Explorer 1: The First U.S. Satellite

 In Space, FVEY, P5

World Space Week 2020 will cel­e­brate the impact of satel­lites on human­i­ty from Oct. 4 to Oct. 10. Find out how to celebrate here and check out the his­to­ry of Explorer 1, the first U.S. satel­lite ever to fly, below!

Explorer 1 was the United States’ first satel­lite in space. The 1958 launch of the satel­lite — twice the size of a bas­ket­ball — was an impor­tant moment for the coun­try, as the Space Race with the Soviet Union was just begin­ning.

The satel­lite marked a moment when the United States got its con­fi­dence back after a series of unsuc­cess­ful launch­es and the Soviet Union’s suc­cess­ful launch of Sputnik. The satel­lite also helped but­tress the nation’s tech­no­log­i­cal con­fi­dence in the eyes of the world. It sig­naled that the coun­try was ready to explore the uni­verse.

Spurred by the Soviets

Explorer 1’s ride to space came through a com­pli­cat­ed set of cir­cum­stances. The United States had at least three main rocket options for send­ing the satel­lite into space. The ones that are most remem­bered today are Vanguard — under devel­op­ment by the Navy — and Juno. The latter rocket was based on an Army rocket designed by German sci­en­tist Wernher Von Braun, who worked on the V‑2 mis­sile pro­gram that sent bombs to England during World War II.

The satel­lite was sup­posed to launch as the United States’ con­tri­bu­tion to sci­ence during International Geophysical Year (which ran from 1957 – 1958). Then his­to­ry inter­vened. The Soviet Union rocketed Sputnik into space on Oct. 4, 1957. This was the first arti­fi­cial satel­lite any nation sent out of the Earth. The launch — revealed only after it was a suc­cess — stunned most of the Western world. It was a coup for Soviet rocket tech­nol­o­gy, and led some to muse that bombs could be launched just as easily as a satel­lite.

This accel­er­at­ed the United States’ plans. Rocket and satel­lite engi­neers quick­ly got to work, trying to prove they were also capa­ble of launch­ing into space.

Behind the Vanguard

On Dec. 6 of that year, a long two months after Sputnik, live reports of the Vanguard rocket car­ry­ing Explorer 1 broad­cast in tele­vi­sions and radios across the United States.

Vanguard, accord­ing to NASA, was chosen because it had more over­tones of a civil­ian pro­gram — a policy deci­sion going all the way up to President Dwight Eisenhower, who did not want the appear­ance of using bal­lis­tic rock­ets intend­ed for mil­i­tary pur­pos­es to usher in the new Space Age.

Unfortunately, the rocket explod­ed moments after the launch in front of TV cam­eras. Amid head­lines such as “Kaputnik,” senior space offi­cials took stock and exam­ined their alter­na­tives. Behind closed doors, they decid­ed to pro­ceed with the Juno rocket.

Preparations at Cape Canaveral went on in secre­cy for weeks, accord­ing to NASA, but as the launch date approached the media was informed. Explorer 1 suc­cess­ful­ly flew into space on Jan. 31, 1958. A female team of sci­en­tists at NASA’s Jet Propulsion Laboratory cal­cu­lat­ed the rock­et’s tra­jec­to­ry, and team member Barbara Paulson recalled in an interview that she was the one con­firm­ing that Explorer 1 made it safely into space.  

One of his­to­ry’s most famous space photos occurred that night. Von Braun and two other people held a model Juno rocket over their heads during a press brief­ing con­cern­ing the suc­cess­ful launch. It was a good night for the Germans, as well as for the American space pro­gram.

Explorer 1’s science

Explorer 1’s launch was a large policy coup, to be sure, but what was also inter­est­ing was the sci­ence the little satel­lite beamed back. Its prime sci­ence exper­i­ment was a cosmic ray detec­tor designed by James Van Allen, a physi­cist at the University of Iowa. Cosmic rays are ener­getic radi­at­ed par­ti­cles from space — bits of atoms that can include pro­tons, elec­trons or nuclei.

The little satel­lite detect­ed fewer cosmic rays in its orbit (which ranged from 220 miles from Earth to 1,563 miles) than Van Allen expect­ed.

The physi­cist pro­posed this might be because radi­a­tion in Earth’s mag­net­ic field may pre­vent the cosmic rays from coming in. Explorer 3, launched in March 1958, dis­cov­ered these mag­net­ic field belts. Today, they are known as the Van Allen Belts.

Simplicity and reliability

Of Explorer 1’s 30 pounds, more than 18 pounds of that was made up of instru­ments. Besides the cosmic ray detec­tors, it also car­ried exper­i­ments such as tem­per­a­ture sen­sors (both inter­nal and exter­nal) and a micro­phone to listen for microm­e­te­orites hit­ting the satel­lite.

NASA paint­ed the instru­ment por­tion of the satel­lite white and dark green, which was sup­posed to reg­u­late tem­per­a­tures on the sec­tion. Dark colors absorb more heat, and white absorb less. The agency notes that the satel­lite was simple by design, as they wanted to ensure it was as reli­able as pos­si­ble.

On that count, NASA suc­ceed­ed. Explorer 1 sent data back to Earth for four months, ceas­ing com­mu­ni­ca­tions on May 23, 1958. The satel­lite remained aloft for more than a decade before re-enter­ing Earth’s atmos­phere on March 31, 1970.

Explorer 1 spawned a series of other satel­lites. While Explorers 2 and 5 failed due to rocket stage prob­lems, Explorers 3 and 4 both launched suc­cess­ful­ly in 1958 and trans­mit­ted sci­ence from orbit.

Even though the satel­lites are no longer work­ing, their legacy remains. They launched the United States into space and showed that it was pos­si­ble to do sci­ence from orbit.

Recent Van Allen belt findings

Explorer 1 dis­cov­ered the Van Allen belts, and sub­se­quent mis­sions in the Explorer series uncov­ered more details about their nature. Today, the belts are being probed in more detail by the Van Allen probes, which launched in 2012. This is the first time that two space­craft simul­ta­ne­ous­ly stud­ied the belts. 

Shortly after their launch, the probes were turned on to sup­ple­ment data from the SAMPEX (Solar, Anomalous, and Magnetospheric Particle Explorer) mis­sion before the latter mis­sion was con­clud­ed. It is not typ­i­cal for a mis­sion to start sci­ence obser­va­tions right away as the instru­ments are still being con­fig­ured. In this case, how­ev­er, NASA wanted to take advan­tage of the probes being in space at the same time as SAMPEX. A for­tu­itous­ly timed solar storm led to an imme­di­ate find­ing: the Van Allen probes uncov­ered evi­dence of a third belt affect­ed by the storm, as well as the two belts that were already known.

The probes’ mis­sion is still ongo­ing, but some of the key sci­ence find­ings include:

  • Examining how the radi­a­tion belts pro­tect Earth from high-energy par­ti­cles;
  • Finding that the belts’ shape depends on what kind of elec­trons are being stud­ied (which means that depend­ing on the elec­tron being looked at, the belts can be uni­fied or sep­a­rate);
  • Ongoing stud­ies on how the belts change during geo­mag­net­ic storms. In 2015, the probes revealed an inter­plan­e­tary shock (when charged par­ti­cles from the sun create a shock in some areas of the belt). 

Space.com source|articles

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