About Delta-V Desk

Delta-V Desk is a free set of orbital mechanics calculators for students, teachers, science writers, space enthusiasts and players of spaceflight simulation games. Each tool takes a textbook formula of astrodynamics, the same ones a flight dynamics course starts from, and works it through with clearly stated constants so that you can check every step by hand.

The Calculators

• Orbital Velocity Calculator: speed on a circular or elliptical orbit from the periapsis and apoapsis altitudes, using the vis-viva equation.
• Orbital Period Calculator: Kepler’s third law in both directions, from altitude to period and from period to altitude, including the geostationary case.
• Escape Velocity Calculator: escape speed from the surface or any altitude, and the extra Δv needed from a circular orbit.
• Hohmann Transfer Calculator: the two burns, total Δv and coast time between two circular orbits.
• Rocket Equation Calculator: Tsiolkovsky’s equation for Δv from masses, or the propellant needed for a target Δv.
• Synodic Period and Launch Window Calculator: how often windows open between two planets, the minimum-energy flight time and the departure phase angle.

Alongside the calculators, our guides work through complete problems from start to finish: raising a satellite from a parking orbit to geostationary orbit, budgeting a minimum-energy trip to Mars, and sizing a two-stage rocket stage by stage.

Constants and Methods

We use published standard values and state them on each page. Earth’s gravitational parameter is 398,600.4418 km³/s² and its WGS-84 equatorial radius is 6,378.137 km; the Moon, Mars, Venus and Jupiter use their IAU and JPL gravitational parameters and mean radii; standard gravity g₀ is 9.80665 m/s², the defined value; planetary orbits use mean semi-major axes and sidereal periods. Where a figure depends on a choice, such as equatorial or mean radius for escape velocity, the page says which one we used and how much the alternative would change the answer.

All of the tools use the two-body model with instantaneous burns and, for transfers, circular coplanar orbits. Those are the assumptions of every introductory astrodynamics textbook. They give answers within a few percent of real missions for most purposes, and the pages explain where reality departs from them: atmospheric drag, gravity losses, plane changes, finite burn times and eccentric planetary orbits.

Who Uses It

• Physics, aerospace and astronomy students checking homework or building intuition for orders of magnitude.
• Teachers preparing worked examples with numbers students can reproduce.
• Players of spaceflight simulators planning burns and transfer windows.
• Writers and journalists who want the numbers in an article about a launch or a mission to be right.
• Anyone who has wondered why the Space Station moves at 7.7 km/s or why Mars missions leave every 26 months.

How We Keep Results Accurate

Every default input on a calculator reproduces the worked example in the article beneath it, so the page you open shows the same number the text explains. We check formulas by back-substitution, for example by confirming that the altitude solved from a period gives back the same period, and we compare results with published reference values such as the 35,786 km geostationary altitude and the 11.19 km/s escape velocity quoted with Earth’s mean radius. Inputs are range-checked, and impossible requests, such as a period faster than a surface-grazing orbit, get an explanation instead of a number.

If you find a result that disagrees with a trusted source, please tell us through the contact page with the inputs you used. We correct confirmed errors quickly and note the change.

What This Site Is Not

Delta-V Desk is an educational resource. It is not mission design software, it does not use ephemerides or numerical propagation, and its results must not be used to plan the operation of a real spacecraft, satellite or launch.

How the Site Is Funded

The calculators are free and need no account. The site is supported by advertising, which pays for hosting and for the time spent checking formulas and writing the guides. Advertising never influences the results, and all calculations run in your own browser.