Launch Vehicles

NEPTUNE Series Rockets

N1 rocket

About the NEPTUNE

Interorbital Systems is developing the NEPTUNE series of modular, low-cost, liquid-bipropellant-powered orbital launch vehicles for unmanned and manned payloads. NEPTUNE series launch vehicles achieve minimum cost and maximum reliability by building most components in-house and by eliminating unnecessary, expensive, failure-prone and performance-limiting systems such as pumps and wings.

Common Propulsion Module

The pressure-fed Common Propulsion Module, or CPM 2.0, is the primary building block of the NEPTUNE series rockets. Each standard Common Propulsion Module is composed of three propellant tanks, one pressurant tank, a single throttleable, ablatively-cooled, gimballed rocket engine, a valve unit, an optional roll system, and a controller. Construction costs are kept low by building the major rocket components in-house, using off-the-shelf subcomponents when necessary (for example: ball valves and micro-controller boards), and applying efficient mass-production methods.

NEPTUNE Nomenclature

Each NEPTUNE rocket variant consists of one or more CPMs connected in parallel, and up to two tandem upper stages. The mission payload capacity is determined by the number of CPMs and upper stages used in the launch-vehicle variant. Variants are designated by their CPM and upper stage count. For example, a NEPTUNE 5 US2, or N5 US2, contains five CPMs and two tandem upper stages. The minimum orbital flight configuration, the N1 US2, has a single CPM and two tandem upper stages, and can place a 6.3 kg payload to a polar Low Earth Orbit.

Upper Stages

Depending on the mission requirements, one or two tandem upper stages may be required. These stages are stacked one-above-the-other on the core Common Propulsion Module.

Liquid Rocket Engines and Propellants

A single, throttleable liquid rocket engine powers each CPM. Two thrust options are available for the CPM engines: 7,500 or 15,000 pounds (GPRE 7.5KNTA or GPRE 15.0KNTA). Storable, high-density white fuming nitric acid (WFNA) and turpentine power the CPMs and the upper stages. These environmentally-friendly propellants provide reliable and efficient hypergolic ignition, eliminating the need for an ignition system. The CPM's main rocket engine is gimballed to provide pitch, yaw and roll control (multiple CPMs). For a standalone CPM (N1 variant), four on/off bipropellant liquid hypergolic thrusters provide roll control. The tandem upper stages are each powered by one or more liquid upper-stage rocket engines delivering 1,000 pounds of thrust each (GPRE 1.0KNTA). All IOS liquid rocket engines are ablatively cooled and are rapidly manufactured using the filament-winding process.

Learn more about NEPTUNE propellants

Pressure-fed System

NEPTUNE rocket engines are pressure-fed with helium or nitrogen using either regulated pressure feed or blowdown. IOS has eliminated the requirement for a pump by developing ultra-lightweight filament-wound propellant tanks and by utilizing high-density propellants that substantially reduce the size of the propellant tanks. The IOS pressure-fed system is lighter, less complex, and therefore cheaper and more reliable than equivalent pump-fed systems. Ablative-cooled and pressure-fed propulsion systems simplify the process of starting and stopping the rocket engines on the ground and in space.

Payload Capacity

Launch Vehicle Variant Payload Mass and Altitude
CPM 2.0 250-kg (551.3-lb) to suborbital 500 km (310.0-mi) apogee (suborbital)
N1 Four Stage 20.0-kg (44.1-lb) to 500 km (310.0-mi) polar orbit
N3 Four Stage 40-kg (88.2-lb) to 500-km (310.0-mi)polar orbit
N5 Four Stage 100-kg (220.5-lb) to 500-km (310.0-mi) polar orbit


Structural components are manufactured using primarily composite materials and aluminum. The launch vehicles' lightweight propellant tanks have a filament-wound carbon outer shell and an aluminum inner shell.


IOS uses a guidance and control system developed in-house. NEPTUNE variants with multiple CPMs use the gimballed main engines for pitch, yaw and roll control. NEPTUNE variants with a single CPM use the gimballed main engine for pitch and yaw control and on-off thrusters for roll control.

Ablatively Cooled Engine

IOS rocket engines are ablatively cooled. Ablative cooling is a reliable, low cost cooling method that was chosen for the Apollo service module and LEM rocket engines. Engines with ablative cooling can be rapidly constructed, and simplify the process of starting and stopping the engines in the vacuum of space.

Mobile Launch Capabilities

Two mobile launch options, the Mobile Land Launch System (MLLS) and the Canister Ocean Launch System (COLS), allow NEPTUNE rockets to launch from any land location accessible by road or any ocean location.

NEPTUNE in Action

CPM TV (Test Vehicle) was launched on March 29, 2014. Its successful launch marked the first NEPTUNE variant ever launched.

NEPTUNE Series Rockets: The Future

Rendering of an N5 launch and flight through the atmosphere

Interorbital Systems is currently focused on launching small payloads to Low Earth Orbit (LEO) and to the Moon. The Common Propulsion Module, the NEPTUNE series building block, is under constant development to optimize performance, price, and ease of manufacturing. NEPTUNE rockets can fly a variety of mission profiles - in addition to launching small satellites to LEO, a lunar impact mission is under development for launch on a NEPTUNE 3 (N3) rocket.

Also in development is a long version of IOS' standard CPM. The first elongated CPMs will be clustered to form the N8 Long launch vehicle, which will be capable of placing a 500-kg (1,102.5-lb) payload into LEO and soft-landing a 30-kg (66.2-lb) payload on the surface of the Moon. IOS is also developing a lightweight two-man capsule that can be launched to LEO using the N8 Long rocket.