Launch Vehicles

NEPTUNE Series Rockets

N1 rocket

About the NEPTUNE

Interorbital Systems is developing a new generation of modular, bipropellant liquid, low-cost, manned and unmanned orbital launch vehicles, entitled the NEPTUNE. NEPTUNE series launch vehicles are designed for minimum cost and maximum reliability. This is accomplished by eliminating unnecessary, expensive, complex, failure-prone, and performance-limiting systems.

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 applying efficient mass-production techniques.

NEPTUNE Nomenclature

Each NEPTUNE rocket variant consists of one or more CPMs connected in parallel, and up to two tandem upper stages connected in series. The mission payload capacity is determined by the number of CPMs and upper stages used in the 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 launch 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 in series on the core CPM booster stage, and are activated after the first stage's burn is complete.

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. 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. The main rocket engine is gimballed to provide pitch and yaw control. For a standalone CPM (or any N1 configuration), four on/off bipropellant liquid hypergolic thrusters provide roll control. The tandem upper stages are each powered by a single liquid rocket engine with 1,000 pounds of thrust.

Learn more about NEPTUNE propellants

Pressure-fed System

NEPTUNE rocket engines use pressurized helium to maintain a constant propellant flow rate during engine operation. IOS has eliminated the requirement for a pump by developing ultra-lightweight filament-wound propellant tanks. The IOS pressure-fed system is lighter, less complex, and therefore cheaper and more reliable than equivalent pump-fed systems. Without pumps, NEPTUNE rockets can also avoid packing heavy batteries required to power standard turbopump pressure systems.

Payload Capacity

Launch Vehicle Variant Payload Mass and Altitude
CPM 2.0 145 kg to suborbital 310 km apogee (suborbital)
N1 6.3 kg to 310 km polar orbit
N3 20 kg to 310 km polar orbit
N5 50 kg to 310 km 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 that prevents leakage.


IOS uses a guidance system developed in-house to provide vehicle control. Engine gimballing built into each CPM adjusts pitch and yaw. NEPTUNE variants with a single CPM use thrusters for roll control, while larger NEPTUNEs can use their multiple gimablled engines.

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 rocket family's 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 planned for launch on a NEPTUNE 3 rocket.

Also in development is a longer 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 payload into LEO and a 100-kg 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.