The James Webb Space Telescope has a problem,
or specifically one of its science instruments has a problem.
That instrument being the Mid-Infrared Instrument, or MIRI.
According to NASA and ESA's press release, MIRI was setting up for an observation
on August 24th, when one of its wheels suddenly got a little bit sticky.
The problem crept up in MIRI’s Medium Resolution Spectrograph, or MRS.
As MRS was setting up to take observations.
It rotates one of two wheels containing
dichroic and diffraction gratings into place so that it can capture
a specific range of wavelengths to take spectra.
As this was being set up, one of those two wheels started to exhibit
some excess friction, and the observation was paused.
Since then, all MRS observations with MIRI have been suspended,
while the Anomaly Review Board works out exactly what the problem is
and what steps would be necessary in order to fix it.
Now, to be clear, Webb has not been placed into a safe mode.
The safe mode occurs whenever there's an anomaly on board a spacecraft.
And in Webb's case, it would stop taking science data,
report the anomaly to the ground, and essentially just wait
until it receives commands on what to do next.
And that doesn't seem to be what happened here.
Instead, the Anomaly Review Board just paused edium resolution spectroscopy
aboard MIRI, but the rest of Webb's instruments,
including the other half of MIRI, are all still functioning.
So Webb is still continuing to take science data, only it's
just not doing any mid-resolution spectroscopy with MIRI.
So what exactly did happen here?
Well, it does not appear to be
something external, such as a micrometeoroid impact.
We've already had a couple of those already,
including a rather large one toward the end of May.
But MIRI and all the other instruments are well encased
inside of the Integrated Science Instrument Module,
and they're very well protected against outside interference.
It also does not appear that this is an anomaly
that would threaten the overall Webb mission.
So let's just talk about what we do know and where the problem appears
to be on board MIRI.
And that also means we should also step back
and just kind of remind ourselves exactly how MIRI works.
MIRI is the only instrument that's capable of observing
at longer mid-infrared wavelengths.
To that end, MIRI is essentially two instruments sandwiched together
with an imager on top and a spectrograph on the bottom.
Together, these two halves support four observing modes aboard MIRI.
There's imaging, coronagraph imaging, low resolution
spectroscopy, and medium resolution spectroscopy.
Believe it or not, the low resolution spectroscopy
is actually done on the imaging side of MIRI.
The bottom half is the mid resolution spectrograph or MRS.
Light enters into the MRS and is split into four spectrometer channels.
Each channel captures a portion of MIRI's wavelength range,
and this four-channel arrangement was chosen to save space
and make the instrument fit into Webb, as well as save mass
so that it could be launched along with everything else.
And then there’s also the thermal and the optical constraints.
And believe it or not, this was also designed to minimize
the number of moving parts that would be absolutely necessary.
But even then, the optical system had to be subdivided further
in order to satisfy all of those constraints.
So MIRI’s designers came up with a clever idea.
Each of the four sub channels was further divided into three sub bands
covering the short, medium and longer wavelength regions of each channel.
So instead of taking one spectrum
across the entirety of each of the four channels, MRS takes three separate
spectra that fill in a portion of each channel's waveband.
To do that, MIRI uses two wheels called
Dichroic/Grating Assemblies or DGA’s.
Dichroics are beam splitters, three of which are used at any
given time to send the light off into the four channels.
Within each channel, the light is sliced and then collimated before
it returns to a set of gratings mounted
on the upper part of the wheels.
The gratings disperse the light into a spectrum
which eventually lands on the detectors.
By rotating these two wheels,
the DGA's present a combination of dichroics and gratings
that are optimized for each of the three sub bands.
Apparently one of these two
wheels is the one that's reporting excessive friction when trying to rotate.
So the Webb team have, I think pretty smartly,
suspended all MRS’ observations until they can understand
exactly what the problem is and work out what steps would be needed to resolve it.
I'm not going to really speculate on exactly how this is going to get resolved,
but I can tell you from my own experience working on the Hubble Space Telescope,
the X-ray Timing Explorer, and flying, commanding and yes,
troubleshooting Small Explorer spacecraft,
that there is a process in place, and you just work the problem
through step by step until you really understand what the problem is,
figure out its fix, test the fixes very carefully,
and then attempt them on board the spacecraft.
Let's give the Anomaly Team some time to do their work.
In the meantime, I do want to say thank you to my Patreon supporters
who are helping to keep Launch Pad astronomy going,
and I'd like to welcome Emily O'Brien as my newest supporter.
And if you'd like to join me on this journey
through this incredible universe of ours,
as well as finding out the latest information from the Webb telescope,
well, please make sure to subscribe and ring this notification bell until...
Okay, so look, guys, I'm doing this, and Leo is in my way, okay?
And, yeah, you're just...you're walking over my keyboard, dude.
You're you've messed up my outro.
Talk about anomalies right here.
Until next time.
Stay curious, my friend.