Space and Investing Glossary: Key Terms Explained

How to use this space and investing glossary

The terms appear in alphabetical order, and each one is explained in one to three short sentences. Space science and engineering words sit alongside the language people use when they talk about funding and building new space ventures, because the two worlds increasingly overlap.

Some definitions link to an interactive tool or a longer guide, so you can move from a quick explanation to a worked example. The investing terms describe ideas and ways of thinking. They are there to inform, not to recommend any particular course of action.

Nicole Junkermann's perspective

Nicole Junkermann, founder of NJF Holdings and its venture capital arm, NJF Capital, has spent around two decades investing at the intersection of technology, healthcare, media and innovation. In her view, a shared vocabulary is one of the simplest ways to open up a complex field. When more people understand words like orbit, upstream or milestone, more people can follow the conversation and ask good questions.

She sees the space economy and artificial intelligence as closely connected. Satellites gather huge amounts of data about Earth, and AI helps people turn that data into maps, forecasts and alerts, while people keep the final judgement. Knowing the terms on both sides makes it easier to see how the pieces fit together.

She has long argued that patient capital matters for deep technology, where research, testing and building hardware can take many years. Her thinking on long horizons and human-led progress is set out in Nicole Junkermann on the future of investing in space.

Try the tools

Definitions are easier to remember when you can see an idea in action. The entries for orbit and technology readiness level each link to a hands-on tool, and three more tools bring other terms in this glossary to life.

• The space economy explorer maps the upstream and downstream layers of the space economy and shows how they connect.
• The space signal delay calculator shows how long a message travelling at the speed of light takes to reach the Moon, Mars, Jupiter and beyond.
• The weight and age on other planets tool compares surface gravity and the length of a year across the Solar System.

Space and investing terms, A to Z

Anchor customer

An early, committed customer whose demand helps a new venture get started. In space, an anchor customer might be a public body or a large organisation that agrees to buy a service, such as satellite data, before it is fully proven. That early demand can help founders plan ahead and attract further funding.

Astronomical unit

The average distance between Earth and the Sun, about 150 million km. Astronomers use it as a convenient yardstick for distances within the Solar System.

Capital intensity

How much money a business needs to spend on equipment, facilities and hardware before it can operate. Space ventures are often capital intensive because rockets, satellites and test facilities are costly to build. That is one reason long time horizons matter in the sector.

Constellation

A group of satellites designed to work together, spread across one or more orbits so that places on Earth are covered more often or continuously. Constellations support communications, satellite navigation and frequent Earth observation.

Cubesat

A small, standardised satellite built from one or more cube-shaped units, each small enough to hold in one hand. Shared designs and off-the-shelf parts help universities, start-ups and researchers build and fly experiments at lower cost.

Deep tech

Technology based on substantial scientific or engineering advances, such as new materials, advanced computing, biotechnology or space systems. Deep tech ventures usually need years of research and testing before they reach customers, which is why they tend to attract patient capital.

Digital twin

A detailed computer model of a real object or system, such as a satellite or a rocket engine, that is updated with data from the real thing. Engineers use digital twins to test ideas, spot problems early and plan maintenance without risking the hardware.

Downstream

The part of the space economy that uses space infrastructure to deliver services on Earth, such as weather forecasts, satellite navigation, connectivity and Earth observation data for farming or disaster response. Many downstream businesses never build hardware themselves and instead turn space data into useful services.

Earth observation

Studying Earth from space with cameras and other sensors on satellites, sometimes called remote sensing. It helps people track crops, forests, weather, water and floods, support disaster response and keep maps of growing cities up to date.

Escape velocity

The speed an object needs to break free of a planet's or moon's gravity without any further push. From Earth's surface it is about 11.2 km/s, compared with about 7.8 km/s to stay in orbit close to Earth.

Exoplanet

A planet that orbits a star other than the Sun. Astronomers find most exoplanets indirectly, for example by spotting the tiny dip in a star's light when a planet passes in front of it.

Geostationary orbit

An orbit 35,786 km above the equator in which a satellite circles once every sidereal day, about 23 hours 56 minutes. Because it keeps pace with Earth's rotation, the satellite appears fixed in the sky, which suits weather watching and broadcasting.

Ground station

A site on Earth with antennas that send commands to spacecraft and receive their data. Ground stations, together with the networks and software behind them, make up what the industry calls the ground segment.

In-orbit servicing

Working on satellites after launch, for example refuelling, repairing, upgrading or moving them to a new orbit. It could help satellites last longer and help keep busy orbits tidy.

In-situ resource use

Using materials found in space, such as water ice or soil on the Moon or Mars, instead of carrying everything from Earth. People are exploring ways to turn local resources into water, oxygen, fuel and building materials.

Lagrange point

One of a few special points near two large bodies, such as the Sun and Earth, where gravity and motion balance so a spacecraft can keep pace with them using little fuel. Some are favoured spots for space telescopes and observatories.

Launch window

The period in which a rocket can lift off and still reach its intended orbit or destination. For journeys to Mars, favourable windows come around only every couple of years, when Earth and Mars are well placed.

Light-year

The distance light travels in one year, moving at about 300,000 km every second. Despite the name, it measures distance rather than time and is used for the vast gaps between stars. Light from the Sun, by comparison, reaches Earth in about 8 minutes 20 seconds.

Low Earth orbit

The region up to about 2,000 km above Earth, home to the International Space Station at about 400 km. Satellites here are relatively close to the ground, which suits detailed Earth observation and fast communications.

Medium Earth orbit

The region between about 2,000 km and 35,786 km above Earth. Satellite navigation satellites fly here, around 20,000 km up, each circling Earth about twice a day.

Microgravity

The near-weightless conditions aboard an orbiting spacecraft, which is falling freely around Earth. Gravity is still there, but everything falls together, so people and objects float. Researchers use microgravity to study materials, fluids, plants and the human body.

Milestone

A clear, checkable step in a venture's progress, such as a successful test, a first launch or a first paying customer. Long-term investors often link funding to milestones, which helps manage technical uncertainty.

Orbit

The curved path an object follows around a planet, moon or star. A satellite in orbit is constantly falling towards Earth but moving sideways fast enough, about 7.8 km/s near Earth, that it keeps missing it. Try different altitudes in the orbit calculator.

Patient capital

Long-term investment that gives a venture time to research, build and test before it has many customers. Patient capital suits deep technology, where progress is often measured in years rather than months.

Payload

Whatever a rocket carries into space for its customers, such as satellites, scientific experiments, supplies or crew. The rest of the rocket exists to deliver the payload safely to the right orbit.

Public-private partnership

An arrangement in which a public body and private companies share the work, costs and risks of a project. In space, a public agency might buy a service, such as launches, cargo deliveries or satellite data, from private companies rather than building and running everything itself.

Re-entry

The stage of a flight when a spacecraft comes back into Earth's atmosphere. It meets the air at very high speed, which creates intense heat, so a heat shield protects the craft and anything inside.

Regolith

The loose layer of dust, soil and broken rock covering the Moon, Mars and asteroids. Lunar regolith is fine, sharp and clingy, and people are exploring ways to use it as a building material.

Reusable booster

The first stage of a rocket designed to land after launch and fly again instead of being discarded. Reuse can lower the cost of reaching orbit and allow more frequent flights. The guide to how rockets work and why reusable rockets matter explains more.

Rideshare launch

A launch that carries many small satellites from different customers on the same rocket, sharing the cost of the ride. Rideshare launches have made it easier for start-ups, universities and researchers to get hardware into orbit.

Rover

A robotic vehicle that drives across the surface of the Moon, Mars or another body, carrying cameras and instruments. Because signals take minutes to reach Mars, rovers handle some decisions on their own using on-board software.

Space debris

Old satellites, spent rocket parts and fragments left in orbit. Because they move very fast, even small pieces can damage working spacecraft, so operators track debris, steer around it and design satellites to leave orbit at the end of their lives.

Space economy

All the activity linked to space, from building rockets and satellites to the everyday services on Earth that depend on them, such as weather forecasts, navigation and connectivity. It is often divided into upstream and downstream.

Spectrum licence

Permission to use particular radio frequencies to communicate with satellites. Because frequencies are shared and limited, operators need licences to avoid interfering with each other, and obtaining them is an important early step for many space ventures.

Sun-synchronous orbit

A low orbit that passes near the poles and is angled so that a satellite crosses each place at about the same local time every day. The steady lighting makes it popular for Earth observation, because images taken on different days are easier to compare.

Technology readiness level

A scale from 1 (basic principles observed) to 9 (proven in operation) that describes how mature a technology is. First developed for space programmes in the 1970s, it is now widely used in research funding and engineering. Explore each level in the technology readiness level explorer.

Telemetry

Data that a spacecraft sends home about its own health and surroundings, such as temperatures, power levels, position and instrument readings. Engineers watch telemetry to check that everything is working and to spot problems early.

Time horizon

The length of time an investor expects to wait before a venture reaches its goals. Space and other deep tech ventures usually call for long time horizons, because research, testing and building hardware take years.

Upstream

The part of the space economy that designs, builds and launches things that go to space, such as rockets, satellites, spacecraft, launch sites and ground equipment. Upstream work is usually hardware heavy and capital intensive.

Venture capital

Investment in young companies with ambitious ideas, usually from specialist firms that work closely with founders over several years. Venture capital accepts high technical and commercial uncertainty in the hope of supporting breakthrough companies early.