Heliophysics Environmental & Radiation Measurement Experiment Suite (HERMES): A Small External Payload for the Lunar Gateway with Big Challenges

Currently scheduled for liftoff in 2024, Gateway will be an outpost orbiting the moon for astronauts headed to and from the lunar surface and serve as a staging point for deep space exploration. In January of 2020 NASA headquarters contacted Goddard Space Flight Center to request that they develop a Heliophysics instrumentation package for Gateway. This package would later become known as HERMES-Heliophysics Environmental & Radiation Measurement Experiment Suite. HERMES consists of a Miniaturized Electron pRoton Telescope (MERIT), an Electron Electrostatic Analyzer (EEA), Solar Probe Analyzers (SPAN)-A-ions, and Noise Eliminating Magnetometer Instrument in a Small Integrated System (NEMISIS), which consists of one fluxgate and two Magneto-Inductive Magnetometers. From the beginning the HERMES mission faced a number of Challenges. It was constrained to fit in a small, half meter, cube and it was required to weigh no more than 25kg. A new boom design for the magnetometer would be required and for safety reasons it must be able to retract autonomously with power removed. To complicate matters the location of the SORI-Small ORU- (Orbital Replacement Unit) Robotics Interface, the primary interface for the HERMES platform to the Gateway elements, was undetermined. Also, the mechanical, thermal and electrical interfaces are not fully defined. The Canadian Space Agency is still in process of designing the version of the SORI that will be flown on the Power and Propulsion Element (PPE) and Habitation and Logistics Outpost (HALO) elements, each of which are being developed by different contractors. At the time of initiating the HERMES project, neither of the Gateway module providers were under contract. Additionally, we would later learn the ISS heritage SORI modules were not originally designed for launching on the Gateway elements with a payload directly attached but rather were intended to be brought up on a separate carrier outfitted with launch locks and specialized launch structures from which the robotic arm on Gateway would then be used to detach the payload and install it on the SORI adapters while on orbit. Launching the integrated Payload/SORI on the PPE and HALO elements complicates the stiffness requirements and coupled loads analysis. Adding to this are serious constraints on Field-Of-View (FOV) for solar viewing and severe radiation exposure considerations brought on by slowly raising the orbit through the Van Allen Belts. Just to make things a little more challenging the budget for the entire project was intended to be a low-cost tailored Class-D mission approach. Plus, the effects of Corona VIrus Disease 2019 (COVID-19) were not factored in from the beginning. This paper will discuss what’s being done to overcome these challenges and put HERMES on track for a 2024 Launch Readiness Date (LRD).