The future space telescopes will blow our mind
Last Christmas, a rocket lifted off from French Guiana carrying the largest space telescope
ever made into space.
Known as the James Webb Space Telescope, astronomers will use this scientific Moloch to study everything
from habitable exoplanets to the formation of the first galaxies.
Webb is the first mega telescope of this size to be launched into space, but it could also
be the last.
Indeed, with astronomers interested in ever-larger telescopes, especially to answer the big question
about the presence of alien life on extrasolar planets, the ability to build telescopes directly
in space will become essential.
As someone put it, "assembling large structures in space is not really a matter of ifs and
buts… it's just a matter of when..."
As we grow more ambitious in our desires to see further and more precisely in space, the
need for larger and larger telescope mirrors becomes inevitable.
The reason is very simple: only with the collection of a large number of photons through a super
large mirror the quality of "seeing" can improve significantly.
Large aperture telescopes benefit all astrophysics as well as planetary and Earth science.
They provide unprecedented spatial resolution, spectral coverage, and signal to noise, advancing
all of these science areas.
The largest mirror in space is currently that of the Webb Telescope, 6.5 meters.
It will only become operational in a few months, but already astronomers and space scientists
are pressing for larger mirrors to accomplish what the space telescopes of today cannot
do.
This is evident in the National Academies of Sciences Decadal Survey underway which
features four candidate Flagship-class Observatories for the 2030s.
Three proposals call for telescope mirrors that are significantly larger than the Hubble’s,
and the most ambitious by far is LUVOIR which has been proposed at 15.1 meters or at 8 meters,
or maybe something in between.
A primary goal of LUVOIR, and the reason for the large size of its mirrors, is that it
will be looking for signs of biology on distant exoplanets - an extremely ambitious and challenging
goal.
The LUVOIR team would have argued for an even larger telescope mirror, around 20 meters,
except that 15 meters is the maximum folded size that would fit into the storage space
available on the super heavy-lift rockets expected to be ready by the 2030s.
This desire for larger and larger space telescopes has rekindled dormant but long-present interest
in having an alternative to sending multi-billion dollar payloads into space via one launch
only.
The alternative is “in-space assembly", and NASA has shown increased interest in pushing
the idea and technology forward.
The fundamental reality behind the push for "in-space assembly" is easy to understand:
Anything going to space must fit within the rocket taking it there.
Even the very biggest - the mammoth 10-meter rocket fairing of NASA’s still-in-development
Space Launch System - would be unable to hold something like the International Space Station
or even the space agency’s smaller “Gateway,” a moon-orbiting space station proposed for
the project Artemis in the 2020s.
Launching such megaprojects piece by piece, for orbital assembly by astronauts or robots,
is literally the only way to get them off the ground.
And coincidentally, even though massive “heavy lift” rockets such as the Space Launch System
remain ruinously expensive, the midsize rockets that could support orbital assembly with multiple
launches are getting cheaper all the time.
The forces demanding supersize space telescopes are straightforward, too: The larger a scope’s
light-collecting mirror is, the deeper and finer its cosmic gaze.
Simply put, bigger is better when it comes to telescopes - especially ones with transformative
objectives such as tracking the coalescence of galaxies, stars, and planets throughout
the universe’s 13.8-billion-year history, learning the nature of dark matter and dark
energy, and seeking out signs of life on habitable worlds orbiting other stars.
Most of today’s designs for space telescopes pursuing such alluring quarry cap out with
mirrors as wide as 15 meters - but only because that is the approximate limit of what could
be folded to fit within a heavy-lift rocket like the Space Launch System.
Astronomers have long fantasized about building space observatories even bigger, with mirrors
30 meters wide or more -rivaling the sizes of ground-based telescopes already under construction
for the 2020s.
Assembled far above our planet’s starlight-scattering atmosphere, these behemoths could perform
feats the likes of which ground-based observers can only dream, such as taking pictures of
potentially Earth-like worlds around a huge sample of other stars to determine whether
those worlds are actually habitable - or even inhabited.
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If our own Earth is any example to go by, life is a planetary phenomenon that can transform
the atmosphere and surface of its homeworld in clearly recognizable ways; provided, that
is, one has a telescope big enough to see such details across interstellar distances.
A recent report from the National Academies of Sciences said NASA should take the lead
on a major new space telescope that begins to approach that grand vision - something
capable of surveying hundreds of nearby stars for snapshots of potential exo-Earths.
That recommendation is reinforced by the core conclusion of another new Academies report
which calls for the agency to make the search for alien life a more fundamental part of
its future space exploration activities.
These reports build on the growing consensus that our galaxy likely holds billions of potentially
habitable worlds, courtesy of statistics from NASA’s deceased Kepler space telescope and
the space agency’s newly launched Transiting Exoplanet Survey Satellite.
Whether viewed through the lens of scientific progress, technological capability, or the
public interest, the case for building a life-finding space telescope is stronger than ever before
- and steadily strengthening.
Sooner or later it seems NASA will find itself tasked with making this longed-for giant leap
in the search for life among the stars.
How big such a telescope must be to offer a reasonable chance of success in that interstellar
quest depends on life’s still-unknown cosmic prevalence.
With a bit of luck, one with a four-meter mirror might suffice to hit the jackpot, locating
an inhabited exo-Earth around one of our sun’s nearest neighboring stars.
But if the cosmos is less kind and the closest life-bearing worlds are much farther away,
something in excess of the 15-meter limit imposed by near-future rockets could be necessary
to sniff out any living planets within our solar system’s corner of the galaxy.
In short, "in-space assembly" may offer the only viable path to completing the millennia-long
effort to end humanity’s cosmic loneliness.
Nick Siegler, Chief Technologist of NASA’s Exoplanet Exploration Program, with others
scientists proposed to NASA a study of robotic "in-space assembly" in 2018, and the idea
was accepted.
Siegler’s study claims that for space telescopes larger than LUVOIR, "in-space assembly" will
probably be a necessity because it’s unlikely that heavy-lift rockets will be getting any
bigger than what’s being built now.
And we have enough evidence to suggest there are benefits to assembling in space with smaller
telescopes, too.
The final conclusion of the study, in fact, is that even with space telescopes in the
range of mirrors of 5-to-7 meters and then above, planners should start thinking of robotic
assembling in space to reduce a significant number of risks and maybe cost.
The idea, however, was certainly not new...
Even when scientists and engineers were contemplating for the first time the concept of LUVOIR,
they proposed that it be at least 18 meters in diameter and that it be assembly in space
by astronauts.
Different components of the observatory would be launched at different times and then the
astronauts would fit the pieces together.
And that would be also a great way to train astronauts for the kind of work they will
have to do in the future on Mars and in deep space, and it was perhaps the only way to
get a really big telescope into space.
The only difference was about who should be in charge of the assembly in space: human
beings or robots?
The answer came shortly.
The effort to understand possibilities and challenges associated with "in-space assembly"
led to a formal NASA study headed by Siegler, and the report released in 2018 concluded
that while “in-space assembly” has a bright future, the idea of using astronauts to do
the assembling - rather than robots - is not considered the way to go now.
A decision that wanted to take into account the safety of astronauts forced to operate
not in low orbit as happened for example on Hubble and the Space Station, but at 1.5 million
kilometers from home, in the region of Lagrange L2.
But in particular, the study must answer the question: “When is it advantageous to assemble
space telescopes in space rather than to build them on the Earth and deploy them autonomously
from individual launch vehicles?”
Well, from the point of view of risk reduction, the answer is definitely yes.
With a telescopic monster like Webb, an explosion on the launch tower or a small inconvenience
in the deployment of the mirror could easily turn the telescope into a $10 billion piece
of space junk.
But if the telescope is thrown into pieces and assembled by robots, the errors become
less devastating.
If something goes wrong, you can simply send a spare part on the next rocket starting.
To give a more complete answer, Siegler and his colleagues also simulated the hypothetical
assembly in space of a 20-meter telescope.
About three times the size of the Webb telescope and twice the size of the Gran Telescopio
Canarias, currently the largest optical telescope on Earth.
This imaginary instrument could be used to search for exoplanets, which means it must
be incredibly stable and precise.
According to Siegler, this was the "hardest case possible".
Things would be like this.
First, NASA would send parts of the telescope on multiple rockets.
The inaugural lot would bring the main platform for the construction of the telescope, some
trusses disassembled for the support structure, and a pair of robotic arms.
For a 20-meter telescope, 11 additional launches would deliver the remaining pieces of the
telescope in capsules that attach to the telescope platform.
At that point, the robotic arms can start to put everything together.
It might sound like science fiction, but at the end of the day, we were doing something
similar 20 years ago.
Remember that the largest artifact made in space, the International Space Station, was
assembled in orbit by astronauts aided by robotic arms.
As well as Hubble during repair missions.
And that even today robotic arms regularly guide cargo capsules to mooring with the Space
Station and wander throughout its length to carry out repairs.
Manual assembly by astronauts is highly cost-inefficient or not feasible due to orbital constraints
and increased radiation above the low orbit.
However, autonomous robotic assembly systems could provide the means to build larger structures
in space in the near future.
Modularity is a key concept for such structures and also for reducing costs in new spacecraft
designs.
The advantage of the modular approach lies in the ability to generate a large number
of unique resources from a small number of building blocks.
Therefore, spacecraft can be easily adapted to particular use cases, and could even be
reconfigured during their lifetime using a robotic manipulation system.
It's complicated, it's expensive, but it doesn't matter, it's just a matter of wanting to do
it!
“The scientific community is sometimes its own worst enemy when it comes to understanding
what it is that’s possible,” says Ken Sembach, director of the Space Telescope Science
Institute.
“Some of us now have the preconceived idea that it is not possible to build another telescope
that is bigger and, yes, maybe more expensive than Webb.
But I talk all the time to younger researchers, Congress and the public, and they all ask,
‘Why aren’t we thinking bigger?’
People want to support ambitious things.
So it is possible - provided there is a damn good reason to do it.”
And if NASA will decide to change gear or not we will know in a short while, when it
will have to choose the space telescope of the next future to propose for funding by
Congress.
Will it be the 15.1 meters LUVOIR-A or the 8 meters LUVOIR-B?
For the first time, we can say with a straight face that we’re conceptually designing missions
with reasonable expectations of finding life on planets outside the solar system.
And to not do that when you have the opportunity to - well, that seems a little crazy.
Doesn't that sound like you too?