Space Sunday: Mars, galaxies and starships

 Mars 2020 mission Sol 46 (April 6th), 2021, a series of 62 images captured using the WATSON imager on the robot arm of the Perseverance rover were used to create this “selfie” of the rover “looking” at the camera, then back at the Ingenuity helicopter sitting on the ground some 4 metres away. Credit: NASA/JPL

NASA has delayed the first flight of the Ingenuity helicopter on Mars after the vehicle detected an issue during one of its pre-flight tests.

For the past week, the agency has been preparing the little helicopter drone, part of the Mars 2020 mission, for the first of a series of 5 pre-planned test flights within Jezero Crater. It had been hoped the flight could take place on Sunday April 11th / Monday April 12th, 2021 (depending on where you are in the world); however it will now not take place until Wednesday, April 14th at the earliest.

After being dropped on the surface of Jezero Crater by the Mars 2020 Perseverance rover (see my previous space Sunday report), Ingenuity successfully recharged its batteries using solar energy and survived its first night alone on Mars without incident. This was a major milestone for the project, as there were fears that if the batteries couldn’t be fully charged and generate sufficient heat, the extreme cold of the Martian night could freeze the vehicle’s electronics, and even crack the batteries themselves.

Since that first night, the helicopter has shown it can keep itself warm and the flight team has spent the week conducting a range of pre-flight checks, including unlocking Ingenuity’s pair of contra-rotating propellers and then testing them under power and at low speeds, then speeding up to higher speeds, including an attempt to reach the 2400 rpm required for take-off.

Part of testing Ingenuity included taking a low-resolution image via its downward-looking camera system while it was still sitting under the rover. April 3th, 2021 / Sol 42. Credit NASA/JPL
All of these tests were completed successfully, with the exception of the final full-speed test attempted on Friday, April 9th. This aborted during the phase when the command programme on Ingenuity was supposed to switch from “pre-flight” to “flight” mode, as will be required ahead of the actual flights. However, a guardian “watchdog” timer designed to oversee the correct execution of command sequences expired before the switch-over occurred, prompting Ingenuity to safely shut-down its motor and await further instructions from Earth.

Following a full evaluation of telemetry received following the curtailed test, the flight team were confident that no actual damage had occurred to the helicopter, stating the full spin-up test of the rotors would be postponed and the flight itself delayed until April 14th. They also indicated that assuming the first flight was completed without incident, the second flight will take place on Sunday, April 18th.

The rotor tests took place once Perseverance was well clear of the helicopter – the rover is gradually making its way to the look-out point where it will record Ingenuity’s flights. However, before it did so, engineers took the opportunity to use the WATSON (Wide Angle Topographic Sensor for Operations and eNgineering) camera on the rover’s robot arm to capture a series of 62 images that were stitched together to produce a picture of Perseverance apparently “looking” back at the helicopter using its mast cam imaging systems, and which can be seen at the top of this article.

Another image Perseverance took that recently caused excitement was one that appeared to show a “rainbow” arcing across the dusty Martian sky. Captured on April 4th (Sol 43), the image spread quickly across social media, as did the “rainbow” explanation.

Captured on April 4th (Sol 43), this image via the rear-facing Hazcam system on Perseverance caused excitement in the media, being described as a “rainbow”. However, it wasn’t any such thing, as NASA was forced to explain. Credit: NASA/JPL

The only problem being, rainbows are impossible on Mars, as NASA quickly stepped in to note through social media:

Many have asked: Is that a rainbow on Mars? No. Rainbows aren’t possible here. Rainbows are created by light reflected off of round water droplets, but there isn’t enough water here to condense, and it’s too cold for liquid water in the atmosphere.

NASA, via the @NASAPersevere Twitter account.

Rather, the “rainbow” was the result of lens flare – light being scattered by the lens of the Hazcam (HAZard avoidance CAMera) that captured the image, to strike the imaging sensor in multiple places like an arc of machine-gun bullets. Such effects are prevented on the front-facing Hazcams (the ones most frequently used by the rover, as they are equipped with sunshades; however, similar shades were deemed superfluous on the rear-facing Hazcams, and so lens flares like this are actually quite common should the system be in use and the Sun happens to be in the right position.

Happy Anniversary, Odyssey

The longest-running mission to Mars marked its 20th anniversary on April 7th, 2021 – and it is possibly the most unknown.  Launched in 2001, NASA’s Mars Odyssey vehicle has been orbiting the planet since October of that year.

Despite its relative (to some) anonymity, Odyssey was the first Mars orbiter mission to offer confirmation that Mars likely has large sub-surface deposits of water ice, when it detected large pockets of hydrogen roughly a metre below the surface in places (2002). By 2008 it had produced the first maps of sub-surface water ice deposits, some of which might actually thaw into aquifers around the equator. It later engaged in a comprehensive infra-red survey of Mars, mapping chemical and mineral deposits around the planet, massively contributing to our understanding of the planet’s development and environmental changes.

Mars Odyssey: 20 years since launch and still going strong. Credit: NASA

Up until the arrival of the Mars Science Laboratory Curiosity rover on the planet, Odyssey was the main communications relay for all NASA surface operations (a role now taken by the Mars Reconnaissance Orbiter mission, with Odyssey forming the back-up), with Odyssey working with MRO to map the best landing point for Curiosity within Gale Crater.

Occupying a Sun-synchronous orbit around Mars, since 2015 Odyssey’s current mission is focused on observing the changing ground temperatures after sunrise and after sunset across the planet; a study could yield insight about the composition of the Martian regolith across the planet and about temperature-driven processes, such as warm seasonal flows observed on some slopes, and geysers fed by spring thawing of carbon dioxide (CO2) ice near Mars’ poles.

As well as being the longest-running mission to Mars, Odyssey is the longest-running mission to orbit any planet other than Earth, and it is expected to continue through until around 2025.

Even Galaxies Die

While he may not have originated the idiom, in 1789 Benjamin Franklin wrote in this world nothing can be said to be certain, except death and taxes. In fact, when it comes to matters cosmological, the first of these two facts is very definitely unavoidable. While we might measure their life spans in billions upon billions of years, stars live and eventually die – as do any planets that might orbit them. And now the Hubble Space Telescope (HST) has given us an image of a dying galaxy.

NGC 1947 (also known as ESO 85-87 and LEDA 17296) was first discovered some 200 years ago by James Dunlop, a Scottish-born astronomer who specialised in the discovery of deep-sky objects whilst working in Australia. Located in the constellation of Dorado, the dolphinfish.

NGC-1947, a dying galaxy, 40 million light-years away, as imaged by the Hubble Space Telescope. Credit: NASA/ESA

Approximately 40 million light-years away from Earth, is believed to have once been a lenticular galaxy, although it was already in is death throes at the time Dunlop discovered it. However, in the 200 years since his initial observations, it has clearly lost most of the material that made up the spiral arms Dunlop was able to see.

Backlit be the light of millions of stars – Dorado is home to multiple galaxies, including the Large Magellanic Cloud, making deep sky views of it particularly bright – the Hubble telescope image reveals all that is left of NGC-1947 – a central band of gas and dust and stars, the spirals of its arms fading wisps that will never more birth stars.

 SpaceX Updates

The fire around the turbopump area of one of SN11’s Raptor engines is thought to have resulted in damage that later may caused the engine to explode, destroying the vehicle. Credit: SpaceX

SpaceX have released an explanation on the airborne loss of the Starship SN11 prototype on March 30th.

As I reported in  Space Sunday: Ingenuity readies for flight, despite thick fog, the flight more-or less went according to plan, the vehicle climbing to `0 km altitude before dropping horizontally back towards Earth. However, come the time the vehicle was supposed to re-light its Raptor motors to “flip up” to a vertical position for landing, it explored.

During the ascent to 10 km, a fire was witnessed in the engine bay, around the turbopumps of engine No. 2, which was later reported as “having issues” during the scent.  While pundits dismissed the fire as “usual”, it now appears it was anything but, as it most likely damaged the avionics associated with the motor and leaving it with too much methane in the turbopumps, resulting in a “hard start” when the attempt was made to re-ignite the motor in readiness for the “flip up” manoeuvre.

A “hard start” is when there is too much fuel in the combustion chamber, over-pressuring it. This is not a good situation for any engine to be in at start-up – and for SN11, it resulted in the Raptor catastrophically exploding – taking the rest of the vehicle with it. As a result of what happened, SpaceX is implementing a series of fixes and changes to the Raptor engine system.

Amidst a flurry of activity during the week, SpaceX rolled-out the first of the next generation of Starship prototypes – SN15 – to a launch stand.

Ahead of it, the company focused on rolling-out and installing the first of seven or eight gigantic Ground Support Equipment (GSE) tanks. Capable of holding 1,825 cubic metres of cryogenic fuel apiece, these tanks – which are so big, SpaceX has to fabricate them on-site – will eventually be used to fuel Starship / Super Heavy booster combinations when orbital flights eventually commence, each launch requiring over 5,000 cubic metres of propellant.

The first of the GSE tanks that will supply propellants to a Super Heavy / Starship “stack” ahead of a launch, is installed at the in-development orbital flight facilities at the SpaceX Boca Chica facilities. Credit: RGV Aerial Photography

SN15 rolled out to its launch stand on Thursday, April 8th in readiness for its test flight. Whilst visually identical to the earlier vehicles (other than the grater number of test heat shield tiles mounted on the leeward hull), SN15 has significant internal structural improvements, avionics upgrades, and updates to the Raptor engine design. Many of these improvements are related to flight capabilities, but equally, many are geared toward more streamlined production and testing of vehicles.

One significant change in the vehicle design is that of the thrust puck. This is a cone-shaped structure that sits at the base of the vehicle and onto which all three of a Starship’s sea level engines (the inner three engines we see on the prototypes) are mounted, and which therefore most directly takes all the stress and load of their thrust. Early Starship prototypes suffered issues with the puck, leading to an interim design that’s been used on all of the flights to date. SN15 is the first prototype to have a completely redesigned thrust puck, one that if successful, will likely be carried forward into the eventual orbital and production versions of the vehicle.

Starship prototype SN15 with a black band of heat tiles fixed to its leeward hull, dwarfs the Starhopper prototype, as it is rolled to the launch stand. Credit: May aka BocaChicaGal / NASAspaceflight.com

As it is the first time the puck redesign is being actively used, SN15 will likely go through some additional pressure tests to simulate the thrust of the Raptor motors ahead of any static fire engine test, in order to confirm the new puck is up to snuff. This likely means that any flight of SN15 is unlikely to be in the coming week.

SpaceX has also officially said farewell to Ms Tree and Ms Chief, the two large, high-speed vessels the company have chartered since 2018 to attempt at-sea recoveries of Falcon 9 payload fairings using large nets suspended over the rear of each ship.

The idea has always been that by catching the fairings before they land in the sea, the company could avoid exposing them to the corrosive nature of salt water and thus reduce the time and cost of refurbishing them for re-use. Additionally, the vessels have also twice been used in the post-splashdown recovery of Dragon capsules returning from the International Space Station.

Ms. Tree during a successful capture of a Falcon 9 payload fairing, 2019. Credit: SpaceX

However, while visually impressive and able to meet with some success, SpaceX has conceded that the complexities of trying to catch returning fairings is far more difficult  – and potentially costly – as simply being on-hand to pull them out of the sea after they’ve splashed down.

So, at the end of March as their charter period ended,  Ms Tree and Ms Chief left the company’s service, sans the large nets and their support arms. In the future, the company will use a new vessel they have chartered, the Shelia Bordelion, to pluck both returning fairings and returning Dragon capsules out of the sea.

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