2019-07-01_Discover

JULY/AUGUST 2019. DISCOVER 51

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A Helicopter on Mars

The air on Mars has just one hundredth the thickness of

Earth’s atmosphere. Even at ground level, it’s a fraction of

the density you’d encounter at the top of Mount Everest.

So when NASA decided to pack a drone on the upcoming

Mars 2020 mission, the Jet Propulsion Laboratory had

to design a copter unlike any ever flown on Earth. The

two rotors, which spin in opposite directions for stability,

turn at 2,800 rpm, up to 10 times the speed of an ordinary

helicopter. They’re also much larger and more rigid than

usual, each spanning 4 feet, totally overshadowing the

5-inch cube beneath, which is also special. This fuselage

is packed with rechargeable lithium-ion batteries that not

only turn the two mighty rotors, but also provide heat to

protect the copter’s electronics when nighttime tempera-

tures dip to minus 130 degrees Fahrenheit. Yet the most

challenging part of flying a drone on Mars has nothing

to do with the temperature or atmosphere — it’s the dis-

tance to Earth. With a minimum of four minutes to relay

a radio signal between the two planets, the copter has to

be basically autonomous — able to fly flawlessly, by itself,

over terrain no human has ever encountered.

1903

The Wright Brothers

invent the airplane,

achieving the first manned

flight in a powered,

heavier-than-air flying

machine. The Wright

Flyer, a small biplane

with two engine-driven

propellers, stays aloft for

a historic 12 seconds. The

brothers harness physical

principles that have

applied to every airplane

since, balancing two sets

of opposing forces, as

shown at right.

1930

Frank Whittle patents

the first jet engine.

This powers an airplane

by igniting compressed

gas to generate forward

thrust. The Royal Air

Force rejects his idea at

first, but comes around

after Germany deploys

its own jet airplanes

in World War II.

1936

Ewald Rohlfs

demonstrates the

Focke-Achgelis

Fa 61, an early fully

functional helicopter.

Its two rotors spin in

opposite directions,

allowing it to take off

and land vertically,

fly forward and

backward, and hover.

1957

The Soviet Union

launches Sputnik 1, the

first artificial satellite.

Lobbed into lower

orbit on a modified

intercontinental

ballistic missile, Sputnik

demonstrates Soviet

technical prowess

at the height of the

Cold War.

1969

Neil Armstrong and

Buzz Aldrin are the

first humans to land

on the moon. After

reaching lunar orbit

in a computer-

controlled rocket,

they descend

in a craft that

Armstrong steers

by hand.

A “rotorcraft” like the one

in this rendering is scheduled

to launch next July with

NASA's Mars 2020 mission.

An upward force

achieved by pushing

air under the wings.

A counterforce

to lift imparted by

Earth’s gravitational field.

A forward force

imparted by the

propulsion system.

A counterforce to thrust

caused by friction and

air currents.

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Sputnik 1