Transatlantic exploration took place centuries before the crossing of Columbus. Physical evidence for early European presence in the Americas can be found in Newfoundland, Canada1,2. However, it has thus far not been possible to determine when this activity took place3–5. Here we provide evidence that the Vikings were present in Newfoundland in ad 1021. We overcome the imprecision of previous age estimates by making use of the cosmic-ray-induced upsurge in atmospheric radiocarbon concentrations in ad 993 (ref. 6). Our new date lays down a marker for European cognisance of the Americas, and represents the first known point at which humans encircled the globe. It also provides a definitive tie point for future research into the initial consequences of transatlantic activity, such as the transference of knowledge, and the potential exchange of genetic information, biota and pathologies7,8.

Laser crosslinks can provide high data rate communications and precision time transfer and ranging, using low size, weight, and power (SWaP) terminals to enable constellations of small satellites. The CubeSat Laser Infrared CrosslinK (CLICK) mission will demonstrate terminals capable of conducting fullduplex, high data rate crosslinks and enabling high precision ranging on 3U CubeSats in low Earth orbit (LEO). An initial risk reduction mission, CLICK-A, will demonstrate a downlink of at least 10 Mbps to a 28 cm aperture optical ground station. CLICK-B and CLICK-C will follow to demonstrate laser crosslinks with data rates of at least 20 Mbps over separation distances ranging from 25 km to 580 km. The CLICK-B/C mission will also demonstrate precision ranging better than 50 cm. Key to achieving these capabilities are the performances of the transmitter and fine pointing, acquisition, and tracking (PAT) system. We present results from recent testing and characterization of the transmitter and PAT subsystems. The testing of the transmitter includes confirming the output power and modulation of the seed laser and semiconductor optical amplifier (SOA) and characterizing the output pulse shape. For the PAT system, testing focuses on characterizing the noise of the quadrant photodiode used for the closed-loop, fine PAT sequence. This testing was conducted using a dedicated hardware-in-the-loop testbed with an optical test setup. CLICK-A is expected to launch no earlier than May 2022 for deployment from the International Space Station (ISS) in June 2022, while CLICK-B/C is anticipated to launch in late 2022.

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