Well, this is interesting: NASA launches a spacecraft to explore asteroids on Artemis I, the first test flight that has pushed it back to the moon.
The probe is called the Near-Earth Asteroid, or NEA Scout, and you get this: it uses a solar sail as propulsion, the first interplanetary mission to do so.
Okay, first: Artemis I is a complete test flight of the space launch system (or SLS) and the Orion capsule. It will be unmanned and will send Orion into orbit around the Moon for a week or so before returning to Earth. It is scheduled to launch this November, but we’ll see; I am NOT a fan of SLS and, given the large number of delays, I doubt it will get underway this year. But it is likely to be released next year if not this one.
Orion is mounted on top of the rocket using an adapter ring, and there are 13 smaller missions that will be mounted inside and deployed from the ring, including NEA Scout.
Scout is a CubeSat, a small spaceship. The CubeSats are standardized boxes of 10 centimeters (!!) on each side, small enough to fit in the palm of your hand. They can also be put together to make a larger configuration; Scouts are six of them in a flat rectangular prism of 10 x 20 x 30 cm, more or less the size of a large shoe box.
Don’t let size fool you. It uses four telescopic aluminum bars that will extend up to 6.8 meters in length (the height of a two-story house), which will deploy a solar candle made of a kind of elegant plastic (aluminized polyimide) that is extremely light because it is only an impressive 2.5 microns thick. For comparison, a typical human hair is 100 microns thick. Then, go.
Once unfurled, the sail will use sunlight as propulsion. While the photons don’t have too much, they do have momentum, so when they hit the candle they give it a kick. That’s why the sail is so thin but big (85 square feet) and the spaceship small and light; the lower the mass the greater the acceleration. While the acceleration is incredibly low, it is continuous. This adds up, so even though it doesn’t move quickly at first, you can increase the speed over weeks and months.
The target of asteroids has not yet been defined, because the launch date is not safe and everything moves in space. After launch, it will be placed in orbit around the Sun (what is called a heliocentric orbit). After that, Scout will use a cold gas thruster to position himself, unfurl the sail, and then leave.
Solar sails have already been tested in orbit and work. In fact, when The Planetary Society tested its solar candle, I wrote about how it all works, so go read this article for more information on photon momentum, candles, and CubeSats.
The plan is for Scout to match speeds with an asteroid measuring 100 meters, with the aim of achieving images with a resolution of 10 to 50 centimeters. We have never seen asteroids so close, but they are large enough to cause a lot of damage if they affect our planet. It is important to know more. They are likely to be piles of rubble, such as Bennu and Ryugu, which are 500 and 900 meters in size, meaning a mixture of very fragile rocks joined by their own gravity. Deflecting an asteroid of this type is complicated and we need to understand them better in case we ever have to take one out.
The other dozen secondary spaceships that will be launched at Artemis also seem quite interesting to me. Several will go into orbit around the Moon; two will look for water ice in deep, dark craters, while another will map for hydrogen (which, really, is also looking for water ice). The Japanese space agency JAXA will also have a lander on board to measure radiation on the lunar surface, a good idea as people will live there someday.
As for the main mission to the Moon, if all goes according to plan, Artemis I will prepare the way for the sequel, Artemis II, a manned mission that will perform an overflight of the Moon in what is called a trajectory free return. We will descend low enough above the lunar surface (approximately 7,500 km) so that the gravity of the Moon will return them to Earth without them having to burn the engine; that way, if something goes wrong, they will at least go home. . They will go into a high orbit around our planet and then return to Earth to touch the Pacific Ocean. The nominal schedule for the mission is 10 days and is scheduled to launch in June 2023 (though again, we’ll see).
All of this is quite ambitious, although of course achievable or NASA would not have carried out these missions. The overall design of the Artemis to Return to the Moon project has changed several times and the initial 2024 deadline to put human boots on the surface was arbitrary and dangerous, and clearly made for political purposes. This made the architecture of the project (the hardware needed to place and return people to the moon safely) difficult to pinpoint, especially with SLS never flying and Congress controlling the budget. Honestly, the architecture is not yet nailed and contracts are still being made. I find it a bit worrisome, given that it is supposed to be a sustainable mission. Such a thing cannot be rushed.
Again, we’ll see. At present, the scientific aspects of this mission, at least, seem pretty cool, so I’m looking forward, above all, to see up close an asteroid on the football field. It will be amazing.