P-21A Press Kit

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    A ANATIONAL AERONA' *mCS AN D SPACE ADMINISTRATION1 5 2 0 H S T R E E T. N O R T H W E S T WA S H I N G T O N 2 5 . D. C.T E L E P H O N E S : D U D L E Y 2 - 6 3 2 5 E X E C U T I V E 3 - 3 2 6 0

    FOR RELEASE: March 23, 1962

    Release No. 62-71 Friday, 2:30 PM

    SECOND IONOSPHERE PROBE

    The National Aeronautics and Space Administration willattempt to launch, no earlier than March 28 , 1962, the secondin a series of ionosphere measurement probes using the four-stage solid fuel Scout rocket.

    The P-21A experiment is designed to measure the electrondensity profile, ion density and type of ions in the ionosphere,the region where some radio signals are reflected back to earth.High radio frequencies are known to penetrate the ionosphere.Such basic research could lead to improved communications onearth and between vehicles in space.

    The 90-pound experiment will be launched from NASA'sWallops Island around midnight when characteristics of theionosphere di.ffer drastically from its daytime state. An alti-tude of about 4,000 miles is expected for the planned 85-minuteflight. Since there will be telemetry throughout the flight,it will not be necessary to recover the payload.

    The P-21 experiment determined the concentration of elec-trons as a function of altitude during the daytime. It wassuccessfully launched by a developmental Scout on October 19 ,reaching a peak altitude of 4,261 miles. Electron density wasobtained to about 1,500 miles marking the first time suchspecific measurements had been made at this altitude.

    NASA scientists at a press conference today outlined ac-complishments of the P-21 probe which, along with discoveriesfrom other NASA programs, have contributed to world scientificconcepts of the upper ionosphere.

    P-21 Project Scientists have announced the followingfindings:

    1. P-21 confirmed the existence of the helium region andmeasured

    the lower boundary of the layer. On that particularday it began about 700 miles above the earth's surface.

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    2. Simultaneously, P-21 measured the temperature ofthe upper atmosphere and found it to be fairly constant at2,000 F from about 300 to 1,800 miles where measurement ceasedbecause of radio frequency interference.

    3. Scientists can now theoretically predict that th elower boundary of th e hellium layer varies with temperature be -cause of new data received from P-21, Goddard's Explorer VIIIIonospheric measurement satellite, and analysis of a Scoutflight on October 4, 1960 made by Hanson of Lockheed under aNASA contract.

    To test this theory, P-21A will be launched on e day nextweek around midnight when th e temperature of the ionosphere ismuch cooler. Theoretically, project scientists expect to findthat the altitude of th e lower boundary of th e helium layershould drop down to 500 miles, compared with th e P-21 Scoutdaytime measurement of about 700 miles. Temperature shoulddrop down to about 1100 0 F.

    To assist scientists in determining where helium ions areoutnumbered by th e hydrogen ions of outer space, th e P-21A will

    carry an additional experiment--an ion trap--similar to thatflown on th e Explorer VIII satellite.

    S. J. Bauer and J. E. Jackson, NASA scientists responsiblefor th e P-21 program, explained that previously i t was general-ly accepted by scientists that hydrogen was the most importantatmospheric constituent at altitudes around 700 miles.

    However, NASA's Explorer VIII, instrumented by th e Plane-tary Ionospheres Branch at Goddard and launched November 3,1960, gave experimental evidence on th e presence of heliumions above 90 0 miles. About th e same time, Dr. W. B. Hanson

    of Lockheed Missiles and Space Division, working under NASAcontract, presented the same type of evidence based on hi e in -terpretation of an ion-density profile obtained on Scout launch#2 fired on October 4, 1960.

    Previously, Dr. Marcel Nicolet of Belgium in the Springof 1961 postulated th e same hypothesis in order to explain th eslow decrease of neutral atmospheric density above 450 milesinferred from th e NASA Echo I balloon satellite.

    Dr. Bauer and Mr. Jackson said that it now appears thatbetween 15 0 to 700 miles ionized oxygen is th e predominantionized consultuent. At lower altitudes, molecular oxygen an dnitric oxide ions are also present. About 700 miles there is atransition from oxygen ions to helium ions an d -ior more than

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    1,000 miles helium appears to be the predominant constituent.On the basis of theoretical estimates, they said, a transitionmay occur at about 2,000 miles from helium to hydrogen whichis the principal constituent~.of interplanetary space.

    P-21A Probe Description

    This eight-sided spacecraft is the last of the NASA P-21series of four rocket flights to investigate ionospheric

    cnaracteristics of importance to radio communication, radiotracking and guidance, and to add to the basic understandingof the earth's ionosphere.

    In the ionosphere, incoming radiations from the sun collidewith atoms of gases, releasing free electrons and positive ions,creating reflective layers fo r radio signals. If it were .notfo r the ionosphere, long range radio communication would notbe possible. Ionospheric data is very scarce between 200 milesand 600 miles, and virtually non-existent above the latteraltitude. Significant results could be obtained if only helpthe planned altitude is achieved.

    Three probes have already been fired in the series. OnApril 27, an Argo D-4 rocket reached an altitude of 450 milesand gave an excellent profile of electron densities during mid-day, fo r a quiet ionosphere. Another D-4 was fired in Juneto compare nighttime electron densities with the daytime dataobtained previously, but rocket failure kept if from achievingits objectives. The P-21 firing on October 19 measured day-time electron concentration. P-21A will chart the nighttimeprofile.

    P-21A contains three experiments: A CW (continuous wave)Propagation Experiment will attempt to determine electrondensity and associated parameters of the ionosphere. A Swept-Frequency Probe will attempt direct measurement of electrondensity. A Positive Ion Experiment will attempt to determineion concentration. Secondar y objectives of the flight areto test the performance of new ionospheric ground stations atBlossom Point, Md. and Wallops Island.

    In the CW experiment, two radio signals are transmittedfrom the rocket to a receiving station on the ground at fre-quencies of 12.3 Mc (1.5 watts of power) and 73.6 Me (0.7 watts).The higher frequency is essentially unaffected by the ionosphereand should provide a reference with which to compare the lowfrequency transmission. The lower frequency will be affectedconsiderably by the physical conditions of the ionosphere,

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    LAUNCH VEHICLE

    Scout is th e nation's first solid propellant rocket toplace a payload in orbit. It did so on February 16, 1961,when it sent aloft Explorer IX, a 12-foot, alurnilum an dplastic sphere to collect data on effects atmospheric drag willhave on space vehicles and th e life of satellites.

    Scout is designed to place a 150-pound satellite in a300-mile orbit or to send a 50-pound scientific package nearly8,500 miles in a probe shot. For re-entry tests, the rocketca n subject a payload to conditions like those encountered byspace vehicles returning to th e earth's atmosphere. In aballistic trajectory, it can provide almost tw o hours ofweightlessness for 100-pound experiments.

    Scout is 72 feet long and weighs approximately 36,600pounds. It s four solid-propellant stages consist of Algolfirst stage, Castor second, Antares third and Altair fourth.

    These four rocket motors, plus th e necessary transitionsections and guidance and control equipment, ar e assembled intoa complete vehicle by th e Astronautics Division of Chance VoughtCorporation, aerospace subsidiary of Ling-Temco-Vought, Inc.,and prime vehicle contractor for Scout.

    Data on Scoutts four stages, named for stars in theconstellations, include:

    Al ol - Thirty feet long, 40 inches in diameter, develop-ing 115,00 pounds of thrust. This motor, th e largest solidrocket flown in the United States, is fin stablized and con-trolled in flight by jet vanes. Developed by Aerojet-GeneralDivision of General Tire and Rubber Company.

    Castor - Twenty feet long, 30 inches in diameter and de-veloping more than 50,000 pounds of thrust. Stabilized an dcontrolled by hydrogen peroxide jets. A modification of th eSergeant motor, it has been used in a cluster in NASA's LittleJo e program in support of the Mercury project. Developed byth e Redstone Division of Thiokol Chemical Corporation.

    Antares II - Ten feet long, 30 inches in diameter an dmore than 13,00 pounds of thrust. Lightweight plastic con-struction. Stablized and controlled by hydrogen peroxide jets.Developed by th e Allegany Ballistics Laboratory of HerculesPowder Company.

    Altair - Six feet long, 18 inches in diameter an d 3,000

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    pounds of t h rus t . This motor, formerly known as th e X-248and developed for the Vanguard t h i rd stage, is spin s t ab i l i zed .It is th e third stage on th e Delta launch vehicle and wa s thefirst fully developed rocket to utilize lightweight plasticconstruction. Also developed by ABL.

    Each stage has a burning time of approximately 40seconds.

    The Scout concept originated in mid-1958 at NASALs LangleyResearch Center in Virginia an d a project office was establishedto develop the vehicle and serve as program manager. Th e firstfull-scale