Roadmap

orbitr is a work in progress. This page is a running list of features I’m thinking about adding in future versions. Nothing here is promised, and the priority order is loose — it mostly reflects what I personally find interesting or what users have asked for. If any of these sound useful (or terrible), let me know. Suggestions, feedback, and pull requests are all very welcome.

Physics

A `radius` argument on `add_body()`

Right now bodies are treated as point masses. This is fine for most orbital distances — gravity outside a sphere behaves exactly as if all the mass were concentrated at its center (the shell theorem) — but it means there’s no concept of two bodies physically touching. Adding an optional radius parameter would enable collision detection, merging on contact, and more realistic close-encounter behavior.

I’d probably add it to add_body() as an optional parameter with a sensible default, something like:

add_body <- function(system, id, mass, x = 0, y = 0, z = 0,
                     vx = 0, vy = 0, vz = 0, r = NULL)

If r is supplied for any body in the system, the integrator would check for overlaps on each step and handle them according to a user-chosen policy (elastic bounce, inelastic merge, simulation halt, etc.).

In the meantime, the existing softening parameter on simulate_system() partly works around the missing-radius problem by preventing the gravitational force from blowing up at very small separations — see The Physics for details.

Non-gravitational forces

Optional support for forces beyond pure Newtonian gravity:

Atmospheric drag for low orbits around bodies with atmospheres
Radiation pressure for small bodies near a star
J2 oblateness corrections for orbits around non-spherical bodies (Earth’s equatorial bulge measurably perturbs satellite orbits)

General-relativistic corrections

A small post-Newtonian correction term would let orbitr reproduce real GR effects like the precession of Mercury’s perihelion. Probably opt-in via an argument on simulate_system(), since most users wouldn’t need it.

Setup helpers

Construct bodies from Keplerian orbital elements

The current add_body() takes raw Cartesian state vectors (x, y, z, vx, vy, vz). For users who think in classical orbital elements — semi-major axis $a$ , eccentricity $e$ , inclination $i$ , longitude of ascending node $\Omega$ , argument of periapsis $\omega$ , true anomaly $\nu$ — a helper that converts those into the right Cartesian inputs would be a quality-of-life win:

add_body_keplerian(system, "Mars", mass = mass_mars,
                   a = distance_mars_sun, e = 0.0934,
                   i = 1.85, Omega = 49.6, omega = 286.5, nu = 0,
                   parent = "Sun")

A `load_solar_system()` convenience

A one-liner that pre-builds the Sun and all eight planets with real ephemeris values, so you can skip straight to interesting experiments without typing out a dozen add_body() calls.

Quality of life

Save and load simulation state

Functions to serialize an orbit_system (or a completed simulation tibble) to disk and reload it later. Useful for long-running simulations and for sharing reproducible setups.

Progress bar for long simulations

A simple progress indicator on simulate_system() for runs that take more than a few seconds, with an option to disable it for scripted use.

Built-in conservation diagnostics

Helpers to compute total energy, total linear momentum, and total angular momentum at every time step, so you can sanity-check an integrator’s behavior over the course of a run. Useful for confirming Velocity Verlet is doing its job, and for spotting cases where the time step is too large.

Suggestions Welcome

If any of these sound useful, if you’d like to see something not on this list, or if you have a use case that orbitr doesn’t currently handle well, please open an issue on GitHub. I’d love to hear about how people are using the package and what would make it more useful. Pull requests are also very welcome.