A program currently in progress to conduct extended duration spectroscopic and photometric observation of solar X-ray phenomena from balloons is described. High photometric sensitivity to weak hard X-ray bursts is attained using a 600 sq cm array of phoswich scintillators. High spectral resolution for stronger bursts is available from an array of planar germanium detectors. These instruments are carried in a novel balloon gondola dssigned for the 15 to 20 day float durations available through using conventional zero pressure balloons in the radiation controlled (RACOON) mode

Burley, K. C.

Curtis, D. W.

Duttweiler, F.

Levedahl, W. K.

Lin, R. F.

Pelling, M. R.

Primbach, H.

English

NASA Technical Reports Server

470 SH 9.1-S
PHOTOMETRIC AND SPECTROSCOPIC GAMMA-RAY OBSERVATIONS OF
SOLAR _q_%NSIENT PHENOMENA USING LONG DURATION BALLOONS
Pelling, M.R. and Duttweiler, F.
UCSD/C/%SS, Code C-011
La Jolla, CA 92093
Lin, R.P., Levedahl, W.K., Primbsch, H., and Curtis, D.W.
UCB/SSL, Berkeley, CA USA
Hurley, K.C.
CESR, Toulouse, FRANCE
ABSTRACT
We describe a program, currently in progress at UCB and
collaborating institutions, UCSD and CESR Toulouse to
conduct extended duration spectroscopic and photometric
observations of solar X-rayphenomena from balloons. High
photometric sensitivit_ to weak hard X-ray bursts is
attained using a 600 cm array of phoswich scintillators.
High spectral resolution for stronger bursts is available
from an array of planar germanium detectors. These
instruments are carried in a novel balloon gondola designed
for the 15 to 20 day float durations available through using
conventional zero-pressure balloons in the radiation
controlled (RACOON) mode.
I. Introduction Important new results concerning energetic flare
processes have been obtained using a unique instrumental complement
combining high spectral resolution and photometric sensitivity in a
conventional balloon flight. The excellent spectral resolution available
through the use of germanium solid state detectors pezmitted the discovery
of a superhot (3.5 x 10 K) flare emission component (1) and the high
photometric sensitivity of a large area phoswich scin%ill_tion counter
permitted detection of -25 "_-flares" with fluxes i0 -i0 lower than
conventionally associated with major flare activity (2). The existance of
superhot emission components has since been indirectly confirmed through
PeXXVI measurements (3) and continuum measurements below 30 keY (4). The
optical counterpart of _-flare events were subsequently discovered
through analysis of co-ordinated H observations (5). The _-flares have a
non-thermal spectral distribution and show evidence for temporal "
structure faster than "I s.
2. Scientific Objectives The general significance of these phenomena is
not clear since the superhot component has been directly observed in only
one flare and the observed _-flares were probably the product of a single
active region. It is interesting to note; however, that the size/frequency
distribution for the _-flares suggests that their underlying particle
population could be significant for heating of the active corona. Thus, it
is of great interest to determine how general the acceleration of >20 keV
https://ntrs.nasa.gov/search.jsp?R=19850026807 2020-03-20T16:50:14+00:00Z
471
SH 9.1-5
electrons is for transient processes on the sun. Other interesting
questions include: How does the superhot component vary from flare to
flare? Indeed, how hot do flare regions get? How are the heating and
acceleration mechanisms related?
In order to clarify the role of these hard x-ray processes in
overall solar energetic phenomena it is necessary to extend the
observations to span a variety of solar activity conditions. The primary
requirement for these follow-on studies is to attain a relatively long
observing period (comparable to solar rotation period ) using
instrumentation having high photometric and spectroscopic sensitivity.
For this purpose we have modified our original balloon instrument to
provide additional sensitivity and to function within the constraints of a
long duration balloon flight.
3. Flight Apparatus To attain the above objectives we have enlarged the
collecting area of the original payload and adapted it to a unique balloon
gondola designed to capitalize on the long float duration available using
standard zero-pressure balloons in the radiation controlled (RACOON)
mode. A block diagram for the detector system is shown in Figure i.
Our detector complement
consists of an array of four
actively shielded high purity
PHOSWICH Ge DETECTORS
cooled planar germaniu_ SC,NT,LL=0RS_
detectors totaling -50 cm
active area plus three large
area NaI(TI )/CsI(Na) phoswich
scintillation counters
ca00oooothe germanium detector array PHApSiS provided by a 160 1 dewar of
liquid nitrogen. The aperture _ _i A_c_ _ i] _
of the germanium array is
oriented vertically with an
acceptance angle of 40 degrees _ _
( full width, zero response).
This permits sensitivity to
solar transient events for
roughly two hours of each day GOESTELEM TRY
at >33% response. _ne phoswich UPL,,K
• VHF
" scintillation counters have 3 GROUNO /_
LINK •
mm thick primary detector
elements and are optimized to Figure I - The _-processor based data
system accommodates a wide dynamic range
• respond in the 15 to 150 keV of detector event rates and prioritizes
energy range. Each phoswich the data for storage or telemetered
has a crossed slat collimator output (see text).
which defines a pyrimidal
angular response with FWHM of
15 degrees.
The phoswich array is carried in an alt-azimuth gimbal which is
slaved to an external aspect sensor platform. The aspect sensor platform
is programmed during the day to track the sun in azimuth and elevation with
a precision of " 1 degree. During night operation or periods when the sun
is too low in the sky to permit useful x-ray observations the aspect sensor
platform may be reprogrammed to track the local magnetic field. This
472
SH9,1-5
operating mode permits observation of non-solar sources via a pre-
programmed tracking routine with an accuracy of "2 degrees. The aspect
sensor platform also incorporates a sunrise/sunset sensor to provide daily
navigation updates to the tracking routines.
The data generated by these detector systems are processed by an on-
board computor and prioritized for output via one or more of three
channels as shown in Figure i. Discrete x-ray event words in which pulse
height and timing information are encoded are read directly into a large
dynamic random access memory via direct memory access c_ntrol. This memory
is sized to hold the transient events totaling up to i0 discrete detected
photons. The raw event rates are monitored in parallel with memory storage
of the detector data streams by the on-board processor to detect the
presence of solar burst events, Data segments which contain such burst
events are then tagged for preferential storage and output. When "50% of
the main buffer RAM is filled ('2 hours under background rate conditions)
the data are transferred to the on-board tape storage system. This system
includes two 3M model ND-75 digital recorders having a total capacity of
136Mbytes which is sufficient to hold all of the data generated during the
nominal 20 day balloon flight. Burst event data from the previous day are
read out of the burst memory section each night and transmitted via the
Geostationary Orbiting Environmental Satellite (GOES) network at an
effective rate of 60 bps. During the day this data channel is used in real
time to transmit the integral rates in three broad energy windows as
monitored by the the phoswich array. This channel provides a rudimentary
data base for studying _-flare characteristics should the tape recorder
data not be recovered. An additional data transmission channel is provided
via line-of-sight VHF telemetry to permit high rate monitoring of the
payload during the initial float checkout phase of the balloon flight
before the payload is committed to a circumnavigation. This channel will
also be used to dump the data stored in the on-board tape recorders as a
precautionary measure before cutdown and recovery of the payload.
Additional features are provided in the balloon gondola system t_
support a nominal 15-20 day float duration. Power is provided by an 8 m
solar panel array which is deployed after launch and operates in
conjuction with a lead acid battery stogage system. The power system is
scaled to support an average energy usage of 2500 watt-hours per day. The
balloon/gondola system incorporates an auto-ballast system which
functions in three stages. Nominal sunset cooling and settling of the
balloon will trigger a minimal ballast drop of "5% of the payload weight.
An anomalous altitude change, as might occur over a cold cloud layer, will
trigger an additional ballast drop of 10%. In the event of a very large
altitude excursion (which might result in the payload descending below the
tropopause) a ballast destruct occurs to provide some possibility of
restoring the payload to a functional altitude. The primary payload is
fully enclosed within an insulation blanket which includes additional
thermal ballast to maintain tempertures above 0 ° C. Additional thermal
isolation and heating is provided for the phoswich scintillator array
which needs a 20-30 °C operating environment.
4. Long Duration Balloon Operation The RAdiation COtrolled balloON
(RACOON) concept offers near ideal conditions for the study of solar
phenomena (6, 7). Since essentially continuous exposure is possible for
periods within ± 4 hours hours of local noon, one is not limited by the "40
minutes of earth occulation which occur for a spacecraft instrument in
473
SH 9.1-5
each 90 minute low earth orbit. The RACOON mode involves the use of a
standard zero pressure polyethelyne balloon for multi- day flights without
the use of extensive ballasting to maintain float altitude through sunset.
The initial float altitude must be chosen such as to ensure that the sunset
altitude change does not bring the balloon below the tropopause where the
negative temperature gradient would result in loss of the flig_. For the
present system we require a daytime float altitude of "3 gm/cm residual
depth to conduct x-ray observations. This is adequate to keep the balloon
safely above the tropopause at night. Allowing 1 to 2 hours to reattain
daytime float altitude we expect "250 hours of total float duration at 3
gm/cm . This should be compared with the nominal maximum float durations
of 25-40 hours which are occasionally attained under normal balloon flight
conditions.
The balloon is to be launched in January, 1986 from Alice Springs,
Australia, where the strong prevailing stratospheric winds will keep the
system within "2 degrees of a constant latitude for the 15-20 day duration
of the global circumnavigation, Cutdown is planned for the Eastern coastal
region of Australia.
5. Summary. We have developed a sophisticated balloon gondola which will
provide the first astronomical observations of solar and cosmic phenomena
from long duration balloons. We will use the RACOON long duration mode
which is ideally suited for observations of the sun. We expect one 20 day
balloon flight to yield "150 hours of solar and "I00 hours of cosmic source
observations. We estimate that "20 flare events strong enough for
spectroscopic analysis should be observed in a January, 1986 flight.
6. Acknowledqements The authors wish to acknowledge the valuable asistance
provided by the National Scientific Balloon Facility in the design and
construction of the payload and planning for the long duration flight
operation. We also wish to thank R. Sood and J. Thomas at the University of
Melbourne for their assistance in preparations for the Australian lauch
and recovery operation. We also wish to acknowledge the generous support
of National Science Foundation Grant ATM-8402231, National Aeronautics
and Space Administration Grant NAGW-516, and California Space Institute
Grant CS30-82.
References
1. Lin, R.P., Schwartz, R.A., Pelling, R.M., and Hurley, K.C. (1981), Ap_.
(tetter_),251, 109.
2. Lin, R.P., Schwartz, R.A., Kane, S.R., Pelling, R.M., and Hurley, K.C.
(1984), Ap.J.,283, 421.
3. Tanaka, K., Nitta, N., Akita, K., and Watanabe, T. (1983), SolarPhysics,
86, 91.
4. Duijveman, A. (1983), SolarPhysics,84, 189.
5. Canfield, R.C. and Metcalf, T.R. (1984), B.A.A.S.,16, No. 4, 891.
6. Lally, V.E. (1981), The RadiationControlledBalloon,Preprint, National Center
for Atmospheric Research.
7. White, R.S. (1983), A Plan for Long Duration Scientific Ballooning, Report of the
Long Duration Balloon Flight Study Committee, printed by the
National Scientific Balloon Facility, Palestine, Texas.


Photometric and spectroscopic gamma-ray observations of solar transient phenomena using long duration balloons

Photometric and spectroscopic gamma-ray observations of solar transient phenomena using long duration balloons

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server