[Reading Science] NASA's Unexpected Praise for 'Danuri ShadowCam': What's the Reason?

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"The ShadowCam onboard Korea's Danuri is performing its mission well."

On the 29th of last month (local time), the National Aeronautics and Space Administration (NASA) of the United States released on its main homepage the detailed lunar surface exploration results captured by the ShadowCam, an instrument onboard Korea's first lunar probe Danuri. This material was posted on the main page four days after South Korean President Yoon Seok-yeol visited NASA headquarters on the 25th of the same month, and as of the 1st, it still adorns the main page of NASA's website.

Regarding this, NASA explained, "Following the success of Artemis 1 at the end of last year and the recent selection of the Artemis 2 crew, preparations for the launch of Artemis 3, which will be humanity's first exploration of the lunar south pole (after 2025), are progressing well." They added, "To this end, we are conducting as much scientific research as possible to increase understanding of deep space exploration and space itself, focusing on the permanently shadowed regions of the Moon."

NASA then focused on introducing Danuri and ShadowCam. NASA explained, "One method of gathering information about the permanently shadowed regions is by using a high-sensitivity optical camera named ShadowCam," adding, "ShadowCam was launched in August last year onboard the Korea Aerospace Research Institute (KARI)'s Danuri (Korea Pathfinder Lunar Orbiter, KPLO) along with five other Korean scientific instruments."

The ShadowCam onboard Danuri is a symbolic project of Korea-US space cooperation. Until now, Korea, with limited experience in space development, had no significant cooperative relationship with the US beyond satellite launch requests. In fact, the US had 'practically' obstructed the development of the Nuri rocket citing the Missile Technology Control Regime (MTCR) and International Traffic in Arms Regulations (ITAR). However, the Danuri production and launch process was different. It was the first full-fledged case of Korea-US cooperation in the space sector. KARI accepted NASA's proposal to carry ShadowCam. No money was exchanged; instead, KARI received support for Danuri's deep space navigation technology, know-how, and deep space communication network. Danuri succeeded in entering lunar orbit after four months of deep space navigation via a ballistic lunar transfer orbit (BLT), a method rarely attempted before, to save fuel and maximize mission lifespan. For KARI, which had experience only in satellite launch and operation, this was a technology never attempted before. The complex attitude adjustments and delicate thruster operations required for lunar orbit insertion were reportedly impossible without NASA's cooperation. Additionally, besides KARI's own deep space antenna network built for communication with Danuri, US support was also provided.

[Image source=Yonhap News]

ShadowCam, a symbol of this Korea-US space cooperation, was jointly developed by the US private company Malin Space Science Systems and Arizona State University (ASU). It boasts extremely high optical sensitivity compared to other lunar observation cameras to capture the permanently shadowed regions near the lunar south pole, where sunlight has never reached. Its primary mission is to select candidate landing sites for Artemis 3, humanity's second lunar landing exploration project after 2025. It plans to capture high-resolution images to map the permanently shadowed regions of the lunar south pole, where water ice is presumed to be buried underground, for exploration and rover operations. It boasts performance over 200 times superior to the camera (NAC) onboard NASA's Lunar Reconnaissance Orbiter (LRO) launched in 2009.

Four days after President Yoon's visit to NASA headquarters in Washington DC, NASA released representative images captured so far by ShadowCam. The first image is a high-resolution photo of Skeleton Crater near the lunar south pole taken by ShadowCam. The terrain features on the surface are vividly revealed, including traces of fallen rocks. NASA stated, "ShadowCam can operate in extremely low-light environments, enabling such high-quality image capture," adding, "ShadowCam can take photos with over 200 times higher sensitivity than LRO's NAC." Regarding the vivid capture of rock traces that rolled down from the high crater wall, NASA emphasized, "By analyzing the shape and speed of the rocks and the characteristics of the regolith, we can enhance our understanding of the Moon's geotechnical properties."

'ShadowCam' installed on Danuri. Photo by Ministry of Science and ICT

NASA also released photos taken using faint reflected light or earthshine to capture detailed images of the lunar surface. The Moon is illuminated by 'earthshine,' similar to moonlight on Earth. When the Earth appears as a crescent from the Moon, the Earth is fully visible like a full moon from Earth, and earthshine is strongest. However, earthshine is only about one-tenth the intensity of sunlight reflection. During test operations, ShadowCam successfully captured images inside Bruce Crater near the lunar equator using earthshine at its strongest during the crescent Earth phase, demonstrating its excellent performance. Additionally, images capturing detailed features of Marvin Crater and others in the permanently shadowed region about 26 km from the lunar south pole using reflected light were also released.