Calibration is a necessary, if typically invisible, step in the successful operation of any scientific telescope. Without a known value to compare its readings against, data from telescopes could suffer from biases or transients that could completely misdirect scientists analyzing it. However, those same scientists also struggle to find good sources of data to calibrate against. Enter Arcstone - a technology demonstration mission that launched earlier this week that plans to use one particular source as a calibration dataset - moonlight.
Arcstone is designed as a 6U CubeSat that launched on a SpaceX rocket on June 23rd from Vandenberg Air Force base. It successfully reached orbit, and should start recording data in about three weeks, with plans to complete a six month mission of collecting moonlight.
But why bother? The moon is highly reflective, and known to be very stable in that reflectance over time, making it an ideal candidate for a calibration data set, as it doesn’t vary like other potential sources. It’s already been used as a calibration tool for years, but, at least so far, there hasn’t been a dataset of sunlight reflected off the lunar surface that can be used as a calibration tool, especially for space-based observational platforms.
Video depicting the Arcstone mission. Credit - Resonon YouTube ChannelData collected from ground-based observatories won’t cut it, as they have to contend with interference from Earth’s atmosphere. And no dedicated space mission has so far collected any useable data that can be considered as the basis for a standard. However, as space-based missions become more important, especially when dealing with Earth observations, the importance of having a reliable set of calibration data increases.
Enter Arcstone - it was originally given project approval by NASA in 2021, but ground-based technology demonstrators go back as far as 2019, proving that the concept would work and provide useful data. Other major project milestones included delivery of the main advanced spectrograph by sub-contractor Resonon in 2021, and integration into the 6U CubeSat bus provided by Blue Canyon Technologies followed shortly thereafter. Blue Canyon also provided the guidance and navigation system that will allow the satellite to “point” at the correct spot every time, ensuring that data is consistent throughout the mission timeline.
This first 6U CubeSat launch is itself only a technology demonstration project. According to a press release from NASA, a successful mission this time around will lead to a longer Arcstone mission that would enable scientists to truly create a standard out of the data they have collected from the Moon, and use that to calibrate all manner of future missions in space. It may also even allow scientists to fill in or correct data from previously launched missions, as offsets may have changed as instruments and data buses aged.
Fraser discusses Moonshine and how it occurs.While that future mission is still a long way off, it’s looking more and more likely as Arcstone continues its commissioning process. In six months we’ll know whether the different sub-components of the CubeSat successfully integrated into a cohesive whole or whether some additional work must be done to prove out the technology. With luck, humanity this work will lead to a baseline where future generations of scientists and refer back to these datasets and be confident in their own space-based observational missions going forward.
Learn More:
NASA - NASA Tech to Use Moonlight to Enhance Measurements from Space
UT - The Moon