Space Sunday: rockets, moons, leaks and a ring

The moment of ignition: 31 Raptor motors ignite: Booster 7 during its full static fire test, February 9th, 2023. Credit: SpaceX

SpaceX has completed the largest static fire test for this Starship / Super Heavy launch system, with the 70-metre tall Booster 7 – expected to be part of the first orbital launch attempt – completing a “full duration” 5-7-second test of 31 of its 33 Raptor 2 engines.

The test was made on Thursday, February 9th, amidst on-going work at the orbital launch facilities at the company’s Boca Chica, Texas Starbase site. It had been intended to be full 33-engine test, but one engine was “turned off” during a pause in the countdown at the T -40 second mark, presumably due to an issue being detected, and a second automatically shut down at, or immediately following, ignition.

Even so, the burn was enough for the SpaceX CEO to proclaim the 31 firing engines developed sufficient thrust that, if sustained throughout an 8-minute ascent, it would be enough for Super Heavy to push a fully laden Starship to an altitude where it could reach orbit under the thrust of its six engines.

Ignition came at 21:13:53 UTC, after a partial filling of the booster’s liquid methane and liquid oxygen tanks – Starship 24 had already been destacked from the booster earlier in the month, leaving just the booster on the launch table. Everything appeared to go well, with SpaceX afterwards reporting the engines reached a peak thrust of 7,900 tonnes, or almost twice that generated by the Space Launch System Block 1/1A launcher, and 3,000 tonnes more than the Block 2 SLS cargo launcher.

However, such comparisons need to be put into context: Super Heavy must lift 1200+ tonnes of Starship to low-earth orbit (LEO), carrying 100 tonnes of cargo. SLS is already capable of lifting 95 tonnes of payload to LEO if required, which will increase to 105 tonnes and then 130 tonnes. It is also capable of delivering 27 tonnes to cislunar space, which will increase up to 46 tonnes. The flipside is that Starship and its booster are fully reusable, lowering launch costs; SLS is not. Also, if the booster is not re-used, they Starship could in theory life up to 250 tonnes to LEO; conversely, SLS can reach cislunar space, whereas Starship cannot, not without a complex series of on-orbit refuelling operations.

The test came after extensive work had been carried out at the launch facility after the first two Super Heavy static fire tests (with 7 and 14 Raptor motors respectively) literally stripped the concrete from the base of the launch stand, peppering the launch mount and its surroundings with high velocity cement debris and necessitating extensive repairs to the site.

The problem was one of basic engineering (and frankly, something SpaceX should have considered): the launch table legs and apron underneath the rocket are coated in concrete. A key ingredient of concrete is water, some of which is retained in the concrete as pockets of moisture. Heat concrete to 600°C or more, that moisture flash vaporises into expanding gases, causing the concrete to violently explode.

As I’ve previously noted, this risk is usually negated by the inclusion of a water deluge system which delivers thousands of litres of water to a launch facility, serving a dual purpose: it both absorbs the enormous heat generated by multiple rocket motors by flashing into stream by the force of that exhaust, and it also absorbs the sound waves generated by the motors, further preventing that sound being deflected back up against the rocket and potentially damaging it at launch.

Following the 14-engine test, SpaceX replaced the concrete at the launch facilities with a type designed to withstand very high temperatures. At the time of writing, it is not clear how well this mix withstood the engine test, however the test came at a time when SpaceX is – belatedly – attempting to install a water deluge system to work alongside the existing (and minimal) sound suppression system already part of the launch table.

Tanks for a water deluge system arrive at Starbase Boca Chica via barge. Credit: RGV Aerial Photography
Many – including the SpaceX CEO – are proclaiming the way is now clear for an orbital launch attempt to be made in March. However, this actually depends on a number of factors – the most key of which is whether or not the FAA is satisfied that SpaceX has done / is doing enough to ensure its compliance with all 75 remedial actions specified in its Programmatic Environmental Assessment (PEA).

NASA Tests Upgraded RS-25 Motor

The SpaceX static fire test overshadowed NASA’s test of its updated RS-25 engine for the Space Launch System.

The initial four SLS launches utilise a total of 16 refurbished RS-25 motors originally used with the space shuttle system and referenced as the RS-25D. However, beyond Artemis 4, NASA will be switching to a version of the RS-25 which has been extensively updated. Called the RS-25E, it will deliver 30% more thrust; allowing SLS achieve the upper end of its payload capabilities noted above.

The test, which took place at NASA’s Stennis Space Centre in Mississippi, saw a test stand mounted RS-25E motor fire at 111% of its rated thrust for a total of 8.5 minutes – the amount of time the engines would be used in an actual launch.

A single RS-25E under 1!1% of rated thrust during testing at Stennis Space Centre. The great cloud to the left of the test stand is, in part, steam generated from the engine exhaust striking water from the deluge system Credit: NASA

The RS-25E will commence operations with the Artemis 5 mission in 2028. They will operate alongside the new Exploration Upper Stage (EUS) which will also help raise the SLS system’s performance. EUS itself will entire service with Artemis 4.

Image of the Week

The image below is a computer-generated top-down view of Jupiter and the orbits of its (currently) 92 moons. At the centre of the image is Jupiter and (purple) the orbits of its four most famous Galilean moons – Io, Europa, Ganymede and Callisto. Beyond them, predominantly shown in red, are the remaining 88 moons.

A computer model of the moons of Jupiter in their orbits, with the planet at the centre, as seen from overhead. Credit: Scott Sheppard

Until recently, Saturn held the record for the greatest number of moons (82), the majority of which (43) have been discovered by a team led by astronomer Scott Sheppard. However, Sheppard’s team have also been busy over the years seeking moons orbiting Jupiter – racking up and impressive 70, including the most recent batch of 12 which handed the moon record back to the largest planet in the solar system.

The newest moons were discovered over a period of observations by Sheppard and his team using a number of observatories around the world across 2021 and 2022. They range in size from 1 to 3.2 km across. Most have very large orbits, with nine having periods of more than 550 days. None have been named as yet, as all are awaiting further independent verification.

“Andrei… You’ve had Another Coolant leak?”*

A second coolant leak involving a Russian space vehicle has occurred at the International Space Station (ISS).

On Saturday, February 11th, 2023, Roscosmos mission controllers reported a “depressurisation” in the Progress MS-21 spacecraft which has been docked at the ISS since October. The statement did not specify the exact nature of the problem, but NASA – who refer to the vehicle as Progress 82 – later confirmed it involved the coolant system on the spacecraft.

Progress MS-21 / 82 imaged shortly after it docked at the International Space Station. Credit: NASA

Coincidentally, the leak followed the arrival of Progress MS-22 / 83 at the ISS, which had docked earlier the same day, with Progress MS-21 scheduled to depart on February 17th – although it is currently unclear whether this will now be delayed in order to facilitate further investigation.

Progress is essentially an uncrewed version of Soyuz. Fully automated, its mission is to deliver supplies – food, water, fuel – and equipment, etc., to the ISS. However, the vehicle is not capable of a return to Earth, but is instead used to transport waste from the station which then burns-up with the vehicle as it re-enters the atmosphere. It was a Soyuz vehicle which suffered a major coolant leak on December 14th, as reported in these pages, thought to be the result of a tiny piece of dust impacting the main coolant loop at a speed of over 18,000 km/h.

The reason for the loss of coolant in the Progress 82 spacecraft is being investigated. The hatches between the Progress 82 and the station are open, and temperatures and pressures aboard the station are all normal. The crew [were] informed of the cooling loop leak [and are] in no danger and continuing with normal space station operation.

– NASA statement

Up until now, NASA has publicly agreed with Roscomos that it was a micrometeoroid strike responsible for the Soyuz leak; however, two vehicles of pretty much the same type both suffering a similar leak within months of one another seems somewhat coincidental. As such some outside of NASA have started questioning the impact claim for the Soyuz incident.

India Expands Launch Capabilities and Resumes Testing for Future Crewed Launches

India successfully launched its new Small Satellite Launch Vehicle (SSLV) on February 8th, placing three satellites into low Earth orbit. The launch was the second attempt to achieve orbit with the launcher, the inaugural flight in August 2022 having failed due to an issue with its upper stage.

SSLV is a small, highly-flexible launch system intended to support the increasingly popular commercial small satellite sector and capable of placing 500 Kg to LEO or 300 Kg to a Sun-synchronous orbit (SSO). It joins Indian’s current launch vehicles, the Polar Satellite Launch Vehicle (PSLV), capable of delivering up to 3.8 tonne LEO or 1.75 tonnes to SSO; and the Geosynchronous Satellite Launch Vehicle (GSLV), capable of up to 6 tonnes to LEO and 3 tonnes to SSO.

India’s second mall Satellite Launch Vehicle lifts off from the Satish Dhawan Space Centre on February 9th, 2023. Credit: ISRO

The same day as the SSLV launch, the Indian Space Research Organisation (ISRO) also announced it has resumed testing of its Gaganyaan human spaceflight programme. This has been in development since the completion of initial design studies in 2006/7, but has been impacted by a number of funding issues, including a complete suspension of work between 2013 and 2014.

In more recent years, the basic vehicle design has been settled on, and ISRO has validated its GSLV as the launch vehicle for the capsule system (and giving it a new designation as the Human Launch Vehicle Mark 3, or HLVM3); testing the launch crew escape system, the parachute descent system and the human-rated new solid rocket boosters HLVM3 requires when launching a crew. However, the COVID pandemic then halted the project entirely, and it has only been in 2022/23 the the project has been ramping back up.

These most recent tests utilise a full-scale mock-up of Gaganyaan and are intended to test and develop the recovery operations the Indian Navy will use following the successful splashdown of a capsule at the end of a mission. They were carried out at the Navy’s Water Survival Test Facility, Kochi. This state-of-the-art facility “simulates different sea state conditions, environmental conditions and day/night conditions,” according to ISRO, allowing teams to develop a range of crew and vehicle recovery options.

Gaganyaan is a two-unit vehicle, comprising a fully autonomous crew module and a service module. The capsule is 5.3 tonne unit capable of carrying a crew of three and returning them to Earth after missions of up to seven days. The service module provides main orbital engine and orbital manoeuvring thrusters, together with power and life support for the main capsule. It masses 2.9 tonnes.

The Gaganyaan crew vehicle, its service module and the evolved GSLV / HLVM3

The first launch of Gaganyaan had been planned for August 2022, coinciding with the 75th anniversary of India’s independence. However, as a result of the pandemic, the first crewed launch will now not occur until the end of 2024.

A New Ring System Discovered in Our Solar System

The solar system comprises more than 3,000 bodies classified as planets of one kind or another. There are the eight major planets, and around 3,000 dwarf planets (including Pluto), most of which sit within the Kuiper belt beyond the orbit of Neptune – and more are being discovered.

One of the more recent of these discoveries is that of 50000 Quaoar, first identified in 2002. Roughly half the size of Pluto, at some 1,110 km in diameter, it is one of the more interesting Kuiper belt objects, in that spectroscopy has revealed evidence of water ice on its surface – suggesting it my be subject to cryovolcanism – and it has a moon orbiting it, Weywot, discovered in 2007.

This little system is so far from Earth, they are very difficult to observe in detail, and astronomers rely on occultation – when an object under observation lines up directly in front of a distant star, allowing the star to reveal all sorts of details. In this case, a ring of debris surrounding Quaoar.

The discovery was confirmed by the European Space Agency’s CHEOPS space telescope – and it is something of a conundrum: it exists well beyond Quaoar’s Roche limit. This is the distance from a planet inside of which a moon will be torn apart by the planet’s gravity, resulting in the formation of one or more rings; outside of it, dust and debris are expected to coalesce of time into a moon.

An artist’s impression of the dwarf planet Quaoar and its ring and moon( Weywot, seen to the left). Credit: ESA

Give its distance from Quaour, it took a number of observations between 2018 and 2021 to confirm the ring actually existed, using a range of occultations. The initial belief was that the dimming being observed was probably the result of a second tiny moon orbiting Quaour (Weywot being just 80 km across).

Over time, astronomers realised what they were seeing was more than the passage of a tiny moon, and Kate Isaak, chief scientist for CHEOPS – normally used to characterise exoplanets – suggested it be used to observe Quaour over a number of additional occultations, allowing astronomers to combine its data with their own Earth-based observations, with the end result they were able to confirm they were seeing an irregular ring of material orbiting the little planet.

The material is described as “clumpy”, likely kilometre-sized moonlets which collide with one another and produce strands of tiny particles that re-accrete into larger objects which then once again collide in what is called a steady-state process. To be clear, Quaour isn’t the first Kuiper belt dwarf planet to have rings:  ground-based observations have confirmed rings around the minor planets Chariklo and Haumea, for example; but those rings are inside the planets’ Roche Limit.

How the ring came into existence and why it continues to survive without the debris coalescing into moonlets is a total mystery to astronomers. It also overturns one of the founding principles regarding ring formation around planets and moons. Given all of this, Quaour is going to be a subject of study for some time to come.

* With apologies to the scriptwriters of The Hunt for Red October.

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