On November 24th, 2021, NASA launched the Double Asteroid Redirection Test (DART) mission, a vehicle aimed at testing a method of planetary defence against near-Earth objects (NEOs) the pose a real risk of impact.
I’ve covered the risk we face from Earth-crossing NEOs – asteroids and cometary’s fragments that routinely zoom across or graze the Earth’s orbit as they follow their own paths around the Sun. We are currently tracking some 8,000 of these objects to assess the risk of one of them colliding with Earth at some point in the future. This is important, because it is estimated a significant impact can occur roughly every 2,000 years, and we currently don’t have any proven methods of mitigating the threat should it be realised. And that is what DART is all about: demonstrating a potential means of diverting an incoming asteroid threat.
Developed as a joint project between NASA and the Johns Hopkins Applied Physics Laboratory (APL), DART is specifically designed to deflect an asteroid purely through its kinetic energy; or to put it another way, by slamming into it, and without breaking it up. Both are important, because by simply slowing an Earth-crossing NEO along its orbit, we give time for Earth to get out of its way; then, by not causing it to break, then we avoid the risk of it becoming a hail of shotgun pellets striking Earth at some point further into the future.
The target for the mission is a binary asteroid 65803 Didymos (Greek for “twin”), comprising a primary asteroid approximately 780 metres across, and a smaller companion called Dimorphos (Greek: “two forms”) caught in a retrograde orbit around it, with both orbiting the Sun every 2 years 1 month, periodically passing relatively close to Earths, as well as periodically grazing that of Mars.
Discovered in 1996 by the Spacewatch sky survey the pair has been categorised as being potentially hazardous at some point in the future. At some 160m across, Dimorphos is in the broad category of size for many of the Earth-crossing objects we have so far located and are tracking, making it an ideal target.
DART actually started as a dual mission in cooperation with the European Space Agency (ESA) called AIDA – Asteroid Impact & Deflection Assessment. This would have seen ESA launch a mission called AIM in December 2020 to rendezvous with Didymos and enter orbit around it in order to study its composition and that of Dimorphos, and to also be in position to observe DART’s arrival in September 2022 and its impact with the smaller asteroid.
However, AIM was ultimately cancelled, leaving NASA to go ahead with DART. To reduce costs, NASA initially looked to make it a secondary payload launch on a commercial rocket. But it was ultimately decided to use a dedicated Falcon 9 launch vehicle for the mission, allowing it to make its September 2022 rendezvous with Dimorphos.
In order to impact the asteroid at a speed sufficient to affect its velocity, DART needs to be under propulsive power. It therefore uses the NEXT ion thruster, a type of solar electric propulsion that will propel it into Dimorphos at a speed of 6.6 km/s – which it is hoped will change the velocity of the asteroid by 0.4 millimetres a second. This may not sound a lot, but in the case of hitting an actual threat whilst it is far enough away from Earth, it is enough to ensure it misses the planet when it crosses our orbit.
This motor is powered by a deployable solar array system first deployed to the International Space Station (ISS). However, what is most interesting about these solar panels is that a portion of them is configured to demonstrate Transformational Solar Array technology that can produce as much as three times more power than current solar array technology and so could be revolutionary should it reach commercial production.
Accompanying DART is Light Italian CubeSat for Imaging of Asteroids (LICIACube), a cubesat developed by the Italian Space Agency, and which will separate from DART 10 days before impact to acquire images of the impact and ejecta as it drifts past the asteroid. To do this, LICIA Cube will use a pair of cameras dubbed LUKE and LEIA.
As the cubesat is unable to orbit Didymos to continue observations, ESA is developing a follow-up mission called Hera, Comprising a primary vehicle bearing the mission’s name, and two cubesats, Milani and Juventas, this mission will launch in 2024, and arrive at the asteroids in 2027, 5 years after DART’s impact, to complete a detailed assessment of the outcome of that mission.
ISS Gets a New Module
On November 26th, 2021, a new Russian module arrived at the International Space Station (ISS).
The Prichal, or “Pier,” module had been launched by a Soyuz 2.1b rocket out of the Baikonur Cosmodrome in Kazakhstan two days earlier. Mounted on a modified Progress cargo vehicle, the module was successfully mated with the Nauka module which itself only arrived at the station in July, at 15:19 UTC.
The four-tonne spherical module has a total of six docking ports, one of which is used to connect it with Nauka, leaving five for other vehicles. However, when first conceived, the module was also intended to be a node for connecting future Russian modules.
But since that time, the Russian space agency, Roscosmos, has abandoned plans to support the ISS with additional modules. Instead, with relations with the west continuing to cool and the ongoing rise in nationalism in Russia, the agency has indicated it plans to orbit its own space station. This being the case, Prichal is viewed as the final element in the Russian segment of ISS, and potentially the first of the new station.
Unlike the arrival of Nauka in July, Prichal managed to dock with the ISS without the additional “excitement” of any thruster mis-firings. Now, the Progress carrier vehicle will remain attached to the module through until December 21st, allowing time for the Russian cosmonauts on the station to carry out a spacewalk to attach Prichal to the station’s power systems. Once it has been detached, the Progress vehicle will be set on a path to burn-up in the Earth’s atmosphere.
As well as expending the docking facilities at the ISS, Prichal delivered some 2.2 tonnes of cargo and supplies to the station. The module will formally commence operations in its primary role in March 2022 with the arrival Soyuz MS-21.
JWST Suffers “Incident”, Launch Delayed
Having arrived at Europe’s Spaceport near Kourou in French Guiana on October 12th, 2021 (see: Space Sunday: Transporting a Telescope, NS-18, LUCY and China, the James Webb Space Telescope has been undergoing check-outs and preparations for launch.
However, on November 11th, 2021, after being integrated with the upper stage of its Ariane 5 launch vehicle, the telescope was lifted up to be mounted on the core stage of the launch vehicle and its boosters. However, during the procedure, a clamp band that secures the telescope to the Launch Vehicle Adapter (LVA) – the element that physically connects the telescope to the rocket – released unexpectedly, causing vibrations throughout the telescope.
Given the sensitive nature of the entire observatory and its instruments, the planned December 18th launch of the telescope was immediately pushed back by four days to allow time for the observatory to be completely checked for possible damage, and tests carried out to ensure the telescope’s instruments were unharmed.
Following the tests – which remain unspecified – verified JWST appeared to have not suffered any ill, NASA confirmed the launch will remain set for December 22nd, clearing the way for the telescope to start receiving the propellants it will need to help maintain its orientation and stability when it reaches its L2 halo orbit. This is another critical aspect of the launch preparations that will take 10 days to complete.
In February 2017, I wrote about the discovery of a 7-planet system of Earth-sized planets orbiting an ultra-cool red dwarf star in the constellation Aquarius. Since its discovery (in 2016), the system has been of particular interest for study for a number of reasons: the sheer number of planets within it, their similarity to Earth in terms of size, their comparative nearest to our own system (around 39 light years) and the fact that three of them are within the habitable zone of their parent star.
The fact that all of the planets are in a Laplacian orbital resonance, with the durations of their orbits having ratios of 8:5, 5:3, 3:2, 3:2, 4:3, and 3:2 between each planet pair, means that the planets collectively exert an increased pull on their parent star, making changes in the star more easily recognisable. This in turn makes studying the system somewhat easier.
The near-perfect harmony between the seven planets offers a way by which scientists might be able to determine how long the seven planets experienced bombardment by materials left-over following by their formation. This is important because such bombardment – also referred to as late accretion, can be an important source of water and volatile elements that can foster life on a planet.
Deciphering the impact history of our own world is relatively easy: we can measure certain types of elements and compare them with meteorites to determine how and when they may have been deposited and the role that played in the planet’s development. We can also, to a point, do the same with planets like Mars. However, it’s not something we can apply to planets tens of light years-away.
However, all planets form within a disk within protoplanetary disks of gas and dust around newly formed stars. These disks only last a few million years, and in the case of chains of planets like the TRAPPIST-1 system, astronomers tend to believe they form as the planets move closer to their parent star and then moving into resonance with one another fairly early in the system’s history and before all of the protoplanetary disk vanishes.
Using computer modelling, a team of researchers have been able to determine the time in which the planets likely formed, and the upper constraints on how long any bombardment period may mat have lasted. In short, and allowing for other factors, such at the age of their star, the likely available mass of material within any protoplanetary disk, etc., the team concluded that TRAPPIST-1’s planets formed fast, in about one-tenth the time it took Earth to form, and likely rapidly migrated and reached paired resonance.
This means they may never have experienced a late accretion period, and the lack of heavy bombardment likely limited the elements reaching their surfaces either through impact or as a result of out-gassing from impacts and resultant volcanism, all of which have major implications for their habitability and atmospheric development.
In particular, it seems likely that early on, the planets probably had hydrogen-rich atmospheres – but given the volatility of their parent star, these atmospheres were probably extremely vulnerable to being stripped away by the star’s solar winds and flares. The lack of volatile release also means it may have been hard for water to form on any of the TRAPPIST planets, further reducing the potential for like to get started.
But, the international team behind the research also acknowledge that it is likely that substantial amounts of water vapour were present in the disk that formed the planets, and these were likely locked up deep inside them. They further acknowledge they are working with “large” margins of error, so it is entirely possible that very early on in their existence, some of the TRAPPIST-1 planets may well have released that water as a result of early bombardment, and that water vapour may have both reshaped their atmospheres sufficiently to allow liquid water to form for a time on their surfaces.
Obviously, there is still the question of whether or not the planets developed dense enough atmospheres to survive the more violet extreme and outbursts of their parent star, but the study does offer-up another reason why the TRAPPIST-1 system should be a prime target for study by the likes of the James Webb Space Telescope.