## What we've been working on these days!

Hey, folks! I hope everyone is okay out there. Today, I am going to explain a little bit about Repeat ground track orbits, and the value that lies behind. Orbits with repeating ground tracks play a significant role in space engineering. Ground tracks that repeat according to any pattern have meaningful applications in remote sensing missions, reconnaissance missions, and numerous rendezvous and docking opportunities with an orbiting spacecraft. Since they overfly the same points on the planet’s surface every repeat cycle, such as those studying gravity, the atmosphere, or the movement of the polar ice cap.

So as you might imagine, this is amazing. In one way, the data we consume relies on these orbits. As mentioned before, Repeat ground track (RGT) orbits allows a satellite to reobserve the same area after a repeat cycle.

# So how do we …

## To Infinity and Beyond!

Hey folks! It's been a while, but here I am to keep you posted about what we've been up to these last days.

# What have we been up to?

We began the coding period with a video call with the mentors, as you might already know, JuanLu and Jorge. We got to know each other a little better, and we started to design what was ahead of our path.

But, before dropping any line of code, we first had to think about what would be the best way to integrate the new features to Poliastro community in order to capture the desired requirements from an end-user perspective. After some deliberation, we came up with the idea of adding two new objects.

By now, I hope to have your attention as well as Spock's. So we created EarthSatellite and Spacecraft. Both …

## GSoC 2020, I am going to an adventure!

Hi, you all! Let me tell you something, this is going to be the beginning of our journey together, we are going on to a spatial adventure! Sit tight, and wait for the countdown!

But first, let me introduce myself, my name is María Eugenia, though everybody knows me as Meuge.

# First things first, SPACE? How did we get here?

All began with the big bang, no wait, that's a story for another time. All began in 2019, when JuanLu reached out to the The Fellowship of the ring Python Científico community to informed us that Poliastro would be part of GSoC 2019. To be honest with you, I had just a slight idea of astrodynamics, so I took a big leap of faith and asked JuanLu where I could make myself useful.

The truth is that JuanLu wasn't that …

## New features after GSOC19

GSOC 2019 Edition has almost finished. All along this last three months lots of issues where solved, poliastro 0.13 was raised, new features were applied and of course, new issues and bugs appeared.

The objective of this post is just to collect all the implementations that have been merged during this GSOC and also those that are still required to be done.

• [x] Lambert minor issues were fixed.
• [x] Lambert as Maneuver instances.
• [x] Docs and notebook on previous implementations.
• [x] Trail plotting option.
• [x] Fix minor issues on CI and tests.
• [x] New twobody propagators.
• [x] Maneuver fixes: Hohmann time to pericenter and units bug.
• [x] Atmospheric models: COESA62 and COESA76.

A detailed description and link to the code can be found in the following lines.

### Izzo Algorithm minor errors

Some errors appeared in the minimum …

## CZML Extractor: An overview

As the proverb says "all good things must come to an end". Unfortunately, it's time to bid adieu to the summer and have a look on what has been accomplished so far.

## The CZML Extractor

This was undoubtedly the main and most time-consuming part of the project. The extractor allows users to easily convert orbital data to CZML. You can find an overview of the extractor's usage in the User Guide or take a look in the more in-depth Jupyter notebook tutorial

## The Cesium Application

Since we need more parameters to accurately represent the data, we also need a specific application to parse said parameters. For this reason, I worked on a Cesium application that allows you to easily visualize the data. At this moment, there are two separate applications: one that runs remotely and one you can copy-paste directly …

## Reformat on poliastro.atmosphere

After implementing the COESA62 and COESA76 models in #738 I was not completly happy because of lots of data and coefficients at the beginning of each script. Therefore and after asking Juanlu, it was finally decided to move all those numbers to text files under the *.dat extension.

Furthermore, I decided not only to do that but also to completely reformat the poliastro.atmosphere module:

• base.py: holds different mother classes for atmospheric models.
• coesa62.py: U.S Standard Atmosphere 1962 model.
• coesa76.py: U.S Standard Atmosphere 1976 model.
• util.py: contains atmospheric utilities.

Documentation was also added together with a notebook to better see not only how these objects work but their differences in output results. In the following image properties for COESA76 against geometrical altitude are plotted:

While working …

## Tasks for this last period...

While checking the stability of the 0.13, GSOC continues and new bugs, implementations, and others need to be solved for the 0.14. Most of them are related to:

• New frame modeling, implementation, and testing.
• New plotting capabilities, such us two attractors in the same plot.
• New orbit creation methods.
• Start using non-dimensional units.
• Different bug solving.

Issues related to frames are the most tricky ones since working with them is not so intuitive. Plotting capabilities are directly related to frames and therefore no major improvements are done in this field without solving something in the previous one.

## New atmospheric models

I have been trying to model and implement some famous atmospheric models for poliastro. Drag is one of the main perturbations for LEO orbits. By making use of Cowell's formulation we can integrate …

## Ground track plotting and Ellipsoids

The second evaluation period has come to the end and with the end of the program drawing ever closer, I'm happy to announce that most work on the additional deliverables has been complete!

## CZML3

I've added polylines and points (along with myriad of other dependent properties/types). These also marked the release of v0.1.3!

## Ground Track Plotting

Having added the necessary CZML properties, I finally managed to add the ground track plotter. It allows to draw both a static path and an animated one. The coolest feature is that it automatically calculates the path's orthographic projection, allowing you to see the satellite in 2D mode. I was also toying with the idea of allowing the users to export gif images directly from the application, which would mean no longer relying on external screen capturing software to create and …

## 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 …