The HERMES project takes advantage of an opportunity to launch space-weather instruments and conduct scientific research with the first two Gateway modules to be placed in lunar orbit. Selection of capable multi-purpose instruments for HERMES was guided and constrained by the need for rapid development to meet an aggressive schedule, and by an overall mass limit of 25 kg (TBR) imposed by Gateway. Scientific goals and objectives leverage Gateway’s proximity to other heliophysical observational assets, its unique polar lunar orbit, and the HERMES complement of instruments.
The initial Gateway modules will be the Power and Propulsion Element (PPE) and the Habitation and Logistics Outpost (HALO). These modules will launch together with the HERMES payload occupying an external site on the HALO. To support human exploration, Gateway will be in a highly eccentric polar lunar orbit with apoapsis 70,000 km, or 11 Earth radii (RE) south of the Moon and periapsis in the north at radial distance 3,000 km. As a consequence, Gateway and HERMES will be in the solar wind for roughly 3 weeks out of 4, and will traverse primarily the midplane and the southern regions of the magnetotail during the remaining week.
As an element of the Heliophysics System Observatory, analysis of spatial structure will leverage simultaneous measurements from the two THEMIS/ARTEMIS probes in equatorial lunar orbits. THEMIS refers to the Time History of Events in the Magnetosphere and Ionosphere during Substorms mission. ARTEMIS refers to the two THEMIS probes which were redirected into lunar orbit and renamed as the Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon’s Interaction with the Sun mission. With HERMES, the 3 spacecraft configuration is especially advantageous for investigation of structures in both the interplanetary medium and in the magnetotail. The ARTEMIS probes’ separation ranges from 2 – 5 RE in the X-Y plane. The orbit of Gateway will provide for a maximum out-of-plane separation of 11 RE. A dedicated effort to study structure over this range of distance has not previously been accomplished. The ARTEMIS probes have thermal plasma instruments and magnetometers with capabilities similar to those on HERMES. The higher energy particle detectors for ARTEMIS and HERMES are complementary in coverage of energies. In addition to this, measurements from solar wind monitors at L1 will provide data for analysis of structures ~0.1 AU.
Below, 3 Scientific Goals of the HERMES project are defined, and specific Scientific Objectives are enumerated.
Goal A: Determine mechanisms of solar wind mass and energy transport
- Objective A1: Determine effects of large-scale structures on plasma transport and particle energies within the solar wind.
- Objective A2: Determine effects of small-scale structures on plasma transport and particle energies within the solar wind.
Goal B: Characterize energy, topology, and ion composition in the deep magnetotail.
- Objective B1: Determine structure and dynamics of the magnetotail at lunar orbit.
- Objective B2: Quantify energy content of the magnetotail at lunar orbit.
- Objective B3: Quantify transport of atmospheric ions.
Goal C: Establish observational capabilities of an on-board pathfinder payload measuring local space weather to support deep-space and long-term human exploration.
- Objective C1: Assess the effects of field of view limitations associated with accommodation on Gateway.
- Objective C2: Assess interference with measurements due to electric currents and surface charging.
The HERMES science payload provides in-situ measurements of electrically charged particles and magnetic fields. To fit within the fairing of the launch vehicle, it is limited in volume at launch to a cube 0.5 meter on a side. For structural reasons, mass cannot exceed 25 kilograms. The instruments are typical of space weather suites. They were selected, in part, for their heritage, to provide confidence that HERMES can meet the aggressive schedule required for launch with Gateway.
There is an Electron Electrostatic Analyzer (EEA) to measure the velocity distributions of low energy, thermal electrons, with energies 5 eV up to 10 keV. These measurements will be used to determine electron density, speed, and temperature.
An ion spectrometer, the Solar Probe Analyzer for Ions (SPAN-i) observes ions with energies about 1 eV to 40 keV to determine mass-resolved ion velocity distributions and density, velocity, and temperature of ion populations.
The Miniaturized Electron pRoton Telescope (MERiT) is an energetic particle telescope with wide bi-directional fields of view to cover the forward and reverse Parker Spiral. Electron energy spectra are captured between 300 keV and 9 MeV, and protons from 1 to 190 MeV.
The Noise Eliminating Magnetometer Instrument in a Small Integrated System (NEMISIS) is a set of 3 magnetometers. The main science magnetometer is boom mounted. It is collapsed and stowed for launch, extending 1 meter above the other instruments after deployment. Two miniature PNI magnetometers are located on the payload deck. Magnetic gradiometry will be used to correct the fluxgate measurements for fields due to electric currents within Gateway, and for currents generated by other HERMES instruments.
All observations are at temporal resolutions given in Table 1. In regions where particle flux is likely to be at or below the threshold of detection, consecutive energy/angle scans can be accumulated on the ground to reach lower thresholds.
The HERMES Project Manager is responsible for the design, development, manufacturing, integration and test, and verification of the HERMES observatory, project documentation, and mission operations. HERMES project management is conducted consistent with NASA Space Flight Program and Project Management Requirements (NASA Procedural Requirements (NPR) 7120.5F), including management practices, milestones, and independent project-level reviews.
The project manager is responsible and accountable for technical, cost, schedule management, and performance of the HERMES project. The HERMES Project Scientist is responsible for management of science elements of the project. This includes coordination and direction of individual instrument teams and of the HERMES Science Working Group in accomplishing mission science objectives and providing data to support research efforts of the broader scientific community, and coordination with the Space Weather Science Operations Center (SOC) and the HERMES Mission Operations Center (MOC).
The HERMES project’s acquisition strategy and processes are in accordance with NPR 7120.5. The Heliophysics Division (HPD) was studying a potential partnership with the Human Exploration and Operations Mission Directorate (HEOMD) on the Gateway lunar missions aimed at flying heliophysics instruments externally mounted on Gateway modules. Because of Gateway’s accelerated schedule, there was a very short timeframe for formulating a response to take advantage of the opportunity. Consequently, HPD decided to invite inputs from several institutions in lieu of issuing a Request for Proposal or Announcement of Opportunity. As part of the formulation of this directed effort, information was sought from Goddard regarding potential solar wind, magnetometer, and energetic particle instrument suite contributions.
Goddard responded with a proposed instrument suite (described in section 1.3), which was approved and Authorization to Proceed was granted. Three of the instruments (EEA, NEMISIS, and MERiT) are in-house builds at Goddard. The SPAN-i instrument is to be built at the University of California, Berkeley. Integration of the HERMES platform will occur at Goddard.
Formulation activities were conducted in accordance with the Authorization to Initiate Project for flying a Heliophysics Instrument Suite on Gateway memorandum from the Heliophysics Division Director to the Center Director, Goddard Space Flight Center on March 11, 2020.
The HERMES Project Scientist has worked collaboratively with NASA Headquarters, the instrument PIs, and the HERMES Science Working Group to define the science goals, objectives, and requirements. Gateway and HERMES project personnel have collaborated to determine the technical interface requirements, which will be captured in a payload-specific Interface Control Document (ICD).
Gateway modules and launch vehicle will be provided by the Gateway Program.