Around 160 km, air stops behaving like a fluid.
Molecules travel farther between collisions than the spacecraft is wide. Continuum CFD no longer applies.
Very low Earth orbit
160 — 450 KM
Less atmosphere.
Still aerodynamics.
Free-molecular flow analysis and mission pre-design for very low Earth orbit. Panel method, gas–surface interaction models, results in seconds.
Every panel meets the flow on its own.
Atmospheric molecules arrive at about 7.7 km/s. Each surface element exchanges momentum with them independently.
Small forces. Mission-sized consequences.
Summed over every panel, those impacts become drag, lift and torque — the numbers behind orbit lifetime and attitude control.
Drag to turn the Earth
04 — Orbit
Pick an altitude. Watch the orbit.
Drag to turn the Earth. Lower orbits are faster and meet denser air — that is where aerodynamics starts to decide mission life.
- Orbital speed
- 7.73 km/s
- Period
- 90.5 min
- Orbits per day
- 15.9
Circular two-body orbit around a spherical Earth (μ = 398 600.4418 km³/s², R = 6 378.137 km). Spacecraft not to scale.
05 — Preview Demo and local engine
Try it on a CubeSat.
The demo shows three CubeSat presets at every orientation, precomputed. With an invite code, the full engine runs on your own computer: every setting, your own geometry, sweeps on all cores.
Drag coefficient Cᴅ—Aref = ½ total area
Drag force Fᴅ— µNAlong incident flow
Projected area A— m²Exposed to the flow
Aerodynamic torque M— µN·mAbout centre of mass
One spacecraft. 37 orientations.
Yaw −90° to +90° in 5° steps. All other parameters are held at the values captured when the sweep starts.
Behind the numbersModel assumptions & scientific references +
Satellite Aero’s own implementation of the Sentman free-molecular panel method, with Schamberg energy accommodation and Koppenwallner’s ½ correction. Each triangular panel contributes pressure and shear; forces and moments are summed about the selected centre of mass.
Panels hidden from the flow by other parts of the spacecraft are excluded, as are back-facing panels. Partial shading, secondary reflections, multiple gas species, atmospheric forecasting, orbital propagation, solar pressure and transitional flow are outside this preview’s scope. The specular option is a hyperthermal comparison. Refine your mesh and verify the free-molecular regime before using results in engineering studies.
By default the coefficients use Aref = half the total mesh area; the projected area can be selected instead. Forces use q = ½ρv². Coordinates are in metres; default flow is along −x, yaw rotates towards −y, and pitch towards −z.
Based on published theory: L. H. Sentman, Free molecule flow theory and its application to the determination of aerodynamic forces (1961); R. Schamberg, RAND Corporation (1959); G. Koppenwallner, Energy accommodation and momentum transfer modeling (2009). Results are exploratory and have not been independently validated.
06 — Access
Who it's for.
Students & educators
Learn free-molecular aerodynamics with every model explained and referenced. Free access for classrooms is planned.
Engineers & researchers
Check drag, torque and attitude sensitivity during pre-design, before committing to high-cost analysis tools.
Emerging space programmes
Check very low orbit concepts with a credible pre-design step, early in the mission.
DemoNo accountThree CubeSat presets at every orientation, precomputed. Sweeps and exports included.Now
Early accessFree · invite codeThe full engine on your own computer: every setting, your own OBJ/STL geometry, multi-core sweeps.Now
ClassroomSchools · studentsFree access for schools and university courses.Next
ProgrammesAgencies · companiesPre-design studies for mission teams and new space programmes.Later
07 — Research
From research to software.
IAC 2025 · SYDNEYAnalysis and Validation of Gas-Surface Interaction Models for VLEO Spacecraft Using ADBSat FrameworkT. Çebi, A. S. Durna — 32nd IAA Symposium on Small Satellite Missions, 76th International Astronautical Congress, pp. 195–206.DOI 10.52202/083084-0023 IAC 2026 · ANTALYADemocratizing VLEO Mission Design: Development of Open-Access Computational Tools for Emerging Space Nations and Commercial NewSpace Ventures77th International Astronautical Congress.IAC-26,E6,IP,24,x116316- NowDemo & invite-only full engine
- NextFree classroom programme for schools and universities
- LaterLive visualization of attitude and flow
- LaterPre-design studies for space programmes
08 — Early access
Get early access.
Request an invite code. It unlocks the full engine in your browser, running on your own computer. Occasional updates only.
We use your email to handle your request and send your invite code. How we process your data: Privacy notice (KVKK).