The Week in Space and Physics: The Dark Side of the Moon
On the dark side of the Moon, the fourth flight of Starship, Hubble and Boeing's Starliner
Though the Moon waxes and wanes in our sky, shifting from new moon to full moon and back again, it always presents the same unchanging face to us. Like most heavenly bodies, the Moon does spin, yet it rotates at precisely the same rate as it revolves around the Earth: turning in such a way that one face is always pointing towards us, and the other is always facing away.
That second face - the one forever hidden to us - is known as the dark, or far, side of the Moon. Until 1959, when a Soviet spacecraft sent back images, it was utterly mysterious; a terra incognita that only the wonders of the space age could penetrate. Logically, of course, science reasoned that it might look much as the near face does, strewn with craters and marked with vast plains of ancient lava.
Yet the first images revealed a startling different view. The far side has no vast plains. It is instead a land of rugged mountains and deep craters. Both the Moon’s highest and lowest points lie on the far side, as do many of its tallest mountains. Placed side by side, the two faces of the Moon appear almost as two separate worlds; a striking contrast that is still not fully understood.
Despite the mystery, few spacecraft have visited the far side. Communications, of course, are hard to manage there. Radio waves cannot penetrate the mass of the Moon, and so a relay satellite must be used. Only in 2018 did one finally get put in place - Queqiao, sent by China. A year later Chang’e 4 touched down on the far side, becoming the first spacecraft ever to do so.
Now China has gone a step further. Last week Chang’e 6, a robotic probe, reached the far side of the Moon. It left behind a rover, Yidong Xiangji, and collected a sample of rocks from the surface. Chang’e 6 then took off - becoming the first probe to ever ascend from the far side - and will soon head back to Earth.
This was China’s second sample return mission. The first - Chang’e 5 - collected a similar collection of rocks from the Moon’s near side in 2020. Moon rocks have, of course, come back to Earth before - the Apollo astronauts collected thousands - but none have ever been taken from the far side.
Chinese researchers are no doubt eager to compare their two samples. The differences between them could reveal the origins of the Moon’s two sides, and help clarify why the far side - the dark side - looks so different to that familiar face so often seen in our sky.
Starship Flies Again
SpaceX’s Starship lifted off for the fourth time last Thursday. Like the previous three flights, this was a test flight, intended to prove and iterate the design of the mammoth super heavy booster and the spacefaring Starship. And, as before, the goals of the test were simple: lift-off, reach space, and see both the booster and the ship later splashdown in the ocean.
Although this had been the primary goal of all Starship tests so far, none of them had successfully achieved it. Flight number one came to an early end as the rocket spun out of control during the ascent. Flight two went better, with Starship reaching space before exploding. In flight three Starship made it all the way to re-entry, before tumbling and burning up in the atmosphere.
This time, however, Starship ticked almost all the boxes. The rocket ascended smoothly upwards, losing just one of its thirty-three engines on the way. The booster separated, fell back to Earth and then relit its engines to slow its descent towards the ocean. Starship continued on its way, reentered the atmosphere over the Indian Ocean and then - dramatically - survived all the way down. A final success came as the ship relit its engines and came to a somewhat controlled splashdown.
Though SpaceX can celebrate the flight, much work remains to be done. Indeed, some problems were obvious. Video footage showed parts of the booster on fire as it descended towards the sea. Starship itself suffered severe damage as it plunged through the atmosphere, and seemingly came close to disintegrating. Starship reentry, for sure, is not something SpaceX has perfected yet.
There are other concerns that Starship development is proceeding more slowly than SpaceX had hoped. Dear Moon - a project funded by Japanese billionaire Yusaku Maezawa - was supposed to send a crew of artists and youtubers around the Moon on Starship last year. That obviously didn’t happen. Maezawa, apparently unimpressed by the delays and seemingly unhappy with Elon Musk, decided to cancel the project instead of postponing it.
A bigger concern, however, is Artemis III. NASA wants to use Starship to carry astronauts to the lunar surface in late 2026. SpaceX’s original schedule proposed an orbital test flight in 2022, followed by longer tests in 2023 and a demonstration landing on the Moon in early 2024. None of these has yet happened - though Starship is capable of reaching orbit, if it tried to do so.
Despite the recent progress, Starship is unlikely to be ready in time for a landing in 2026. The sheer amount of work left to do, the number of tests needed, and the number of flights to fuel a lunar landing all but rule out an attempt by then. Starship may well carry astronauts to the Moon one day, but it certainly won’t do that in time for Artemis III.
The Future of Hubble
Of all the space telescopes, Hubble is perhaps the most loved. The telescope launched in 1990, lofted into orbit by the Space Shuttle Discovery. At first it seemed like a failure - the telescope’s mirror turned out to be flawed, and sharply limited the quality of its images. Fortunately Hubble was designed to be serviced by astronauts, and a repair was made a few years later.
Since then, Hubble has returned a stream of fantastic images of the universe. The James Webb may now outshine it, but the sheer versatility of Hubble - it can view the cosmos in far more wavelengths of light than the James Webb - means it still has plenty to offer. Yet Hubble is also getting old. The last servicing mission flew in 2009, and with the space shuttle then retired, no others were planned.
A few years ago, however, the billionaire Jared Isaacman proposed funding his own visit to the telescope. A crew could come along with him, he said, and carry out any servicing the telescope needed. All this would be done with SpaceX’s Dragon capsule, and would form part of his ambitious Polaris project.
After looking into the idea, however, NASA have now turned it down. The concept presented too many risks, they said, and could accidentally damage the telescope. Hubble is currently high enough to remain in orbit until at least the 2030s, and NASA thinks the telescope will keep working until then, even without further repairs.
Starliner Reaches the Space Station
Boeing’s Starliner capsule reached the International Space Station last week, bringing a crew of two American astronauts with it. The flight - the first to carry astronauts - marked an important milestone for the troubled capsule.
Starliner flew for the first time in 2019, in an uncrewed test flight that was supposed to prove the capsule was safe for astronauts to use. Yet the mission ended in failure after a software bug left Starliner in the wrong orbit, and so forced an early return to Earth. A second, more successful, test flight came in 2022.
Last week’s flight was not entirely without fault, however. Engineers found signs of a helium leak before lift-off, though they determined it did not present a major danger. Two more leaks were found in orbit, and problems with the capsule’s thrusters then delayed its arrival at the station. Still, the two astronauts did arrive safely. The test is not quite over, of course: Starliner still needs to bring them safely back to Earth, a feat it will attempt sometime in the next few weeks.
Nice summary of an eventful month.
I’d like to offer a couple points of clarification …
First, the far side of the Moon is referred to as “dark” only by fans of Pink Floyd and those unfamiliar with how lunar phases work. I do suppose one could make an argument that it used to be “dark” in the sense that Earthlings were absent the benefit of enlightened knowledge about what it was like prior to the arrival of lunar orbiting spacecraft. But, that may be a stretch.
Second, the Hubble’s mirror was not replaced (if that’s what you meant to say). Instead, an assembly of corrective optics was installed to give the various instruments a sharper image coming from the still flawed primary mirror.
Otherwise, another interesting article.