X-690-71-4522-:EPRIN?

MAGNETIC FIELD MEASUREMENTS,BY PIONEER 7

I. Hourly Average. . \ .,.~~~~~~~

Elements from- 17to 29 October 1967

'RotationI

s of the Field-August 1966' (Bartels' Solar

1820 to 1836),

GODDARD SPACE ,FLIGHT CENTER "GREENBELT, MARYLAND , .

N N72- $2 3 3

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7 (NAS A-TM-X-65169) HAGNETIC FIELDMEASUREMENTS BY PIONEER 7. 1: HOURLYAVERAGES OF THE FIELD ELEMENTS FROMI17 AUGUST 196 TO 29 N.F. NeSS, et al

(NASA) Nov. 1971 42 p S

< (NASA CR OR TMX OR AD NL Reproduced byNATIONAL TECHNICALINFORMATION SERVICE

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X-690o-71- 452

MAGNETIC FIELD MEASUREMENTS BY PIONEER 7

I. Hourly averages of the field elements from 17 August1966 to 29 October 1967 (Bartels' Solar Rotation 1820to 1836)

Norman F. NessFranklin W. Ottens

Laboratory for Extraterrestrial PhysicsNASA-Goddard Space Flight Center

Greenbelt, Maryland USA 20771

November 1971

1. Introduction

The Pioneer 7 spacecraft is a spin stabilized interplanetary

probe launched from the Eastern Test Range, Cape Kennedy, Florida on

17 August-196 6 . The geocentric orbit of the spacecraft has an aphelion

of 1.125 AU, a perihelion 1.010 AU, inclination to the ecliptic of 00

and orbital period of 403 days. This spacecraft was the first of a

series of four Pioneer spacecraft with identical structures but slightly

different complements of experiments. A NASA-GSFC magnetic field

experiment was proposed, accepted and flown on Pioneers 6 (in 1965)--and 7.

Subsequently, unique circumstances presented an opportunity for flight

of a similar experiment by the GSFC group in collaboration with the

University of Rome, Laboratory for Space Plasma Research group on

Pioneer 8 (in 1967).

The magnetic field experiment detector is a monoaxial fluxgate

magnetometer sensor mounted on the end of a boom at a distance of 2.1

meters from the spacecraft spin axis. The initial spin period was

approximately one second and the field measurements were synchronized

with the rotation of the spacecraft. The monoaxial sensor was oriented

at an angle of 540 45' to the spin axis so that during one spacecraft

rotation three samples of the magnetic field at equal intervals yielded

three independent measurements in mutually orthogonal directions. These

basic measurements, obtained in a time interval of 2/3 of a second,

define the total vector magnetic field in a spacecraft coordinate system.

-2 -

The spin axis of the spacecraft was oriented orthogonal to the ecliptic

plane with the high gain antenna of the spacecraft pointing to the south

ecliptic pole.

Data transmission from the spacecraft experiment was synchronized

with telemetry, which ranged from 8 to 512 bits/sec during the lifetime

of the spacecraft. A complete three component measurement was not read

out during each spin period and so individual data points are not

equally spaced in time (see Scearce et al., 1968 for description of

the experiment).

The Pioneer 7 instrument was a single range magnetometer (+32r)

which with the 8 bit quantization of the analog to digital converter

yielded a digital window size of +O.125y. The RMS noise level of the

sensor was 0.12y and the bandwidth 0 to 5 cps. The magnetic field of

the spacecraft and associated solar array as measured at the sensor

location was estimated to be less than 0.6y. Periodic sensitivity

calibrations were made once each day as well as zero level checks

approximately once every several months. The projection of the orbit

described by Pioneer 7 on the ecliptic plane, relative to the earth-

sun-line, is shown in F-i-gure 1.

-3-

2. Data

The magnetic field elements have been computed in a spacecraft

centered solar ecliptic system in which the X axis points from the

spacecraft to the sun, the Z axis to the ecliptic north pole and the-

Y axis being the third axis of the orthogonal right handed coordinate

system.

The standard data analysis was performed to yield 30 second averages

of the field components and the field magnitudes as

n n-1 XtFn 1Fi, F =Nf`xL+(Y)2+(Z(1)

Xi etc., F =/))+ (1)i=l i=l

Also RMS deviations ( X' By, 8Z) of the magnetic field were computed

routinely for each component and for the field magnitude. The Pythagorean

variance, which is an invarient of the coordinate system, is obtained

from the component deviations as

2 2 2

6= i8x + By +8 z(2)

The choice of a 30 second time interval was based upon a desire

to provide correlative data to each of the plasma probes on the Pioneer

6 and 7 spacecraft whose fastest cycle times were on the order of one

minute.

Data shown in Figures 2 through 17 represent for each solar rotation

the hourly averages of the field elements F, F, 0 (latitude) and 0 (longitude).

The data are plotted in 27 day increments corresponding to Bartels' solar

-4-

rotation numbering system. The two variances D1 and D2 are obtained by

different means. D1 is a variance computed from equation 2 for each

hourly interval using the hourly averaged components (and deviations from

them). D2 is the hourly average of the individual Pythagorean variance

for each 30 time interval. The days of the year are indicated as calendar

days and most of the missing data corresponds to gaps in tracking

coverage of the spacecraft. Publications utilizing Pioneer 7 data which

have already appeared are given in the reference list. This does not

include those publications by other non-GSFC associated authors who have

used Pioneer 7 data.

-5-

3. Summary

The orbit of Pioneer 7 was such that for much of its early

lifetime (several months) it was located in the aftward portion of

the disturbed solar plasma caused by interaction with the geomagnetic

field. Observations of the geomagnetic tail at the greatest distance yet

achieved (100O RE) were performed by this experiment. (Nest et al.,

1967; Fairfield, 1968). Important simultaneous correlated measurements

of the electron component of the plasma in the neutral sheet and the

associated magnetic field were first performed by Pioneer 7 (Lazarus et

al, 1968).The 30 second average detail data and hourly average data are

available from the National Space Science Data Center at NASA-GSFC

(Mail Code 601), Greenbelt, Maryland 20771. This present document

provides, in summary graphical form, a working data set which was used

internally at the NASA-GSFC and parts of which have been made

available to other groups.

-6-

4. References -(in chronological order)

1. Ness, N. F., C. S. Scearce and S. C. Cantarano, Probable Observation

of the Geomagnetic Tail at 103 RE by Pioneer 7, J. Geophys. Res., 73,

3769-3776, 1967. (Also X-612-67-183).

2. Lazarus, A. J., G. L. Siscoe and N. F. Ness, Plasma and Magnetic

Field Observations During the Magnetosphere Passage of Pioneer 7,

J. Geophys. Res., 73, 2399-2409, 1968.

3. Fairfield, Donald H., Simultaneous Measurements on Three Satellites

and the Observation of the Geomagnetic Tail at 1000 RE, J. Geophys.

Res., 73, 6179-6187, 1968.

4. Ness, Norman F., The Geomagnetic Tail, Revs. Geophysics, 7, 97-128,

1969, (Also X-616-68-345).

5. Scearce C. S., C. Ehrmann, S. C. Cantarano and N. F. Ness, Magnetic

Field Experiment: Pioneers 6, 7 and 8, X-616-68-370.

6. Ness, Norman F., The Magnetic Structure of Interplanetary Space,

Proceedings Budapest XI International Cosmic Ray Conference,

(Also X-6X6-69-334.)

7. Mariani, F., B. Bavassano and N. F. Ness, Magnetic Field Fluctuations

in the Magnetosheath Observed by Pioneer 7 and 8, J. Geophys. Res., 75

6037-6049, 1970 (Also X-616-69-541).

List of Figures

1 Projection of the orbit of Pioneer 7 on the ecliptic plane. Positionof the spacecraft for the first day of each month is indicated bymonth/year.

2- Hourly averages of the magnetic field elements F, Fs, , 0, D1 and18 D2 for the Bartels' solar rotation number specified on the left

hand side. The lack of two values for F, F, means that thespacecraft was in the DCS (Duty Cycle Storage) mode of operationwith delayed transmission of data. The character A representsthe "folding over" of the corresponding scale by the maximum valueof the scale as shown on the left, Hence the correct value is tobe read = A + Max Scale. Gaps in data are due to lack of telemetryrecording by NASA-JPL DSN stations.

I SUN 1.0

EARTH 10/66

12/66

PIONEER 7 7._.

2/67

10/67 4/678/67

6/6712/67 30o

VFIGiRE 1

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SEPT. 196624 28 5

OCT. 1966

FIGURE 4

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FIGURE 6

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FIGURE 11

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PIONEER HOURLT AVERRGES

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