02Space without the math

Audience: absolute beginners. Goal: by the end you'll understand every word the platform shows you. There is no math you have to do — just pictures and analogies.

This is the only "physics class" you need. Read it once and the whole platform will make sense. We'll build up nine ideas, each with an everyday analogy.

1. What is an orbit, really? (The cannonball idea)#

Here's the single most important mental model, and Isaac Newton drew it 300 years ago.

Imagine standing on a very tall mountain with a cannon. You fire it horizontally. The cannonball arcs out and falls to the ground. Fire it harder — it goes further before landing. Fire it harder still — the Earth curves away beneath it as fast as it falls. Now the cannonball is falling forever, always pulled toward Earth but always missing it because it's moving sideways fast enough.

That's an orbit. An orbit is falling around the Earth and continuously missing. The space station isn't "up where there's no gravity" — gravity up there is almost as strong as on the ground. The astronauts float because they, and the station, are falling together in a permanent free-fall, sideways, fast enough to keep missing the planet.

To stay in low orbit you have to move incredibly fast sideways — about 7.7 kilometres every second (~28,000 km/h, ~17,500 mph). That speed is the whole game.

2. The shape of an orbit (ellipses, not circles)#

Most orbits aren't perfect circles — they're ellipses (squashed circles). The Earth sits at one focus (not the center). Two words you'll see constantly:

• Apogee — the high point of the orbit, farthest from Earth. (Apo- = away.)
• Perigee — the low point, closest to Earth. (Peri- = near.)

Analogy: a skateboarder in a half-pipe. At the bottom (perigee) they're moving fastest; at the top of the ramp (apogee) they slow almost to a stop, then come back down. Orbits do the same — fast and low, slow and high. This trade between speed and height is the rhythm of everything in space.

A perfectly round orbit has the same height everywhere. A very stretched one (like a comet's) dives in close and swings way out.

3. The six numbers that name any orbit (orbital elements)#

You can describe any orbit completely with six numbers, called orbital elements. Think of them as the orbit's "address." Don't memorize — just recognize them when the platform shows them:

The first two (size and shape) plus inclination (tilt) are the ones you'll feel most. Inclination especially: an orbit at 0° inclination hugs the equator; at 90° it flies over both poles; the ISS is at about 51.6°, which is why it passes over most of the populated world.

4. Δv — the currency of spaceflight (the most important idea)#

We named the company after this, so it matters.

Δv ("delta-vee", change in velocity) is how much you can change your motion over the mission. Every maneuver costs some Δv. Your rocket has a fixed "budget" of Δv set by how much fuel it carries and how efficient its engine is.

The analogy that makes it click: Δv is money, and space destinations have prices.

• Reaching low Earth orbit from the ground: ~9,400 m/s (the big one — that's why rockets are mostly fuel tanks).
• Low orbit → the Moon (a "trans-lunar injection" burn): ~3,100 m/s.
• Low orbit → geostationary orbit (where TV satellites live): ~3,900 m/s.
• A small nudge to a slightly higher orbit: maybe 50 m/s.

You "shop" for a mission within your Δv budget. If a trip costs more Δv than you have, you can't go — full stop. This is why mission designers obsess over it, and why Delta V puts a Δv price tag on every maneuver you plan.

5. Why rockets have stages (the empty-suitcase problem)#

Rockets are mostly fuel — often 90%+ of the launch weight. Here's the cruel twist: once you've burned the fuel in a tank, the empty tank is now dead weight you're paying to keep accelerating.

Analogy: imagine climbing a mountain carrying water bottles. Once a bottle is empty, why keep lugging it? You'd drop it and climb lighter. Rockets do exactly this — they stage: burn the first set of tanks-and-engines, then drop the whole thing, and a smaller, lighter rocket continues. The Saturn V that flew to the Moon had three stages.

The math behind this is the Tsiolkovsky rocket equation (you'll see it referenced as "the rocket equation"). You don't need the formula — just the intuition: efficiency (a property called specific impulse, or "Isp") and shedding dead weight are what let you afford big Δv. Delta V computes this for you when you build a vehicle.

6. How you change orbits (transfers and burns)#

You can't "steer" in space like a car — there's nothing to push against. You change your orbit by firing your engine, called a burn, which gives you a shot of Δv.

The classic, fuel-efficient way to move from a low circular orbit to a higher one is the Hohmann transfer (you'll see this word a lot):

1. Burn 1 — speed up at your low orbit. This stretches your orbit into an ellipse whose high point (apogee) just touches the target altitude. You now coast "uphill" along this transfer ellipse.
2. Coast — drift up to the apogee. (Free — no fuel needed while coasting.)
3. Burn 2 — speed up again at the top to circularize at the new height.

Analogy: it's like merging onto a higher highway. You accelerate to get onto the on-ramp (burn 1), coast up the ramp, then accelerate again to match traffic speed on the upper highway (burn 2). Two burns, a coast in between. Delta V's Maneuver tool plans exactly this and tells you the price of each burn.

Two kinds of burn you'll meet:

• Impulsive burn — we pretend the engine fires instantly (a perfect kick). Great for planning; a useful idealization.
• Finite burn — the real thing, where the engine pushes for minutes while you drift and gravity keeps acting. Real burns are slightly less efficient because some thrust fights gravity ("gravity loss"). Delta V can model both, so you can see the difference.

7. The "porkchop plot" — when to leave for Mars#

You can't fly to Mars whenever you feel like it. The planets are moving, so the cost of the trip depends on when you leave and how long you take. Plot the cost for every possible departure date and trip length, color it in, and you get a chart shaped like a porkchop — hence the name.

Analogy: airline ticket prices. Flying on the wrong date costs a fortune; there's a cheap window if you time it right. The porkchop plot is the "fare calendar" for interplanetary travel. The cheap valley in the middle is the launch window missions actually wait for. Delta V draws real porkchop plots for Venus, Mars, and Jupiter.

The underlying tool is the Lambert problem: "given where I am, where I want to be, and how long I'll take, what's the exact path and what does it cost?" Solve that for thousands of date-and-duration pairs and you've got a porkchop.

8. Talking to satellites (access, ground stations, link budgets)#

A satellite is only useful when you can talk to it — send commands up, get data down. But a ground station (a dish on Earth) can only "see" a satellite when it's above the horizon. Those visibility windows are called passes or access intervals.

Analogy: a lighthouse on the coast and a ship at sea. The lighthouse keeper can only signal the ship while it's above the horizon — when it's around the curve of the Earth, they're blind to each other. As the ship sails (the satellite orbits), there are windows of contact and gaps in between.

Three things engineers compute, all of which Delta V does:

• Access intervals — when can station X see satellite Y, for how long, and how high in the sky (elevation)? The single most-used output in the industry.
• Link budget — can the radio signal actually get through at that distance, and how fast can data flow? (A signal weakens with distance, like a flashlight beam spreading out.)
• Coverage — for a whole constellation of satellites (like GPS or Starlink), what fraction of the Earth can be seen at any moment, and how long are the gaps?

9. Finding planets around other stars (the transit method)#

This powers the Deep Field room, and it's beautifully simple.

When a planet passes in front of its star (from our point of view), it blocks a tiny sliver of the star's light — the star dims by a fraction of a percent, then brightens again. Watch a star's brightness over time and you'll see a little dip every time the planet goes around.

Analogy: a moth flying in front of a distant streetlight. You can't see the moth, but you'd notice the streetlight flicker a hair dimmer each time the moth crosses it. If the flicker repeats like clockwork — every 6.27 days, say — there's something orbiting on a schedule.

That repeating dip is a transit. Its depth tells you the planet's size, its period (time between dips) tells you the orbit. NASA's TESS and Kepler telescopes recorded brightness for millions of stars; Delta V lets you analyze that real data and rediscover the dips yourself. (Honest caveat that you'll see in the room: finding a dip makes a candidate, not a confirmed planet — confirmation needs follow-up the platform can't do.)

A few units, so nothing surprises you#

Delta V uses SI units everywhere (the scientist's metric system):

• Distances in metres (m) or kilometres (km). 1 km = 1,000 m.
• Speeds in metres per second (m/s) or km/s. Orbital speed ≈ 7,700 m/s = 7.7 km/s.
• Angles in degrees (°) in the interface (the engine uses radians internally; you never have to).
• Time often in seconds, sometimes hours or days for long missions.
• Altitude means height above Earth's surface (Earth's radius is ~6,371 km), not distance from Earth's center.

One golden rule the whole codebase obeys: never mix kilometres and metres in the same calculation. The interface handles all conversions for you, so you just read the labels.

The one exception: the Deep Field astronomy room speaks the astronomer's units (days, parts-per-million, hours) instead of pure SI, because that's the language the global exoplanet community uses. It's a deliberate, documented choice.

You're ready#

That's the whole foundation. To recap the nine ideas:

1. An orbit is falling sideways and missing the Earth.
2. Orbits are ellipses — fast and low, slow and high.
3. Six orbital elements are an orbit's address (size, shape, tilt…).
4. Δv is money; destinations have prices.
5. Rockets stage to drop dead weight.
6. You change orbits with burns; the Hohmann transfer is the efficient two-burn move.
7. Porkchop plots are the fare calendar for interplanetary trips.
8. Access, link, coverage = when and how well you can talk to satellites.
9. Transits (tiny star dips) reveal planets around other stars.

Now go fly something → Your first flight.