Artist rendition of a suborbital Phantom Express with side mounted payload rocket (Credit: Boeing Aerospace)

During a recent 10 day testing period, Aerojet Rocketdyne successfully hot-fired its new Space Shuttle Main Engine (SSME) derived rocket engine-- the AR-22. The Sacramento, California headquartered company successfully demonstrated that the AR-22 could be restarted every 24 hours for ten consecutive days. And this is a major step towards testing the new rocket engine's reusability in Boeing's future unmanned space plane-- the Phantom Express.

Boeing's first test flights of the Phantom Express are currently scheduled for 2021. But the final test of the reusable space plane will entail launching the Phantom Express ten times in just ten days while deploying payloads between 3000 to 5000 lbs (1.36 tonnes to 2.27 tonnes) to LEO with an expendable upper stage.

Launching the Phantom Express with a single rocket engine, the AR-22 will be designed to be utilized up to ten times before requiring refurbishment. And each AR-22 engine will have an ultimate lifetime of 55 missions before before being completely replaced by a brand new AR-22 engine. Boeing estimates the cost to launch a the Phantom Express to be less than $5 million. And Boeing plans to commercialize the Phantom Express, offering the space plane to both US government and commercial customers.

Artist rendition of Phantom Express at launch pad with side mounted cargo rocket (Credit: Boeing Aerospace)

Just seven AR-22 engines would have to be produced every year in order for the Phantom Express to be continuously launched on a daily basis.

If the Phantom Express were used to transport a valuable commodity such as water to LEO then 13 to 22 tonnes of water could be launched into orbit in ten days for less than $50 million, more than 40 tonnes of water in a month, and for less than $100 million. Optimally, the most advanced version of NASA's Space Launch System is eventually supposed to be able to deploy up to 130 tonnes of payload to orbit for about $500 million per launch. But for less than $500 million, 100 hundred launches of the Phantom Express could deliver between 130 tonnes to 220 tonnes of water to LEO.

Total mass of a commodity that can be deployed to LEO via daily launch of a single Phantom Express space plane:

Daily - 1.36 to 2.27 tonnes

Monthly - 40.8 to 68.1 tonnes

Yearly - 496.4 to 828.6 tonnes

Water, of course, is an indispensable commodity for human survival on Earth. And water would be even more valuable for human commerce and survival in extraterrestrial environments. Aboard the ISS, water is used for drinking, washing, food preparation, and for the production of air through electrolysis. Water can also be used for growing fruits and vegetables, aquaculture, animal husbandry. Water can also be used for shielding astronauts from the extremely deleterious heavy nuclei component of cosmic radiation while also mitigating the effects of cosmic radiation in general and ions from major solar events (solar storms).

But electrolysis used to produce oxygen for air also produces hydrogen. And electricity can also be used to liquefy both oxygen and hydrogen for use as a propellant for reusable extraterrestrial vehicles. While the current SLS could deploy up to 90 tonnes to LEO, it can only transport about 25 tonnes of cargo on a trans lunar injection trajectory. But with the assistance of LEO orbiting propellant producing water depots, a reusable extraterrestrial vehicle such as the ULA's future LOX/LH2 fueled Integrated Vehicle Fluids (IVF) ACES-68 could transport more than 50 tonnes of payload on a trans lunar trajectory. And a notional IVF modified SLS Exploration Upper Stage (R-EUS) could be used to transport more than 100 tonnes of payload on a trans lunar trajectory.

Notional propellant producing water depot with twin solar array (Credit: Lockheed Martin)

The propellant producing water depots could be simply derived from the propellant tanks of extraterrestrial vehicles with the edition of radiation panels, water storage, electrolysis plants for splitting the water into hydrogen and oxygen , and cryocoolers to liquefy the gaseous hydrogen and oxygen. Such depots could also be equipped with IVF thrusters for station keeping and with rocket engines to enable the depot to self deploy practically anywhere within cis-lunar space and even into orbit around Mars, Venus, Jupiter, and the asteroids in the asteroid belt.

A depot derived from the ACES upper stage could store up to 68 tonnes of LOX/LH2 propellant while an EUS derived depot could store up to 128 tonnes of LOX/LH2 propellant. Reusable upper stage rockets that use liquid methane instead of hydrogen as fuel, could utilize the excess amount of oxygen (22%) produced at depots that can't be used by the limited amount of hydrogen produced.

The large solar arrays needed to provide power for propellant producing water depots in orbit could be deployed by commercial launch vehicles. The ULA's future Vulcan spacecraft with its 5.4 meter in diameter payload fairing could deploy a 300 MWe solar array to LEO with a single launch. Two such solar arrays docked to each other could provide up to 600 MWe of power within cis-lunar space. Orbiting at LEO, such depots should have access to ample sunlight for producing propellant 61% of the time. But at the Earth-Moon Langrange points, such as NRO, solar energy would be uninterrupted, allowing water depots to produce liquid hydrogen and oxygen continuously as long as water is provided.

Reusable ACES or R-EUS derived orbital transfer vehicles could transport water from LEO to other propellant producing water depots located at the Earth-Moon Lagrange points. But once water is manufactured and exported from the Moon's low gravity well, exports of water from LEO to the rest of cis-lunar space would probably be commercially non competitive. In fact, lunar sources of water might someday compete with water resources being exported to LEO from the surface of the Earth via the Phantom Express.

Notional crewed Orion-ACES reusable shuttle approaching EUS derived propellant producing water depot @ NRO with 600 KWe solar array. The notional WPD-OTV-125 would be capable of storing up to 200 tonnes of water and up to 125 tonnes of LOX/LH2 water derived propellant.

Traveling to the moon using a propellant producing water depot architecture could be much easier and safer since vehicles returning from deep space would simply return to Earth orbit instead of plunging directly through the Earth's atmosphere to the Earth's surface. Commercial Crew launched vehicles could simply launch astronauts or paying tourist to LEO to dock with a commercial space station. A reusable ACES upper stage perhaps joined with an Orion capsule with no Service Module would refuel at a nearby propellant depot and then dock with the space station to pick up the passengers from Earth. The Orion-ACES would then travel for about five days to an orbiting commercial outpost located at NRO (Near Rectilinear Lunar Orbit). A XEUS vehicle would refuel at a nearby propellant depot and then dock at the deep space habitat to pick up the passengers. Less than 12 hours would be required to transport the passengers to the lunar surface and the XEUS would still have enough propellant to return the crew back to the NRO habitat for the return trip to LEO and then back to the Earth's surface.

The daily deployment of water to LEO by the Phantom Express could allow other launch vehicles to focus their efforts on deploying passengers and large and heavy habitats, crewed interplanetary spacecraft, and other large structures to LEO where they could easily be transported to other areas of cis-lunar space and beyond by reusable orbital transfer vehicles such as the future ACES or IVF modified EUS.

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