Space Sunday: Comet NEOWISE, Starship and Starliner

Comet C/2020 F3 seen in the eastern horizon above Earth shortly before sunrise, as seen from the ISS, July 5th, 2020. Credit; NASA / Bob Behnken

Those in the northern hemisphere wishing to see a comet in the night sky currently have an excellent opportunity to do so. Comet NEOWISE (officially C/2020 F3 (NEOWISE)) is currently approaching Earth and will reach its closest point of approach on July 23rd, 2020, before starting its trip back out to the depths of the solar system.

Having passed around the Sun (reaching perihelion on July 3rd, 2020), NEOWISE has been an early morning, pre-dawn object in clear northern hemisphere skies. however, in the coming week it switches to being twilight object, potentially making opportunities to view it much better for many people.

Comet C/2020 F3 seen early in the morning of July 9th, from the grand view lookout at the Colorado National Monument, Grand Junction, Colorado. Credit: Conrad Earnest

The comet is a relatively “new” object in terms of its first observation – it was initially spotted on March 27th, 2020 by NASA’s Wide-field Infra-red Survey Explorer (WISE), a polar-orbiting space telescope. Launched in December 2009, WISE has been responsible for the discovery of thousands of minor planets within the solar system, and star clusters beyond. It is also a telescope with an interesting history.

Originally given a primary mission of just 10 months – the amount of time required to deplete the hydrogen coolant reserves the telescope needed to successfully operate two of its primary instruments – WISE was afterwards given a 4-month mission extension dubbed NEOWISE. For this mission it was tasked with looking for asteroids and comets that can come close to Earth (and are therefore known as Near Earth Objects, the “NEO” in the mission’s name). That mission drew to a close in February 2011, the telescope having completed an “all sky” survey, and it was ordered to place itself into hibernation, powering-off everything bar its communications link with Earth.

An artist’s impression of the WISE telescope in Earth orbit. Credit: NASA

Then in August 2013, NASA decided to give the telescope a formal wake-up call, tasking it to resume its NEOWISE mission, this time with the emphasis on locating asteroids that may pose a risk of impacting Earth in the wake of the 2013 Chelyabinsk meteor incident. After a period of naturally cooling the vehicle and re-calibrating its instruments, WISE officially resumed NEOWISE operations at the end of 2013, and has gone on to observe more than 26,000 previously known objects, and has additionally identified more than 400 that had not been previously recorded, 25% of which have been classified NEOs.

C/2020 F3 (NEOWISE) is one of those 400+ “new” objects. After it’s initial identification, it was confirmed as a retrograde comet (i.e. it is travelling around the Sun in opposition to the Sun’s rotation), with a near-parabolic orbit. Its nucleus is believed to be about 5 km across, and covered with sooty material dating back to the origin of our solar system, 4.6 billion years ago. At the time of its closest approach to the Sun, the comet was just 43 million km from our star – causing speculation that it might not survive the encounter in one piece.

However, as it once again came into view from Earth, the comet had brightened considerably  – to magnitude +1, while the out-gassing of material saw it develop two tails (although only one or the other tends to be visible in many photographs taken of it so far). The first is blueish in colour, and largely comprises gas and ion; the second is a more yellow-gold in colour, and thought to be largely made of dust.

At its closest approach to Earth, on July 23rd, the comet will be just 103 million km away, potentially offering the best time to see it – although binoculars will be required for the best view. However, it is not clear just how active the comet will remain as it moves away from the Sun, so there is a chance that the currently spectacular tail(s) extending from it may fade before then. As such, astronomers are recommending that the upcoming week should offers the “guaranteed best” opportunities to see the comet (local sky conditions allowing!).

How to see Comet NEOWISE, July 14th-23rd, 2020 from moderate northern latitudes. For those further north, it will appear higher above the horizon. As the month progresses, the comet will move more westward. Credit: Earthsky.org

Having been an early-morning object up until now, C/2020 F3 should switch to being an evening object from July 14th onwards, roughly 80 minutes after local sunset (during the nautical twilight period), and appear up to 20º above the local horizon, depending on your line of latitude in the north-eastern sky.

Beyond July 19th, the comet will remain visible increasing in altitude up to around 30º above the horizon for northern latitudes, and in the same part of the sky – but may see some reduction in brightness if the tail(s) do show a rapid fall-off due to cooling.  After July 23rd, the comet will remain visible, but will fade more rapidly as it moves away from both the Sun and Earth. By August, it will likely only be visible via telescope.

Such was the comet’s close approach to the Sun, its its orbit was altered as a result of acceleration, increasing its orbital period from around 4,500 years to 6,800. So if you want to see it, this is the time to do so.

Starship Prototype SN5 to fly this week?

SpaceX is rapidly moving forward with their Starship plans – and may possibly see the first flight of a prototype vehicle in the coming week.

Starship prototype SN5 on the Boca Chica test stand, July 10th. To the left of the craft is the fuel farm used to fill the test vehicles with inert liquid nitrogen for testing, or with fuel. Credit: RGV Aerial Photography

As the end of June, the prototype vehicle, SN5, comprising just the lower section of the craft’s hull that contains the fuel tanks and engine mountings, was raised onto its test stand. Since that time, the tanks have undergone what is called “ambient temperature pressure tests” – filling the tanks with inert liquids at normal temperatures to test for leaks – and cryogenic pressure tests: filling the tanks with super-cold liquid nitrogen to the pressures they will face during a flight,  the liquid nitrogen mimicking the super-cold temperatures the tanks will face when fuelled.

In the past week, the single Raptor engine that will be used in any test flights – number SN27 – was delivered to the test stand and installed on the prototype, with SpaceX announcing that a series of wet tests would be carried out over the weekend of July 11/12th, to be followed by a potential static live fire test of the motor on Monday, July 13th.

A starship cutaway showing the fuel tanks and engine bay (outlined in red) that form the prototype vehicles like SN5, and the upper cargo / habitation space and aerodynamic surfaces that are not included on the current prototypes. Credit: WAI (with additional annotation)

Assuming the wet tests and static fire test – actually igniting the Raptor engine and running it at thrust for several minutes to simulate a launch burn – are successful, SpaceX have pencilled-in a possible 150m straight-up, straight-down flight test for SN5 for Thursday, July 16th. However, the company acknowledge this could easily slip. Once it does occur, the flight will be followed by more ambitious flight tests, which will also likely include the next prototype, SN6, currently housed in the assembly mid-bay building, and include flights with prototypes fitted with the vehicle’s upper sections and dynamic flight surfaces.

At the same time as the SN5 work has been continuing, SpaceX has commenced construction on the massive “high bay” building that will be used in the assembly of the gigantic Super Heavy booster that will eventually be responsible for the grunt work of lifting Starship vehicles into the sky in the first part of their flights. To be powered by 31 Raptor engines, the Supper Heavy is a gigantic first stage booster measuring 70 metres (230ft) in height and 9 metres in diameter  – the same diameter as the Starship vehicle. It is expected that construction of this high bay will take around 4-6 weeks.

Construction of the Super Heavy booster launch site at the SpaceX Boca Chica facilities, Texas. Credit: RGV Aerial Photography

In addition, and also at the SpaceX Boca Chica facilities, work has commenced on building the Super Heavy launch pad facilities that will be used for future test-flights of the booster, all of which suggests the company is following through on its promise to significantly accelerate work on the Super Heavy / Starship.

Yet Another Planet Nine Theory

Planet Nine – the idea that there is a Neptune-size planet (or other object) far out in the solar system that is perturbing the orbits of a number of Kuiper Belt Objects (KBOs), pushing them into eccentric orbits  – is a theory that doesn’t want to go away.

In the last instalment of the saga, it seemed that an extensive study added weight to the idea that far from being under the influence of a distant object with a sufficiently large gravity well (“Planet Nine”), the KBOs in question actually reached their eccentric orbits via perfectly natural means and as a result of our existing family of large planets in the outer solar system (see: Space Sunday: moving a mole and Planet Nine, June 2020).

Now, however, a further theory has been put forward: the KBOs have been shifted under the influence of a black hole companion to the Sun.

As theories go, the black hole companion isn’t entirely new: some astronomers have long postulated the idea that the Sun has a “cold star” or a black hole lying far, far away from the core of the solar system, with an eccentric orbit lasting for millions of years. Called “Nemesis”, the idea is that this companion passes through the Oort cloud every several million years, disrupting it and sending objects in towards the Sun, some of which have caused extinction-level events on Earth, whilst the long fingers of its gravitational influence has tickled some KBOs into their more extreme orbits.

There are numerous holes in the Nemesis theory. It’s been pointed out that were it true, there would be a degree of regularity in some extinction events on Earth – and no such patten has not been found, for example. Also, such a massive gravitational influence would have a more noticeable effect on the outer planets. However, in the new “Planet Nine” theory, it’s been suggested that indeed, there is a black hole “out there” – but it is only about the size of a grapefruit, reducing its overall gravitational influence.

An artist’s impression of a small Oort cloud object falling into a hypothesised black hole far out in the solar system and giving of a burst of radiation known as an accretion flare. Credit: M. Weiss

The authors of the study suggesting this mini black hole companion are hoping the upcoming Vera C. Rubin Observatory under construction in the Chilean Andes will find it.

In 2022, the telescope will start a decade-long survey of the southern sky called the Legacy Survey of Space and Time (LSST), and its is hoped the telescope’s sensitive equipment will also detect any tiny black hole sitting close enough to the Sun to exert some influence over the orbits of KBOs.

Occam’s Razor would suggest the studies pointing to KBOs arriving in eccentric obits as a result of the natural influence of the known gas giants of the solar system are most likely to be correct. However, other mechanisms cannot currently be ruled out. So leaving the broader aspects of the LSST survey aside, perhaps it’ll help put the more dramatic ideas for eccentric KBOs  finally to bed.

NASA Lists 80 Updates Boeing Must Make to Starliner

In December 2019, Boeing’s CST-100 Starliner, designed to carry crew to and from the International Space Station (ISS), undertook its first uncrewed orbital test flight, intended to test the vehicle up to and including docking with the ISS. However, as I reported at the time, issues – a mix of set-up problems, software errors and vehicle-to-ground communications problems – meant that the vehicle could not make its rendezvous with the ISS, although all other aspects of the mission were completed successfully (see: Space Sunday: Starliner’s first orbital flight).

The CST-100 Starliner Calypso inflates its airbags just seconds ahead of its landing, December 22nd, 2019. Credit; Boeing

Since that time, both NASA and Boeing have been carrying out reviews of the flight, including all the pre-launch preparations, to determine where and how changes to the CST-100 programme need to be made before the Starliner can conduct another orbital flight test. The results of these reviews have now been made available, and they include 80 recommendations for changes to CST-100 processes from the US space agency. These comprise: 21 recommendations relate to pre-flight integration, testing and simulation, 52 relate to software requirements and process and operational improvements, and 7 related to hardware / system improvements.

No time frame has been given for completing these updates, but Boeing has stated that once completed to NASA’s satisfaction, they will carry out a further uncrewed flight test of the vehicle at their own cost to prove the vehicle ahead of any crewed flights.

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