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## What are propagators and why do we care about them?

One of the most common problems in astrodynamics and orbital mechanics is that we want to know where a body will be at a given position along its orbit for a given time. It is possible to integrate by hard the two-body equation and then apply some boundary conditions. However, this last option is just insane and would take several hours or days to be done by a human.

There is a better way to get the position as a function of time or propagate an orbit. Johannes Kepler's contributions to the astrodynamics and orbital mechanics field were really important and can be summarized here, in the so-called Kepler's Laws:

• Planets' orbits follow an elliptical path around the Sun, which is located in one of the focus.
• Planets cover equal …

## Moving forward with the Cesium application

I feel like in the last couple of weeks I got to work a little in several aspects of the project. While this didn't allow me to focus on a single feature, it allowed me to make progress in various different areas.

## Bug resolving and 2D mode

First and foremost, I got rid of a particularly frustrating bug in the application. Certain javascript events (such as the one that allows the inertial view), where tied to a single Viewer and thus wouldn't trigger when the Viewer was destroyed (which is the case when, for example, loading the data from the file). I also made a few minor changes in the code and introduced the option to set the Viewer mode to 2D. This isn't any useful as of now, but it will be with the new feature I'm planning to …

## Converting to CZML and next steps

So the first phase of GSoC is over and with it, it's time to reflect what has been achieved in the last couple of months.

# CZML3

As I mentioned in the last blogpost this is a very useful library created by juanlu. After a few patches, the library now supports most CZML properties and - as far as I can tell - this is the only currently mantained Python library for creating CZML packets.

# CZML Extractor

This is the first feature I've started to work on and while it is still far from complete, I'm happy to say that it is now usable.

At first, the czml document was represented by a nested dictionary and then converted to valid JSON format. This worked ok and I did write a function which made manipulating the dictionary a tad more intuitive, but it was …

## Version 0.13 is getting closer

Version 0.13 is expected to be tagged in about a month. As any other release, it includes new features such as a new method in the Orbit class called change_attractor or the trail parameter in StaticOrbitPlotter. However, this release will also include really important bug fixes such as:

• Minor issues related to Lambert's problem.
• Propagator's are supposed not to hang out anymore due to robust solutions and propagation methods.

Now that my final exams ended I am completely free to work in poliastro and direct all my efforts to the software. I want to close issues #495 and #475 in the next days since they are previously commented bugs.

### Propagator methods in the twobody problem

Kepler's equation (KE) allows us to solve either for the time at a given position or the position …

## Communication satellites and refactoring

Those couple of weeks were spent mainly on setting future milestones and improving the quality of the code. In a way, Tom Cargill's famous aphorism came to my mind:

The first 90 percent of the code accounts for the first 90 percent of the development time. The remaining 10 percent of the code accounts for the other 90 percent of the development time.

Writing stuff that "just works" is relatively easy. But when programming, you always have to keep track of myriad variables including but not limited to: maintanability, integration and readability.

# CZML3

My mentor, Juanlu, wrote a fully-fledged library for composing czml packets. While it's still in the early stages of development, I would urge anyone interested to check it out. I'm currently trying to refactor the czml core, so it utilizes the library instead of the current approach …

## What's new?

Three weeks have passed since the coding phase began and new features have been added to the software:

• Lambert is now a Maneuver instance.
• A trail keyword in StaticOrbitPlotter for showing orbits' trails.

### Lambert just needs now two orbits!

Although the raw algorithms are kept under the module poliastro.iod, it is possible now to simplify the process of solving this famous astrodynamics problem by making use of the poliastro.maneuver module.

Imagine that we want to solve the classical problem ongoing from Earth to Mars for a trip of 600 days duration. Let us compare before and after Maneuver.lambert implementations:

With 0.12 version:

from astropy import units as u
from astropy.time import Time

from poliastro.bodies import Earth, Mars, Sun
from poliastro.iod.izzo import lambert
from poliastro.twobody import Orbit

LAUNCH = Time.now …

# Let the coding begin

So the bonding period is over, which means that the coding phase has officially begun. I've already worked on some of the key features I'd like to add since my examination period is around the corner. Hopefully, this won't slow me down and I'll keep up with the workload.

# The work so far

I've worked on the main part of the project, which was to connect poliastro to the visualization capabilities offered by the Cesium API. There is already the possibility of adding orbits and defining custom attractors, along with various visual customizations. As exciting as this is, there are still way more things that could be added to give life to the project, rendering it more useful and interesting.

# Communications satellites

In the past days, I became increasingly interested in adding communication satellites and visualizing …

## The End of the bonding period

Today bonding period ends for all students selected at GSoC'19. The aim of this period was to learn more about your project community: get in touch with mentors, other developers and their future ideas on the software...

As I said in my last post, I started contributing to poliastro several months ago, even before GSOC was announced. Therefore, and since I am taking my final exams, all my efforts were towards passing them.

But today the coding phase starts! That means we all should start working on our proposal features.

## The coding phase at poliastro

The release of poliastro version 0.13 is getting closer. During this first part of the coding phase, I am planning to solve for different issues, most of them related to frames, check out milestones 0.13.

Frames are …

## The beginning of GSoC

Hello everyone, I'm Eleftheria and this summer I'll be working with poliastro under Open Astronomy as part of GSoC 2019. I'm hoping this blog will prove to be interesting to those who are interested in poliastro or simply a source of inspiration to those looking for a way to get their feet wet with open source.

# The beginning of a journey

After forking poliastro, I immediately dived in and tried to make sense of the codebase. Fortunately, poliastro is extensively documented so the learning curve wasn't as steep as I expected. After getting familiar with the project structure, I started browsing the open issues to find ways to make myself useful. What caught my attention was the ongoing process of adding visualization features to poliastro, which would make the library more accessible to professionals and beginners alike.

It should be …

## From my first pull request to GSOC student

Hi, my name is Jorge, and I am one of the selected students for this GSOC edition at poliastro under the OpenAstronomy organization. I started working on poliastro project after Juanlu came to my university to give a talk about Open Source software in engineering.

After forking poliastro, I decided to improve API Docs, which gave me an overview on how the project was built and how the different modules talked among them. I had no idea on how Git and GitHub worked and therefore, when finished with the docs my first pull request was quite massive...

But after that I started feeling more confortable with GitHub and Sphinx, the tool used nowadays in poliastro for building documentation. Then, I decided to work on a porkchop plotter.

I spent the week after …