The PPE development effort started at the Jet Propulsion Laboratory as a part of the Asteroid Redirect Mission (ARM), but is now managed by the NASA John H. Glenn Research Center. When ARM was cancelled, the solar electric propulsion was repurposed as the PPE for the Gateway.[4][5] The PPE is designed to be able to transfer the reusable Gateway to lunar orbit.[6] It will also serve as the communications center of the Gateway.[7] The PPE is intended to have a launch mass of 5,000kg (11,000lb) with propellant accounting for half that mass [1] and the capability to generate 50kW [8] of solar electric power using Roll Out Solar Arrays for its Hall-effect thrusters, which can be supplemented by chemical propulsion.[9] NASA currently plans to integrate PPE with the HALO module and launch them together on a Falcon Heavy, no earlier than 2027.[2][10]
The Asteroid Redirect Vehicle was a robotic, high performance solar electric spacecraft for the Asteroid Redirect Mission (ARM). The mission was to send the spacecraft to a near-Earthasteroid and capture a multi-ton boulder from the surface with a grappling device. It would then transport the asteroid into orbit around the Moon where crewed missions to study it could be conducted more easily.[5][11] The mission was cancelled in early 2017 and the spacecraft's propulsion segment became the Power and Propulsion Element (PPE) for the Deep Space Gateway, now known as the Gateway.[4]
Reusable Space Tug missions
During the Asteroid Redirect Mission, space tug missions were proposed to separate Mars logistics that can spend a longer time in space than the crew into a separate mission, which could have reduced the costs by as much as 60% (if using advanced solar electric propulsion (ion engines) [12]). They would also reduce the overall mission risk by enabling check-out of critical systems at Mars before the crew departs Earth. This way if something goes wrong in those logistics, the crew is not in danger and the hardware can simply be fixed or relaunched.[13][14][15][16][17][18]
Not only would the solar electric propulsion (SEP) technologies and designs be applied to future missions, but the ARM spacecraft would be left in a stable orbit for reuse.[13][15][14] The project had baselined any of multiple refueling capabilities. The asteroid-specific payload was at one end of the spacecraft bus, either for possible removal and replacement via future servicing, or as a separable, reusable spacecraft, leaving a qualified space tug in cislunar space. This made adaption for Gateway easy, as the propulsion system was already designed to be multi-mission reusable.[19][20][21][22][23] When the ARM was cancelled however, development on the bus and any reusable tug ideas died, temporarily.[4]
Power and Propulsion Element
A diagram of the Gateway identifying the Power and Propulsion Element, along with the other modules planned.
In 2017, a year after the Artemis program came into existence, the ARM space tug/propulsion bus was repurposed as the main propulsion system for the Gateway space station. It officially became known as the Power and Propulsion Element or PPE.[4] The PPE will be a smaller version of the Asteroid Redirect bus.[4][24] In 2018, the Gateway was split off from Artemis as a separate program to allow a Moon landing by 2024 without having to wait for the Gateway to be completed.[25][26]
Commercial company studies
On 1 November 2017, NASA commissioned 5 studies lasting four months into affordable ways to develop the Power and Propulsion Element (PPE), hopefully leveraging private companies' plans. These studies had a combined budget of US$2.4 million. The companies performing the PPE studies were Boeing, Lockheed Martin, Orbital ATK, Sierra Nevada and Space Systems/Loral.[27][8] These awards are in addition to the ongoing set of NextSTEP-2 awards made in 2016 to study development and make ground prototypes of habitat modules that could be used on the Gateway as well as other commercial applications,[28] so the Gateway is likely to incorporate components developed under NextSTEP as well.[8][29]
Contract awarded
In May 2019, Maxar Technologies was contracted by NASA to manufacture this module, which will also supply the station with electrical power and is based on Maxar's SSL 1300 series satellite bus.[30] The PPE will use Busek 6kW Hall-effect thrusters and NASA Advanced Electric Propulsion System (AEPS) Hall-effect thrusters.[31][32][33] Maxar was awarded a firm-fixed price contract of US$375 million to build the PPE. Maxar's SSL business unit, previously known as Space Systems/Loral, will lead the project. Maxar stated they will receive help from Blue Origin and Draper Laboratory on the project, with Blue Origin assisting in human-rating and safety aspect while Draper will work with trajectory and navigation development.[7] NASA is supplying the PPE with a S-band communications system to provide a radio link with nearby vehicles and a passive docking adapter to receive the Gateway's future Utilization Module.[7] Maxar stated they are experienced dealing with high power components from making satellites. They did mention that their satellites are around 20 to 30 kilowatts, while the PPE will be about 60 kilowatts, but they say much of the technology they have already developed will still be applicable.[7] After a one-year demonstration period, NASA would then "exercise a contract option to take over control of the spacecraft".[26] Its expected service time is about 15 years.[25]
In 2020 NASA introduced new requirements, including integration of PPE and HALO before launch.[35] PPE thus does not need to dock with HALO in space, and its docking port was eliminated. Thus it will no longer be able to undock from HALO.[36] In February 2021 NASA contracted with SpaceX for launch of the integrated elements by a Falcon Heavy launch vehicle.[37]
In mid 2024, the HALO module reached significant completion and entered into the stress test phase in Thales Alenia's facilities. Upon successful completion of the stress tests, it is planned to be shipped to the US Northrop Grumman facilities to undergo final launch preparation and integration with the Power and Propulsion Element.[38]
PPE construction
The central component of the PPE module.
In 2025, the solar array which provides power to the module successfully passed testing.[39]
↑ McElratht, T.; Elliott, J. (January 2014). "There and Back again: Using planet-based SEP tugs to repeatably aid interplanetary payloads". Advances in the Astronautical Sciences (152): 2279–2298.
↑ Price, Humphrey W.; Woolley, Ryan; Strange, Nathan J.; Baker, John D. (2014). "Human Missions to Mars Orbit, Phobos, and Mars Surface Using 100-kWe-Class Solar Electric Propulsion". AIAA SPACE 2014 Conference and Exposition. doi:10.2514/6.2014-4436. ISBN978-1-62410-257-8.
↑ Manzanek, D. (20 May 2016). The Asteroid Redirect Mission. USNO Scientific Colloquium.
↑ Gates, M.; Manzanek, D. (28 June 2016). Asteroid Redirect Mission (ARM). 15th Meeting of the NASA Small Bodies Assessment Group.
↑ Manzanek, D.; Reeves, D.; Hopkins, J.; Wade, D.; Tantardini M.; Shen, H. (13 April 2015). "Enhanced Gravity Tractor Technique for Planetary Defense". IAA-PDC.
↑ NASA RFI: Spacecraft Bus Concepts to Support the ARM and In-Space Robotic Servicing- Section "Separable Spacecraft Architecture ARRM Concept".
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