Thursday, October 29, 2020

Behind the scenes on Artemis, Nasa’s next Moon mission

Behind the scenes on Artemis, Nasa’s next Moon mission

In 2024, the first female astronaut will set foot on the surface of the Moon, 55 years after Neil Armstrong took his iconic one small step. Nasa’s Artemis mission, named after the Greek goddess, involves designing new space suits, building a new spacecraft and launching with the most powerful rocket in the world. The first mission, Artemis I, is planned for launch in 2021 to complete a flyby of the Moon with no crew. In 2023, Artemis II will send a crew on a flyby before the Artemis III mission in 2024, in which two astronauts – one woman and one man – will land on the lunar surface.

Ensuring the spacecraft is ready for the journey is a lengthy process, involving months of testing, much of which was completed in late 2019 and early 2020 at Nasa’s Plum Brook Station in Ohio. “We ensure all systems on the spacecraft will work in the extreme environments of space,” says Nicole Smith, chief of Exploration Systems Office at the Nasa Glenn Research Center.

In November 2019, the Orion spacecraft, which will be used on the Artemis I mission, is flown from Florida to Mansfield Lahm Airport in Ohio, before heading to Plum Brook Station. The crew and service modules travel on Nasa’s Super Guppy, a plane 43.8 metres long and capable of carrying more than 20 tonnes, which has been used to transport sections of the International Space Station. The plane was first used in 1965, when Nasa wanted to transport large rocket parts during the space race and needed them to travel faster than was possible by boat.

After landing in Ohio, the nose of the Super Guppy is opened to offload the spacecraft to the cargo bay. The crew module and service module, with a combined weight of 25 tonnes, are the heaviest payload ever transported in the plane – Nasa had to modify the aircraft to make sure it could accommodate the weight. Preparations for the flight started in 2014 and involved building a horizontal transporter fixture and adapting the plane internally to ensure the spacecraft would fit. Four Orion spacecraft have been built to date, but Nasa plans on commissioning up to 12 for future Artemis missions.

The spacecraft is driven 66km from the airport to Nasa’s Plum Brook Station, where it will spend four months undergoing testing in the Space Environments Complex (SEC). The facility is home to the largest vacuum chamber in the world, used to simulate the conditions of space. Called the Space Power Facility (SPF), the chamber has a volume of 22,653 square metres and is capable of reaching 0.000004 torr. Compared to normal atmospheric pressure, which is 760 torr, this is the closest a spacecraft can get to the vacuum of space outside of experiencing the real thing.

The vacuum chamber is cylindrical with a domed top, and has walls of aluminium 30.5 metres in diameter and 37.2 metres high. The first tests Orion undergoes are thermal vacuum tests: it is flushed with nitrogen and all the air removed, then exposed to very hot and very cold temperatures. Next, it is put through electromagnetic testing. Radio waves are used to check spacecraft systems will not interfere with each other, since each bit of kit creates its own electromagnetic field, and to make sure external radio sources do not affect the equipment.

The cage-like structure in this image is the Heat Flux System, used for thermal vacuum tests. “The bars in the cage are all heater bars,” says Smith, “which allows us to do a lot of types of tests.” The bars can separately heat different parts of the spacecraft to simulate travelling towards or away from the Sun. In total, Orion spent 47 days inside the chamber cycling from about -156°C to 149°C – close to but not quite the extreme temperatures it will experience in space.

In 2018, a test version of the Orion crew module, shown here, was placed in the SEC’s Reverberant Acoustic Test Facility. The largest facility of its kind, it exposes spacecraft to the kind of sound volumes they will experience during launch and ascent. The reverberant acoustic chamber has concrete walls 1.8 metres thick and is designed to create as much noise as possible, producing up to 163 dB within the 2,860 m3 chamber. While tests are going on, the room is filled with nitrogen to minimise any absorption of sound.

The horn wall in the Reverberant Acoustic Test Facility has 36 horns of various sizes, each capable of producing different frequencies. The metallic horns are hydraulic, while the white ones are electrically powered. Once the Artemis I crew module splashes down after its mission, it will be brought back to the facility in Ohio for more acoustic tests. “They’ll fish it out of the ocean, refurbish it a little and clean it up,” says Smith. “Then it’ll be back here in a couple of years.” Nasa aims to reuse the crew modules used on most of the missions at least once, starting with the Artemis II module.

After four months of testing, the Orion spacecraft is packed up and ready to send back to the Kennedy Space Center in Florida, where it will go through final processing and preparation before its 2021 launch. During the Artemis I mission, Orion will spend three weeks in space, travelling past the Moon before entering its orbit and finally returning to Earth, splashing down in the Pacific Ocean. While in space, it will also deploy 13 cubesats to study the Moon. This will mark the first step in getting the first female astronaut onto the surface of our natural satellite.

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