Radio Experiment Launches With China’s Moon Orbiter

A Dutch radio astronomy experiment hitched a ride today with China's relay satellite for the upcoming Chang'e 4 mission.

Moon farside

The lunar farside and Earth, as captured by the Chang'e 5 test mission that flew in 2014.
Chinese National Space Administration / Xinhuanet

A Long March-4C rocket roared to life last night, lighting up the night skies over China and opening up the next chapter of lunar exploration. Aboard the rocket: an innovative lunar relay orbiter and a ground-breaking radio astronomy experiment.

The launch occurred at 21:28 UT from Xichang Space Center in Sichuan, China. This orbiter is part of China's ambitious first attempt to deploy a lander and rover on the farside of the Moon later this year. All lunar landings to date, including the Apollo missions and China's 2013 Yutu Jade Rabbit lander and rover, have been conducted on the Moon's near side, within sight of Earth and radio communications. Chang'e 4, however, will land and rove on the farside of the Moon, requiring a dedicated relay.

The relay orbiter is named Queqiao (pronounced Cheh-chow), Chinese for “Magpie Bridge.” The name comes from a Chinese folktale of a bridge that formed once a year across a river (the Milky Way) to join two separated lovers, represented by the stars Vega and Altair.

The China National Space Administration (CNSA) reported that the orbiter successfully separated 25 minutes after launch, deployed its antennas (including a 5-meter-diameter antenna, the largest used to date for deep space exploration), and solar panels. Queqiao is now in an elliptical lunar transfer orbit and will eventually enter a lissajous (halo) orbit around the stable Lagrangian L2 point, which lies 283,000 miles (455,000 kilometers) from Earth and 37,300 miles (60,000 kilometers) beyond the Moon.

"The launch is a key step for China to realize its goal of being the first country to send a probe to soft-land on and rove the farside of the Moon,” says Zhang Lihua (CNSA) in a recent press release.

Chang'e-4 orbit

The orbit of the Chang'e 4 lunar relay.

Moon-based Astronomy

A few innovative payloads hitched a ride as well, including the Netherlands-Chinese Low-Frequency Explorer (NCLE) fielded by the ASTRON, the Netherlands Institute for Astronomy, Innovative Solutions in Space (ISIS), and Radboud Radio Lab.

NCLE will observe low-frequency (below 30 MHz) radio waves from its lunar L2 vantage point. On Earth, radio waves below 30 MHz are absorbed by the ionosphere. But cosmologists would like to access radio waves at these low frequencies to study the era when the first stars and galaxies were forming. The farside of the Moon provides a “radio-quiet” zone largely free of terrestrial interference that plagues modern radio observatories.

"We are interested in the time when neutral hydrogen gas started for the first time to form stars and galaxies," says Albert-Jan Boonstra (ASTRON). "This started 380,000 years after the Big Bang, at that time the Universe was cool-down and dark. This star-forming process should be visible as a small bump in the spectrum, and with NCLE we aim to find it."

This task is challenging, as the signal is expected to be weak. NCLE won't form an all-sky map at low frequencies but instead will serve as a proof of concept for future efforts. Previous efforts at low-frequency investigations used narrowband receivers, but NCLE will make the observations using a broadband receiver, another first.


The Netherlands-China Low frequency Explorer (NCLE) in the lab.
Radboud Radio Lab / ASTRON / Albert-Jan Boonstra

"The last few months have been quite challenging for the Dutch team,” says Marc Klein Wolt (Radboud Radio Lab) in a recent press release, “The Chinese lunar program is like a bus we were trying to catch, mostly due to the hard work and enormous dedication from the teams on both sides.”

Two other micro-satellites, Longjiang-1 and Longjiang-2 (Chinese for “Dragon River” referring to the Heilongjiang/Amur River between Russia and China), were also deployed to orbit the Moon. Their mission is to conduct ultralong-wave astronomical observations of their own. Saudi Arabia also fielded a small lunar optical imager aboard the orbiter.

Once Queqiao is in place, the stage is set for the launch of the Chang'e 4 lander and orbiter, which will head for the Von Kármán crater in the South Pole-Aitken Basin on the lunar farside. Launch of Chang'e 4 is set for late 2018.

Perhaps, Queqiao and the NCLE experiment will end up paving the way for a full-scale radio observatory on the lunar farside, something astronomers have wanted for years.

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