Astronomy & Space Calculators — United Kingdom
Orbits, distances and optics. Universal physics: the same answer from anywhere on Earth.
Orbits & gravity
Orbital Period Calculator
How long an orbit takes and how fast the orbiting body moves — Kepler's third law.
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Rocket Equation Calculator
Delta-v from mass ratio and exhaust velocity — Tsiolkovsky's equation, and why rockets are mostly fuel.
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Rocket Fuel Mass Calculator
How much propellant a rocket needs to deliver a given change in velocity, from its dry mass and engine efficiency — the Tsiolkovsky rocket equation, which is why rockets are almost all fuel.
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Satellite Coverage Calculator
How much of the Earth one satellite sees from a given altitude — the footprint radius and area, the share of the globe, the minimum satellites for continuous coverage, and the orbital period.
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Space Debris Decay Calculator
How long an object stays in low Earth orbit before atmospheric drag brings it down — from its altitude, mass and cross-section — and whether that meets the 25-year disposal guideline.
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Planet Surface Gravity Calculator
A world's surface gravity, escape velocity and mean density from its mass and radius in Earth units — and what a person would weigh standing on it.
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Schwarzschild Radius Calculator
The Schwarzschild radius of any mass — how small it would have to be compressed to become a black hole — with the density inside the horizon, the tidal stretch at it, and the Hawking temperature.
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Hohmann Transfer Calculator
The two burns of a Hohmann transfer between circular orbits — each delta-v, the total, and the transfer time — for any body, with low Earth orbit to geostationary as the worked default.
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Synodic Period Calculator
How often two orbiting bodies return to the same alignment — the synodic period — from their orbital periods, with the time to the next window from the last one and the windows in a decade.
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Delta-V Budget Calculator
Add up the velocity changes of every leg of a mission, apply a margin, and turn the total into propellant for a given dry mass and engine — the delta-v budget that every mission plan starts from.
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Launch Cost Per Kilogram Calculator
The cost of putting a kilogram into orbit from a launch price and payload capacity — to low Earth orbit and to geostationary transfer — with the effect of flying part-full and what a given payload costs to launch.
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Orbital Assembly Launches Calculator
How many launches it takes to put a large structure in orbit — limited by the payload mass or the fairing volume, whichever binds — with the schedule at a launch cadence and the cost.
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Distance & light
Apparent Magnitude Calculator
How bright a star appears from a given distance, from its absolute magnitude — with its luminosity in Suns, the distance modulus, and how far away it would still be visible to the naked eye.
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Exoplanet Habitable Zone Calculator
The habitable zone of a star from its luminosity — the inner and outer edges where a planet could hold liquid water — with a planet's equilibrium temperature, stellar flux and year at any orbit.
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Parallax Distance Calculator
The distance to a star from its parallax angle — in parsecs, light-years, astronomical units and kilometres — with the uncertainty that follows from the measurement error and the distance modulus.
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Redshift Calculator
What a galaxy's redshift means — its recession velocity, the Hubble-law distance, the shift of a spectral line and the scale of the universe when the light left.
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Solar Constant Calculator
The intensity of a star's light at any distance — the solar constant, 1,361 W/m² at Earth — and what a solar panel of a given size and efficiency would produce there, in continuous sunlight.
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Hubble Time Calculator
The Hubble time — one over the Hubble constant — and the actual age of a flat universe with matter and dark energy, from H₀ and the density parameters, with the Hubble distance and how the tension between H₀ measurements shifts the age.
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Relativistic Rocket Trip Calculator
A trip to another star under constant acceleration — accelerating to the halfway point and decelerating the rest — with the time that passes aboard, the time that passes on Earth, the peak speed and the peak time dilation.
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Telescopes & observing
Telescope Magnification Calculator
Magnification, field of view and the limits your aperture actually sets.
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Telescope Resolution Calculator
What a telescope can resolve and how faint it can see from its aperture — the Rayleigh and Dawes limits, limiting magnitude, light grasp, and the useful range of magnification with a given eyepiece.
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Drake Equation Calculator
The Drake equation — the number of civilisations in the galaxy we could detect, as a product of star formation, planets, habitability, life, intelligence, technology and longevity — with the running product and the factor that matters most.
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Life Support Mass Calculator
The consumables a crew needs for a mission — oxygen, water and food by the day — and how much recycling cuts what must be launched, with the mass per person-day and what it costs to lift.
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About these calculators
Constants are the CODATA 2018 and IAU 2015 nominal values. Orbital calculations assume a two-body problem with a circular or Keplerian orbit and ignore perturbations, atmospheric drag and relativistic corrections, all of which matter for real mission planning.