Lunar
Starshot White paper
GUY / Lunar Starshot — index

A GUY research study and proposal / Lunar Starshot

Beyond
our Sun.

The photonics are ready to test. The spacecraft fits on a chip.
Now, build the path to another star.

Explore the proposal

Research study and proposal / 2026 · Revision BA
Proxima Centauri · 4.24 ly

0.20c
Planning speed
3.56g
Sail + StarChip
4.24ly
Proxima Centauri

01 — The first attempt

Starshot set the goal. Then it stopped.

In 2016 Breakthrough Starshot put laser-driven interstellar flight on the research agenda, with about $100 million of research funding and a public list of 29 engineering challenges. The goal was gram-scale probes at about a fifth of the speed of light, reaching the Alpha Centauri system within roughly 20 years. In September 2025 Scientific American reported that the effort was on indefinite hold.

  1. Left open · 01

    Keeping a sail on the beam

    A flat, nanometre-thin film pushed by an intense beam tends to slide off it, tip over or ripple itself apart.

    This design: a curved, stiffened silicon-carbide sail, spun and flown in a hollow shaped beam. It shows no flutter in the models; Gate A builds the first test pieces.

  2. Left open · 02

    Surviving the light

    Even a tiny absorption in a film that thin, under a beam that bright, turns into heat the film cannot shed. How hot the real material runs was never measured.

    This design: that measurement comes first, in Gate A, before anything is built. The burn is planned under a 1,300 K material limit.

  3. Left open · 03

    Firing through the sky

    A kilometre-scale laser array on the ground must push its beam through air that blurs, bends and absorbs it.

    This design: the laser moves to the far side of the Moon. No air, no weather, and Earth never rises over it.

  4. Left open · 04

    Dust at a fifth of light speed

    At 0.2c a grain of interstellar dust hits like a bullet. Protecting a gram of electronics for the whole cruise was unsolved.

    This design: the StarChip flies end-on behind a dust-breaking disc. Gate A tests it against real dust impacts.

  5. Left open · 05

    A research budget, not a path to build

    The programme was $100 million of study. No staged plan turned measurements into a decision to build, or stopped early if they failed.

    This design: four gates, each able to stop it. The first is two years of laboratory work.

  6. What decides it

    Two measurements come first

    Can ytterbium lasers cover the whole band, and how much light does the hot sail absorb? Gate A answers both in two years, and the build goes ahead only if they pass.

Lunar Starshot improves on the ideas of Breakthrough Starshot, including the StarChip, its name for a gram-scale probe. Based on public reporting; we do not claim to know why the programme paused. This proposal is independent of Breakthrough Initiatives.

Read the 2025 reporting

02 — The case

The world has changed. So has the mission.

Lunar Starshot is a research study and a proposal from GUY: a laser facility on the Moon's far side and 10,000 StarChip probes bound for Proxima Centauri, built only as fast as decisive experiments allow.

The photonics are now ready to test, which turns the ambition into an engineering programme. The proposal brings those advances together with heavy lunar logistics and a stiffened sail, powered in the reference design by lunar solar arrays and flywheel storage. Nothing has been built yet: the figures here are results of the design study, and the first gate exists to measure them.

  1. 01

    Photonics moves from theory to hardware

    Laboratory radiation-pressure measurements give sail research a stronger experimental foundation.

  2. 02

    The Moon is becoming more accessible

    Commercial landers now deliver to the lunar surface. Industry at this scale is new, so a pilot plant tests it in Gate C.

  3. 03

    An engineering programme with clear gates

    Measure the sail and the lasers. Demonstrate control. Establish lunar production. Scale the mission.

How it works, in five steps

  1. 01 · Build

    Factories on the Moon make ~11.3 Mt of mirrors, flywheels and structure from regolith. A 12 km array of ~90 million ytterbium amplifiers rises at Schrödinger basin, on the far side.

  2. 02 · Push

    For ~19 minutes, slowly at first, the array pushes a 3.56 g sail and StarChip with up to 269 GW of infrared light, sweeping 1.12 → 0.97 µm, to 0.20c.

  3. 03 · Coast

    The sail is released. The StarChip sleeps for 21 years, its end held behind a dust-breaking disc.

  4. 04 · Look

    It wakes 36 hours out, powers itself on Proxima's red light, images the planets in 12 bands, and flashes ~0.55 Mbit home by UV laser.

  5. 05 · Listen

    4.24 years later the same 113 km² of mirrors, switched to receiving, catch the flashes: about 25 years after each launch.

03 — The spacecraft

The StarChip.
A spacecraft on a die.

About 0.6 g carries the whole mission: a 1 cm flat-lens camera with twelve colour bands, a millijoule ultraviolet pulse laser, a radiation-tolerant processor and memory, and a timer on a nuclear battery. It hangs on the sail's axis, about 0.7 m in front of the dome, inside the beam's dark centre. In cruise a 2.1 m boom holds a 20 nm beryllium disc ahead of it to shatter dust grains, and LED photon thrusters keep its 1.22 mm graphite face tucked behind the disc.

The pod points itself with LEDs; Gate A tests that (T34).

Almost nothing.
Almost everything.

A 2.8-metre dome catches the laser and tows the StarChip. It is a stiffened sandwich: a silicon-carbide ring grating on 66 nm of silica, and a 15 nm SiC back face 6 cm behind on a fibre truss. Why not push the chip alone? 269 GW would vaporise it; the sail spreads the light, which is kept under a heat limit of 8.8–15.1 GW/m².

2.8 m
Sail diameter
6 cm
Between the two faces
~2,400
Silica tendons

Exploded view, to show the parts. The sail does not deploy this way.

Like an umbrella
facing the wind.

The dome bulges toward the laser. Tilt it and the light pushes it back upright. The array shapes a hollow, bowl-shaped beam with a bright ring just outside the rim, so a sail that drifts sideways is pushed back to the centre. A single thin film would flutter, so the sail is stiffened, spun at 330 rad/s, and kept in tension by shaping the beam. The stiffened sail shows no flutter in the models; Gate A tests that on real coupons (T33, T36).

3.56 g
Sail + StarChip
330 rad/s
Spin in the burn
~1,100 K
Hottest sail element

04 — The burn

Leave the engine
on the Moon.

A 12 km array of ytterbium lasers on the lunar far side supplies the push. The burn starts slowly: about 11 of its 19 minutes go to reaching 0.05c. As the sail speeds away its light is Doppler-stretched, so the array sweeps from 1.12 to 0.97 µm. The band has zero margin for 0.20c.

~19 min
Burn · 1,151 s
12,300 g
Peak · mean ~5,300 g
269 GW
Full beam power

The ~1 µm infrared beam is invisible; it is drawn in orange.

05 — Build the departure point

Starships land.
An industry begins.

Starship is the only lander in sight that can put thousands of tonnes on the Moon, so the plan starts with it: about 270 heavy-cargo landings carrying ~27 kt from Earth. Starship is a planning choice, not a partnership; other heavy landers can carry the same cargo as they mature. Lunar regolith supplies the bulk, and the industrial base builds the laser field where it will operate.

~27 kt
Imports from Earth · ~270 landings
~11.3 Mt
Made on the Moon

Concept. No SpaceX partnership is implied.

Power from
the Moon itself.

The reference design runs on sunlight: 52 GW of solar arrays on the polar ridges recharge flywheels spun from lunar rock. Each burn draws 121 GWh, released at up to ~770 GW. The proposal also includes a helium-3 workstream, extracting lunar fuel for future fusion power.

52 GW
Reference solar plant + flywheels
³He
Proposed workstream

Helium-3 is a separate workstream. The costed design runs on solar power and flywheels.

A field of light
on the far side.

113 km² of mirrors push a 3.56-gram probe to 20% of the speed of light in about 19 minutes. The same mirrors, switched to receiving, listen for each StarChip's faint flashes about 25 years after its launch.

Scale exaggerated so the array is visible.

06 — The campaign: 100 × 100

100 cohorts.
100 StarChips each.

One spacecraft opens a possibility. Ten thousand build a campaign. Manufacture, qualification and launch are organised into 100 cohorts of 100 StarChips over twelve years, launching only while Proxima stands at least 50° above the lunar horizon: 31% of the time.

The spacing of the probes is illustrative.

07 — Proxima Centauri / the encounter

Twenty-one years.
One close look.

After the burn the sail is released. The StarChip coasts on alone at 0.20c for 21 years, asleep for almost all of it at about 155 K, then wakes for its flyby of Proxima Centauri.

21.2 yr
Cruise at 0.20c
~54%
Of survivors pass within 0.01 AU

Wake. Look.
Send it home.

Thirty-six hours before closest approach the StarChip wakes, opens its petals and cell membrane, and harvests ~2.8 kJ of Proxima's red light: enough to image the planets, choose what to keep, and fire its laser home, offset from the Sun toward the Moon.

10,000
StarChips in the campaign
~0.55 Mbit
Modelled return per StarChip

First launch around programme year 20. Each probe's flashes arrive about 25 years after its launch (21.2 years of cruise, 4.24 of light travel), so first data comes around programme year 45. At 63% survival the swarm returns ~3.5 Gbit (1.4–4.8 Gbit).

08 — The path forward

Earn the next
commitment.

Start with the decisive measurements: two years of laboratory work. The solar-powered reference design places the full programme near $574 B (P10–P90 $323–1,171 B), and about 98% of it comes after Gate D.

  1. Gate A

    Measure

    Sail absorptance at 1.1 µm and temperature (T5), grating force at the rim and ±10 nm fabrication (T29), ytterbium amplifiers across 0.97–1.12 µm (T30), dust (T31), flutter coupons with faces held in tension by the light alone (T33), the LED-gimballed pod (T34) and a taut 15 nm back face (T36).

    Years 0–2Laboratory scale
  2. Gate B

    Demonstrate

    Prove beam shaping, beam-pointing stability, a clean fade-out and repeatable sail deployment at component scale.

    Years 2–6~$1.4B cumulative
  3. Gate C

    Fly and manufacture

    Test a lunar industry pilot and a smaller flight demonstration, and learn what lunar production really costs.

    Years 5–10~$14B cumulative
  4. Gate D

    Decide to build

    Fix the final speed and size the facility from measured performance and independently reviewed costs. Phase 3 engineering (~$10 B), then the build.

    Years 10–20Full build only after review
  5. The first questions

    Can the lasers cover the band, and can the sail be built?

    Ytterbium amplifiers must hold efficiency and coherence at both band edges, 976 nm and 1.12 µm, with zero margin for 0.20c. The stiffened sail shows no flutter in the models, but it must be built at 0.44 g/m² with a 15 nm back face and be kept in tension by beam shaping through a burn that peaks near 15 GW/m². If either fails, the programme stops or changes direction before the major spend.

Each gate can stop or redirect the programme.

09 — Cost and range

About $574 billion. Invested in photonics, the space economy and the mission.

The 10,000 probes are about $2 billion of it. The whole is one coordinated investment in three things: photonics, the space economy, and the mission itself. It is released through one set of gates, so each part is proven before the next is asked to scale. Most of what it builds stays on the Moon.

  1. Photonics · ~$126 B · 22%

    Lasers and optics

    About 90 million kilowatt-class ytterbium amplifiers, phase-locked into one 269 GW beam, and 113 km² of mirrors. The laboratory work on the lasers and the sail comes first, in Gate A.

  2. Lunar industry · ~$242 B · 42%

    Factories on the Moon

    Plants that turn regolith into ~11.3 Mt of mirrors, flywheels and structure. A pilot in Gate C measures what lunar production really costs.

  3. Lunar power · ~$103 B · 18%

    Power on the surface

    52 GW of solar arrays on the polar ridges, flywheels spun from lunar rock, and the pulsed power that releases 121 GWh in each burn.

  4. The mission · ~$102 B · 18%

    The flight to Proxima

    Research, engineering, 10,000 probes, 12 years of launches and 21 years of caretaking and reception: the first close look at another star's planets, about 45 years in.

Groups are sums of the cost lines below: optics and lasers; pulsed power, flywheels and solar; operations, other hardware, research, engineering and the probes. Transport from Earth, about $267 B, is counted inside them. The study prices the build, not the returns to either industry. A programme stopped at a gate still keeps what that gate measured.

$574 BNominal · 10,000 probes

Economic inputs alone put the 10th–90th percentile range at $323–1,171 B; with the sail's absorptance also unknown, $361–1,568 B. The median is a little higher, about $583 B, because the inputs are skewed. With lunar cargo at $2,000/kg, it falls to about $360 B.

What moves the range

  1. Lunar transport price33%
  2. Lunar factory productivity31%
  3. Sail absorptance21%
  4. Factory equipment price9%
  5. Flywheel storage mass1%

Where the money goes $ B

  1. Lunar industrial base242
  2. Optics · 113 km² of mirrors79
  3. Operations57
  4. Pulsed power54
  5. Lasers · 269 GW47
  6. Flywheel storage28
  7. Solar plant · 52 GW21
  8. Other hardware18
  9. R&D · Phases 0–215
  10. Engineering · Phase 310
  11. Probes2

Transport of ~27 kt from Earth (~$267 B) sits inside these lines. Lasers are about 8% of the total.

Which speed

Going faster brings data home sooner, but each year saved costs more. The study's rule is to pay no more than about $27 B per year of earlier data, which picks 0.18c at $489 B. 0.20c is a programme choice: the last step buys its earlier data at ~$36 B a year. The final speed is fixed only after the sail's absorptance is measured.

Cost, laser power and first-data year by cruise speed, at the planning absorptance of 3×10⁻⁷
SpeedCostLaserFirst data (year)Per year earlier
0.10c$342 B66 GW~67—
0.12c$371 B98 GW~60~$4 B
0.14c$402 B133 GW~55~$6 B
0.16c$441 B169 GW~51~$10 B
0.18c Rule$489 B230 GW~48~$17 B
0.20c Plan$574 B269 GW~45~$36 B

If ytterbium cannot cover the band, the fallback is a thulium design: 0.12c at about $502 B (P10–P90 $290–1,010 B), a figure not yet re-run with this revision's corrections.

10 — What could stop it

Test the hard parts first.

Each of these could change the design by hundreds of billions or end it. They are listed in the order they should be tested, and Gate A is built around them.

  1. 01 · T30

    Ytterbium lasers across the whole band

    About 90 million kilowatt-class amplifiers must stay efficient and phase-locked while sweeping 0.97–1.12 µm. Both edges are hard, and the band has zero margin: each 1% lost costs about 0.01c.

  2. 02 · T33 · T36

    The stiffened sail

    The stiffened sail shows no flutter in the models, which keep its thin faces in tension by shaping the beam and limiting power early in the burn. That is why the burn starts slowly. The check has three limits: early in the burn it rests on a simpler calculation; the spin margin is 1.15×, not the usual 1.2×; and the models re-set the tendon loads at each stage, where real tendons have one set of lengths. It now has to be built: a 2.8 m dome, one face only 15 nm thick, on a 6 cm truss, kept taut at up to ~12,300 g.

  3. 03 · T5

    How much light the sail absorbs

    Absorptance at 1.12–1.19 µm and at temperature sets the heat limit, which the sail runs at through the middle of the burn. It is cheap to measure and comes first. It drives about a fifth of the cost range, and at 10⁻⁶, about three times the planning value, the speed rule drops to 0.14c.

  4. 04 · T32

    A steady beam, a clean release

    By the end of the burn the array sees the sail ~175 s late, so the sail must hold itself. Beam jitter must stay below ~3.6 pm/√Hz of correlated tilt across 12 km, and the beam is cut at 12% power.

  5. 05 · T29

    The grating, made to ±10 nm

    The design depends on the grating's computed push at each wavelength and angle. Rings 0.87 µm apart must be made to ±10 nm so an absorbing dark mode stays out of band.

  6. 06 · T31 · T34

    Dust at a fifth of light speed

    The disc must break grains, the boom must survive the burn stowed, and LEDs must hold the pod's attitude for 21 years. The fallbacks raise the programme to $1,008 B or $1,319 B.

  7. 07 · R51

    A 20-year sleep, and enough data

    About 63% of probes are expected to work at Proxima. The pessimistic science case needs about 9,700 of the 10,000 planned, so the margin is thin.

  8. 08 · Gate C

    The price of lunar industry

    Factory productivity and transport price drive nearly two-thirds of the cost range. Only a working pilot can pin them down.

11 — Evidence and sources

The science behind the ambition.

What has been demonstrated

Microscale lightsail force measurements and commercial lunar science delivery are the evidence this proposal builds on. They support parts of the design, not yet the whole.

Direct radiation-pressure measurements for lightsail membranes Scalable photonic reflector research NASA's Blue Ghost mission account

The engineering programme ahead

A stiffened sail that stays flutter-free in tests, hot-sail absorptance at 1.1 µm, kilowatt-class coherent ytterbium amplifiers swept across 0.97–1.12 µm, a deployable tendon network, beam control, lunar manufacturing, and electronics that survive decades.

Read the full technical case · PDF
How this proposal relates to Breakthrough Starshot

GUY's Lunar Starshot is independent. It is not endorsed by Breakthrough Initiatives and is not a restart of Breakthrough Starshot. It improves on the ideas Starshot made public, including the StarChip, Starshot's name for a gram-scale probe.

Read the 2025 reporting

Sources and credits

  • Figures: Lunar Starshot design study, Revision BA, October 2026; the technical case is in the white paper.
  • Breakthrough Initiatives, Starshot challenges and system model (Parkin, 2018).
  • Holdman et al. (2022), thermal runaway of silicon laser sails, Advanced Optical Materials.
  • Ilic & Atwater (2019), passive stabilisation of photonic lightsails.
  • Krüger et al. (2015), Ulysses interstellar dust; Landgraf et al. (2000), interstellar dust fluxes.
  • Hoang et al. (2017), relativistic spacecraft and the interstellar medium.
  • Goodno et al. (2011), single-frequency thulium fibre amplifiers; published ytterbium and erbium fibre-laser power records.
  • Lunar imagery: NASA Scientific Visualization Studio, CGI Moon Kit.
  • 3D rendering: three.js (MIT licence). Type: Archivo and IBM Plex Mono (SIL Open Font License).

12 — GUY / Lunar Starshot

Measure first.
Then fly.

The photonics are ready to test. Gate A is two years of laboratory measurements. The white paper sets out the full technical case for Revision BA.

Download the white paper Editable document · DOCX