Aerojet cite Solar Electric Propulsion as an enabler for an Exploration Gateway

by Chris Bergin

Aerojet – famous for being a key element of numerous launch vehicle and satellite propulsion systems – believe their Solar Electric Propulsion (SEP) technology can be positively applied to an Exploration Gateway Platform – which has been touted as a potential – and often favored – approach in NASA’s ongoing studies into a long-term exploration plan.

Exploration Gateway:

With a return to the Moon’s surface returning to the table mid-way through 2011, during NASA evaluations into the new exploration plan, the concept of building a Gateway Platform at the International Space Station (ISS) and hosting it at a Lagrange point has become a large item of interest – not least since the Global Exploration Workshop last November.

Using the Gateway approach – the meeting concluded – utilizes “Near term focus on guiding capabilities, technologies and leveraging ISS,” prior to expanding to “Long term focus (on) Discovery Driven – and Enhanced by – Emerging Technologies.”

While the opening two missions of the Space Launch System (SLS) and Orion (Multi-Purpose Crew Vehicle) are currently manifested for trips around the Moon, the bulk of the schedule for the 2020s remains undefined, bar indicators that the roadmap would include missions to Near Earth Asteroids (NEA) and eventually Mars.

A Gateway would provide numerous supporting elements to a wide-ranging roadmap, not least an initial target of the Moon’s surface, but also via the potential for international collaboration, as overviewed in documentation into a crewed return to the moon – part of an ambitious plan put forward under the Boeing banner.

Such a deep space platform would be located at Earth-Moon Lagrange (EML) point 1 or 2, after being built from pre-launched hardware, providing the host station for a Lunar Lander (potentially reusable) – which would also be launched by the SLS.

The Gateway would first be constructed at the ISS, mainly using the Node 4/DHS (Docking Hub System), an orbiter external airlock, an MPLM (Multi-Purpose Logistics Module) habitat module, and an international module.

Once constructed, a space tug – powered either by solar electric or chemical propulsion – would be utilized to raise the platform to the EML point.

Such a proposal claims to have the platform ready for the arrival of crewed missions via the SLS by 2022.

While questions remain on the schedule of SLS’ availability, a potential solution to some of the challenges of enabling a space platform in the first place have been forwarded by Aerojet, promoting their current Solar Electric Propulsion technology – the same technology which enjoyed a staring role in the rescue of the Advanced Extremely High Frequency satellite (AEHF-1).

Despite a nominal launch atop of an Atlas V – incidentally aided by three of Aerojet’s strap on solid rocket boosters – in August, 2010, a failure of the satellite’s subsystem resulted in the AEHF-1’s hydrazine-fueled liquid apogee engine (LAE) failing to carry out the required burns to place it correctly into Geostationary Orbit.

Thanks to some clever work via the satellite’s United States Air Force controllers and AEHF-1 teams, the $2 billion bird was saved via the ingenious use of the two smaller engines – namely the hydrazine-fueled Reaction Engine Assemblies (REAs) and later by the xenon-fueled Hall Current Thrusters (HCTs) – despite their primary role being one of positional stability on orbit.

The HCT thrusters – small motors that use electricity and xenon gas as propellant – do not have a large thrust level, but sport some amazing stamina, allowing them to fire over and over again for thousands of times.

While these motors can look forward to providing positional stability for upcoming satellites, along with long-distance trips with deep space spacecraft – a role Aerojet’s electric propulsion has successfully carried out on a huge range of spacecraft (a large amount remain operational today – click image for larger graphic) – a potential marriage between SEP and the Exploration Gateway plan has been promoted by the Californian company.

“We believe that Aerojet’s current Solar Electric Propulsion technology, such as that used to rescue AEHF, is immediately applicable to a key role in Human Space,” noted Julie Van Kleeck, Aerojet Vice President, Space & Launch System in an interview with

“For example, a 25-40 kW SEP vehicle using current technology can pre-position a human-tended habitat at L-2 to support initial Orion missions. This approach would provide an immediate deep space destination for astronauts, and L-2 is an excellent way-station to the rest of the solar system.”

Playing to one of SEP’s strengths, such a vehicle would be relatively low in mass – when compared to its liquid propellant counterparts – aiding the launch vehicle used to loft such a vehicle en-route to its in-space role, while reducing the need for numerous refueling stations to assist thirsty spacecraft – otherwise known as propellant depots.

“In addition to delivering habitat modules to L-2, this 25-40 kW SEP vehicle enables an affordable and sustainable logistics transportation system for an L2 human outpost,” added Ms Van Kleeck. “Additionally this same vehicle supports a wide range of other potential destinations such as L-1, a 70,000 km way-station and lunar orbit. 

“The dramatic reduction in in-space propellant requirements enabled by SEP results in a 2X reduction in launcher delivery requirements to complete a mission, which will reduce the need for architectures like propellant depots.”

In recommending SEP technology for a role in NASA’s opening salvo of exploration missions, Aerojet believe they can assist as a facilitator towards enabling and supplying a platform, which itself would provide a key element of a viable exploration plan.

“A near-term operational SEP mission using current technologies serves three critical functions for human spaceflight,” Ms Van Kleeck noted.

“First, it provides an affordable transportation approach for the first deep-space destination for Orion.  Second, it establishes mission operation techniques and capabilities necessary for deep-space exploration.  Third, it provides a low-risk platform on which to validate subsystem/component technologies for follow-on vehicles. 

“These three critical outcomes, which follow the building block approach used over the past 50 years in the human spaceflight program, are why Aerojet recommends this near-term use of current technology Solar Electric Propulsion.”

Aerojet also have ambitions with the key component of the current exploration plan, via the upcoming evaluations into the advanced boosters which will provide the long-term assist of SLS’ ride uphill during first stage.

An article on Aerojet and SLS, along with other items of interest, will be forthcoming.

(Images: Via Aerojet, NASA and L2 content, driven by L2′s fast exapanding SLS specific L2 section, which includes, presentations, videos, graphics and internal updates on the SLS and HLV, available on no other site.)

(L2 is – as it has been for the past several years – providing full exclusive SLS coverage, available no where else on the internet. To join L2, click here:

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