Author: Inara Pey

A lot of people laughed when China announced it planned to develop a launch vehicle with a reusable first stage that would, on its return to Earth, be caught by a net. Well, they’re not laughing any more.

On Friday, July 10th, a Long March 10B (CZ-10B) medium lift launch vehicle (MLLV) lifted-off from the Wenchang Commercial Space Launch Site, China’s first commercial spaceport on the type’s maiden flight. Roughly in the same class of vehicle as the SpaceX Falcon 9, the CZ-10B has a 16-total maximum payload capacity and is a derivative of the the CZ-10 design, specifically developed for the commercial space sector and for its first stage to be recovered.

This maiden flight not only tested the system for recovering the rocket’s first stage but confirmed the rocket’s ability to deliver payloads to orbit, which it did so successfully. The vehicle lifted-off at 04:14 UTC, climbing up through Max Q and to upper stage release altitude. Following separation, the booster stage then continued on an upwards ballistic trajectory before starting a fall back towards Earth, deploying a set of grid fins to maintain its vertical orientation and providing steering during the passive descent for an at-sea recovery.

Following a powered re-entry into the denser atmosphere – lessening the dynamic stresses on the booster – it dropped in an unpowered state to just over 1 km altitude, when the 7 YF-100K motors were relit and, under automated control, the booster steered towards the recovery vessel LingHang Zhe (“Navigator”) with its huge recovery gantry. Under the guidance of four LIDAR systems mounted on the gantry, the booster positioned itself over the middle of the gantry, and began a slow final descent, deploying four hooks on its upper end.

At the same time, the LIDAR system guided four arresting cables along the gantry so they enclosed the booster which was then commanded to shut down its engines. Doing so, it gently dropped the last couple of metres, the hooks catching the arresting cables, which acted alike shock absorbers, bringing the booster to a gentle stop before tensioning. Whilst not seen in the videos released of the landing, the gantry includes a circular restraining mount which can be rotated out, allowing the booster to be placed within it by the arresting cables, securing it for the voyage back to port.

Incidentally, if you’re wondering about the thick black smoke pouring out of the top of the booster as seen in the video below, it is believed that dumping excess RCS propellants out through valves in the top of the booster (designed to minimise shipboard crew exposure to toxic hypergolic propellants) resulted in a small fire in the booster’s interconnect bay.

If this all sounds mind-bogglingly crazy compared to putting landing legs on the booster and allowing it to land directly on the ship a-la SpaceX / Blue Origin, it actually isn’t. A direct landing system requires landing legs, shock absorbers, a deployment mechanism, etc., whilst the booster itself requires strengthening against the shocks and stress of landing. All of this makes the booster heavier, more complex and thus less payload-capable. It also means the structure of the booster has to be extensively checked for micro fractures, etc., and multiple landings take their toll. None of this is the case when the booster a captured like this. As a result, the booster can be simpler, lighter and lift heavier payloads. Hence why SpaceX discarded landing legs for Starship / Super Heavy.

Following the CZ-10B success some critiqued the Chinese system because any collision between a descending booster and the gantry / capture system could destroy the latter. However, the same is true for Starship / Super Heavy, only more so: it is easier to replace a damaged gantry system when the ship returns to port (or on land, if the Chinese also go on to use land-based captures) than have to completely rebuild an entire launch / return site).

One other interesting offshoot of this is that the CZ-10B first stage is nigh-on identical to the CZ-10 first stage (other than the latter not being reusable). Three of the CZ-10 first stages are to be used to initially power the full CZ-10 which it commences operations – much as three Falcon 9 first stages power the Falcon Heavy. Therefore, it is possible that has experience is gained with capture operations, the Chinese might also launch the CZ-10 using one or more recoverable CZ-10B first stages, thus lowering CZ-10 lunch costs somewhat.

 Asteroids, Collisions and Dust

The subject of asteroid impacts on Earth has come up numerous times in this column. While the risk of such an impact is – relatively speaking – small, it is far from non-existent. The 2013 Chelyabinsk meteor at 18 metres across, for example is in the size category of asteroids liable to strike Earth once every decade (ish). Then there is the Tunguska event of 1908. That’s thought to have been caused by a stony asteroid 50-60 metres across and devastated 2,150 square kilometres of forest. This kind of impact is believed to happen once every 1,000 years.

Both of these were air-burst events, the Chelyabinsk object exploding at an altitude of some 30km, and the Tunguska object at around 7km.

The latter came apart with an energy yield of 22.79 megatons. If such a blast were to occur over a city like New York, the thermal radius (the distance at which people exposed to the blast would receive at least third-degree burns) would be 112 km, whilst the 20psi blast radius (enough to demolish buildings and cause 100% fatalities among those caught by the shockwave) would be 21 km.

However, if the Tunguska object had been an iron-nickel asteroid rather than stony, things get a lot worse because the asteroid would be solid enough to impact Earth, causing a crater some 2.5 km in diameter. The energy yield from the impact would be around 59 megatons; the 20psi blast radius some 24.2 km; and the thermal radius 220 km, while estimated immediate fatalities would be in the 1-3 million range.

This is why decades have been devoted to identifying and tracking near-Earth asteroids in order to assess the threat of one striking Earth at some point in the future. Thus far, over 32,500 such objects have been catalogued, ranging in size from a few metres in diameter to over 1 km across (853), with over 10,500 around three times the size of the Tunguska object. While none has been identified as presenting a real threat of hitting Earth, they represent less than half of the estimated total number of potentially threatening NEAs.

Hence why, as well, the news that China is planning on joining the hunt to find more potentially dangerous NEAs has been welcomed. The announcement was made on June 30th, International Asteroid Day and was a little lean on details. However, based on recently-published papers coming out of China, it appears the broad plan is to establish a combined ground / space effort to hunt and track NEAs and add gathered the information to the growing international database on the subject.

The ground-based effort is to be a chain of large-aperture optical telescopes placed at advantageous high-altitude locations around the world where they can scan the skies continuously at night. In space, China is looking to launch an observatory to the Sun-Earth Lagrange L₁ position where it has the Sun behind it and so can much more effectively scan for NEAs both visually and in the infrared – the latter being the route the European Space Agency is taking with its planned NEOMIR (Near-Earth Object Mission in the Infrared), due to launch in the 2030s.

This point in space is important because many NEAs come at us “out of the Sun”, so we’re unable to see them until they are literally right on top of us – or worse, have zipped by without being seen, and we only spot them as they head off back around the Sun – so if one of that had hit Earth, we’d only have known about it after the bang (if at all).

In addition to the Sun-Earth Lagrange L₁ position, China has indicated it may also place an observatory in orbit around Venus and another in what is called a distant retrograde orbit around the Moon. Both of these positions would again allow near-continuous observation of the space around the Earth-Moon system.

Of course, identifying a potential threat is one thing; what to do about it is quite another – which is not to say we don’t have any ideas. If the threat is identified whilst it is far enough away (or when its current orbit will not result in a collision), then the solution could be to give it a short, sharp nudge so its trajectory and orbit changes sufficiently such that it will no longer strike Earth. This is the concept put to test in NASA’s 2021/2022 Double Asteroid Redirection Test (DART), which deflected one asteroid orbiting another by slamming a spacecraft into is at a precise angle and velocity.

For larger objects, a proximity blast from a nuclear warhead could achieve the same by vaporising a portion of the object’s surface and generating the thrust needed to divert it. If the object cannot be deflected, it could potentially be vaporised using a combination of kinetic impactor and nuclear warhead – the impactor driving the warhead deep into the object prior to detonation, leaving a cloud of dust and debris small enough none of it would survive re-entry into the atmosphere.

Or that has been the perceived thinking until now. Also at the International Asteroid Day astronomers from the University of Edinburgh presented a paper demonstrating how dust from an impact with an NEA – and more particularly “space dust” in general – is now posing a very real threat to our ever-increasing orbital infrastructure and our reliance upon it; a threat that has not really been considered until now.

As we’re all aware, the space around Earth is getting very crowded. The number of satellites in orbit, for example has risen from 1,500 just under 10 years ago to over 12,000 today – and that number is steadily increasing. On top of this, there are literally tonnes of human-made junk in orbit – decommissioned or failed satellites, parts of launch vehicles, debris from anti-satellite missile tests, even bits of equipment lost during spacewalks. All of this has given rise to fears of a Kessler Syndrome event: a single collision between, say, a lump of junk and a satellite starting a cascade of collisions between debris and satellites until much of that orbital infrastructure (potentially including the space stations) becomes a massive orbital cloud of debris that renders large part of the space above us unusable.

Hence why there are increasing efforts to try to clean-up the “junk”.  Unfortunately, most of these rely on shunting dead satellites and other large objects into the atmosphere to burn up – which leads to a whole other problem of atmospheric pollution I’ve previously covered (see here and here for example) and outside the scope of this piece.

However, in their paper the Edinburgh team points out that the dust created by something like an asteroid impact mission, or those that give rise to the annual series of meteor showers we witness each year  – such as the Perseids every July / August (the result of our passage through a cloud of debris left by the passage of comet Swift-Tuttle around the Sun once every 133 years), or the Geminids (the result of trails of dust almost constantly being thrown off by the asteroid 3200 Phaethon as it zips around the Sun) – is travelling at tens of kilometres per second. Just a single impact from one piece of this dust could be catastrophic for a satellite or space craft.

This certainly happened in 1993, when particles later identified as being from the dust cloud causing the Geminids struck Europe’s $1.2 billion Olympus 1 communications satellite, resulting in its loss. It is also possible (but unconfirmed) that the dust responsible for 2022’s coolant leak aboard Soyuz MS-22 may have come from the dust that generates the Geminids meteor shower.

The point here is, as the paper notes, that while many clouds of dust and particles are known, how we pass through them is variable; most of the time Earth tends to whisk through the outer limits of such clouds. But once every 2-3 decades orbital mechanics dictate that we pass far deeper through several of them over the course of a few years, experiencing far more spectacular meteor showers in our night skies.

One of those periods is due to start in 2028 and run through until 2034. It will be the first one we’ve experienced since the “orbital boom” in satellites in low and medium Earth orbit began – and right at the time we’re trying to get back to the Moon and when activities in orbit will be expanding with new commercial space stations, etc. The University of Edinburgh study suggests that just a 5% uptick in the volume of dust encountered during this period could be enough to trigger on or more Kessler Syndrome events sufficient to cause major damage to most communications, defence data, relay, GPS, and other satellites in relatively short order – and could even impact activities on the Moon or cislunar space. Or it may not; the point is, we simply don’t know.

Another problem here as well is that dust cannot be deflected, so we need spacecraft and satellites better able to deal with it. Thus, the Edinburgh study calls for the formation of two international bodies: the International Commission on Space Infrastructure Resilience (ICSIR), and WARDEN (Warning-network for Asset Resilience from Dusts, Ejecta, and NEOs).

ICSIR, an independent group of experts would investigate the aforementioned risks, and work to integrate our space-based infrastructure into planetary defence systems and methodologies, and establish a managing framework to deal with the treat in cooperation with other planetary defence initiatives.

WARDEN, meanwhile, would use ICSIR’s finding to work with spacecraft and satellite manufacturers to try to mitigate as many of these threats as possible through improved engineering and hardware resilience.

It’s not clear if the recommendations of the report will be taken up directly, but it does offer a startling reality check on the continuing efforts to just lob everything into orbit to solve whatever the problem of the day might be (yes, I’m looking at you, “space data centre” enthusiasts).