Tag: Astronomy

In December 2020, and following the not-quite-successful flight of Starship prototype SN8, SpaceX suffered what might have been a further setback in their flight test plans for the Starship vehicle, when prototype SN9 toppled sideways whilst in the stacking facility at the company’s Boca Chica, Texas, construction and flight test centre (see: Space Sunday: the flight of SN8 and a round-up).

However, the vehicle was quickly righted and following examination, work commenced on repairing / replacing the damaged elements (notably one of the forward aerodynamic surfaces). This work proceeded at a surprising pace; so much so that on December 22nd, 2020, it was delivered to he Starship launch platform.

Since then work has continued at the same rapid pace, such that within the two weeks since its arrival on the stand, SN9 has completed the majority of its pre-flight checks that took around 2 months to complete for SN8. These included initial fuel tank pressurisation tests using inert liquid nitrogen (to test the tanks and structure for leaks), partial and fuel test fuelling operations, vent system tests, testing of the reaction Control system (RCS) thrusters that help maintain the vehicle’s orientation in the atmosphere and will provide manoeuvring capabilities in space, and even a full static fire test of the vehicle’s three Raptor engines, which took place on January 6th.

Two tests were skipped in the process – but this is seen as not so much because the company is trying to make up for any “lost time”, but rather the result of growing confidence in the process of taking a prototype vehicle from fabrication to test flight. However, while the engine firing was successful, it was somewhat shorter than those for SN8 – the Raptors fired for less than 2 seconds – so it is not clear whether or not an issue was encountered, forcing a premature shut-down.  If this is the case, then it might be that further static fire tests may be announced ahead of any flight; if the brief firing was intentional, then it is possible a flight test could come within the next week or so.

As it is, the exact date of any actual flight test for SN9  – which will seek to repeat the 12.5 km altitude reached by SN8, but hopefully follow it with a successful landing – hasn’t been confirmed. However, to avoid a repeat of the SN8 crash, SpaceX CEO Elon Musk confirmed that the Methane header tank – a smaller tank designed to feed fuel to the Raptor motors during the landing sequence  – for SN9 and at least some of the prototypes that follow it will be “pressed” with helium (this is, helium will be forced into the tank in order to force the methane out and to the engines) in order to avoid any pressurisation issues. However, it is not clear if this will be the permanent solution to the problem, or an interim update to allow test flights to continue whilst SpaceX develop a more permanent solution to the problem.

At the same time as pre-flight tests have been continuing with Starship SN9, work has been continuing with a number of further prototypes. SN10 very close to completion, with just engines and aft aerodynamic flaps to be mounted, and SN11 will be receiving its upper sections in the coming week. Further down the chain, SN15 is also progressing, as is SN16. These will likely be the first two prototypes fully fitted with the thermal protection system used to safeguard the vehicle’s hull during atmospheric entry. This doesn’t necessarily mean either will make an orbital flight – SpaceX will doubtless want to text how the entire thermal system holds up under atmospheric flight prior to committing to an orbital attempt.

However, work currently appears to be on hold for vehicles SN13 and SN14, and SN12 has yet to be stacked. Whether these vehicles will be completed remains to be seen: Musk has previously indicated that the SN15 vehicle and beyond will include “significant upgrades” compared to earlier vehicles, so it is possible SpaceX may opt to skip from SN11 to SN15 in the flight test programme.

Puerto Rico Governor  Supports Rebuilding Arecibo

The outgoing governor of Puerto Rico, Wanda Vázquez Garced, signed an executive order on December 28th, 2020 backing the rebuilding of the 305-m diameter Arecibo radio telescope that collapsed in November 2020 (see:  Space Sunday: returns and a collapse).

The order states that US $8 million is to be “assigned and allocated” for removing the debris of the collapsed telescope and “remedial environmental” work be completed at the site. It further states that the Puerto Rico government wishes to see the development of a telescope with a larger effective aperture,  wider field of view and a more powerful radar transmitter to replace the original, thus providing the nucleus of “a world class science and education facility”.

However, things are not as clear cut as this. For one thing, the construction of a new telescope is liable to cost more than ten times the funding stated in the order. It’s also not clear where the $8 million will come from; the order only suggests it could be provided through “state, federal and private sources (including public-private partnerships and state-federal partnerships)”.

More particularly, Arecibo is not under the funding auspices of the Puerto Rican government, but rather that of the National Science Foundation (NSF), which it turn is funded directly by the US government. Thus far, the NSF has not committed to any rebuilding / replacement at the site, nor have any funds been allocated by Congress in the 2021 federal budget – although the NSF has been directed to prepare a study / report on the telescope’s collapse, the clean-up operation and to determine whether a replacement / comparable facility should be established at the sit, together with the associated costs for doing so.

NSF has a very well-defined process for funding and constructing large-scale infrastructure, including telescopes. It’s a multi-year process that involves congressional appropriations and the assessment and needs of the scientific community. So, it’s very early for us to comment on the replacement.

– Ralph Gaume, director of NSF’s Division of Astronomical Sciences

Continue reading “Space Sunday: starships, dishes and microbes” →

Monday, December 21st, the winter solstice, saw Jupiter and Saturn reach their closest point of mutual approach to one another when viewed in our evening skies, in what is referred to as a great conjunction.

I covered the event in some detail in my previous Space Sunday report, noting that 2020 would see the two planets appear to come with 6 arc minutes of one another as they lay low over the south-western horizon in last light following sunset.

Unfortunately, British weather being what it tends to be, I didn’t get to see things on the night thanks to cloud and rain.  To add insult to injury, the skies were clear just 40 km away, allowing friends to witness the event on the night, while the rain and cloud continued here most of the rest of the week, preventing me from getting a further look at the two planets as they dropped ever closer to the horizon. Ho hum.

Fortunately, however, many around the world did have clear skies and captured the event using cameras equipped with telephoto lenses or attached to telescopes. I’ve included a handful of my favourites shots here.

The event was also captured on film by Jason De Freitas, who captured the space between Jupiter and Saturn being neatly “cut” by the passage of the International Space Station.

ET Probably Isn’t Radioing Us

A radio signal detected in a part of the sky that neatly aligns with our closest stellar neighbour,  Proxima Centauri, is unlikely to be of extra-terrestrial origin.

The radio burst was detected in  April-May 2019 by the Parkes Radio Telescope in  Australia, one of two radio telescopes used by the Breakthrough Listen project, which since 2015 has been listening to the one million closest stars to our own in an attempt to pick up artificial radio signals that might indicate extraterrestrial intelligence.

At the time the signal was detected, the telescope was engaged in radio observations of Proxima Cantauri, some 4.2 light years away, and a star known to have two planets orbiting it, one of which – Proxima b – is a rocky world about 1.7 times the size of Earth that sits within the star’s  habitable zone.

Parkes wasn’t listening for radio signals at the time they were picked up, but was engaged in radio observations of flare activity from the star. However, when detected, the signal was immediately intriguing due to its relatively narrow frequency – 982.002Mhz – which ruled out it being caused by known natural phenomena. In order to verify it, the Breakthrough Listen team received permission to “nod” the telescope dish.

This is a common technique used to verify radio signals that involves deliberately swinging the receiving dish away from a signal for a period of time, and then back towards it in order to see if it can be re-acquired (indicating it is not an artefact of the telescope itself), and to measure whether the signal has moved relative to the dish (which would indicate the source is likely in Earth’s orbit). In this case, the signal was reacquired, with measurements suggesting it could be emanating from Proxima b.

When news of the signal, and the on-going analysis to try to determine it’s likely point of origin / cause, was anonymously leaked recently, it was picked up by a number of media outlets and caused something of a stir. However, before ET Hunters get too excited, there are a number of additional facts to consider.

Firstly, it is devoid of any modulation – and so is likely devoid of any meaningful data, were it indeed to by an extra-terrestrial, which makes sending it a little pointless. Secondly, it was entirely transient; following the period of initial detection in April / May 2019, it was “lost”, and has never been re-acquired. Were it a deliberate signal, it would not be unreasonable to expect it to remain fairly constant in terms of detection, either by Parkes or (preferably) other centres around the world.

But the biggest counts against it being ET “‘phoning home” (or at least us), lies with the fact that the signal came from the general direction of Proxima Centauri. As our nearest, and oft-observed stellar neighbour, the star has been under observation for decades, and nary a once have we received anything amounting to an peep out of it that might suggest aliens are playing with radio systems there.

More particularly, however, is the fact that Proxima Centauri is a red dwarf star. As I’ve noted numerous times in these pages, these  M-class stars are prone to exceptionally violent solar flare. Given the close proximity of Proxima b to its star, these flares would likely, at a minimum, be bathed in hard radiation, and at worse, completely rip away the planet’s atmosphere within a period of around 100-200 million years. Therefore, it is highly unlikely the planet really is the point of origin for the signal.

instead, the most likely explanations for the signal are that it might either be something like the carrier wave from a long-forgotten piece of orbital debris of human manufacture or – mostly likely – actually originated on Earth, with conditions in the upper atmosphere serving to “bounce” it into the Parkes Telescope sphere of detection.

The Breakthrough Listen team and their partners certainly lean towards the latter as an explanation, although as noted,  they are still analysing the data gathered on the signal.

This is not a natural phenomenon—I haven’t seen the data, but if it passed BL’s tests then it’s too narrowband to be natural. It’s definitely caused by technology. But it’s almost certainly our own technology.

– Jason Wright, Professor of Astronomy and Astrophysics at Penn State University

Continue reading “Space Sunday: conjunctions, radio signals and budgets” →

For those who have not already seen it, the next two weeks present an opportunity to witness a unique event – a very close conjunction between Jupiter and Saturn.

“Conjunction” is the term astronomers used to describe two astronomical objects or spacecraft having either the same right ascension or the same ecliptic longitude, and thus when seen from Earth, appear to be close together.

With the planets, such events are not especially rare – in fact as they and the Earth circle the Sun, conjunctions between Jupiter and Saturn tend to occur once every 20 years. However, most of these only see Jupiter and Saturn close to around one degree of one another, or about one-fifth the diameter of the Moon as seen from Earth. But sometimes they appear to get much closer, creating what is referred to as a “great conjunction”. This year, the two planets will appear to be just 6 arc minutes apart as seen from Earth on December 21st, 2020; so “close” (remembering that their respective orbits around the Sun will still be separated by 883 million km), they will almost, but not quite, appear as a single point of light when seen with the naked eye.

These “great conjunctions” occur, on average, once every 300-400 years, although such is the nature of orbital mechanics, they can actually occasionally occur more frequently, or have longer time gaps between them. As it is, the last time Jupiter and Saturn appeared as close as the will be between December 20th and 22nd was in 1623, not long after Galileo had observed both planets – although he was unable to witness the event, as the rising Sun would have rendered them invisible in its glare.

What is most rare is a close conjunction that occurs in our night time sky. I think it’s fair to say that such an event typically may occur just once in any one person’s lifetime, and I think ‘once in my lifetime’ is a pretty good test of whether something merits being labelled as rare or special.

Astronomer David Weintraub

However, the two planets can appear to be much closer. In 1226, and in the skies over the Mongol Empire, when the planets appear to be just 2 arc minutes apart.

Tracing these great conjunctions back in time reveals that Jupiter and Saturn may well have played a role in the legend of the Star of Bethlehem. In 7 B.C. not one, but three great conjunctions occurred, with the two planets again being within 2 arc minutes of one another as seen from Earth.

The first occurred in May of that year, when Jupiter and Saturn appeared as a morning star over the middle east. As  the Magi were practitioners of (among other things) astronomy and astrology – both at that time pretty much joined at the hip – such an event may well have caused them to start out on their long journey towards Judea, the second conjunction, in September of the year, encouraging them to continue. The third conjunction occurred in December, 7 B.C., the time at which they were said to have met with Herod the Great.

This year’s conjunction will be not long after sunset, with the two planets located low over the south-west horizon. With a reasonable telescope or good pair of binoculars, you’ll have an ideal opportunity to see both planets and their major moons in the same field of view.  Should you do so, you’ll be looking at over 90% of the planetary mass of the entire solar system.

Beyond the 21st, the two planets will gradually move “apart” as noted, until by the 25th December, they’ll be separated in the night sky by roughly the diameter of a full Moon, and will continue to draw apart relative to Earth as they pass below the horizon.

And if you miss this close conjunction between the two, the next will be along in a relatively (and unusually) short period, occurring on March 15th 2080. The next time they’ll be as apparently close as they were in 7 B.C. will be on Christmas Day, 2874.

Continue reading “Space Sunday: Conjunctions, China & the Sun as a telescope” →

On Wednesday, December 9th, SpaceX Starship prototype SN8 finally took to the skies in what was to be a very mixed ascent to around 12.5 km altitude and return to Earth.

The much anticipated flight of the prototype vehicle, weighing approximately 672 tonnes with its partial fuel load, was far more successful than SpaceX had anticipated, even if the vehicle was lost in what SpaceX euphemistically calls a “rapid unplanned disassembly” or RUD.

The first attempt at a launch of the 50m tall vehicle was made on Tuesday, December 8th; but this was scrubbed after a pre-flight engine issue caused an automatic shut-down on all three Raptor motors. The second launch attempt, in the morning of Wednesday, December 9th, was aborted just 2 minutes and 6 seconds before engine ignition when a light aircraft strayed into the no-fly zone around the SpaceX facilities in Boca Chica, Texas.

However, at 16:00 CST (22:00 GMT) that day, the countdown resumed, and at 16:45:26 p.m. CST (22:45:56 GMT), the three Raptor engines on the vehicle ignited and ran up to around 80% thrust, lifting prototype SN8 into the air.

The entire flight was live streamed by SpaceX, with the initial ascent proceeding as anticipated. At 1 minute and 40 seconds into the flight, one of the Raptor engines shut down and gimballed itself away from the remaining two operating motors. 94 second later, a second of the Raptors did the same. At the time, some pundits commenting on the flight speculated the shut-down indicated something was amiss.

In actual fact, both engine shut-downs were planned. As the vehicle was flying with around 1/2 its normal fuel load, and getting lighter at the rate of 2.2 tonnes every second, the engines were shut down to reduce SN8’s thrust-to-weight ratio, naturally reducing its rate of ascent.

Even so, SN8 continued upwards under the thrust of the one remaining Raptor – Number 42, the latest and most modern Raptor engine evolution, with the vehicle’s reaction control system (RCS) firing thrusters around its hull in order to stay upright, until it reached a point where it was effectively hovering.

What happened next was one of the two most incredible sights witnessed in the testing of a space vehicle: as SN8 started to drop vertically backwards, Raptor 42 gimballed to direct its thrust at an angle, working with the RCS system to tip the entire vehicle over until it was falling more-or-less horizontally. At this point, the fore and aft flaps came into their own, working in tandem to hold the vehicle steady, much like a skydiver uses their arms and legs to maintain stability.

This skydive / bellyflop (as some unkindly refer to it) is how a Starship will make a return from orbit. Dropping into the atmosphere with the fore and aft flaps folded back against the hull to minimise their exposure to the fictional heat of atmospheric  entry, an operational starship will be protected by heat shield tiles along its underside, after which the flaps fold out, acting as air brakes to slow the vehicle’s velocity as well as keeping it stable.

Dropping back through the atmosphere for almost two minutes, SN8 then completed the second most incredible sight seen in the testing of a spacecraft when, six minutes after launch, two of the Raptor motors re-ignited, using fuel from two small “header” tanks. These, coupled with the vehicle’s RCS tipped SN8 back to an upright position just 200 metres above ground.

The idea had been for the vehicle to then descend tail-first over the landing pad, deploy its landing feet and touch-down. However, it was at this point things went wrong. With just tens of metres to go, one of the two operating engines shut down. For several seconds, the remaining engine fought to maintain vehicle stability, its exhaust plume turning bright green. Seconds later, its landing legs having failed to deploy, SN8 slammed into the landing pad and exploded in the RUD SpaceX thought might occur at some point in the flight.

Initial analysis of data from the flight suggests that the header tanks suffered a pressurisation issue that prevented them pushing sufficient fuel into the two Raptor engines, causing one to shut down completely. The green plume from the second motor is thought to be one of two things: either that a) as the motor was so starved of fuel, it started consuming itself, material inside its turbopumps turning the exhaust green; or that b) as one engine shut-down unexpectedly, the second started gimballing wildly to try an maintain the vehicle’s orientation, and in doing so, smashed its engine bell into the other motor, exposing its copper cooling circuits, which caught fire and turned the exhaust plume green.

Continue reading “Space Sunday: the flight of SN8 and a round-up” →