Happy new year everybody and so far so good with the deployment of the James Webb Space
telescope.
I wanted to come on and give an update on how things are going because, well, everything
is going quite well.
And for icing on the cake, we have a new mystery that conceivable JWST could help solve.
The launch of the telescope from Kourou, French Guiyana was nothing short of picture perfect.
The European Space Agency’s Ariane 5 launch vehicle lived up to its highly reliable record
and not only put Webb into space, but did it very efficiently which means that the telescope
didn’t have to expend as much fuel making adjustments to its trajectory.
This is important because it has extended the life of the telescope dramatically.
Indeed it very likely doubled it or more.
One very important point in the success of the mission is that it has a gas tank, and
the more fuel that is conserved, the longer the telescope can tentatively operate.
This is because unlike the Hubble space telescope which was designed for servicing and upgrading,
James Webb is not.
The reason for this is simple, Hubble is in earth orbit, it functions like a satellite.
Webb is not, it’s in a complicated solar orbit that follows earth and is always much,
much more distant from earth than Hubble making it very difficult to service.
And it’s not really even designed for it if we could.
So the mission was designed to last a bit over 5 years, depending on the fuel used.
But since the launch basically nailed it, and the Ariane Rocket put Webb on a trajectory
that did not require drastic course corrections, so now we should have over ten years of service,
if not significantly longer if the JWST team can conserve even more fuel over the course
of its operation.
And that brings us to the course correction burns of the telescope itself.
It has successfully performed two of the three burns needed to put it into its L2 orbit.
The last is set for about one month after launch, and the first two went normally.
Other things that have gone well so far is the deployment of Webb’s solar panels and
the charging of its batteries, which again because of the successful launch was able
to be deployed earlier than expected.
There was some adjustment needed to the battery and solar array system, but it was never in
danger of failing; rather it’s one thing to work with a spacecraft on the ground, but
another as you learn how that spacecraft behaves in space and on its own in zero-G.
After that came the long process of unfurling JWST’s various components.
First of these was the high gain antenna, which happened about a day after launch.
This antenna allows for full high speed communications with the telescope, though it does have a
weaker transmitter that was used during the initial launch phase.
After that came the deployment of a momentum flap designed to help mitigate pressure from
the solar wind, and the telescope assembly itself raised up about four feet, all went
well, and then came the scariest part, the unfurling of the sun shield.
This multiple day process first involved deploying the sun shield, which went smoothly other
than some sensors on its protective cover not reading that the cover was unfurled, when
other instruments showed that it was.
This did not cause any problems however.
The next step is the tensioning of the sun shade.
This is scary, but well rehearsed here on earth.
In fact, one of the delays in the telescope’s construction was when a sun shade tore during
testing, so a lot has gone into designing the sun shade to deploy properly.
As of the writing of this episode, hot off the presses, this process is complete as of
a few hours ago and all seems to have worked normally.
This is important because of temperature regulation.
Being an infrared telescope, JWST is sensitive not only from the sun’s heat, but some of
its own equipment.
The sun shield is designed to dissipate that heat away from the telescope’s assembly,
and will produce temperature differences to the tune of about -370 degrees fahrenheit,
-223 degrees celsius, with the the hot side absorbing and radiating the full fury of the
sun averaging 185 degrees fahrenheit, or about 85 celsius.
Quite a temperature difference across a single instrument, and it happens over a distance
of only about 1.8 meters or six feet.
Now that that step is finished, and the temperature sensors turned on, in the coming weeks we
will see the deployment of the secondary mirror assembly and the unfolding of the primary
mirror itself.
All in all, JWST has 344 single point failures that could happen, where one component fails
and ends the mission due to no backups for the component.
That may sound scary, but with something this complex, not everything can realistically
have a back and after tensioning we’re now past about three quarters of them.
NASA is no stranger to high numbers of single failure points, the most recent Mars rover
had over 100, and all worked perfectly.
And, as I said, everything with JWST was very thoroughly tested down here on earth many
times.
But a clean room on earth is not zero gravity space, so things can still go wrong.
After the mirror deployments begins the long process of calibrating the space telescope
and preparing it for service.
This is a long, but somewhat mundane process.
And it’s very slow, the motors that position the individual mirror segments move excruciatingly
slowly in order to deliver the needed precision for optimal observation.
By the end of the year, the telescope should be in full operation, and so far so good with
the deployment of the instrument.
Once operational, Webb is planned to look at the very earliest galaxies in the universe
to try to determine the conditions of early galaxy and star formation.
Other things to tackle are the characterization of exoplanet atmospheres, studies of distant
asteroids in the solar system, and many other observations are planned.
And, as I’ve mentioned before, there is a ton of time intentionally built into the
telescope’s scheduling for transient events where the telescope can drop everything to
take a look at something unexpected or new happening in the universe.
And we have a new one of those as of very recently, that might make for an attractive
target for Webb once it gets going, specifically as an infrared telescope where it may be able
to lend a hand characterizing what’s going on here.
In a paper by Briann Powell and colleagues, link in the description below, they detail
the discovery of yet another peculiar star dipping in its light curve.
This is in regards to the mysterious variable star TIC 400799224, for those wondering what
that stands for, is that it’s that star’s numerical entry into the TESS Input Catalog,
compiled in conjunction with that mission that includes over a billion objects.
The team used machine learning programs to pick out this object and differentiate it
from the myriad of other possible variable star types in the catalog with this one being
unique so far.
Long-time viewers of this channel and Event Horizon will know of another star that mysteriously
dims like this, tabby’s star or KIC 8462852, incidentally that star’s number is its entry
into the Kepler Input Catalog done for that mission.
Now, it seems that multiple examples of this type of dimming have been seen, and oddly
enough seem to cluster in space for no good reason, but TIC 400799224 acts somewhat differently.
It’s dips are very rapid, this star can dramatically dip by 25 percent over four hours,
and they can be very sharp, almost like an eclipse.
This is very different from Tabby’s star which used to go into sharp dips but a bit
differently, but now tends toward long shallow fades.
But it’s possible that these two stars may be related with similar collisional events
within those systems, but not apparently under the same circumstances.
So here is what’s going on.
TIC 400799224 seems to be a binary star system, where one of the stars is being occluded by
dust.
This dust is governed by some kind of periodicity, probably a periodicity of the parent body
creating the dust, which is on a 19.77 day orbital period.
But there’s a difference between that periodicity and the appearance of the dust, which is much
more erratic.
This seems a lot like something like an asteroid or small planet disintegrating, which has
been seen before in nature, but what’s odd here is that it’s producing a LOT of dust,
enough to be optically thick.
This should mean that whatever is emitting the dust should be evaporating and losing
mass, but over the last six years the object has been observed, it doesn’t seem to be
doing this.
So now it's time for the researchers to go back to past sky surveys and try to determine
what this phenomenon has been doing over a much longer period of time, as was done with
KIC 8462852.
But Webb might be of use in further characterizing the dust during a dip in a similar manner
as it would be for KIC 8462852 in that the dust should glow in the infrared due to absorbing
light from the star and remitting it in infrared, especially with such a tight periodicity.
We shall see, and there are past infrared sky surveys that could also be consulted to
help further figure it out.
I’ll continue updating on this star, as I do with any of these strangely dimming stars
as more information comes available.
So in the end, we now sit with more than 70 percent of the JWST deployed, with only the
mirrors to go before the final burn to insert it into its L2 orbit, to then begin the process
of calibrating the instrument.
This will take months, but once finished, we should get over a decade of observations
from the instrument, and if all goes well, it will take its place amongst the most successful
spacecraft deployments ever attempted by humans thus far.
Thanks for listening!
I am futurist and science fiction author John Michael Godier wishing my telescopes deployed
as reliably as James Webb.
One of the reasons I don’t live stream my amateur astronomy sessions is because I’m
always fumbling around with eyepieces and I’m no better at doing things like polar
alignment than I was in 1992.
Decades with no progress and be sure to check out my books at your favorite online book
retailer and subscribe to my channels for regular, in-depth explorations into the interesting,
weird and unknown aspects of this amazing universe in which we look.