Four spacecraft, ten kilometres apart, and one place where a magnetic field breaks.

The first game showed where MMS4 was. This one asks what it found.

The first MMS4 Ephemeris Lens turned a 15-second slice of ephemeris into a place you could walk around. It answered one question: where is the spacecraft? The sequel follows the mission's real question. The four MMS spacecraft fly in a tetrahedron about 10 km across. Together they can measure something one spacecraft can't: the curl of the magnetic field. That gives you the electric current at a point, and at the right point it shows where magnetic field lines break and reconnect.

On 16 October 2015 at 13:07:02 UTC they found such a point. For a fraction of a second the field around them nearly vanished, and the current passed a microamp per square metre. When you load the real burst data into this game's curlometer, the peak lands at 13:07:02.4.

A cutscene, then four labs you can break

The opening runs about a minute and you can skip it. It follows the countdown, the RD-180 lighting before the solid boosters, staging, the fairing opening, and the four releases five minutes apart. Then one observatory unreels its booms until it is 120 m across. Every event time comes from the real flight.

1. Ephemeris. MMS4's real orbit for 16–17 Oct 2015, coloured by the field it measured. Start a gravity model from NASA's state vector and race it. Two-body gravity drifts about 100 km. Adding Earth's bulge and the Moon and Sun keeps it within a kilometre. What-ifs: the 2017 apogee raise to 25 RE, or a perigee dropped into the atmosphere.
2. Trapped. Release an electron, a proton or an oxygen ion and watch it spiral, bounce and drift. The lab switches between three integrators so each timescale stays honest. Aim inside the loss cone to light an aurora, build a storm ring current, or weaken Earth's field until particles stop behaving.
3. Bow Wave. Set the solar wind's density, speed and field direction, and the magnetopause and bow shock move with it. Replay the real wind for the whole day of the event. Push the shield inside geosynchronous orbit, or switch Earth's field off and see what Mars lives with.
4. Diffusion Region. Run the four-spacecraft curlometer on the real 2015 dayside and 2017 magnetotail bursts. Then shape your own tetrahedron and fly it through a reconnecting current sheet. Make it too big or too flat and watch the current estimate fall apart.

It runs in portrait and landscape on a phone and on a desktop display. On a phone the controls slide up as a sheet you can tuck away.

From the flame trench to the diffusion region

Build notes: real archives, checked physics, synthesised sound

Read the original MMS4 2.0 article, published October 7, 2026.

Data. A data.gov search for "mms4" returns eight datasets: the fluxgate magnetometer (FGM) for all four spacecraft, in survey and burst mode. The game pulls them through NASA CDAWeb. It uses 30 hours of MMS4 survey field for the orbit, and 128-samples-per-second burst field from all four spacecraft for the two diffusion-region events. MEC ephemeris supplies the positions, and the OMNI solar wind drives the replay. The FGM files print positions to only three significant figures, which is useless for a 10 km tetrahedron, so the curlometer takes its positions from MEC.

Physics. Every lab has a model and a test. The orbit propagator is RK4 with J2 and the Moon and Sun. Started at apogee, it stays within 0.6 km of NASA's definitive ephemeris over 18 hours. The particle integrators reproduce analytic bounce and drift periods to within 1%. With the real wind at 13:07, Shue's magnetopause sits 0.18 RE from where MMS actually was. The game's curlometer matches an independent Python version on the real burst to within 0.1%.

Models. A Blender 5.2 Python script builds the MMS observatory, the Atlas V 421 and the pad from dimensions. The observatory has an octagonal deck, solar panels, instrument heads and rigged booms. The Atlas has separable boosters, core, interstage, Centaur and fairing halves. The same script runs headless or inside Blender. The Earth uses NASA's Blue Marble, Black Marble city lights and GEBCO relief, under an atmosphere that is ray-marched per pixel.

Sound. There isn't a single sample in the game. The rocket roar, the pyro bangs, the boom-reel ratchet, the whistler, the aurora and the music are all synthesised live. A test renders each one offline and checks its waveform and spectrum. The first pass caught a clipping pyro, a DC-shifted rocket, a clicking whistler and two sounds 20 dB too quiet. All four are fixed.

Read the full build notes

Changelog

v2.3: the real Sun. The Sun is now built from SDO and SOHO data for 16 Oct 2015 13:07 UTC, the minute MMS crossed the diffusion region. It has white-light limb darkening and sunspots, the 304 Å prominence on the east limb, 171 and 193 Å coronal loops, and LASCO streamers. The day's real flares replay as a time-lapse, each one with a type III radio burst, and the CME scenarios launch a halo CME. A new Sun view in every lab zooms in and switches between composite, white-light, 304 Å and 171 Å.

v2.2: launch-site terrain. The pad now sits in a modelled Cape Canaveral site, using the terrain techniques from FIELDWORK and the scatter approach from the island project. It has a heightfield with dunes, swales and a perimeter berm, plus a retention pond and marsh ponds. The Banana River lagoon lies to the west and the Atlantic surf to the east. Roads carry sodium lamps and the rails run out to the VIF. Instanced saw palmetto sways in the sea breeze and flattens as the ignition pressure wave passes. Scrub oak and sabal palms fill the land around, and storage tanks and a fence stand on the pad apron. The pond mirrors the rocket and its flame, and the deluge leaves the apron wet.

v2.1: planet, aura and shield pass. The Earth is now built from NASA Blue Marble, Black Marble, GEBCO relief and a real cloud map. It sits under a ray-marched Rayleigh and Mie atmosphere with airglow, and the auroral ovals have curtains in the geomagnetic frame. The magnetosphere is now traced through a dipole, image-dipole and tail-current field. It has cusps, Kelvin–Helmholtz waves on the magnetopause, a turbulent foreshock and a plasmasphere. The spacecraft, rocket and pad got a Blender detail pass.

v2.0: sequel release. Launch cutscene, four labs with objectives and what-ifs, Blender-built spacecraft and launcher, real MMS FGM, MEC and OMNI data, procedural audio, and layouts for portrait, landscape and desktop. It rebuilds MMS4 Ephemeris Lens around the mission's four-spacecraft science. Full changelog.

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