Not a wall of text with a picture. Every number below is produced by a formula you can move with a slider. By the end you should be able to re-derive the whole chain on a napkin — field of view, cell size, beam count, per-beam bitrate, and the spectrum wall the constellation is walking into.
Assumes algebra and a little trigonometry. No RF background required — the two facts you need are beamwidth is set by antenna aperture and bits/second is bandwidth × spectral efficiency. Everything else is geometry.
SpaceX's V3 satellite carries 1 Tbps of downlink. The V2 it replaces carries about 100 Gbps. Ten times the satellite. The obvious inference — ten times the service — is wrong, and the reason it's wrong is the entire content of this page.
A satellite in low Earth orbit does not serve a point. It serves a disc — everything on the ground it can see above some minimum elevation angle. That disc is enormous, roughly the size of Western Europe. Whatever capacity is aboard gets divided across it. So the quantity that actually matters to a user is not gigabits per satellite, it's megabits per square kilometre, and there are exactly three things that set it:
The rest of this page derives each of those three terms from first principles, shows how far today's hardware sits from the ceiling, and then shows the three ways out. Open ▸ open the model above to see the sliders driving every number on the page; the V2 / V3 buttons snap them all to real hardware.
Draw the triangle. Earth's centre O, the satellite S at altitude h, and a user
U at the far edge of the coverage disc. Three facts pin it down: |OU| = R,
|OS| = R + h, and at U the satellite sits at the minimum elevation angle ε
above the local horizon — below that the dish can't close the link (too much atmosphere, too much
ground clutter, regulatory interference limits). Starlink uses ε = 25°.
The angle at U between the local vertical UO and the line US is 90° + ε. Law of sines on triangle OUS:
At 550 km and ε = 25° you get a disc of radius ≈ 940 km — about 2.78 million km², a bit larger than the EU. One satellite's entire downlink is spread over that. Drop ε to 10° and the disc more than doubles; that's why elevation masks are a capacity decision, not just a link-budget one.
Starlink doesn't aim a beam at your dish. It aims at a fixed cell on the ground — a hexagon from a global grid (an H3-style hierarchical hex tiling), locked to the Earth, not to the satellite. Beams are steered from cell to cell; terminals inside a cell are served when their cell's turn comes. The published grid uses hexagons inscribed in a 15-mile (24.14 km) circle.
A regular hexagon whose vertices touch a circle of radius r (the circumradius) has area
(3√3 / 2)·r² — it's six equilateral triangles of side r, each of area
(√3/4)r².
The cell (24.1 km across) is the scheduling unit. The −3 dB beam spot (≈ 14 km across for a 1.5° beam at 550 km) is the antenna's main lobe. The spot sits inside the cell; the beam's skirts and the pointing/steering margin fill the rest. They are different objects and the page keeps them separate — but they scale together, which is what matters for Step 3 and Step 6.
Now the punchline of the first half. A satellite has Nbeams downlink beams; each one lights exactly one cell at a time. So the fraction of its own field of view it is illuminating right now is just beams divided by cells.
V2 lights 2.6% of what it can see. V3 lights 28%. Flip the preset buttons and look at the same disc twice.
Ten times the beams, ten times the instantaneous coverage. This is real and it is the main thing V3 buys. But note what it is not: it is not ten times the bits in any cell that was already being served — see Step 4.
The intuition "fly lower, cover less, so each satellite serves fewer people better" is only half
right. Yes, the field of view shrinks. But the beam footprints shrink too, and — for a fixed antenna —
they shrink as h², because a beam of fixed angular width θ paints a spot of diameter
2h·tan(θ/2). Both terms in the coverage fraction move together.
Try it: switch on “cell size scales with altitude” in the model, then sweep the altitude slider from 1200 km down to 200 km. The coverage readout wobbles by well under a factor of two across a 6× change in altitude. Altitude is a lever, but it's a lever on capacity density (Step 6), not on this ratio.
Divide each satellite's downlink by its beam count.
Two completely different routes — a published system spec, and one 240 MHz channel at about 2 bits per hertz — land on the same half-gigabit. That's not a coincidence: one beam is one channel, and the channel plan didn't change between V2 and V3.
The V3 upgrade bought ten times more beams of the same width — not fatter beams, not narrower ones.
Beamwidth is aperture. θ ≈ λ/D: to halve the beamwidth you must double the antenna's linear size. That's physics, and it's bounded by what fits in a launch fairing. Beam count is silicon. It's how many independent phased-array chains your beamformer can run at once. SpaceX got 2048 beams out of new beamformer chips and roughly 64× the throughput per modem chip. Silicon scaled; aperture didn't.
So V3 is a parallelism upgrade, not a density upgrade. It serves ten times as many cells simultaneously, at the same bitrate each. Which is exactly why the ceiling in Step 5 is the thing it runs into.
Prove it to yourself with the sliders: move beams per satellite and satellite downlink total together and per-beam capacity stays pinned near W·η. Move beams alone and per-beam capacity falls — because you're now claiming to split a fixed pipe more ways, which the radio won't let you do for free.
Here is the constraint that doesn't care how many satellites you launch.
Starlink's Ku-band user downlink is 8 channels of 240 MHz — 1.92 GHz of spectrum. Each channel can be used twice over, on two orthogonal polarisations. That gives 8 × 2 = 16 orthogonal channel/polarisation slots.
Sixteen slots means one ground cell can accept 16 simultaneous beams from 16 different satellites without them colliding — terminals inside the cell are pointing their dishes at different satellites, so the beams arrive on separable slots. Beyond 16 you're re-using a slot in the same cell from a different direction, and the dish's angular discrimination is all that saves you. That's the wall.
| Quantity | V2 (192 beams) | V3 (2048 beams) | Ku wall |
|---|---|---|---|
| Downlink per satellite | 100 Gbps | 1,000 Gbps | — |
| Capacity per beam | 521 Mbps | 488 Mbps | ≈ W·η |
| Instantaneous coverage of FOV | 2.6% | 27.9% | — |
| Delivered per km² (1 satellite) | 0.036 Mbps | 0.360 Mbps | — |
| Satellites needed to saturate a cell | ≈ 560 | ≈ 56 | 16 slots |
| Satellites actually in view (8,000 up) | ≈ 44 | ≈ 44 | — |
| Verdict | beam-limited | at the spectrum wall | 20.3 Mbps/km² |
V2 sat an order of magnitude below the spectrum wall. In that regime the engineering is easy and the economics are linear: launch more satellites, get more capacity, repeat. Roughly 560 overlapping V2s would have been needed to saturate Ku — nobody was ever going to get there.
A fleet of V3s arrives roughly at the wall. About 56 overlapping satellites saturate the slots, and about 44 are already in view with today's ~8,000-satellite constellation. Same order of magnitude. That is a qualitatively different regime: from here, more satellites of the same design stop buying capacity in the busiest cells, and the only moves left are the three in Step 6.
This is a ~2030 scenario, not today. As of 2026-07-24 there are zero operational V3s in orbit — the first 20 flew suborbitally on Starship Flight 13 and reentered as planned. SpaceX has FCC authorisation for 15,000 Gen2 satellites, with 50% required to be deployed by December 2028 and the remainder by December 2031. Everything above describes the constellation those milestones imply, not the one currently overhead.
Two more caveats worth holding: the "16 slots" figure is the clean orthogonal case — real systems get some extra reuse from dish directivity and some loss from guard bands and interference coordination. And demand is wildly non-uniform; the wall bites in dense cells long before it means anything over the Pacific.
Back to the one-line model. If capacity/km² = B · η · (1/Acell), then there are
exactly three levers, and they multiply.
The only unbounded axis — shrink the cell and you get the whole spectrum again in the space you freed. Two ways: fly lower (footprint ∝ h², so 550 → 350 km is 2.5×) or build a bigger antenna (θ ≈ λ/D, so 2× linear aperture = ½ the beamwidth = ¼ the area = 4× reuse). Starship removes the fairing constraint that capped aperture on Falcon-launched satellites.
The FCC's 9 January 2026 Gen2 order authorises Ku, Ka, V and W and folds SpaceX's separate V-band constellation into Gen2. V-band downlink alone (37.5–42.5 GHz) is 5 GHz against Ku's 2 GHz. Add Ka migrating from gateway duty to user duty as E/V/W take over backhaul — precisely what V3's four quad-band 1.2 Tbps backhaul antennas are for.
About 2 bps/Hz today. Shannon (log₂(1+SNR)) leaves real room, and it compounds with
lever 1: narrower beams are higher-gain beams, higher gain is higher SNR, higher SNR unlocks
higher-order MODCODs. The gain is bounded and logarithmic in power, so this is the smallest of the
three — but it comes almost free with the aperture you already built.
Note which lever is cheap and which is expensive, because it isn't obvious. Lever 1 is a satellite-side change — new hardware on new launches, and the terminal on your roof doesn't care. Lever 2 is the awkward one: adding V-band user service means replacing the terminal fleet, because a Ku dish cannot receive at 40 GHz. The gating cost of the spectrum lever is on the ground, not in orbit. That asymmetry is why the satellite roadmap runs ahead of the spectrum roadmap.
sin η = R·cos ε/(R+h) → γ = 90° − ε − η →
AFOV = π(Rγ)². At 550 km / 25°: ≈ 2.8 M km².(3√3/2)r² =
378 km². So ≈ 7,300 cells per field of view.Nbeams/Ncells —
2.6% for V2, 28% for V3. Nearly altitude-invariant, because
footprints and the disc scale together.If you can reproduce those six lines, you can evaluate almost any LEO broadband claim you'll read. The question to ask is never "how many gigabits is the satellite?" It's "over how many square kilometres, in how much spectrum, reused how many times?"