commands. How these commands are generated is irrelevant to the spacecraft. ...
Ludo's user avatar
  • 14.4k
11 votes

Thrust and rotation strategy to circularize a standard GTO orbit using ion propulsion?

TL; DR: Trajectory optimization for continuous thrust is difficult and this field is very active in research. 2021 clarifications: Methodology For the least amount of fuel, the best is the thrust the ...
ChrisR's user avatar
  • 6,180
11 votes

Does the Voyager team use a wrapper (Fortran(77?) to Python) to transmit current commands?

I didn't work on Voyager, but can tell you that deep-space missions tend to retain the original ground hardware, software, language, and build environment, both for continuity/safety as well as budget ...
stevegt's user avatar
  • 391
9 votes
Accepted

How to calculate the flight path angle, γ, from a state vector?

This is a problem that has plagued groups of people very knowledgeable about orbital dynamics but who learned using different textbooks: there are two different definitions of "flight path angle"!! ...
Tom Spilker's user avatar
  • 18.3k
7 votes
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How to best think of the State Transition Matrix, and how to use it to find periodic Halo orbits?

The State Transition Matrix (STM) The STM is a linearization procedure of a dynamical system. It can be used for any non-linear dynamical system and is used to approximate the dynamics of a system ...
ChrisR's user avatar
  • 6,180
7 votes
Accepted

Get dates when a satellite has performed maneuver from historical TLE data (python)?

For Python and TLE propagation using SGP4 one very handy option is https://rhodesmill.org/skyfield/ As you probably already know a TLE is a strange animal. It does not really contain proper orbital ...
uhoh's user avatar
  • 149k
7 votes
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How to solve the two-body problem in the ECI frame through numerical integration?

There are several ways to do this. The easiest and most straightforward is to break it into two sets by including velocity as a variable, and solve together. Instead of a single second order ...
uhoh's user avatar
  • 149k
6 votes

What formulas do I use to calculate the gravity and drag forces on an object ascending from Earth's surface?

One thing that may be tripping you up is that the d term in the gravitational formula is the distance between the centers of mass of the objects, not the altitude ...
Russell Borogove's user avatar
6 votes

How can I plot satellite's trajectory from three different TLEs to detect any deviation on path with time?

You're plotting the orbit of a geosynchronous satellite in active commercial use. At the scale you've drawn it, it has to overlap exactly, because variation smaller than you can see at this ...
Ryan C's user avatar
  • 7,962
6 votes

Why did my vis-viva math solution get so close despite being wrong? Under what conditions would it have been a good approximation?

First, you appear to have the following misunderstanding of the solar sail force vectors: Tilt it at 45 degrees to make the thrust tangential Thrust is not tangential at 45 degrees. In fact, a ...
SE - stop firing the good guys's user avatar
6 votes
Accepted

Has Skyfield or any other SGP4-capable open-source Python package yet wrapped/implemented the new, improved SGP4 (version 8+)?

The new SGP4 library comes with a Python wrapper in the same zip archive file (also Java, Matlab, and Visual Basic, and documentation for the C API), but it's not at all idiomatically Pythonic, since ...
Ryan C's user avatar
  • 7,962
6 votes
Accepted

How is an input card for SGP4/other astro standards packages crafted?

I completely agree, the 6P card input is very annoying to use and its documentation is terrible. Here is an example of how to use it, as I did in preparing my answer to Failing at getting apogee and ...
Ryan C's user avatar
  • 7,962
6 votes

Modelling ISS orbit in GMAT

The reason my GMAT model was not giving the correct results was that I changed the Epoch without changing the TA - user @notovny pointed that out which was very helpful. I used TLE-tools to get the ...
wolf72's user avatar
  • 141
6 votes

Calculating and Drawing the orbit of a body in a 2D gravity simulation in python

The easiest initial approach to this is probably to propagate your state forward in time steps, with a time delta small enough to have reasonable accuracy. You can ...
SE - stop firing the good guys's user avatar
5 votes
Accepted

A software for orbit propagation, considering Moon, Sun and zonal harmonics

I would highly recommend NASA Goddard's GMAT (General Mission Analysis Tool). It is quite user friendly, has a number of tutorials, and has been used in spacecraft operations.
ChrisR's user avatar
  • 6,180
5 votes
Accepted

Python API for JPL Horizons?

callhorizons is depricated now and refers to the python library astroquery which now seems to be the way to go. astroquery (GitHub, readthedocs) is "an astropy ...
Gandalf Saxe's user avatar
5 votes
Accepted

"Pythagorean Three Body Problem" - need some points from an accurate solution for comparison

I just ran it, and mine look pretty much like those in the paper. See some coordinates at the bottom. Here are some {x,y} coordinates at the times in the left column: ...
Mark Adler's user avatar
  • 58.2k
5 votes

Saving STK Scenario from Python app

Your variable root is of type IAgStkObjectRoot. If you search the Programming Interface Help, there are five save related ...
Carlos N's user avatar
  • 4,474
5 votes
Accepted

How to calculate position of GPS Satellite with transmitted ephemeris data?

You can find a C++ method contained in the source code of Andrew Holme homemade GPS receiver project. The method is called GetXYZ and is the EPHEM (ephemeris) namespace and looks as the following: <...
cy8berpunk's user avatar
5 votes

Python Libraries: Numerical Propagators and Access Calculations

Check out PoliAstro by Juan! It's got great visualisation tools in addition to its propagation. Plyades too, is a library for orbit propagation with visualisation. I have heard that there is a ...
Samuel Low's user avatar
5 votes

Simulating engine burn with scipy ode solve

For an instantaneous delta V, you definitely want to have the integrator stop exactly at the point in time where the change in velocity is to be applied. Dynamic step sized integrators stop where they ...
David Hammen's user avatar
  • 74.9k
5 votes
Accepted

How much delta-v have I used here? What's the "official" equation for delta-v from parametric thrust?

As $\Delta v$ is just change in velocity, we can just integrate the norm of the acceleration function over time: $$\Delta v = \int|\mathbf{a}(t)| dt$$ You're out of luck getting a closed form of that ...
SE - stop firing the good guys's user avatar
5 votes
Accepted

Skyfield, how to use https:// instead of ftp://?

Looks like this was an issue that was fixed and closed recently so try updating your copy of Skyfield to at least version 1.31.
astrosnapper's user avatar
  • 2,506
5 votes

GMAT - Locating inter-spacecraft contact instead of spacecraft to ground station

I am not familiar with GMAT, but there is another route to solve this challenge using an extensively validated open-source solution. You can use the Orekit Astrodynamics library to build one Moon-...
Manny's user avatar
  • 710

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