Space Sunday: ups and downs, and returns

A rendering of Starship prototype SN8 in “belly flop” mode, returning to Earth after an ascent to 15 km and using the fore and aft flaps to steady itself like a skydiver uses their arms and legs. Credit: Bart Caldwell (aka Neopork)

It had been anticipated that mid-November would see the 15km flight of  the SpaceX Starship prototype SN8.  As I’d reported last month, that vehicle had completed its initial static fire tests before going on to be fully stacked with the intermediate ring and forward nose cone with aerodynamic canards.

Speculation had been that the test flight could come around the time of the SpaceX / NASA Crew-1 mission for Crew Dragon to the International Space Station which lifted-off from Kennedy Space Centre on Sunday November 15th (see: Space Sunday: a Dragon, a telescope and a heavenly princess). However, a final static fire test of the three Raptor engines during the week leading up to the possible launch window saw an issue occur, prompting SpaceX to place all launch plans on hold until the issue had been investigated and resolved.

The was done during the week following the 15th, and SpaceX has set the first part of the week commencing Monday, November 23rd as the target time frame for that static fire test, which eventually came on Tuesday, November 24th, when all of the vehicles fuel tanks – main and “header” tanks (the latter required to provide fuel to the engines during descent) – pressured prior to a 3-second and successful simultaneous firing of all three main engines.

The moment of ignition: with flaps folded back, Starship prototype SN8 fires its three Raptor engines in a pre-flight static fire test. Credit: Mary (aka BocaChicaGal)

Currently, documents filed with the Federal Aviation Authority (FAA) show that SpaceX have requested further road closures around their Boca Chica, Texa, test facility starting on Monday, November 30th –  with Elon Musk indicating that this is likely to be the launch period for the vehicle.

The test flight itself is intended to test three core aspects of the vehicle’s flight envelope:

  • Powered ascent to altitude.
  • Controlled “belly flop” decent whilst horizontal, utilising the fore and aft flps to maintain stability and rate of descent.
  • Orientation to vertical during the final 100 metres or so, and descent to a tail-first landing under engine propulsion.

The flight comes with a high degree of risk – nothing quite like it has ever been attempted before – and SpaceX are anticipating only around a 33% chance of success, and that SN8 will in fact be lost in what they euphemistically refer to as an “unscheduled disassembly of the vehicle”.

However, Starship prototype SN9 is almost ready to start ground tests, and SN10 is following up behind it, meaning that if SN8 is lost, flight testing shouldn’t suffer too much of an interruption, and if the initial 15 km flight is successful, then SN9 and SN10 will be available to extend the testing programme such as flying to higher altitudes and / or flying with a full fuel load – SN8 will fly with its tanks carrying only the fuel to get to 15 km and then make a (hopefully) safe return and landing.

At the same time as work is continuing on the starship prototypes, SpaceX has also been engaged on the development of the test launch platform for the Super Heavy Booster and the assembly of components for what will be the first of these boosters, called simply BN1. Also appearing at the site is a mock-up of a section of the “lunar starship”, the vehicle SpaceX has put forward to help NASA in its plans to return humans to the Moon.

The SpaceX Boca Chica vehicle assembly area, complete with the new High Bay for stack the Super Heavy booster (right) and various vehicles and vehicle components. Credit RGV Aerial Photography

In terms of the Super Heavy booster, SpaceX appear to be reconsidering the idea of trying to bring such a massive beast back to Earth to land directly on the launch platform. While this would undoubtedly allow for a faster turn-around of the vehicle between launches, it also requires a high degree of pin-point accuracy on landing, and opens the launch mount to the risk of damage should any go awry with a returning booster. In a recent tweet on the subject, Musk indicated that the initial Super Heavy booster flights will aim to land the vehicles on the concrete apron alongside of the Boca Chica launch mount.

But  it is not all good news for SpaceX, as the company has been informed it must undergo a new FAA environmental  review and re-licensing specifically for the launch of the Super Heavy vehicles.

This is because at the time the original environment review took place in 2014, the license granted was for test flights of the Falcon 9 and Falcon Heavy, not the Starship or Super Heavy. The FAA allowed flight testing of the former to occur at the site, as it was deemed to pose no greater impact than flight testing either of the booster systems. However, with some 30 Raptor rocket motors powering it, the super Heavy is a significantly different proposition, particularly as SpaceX now intend to use Boca Chica not just as their test facility, but an operational launch facility – a move which has angered local environmental groups.

They went from proposing a few launches per year of an already field-tested rocket to ongoing experimentation of untested technology without doing the studies that would ensure environmental protection and public safety and without giving the local community a chance to have a say.

– Jim Chapman, president of Friends of the Wildlife Corridor

This has resulted in significant pressure on the FAA to carry out a new full review, called an Environmental Impact Statement (EIS), which could take up to two years to complete (from initial assessment through to drafting the report to debate and final report). Currently, it is not clear what impact this will have on the company’s plans for Super Heavy test flights.

Hyabusa2 Almost Home

Japan’s Hyabusa2 is approaching Earth as it nears the end of its mission to return samples from asteroid 162173 Ryugu.

Launched in 2014, the spacecraft into an extended Earth orbit that allowed it to use a gravity assist as it swung by Earth in 2015 to push itself out to the asteroid, which it reached in 2018. Once there, it commenced an extensive study of the asteroid in an ambitious mission that included deploying four mini-rovers – Rover-1A (Hibou), Rover 1-B (Owl) and Rover-2, all developed by Japan, together with the European / German MASCOT – to the surface of the asteroid, allowing them to gather further data on about it.

An artist’s impression of Hyabusa2 under thrust from its ion engines, en route to Ryugu. The sample capture arm can be seen extended beneath the space craft Credit: JAXA

Originally, Hyabusa2 was to collect three samples sets from Ryugu, two of which would comprise surface material (regolith). However, the rovers revealed that the asteroid’s surface to be almost devoid of the dust and material that makes up regolith, and so the sampling mission was postponed until 2019, allowing the science teams to identify where some surface material could be collected, allowing one of the surface sampling operations to be completed in February 2019, the second being cancelled.

Instead, the mission moved to gathering a sub-surface sample. decision was taken to move to the sub-surface sample recovery operation. This took place in April 2019, when Hyabusa2 deployed a free-flying “gun” and camera system some 500 metres above the surface of the asteroid, before backing off to a safe distance.  The “gun” was then fired remotely, propelling a 2.5 kg explosive charge into Ryugu, creating a new 10-metre diameter crater in the surface, to expose subsurface material, which Hyabusa2 was able to descend and collect once the dust and debris from the impact had eventually selected.

A photograph taken by Hyabusa2 of its own shadow of Ryugu, captured in February 2019 during the first sample gathering operation. Credit: JAXA

The vehicle started on its way back to other a year ago, and will fly past Earth on December 6th. As it does so, it will eject a capsule containing the samples that will will enter the atmosphere to make a parachute descent and land in southern Australia. To help with recovery of the 40-cm diameter capsule, the Japanese space agency has set-up an array of satellite dishes around the intended landing site in the hope that they will pick up radio signals from the incoming capsule, allowing them to track it down to the ground and triangulate the precise point of impact.

Once recovered, the samples will be subjected to extensive analysis  in an attempt to answer multiple questions – including whether asteroids like Ryugu may have deposited minerals essential to kick-starting life here on Earth. However, the return of the sample capsule is not the end of Hyabusa2’s potential. Given the vehicle still has just under half of its propellant left, it is liable to be tasked with rendezvous and studying at least one of a number of potential targets, with the first – asteroid (98943) 2001 CC – possibly occurring in 2026.

Rocket Lab Achieve At-Sea Booster Recovery

SpaceX aren’t alone in pursuing launch vehicle reusability. Rocket Lab, the New Zealand / US commercial launch developer I’ve previously written about (see: Space Sunday: 3D printed rockets; pi for a planet and solar cycles) is also seeking to reduce costs by recovering and reusing the first stage of is small satellite and payload launcher, the Electron.

There are significant issues in trying to do this: most notably the fact that the Electron is a small rocket, and really doesn’t have the capability to make a controlled descent and landing in the manner of the SpaceX Falcon 9. Instead, Rocket Lab have come up with an approach that is not unfamiliar to space-related activities: plucking the booster out of mid-air using a helicopter.

The approach, referred to as mid-air retrieval, and within space flight, it’s a technique that dates back to the 1960s and the US Corona strategic reconnaissance satellite programme (the start of America’s Keyhole (KH) programme) that would see orbiting satellites drop their exposed film cassettes back to Earth return film cassettes back to Earth in special re-entry capsules that would be caught in mid-air by an aeroplane snagging the lines from their decent parachutes.

Rocket Lab first tested the idea in a simple drop test back in April 2020, when a helicopter lifted the first stage of an Electron to altitude before dropping it to allow the parachute system to deploy. A second helicopter then manoeuvred over the descending booster and snagged the cable between the booster’s drogue and main parachutes using a grapple suspended from underneath it.

On November 19th, 2020 (November 20th local time), Rocket Lab took the testing a stage further – recovering the first stage of an electron used in an actual launch. For this test, the helicopter capture was not used, but rather, recovery was made at sea, following a successful splashdown for the booster – splashdown and at-sea recovery being a potential back-up to  the airborne recovery.

The launch, carrying a small satellite mission called – appropriately enough, Return to Sender -, took place from rocket Lab’s  Launch Complex 1 on New Zealand’s Mahia Peninsula. After separating from the second stage, the booster used small manoeuvring  jets to reorient itself to an upright position, allowing the drogue parachute to deploy, acting as an initial brake to bring the speed of descent down to a point where the main ‘chute could deploy, with splashdown in what was a relatively rough sea with 2m swells some 650 km off the coast of the launch site.

The Electron booster, post-splashdown, as seen by one of the recovery boats deployed to assist in getting the booster onto the recovery ship. Credit: Rocket Lab

Despite the rough waters, the stage remained afloat and the recovery boat was able to come alongside and secure it before transfer to the recovery ship, which then encountered 5m swells on its return to port, experiencing a degree of deck damage, although the booster appears to have survived the trip.

The booster – which will not be re-flown – will be subject to extensive analysis with a view to determining if improvements  / changes need to be made to things like the heat shield protection. However, components of the booster will, after analysis, be used on other Electron vehicles.