Scientific American - USA (2020-05)

74 Scientific American, May 2020

SOURCE: JONATHAN M

CDOWELL’S SPACE REPORT, 2019 (HTTPS://PLANET4589.ORG)

1,000–10,000 kg

100–1,000 kg

1–10 kg

1,000–10,000 kg

100–1,000 kg

1–10 kg

1,000–10,000 kg

100–1,000 kg

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

2010

2015

1,000–10,000 kg

1–10

10–100

100–1,000

1,000–10,000

Heavier Above 10,000

Lighter

International

Space Station

begins

Width represents the number

of active satellites in a given year.

At the start of 2000, there were

287 in geosynchronous orbit:

15 weighed 100–1,000 kg;

272 weighed 1,000–10,000 kg.

Weight classes within

an orbit are arranged

from least prevalent (left)

to most (right).

100–1,000 kg

Active satellites
in July 2019
(2,244 total):

10–100 kg

Hubble

Space

Telescope

begins

10–100 kg

Time

How to Read This Chart

More recent years are given more space,

so new trends toward the bottom are easy to see.

Orbits (in kilometers)

Geosynchronous (35,786)

Medium Earth (2,000–35,786)

Upper Low Earth (550–2,000)

Lower Low Earth (below 550)

Satellite weights (in kilograms)

121 495 254 154 4 99 104 111 336 5 68 125 181 493

GRAPHIC SCIENCE
Tex t by Mark Fischetti | Graphic by Nadieh Bremer

Satellite

Surge

Low-orbit instruments

are taking over the skies

For decades the number of satellites orbiting Earth rose

at a gentle pace, but growth has soared recently. By July

2019 more than 2,200 satellites were aloft. In the 1980s

and 1990s the action was in geosynchronous orbit

( blues ), says Jonathan McDowell, an astrophysicist at

the Center for Astrophysics|Harvard & Smithsonian. But

now the action is in the lowest Earth orbits ( yellows ),

he says, and increasingly dominated by young compa-

nies rather than government, military or academic

owners. Today the push is from Starlink—constella-

tions of satellites weighing 260 kilograms, being

launched by SpaceX to deliver high-speed Internet.

The uptick started around 2014, stemming largely

from CubeSats—diminutive satellites, each lighter

than 12 kilograms, that were lofted in groups. They

are fulfilling a desire to observe changes on Earth

every day. CubeSats could reveal, for example,

how people were moving around Wuhan, China,

during the coronavirus outbreak. And instead

of Google Earth showing driveways with cars

from 10 years ago, it could display vehicles

purchased last week.

Tiny CubeSats have

flourished, trimming

the median mass of

objects in the lower

low-Earth orbit.

SpaceX had

launched 240

Starlink satellites

(260 kilograms each)

as of Februar y 2020.

It has permis sion to

send almost 12,000

more into the two

l o w - E a r t h o r b i t s ,

roughly six times

all satellites aloft.

Low-Earth orbit is split because atmospheric friction

below about 550 kilometers will drag satellites back

to Earth within a few decades. Craft above that

altitude can avoid orbital decay for hundreds of years.

Active Satellites