Comprising the overall design of the telescope as well as the procurement and construction of its components, this project phase was a significant undertaking. Scientists, engineers, and technicians were tasked with developing a one-of-a-kind scientific instrument with strict, and often competing, mass and energy consumption limits for each component. The successful completion of the phase marks a substantial scientific and engineering achievement - and a key milestone for the entire LuSEE-Night project.
"I'm really proud of what the team managed to build," said Gabriella Carini, associate laboratory director for the Discovery Technologies Directorate at Brookhaven Lab. "With DOE's support, we've built a telescope that I think truly advances the state of the art in the nascent field of space-based radio astronomy."
But in exchange for harsh conditions, there is enormous scientific opportunity. Thanks to the moon's own mass, the lunar far side is shielded from radio interference coming from the Earth and sun. The lunar far side is so "quiet" that it's a prime location for tapping into the whispering radio waves, and therefore the history, of the universe.
In particular, cosmologists seek to detect what is known as the "Dark Ages Signal." Deep in the universe, radio waves linger from the Dark Ages, an early era of cosmological history that began about 380,000 years after the Big Bang. It's an epoch in time before stars and planets existed, and scientists have never been able to observe it due to the abundance of radio interference on Earth. Uncovering the Dark Ages Signal could reveal answers to some of the universe's biggest mysteries, such as the nature of dark energy or the formation of the universe itself.
The collaboration, led by UC Berkeley's Space Sciences Laboratory (SSL), strategically distributed the engineering challenges among the participating institutions. While SSL was responsible for the overall integration of LuSEE-Night, the DOE team, led by Brookhaven Lab, designed and built the core scientific instrument. Brookhaven Lab built or procured more than half of its components, including those for power management and communication. DOE's Lawrence Berkeley National Laboratory developed the antennas for capturing the faint signal of the universe.
At the heart of LuSEE-Night's scientific instrumentation is its radio spectrometer, a highly sensitive piece of instrumentation that was custom built at Brookhaven Lab. The spectrometer turns raw radio signals captured by the telescope's antennas into spectra for scientific analysis. It is what will enable LuSEE-Night to sense low-frequency radio waves and demonstrate the feasibility of lunar radio astronomy.
"This is a very powerful and flexible spectrometer that is packed with features, both in hardware and software," said LuSEE-Night science collaboration spokesperson Anze Slosar. Slosar is a physicist at Brookhaven Lab, and he leads DOE's contributions to the LuSEE-Night science program. "The spectrometer can do calibration, adjust itself according to gain, and filter out its own radio interference. It's a highly programmable instrument."
Perhaps most importantly, LuSEE-Night's spectrometer is able to listen to the full radio band of the early universe 100% of the time; it's like simultaneously listening to every radio station at the same time. Other similar instruments are unable to continuously listen and process, only capturing about 1% of the available information.
"That's really why Brookhaven took on the challenge of leading the LuSEE-Night science instrument. We knew we had the expertise to create an advanced spectrometer capable of observing these highly sensitive radio signals," said Sven Herrmann, the LuSEE-Night construction project manager for DOE's part of the mission. "Our final product is a clear case of Brookhaven's strengths as a DOE lab. We are experts in low-noise and high-performance electronics. Usually, we build these electronics on a much bigger scale for major ground-based experiments like the Large Hadron Collider, the Deep Underground Neutrino Experiment, and the Rubin Observatory. But here, we've taken a slice of those world-leading electronics and built them into the spectrometer for the moon telescope."
Beyond building the spectrometer, developing and procuring LuSEE-Night's other components was like solving a puzzle - one where none of the pieces were provided. Under the leadership of SSL, the LuSEE-Night team had to create each "puzzle piece" while envisioning how they would all fit and work together under the strict mass and energy consumption limits. LuSEE-Night needed to be no more than 282 pounds (128 kilograms) to be fitted on a lander. And since the telescope will be powered by solar panels and a battery that can only be charged during the lunar day, LuSEE-Night's design needed to make the most use of every watt of power.
"One of the first decisions we made was to determine the size of the battery," Herrmann said. Batteries are heavy, and a battery capable of powering and keeping a telescope operational through 14 days of darkness can only be so small. Moreover, manufacturers only produce them in so many sizes, and they aren't highly customizable. "We ended up choosing a battery that was about 110 pounds (50 kilograms), including the cables, bolts, and everything else the battery requires."
Immediately, about half of the telescope's mass limit was accounted for. But according to this team of experts, many other decisions related to mass were straightforward - components like the main electronics crate and the radiofrequency communication radio. Ultimately, Brookhaven Lab delivered components with a combined weight of 168 pounds (76 kilograms), which was significantly below the 187-pound (85-kilogram) limit set by SSL. Managing LuSEE-Night's energy consumption and temperature, however, was an even bigger challenge to address.
"We can easily measure the telescope's mass, but we can't measure the heat that the telescope will lose in the lunar night in the lab," Herrmann said. "We can model this heat loss, but we don't have a heritage mission to draw direct guidance from. Other moon missions that operated through the lunar night used nuclear batteries or operated very differently."
During the brutally hot lunar day, LuSEE-Night must reject heat in a vacuum environment. Then, during a dangerously cold lunar night, LuSEE-Night must keep itself from freezing with no external heat source. Finding materials that can withstand these conditions is one problem, but building a scientific experiment that remains operational during these conditions is a much more difficult challenge. Scientific operations draw power, creating more heat during the already-sweltering lunar day and taking away energy from the telescope's small power and heat source during the lunar night.
"It was really an exquisite dance that we had to do, to determine how to deal with the power that we need to get science out and the battery capacity we need just to stay alive," said LuSEE-Night Project Instrument Scientist Paul O'Connor, a senior scientist at Brookhaven.
To mitigate these polar-opposite challenges, the collaboration incorporated several components that work in harmony to keep the telescope running at a stable, appropriate temperature. Under SSL's leadership, the team included a heat pipe that moves heat from where it's generated to a heat radiator that faces cold space. They also included a set of thermal switches, which acts like a thermostat.
The LuSEE-Night science team will also have full control to manage the telescope's operations from Earth. To manage energy consumption, for example, they can take the spectrometer out of maximum power mode, stop data collection, and then resume full operations as needed. Of course, every moment that the spectrometer is turned off is an opportunity for signals to be missed. But that's a risk this team is willing to take.
As enticing as the Dark Ages Signal may be, detecting those ancient radio waves is a secondary objective for LuSEE-Night. Primarily, the collaboration sees this telescope as a pathfinder, an instrument to pave the way for the next frontier in space science. Scientists know that the lunar far side is a haven for radio astronomy. What they don't know is what a radio telescope needs to operate on the lunar far side for an extended period of time. LuSEE-Night will provide that answer - and perhaps much more.
Meanwhile, at home on Long Island, the LuSEE-Night science team at Brookhaven will await launch day by refining the telescope's operations plan. They'll run "a day in the life" test, during which they'll simulate a moon landing, exercise a few days of operations, and interpret sample data packages. That way, once LuSEE-Night reaches the lunar far side, "we'll be ready," Herrmann said.
In the spirit of preparation, the team has also made a change to the telescope's operations plan since LuSEE-Night was initially announced. Originally, scientists planned to patiently wait 14 days for the telescope's first dataset to be sent to Earth. But now, in case LuSEE-Night runs into trouble during the first lunar night, they plan to run two small data transfer sessions on the first lunar night of the mission.
"The compromise is that these data transfer sessions will draw even more power from the telescope's battery," Slosar said. But early data collection could be essential to the longevity and impact of the mission.
The LuSEE-Night collaboration's goal is to operate the telescope on the moon for up to two years, and hopes are high.
"We're in a new era of space science," O'Connor said. "Launch prices have come down. Instrumentation is more sophisticated. It's very exciting to be part of this. I'm hopeful for the path forward, because there are a lot of basic science experiments that can be done in space. And now we can do them efficiently."
Slosar said, "We're doing something truly novel. We're going to learn a lot."
LuSEE-Night is a collaboration between NASA and DOE. SSL's portion of the project is supported by NASA and Brookhaven Lab's portion of the project is supported by DOE.
Research Report:LuSEE 'Night': The Lunar Surface Electromagnetics Experiment
Related Links
Brookhaven National Laboratory
Stellar Chemistry, The Universe And All Within It
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