CHARON

Mission

Moving something faster than an adversary can react to its having moved

CHARON is deliberately, and expensively, the wrong propulsion choice by every metric except the one that matters.

It carries up to 250 kg — a LANTERN replacement, a SHROUD, a sensor, a spare — from wherever a launch happened to put it to wherever the fight is, on a timescale measured in hours and days. Chemical propulsion. Storable bipropellant. A single 445 N engine with twenty-two qualified restarts, and 1,011 kg of MON-3 and MMH to feed it.

An electric tug would do the same 3.1 km/s on 131 kg of propellant instead of 1,011. It would be smaller, cheaper, lighter and more elegant in every respect. It would also take nine months. At 78 mN of thrust on a 1,600 kg vehicle the acceleration is 4.9 × 10⁻⁵ m/s², and accumulating 3,100 m/s takes 733 days of continuous thrusting before you subtract eclipse. Even a five-kilowatt system needs six months.

CHARON's main engine gives 0.275 m/s², a factor of 5,600 higher. We chose a specific impulse of 323 seconds over one of 1,500 seconds on purpose, we pay for it in a 1,620 kg launch mass, and that trade is the product. An electric tug buys you delta-v. CHARON buys you time. They are not the same commodity, and a fight is fought in the second one.

3.1km/s Delta-v with a 250 kg payload attached

512m/s Ninety degrees of GEO longitude in 24 hours

62.4% Propellant mass fraction at 1,620 kg wet

5yr Fuelled on-orbit loiter under 2% propellant loss

The arithmetic, in the open

Where the 3.1 km/s comes from

Δv = I_sp · g₀ · ln(m₀/m_f)
Propellant	MON-3 / MMH, storable bipropellant
Main engine	1 × 445 N, I_sp 323 s vacuum, pressure-fed, 22 qualified restarts
Effective exhaust velocity	323 × 9.80665 = 3,167.5 m/s
Required mass ratio	e^(3100/3167.5) = 2.661
Propellant mass fraction	1 − 1/2.661 = 62.4%

Which sizes the vehicle
Wet mass at separation	1,620 kg
Propellant	1,011 kg
Burnout mass	609 kg
— payload	up to 250 kg
— dry bus	359 kg
Dry bus fraction	26.2% of bus plus propellant

On that 26%

Twenty-six per cent dry is not a stage number. It is a spacecraft number, and it has to be, because CHARON carries avionics, a full attitude control system, deployable arrays, a rendezvous sensor suite, thermal control sized for a five-year loiter, and a payload interface. A dumb kick stage would beat it on paper. A dumb kick stage also cannot wait on orbit for two years and then fly a rendezvous.

The price list

What 3.1 km/s actually buys — including what it does not

Plane change costs 2·v·sin(Δi/2). At 400 km, v = 7.669 km/s.
5° inclination change at 400 km	669 m/s · about one orbit · 22% of budget
10° inclination change at 400 km	1,337 m/s · about one orbit · 43%
23.2° inclination change at 400 km	3,084 m/s · about one orbit · 99% — the whole vehicle
40° inclination change at 400 km	5,246 m/s · impossible
400 → 1,200 km and return	832 m/s · about 4 h · 27%
90° of GEO longitude in 24 hours	512 m/s · 1 day · 17%
90° of GEO longitude in 3 days	171 m/s · 3 days · 6%
90° of GEO longitude in 9 days	57 m/s · 9 days · 2%
GTO at 28.5° → GEO, circularise and turn the plane	1,837 m/s · about 5 h plus coast · 59%
LEO at 28.5°, 400 km → GEO	4,291 m/s · beyond the vehicle
Controlled deorbit from 400 km	about 120 m/s · 4%
Disposal from 1,100 km	223 m/s · 7%

Read the impossible rows first

Large plane changes in low Earth orbit are not affordable at any specific impulse anyone can fly, and the three-burn bi-elliptic trick does not rescue them: raising apogee to 60,000 km to turn the plane cheaply costs 2,611 m/s in the first burn alone, which is eighty-four per cent of the budget before the plane change starts. CHARON also cannot reach geostationary orbit from a 28.5° low parking orbit; it needs a transfer-orbit drop-off. If any page on this site implies otherwise, that page is lying.

Now read the geostationary rows, because they are the product. A satellite that needs to relocate ninety degrees of longitude does it by dropping into a slow drift orbit, typically one to three degrees a day, and it takes one to three months during which it is not doing its job. Doing it in twenty-four hours requires a 7,027 km offset in semi-major axis and costs 512 m/s round trip — about ten years of that satellite's entire station-keeping budget. That is precisely why the satellite cannot do it and CHARON can. And 3.1 km/s is six of those slews, or one transfer-orbit insertion followed by two and a half.

Specification

CHARON parameters

Mass and propulsion
Wet / burnout / dry bus	1,620 kg / 609 kg / 359 kg
Payload capacity	250 kg on a 24-inch ESPA-class bolt circle; optional soft-capture grapple kit at a 30 kg payload penalty
Main engine	1 × 445 N MON-3/MMH, I_sp 323 s, 22 restarts
Attitude control	12 × 22 N MON-3/MMH, I_sp 290 s, off the main tanks
Tankage	4 × 208 L titanium; 2 × 74 L composite-overwrapped helium at 310 bar, regulated with a blowdown terminal phase
Acceleration, full	0.275 m/s²
Δv, 250 kg payload attached	3,100 m/s

Bus
Power	2 deployable wings, 2.1 kW BOL / 1.8 kW EOL, 45 Ah Li-ion
Navigation	2 star trackers, fibre-optic gyro IMU, GNSS in LEO and GTO, sun sensors
Rendezvous sensors	Scanning LIDAR 5 km to 5 m (±2 cm at 100 m), flash LIDAR for six-DOF pose under 200 m, visible and long-wave infrared cameras
Comms	S-band TT&C, Ka 400 Mbit/s, optical crosslink compatible with LANTERN and BEACON
Autonomy	REVENANT CORE — plans and flies its own transfer from an intent statement, and signs the plan before ignition
Thermal	Propellant held above −5 °C; about 90 W of survival heating in eclipse-heavy orbits
On-orbit loiter	5 years fuelled, under 2% propellant loss
Launch interface	1,620 kg — dedicated slot or a large rideshare port. Not ESPA-class.

Concept of operations

Seven phases from cold storage to disposal

Loiter. CHARON sits fuelled in a parking orbit — low Earth, transfer, or a near-geostationary storage slot — in a low-power state. Survival heaters, one star tracker, a receive-only S-band watch. Under two per cent propellant loss over five years.
Alert. A tasking arrives as an intent statement, either from the ground or directly from a LANTERN manoeuvre alert over the optical mesh. The vehicle carries a signed authorisation envelope defining what it may do without further release.
Plan. On-board trajectory optimisation across available delta-v, time, illumination and thermal constraints. CHARON returns the plan, the propellant cost and the arrival state, signs all three, and — if the plan falls inside the envelope — proceeds without waiting for a reply.
Transfer. Burns execute. Large low-orbit delta-v is split across multiple perigee passes. Each burn's commanded and measured performance is signed at completion, so the propellant book is auditable rather than asserted.
Terminal. Inside 5 km, LIDAR acquires and relative navigation closes to the delivery or inspection standoff along a passively safe corridor. No burn is planned whose failure would leave the vehicle on a collision trajectory.
Deliver or service. Payload release, station-keeping as a host, or a cooperative docking to a Fantom asset that carries the mating interface. CHARON does not grapple third-party spacecraft.
Reposition or dispose. Remaining propellant buys the next tasking or the disposal burn. Disposal delta-v sits in a reserve that on-board planning cannot spend.

Engineering rationale

Why it is built this way

Why speed is an operational requirement and not a brochure line

Gap-filling a killed sensor. If a LANTERN-G satellite is lost, the belt shell has a seventy-degree hole in it. A replacement launched to order takes six to eighteen months. A CHARON already on orbit with a spare on the ring closes it in under a week. The hole exists for exactly as long as the response takes, and the duration of the response is the entire question.

Denying a predictable arrival. An adversary planning a co-orbital approach computes our assets' positions weeks ahead, because for practical purposes those positions are fixed. A US space order of battle that can be materially rearranged inside the adversary's own planning cycle is a targeting problem they cannot close. Repositioning speed is a form of survivability, and it is the only one available in an environment with no cover.

Reaching a plane the launch did not serve. Rideshare economics put payloads into whatever orbit the primary bought. CHARON converts one launch into access to a band of orbits — twenty-three degrees of inclination, any altitude within 800 km, or a geostationary slot. That is the difference between a launch schedule and a launch option.

Autonomy is a schedule requirement, not a feature

If the ground computes the burn plan, uplinks it and waits for a confirmation pass, a twenty-four-hour repositioning becomes a thirty-six-hour one and the headline claim evaporates. CHARON is given an intent — be within 50 km of this object, sun-behind, in 19 hours, with 900 m/s remaining — and it solves the transfer, plans the burns, executes them, and signs the whole plan and its execution into REVENANT LEDGER before ignition. The ground reviews the record. It does not sit inside the loop.

The argument · time, not delta-v

Delta-v is not the commodity. Response time is.

High-specific-impulse electric propulsion is the efficient way to move mass in orbit, and for the commercial mission — moving a satellite from a rideshare drop to its operational slot, once, cheaply — it is the right answer. It is the wrong answer for a fight. A manoeuvre that takes six to nine months to execute delivers its answer after the question has changed. CHARON burns chemical, pays for it in a 1,620 kg launch mass, and does the same plane change in a day.

The operational figure is 512 m/s for ninety degrees of the belt in a day. That is ten years of a geostationary satellite's own station-keeping budget, spent in twenty-four hours, by a vehicle whose entire job is to spend it. Six times over. And because CHARON plans and signs its own transfer, the twenty-four hours is twenty-four hours — not twenty-four plus a planning cycle plus a confirmation pass.

What tasks it

Program candor

Open engineering risks

Finite-burn losses in low orbit are real and we do not hide them. At 0.275 m/s², a 2,454 m/s perigee burn takes 8,924 seconds — more than an orbit and a half. It has to be split across roughly six perigee passes, which costs three to six per cent of the propellant to gravity losses and eight to twenty hours of elapsed time. The vehicle is optimised for the belt, and in low orbit that shows.
Single-string main engine. See the rationale above. It is a deliberate choice and it is still a single point of failure.
Storable propellant plus a five-year loiter is a leakage and freezing problem. MON-3 freezes near −11 °C. Ninety watts of survival heating is the largest continuous load on a loitering vehicle, and it sizes the solar array for a spacecraft that spends most of its life doing nothing.
Five-year fuelled loiter has never been demonstrated at under two per cent loss. Heritage exists for two to three years. Five is an extrapolation and we are calling it one.
A vehicle that can reach anything is indistinguishable from a co-orbital weapon. There is no engineering answer to this. The answer is REVENANT LEDGER: every plan, every burn and every approach corridor hash-chained and signed before execution, mirrored outside US custody, and exportable with selective disclosure. The argument is developed on the SHROUD page and it applies here with equal force.
1,620 kg is a launch problem. Not a rideshare. The cost of access is a large fraction of the vehicle's cost.
Nothing has flown. The 445 N engine class has deep heritage. This vehicle, its tank set and its five-year loiter have none.

FSV-3 Shroud Shares the rendezvous sensor suite. CHARON is the only path to refilling its chemical reserve.

Autonomy OS Ledger Every burn plan signed before ignition. The only reason a go-anywhere vehicle is fieldable.

Responsive space programs

Give us the manoeuvre and the deadline

Starting orbit, target orbit, payload mass, and the hour it has to be there by. We will send back the burn sequence, the propellant, the arrival state, and the profiles this vehicle cannot fly.

Contact Fantom Defense

Every figure on this page is a design target derived from first-principles analysis, not a measured result. Nothing has flown. The vehicle, its tank set and its life kit are a design. Where a number here is later measured and comes out worse, we will publish the measured number. No export-controlled information is published on this site.