Sky & Telescope - April 2023 - 18

Altitude (kilometers)
GREGG DINDERMAN / S&T
Science & Society
The German Aerospace Center also appears to have been
left out of the loop. Krabbe and his colleagues were shocked
to learn the same news. " It was a one-sided decision, " Krabbe
says. " As far as I know, the German Aerospace Center never
agreed to that. "
The change was a major blow to the SOFIA project. " That
was a death sentence, " Schulz says.
Money Matters
The sad reality is that NASA doesn't have the money to fund
every worthy project. " There has never been a budget where
we could cover everything we would like to do, " says Thomas
Zurbuchen, who served as NASA's associate administrator for
science until the end of 2022.
And SOFIA is far from cheap. Jet fuel, maintenance, and
overhead for safe flight operations all cost money. In 2021,
SOFIA accounted for 6% of the overall astrophysics budget,
a larger share than any other program except for the Hubble
Space Telescope. (Development of the James Webb Space
Telescope is not included in the astrophysics program; it's a
separate line item in the budget.) And NASA covers 80% of
SOFIA's budget; DLR only supplies 20%.
" It just comes down to a numbers game, " Lucey says. " So
the astrophysics program, every dollar it spends on SOFIA is a
dollar they can't spend on something else. And the amount of
science per dollar is kind of low. It does great science, but just
not enough of it for every dollar spent. "
NASA runs a careful calculation of operating costs relative
to scientific output, and the result has changed dramatically
over the last three decades, Zurbuchen explains.
Observatories by Altitude
50
Space telescopes (HST, JWST, etc.)
40
Scientific balloons
30
Scientific balloons fly above nearly all of Earth's atmosphere
and water vapor.
Space telescopes can observe infrared wavelengths without interference
from Earth's atmosphere - and the farther from Earth, the better.
When SOFIA was first conceived in the 1990 decadal survey,
it was a lot more complicated and expensive to send an
observatory to space. So the solution seemed simple: Use an
airplane to capture infrared science faster. But SOFIA wasn't
fast enough. Space-based technology evolved at a rate that
outpaced SOFIA's delays, allowing observatories like Herschel
and Spitzer to launch in the interim.
" There are science opportunities that have a window of
opportunity, and if you miss it, it's going to get harder, "
Zurbuchen says. " And the case that was at the heart of SOFIA
became less important. "
That explains why SOFIA has often been on the cutting
block. In 2006, NASA tried to cancel the project, but Congress
and Germany forced the agency to restore it. In 2014,
NASA again threatened SOFIA's funding - just 11 days after
the observatory became fully operational. And NASA continued
to try to nix SOFIA in 2020, 2021, and 2022, until it
finally succeeded.
Many argue, however, that you can't look at the yearly
budget alone. Yes, SOFIA is more expensive to operate on a
year-to-year basis than a satellite, but its overall expenses are
much lower. The Hubble Space Telescope, for example, cost
roughly $4 billion to build, launch, and operate for the first 8
years of its lifetime. SOFIA has only cost $1.8 billion. Other
space-based observatories, on the other hand, have cost much
less: The Kepler Space Telescope, which ran for 9 years, was
only $704 million.
Although Meixner respects NASA's right to make this
decision, she thinks that the numbers argument is flawed.
" If they had let it go on for three more years, we would have
20
SOFIA flew above 99.9% of the water vapor in Earth's atmosphere,
enabling it to study far-infrared wavelengths inaccessible from
the ground.
10
Keck
VLT
18 APRIL 2023 * SKY & TELESCOPE
SOFIA
ALMA
The highest ground-based observatories sit above roughly 80% to 90%
of the water vapor in Earth's atmosphere in order to observe infrared
and submillimeter wavelengths. But water-vapor levels change notably
by day, season, and weather, sometimes preventing observations.
Sky & Telescope - April 2023

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