Editing Explorer II

{{Short description|1935 American high-altitude balloon}}
{{hatnote group|
{{about|the high-altitude balloon mission|other uses|Explorer Two (disambiguation)}}
{{confused|Explorer 11}}
}}
{{italic title}}
{{Infobox
| bodyclass  = vcard
| titleclass = fn org
| title      = ''Explorer II''
| image      = [[File:Explorer II Gondola.jpg|240px]]
| caption    = ''Explorer II'' gondola on display at the [[National Air and Space Museum]]
| label2     = National origin
| data2      = United States
| label3     = Cost
| data3      = 
| label4     = Mass
| data4      = {{Convert|15,000|lb|kg|abbr=on|disp=flip}}<ref name="FWP2008"/>
| label5     = Balloon volume
| data5      = {{Convert|3,700,000|cuft|m3|abbr=on|disp=flip}}
| label6     = Crew
| data6      = 2
| label7     = Purpose
| data7      = Stratospheric flight
| label8     = Operator
| data8      = National Geographic Society<br>U.&nbsp;S. Army Air Corps
| label9     = First flight
| data9      = July 10, 1935
| label10    = Maximum altitude
| data10     = {{Convert|22,066|m|ft|abbr=on|lk=off}}
| label11    = Status
| data11     = Retired
}}
'''''Explorer II''''' was a crewed U.S. [[high-altitude balloon]] that was launched on November 11, 1935, and reached a record altitude of {{Convert|22,066|m|ft|abbr=on|lk=off}}. Launched at 8:00 am from the [[Stratobowl]] in [[South Dakota]], the helium balloon carried a two-man crew consisting of [[United States Army Air Corps|U.S. Army Air Corps]] Captains [[Albert W. Stevens]] and [[Orvil A. Anderson]] inside a sealed, spherical cabin. The crew landed safely near [[White Lake, South Dakota]], at 4:13 pm and both were acclaimed as national heroes. Scientific instruments carried on the gondola returned useful information about the [[stratosphere]]. The mission was funded by the membership of the [[National Geographic Society]].<ref name="AmExp">{{cite web |title=Space Men: They were the first to brave the unknown - Transcript |url=https://www.pbs.org/wgbh/americanexperience/films/spacemen/#transcript  |website=American Experience |publisher=PBS |accessdate=2 January 2019 |date=1 March 2016}}</ref>

==Background==
In January 1934, the [[National Geographic Society]] (NGS) and the [[United States Army Air Corps|U.S. Army Air Corps]] decided to collaborate on a program to build and launch a manned balloon to the then record altitude of {{Convert|15|mi|km|abbr=on|disp=flip}}. This vehicle would be capable of carrying a crew of three in an airtight capsule, along with a laboratory of instruments. The hydrogen balloon, named ''Explorer'', was completed by July at a cost of around $60,000; {{Inflation|US|60000|1934|fmt=eq}} currency.<ref name="Ryan2003"/>

The balloon was launched from a canyon in the [[Black Hills]] of [[South Dakota]]—dubbed the [[Stratobowl]]—on July 28, 1934 and reached a near-record altitude of {{Convert|60613|ft|m|abbr=on|disp=flip}}<ref name="Shayler2000"/> before tears in the fabric led the crew to begin reducing their altitude. A rupture in the balloon resulted in a precipitous descent, followed by a spark that caused the hydrogen to ignite and destroy what was left of the balloon, leaving the capsule to plummet toward the ground at [[terminal velocity]]. The crew just managed to escape using their parachutes, with the last man bailing out at {{convert|500|ft}} above the ground. Their capsule was almost completely destroyed upon impact.<ref name="Ryan2003"/><ref name="AmExp"/>

The crash resulted in a national embarrassment, leading Captain [[Albert W. Stevens]], the scientific observer on board the ''Explorer'' balloon, to lobby for another attempt with an improved balloon to be named ''Explorer II''. But news of the [[Osoaviakhim-1|fatal crash of a Russian stratospheric attempt]] in 1934 left President [[Gilbert Hovey Grosvenor|Gilbert H. Grosvenor]] of the NGS sobered by the risk.<ref name="DeVorkin1991"/> A review of the crash by the [[National Bureau of Standards]]<ref name="DeVorkin1991"/> (NBS) was held between July and September, revealing that the balloon had not opened symmetrically during the ascent, causing stresses that led to the fabric tears. A month-long delay prior to launch had allowed the rubberized cotton to stick together, which created the uneven expansion. The hydrogen explosion followed when the gas in the bag mixed with the oxygen in the atmosphere.<ref name="Shayler2000"/>

==Preparation==
Despite the concerns, in 1935 the NGS and Army Air Corps decided to make another attempt. To eliminate the hazard of the hydrogen lifting gas, it was decided instead to use helium<ref name="AmExp"/>—to which the United States had a monopoly. The lower lifting efficiency of helium gas meant that a larger balloon would be needed,<ref name="DeVorkin1991"/> so [[Goodyear Tire and Rubber Company|Goodyear-Zeppelin]]<ref name="Ryan2003"/> increased the volume to {{Convert|3,700,000|cuft|m3|abbr=on|disp=flip}}. [[Dow Chemical Company]] assembled a larger, lighter gondola<ref name="Maurer1987"/> made of "Dowmetal"<ref name="Ryan2003"/>—a magnesium-aluminium alloy<ref name="SI"/>— that would carry a two-man crew with a reduced amount of scientific instrumentation. The cabin was {{Convert|9|ft|m|abbr=on|disp=flip}} in diameter with a mass of {{Convert|640|lb|kg|abbr=on|disp=flip}} and could transport a {{Convert|1500|lb|kg|abbr=on|disp=flip}} payload.<ref name="SI"/> It was manufactured from a single, large plate that was cut up into form that could be reshaped and welded into a sphere.<ref name="Froes2006"/> In order to make crew escape easier, the portholes were made wider than on the ''Explorer I''.<ref name="SI"/> The atmosphere in the interior of the capsule was supplied from liquid air instead of liquid oxygen in order to reduce the fire hazard.<ref name="Davis2008"/> The modified balloon was ready by the spring of 1935 and the first launch occurred July 10, 1935. Unfortunately, this too proved a failure with the balloon rupturing at liftoff.<ref name="DeVorkin1991"/>

Following a review by the NBS, the balloon was prepared for another attempt after Goodyear strengthened the material. Examination of climatological data for the Stratobowl collected over the previous fifteen years was examined, and it was determined that the month of October typically had periods of good weather that would last sufficiently long for a flight attempt. A team of meteorologists was assembled at the Stratobowl in early September and they proceeded to put together a weather station. The meteorological requirements for the launch was for clear skies—with no precipitation—lasting for the duration of the flight, as well as surface wind speeds that were not to exceed {{Convert|14|mph|kph|abbr=on|disp=flip}}.<ref name="Potter2010"/>

With a [[cold front]] approaching, on the night of November 10, 1935, the balloon was prepared for launch. The temperature dropped to {{Convert|6|°F|°C|disp=flip}} overnight, so the {{Convert|115,845|sqft|m2|abbr=on|disp=flip}} of fabric was kept warm and pliable through the use of stoves. The task of inflating the balloon with helium from the 1,685 steel cylinders<ref name="Ryan2003"/> took eight hours,<ref name="Potter2010"/> during which the team needed to repair a {{Convert|17|ft|m|abbr=on|disp=flip}} long tear that formed in the fabric.<ref name="Maurer1987"/> Once inflated, the balloon stood {{Convert|316|ft|m|abbr=on|disp=flip}} tall.<ref name="FWP2008"/> The gondola was kept anchored to the earth by a team of more than 100 soldiers holding cables.<ref name="Ryan2003"/> Preparations were complete by 7:01&nbsp;am the following morning<ref name="Potter2010"/> and the conditions were deemed suitable for a launch.<ref name="DeVorkin1991"/>

==Flight==
[[File:Historic weather balloon "Explorer II." Lake Andes NWR, South Dakota. - NARA - 283835.jpg|right|thumb|''Explorer II'' gondola at the landing site]]

The crew of the ''Explorer II'' consisted of Captain Albert W. Stevens, in command of the mission, and Captain [[Orvil A. Anderson]].<ref name="Davis2008"/> A crowd of around 20,000 viewers gathered to watch the event. (The local residents had raised and contributed $13,000 for the mission.<ref name="Ryan2003"/>) Lift-off occurred at precisely 8:00 am with the release of {{Convert|75|lb|kg|abbr=on|disp=flip}} of ballast made of fine lead shot. A few moments after liftoff, wind shear propelled the balloon into a side canyon, but thereafter it ascended normally.<ref name="Ryan2003"/>

The ''Explorer II'' reached a peak altitude of {{Convert|22,066|m|ft|abbr=on|lk=off}}<ref name="Bilstein2001"/> at 12:30 pm and remained there for 80 minutes.<ref name="Ryan2003"/> This set a new world altitude record, and one that would last for nearly two decades.<ref name="Bilstein2001"/> The crew became the first humans to document the [[curvature]] of the Earth. Unfortunately, the fan that was to be used to rotate the gondola proved ineffective at that altitude, so they were unable to avoid the Sun's glare. This made viewing from one side of the capsule nearly useless. Despite this, Captain Stevens reported seeing details of the Earth's surface for hundreds of miles. They were too high up to be able to view any movement on the ground,<ref name="Ryan2003"/> but their photography showed the potential of high-altitude [[reconnaissance balloon]]s.<ref name="SI"/>

''Explorer II'' included communications equipment, and constant radio contact was maintained throughout the flight with the signal being broadcast across the U.S. and in Europe.<ref name="Ryan2003"/> The onboard instruments collected data on [[cosmic rays]], the ozone distribution and electrical conductivity of the atmosphere at different altitudes, the atmospheric composition of the stratosphere, and the luminosity of the Sun, Moon and Earth. In addition, microorganisms were collected from the stratosphere.<ref name="Maurer1987"/> Mold samples were carried along to determine the effects of cosmic ray exposure. Stevens took along a camera to take pictures, including the first ever motion pictures shot from the stratosphere.<ref name="Ryan2003"/> The collected data showed that the ozone in the upper atmosphere was effective at blocking most of the ultraviolet radiation from the Sun. It was also found that the percentage of oxygen at the peak altitude was about the same as that at sea level.<ref name="Davis2008"/>

Finally, the descent was begun and it proceeded normally. At an altitude of {{Convert|1000|ft|m|abbr=on|disp=flip}}, the crew began releasing scientific instruments that would descend by their own parachutes. This was done to protect the data in case the gondola had a rough landing. The precautions proved unnecessary as the balloon landed gently in an open field near the town of [[White Lake, South Dakota]] at 4:13 pm.<ref name="Ryan2003"/>

==Aftermath==
The success of the mission was much celebrated in the press and the aeronauts were invited to an audience with U.S. President [[Franklin D. Roosevelt]]. They became national heroes and both men were presented with the [[Hubbard Medal]] of the National Geographic Society by General [[John J. Pershing]].<ref name="NYT19351212"/> The Air Corps awarded them the [[Mackay Trophy]] for the most meritorious flight of the year.<ref name="Fredriksen2011"/> Both men were also awarded the [[Distinguished Flying Cross (United States)|Distinguished Flying Cross]] for each of the Explorer flights.

Scientific observations made during the mission were highly successful and much data was collected,<ref name="DeVorkin1991"/> with the results appearing in scientific journals.<ref name="Weightman1937"/><ref name="SI"/> The data and the crew experiences were later used when designing flight crew equipment and methods for high-altitude combat operations during [[World War II]].<ref name="Bilstein2001"/> The balloon used for the ''Explorer II'' expedition was cut up into a million {{Dubious|Talk Million pieces?|date=March 2025}} strips and distributed as commemorative bookmarks among the NGS members who supported the mission.<ref name="Shayler2000"/><ref name=Gannon_2010/> The gondola is on display at the [[Smithsonian Institution]]'s [[National Air and Space Museum]].<ref name="SI"/>

==See also==
*[[Flight altitude record]]

==References==
{{Reflist|colwidth=30em|refs=
<ref name="DeVorkin1991">{{Citation
 | first1    = David
 | last1     = DeVorkin
 | editor1-first = Sallie
 | editor1-last  = Baliunas
 | editor2-first = John L.
 | editor2-last  = Richard
 | title     = Robotic Observatories: Present and Future. Proceedings of the 1990 11th Annual Smithsonian/Fairborn/I.A.P.P.P Symposium on Automatic Photoelectric Telescopes
 | chapter   = Social Determinism in Space: Depression Era Apollo
 | publisher = Fairborn Press
 | pages     = 3–9
 | year      = 1991
 | isbn      = 3642297188
 | location  = Mesa, Arizona
 | url       = http://www.bbastrodesigns.com/HistoryOfComputerizedTelescopes/Baliunas.1991.Robotic.Observatories.1.pdf
 | accessdate= 2013-04-20
 | postscript= .
}}</ref>

<ref name="Weightman1937">{{Citation
 | first1    = R. Hanson
 | last1     = Weightman
 | title     = Some results of the stratosphere flight of explorer II in America
 | journal      = Quarterly Journal of the Royal Meteorological Society
 | volume    = 63
 | issue     = 268
 | pages     = 75–78
 |date=January 1937
 | doi       = 10.1002/qj.49706326813
 | bibcode   = 1937QJRMS..63...75W
 | postscript= .
}}</ref>

<ref name="Maurer1987">{{Citation
 | first1    = Maurer
 | last1     = Maurer
 | title     = Aviation in the U.S. Army, 1919-1939
 | publisher = DIANE Publishing
 | volume    = 63
 | issue     = 268
 | pages     = 424–425
 | year      = 1987
 | location  = Washington, D.C.
 | isbn      = 142891563X
 | url       = https://books.google.com/books?id=E1gGW_TqLawC&pg=PA424
 | postscript= .
}}</ref>

<ref name="Potter2010">{{Citation
 | first1    = Sean
 | last1     = Potter
 | title     = Retrospect: November 11, 1935: Explorer II Stratospheric Balloon Flight
 | work      = Weatherwise Magazine
 | publisher = Taylor & Francis Group
 |date=December 2010
 | url       = http://www.weatherwise.org/Archives/Back%20Issues/2010/November-December%202010/retrospective-full.html
 | accessdate= 2013-04-20
 | postscript= .
}}</ref>

<ref name="Shayler2000">{{Citation
 | last1     = Shayler
 | first1    = David
 | title     = Disasters and Accidents in Manned Spaceflight
 | publisher = Springer
 | page      = 22
 | year      = 2000
 | isbn      = 1852332255
 | url       = https://books.google.com/books?id=ng9i5IMtlpsC&pg=PA22
 | postscript= .
}}</ref>

<ref name="Ryan2003">{{Citation
 | last1     = Ryan
 | first1    = Craig
 | title     = The Pre-astronauts: Manned Ballooning on the Threshold of Space
 | publisher = Naval Institute Press
 | pages     = 51–61
 | year      = 2003
 | isbn      = 1591147484
 | url       = https://books.google.com/books?id=1QS38bu9iTwC&pg=PA51
 | postscript= .
}}</ref>

<ref name="Davis2008">{{Citation
 | editor1-first = Jeffrey R.
 | editor1-last  = Davis
 | editor2-first = Robert
 | editor2-last  = Johnson
 | editor3-first = Jan
 | editor3-last  = Stepanek
 | title     = Fundamentals of Aerospace Medicine
 | publisher = Lippincott Williams & Wilkins
 | page      = 17
 | edition   = 4th
 | year      = 2008
 | isbn      = 978-0781774666
 | url       = https://books.google.com/books?id=_6hymYAgC6MC&pg=PA17
 | postscript= .
}}</ref>

<ref name="NYT19351212">{{Citation
 | title     = Honored on Flight into Stratosphere
 | work      = The New York Times
 | date      = December 12, 1935
 | url       = http://select.nytimes.com/gst/abstract.html?res=F10715FE3F5B1B7B93C0A81789D95F418385F9
 | accessdate= 2013-04-21
 | postscript= .
}}</ref>

<ref name="FWP2008">{{Citation
 | author1   = The Federal Writers' Project
 | title     = The WPA Guide to South Dakota
 | publisher = Minnesota Historical Society
 | page      = 295
 | year      = 2008
 | isbn      = 978-0873517102
 | url       = https://books.google.com/books?id=lqnYmaR2iRcC&pg=PA295
 | postscript= .
}}</ref>

<ref name="Bilstein2001">{{Citation
 | last1     = Bilstein
 | first1    = Roger E.
 | title     = Flight in America: From the Wrights to the Astronauts
 | publisher = JHU Press
 | page      = 118
 | edition   = 3rd
 | year      = 2001
 | isbn      = 0801866855
 | url       = https://books.google.com/books?id=PKeVjYtzLr0C&pg=PA118
 | postscript= .
}}</ref>

<ref name="SI">{{Citation
 | title     = Cabin, "EXPLORER II"
 | work      = National Air and Space Museum
 | publisher = Smithsonian Institution
 | url       = https://airandspace.si.edu/collection-objects/cabin-explorer-ii/nasm_A19370060000
 | accessdate= 2021-03-21
 | postscript= .
}}</ref>

<ref name="Fredriksen2011">{{Citation
 | first1    = John C.
 | last1     = Fredriksen
 | title     = The United States Air Force: A Chronology
 | publisher = ABC-CLIO
 | page      = 50
 | year      = 2011
 | isbn      = 978-0873517102
 | url       = https://books.google.com/books?id=Br3zsp8pvGYC&pg=PA50
 | postscript= .
}}</ref>

<ref name="Froes2006">{{Citation
 | first1    = Francis H.
 | title     = Magnesium Technology: Metallurgy, Design Data, Automotive Applications
 | last1     = Froes
 | first2    = Dan
 | last2     = Eliezer
 | first3    = Eli
 | last3     = Aghion
 | editor1-first = Horst E.
 | editor1-last  = Friedrich
 | editor2-first = Barry L. 
 | editor2-last  = Mordike
 | chapter   = Magnesium Aerospace
 | publisher = Springer
 | page      = 608
 | year      = 2006
 | isbn      = 3540308121
 | url       = https://books.google.com/books?id=2z4UrFgJ2mkC&pg=PA608
 | postscript= .
}}</ref>

<ref name=Gannon_2010>{{citation | postscript=.
 | title=Explorer II Balloon Bookmark
 | first=Charles | last=Gannon | date=March 14, 2010
 | work=National Geographic Collectors Corner
 | url=https://ngscollectors.ning.com/forum/topics/explorer-ii-balloon-bookmark
 | access-date=2025-03-20
}}</ref>

}}

==External links==
* {{cite web | first=Gregory P. | last=Kennedy | website=stratcat.com.ar | date=February 25, 2018 | title=The Two Explorer Stratosphere Balloon Flights | url=http://stratocat.com.ar/artics/explorer-e.htm | accessdate=2020-10-03 }}
* {{cite web | title=1936 National Geographic View from the Highest Point Above Earth (South Dakota) | quote=The first photograph ever made showing the division between the troposphere and the stratosphere and also the actual curvature of the Earth. | website=Geographicus Rare Antique Maps | url=https://www.geographicus.com/P/AntiqueMap/WorldHighestPoint-natgeo-1936 | accessdate=2019-05-13 }}
* {{commonscat-inline|Explorer II}}

{{S-start}}
{{Succession box
 | title  = Human altitude record
 | years  = 1935-1951
 | with   = 
 | before = [[Osoaviakhim-1]]
 | after  = [[Bill Bridgeman]]
}}
{{S-end}}
[[Category:Aviation records]]
[[Category:Individual balloons (aircraft)]]
[[Category:National Geographic Society]]
[[Category:Aircraft flown once]]
[[Category:Aircraft first flown in 1935]]