Warfighters depend on high frequency (HF) radio transmissions to operate military systems in the space, air, land and sea domains. Current understanding of how HF waves propagate in the electromagnetically noisy ionosphere generally depends on ground-based methods. A better understanding of HF propagation in space requires scientific measurements taken from the ionosphere itself.
DARPA’s new Ouija program aims to use sensors on low-orbiting satellites to provide new insights into the propagation of HF radio waves in the ionosphere, which extends from the upper edges of Earth’s atmosphere to the lower regions. from space. The program aims to quantify the space HF sound environment and improve the characterization of the ionosphere to support warfighter capabilities.
“Ouija will augment ground-based measurements with in-situ measurements from space, in very low Earth orbit (VLEO), to develop and validate accurate, near real-time HF propagation predictions,” said Jeff Rogers, head of the Ouija program at DARPA. Office of Strategic Technology. “The VLEO upper-air regime, about 200 km – 300 km above Earth, is of particular interest because of its information-rich environment where the ionospheric electron density is at its maximum. A detailed knowledge of the spatio-temporal characteristics of the electron density at these altitudes is necessary for an accurate prediction of HF propagation.
The program includes two technical areas. The first technical area, announced in a solicitation published on April 21, 2022, aims to develop, qualify, launch and operate several small satellites carrying scientific and mission instruments. The Ouija science payload will measure electron density both by direct sampling and indirectly by radio occultation using navigation satellites. It is expected that the science payload will use or adapt commercial off-the-shelf (COTS) components, but innovative instrumentation proposals that improve the functionality of the science payload over a baseline COTS are welcome. .
“The HF mission payload will require a high-sensitivity, high-dynamic-range, low-noise HF measurement subsystem,” Rogers said. “The antenna for this subsystem is a particular challenge because efficient HF antennas that operate at the lower end of the frequency band are long, presenting deployment and drag challenges for space vehicles.”
The second technical area, which will be fully detailed in a separate solicitation at a later date, aims to develop assimilation models that ingest direct, in situ measurements of a satellite’s electron density into VLEO. The derived electron density models will be introduced into the HF propagation code and then validated with data measured in orbit. The goal is to improve fidelity over current state-of-the-art assimilation models by incorporating high-resolution local measurements (in time and space) with low-latency updates.
Ouija uses a simplified Other Transactions (OT) process aimed at reducing the bureaucratic barrier for companies wishing to make proposals, especially those seeking to work with the DoD or DARPA for the first time.
The solicitation for the Ouija Technical Area 1, including full technical details, program structure, and instructions for submitting a proposal, is available here: https://go.usa.gov/xu8jm.