A second wind in space
Lunar instrument remains on its mission after 11 years on orbit
Every space instrument has a required design life – the time it must be able to operate in space. Depending on the mission, that can vary from as little as days or months to as long as decades. After an instrument goes dark, its mission is over.
In 2009, NASA’s Lunar Reconnaissance Orbiter, or LRO, launched with seven instruments aboard, including the Miniature Radio Frequency radar. Raytheon Intelligence & Space, one of four businesses that form Raytheon Technologies, was part of the former Raytheon Company, a predecessor to Raytheon Technologies. It built the Mini-RF’s receiver and another company built the transmitter.
The Mini-RF mission: to look below the moon’s surface to hunt for buried ice deposits in the permanently shadowed regions of polar craters. After reaching its two-year design life, the transmitter went dark, but the instrument unexpectedly got a second wind – in large part because the receiver still worked.
“Mini-RF was truly an experimental space program – built fast and lean, and designed to last two years,” said Wallis Laughrey, vice president of Space Systems at RI&S. “The fact that it’s still supporting science missions 11 years later is a testament to its design and out-of-the-box thinking.”
Researchers at John Hopkins University Applied Physics Laboratory, who run the day-to-day operations of Mini-RF, reconfigured it to operate in what’s called a bistatic mode.
“In this mode, we’re splitting the responsibilities,” said Jim Cannon, senior program manager, Space Systems at RI&S. “Rather than one system transmitting and receiving radar signals, we have two.”
The ground-based Arecibo Observatory radio telescope in Puerto Rico transmits the signal, and the signal that bounces off the moon is received by Mini-RF.
The signals that Mini-RF receives are used to calculate circular polarization ratio, or CPR. Different materials, such as ice and lunar soil, scatter radar signals in different ways to create unique CPR signatures.
Researchers process Mini-RF’s data to look inside the moon’s craters for areas with high CPR, which is an indicator for the presence of ice. The location of the crater, steepness of the crater sidewalls and distribution of high-CPR signals are also taken into consideration.
“Mini-RF has enabled the examination of hundreds of craters, allowing researchers to identify strong candidates for exploitable ice deposits,” said Cannon. “These ice deposits could one day be used for personal consumption on future colonies or as a source of hydrogen and oxygen for fabricating rocket fuel on the moon.”
Different angles from the telescope signal also allow scientists to observe the moon’s ground in new ways to find new data. Collecting data over a range of bistatic angles helps analysts distinguish between high CPR due to water rather than crater surface roughness.
The Mini-RF data also gives NASA valuable data for its Artemis lunar exploration program, whose goal is to return American astronauts to the moon by 2024. The moon’s south pole – with its ice deposits and other potential resources – has emerged as a likely landing site for the mission. The ice mapped by Mini-RF could also play an important role in NASA’s efforts to send astronauts to Mars.
“Many lessons from the Mini-RF program have influenced today’s approach to how we ‘go fast’ while still designing instruments that go well beyond design life requirements,” said Laughrey.