Asteroid and Comet Trajectory Propagator (NEOPROP)
In 2012, Astos Solutions developed for ESA a new orbital propagator algorithm in order to assess the potential risk of impact of a NEO. The objective of that activity was to come up with a different trajectory prediction algorithm, which allows an independent validation of the current algorithms within the SSA-NEO segment. Analytical and numerical algorithms were developed in order to assess minimum orbital intersection distances and close approaches with other celestial bodies.
In 2015, a new version of the tool was developed to improve and extend its functionalities. The following new algorithms were added:
Estimation of impact probabilities as Torino and Palermo scale values, after propagating virtual asteroids computed along the line of variation. These figures are important characteristics for Governments to identify potentially catastrophic scenarios and to prepare counter-measures or evacuations.
New orbital perturbations (e.g. Poynting-Robertson effect, solar radiation pressure, outgassing) to improve the propagator accuracy and to allow the identification and propagation of any celestial body (not only NEOs but also moons, comets, planets, etc).
The pre-existing algorithms have been further improved in order to increase the performance and reduce the need for human intervention. Robust and redundant preliminary orbit determination techniques have been added in order to deal with very long and disrupted observational arcs, which usually would require a manual split of the observations.
NEOPROP has two separate modules:
1. The Analytical Module makes use of analytical algorithms in order to rapidly assess the impact risk of a NEO. Orbit determination algorithms determine the initial state, along with its uncertainty, and the minimum orbital intersection distances (MOID) of the NEO (computed analytically).
2. The Numerical Module makes use of numerical algorithms in order to refine and to better assess the impact probabilities of a NEO. The initial state provided by the Analytical Module is used for the numerical propagation of the trajectory (backwards propagation is supported), which can be run in two modes: one faster, in order to get a quick estimate of the trajectory (fast analysis) and one more precise, taking into consideration more detailed and complex models (complete analysis). Along with the numerical propagation of the nominal state, Virtual Asteroids (VAs) can be numerically propagated in order to determine the (numerical) MOID and assess the impact risk of the asteroid, in case at least one virtual impactor is found.
An aspect common to both the modules is the usage of multi-threading. The tool is able to detect how many threads are available and to assign them in order to parallelize some computations.
Moreover, in order to improve the usability of the tool a Graphical User Interface (GUI) has been developed. It allows the user to quickly create a new scenario and to easily retrieve from internet observations and physical properties for the NEO to be analyzed. With the GUI, the user can run the modules without having to use the command-line interface and can rapidly visualize and export the most important results in an html file. If requested, the GUI can retrieve the orbital elements, MOID and risk figures from the NEODyS and Sentry systems and compare them with the results obtained by NEOPROP.
Figure 1. NEOPROP GUI screenshot
The GUI provides a dedicated panel, where anew scenariocan be created, allowing the user to collect with few clicks all the inputs required to set up a new test case. All the requested input files are automatically created. Once the ‘Create' button in the ‘New Scenario' dialog panel is pressed, a new scenario is created. If the ‘Download observations from MPC' checkbox is selected, the tool tries to download the observation file from the MPC website, using the provided identifier, which therefore needs to be consistent with the one used by the MPC website. The diameter of the NEO can be also retrieved from internet and used to estimate its mass. Alternatively, the user can provide numerical values.
Figure 2. GUI dialog panel for the creation of a new scenario
Once a scenario has been created or loaded, the user can access some useful internet links to the MPC, JPL, ESA SSA, NEODyS and Sentry pages through the ‘Links to NEO' menu. Moreover, links for the selected NEO to the NEODyS and Sentry pages are available. If the NEO is inserted in the risk list, links to the NEODyS and Sentry risk pages are accessible too, instead of being greyed out.
The toolbar allows the user to run (and stop) any NEOPROP module, to create a scenario summary or results comparison and also to save or load the content of the log pane, which visualizes in real time the output stream of a running executable. In this way the user is informed about the current status of a certain action/analysis. The log pane is also used to visualize (in html format) the scenario report and results comparison.
Users can generate a scenario summary and/or compare the results obtained by NEOPROP with the values reported by NEODyS and Sentry. In both cases results are separated in three sections, one per task (Analytical Module, Numerical Module fast and complete). The scenario summary functionality collects all the information from the output files stored in the output folder and writes them into the log pane. In this way the user gets a rapid overview of the results without the need of accessing manually all the files. Orbital elements, MOID, close approaches, Earth virtual impactors and risk figures are reported.