Project Selections for InVEST-23

05/03/2024 – NASA’s Science Mission Directorate, NASA Headquarters, Washington, DC, has selected proposals for the In-Space Validation of Earth Science Technologies Program (A.55 of the 2023 Research Opportunities in Space and Earth Sciences omnibus solicitation) in support of the Earth Science Division (ESD). The space environment imposes stringent conditions on components and systems, some of which cannot be fully tested on the ground or in airborne systems. Because of the harsh conditions, there has been, and continues to be, a need for new technologies to be validated in space prior to use in a science mission. The In-Space Validation of Earth Science Technologies (InVEST) program element is intended to fill that gap.

This InVEST solicitation was targeted to small instruments and instrument subsystems that can advance technology to enable relevant Earth science measurements. The call was limited to in-space validation only, and targeted technology validation on the CubeSat, SmallSat, and hosted payload platforms. NASA received a total of 15 proposals in response to this NRA and has selected one proposal and categorized one additional proposal as selectable for funding. The total funding for these investigations is approximately $18 million dollars. The selected proposal is as follows:

Gravitational Reference Advanced Technology Test In Space (GRATTIS)
John Conklin, University of Florida, Gainesville

The Gravitational Reference Advanced Technology Test In Space (GRATTIS) mission will demonstrate the end-to-end functionality and sensitivity performance of the Simplified Gravitational Reference Sensor (S-GRS), an ultra-precise inertial sensor for future Earth geodesy missions. These sensors are used to measure or compensate for all non-gravitational accelerations of the host spacecraft so that they can be removed in the data analysis to recover spacecraft motion due to Earth’s gravity field, the main science observable. Low-low satellite-to-satellite tracking missions like GRACE-FO that utilize laser ranging interferometers are technologically limited by the acceleration noise performance of their electrostatic accelerometers, as well as temporal aliasing associated with Earth’s dynamic gravity field. The current accelerometers, used in GRACE and GRACE-FO have a limited sensitivity of ~10E–10 m/s^2Hz^1/2 around 1 mHz. The SGRS is estimated to be at least 10 times more sensitive than the GRACE accelerometers and more than 500 times more sensitive if operated on a drag-compensated platform.

The S-GRS concept is a simplified version of the flight-proven LISA Pathfinder GRS. It consists of a free-falling cubic test mass inside an electrode housing that senses the position and orientation of the test mass and electrostatically applies forces and torques to it to keep it centered at a nanometer-level. The applied forces and torques required to do so are also used to precisely determine the non-gravitational forces acting on the host spacecraft, as well as the spacecraft’s angular acceleration. The full functionality and acceleration noise sensitivity of the S-GRS can only be measured in space. This is because the electrostatic actuation system is only capable of producing micronewtonlevel forces, which means that it is incapable of suspending the 0.5 kg Au-Pt test mass in a 1 g environment. The improved performance of the S-GRS is enabled by removing the small grounding wire used in the GRACE accelerometers, which limits its performance, and replacing it with a UV LED-based charge management system, increasing the mass of the sensor’s TM, and increasing the gap between the TM and its electrode housing.

GRATTIS will fly two identical S-GRS mounted next to one another at the center of mass of a 160 kg ESPA-class commercial microsatellite. The six-axis acceleration measurement capability of the S-GRS allows precision measurement of the spacecraft drag-induced linear acceleration, as well as the residual angular acceleration of the nominally inertially-pointed bus. By combining the outputs of each sensor and with the known relative position of the two TMs, we can recover the acceleration sensitivity (noise floor) of the S-GRS. The minimum mission success criteria for GRATTIS is to demonstrate an S-GRS acceleration noise of ?10E–10 m/s^2Hz^1/2 between 1-10 mHz, the primary accelerometer requirement for GRACE-FO and the Mass Change mission. Our mission goal is to demonstrate acceleration noise performance of ?10E–11 m/s^2Hz^1/2.

The PI and science team is led by the University of Florida (UF) and includes relevant experts from Texas A&M University and CrossTrac Engineering. The S-GRS mechanical sensor heads are provided by Ball Aerospace, while the S-GRS electronics units are provided by Fibertek, Inc. CrossTrac Engineering provides the S-GRS software and program management. The UF-led team will integrate the flight payload into a single thermal/mechanical enclosure and perform ground testing to the extent possible. Apex Space will provide the Aries microsatellite bus, spacecraft-payload integration, and launch services via a SpaceX F9 Transporter mission planned for October 2026. After launch, Apex will perform on-orbit bus commissioning, then they will hand over GRATTIS mission operations to the UF-led science team while continuing to provide support. The S-band ground network is provided by Amazon Web Services.

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