Maxar, Busek Conclude End-to-End Testing of SEP System for Lunar Gateway Element

The Power and Propulsion Element (PPE, at right) and Habitation and Logistics Outpost (HALO, at left), will be launched together atop a SpaceX Falcon Heavy, no sooner than May 2024. Image Credit: NASA

Maxar Technologies, Inc., and Busek Co., Inc., have completed an end-to-end series of hot-fire tests to validate all major elements of the six-kilowatt Solar Electric Propulsion (SEP) subsystem under development for a critical component of NASA’s Lunar Gateway. The Power and Propulsion Element (PPE)—a 19,000-pound (8,600 kg) spacecraft, tasked with providing communications and maneuvering functionality for the Gateway—is targeted to launch atop a triple-barreled SpaceX Falcon Heavy booster no sooner than May 2024. The multi-week hot-fire campaign was conducted at Busek’s facilities in Natick, Mass.

A key accomplishment of this end-to-end hot fire test was the demonstration of stable, repeatable thruster startups. Reliable and repeatable startups are critical to in-space operations of the PPE. Image Credit: Maxar

Funded by NASA’s Space Technology Mission Directorate, under a Tipping Point public-private partnership, the multi-week series of ground demonstrations validated high-powered control electronics (PPU-6000) built by Maxar, a xenon-feed system provided by Moog, Inc., and four BHT-600 Hall-effect thrusters fabricated by Butek Co., Inc.

The system is described as being 30 percent more powerful than any previously-flown Maxar or Busek system and, when combined with other, high-powered thrusters, will furnish an SEP system for the PPE module in the region of 50 kilowatts. This capability makes the PPE the most powerful electric-propulsion spacecraft ever launched.

Video Credit: NASA Glenn Research Center (GRC)

According to Maxar in a Wednesday update, the campaign principally sought to demonstrate stable and repeatable start-ups of the thrusters, affording a crucial performance benchmark for future PPE operations. Specific focuses included the dual-mode operation of the SEP “string” at 300 V/600 V and power levels up to six kilowatts and 600 V.

“Busek’s BHT-6000 electric thrusters offer high-power capabilities at a competitive price-point and are a great fit for both our near-Earth and deep-space programs,” said Maxar’s newly-appointed Senior Vice President of Space Capture Robert Curbeam, a former shuttle astronaut and the most seasoned African-American spacewalker.

PPU hot check (left) and closure of the vacuum chamber (right). Photo Credit: Maxar

“The SEP systems we are evolving for PPE are a fantastic example of innovative commercial technology with great flight heritage being leveraged for NASA programs. We continue to make steady progress on the Power and Propulsion Element, with the next major milestone being the spacecraft Preliminary Design Review, which is targeted for later this year.”

The conceptual development of the Gateway—a complex about one-sixth as large as the International Space Station (ISS) in terms of volume—has been in the works for several years, its nomenclature having subtly changed on several occasions: initially known as the Deep Space Habitat (DSH), then the Deep Space Gateway (DSG), then the Lunar Orbital Platform-Gateway (LOP-G), it today answers simply to “Gateway”.

The Power and Propulsion Element (PPE) is the most powerful Solar Electric Propulsion (SEP) spacecraft ever flown. Image Credit: NASA

As well as serving as a staging-point for a sustained human presence on the surface of the Moon, the complex will support a multitude of investigations in planetary science, astrophysics, Earth observations, heliophysics, fundamental biology and human health and performance.

And the 4,400-cubic-foot (125-cubic-meter) Gateway boasts a strong international flavor, with Canada having committed to build its robotic assets, Japan contributing to its Environmental Control and Life Support System (ECLSS), batteries, thermal control and imaging systems and the European Space Agency (ESA) providing habitation, refueling and communications capabilities.

Video Credit: Maxar

Two years ago, in May 2019, NASA selected Maxar—formerly Space Systems/Loral (SS/L)—to build the Power and Propulsion Element (PPE), which then-Administrator Jim Bridenstine labeled “the cornerstone” of the effort to create a sustainable and reusable human presence “on and around the Moon”. The module is managed by the agency’s Glenn Research Center (GRC) in Cleveland, Ohio.

A System Requirements Review (SRR) in October 2019 enabled its technical risks and functional and performance needs to be formally baselined. And last June, NASA announced that it would fly, pre-integrated with the Habitation and Logistics Outpost (HALO) pressurized module, atop a commercial booster, with launch moving from 2022 to no earlier than November 2023. This was expected to save NASA the expense of two rocket launches and the associated risks of sending a pair of spacecraft under their own steam to lunar distance, then autonomously docking them together.

The PPE/HALO “stack” will ride atop a triple-barreled Falcon Heavy. Photo Credit: Mike Killian / AmericaSpace

Also last summer, Northrop Grumman Corp. was contracted to develop HALO through its Preliminary Design Review (PDR) phase. The module will carry radial docking ports, Body-Mounted Radiators (BMRs), batteries and communication hardware and affords early Artemis crews a functional pressurized volume capable of sustaining four people in Near-Rectilinear Halo Orbit (NRHO) around the Moon for up to a month.

Northrop Grumman announced the successful conclusion of the PDR last November, with HALO expected to leverage mature Cygnus spacecraft technology in its design. Following the completion of the PDR, a multi-element critical design assessment and Systems Critical Design Review are anticipated later in 2021.

The PPE/HALO “stack” will launch atop a SpaceX Falcon Heavy, no sooner than May 2024. Video Credit: AmericaSpace

Earlier this year, Maxar and NASA wrapped up the Delta System Requirements Review (DSRR) and Tailored System Definition Review (TSDR) for the PPE to ensure that the development of the spacecraft remained on track.

Last month, NASA selected SpaceX’s Falcon Heavy—currently the world’s most powerful active operational rocket—for a $331.8 million contract to launch the PPE/HALO “stack” in May 2024, only days after the Biden Administration signaled its support for the Artemis Program and its goal to return humans to lunar distance and plant boots on the surface of the Moon for the first time since Apollo 17, almost a half-century ago.

Image Credit: NASA

Delivery of the PPE/HALO “stack” is expected to mark one of the earliest uses of the NRHO, which envisages a seven-day orbital period around the Moon, in which the Gateway will approach the lunar north pole as closely as 1,900 miles (3,000 km) at “perilune” and travel as far as 43,000 miles (70,000 km) over the lunar south pole at “apolune”.

Later this year, NASA’s Cislunar Autonomous Positioning System Technology Operations and Navigation Experiment (CAPSTONE) orbiter will launch atop Rocket Lab’s Electron booster from the Mid-Atlantic Regional Spaceport (MARS) on Wallops Island, Va., to conduct the first demonstration of the stability characteristics of this never-before-tried orbit.

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