Calling Hohmann from a public URL
On 13 August 2026 I pointed a client at https://sidus.tools/api/mcp and called hohmann with r1_m = 6578137 and r2_m = 42164137. Those radii are a circular transfer from about 200 km LEO to GEO, using educational Earth μ, in SI the whole way.
The tool came back with dv1 2454.59 m/s, dv2 1477.27 m/s, and a total of 3931.86 m/s. Time of flight was 18931.92 s, about 5.3 hours. Transfer semi-major axis 24371137 m. v1 7784.26 m/s, v2 3074.66 m/s.
That is an educational two-body Hohmann transfer: five hours and a bit from LEO to GEO, a number I can hold in my head, on a public URL an agent can call. You can type the same radii in the browser, see the formula, and get 3931.86 m/s if you use these defaults. Then you hit the MCP and get the same SI out.
That sharing is the point of sidus.tools. The page and the protocol import the same physics functions. If Hohmann is wrong in one place, it is wrong in both, and you fix it once.
What SIDUS is
SIDUS is a free MIT catalog of educational space-engineering checks in SI. The pages cover orbital mechanics, propulsion, satellite and RF, launch, crew ECLSS, geometry, planetary, and utilities. There is no account. Source is github.com/massimodeluisa/sidus-tools. The card at the top is the live Open Graph image from the site.
I write software, and I am not a space engineer. I published sidus.tools so these checks would live in SI, on a page I could read, and on a protocol a client could hit without a second physics library quietly drifting. The formulas, and the code you can export from a page, should be reviewed and tested.
Defaults are educational WGS-84-class Earth: μ⊕ = 3.986004418×10¹⁴ m³/s², equatorial radius 6 378 137 m. The models stay small on purpose: two-body, impulsive burns, circular Clohessy-Wiltshire, ideal rocket, ISA aero. You can hold the assumption in your head and finish a check before the coffee cools.
Two-body pages carry Vallado’s Fundamentals of Astrodynamics and Applications and Curtis’s Orbital Mechanics for Engineering Students. Automated checks want a real HTTPS source URL before a tool ships. If the citation 404s, the tool stays home.
Units stay in SI. If you want kilometres, you convert on purpose, because that conversion is a decision and I want it visible. Pages can export the same number into other languages. If the two disagree, I have a bug.
The Hohmann I ran is a class of transfer: two-body, impulsive, educational μ. You can disagree with the model. You can see the formula. You can call it again.
The public MCP
The same catalog is on a public MCP at https://sidus.tools/api/mcp, over Streamable HTTP, with no API key. GET returns discovery JSON. POST is the tool call. You do not need to clone the repo to use it.
If you want it as an agent skill:
npx skills add massimodeluisa/sidus-tools --skill sidus
Listed at skills.sh/massimodeluisa/sidus-tools/sidus.
If a check helps, use it. If a default is wrong, send a PR. Edit on GitHub.