NASA management updated the agency’s human exploration plans for the 2020s to the NASA Advisory Council’s (NAC) Human Exploration and Operations (HEO) Committee last month at the Ames Research Center in California. The focus of the evolving plans for the next decade is launch, assembly, and operations of a human-tended space station in high lunar orbit.



Separate modules of the lunar gateway are planned to be launched to the Moon beginning in 2022, and NASA provided the latest look at the pieces and a forecast of their launch schedule. A commitment of funding for the gateway project is still forthcoming, but the Power and Propulsion Element (PPE) is the module that would launch first.

NASA plans to award contracts to one or more of the commercial bidders early next year to build, launch, and demonstrate an electric propulsion spacecraft that meets requirements for a Gateway PPE. After a one-year demonstration period, NASA would then exercise a contract option to take over control of the spacecraft.

New name, new modules

Now just referred to as “The Gateway,” the spacecraft formerly known as the “Deep Space Gateway” and referred to in this year’s budget request as the “Lunar Orbital Platform – Gateway” (LOP-G) is planned to orbit high above the poles of the Moon in support of crew visits and science experiments. The plan briefed to the HEO committee last week updated earlier initial looks at the Gateway’s specifications.

When assembled, the lunar outpost would support Orion missions of between one and three months from launch to splashdown. Month-long missions could be supported initially and that is being looked at now for the first crew visit on Orion to dock to the PPE on Exploration Mission-3 (EM-3).

“Our very first flight to the Gateway we expect to have an expedition length of about 30 days from launch to landing,” Jason Crusan, Advanced Exploration Systems Director and Gateway Formulation Lead for NASA, said. “We have a twenty-some day capacity on Orion [and] we have the ability to be on Gateway.”

“As we get into the mission design we’ll figure out the total length, but we’ll have the full duration Orion plus anywhere from six to thirteen days on the actual Gateway on the very first mission.”

The basic elements of the proposed lunar space station were the PPE, a crew habitation module, an airlock for extra vehicular activity (EVA), and support for logistics supplies that would be launched from Earth. The latest look now has two additional modules that would follow the PPE to the Moon on EM-3, a European System Providing Refuelling, Infrastructure and Telecommunications (ESPRIT) module and an American-provided Utilization module.

“That’s our first launch package that goes up to the Gateway,” Crusan said. “[ESPRIT] provides augmentation for additional fuel capacity [and] it actually adds a scientific airlock.”

“So the ability to move payloads internal to external is there on the very first pressurized volume that we add. That was actually a very conscious choice in order to enable very early science. We will a number of payload attachment locations on the outside of the Gateway for that.”

“The other half of that launch package is a small pressurized volume,” he added. “That pressurized volume will enable a crew ingress on the very first mission to the Gateway assembly sequence.”

“It will add that volume, some consumables and on the very first mission crews will be able to extend their stay in cislunar space with Orion and the utilization module enabling that.”

The ESPRIT and Utilization modules would launch together with Orion and crew on EM-3; following launch on a Space Launch System (SLS) rocket, Orion would dock to the modules that rode underneath it inside the SLS upper stage, then rendezvous with the PPE in lunar orbit and dock them, adding them to the Gateway.

The Gateway is also now expected to need two habitation modules rather than one, as the earlier minimum of 55 cubic meters of habitable volume wouldn’t meet the requirements developed between NASA and several of its international partners working on the International Space Station (ISS).

“One of the things in our analysis, both with our U.S. industry and our international partners, the Hab volume that we had originally…didn’t quite meet what we needed to get there as far as the crew health and other accommodations we have there. So we expanded that to the two Habs in concert providing that overall function; this also increased the internal space for biological-type research that folks would like to do there.”

The two Hab modules, one provided by the United States and one provided internationally, would now provide at least 125 cubic meters of habitable volume. Those would be launched with Orion on separate SLS flights following the ESPRIT and Utilization modules on EM-3.

Updated launch sequence

The new elements and new developments in NASA’s Human Exploration divisions are reflected in the current schedule and sequence of launches now planned to begin in 2020. NASA is developing the Orion spacecraft to fly crews back and forth between cislunar space where the Gateway would orbit the Moon and Earth and the SLS rocket to launch it.

Both were already integral to plans for launch and assembly of the Gateway, but both still must fly integrated for the first time before being applied to those uses. In addition, the unexpected government commitment to and initial funding of a second Mobile Launcher (ML-2) to launch SLS rockets in late March also changed the baselined sequence of launches and their schedule.

The presentations to the NAC HEO committee show Exploration Mission-1 (EM-1) and Exploration Mission-2 (EM-2) as the first two missions, launching in 2020 and 2022, respectively. Both of those missions are test flights for Orion and SLS; the first mission will fly uncrewed in a Distant Retrograde Orbit (DRO) and the second test flight will take the first Orion crew on a Lunar flyby.

Altogether the first three SLS launches would fly on the Block 1 vehicle, the two Orion test mission launches and the launch of the Europa Clipper probe directly to Jupiter. Although U.S. federal appropriations bills enacted into law for the last three fiscal years mandate a Europa Clipper launch on SLS and “no later than 2022,” the presentations to the HEO committee show that launch on a Block 1 Cargo vehicle in 2023.

Both the crewed Orion configuration that will first fly on EM-2 and Europa Clipper are still in development, so it remains to be seen how future engineering and political developments could influence the timing of those launches — and in the case of Europa Clipper, the launch vehicle.

While Orion and SLS are flying their test flights, the first Gateway launch is planned in the last half of 2022 with a U.S. commercial launch vehicle placing the PPE on a trajectory towards the Moon. The PPE will perform its own insertion into lunar orbit and its commercial developer would then spend most of 2023 demonstrating the spacecraft’s capabilities to NASA.

The ESPRIT and Utilization modules would then fly with Orion and crew on EM-3 in 2024, which would be the debut of ML-2 and the SLS Block 1B vehicle with the larger Exploration Upper Stage (EUS). Although NASA indicated there weren’t any notional masses for the modules, the initial SLS Block 1B launch is expected to be able to place both the 25-metric ton Orion spacecraft and several metric tons of secondary, “co-manifested” payloads on a trans lunar injection (TLI) trajectory.

“Our initial TLI capability we’re targeting nine metric tons (co-manifested payload) on the first one because we’re holding some margin, but after that we’ll do ten metric tons,” Exploration Systems Development (ESD) Deputy Associate Administrator Bill Hill said during one of the presentations to the HEO committee. The habitation modules would then follow one at a time on EM-4 and EM-5.

PPE award(s) next year if funding approved

The final Broad Agency Announcement (BAA) solicitation for the PPE, “Spacecraft Demonstration of a Power and Propulsion Element,” was released by NASA on September 6. Originally released for comments in draft form in July, the solicitation defines a set of NASA unique requirements that the spacecraft must meet, but the BAA is intended to allow bidders to use as much off the shelf technology as possible.

“We believe can basically use a commercial satellite bus augmented with electric propulsion to meet our needs,” Bill Gerstenmaier, NASA Associate Administrator for the Human Exploration and Operations Directorate (HEOMD), said. “So we don’t need a unique spacecraft design, we don’t need a unique bus, we believe what’s available in industry can be used with augmentation of the solar electric propulsion, and that’s what we’ll find out with this BAA activity.”

The main technology development to be integrated into the spacecraft is a solar electric propulsion (SEP) system. The final BAA requirements state: “The PPE Flight System shall utilize an electric propulsion system with the capability to operate over a thrust-to-power ratio range of at least 43 – 52 mN/kW (millinewtons per kilowatt).”

The final BAA set a deadline for bidders to submit proposals of November 15. “NASA and its PPE partner(s) will begin the project upon contract award, which is targeted for March 2019 (TBD), and conclude 24 months after the successful spaceflight demonstration if all of the options are executed,” the final BAA adds.

“The Offeror shall propose a schedule with a launch date no later than September 2022 with a demonstration to last no longer than one year in duration to be completed no later than September 2023.”

An award or awards of firm, fixed price contracts are currently anticipated to be announced next March; however, the timing and nature of the initial announcements are contingent on the outcome of the Fiscal Year 2019 federal government budget process. The gateway was a “new start” in the FY 2019 budget request submitted by the Trump Administration in February; the project must receive enacted language that includes the authority to proceed and also enacted appropriations before efforts can proceed beyond studies.

Appropriations committees in both houses of Congress have approved bills for FY 2019 providing that authority and $504.0 mission for the Gateway, but neither bill for “Commerce, Justice, Science, and Related Agencies” has been voted on by the full House of Representatives and Senate. In recent years few of these bills have come to the floor of either chamber to be voted on by the time a fiscal year begins on October 1; instead, a series of “Continuing Resolutions” (CR) are passed until a compromise is agreed on or in a few cases, the fiscal year ends.

Continuing Resolutions only fund programs previously authorized, which wouldn’t include the Gateway as a project or the PPE specifically.

“NASA may not make any awards to those selected until NASA receives the fiscal year 2019 appropriations or may choose to only award a portion of those selected and reserve the remaining awards pending the final appropriations for the fiscal year,” the final BAA notes. “Any reduced appropriations or continuing resolution may affect NASA’s ability to award selected Offerors.”

PPE requirements

High-level PPE requirements are for the spacecraft to have a 15-year on-orbit operational lifetime, beginning at separation from the launch vehicle. The PPE will include both SEP and chemical propulsion systems, with the latter being based on monopropellant hydrazine.

The PPE is the core element of the Gateway. “It will provide transportation for the LOP-G between cislunar orbits with the option to perform any needed orbital maintenance,” the FY 2019 budget request stated. “It will provide attitude control for the LOP-G in multiple configurations, communication to and from Earth, space-to-space communication, space-to-lunar communication, and in support of astronaut EVA. PPE will also deliver systems necessary for deep space navigation, docking, and refueling. At the end of the LOP-G operational life, PPE will move the integrated LOP-G stack to a disposal orbit.”

Awardees will spend up to a year after launch demonstrating that the spacecraft meets the different requirements.

Operationally, the requirements are for the PPE spacecraft to fly itself from its trajectory at the time of separation from the launch vehicle into lunar orbit: “The PPE Flight System shall utilize the Ion Propulsion System for orbit insertion into the Near Rectilinear Halo Orbit,” the final BAA requirements say. “Chemical propulsion may be used in combination with SEP.”

“In looking at different orbits to put the Gateway in, there’s been a lot of discussion of low lunar orbits, distant retrograde orbits, halo orbits of different families — L1, L2-type orbits,” Crusan said. “The orbit that we’re putting Gateway nominally in to begin with is what we call a near rectilinear halo orbit, likely optimized for the South Pole.”

L1 and L2 refer to two of the Lagrangian points in the Earth-Moon system. “There’s different families of different orbits,” he added. “You can bias them with an L1 bias or an L2 bias and you can do a North and South version of those as well. We are optimizing for the South because we believe that’s a more target rich areas for surface activities as well.”

The PPE is required to be in the NRHO chosen for Gateway one year after launch. Its fuel load is sized to meet requirements based on overall operating expectations over its lifetime.

“We have enough propellant in the Power Prop Element to handle orbital maintenance for fifteen years and two large maneuvers, the most pressing case maneuvers of the entire Gateway stack back and forth, we have that all in the Power Prop Element,” Crusan noted. “The ESPRIT capability will actually increase our overall propellant capacity and could be as high as doubling that before we need our first refuel; but we will be able to refuel if we wanted to move it around more often.”

The requirements indicate maintenance of the NRHO chosen for the Gateway are relatively low: “The PPE Flight System shall conduct orbit maintenance maneuvers in the Near Rectilinear Halo Orbit with a maximum magnitude of less than 10 m/s of delta-v per year.”

Following the demonstration period when NASA would exercise the option to assume ownership of the spacecraft, the PPE mass is required not to exceed 8000 kg, including a minimum of 1050 kg of Xenon for SEP and 800 kg of hydrazine for the Reaction Control System (RCS). The Xenon tank in the PPE is required to have a minimum capacity of 2000 kg, and both the Xenon and hydrazine propellant tanks will have the capability to be refueled.

Commercial cargo resupply

One of the factors that went into consideration for choosing a target lunar orbit for the Gateway was access by U.S. commercial launch services. “In the orbit that we’re picking we’re looking at an optimization of where we know we can fly with our Orion and our SLS vehicles, but also equally as important [is] where do we stage it [for] commercial launch vehicles doing cargo, as well,” Crusan said.

“Our minimum that we want to be able to deliver logistics-wise [is] at least three to four metric tons per delivery; the NRHO orbit is optimized for commercial industry delivery in addition to fly Orion and SLS there.”

The SpaceX Falcon Heavy that began flying in February and Blue Origin’s New Glenn under development were noted as launchers that can deliver large enough resupply packages to the Gateway. “Commercial launch vehicle performance to TLI is predicted, so Falcon Heavy, New Glenn, and those types of rockets, are in the family of anywhere from eleven to fourteen metric tons of TLI performance; for SLS it’s about thirty-four,” Crusan added.

“You take the anywhere from twelve to fourteen metric tons of TLI performance, the logistics vehicle, so [the] pressurized volume and service module to deliver it, and you have the payload that sits inside of it much like Commercial Resupply Services does for us today in ISS (International Space Station) and you end up with about a three to four metric ton of available payload, pressurized payload to NRHO,” he explained.

Existing U.S. launchers such as United Launch Alliance’s Atlas V and Delta IV Heavy could also provide some of these services, but they may be phased out in the 2020s by the Vulcan launcher they are developing. Notionally, one of presentation slides shows Falcon, New Glenn, Vulcan, and the OmegA launcher being developed by Northrop Grumman Innovation Systems (NGIS – formerly Orbital ATK).