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EI2GYB > ASTRO 27.08.21 11:23l 175 Lines 8435 Bytes #999 (0) @ WW
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Subj: Arecibo is dead. Should we build its replacement on the Moo
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Arecibo is dead. Should we build its replacement on the Moon?
NASA may finally be serious about the idea of building a large
radio telescope in a lunar crater.
When the 60-year-old Arecibo Observatory collapsed in 2020, the crash
didn't just take down one of the world's preeminent radio telescopes, it
also dealt a massive blow to the future of radio astronomy.
Arecibo may have been old, but it also had unique capabilities that made
it ideal for studying things like gravitational waves, as well as
mapping the surfaces of asteroids as they slip by Earth.
Now, radio astronomers around the world are debating what comes next.
Should Arecibo be rebuilt anew? If so, where would the money come from?
Those questions don't have easy answers, but the discussions are happening.
Preliminary plans for another revolutionary radio telescope continue to
inch forward every day.
And interestingly, these talks have led NASA to reconsider a bold idea
that was first dreamed up a half-century ago: building a behemoth radio
telescope on the farside of the Moon.
Arecibo's design benefited from being built in a natural sinkhole in Puerto Rico.
Similarly, astronomers could use existing lunar craters to build a
radio telescope on the Moon for (relatively) cheap; impacting space rocks
have already done the digging for them. And unlike Earth, the Moon
has no weather or wind to accelerate erosion.
Even the pull of gravity itself is weaker on the lunar surface.
Arecibo on the Moon
===================
As early as the 1960s, astronomers wanted to build a radio telescope on
the farside of the Moon.
That's because the lunar farside always faces away from Earth, which
means the entire Moon acts as a sort of shield that blocks Earth's
cacophony of outgoing radio noise.
This creates an environment where scientists could theoretically
observe the universe in wavelengths that can't be easily analyzed
from our planet - or even in orbit.
An Arecibo on the Moon would be more than a replacement, though.
The premise is similar to the way astronomers decided to replace the
Hubble Space Telescope.
Rather than replicating the original, the community embraced the
idea of building something entirely different.
The James Webb Space Telescope (JWST) used insights gleaned from
Hubble's tenure, sure.
But JWST was specially built to study the universe primarily through
infrared light, while Hubble focuses on visible and ultraviolet light.
That spectral shift means JWST will be able to investigate previously
unexplored aspects of the universe with impeccable detail.
The same is true of building a large radio telescope on the Moon.
While Arecibo dedicated a half-dozen decades to studying radio waves
at the centimeter- and millimeter-scale, a lunar radio telescope could
monitor wavelengths larger than a meter, something astronomers can't
do from Earth.
If an Arecibo-like observatory was built on the Moon, it could potentially
spot many exotic cosmic phenomena, such as auroras around distant
Earth-like exoplanets. Most alluringly, it could even pick up
radio signals from the earliest days of the cosmos, before the
first stars and galaxies were born.
Frank Drake, a world-renowned astronomy, even once pitched the idea for
a "Very Large Arecibo-Type Telescopes" on the Moon at a NASA conference
in 1986. Drake reasoned that utilizing a lunar crater would minimize
the need to build large structural elements. Some panels, platforms,
and a slew of cables might suffice, he suggested.
The Moon also holds so many craters that it should be relatively easy to
find one with a sturdy enough rim that it can serve as the anchor point
for the telescope's support cables.
This would avoid the cost of the expensive towers that anchored cables
at Arecibo.
(In fact, the telescope collapsed in 2020 after the cables attached
to its towers failed.)
"Reasonable valley and crater cross sections fulfill this need quite
nicely," Drake wrote.
"In this case, a substantial saving in cost and materials accrues.
This approach could be used to build Arecibo-style telescopes on the
Moon or on the Earth at substantial savings over the cost of the actual
Arecibo design."
Lunar Crater Radio Telescope
============================
In recent years, NASA has shown support for these ideas at levels never
seen before. The space agency has even funded studies on several early
proposals to finally build an Arecibo-like observatory on the Moon.
Of these proposals, the Lunar Crater Radio Telescope (LCRT) echoes some
of the same ideas Drake brought up a generation ago.
But unlike previous mission designers imagined, the latest iterations
of Moon-based telescopes wouldn't rely on astronauts to construct them.
Saptarshi Bandyopadhyay, a robotics technologist at the Jet Propulsion
Laboratory and leader on the LCRT project team - says they intend to
build LCRT using simple lunar rovers like the ones NASA has already designed.
LCRT would land a spacecraft full of rovers outside the crater.
These would then retrieve the support wires, take them to the crater
rim, and assemble a mesh system spanning approximately 0.6 miles
(1 kilometer). However, the whole system would have to fit inside a
single lunar-landing spacecraft, like Blue Origin's Blue Moon.
By depending on robots instead of astronauts, the project can save a
significant amount of money.
Any mission involving astronauts requires extensive - and expensive -
safety precautions.
Every potential problem requires extra scrutiny and engineered safeguards.
For example, sharp edges can slice through spacesuits, so they're avoided
on crewed flights.
But rounded edges don't allow you to maximize cargo space, which
you'd want to do for a robotic trip to the Moon.
NASA has also already begun testing a versatile model of a rover
called DuAxel, which could be used for a number of different lunar missions.
Among other things, DuAxel can climb crater walls. And as a bonus,
it's relatively cheap.
"If we send 10 of these robots and two of them die; it's fine,"
Bandyopadhyay says.
"Two of them are dead, but eight robots are still working.
It's not like that with astronauts."
However, even with all the potential advantages of robotic builders,
the current cost of the technology likely puts the mission out of reach.
SAPART estimates that building a radio telescope on the Moon would cost
billions of dollars.
That's why his team is trying to develop new kinds of cables and mesh
that would be dramatical cheaper to use than what's available now.
LCRT's initial study relied on $120,000 of NASA Innovative Advanced
Concepts (NIAC) project funding to investigate the concept.
And the next stage of their mission plan would let engineers get to work
on developing the mesh. By spring, Bandyopadhyay says, his team hopes
to publish their initial results.
"We have a good first design now that makes sense and that we could
potentially fly," he says.
"If you gave us four or five billion dollars we could launch it tomorrow."
But despite the enthusiasm, Bandyopadhyay isn't optimistic we'll see
an Arecibo-style telescope on the Moon in the near future.
After all, science tends to be slow.
"I would be very surprised if I see LCRT deployed before I retire,
and I'm a very young scientist," Bandyopadhyay says. "These things are hard.
These questions we are trying to solve are hard. And the science
windows these questions will open are hard. Everything is hard.
If it was easy, we would have done it already."
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