The Geography of Space
You probably know that satellites orbit the earth. If you don't know that, I'm worried about you. And the rest of this is probably is of no interest to you.
Satellites stay in orbit because of one foundational concept — gravity. Earth's gravity has less pull as you get further away. That's why satellites in Low Earth Orbit (300mi-750mi away) fall back to earth within 5 years. While satellites in Geosynchronous orbit (22,000mi) can operate for decades.
Gravity determines how everything works up there.
I’m here to tell you that orbits are just the beginning of the geography of space.
Recently we’ve seen 2 different private companies land on the moon, the first asteroid mining mission, Starship launches, and hysteria over an approaching asteroid. Space is booming.
If you want to envision what the future of our activity in space will look like, it helps to start with a map.
Asking for Directions in Space
Orientation in space is determined by gravity, whereas Earth geography is determined by direction and features like oceans or mountains.
The more massive an object is, the stronger it's gravitational pull. Gravity is the force that holds planets, moons, and galaxies together. If you asked me to explain gravity I would sincerely ask you to use ChatGPT. Sir Issac Newton developed his Law of Universal Gravitation in 1687 — 337 years ago. No ChatGPT was used.
The sun is 330,000x the mass of the Earth and accounts for 99.9% of all the mass in our solar system. This is why everything revolves around the sun. The Sun is like the Homeowner's Association for the Solar System. Every thing that happens in space needs to take into account the sun.
Dude, Where's My Satellite?
As the Earth orbits the Sun, the gravitational forces of both objects create whats called a Lagrange Point. Think of these as orbital sweet spots that balance the gravitational pull of two objects.
Lagrange Points are gravitational parking lots, places where objects can stay in position with minimal effort. Being able to park is space is going to be big business. Email me if you want to open up a parking lot.
Lagrange Points follow the naming convention L1, L2.. through L5. These points exist for all large objects - so the Earth & Moon have Lagrange Points, the Earth & Sun, and Jupiter & Europa, etc.
The L1, L2, L3 points are fairly stable, objects there may require occasional ( trajectory corrections to stay in place. While L4 and L5 are truly stable but not yet used by humans.
L2 is home to the James Webb space telescope which continues to release stunning new photos of Deep Space. L1 is my personal favorite Lagrange point - for reasons I'll get to another time.
Gravitational Topography
Now, if you’ve ever climbed a mountain or used a phone to navigate on a hike, there’s a chance you’ve seen contour lines on the map. Contour lines show changes in elevation. The closer the lines are together, the steeper the slope. And the farther apart, the gentler the slope.
Since gravity affects everything up there, space has it’s own type of contour lines, called equipotential lines or gravitational potential contours. Instead of slope, equipotential lines represent gravitational potential. Think of this as if you started walking up a super steep slope and tripped, you'd have really strong gravitational potential to tumble for awhile.
Above you can see gravitational pull of the Sun-Earth Lagrange Points. Notice how the areas surrounding the Earth and Sun don’t have lines? That’s where gravitational pull is strongest.
Defying Gravity?
Space navigation relies on managing this gravity—either escaping it, using it for orbit, or leveraging it for what's called a gravity assists. Massive objects create what’s referred to as a gravity well, which is why it is so difficult to get off of Earth.
Escaping this gravity requires reaching a specific speed that depends on the mass of where you're taking off from, this is called escape velocity. It's the minimum speed needed for an object to break free from a planet’s gravitational pull.
Earth's escape velocity is about 11.2 km/s (25,000 mph). Since reaching 11.2 km/s instantly from the ground is challenging, most rockets first enter Low Earth Orbit, then hit their engines once more to break free of Earth's gravity.
Gravitational Assists
Spacecraft often utilize gravitational assists, harnessing gravitational potential to “slingshot” around planets and gain speed. Europa Clipper recently used Mars for a gravitational assist on its journey to Jupiter. As Clipper leaves Mars behind, it will be traveling at a speed of about 14 miles per second (22.5 kilometers per second).
The fact that we slingshot objects in space repeatedly blows my mind. This is just how NASA Mission planning rolls but it's mind boggling. For Europa Clipper, they planned gravity assists of Mars & then Earth before heading out to Europa by 2030.
NASA will send Europa Clipper over 200 trajectory correction maneuvers over it's mission. These are all taking into account it's flight path, the gravity of neighboring objects, and desired destination. I guess that's why rocket science is hard. But I did see a video that says it's all just math which made me turn it off immediately.
One thing about performing a correction maneuver - you need good WiFi to do it. You need the satellite to be able to lock onto a telescope at home to send & receive data. If you lose connectivity, you're doomed. More on that another time.
Gravitational assists are essential to space activity. You can reduce the amount of fuel and increase the size of the onboard equipment you need to do bigger and better missions.
Future of Space Development begins with Geography
- Orbits
- Lagrange Points
- Gravitational Topography
- Gravitational Assists
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Some ideas for next time: the future of propulsion & sailing the ITN