Drag the cable-length slider past the blue geostationary ring to see why a real space elevator needs a counterweight beyond that ring to stay taut, then move the climber slider to see how far up the cable it has traveled.
Drag to orbit and scroll or pinch to zoom on the scene above. The cable-length slider swaps between a cable that stops right at geostationary orbit and one extended to the reference 100,000 km design with a counterweight; the climber slider moves a capsule along whatever length of cable currently exists.
Space Elevator Physics 3D Explorer
This browser explorer shows why a cable anchored to Earth's equator needs a counterweight beyond geostationary orbit to stay taut - drag the cable-length slider past the real geostationary-orbit ring and the tether turns from red to green, then move the climber slider to see how far up that cable a capsule has traveled.
The blue ring marks geostationary orbit at its real, uncompressed ratio to Earth's size - about 6.6 Earth radii, or 35,786 km altitude. Below that ring, a point on the cable moves slower than a circular orbit at that height would need, so it pulls inward; above the ring, a point moves faster than a circular orbit needs, so it flings outward. A cable that stops right at the ring, with nothing beyond it, has its combined weight sitting below geostationary orbit, so it stays red - not stable enough to stay in tension on its own. Drag the cable-length slider to 100% and the tether extends to NASA's NIAC-funded reference design length of about 100,000 km with a visible counterweight, turning green: now the outward pull from the part beyond geostationary orbit overcomes the inward pull from the part below it.
- Cable-length slider (0 to 100) swaps between a cable ending at geostationary orbit (red, not stable) and one extended to the 100,000 km reference design with a counterweight (green, stable)
- Climber-altitude slider moves a capsule along whatever length of cable currently exists, and the facts panel reports its altitude in kilometers plus which zone it is in
- Facts panel states the cable state, the climber's altitude and zone, geostationary orbit's real altitude and radius, and the published cable-strength figures
- Geostationary orbit is rendered at its real, uncompressed ratio to Earth's radius - no distance compression needed for this scene
- Drag to orbit, scroll or pinch to zoom
- Runs fully in the browser with the vendored three.js engine - no account, no upload
| Figure | Value | Source |
|---|---|---|
| Geostationary orbit altitude | 35,786 km above the equator | Standard IAU/NASA figure |
| Geostationary orbit radius from Earth's center | 42,164 km | Standard IAU/NASA figure (6,378 km Earth radius + 35,786 km altitude) |
| Reference cable length (ocean anchor to beyond GEO) | about 100,000 km | Edwards, NASA NIAC feasibility study (2003) |
| Alternative counterweight-extension length | about 144,000 km | Edwards, NASA NIAC feasibility study (2003) |
| Minimum required cable specific tensile strength | about 48.5 to 62.5 GPa | Edwards, NASA NIAC feasibility study (2003) |
| Commonly cited real-world safety-margin target | about 100 GPa or higher | Edwards, NASA NIAC feasibility study (2003) |
| High-strength steel tensile strength | under about 5 GPa | Standard materials-science comparison figure |
| Kevlar tensile strength | about 3.6 GPa | Standard materials-science comparison figure |
| Carbon nanotube strength (single fiber, simulated) | up to about 130 GPa | Peer-reviewed nanotube-strength modeling studies |
| Carbon nanotube cable strength (realistic macroscale, with defects) | around 10 GPa | Peer-reviewed nanotube-cable modeling studies |
| Reference climber capacity | about 20-tonne climber, 13-tonne payload | Edwards, NASA NIAC feasibility study (2003) |
Students studying orbital mechanics or materials science, and anyone who has heard of the space-elevator concept and wants to see WHY a counterweight beyond geostationary orbit is the key requirement, can use the two sliders to connect the force-balance concept to the real published cable-length and cable-strength figures without reading an engineering paper first. For the speed a free orbit needs at a given altitude instead of a structure fixed to the ground, see the Orbital Velocity 3D Explorer. For the speed needed to leave a body's gravity outright rather than stay in orbit, see the Escape Velocity 3D Explorer.
Everything renders on your device with WebGL. The 3D engine loads once (about 0.7 MB) and is cached.
This is an educational approximation, not a physics or structural simulation. The scene does not solve tether elasticity, sag, vibration, orbital perturbation, or materials-engineering physics; the cable-length slider models the force-balance concept, not a real-time dynamics solver; the climber's position is illustrative and does not model climb speed or power-beaming. No material manufactured today reaches the required strength-to-density ratio at the scale a real cable needs, and no space elevator has been built - the concept remains 100% theoretical, limited by materials science rather than orbital mechanics.
Frequently Asked Questions
Why does a space elevator need a counterweight?
Below geostationary orbit, a point on the cable moves slower than a circular orbit at that height would need, so it pulls inward. Above geostationary orbit, a point moves faster than a circular orbit needs, so it flings outward. For the whole cable to stay taut, it must extend far enough beyond geostationary orbit - or carry a counterweight there - that the outward pull overcomes the inward pull from the lower part.
How far up is geostationary orbit?
35,786 km above Earth's equator, or 42,164 km from Earth's center - the altitude where an object's orbital period matches Earth's rotation, so it appears to hover over the same point on the ground.
How long would a real space elevator cable be?
NASA's NIAC-funded feasibility study (Edwards, 2003) described a reference design about 100,000 km long, from an ocean-anchor platform to beyond geostationary orbit. Some published designs extend the counterweight end to about 144,000 km instead of using a heavier counterweight mass.
Why hasn't anyone built a space elevator?
Materials science, not orbital mechanics. The 2003 NASA NIAC study estimated the cable needs a minimum specific tensile strength of about 48.5 to 62.5 GPa, with a safety-margin target nearer 100 GPa. Carbon nanotubes have been simulated at up to about 130 GPa for a single defect-free fiber, but realistic macroscale cables accounting for real manufacturing defects top out around 10 GPa today - no manufactured material yet reaches the required strength at the scale a real cable needs.
How does a space-elevator cable compare to steel or Kevlar?
High-strength steel is under about 5 GPa tensile strength and Kevlar is about 3.6 GPa - both far short of the roughly 48.5 to 100+ GPa a real space-elevator cable would need.
Who first proposed the space-elevator idea?
Konstantin Tsiolkovsky described a compression tower to geostationary altitude in 1895. Yuri Artsutanov proposed the tension-cable version in 1960, and Jerome Pearson published a tapered-cable engineering design with a counterweight in 1975. Arthur C. Clarke's 1979 novel "The Fountains of Paradise" popularized the idea.
What would a climber on a real space elevator carry?
NASA's NIAC reference design described a climber of about 20 tonnes carrying about 13 tonnes of payload, with follow-on payloads proposed to launch roughly every 4 days once an initial multi-year cable-thickening phase was complete.
Is this scene a real physics or structural simulation?
No - it is an educational approximation of a real, published concept. It does not solve tether elasticity, sag, vibration, orbital perturbation, or materials-engineering physics; it illustrates the force-balance concept and the real published length and strength figures honestly.