How Does NASA Schedule Space Launches?

To launch a spacecraft successfully, the stars (and moon, and planets) must literally align. Learn about all the factors that are taken into account to schedule a space launch in this episode of BrainStuff.

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Episode Transcript

Speaker 1 (00:01):
Welcome to brain Stuff production of iHeart Radio. Hey, brain Stuff,
Lauren vocal bomb here. It's hard to believe that as
I'm saying these words, almost half a century has gone
by since Neil Armstrong, Edwin buzz Aldrin, and Michael Collins
blasted out of the Kennedy Space Center in Cape Canaveral,
Florida with the presidential promise to fulfill. But here we are.

(00:22):
The Apollo sixteen mission launched on July six, nine, sixty nine,
at ninety two am Eastern Standard time, and NASA didn't
pick that start time at random. It was chosen because
it checked off the right boxes on a long list
of requirements. Crafting launch schedules has always been a rigorous science.
Every mission has its goals. In Apollo eleven's case, the
main objective was to put an American astronaut on the Moon,

(00:45):
winning the space race for old Uncle Sam. To that end,
NASA selected five potential landing sites just above the lunar equator,
since nobody likes a bumpy landing zone. The candidate sites
were geographically flat, but the astronauts couldn't just head out
at their earliest convenience, a lunar day lasts for twenty
nine point five Earth days, so if you were to
stand at given point on the Moon's surface for that

(01:06):
amount of time, you'd experience about fourteen straight days of
NonStop sunlight, followed by roughly fourteen uninterrupted days of darkness.
For Apollo eleven, NASA went full Goldilocks. The agency decided
that the cruise now famous Eagle module needed to land
at lunar dawn, when the sun is low but still visible.
Shadows became a topic of discussion. If the ground level

(01:27):
shadows were too long or too short when Armstrong and
company first arrived, they'd cause visibility problems. Therefore, the Eagle
would have to touch down while the sun was between
fifteen and forty five degrees above the lunar horizon. These
factors helped give NASA a set of launch windows. A
launch window is the time frame in which a spacecraft
can leave the Earth. They're often quite narrow, especially when

(01:48):
complex maneuvering is involved. With the Apollo eleven, the crew
had to blast off, position themselves over a specific corner
of the Earth, shoot toward the Moon, and then land
the Eagle at a pre approved site during lu or
dawn when the sun was fifteen to forty five degrees overhead.
Of the five possible landing areas, NASA ultimately chose the
Sea of Tranquility. They wanted to put Armstrong and Aldrin

(02:10):
up there late in the summer of nineteen sixty nine.
The lunar orbit meant that NASA would only get two
chances to hit its moving target. In order to reach
the Sea of Tranquility under the perfect set of conditions,
Apollo eleven had to take off on either July six
or August fourteen. NASA picked the former date. The July
sixteenth launch window was open from ninety two am to

(02:30):
one pm to buy the cruise of extra time in
case they needed it later. Apollo eleven was set to
head skyward at the earliest possible opportunity, which is to say,
right when the window opened. Within four days, Armstrong and
Aldrin were doing the moonwalk. The astronauts returned to Earth
on July. Fifty years later. Launch schedules are still notoriously
hard to plan. As NASA's official website dryly notes, this

(02:54):
is not a job for someone who slept through physics class.
Launch windows are inevitably shaped by mission objectives want to
send her over up to Mars. Your best bet might
be to wait until Mars and Earth find themselves in opposition,
a point when the gap between the two planets is
fairly short and they're both on the same side of
the Sun. That opportunity only comes along once every twenty
six months. When a spacecraft is supposed to visit another

(03:17):
heavenly body like Mars or the Moon, its travel plans
will be dictated by the other body's orbital pathway and
Earth's own trajectory. And that's not all. The gravitational influence
of other bodies such as the Sun must also be considered. Plus,
man made devices always encounter friction and wind when they
pass through Earth's atmosphere. That interference is guaranteed to affect

(03:37):
launch trajectories and by extension, launch windows, and of course,
atmospheric pushback isn't just a problem for deep space missions.
Even crafts that were built to orbit the Earth and
go no further have to deal with this issue. One
such object is the International Space Station, aboard a crude laboratory,
the i S s orbits roughly two and twenty miles
above the Earth or about three D fifty KOs and

(03:59):
completes about six teen revolutions around the planet every day.
NASA used to send astronauts up to the I S
S in reusable space shuttles every day. The I S
S would pass over or near the launching site at
Cape Canaveral. For a successful rendezvous to occur, NASA's shuttles
needed to take off within five minutes of that passage,
and to avoid dumping fuel tanks onto populated areas, the

(04:21):
ships had to follow a south to north trajectory over
the Atlantic Ocean. You won't see any of those launches
on NASA's twenty nineteen schedule. The American space shuttle program
was retired in twenty eleven, and NASA no longer ferries
astronauts to the I S S. At the moment, that's
Russia's job, regardless of the county. Space Center sees off
loads of other missions every year, and by the way,

(04:42):
NASA's got plenty of other launch sites at its disposal,
including the Vandenburg Air Force Space in southern California. And
wherever a launch is scheduled to begin, you can bet
that meteorologists are paying close attention to the weather. Early
in twenty nineteen, the much anticipated lift off of a
space X Falcon heavy rocket at Cape Canaveral was delay
aid due to high winds. Back in nineteen seventy one,

(05:03):
weather constraints forced NASA to postpone the Apollo forteen launched
by forty minutes. These delays were imposed after a close
call in November of nineteen sixty nine, when the Apollo
twelve crew launched on a murky morning from Kennedy Space Center.
Just thirty six and a half seconds later, when the
crew was about a mile and a half or two
and a half kilometers above the ground, the first of
two lightning bolts struck the vessel. Nobody panicked. Astronauts Charles Pete, Conrad,

(05:26):
Alan Bean, and Richard Gordon followed mission controls instructions carefully,
and within a week Apollo twelve made it to the Moon,
but NASA set up strict launch standards that prevented this
from ever happening again. But rain, lightning, and wind aren't
the only things that could potentially interfere with the launch.
To avoid putting any passing airplanes in harm's way, NASA
collaborates with the U. S Air Force and Federal Aviation

(05:48):
Administration to close large squads of commercial airspace during launch windows.
Today's episode was written by Mark Bancini and produced by
tie Are Playing brain Stuff is a production of I
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(06:09):
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