ESA proposes new logistics vehicle for cis-lunar outpost
A dramatic re-write of the assembly schedule for the Deep Space Gateway at the beginning of 2017 has put severe mass restrictions on the first component of the cis-lunar outpost. To resolve the problem, the international team of experts considered various solutions, including in-flight refueling. According to European engineers, a newly designed robotic vehicle could save the day by taking some of the tasks of the original Power and Propulsion Bus.
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The most obvious solution to the lack of propellant on the Power and Propulsion Bus, PPB, of the cis-lunar station would be in-flight refueling, because it could dramatically extend the service life and capabilities of the future outpost.
In-flight refueling has been used very successfully on the Soviet Salyut and Mir space stations and on the Russian segment of the International Space Station, ISS. However the latest proposal to employ the same procedure on the Deep Space Gateway could be problematic. The new outpost's reliance on electric thrusters powered by xenon means that the transfer of such a propellant from a tanker to the station would have to be a rather slow affair to prevent the liquefied xenon from heating up. In fact, it could take up to several months to pump a few hundreds kilograms of xenon. Otherwise, the tanks and propellant lines would have to be equipped with a special refrigeration system, hugely taxing the already mass-constrained system.
As an alternative to refueling the PPB, engineers working for the European Space Agency, ESA, proposed to split the module into the two independent sections. According to one of such scenarios, the first vehicle would be the propulsion module based on NASA's spacecraft previously planned for the Asteroid Retrieval Mission, ARM. It would be upgraded with the European electric engine known as ESA Hall Effect Auxiliary Thruster or eHEAT and loaded with a maximum of xenon propellant reaching 2.2 tons.
At the same time, additional tasks previously assigned to the PPB module would be "off-loaded" to the newly proposed Logistics Communication and Utilization Bay, LCUB. It could take over a Canadian-built robotic arm and a small airlock for scientific experiments, as well as a communications gear. Additionally, it could also feature an observation window in its airlock, which would be accessible by the inhabitants of the Deep Space Gateway via a standard docking port. This component would be built light enough to be launched on a standard rocket such as Europe's prospective Ariane-6. It would lift off from Earth around nine months after the EM-2 mission deploying the "abbreviated" PPB bus.
A space tug would have to be developed to boost LCUB from its initial orbit and dock it to the Deep Space Gateway in the cis-lunar space. Ultimately, the LCUB would end up permanently attached to the cis-lunar station between the PPB module and the habitation module, which would arrive with the Orion crew vehicle during its EM-3 mission.
The LCUB module could still serve as a tanker carrying up to 1,100 kilograms of propellant. It could employ traditional refueling methods, if they are proven workable for the transfer of propellant. Alternatively, it could feature replaceable "plug-in" propellant tanks to avoid pumping the capricious xenon between modules.
However, if the refueling was deemed unnecessary after all, the LCUB could feature a larger airlock, which could also double as a pressurized cargo compartment on the way from Earth to the cis-lunar space. Measuring three meters in length and two meters in diameter, this version of the LCUB module could provide up to eight cubic meters of pressurized volume and accommodate up to 1,070 kilograms of supplies.
Engineers at Airbus Defense and Space, Thales Alenia Space and OHB System working on the issue for ESA have also conceived a number of other arrangements and architectures aimed at splitting various components of the original PPB module.
The idea to split the Power and Propulsion Bus was presented at the May 2017 meeting in Montreal and the partners agreed to weigh pros and cons of the various alternatives this option could provide.
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The LCUB module would be equipped with a pair of International Berthing and Docking Mechanisms, IBDM, enabling its docking with the PPB module on one end and the Hab module on the other. Credit: QineticQ via Claude Mourier
The LCUB vehicle could be launched on a standard rocket, such as Ariane-64. Credit: ESA