Space Sunday: JWST and a touch of SpaceX

The James Webb Space Telescope. Credit: NASA

The world’s largest and most powerful space telescope yet built – the James Webb Space Telescope (JWST) – finally made its way into space on Christmas Day, December 25th, 2021, marking the start of a mission almost 30 years in the making.

That mission is multi-part in its scope, encompassing as it does looking back to the origins of the universe and the galaxies around us, together with gaining a greater understanding of the nature and formation of galaxies, stars and planetary systems, and learning more about the nature of worlds beyond our own solar system, as well as seeking signs of the potential origins of life. It is a mission that has been plagued by technical and other issues that have repeatedly delayed its launch – and high winds along its path of ascent to orbit caused one final delay, pushing the launch back from Christmas Eve to Christmas day.

Final countdown commenced several hours ahead of lift-off, with the Ariane 5 launch vehicle igniting its engines as scheduled at 12:20 UTC, rising into the sky over the European Spaceport near Kourou, French Guiana, carrying the US $10 billion telescope on the first leg of a journey to its operational destination that will take it almost a month to complete. Along the way it will go through a series of complex activities along the way, each one vital to its operational success.

The European Ariane 5 launch vehicle carrying JWST (designated flight VA256) lifts-off from the European spaceport, French Guiana, December 25th, 2021. Credit: ArianeSpace / ESA / NASA

The first three of these activities came just half-an-hour after lift-off, with the separation of the telescope from its Ariane upper stage after the latter had boosted it onto the start of its 1.6 million kilometre journey away from Earth. Almost at the same time, JWST deployed the solar array vital for supplying it with electrical power. This was followed two hours later by the deployment of the high gain communications antenna and, 12 hours after launch, JWST completed the first “mid-course” correction to its trajectory, steering itself more closely towards its final destination.

This destination lies close to the Earth- Sun L2 Lagrange point, 1.6 million km further out from the Sun than Earth’s orbit, but which orbits the Sun in the same period of time as Earth. It’s a location selected for JWST’s operations for a number of reasons, including:

  • It effectively puts the Earth, Moon and Sun “behind” the telescope, affording it uninterrupted views of the solar system and all that lies beyond it.
  • It is a semi-stable position in space that orbits the Sun at the same time as Earth. This both allows for continuous direct-line communications, and reduces the amount of propellants JWST would otherwise require for basic operations such as station-keeping and orbital corrections.

Even so, operations at the position will not be straightforward. As the L2 position is a point of gravitational equilibrium, JWST will operate in an orbit 800,000 km wide around it. Whilst relatively stable, this orbit will require JWST to make small periodic adjustments every 23 or so days. Given it can only carry a finite amount of propellants (168 kg) for these adjustments, the telescope effectively has an operational “shelf life”: it’s primary mission is set at just 5 years – although it is hoped it has sufficient propellants for at least 10 years worth of controlled observations.

Having been launched in a “packed” form that allowed it to fit inside the payload fairing of its launch vehicle, JWST will spend the next two weeks gradually “unfolding” itself, as per the video below, with a number of firings of its thrusters to fine-tune its flight to its intended orbit.

All of these activities are vital to JWST being able to perform its desired mission, but perhaps the two most important are the deployment of the telescope’s secondary and primary mirrors, and that of its incredible and delicate heat shield.

The optics deployment will see the booms supporting the secondary mirror that reflects light gathered from the primary back to where it can be delivered by a third mirror to the instruments deep inside JWST. The second part comes with the unfolding of the “table flap” elements of the primary mirror, allowing it to reach its full 6.5 metre diameter, almost 2.5 times the diameter of the primary mirror on the Hubble Space Telescope. (HST), and with potentially 100 times its power.

JWST is primarily intended to operate in the infrared, but in order to do so, its instruments and science systems must be kept very cold. If any of them exceed 50ºK (-223.2ºC), the heat they generate will be registered in the infrared; potentially overwhelming the telescope’s ability to capture the infrared light of stellar objects. Given that JWST will be in permanent sunlight, maintaining such an incredibly low temperature this is a considerable challenge – hence the vital role of JWST’s remarkable heat shield.

How the heat shield will keep the operational surfaces of JWST super-cold. Credit: NASA

This comprises 5 layers of Kapton E polymide formed into sheets as thin as a human hair and then covered on both sides with a thin membrane of aluminium, this shield is carried folded within two “pallets” that also need to be unfolded to form the “base” of the telescope.

Once these pallets have unfolded, booms can be extended on either side of JWST, allowing the 5 layers of the heat shield to be unfurled like the sails of a ship, and then tensioned off. This will provide an area of shadow the size of a tennis court within which the instruments and optics of the telescope will sit, while radiators behind the main mirror will circulate the heat absorbed by the shield and radiate it back into the cold shadow without impacting telescope operations.

A view of JWST during a test deployment of its heat shield system, showing the 5 aluminium-covered membranes deployed and under tension, as they will (hopefully!) be in about a week’s time of this article. Note the primary mirrors and secondary mirror system booms still in their “stowed” orientation. Credit: NASA

It is this ability to operate in the infrared that is the key differentiator between JWST and HST; one that makes JWST more of a complimentary observatory with Hubble, rather than (as is often couched), an outright replacement: Hubble operates primarily in the visible light spectrum but can dip into the ultra-violet and near-infrared; JWST goes the other way, focusing in the full range of infrared and dipping, then required, into the visible light.

Seeing deep into the Infrared is important due to the fact our universe is constantly expanding and all of the galaxies within it are moving away from one another, and so the light from them is red-shifted, with the oldest being the most red-shifted of all. Thus, the further JWST can see into the far infrared, the more of the light from the farthest – and oldest – stars in the universe can be seen, and we are effectively “looking back in time” – but as much as 13.7 billion years – just short (by a few hundred million years) of the actual age of the universe.

In addition, infrared can also reveal more of the nature of planets orbiting other stars within our own galaxy, allowing us to better understand their nature and composition and their potential for being possible centres of life. Such is JWST’s capabilities, it should also allow us to “see” a class of planet that is believed to exist but has yet to be detected: relatively cool Saturn-sized gas giants with very wide orbital separations from their host star (e.g. equivalent to or grater than, Saturn’s orbit around the Sun).

Although JWST is set to arrival in its halo orbit in around a month, it could be a further six months before it actually starts science operations. This is because following its arrival, it must go through a period of instrument testing, calibration and commissioning. Among other things, this will include correctly aligning the eighteen motorised hexagonal, gold-faced elements of the primary mirror to ensure they all provide the required amount of collected light to the secondary mirror for focusing into the telescope’s instruments without interfering with one another or giving blurred or other inconsistent results.

Whilst primarily a US mission, JWST is also a collaboration between America and 19 other nations (the majority of them from Europe / the EU) involving a total of 258 companies, government agencies, and academic institutions (142 from the United States, 104 from 12 European countries, and 12 from Canada).

SpaceX Starship Update

SpaceX are continuing with preparations for their first orbital launch attempt with prototypes of their massive Starship / Super Heavy booster launch system. Due to take place in either January or February 2022, utilising Starship 20 and Booster 4.

Most recently, Booster 4 completed two cryogenic proof tests. In the first of these, on Tuesday, December 21st, the booster’s two propellant tanks were partially filled with inert liquid nitrogen in what was a comparative short test, with the liquid being pumped back to the fuel farm a few hours after operations stated. A more substantial test then took place on Wednesday, 22nd December. This saw both tanks almost completely filled with liquid nitrogen, giving rise to much of the booster’s outer skin gaining a coating of frost. Once pressure and leak tests had been completed, the tanks were again drained.

Frost forms on the outer skin of Booster 4 and the lower liquid oxygen and upper liquid methane tanks are filled with liquid methane during a cryogenic load test on Wednesday, 22ns December. Credit: LabPadre

The completion of both tests moves booster preparations closer to the static fire tests of its Raptor engines. Just how many of these tests there will be is unclear. It would seem likely, there would be at least two: one with the nine inner, sea-level motors, and a second involving all 29 engines; but it is possible that SpaceX might option for a broad series of tests, building up to firing all 29 engines a step at a time.

Meanwhile, activities around Starship 20 during the week saw the hoist attachment bars on the nose cone of the vehicle were removed, and their hard point mounted covered by heat shield tile frames and then the tiles themselves. This appeared to leave SpaceX with no means to lift the vehicle off of the sub-orbital launch stand it has been occupying for transfer to the orbital launch facilities, which in turn led to all sorts of speculation about ship 20’s future or how SpaceX might might it mounted on Booster 4 and ready to fly.

However, there is a potentially simple explanation for what has been going on. The attachment bars are only are only required for physically moving a Starship (e.g. into its transport to move it to / from the launch pad); they are not needed for actual flight. Further, two of them are located on the side of the vehicle that will be exposed to the greatest heat during re-entry into Earth’s atmosphere, and thus represent points of vulnerability.

Thus, it would make sense for the attach point to be removeable and their hard points capable of being covered by shaped elements of the thermal protection system. Such a capability would require testing in terms of checking the fit of the thermal panels – and doing this with the vehicle sitting on an sub-orbital stand is a lot easier than testing it for the first time when the Starship is sitting on top of its booster and then finding something needs to be adjusted. Of course, the proof of this will come if the cover panels are removed and the attachment bars re-installed.

The hoist attachment points at the nose of Starship vehicles (inset) appear to be removal, allowing their hard points to be covered with mounting frames that in turn can be fitted with thermal protection titles. Credit: What About It

During the week, Musk also announced that after the flight of Booster 4 / Starship 20, SpaceX will be switching to using only the new Raptor 2.0 engines in future testing, with Super Heavy moving directly to its 33-engine version, and Starship eventually moving from the current 6 engine configuration to 9 engines. It this respect, the first thrust puck for a 33-engine booster has already been delivered to the Starbase fabrication and assembly facilities at Boca Chica. Quite what the switch in engine type and count means for the almost-complete Booster 5, and the under-construction Booster 6 is unclear. Both are currently built around using 29 Raptor 1 engines – so neither of them may actually fly.

It’s not clear when the 9-engine variant of Starship will appear, but the addition of 3 extra vacuum rated Raptors 2.0 engines will see its maximum payload to low Earth orbit increase from 100 tonnes to 150 tonnes. The additional engines also main Starship will increase in overall length from the current 50 metres to at least 57 metres in order to accommodate the larger propellant tanks needed to feed all nine engines.

A rendering showing how a current 50-metre tall Starship vehicle with 6 Raptor engines might compare in height with a 9-engined version, the latter being “stretched” by four ring segments (shown in red) to accommodate its longer propellant tanks, leaving it standing at around 57.2 metres. Credit: SpaceX 3d Creation Eccentric

And if that weren’t enough, Musk has stated that SpaceX will start manufacturing propellants for Starship / Super Heavy from carbon dioxide drawn out of the atmosphere. They will do so using the Sabatier reaction, which takes atmospheric carbon dioxide and combines it with a measure of hydrogen, heating both in the presence of a catalyst to produce methane (fuel) and water. Electrolysis can then be used to split the water into oxygen and hydrogen – the latter being used to further the initial Sabatier reaction, and the former liquidised for use as an engine oxidiser.

Should SpaceX be able to use this capability at scale on Earth, they will have the means to produce fuel on Mars that can be used to both power ground vehicles and – more importantly – refuel starships so they can make the return trip to Earth. It is an approach I’ve covered previously in these pages, and one first proposed for Mars missions by Robert Zubrin and David Baker, back in the mid 1990s.

Finally, and as I recently reported, at the start of December 2021, SpaceX resumed work on building a Starship / Super Heavy launch pad at Kennedy Space Centre’s (KSC) Launch Complex 39A, currently the home of Falcon 9 / Falcon Heavy launches. However, on December 22nd, 2021, NASA confirmed SpaceX is seeking permission to build a second facility for Starship / Super Heavy launches out of KSC.

The planned expansion of Kennedy Space Centre showing the proposed LC-49, sitting to the north of Launch Complex 39 (LC-39B, still used by NASA and LC-39A (currently leased to SpaceX). Also shown is LC-48, a recently-completed launch facility, and Space Launch Complex 41 within the Cape Canaveral Space Force facilities that adjoin Kennedy Space Centre. Credit: NASA / KSC

For this, SpaceX have applied to use a site designated Launch Complex 49 (LC-49) first proposed as a new launch facilities by NASA in 2014, although a lack of demand meant no work was ever started.

However, before any work can commence, any plans must be subject to public and environmental impact review – the latter because KSC sits within the 570 sq km Merritt Island National Wildlife Refuge. This is home to over 1,500 species of plants, fish, reptiles and amphibians, birds and mammals, 21 of which are listed as endangered either by the state of Florida or by the US federal government. As the first phase of these reviews NASA has already posted details of a public “scoping period” to gather initial to collect public input on the proposal, and for SpaceX to disclose further details of their plans.


2 thoughts on “Space Sunday: JWST and a touch of SpaceX

Comments are closed.