Three rocket flights to measure the solar constant and provide calibration data for sensors aboard Nimbus 6, 7, and Solar Maximum Mission (SMM) spacecraft were accomplished. The values obtained by the rocket instruments for the solar constant in SI units are: 1367 w/sq m on 29 June 1976; 1372 w/sq m on 16 November 1978; and 1374 w/sq m on 22 May 1980. The uncertainty of the rocket measurements is + or - 0.5%. The values obtained by the Hickey-Frieden sensor on Nimbus 7 during the second and third flights was 1376 w/sq m. The value obtained by the Active Cavity Radiometer Model IV (ACR IV) on SMM during the flight was 1368 w/sq m

Duncan, C. H.

English

NASA Technical Reports Server

N82' 17019
A SUMMARY OF RESULTS FROM
SOLAR MONITORING ROCKET FLIGHTS
Charles H. Duncan
Goddard Space Flight Center
ABSTRACT
Three rocket flights to measure the solar constant and provide cal-
ibration data for sensors aboard Nimbus 6, 7, and Solar Maximum Miution
(SMM) spacecraft have been accomplished. The values obtained by the
rocket instruments for the solar constant in SI units are: 1367 wm -2 on
29 June 1976; 1372 wm -2 on 16 November 1978;and 1374 wm -2 on 22
May 1980. The uncertainty of the rocket measurements is +0.5%. The
values obtained by the l-lickey-Fr!eden (H-F) sensor on Nimbus 7 during
the second and third flights was 1376 wm-2 . The value obtained by the
Active Cavity Radiometer Model IV (ACR IV) on SMM during the flight
was 1368 wm -2.
INTRODUCTION
Three rocket flights to measure the solar constant and provide "ground truth" calibrations for
spacecraft sensors have been accomplished to date. The first flight was initiated by NASA Head-
quarters in January 1976 because the values being obtained for the solar constant by the ERB fiat-
plate detector on Nimbus--6 were 1.5 percent higher than e×pected, i.e., ]392 wm-2 . Nimbus-6
first began taking data on July 2, 197-5. This first flight identified a calibration error of+1.6 per-
cent in the Nimbus-6 ERB channel 3 values. Subsequently, Hickey, et ai., have identified the cause
for +0.7 percent of this calibration error. The reasons for the remaining +0.9 percent error has not
been identified to date. However, Hickey only claimed ±0.75 percent accuracy for this detector 1,
so the values obtained from both spacecraft and rocket during the f'trstflight are within the bounds
of uncertainty of ±0.5 percent. 2 This paper provides some background on the history and results
of these rocket flights.
FIRST ROCKET FLIGHT
Prior to authorizing the f'trstrocket flight, NASA HQ convened an Ad Hoc Science Review
Committee to consider the merits, probability of success and selection of experiment payload. The
committee met initially on January 26, 1976. The personnel were:
Guenther Brueckner - Naval Research Laboratory, Wa_ington, DC
Louis Drummeter - Naval Research Laboratory, Washington, DC
John Gille - National Center for Atmospheric Research, Boulder, CO
Verner Suomi - University of Wisconsin, Madison, Wl
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p,_ ..
1982009140-048
https://ntrs.nasa.gov/search.jsp?R=19820009145 2020-03-21T10:38:46+00:00Z
Robert Madden - National Bureau of Standards, Washington, DC
Jon Ge_ -- National Bureau of Standards, Washington, DC
This committee made the following recommendations:
I. Ground intercomparisons at a high mountain site among rocket payload and nevtral outside
sensor [recommend_ _MO (Phys.._alisch--},leteorologisches Observatc:ium) Davos, Swl,zerland sen-
sor developed hy C. Fr_hlich] be conducted prior to/'light unde: _.,:'.._ientand vacuum conditions
(I 0.4 Tort) and that agreement among all instruments be better than ±0.5 percent.
2. Tests to be conduct_ to verity behav!-,r of payload upon exposure to the pressure temper-
ature profile of the mission using thermal vacuum chambers and a solar simulator. Any effects
upon performance to be noted and miss/on a_oned if these effects cause more than 0.I percent
changes in response of indi_'id ,al inslruments.
3. To minimize thermal problems and to eliminate all windows, payload to be launched in an
evacuated conf'_uration ( 10 -4 Ton').
4. Instrument payload to consist of prototypes of ER.B solar channels and as many self-
calibrating radiometers as pox'hie.
Subsequent to this meeting and prior to the flight, a final review of the results of intercom-
parisons, pressure-temperature proTlle testing, and related factors was held at NASA HQ on June 3,
1976. Upon presentation of the data, the Ad Hoc Committee gave its fi,-_alapproval for flight.
Pertinent test results presented at this meeting i_.cluded:
I. Ratios of irradiance by the l'we payload instruments were shown to be constant _t all irra=
diance levels at ali pressures.
2. Calibration factors for pressure intermediate between 50Tort and 10"4 Tort for ERB 3,
ESP, and PACRAD were derived.
3. Simulation of launch pressure v_riations showed that all/'we instruments _' >uld read the
solar constant within less than 45 seconds after first acquisition of the run.
4. The five solar constant detectors (rocket payload plus two PMO detectors) agreed with each
other within ±0.3% during the South Baldy intercomp_isons at both .;mbient snd v_cuum I.10.4
Tort).
5. An insect was trapped in canister upon placemen_ of quartz wi.ndow on payload _t South
Baldy and subsequentl._' fell into the receiver of the PACR,AD causing a 2.83 percent decrease in
measurement data. Quartz w_s removed, bug was removed, PACRAD re-exposed to sun and ob-
tained original results as compared to other instrume_ts.
46
1982009140-049
6. Payload instruments viewed LN2 target (-185°C) at 10"° Torr to determine zero offset. .
TableIListsheinstrumentsandinvestigatorsforeachoftherocketflights.The firstflight
was launchedon June29,1976at12:20PM MDT fromWhiteSands,New Mexico.Duringlaunch,
accordingtoreadingsobtainedby theERB-3 sensor(fastimeconstant,pressuresensitive)the
canisterlostvacuum duringtheinitiallaunchphaseanddidnotrecoveruntilthenoseconewas
blown.Thisfactwas alsoverifiedby thePACRAD. The ACR IV,nothavingdemonstratedpres-
suresensitivity during five track tests, did not note this fact.
The initial values reported by the investigators at about 3 minutes into fright did not change
by more than 1 wm "2 except for the ERB-3 value which was initially reported as 1374 wm "2 and
subsequently changed to 1389 wm "2. The justifieztion being: ERB on Nimbus-6 when pointed to
TABLE I. SOLAR MONITORING ROCKET FLIGHTS
e PAYLOAD FOR IS'I"FLIGHT
INVESTIGATOR/ SUPPORT
INS'TRUMENT INSTITUTION CONTRACTOR
i
ACR IV 402A R.C. Willson/.WL TRW,
ACR IV 402B Los Angeles, CA1
PACRAD J.Kendall/JPL None
R. Harrison/JPL
ERB-ESP J.Hickey/Eppley GultonIndustries,1
Channels Albuquerque,NM
d,.
3
J 4
5
ofNimbus-6ERB
e CHANGES FOR 2ND AND 3RD FI,IGHTS
- ERB-ESP - ELiminateChannels2,4,and 5
- Add Channel3 WithAnodizedBaffles
- Add H-F Sensor
I0127180
IFor Flighzs1 and2 only;no supportcontractorsfor third flight.
67
1982009140-050
space produced a negative count equal to 15 wm =2. If this negative offset were applied to the
rocket data then 1374 +I 5 = 1389 wm "2 which made perfect agreement between rocket I and
Nimbus-6 ERB. Table II fists the values obtained by the rocket instruments and Nimbus 6 ERB.
SECOND ROCKET FLIGHT
The programlaydormantfrom thefirstflighton June 29,1976,untilOctober27,1977,when
anAN proposalwas acceptedforfouradditionalrocketflightsobe conductedunderthegeneral
pl_ilosophydevelopedby theAd Hoc ScienceReviewCommittee.
The payloadwas refurbished;Hickeysubstitutedan ERB-3 channelwithanodizedbafflesand
an improvedversionof theESP,termedan H-F, forthefiltersolarchannelsflownon thefirst
flight.Thesechannelsdidnotobtainanydatawhichgavemeaningfulinsightintothebehaviorof
thesamechannelson Nimbus-6ERB. Eachofthesechannelswas coveredwitha filterand some
valueswerehigherand some loweron therocketascomparedtothespacecraftwithdifferencesof
27 wm -2,20 wm -2,and lwm -2 noted.
The addition of the ERB-3 with anodized channels was added to try to identify the source of
the calibration error of Nirnbus-6 ERB discovered by the first rocket flight. The H-F sensor was
added because it had become part of the payload of Nimbus-7 as channel I0 C.
The intercomparison of the Nimbus-'/channel l0 C detector with the rocket oayload prior to
the lau oF. of Nmlbus-7 could not be accomplished. Subsequently, the second rocket flight was
launched on the same day and obtained values at the same time as the Nimbus-7 ERB was first
turned on. Also, during the second flight, the payload was pointed off sun for 30 seconds to try to
verify that the space offset of ERB-3 was really 15 wm-2. The payload also lost vacuum about 15
minutes prior to launch.
The primary result from the second flight was an apparent increase in the solar constant since
the first flight. The result of off sun pointing was inconclusive since the ERB detector first began
exhibiting negative counts, then reversed this trend, then became negative again for a few seconds,
then acquired the sun. Th_s effect was most probably due to the fact that the nose cone was drift-
ing into and out of the field of view of the instrument. The negative offset maximum observed was
equivalent to approximately 12 wm "2 . This verifies that the space offset observed for Nimbus 6
was most probably the same for the rocket although sufficient observation time was not available
to reach 15 wm "2 . It should be noted that: according to Hickey I "The space look offset amounts
to almost 0.9 percent of the solar constant value for ERB channel 3."
'Fhc most disappointing a:'pccts of this llight were the ,_lturation of tile II-F sensor in Ilight duc
to tile wrong value el heater power being _'t, the _lturation of tile ACR IV-B, and the initial ]o',v
• lower than expected, obtained by the FSP. The FSP lower wdues were latervalues, ,-3 percent
1Prlva(econwmniettion.
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1982009140-051
tTABLE II. SOLAR MONITORING ROCKET FLIGHTS !
Results of 1st Flight - June 29, 1976 @ 12:20 PM MDT - White Sands, NM
INSTRUMEN"£ VALUE
PACRAD 1364 wm-2
ACR A 1368 wm -2
ACR B 1368 wm =2
ESP 1369 wm =2 ,
Mean 1367 wm=2 I'
ERB Rocket Channel 3 1389 wm"2
ERB Nimbus Channel 3 1389 wm=2
Difference ERB Channel 3 ")'22wm =2 or +1,6%
and Rocket Payload Mean :'
10/28/80
49
1982009140-052
t: found to be due to aperture contamination and a change in the parameters relating back heater
power to irradiance. A recharacterization of the ERB sensors accomplished during this activity dis-
covered a +0.7% calibration error for the Nimbus-6 ERB sensors as flown on Nimbus-6 and the first
rocket flight. The anodized baffles on ERB-3 gave the same results as the painted baffles so this
channel yielded no new information to resolve the calibration anomaly noted on the first flight.
Table IIl lists the values for this flight along with the Nimbus 6 & 7 ERB values. The values shown
for the ESP include the convection of 1.96% for aperture contamination and 0.3% for heater power
parameter changes. Both values are shown.
Because of the importance of the possible increase in the solar constant, a post-flight inter-
comparison was held at Table Mountain, California, on 10-13 December 1978. Hickey was unable
to participate in this intercomparison. However, Fr_hlich of WMO and Crommelynck of Belgium
both participated. Crommelynck has been selected to fly a solar constant experiment aboard the
shuttle and brought his prototype for this flight to Table Mountain. Fr_hlich brought wRh him the
same instruments which had initially been used at the South Baldy intercomparisons. The results
of this intercomparison were that the PMO and ACR IV-A were still reading within 0.06 percent of
the intercomparison values at South Baldy while the PACRAD was reading 0.5 percent higher.
KendaLl and Harrison reported subsequently 2 that an incorrect characterization had been used in
the South Baldy intercomparisons, but the correct characterization had been used for both the first
and second rocket flights and for the post-flight intercomparisons, after the second rocket flight.
The)' maintained that their instrument had truly shown an increase in the solar constant between
the two flights.
During this time period, Willson intcrcompared his three sensors flown on the SMM with the
rocket ACR IV instruments. In comparison to the rocket ACR IV-A, the SMM sensors A, B, and
C read 0.2 percent, 0.04 percent, and 0.3 percent higher respectively. The Crommelynck sensor
read 0.7 percent lower, the PMO2 read 0.5 percent lower and the PMO6 read 0.15% lower than the
ACR 402A.
The value derived from the second rocket flight for the solar cor_stant of 1372 wm -2 was
4 wm -2 lower than the value obtained simultaneously by Nimbus-7 channel 10 C (H-F). However,
the rocket instruments were not intercompared with the Nimbus-7 channel 10 C before launch of
Nimbus 7 so the bias between the rocket instruments and the H-F could no: be identified since the
rocket H-F saturated. These two values were within the uncertainty of the measurements however.
THIRD ROCKET t- 'rr
As a result of the values obtained from the second flight, the investigators (Willson, Hickey,
Kendall. Harrison) took extreme care in the preparation and execution of the third flight.
Extensive intercomparisons before the flight were made on 15-19 April 1980. During this
intercomparison, the relative performance of the rocket sensors was established again. The
2Privatecommunication.
5O
1982009140-053
TABLE III. SOLAR MONITORING ROCKET FLIGHTS
Results of 2rid Flight - November 16, 1978 @ 11 :15 MST - White Sands, NM
INSTRUM ENrr VALUE
PACRAD 1371 wm "2
ACR A 1373 wm -2
ACR B Saturated
ESP 1373 wm -2. -
1378 wm -2
H-F Saturated
Mean (No-ESP) 137"_,m "2
Mean (With-ESP) 1372=I374 wm -2
ERB RocketChannel3 1383wm -2
ERB Nimbus-6Channel3 138"/wm"2
ERB Nimbus-7Channel3 1383wm =2
Mean 1384 wm =2
Nimbus-7 H-F Channel 10C 1376 wm "2
Difference ERB Channels 3
and Rocket Payload Mean +l 2 wm "2 or +0.9%
Difference H-F Channel 10C
.-ndRocketPayloadMean +4 wm -2or+0.3%
"Value derivedafterdisassemblyof mnsor.
51
1982009140-054
PACRAD and ACR IX"were consistent with their performance during the initial intercomp_isons
at South Baldy peak. The ESP read about 0.3% higher than during the intercomparisons before the
fu'st flight. The H-F which had never been intercompared previously read about the same as the
PACRAD; about 0.3 percent lower than the ACR's, and about 0.8 percent lower than the ESP.
The decision was made prior to the third rocket flight not to try to evacuate the canister since
vacuum had not been maintained after launch for either of the two previous flights and the effects
of dynamic heating were negligible on causing temperature excursions on the instruments.
Consequently, the payload was purged with dry air for a week before launch whenever pos_a'ble
and continuously until launch after the horizontal test was complete, a period of about 48 hours.
The third flight had been scheduled to coincide with the first turn-on of SMM ACRIM. Prob-
lems with the Aerobee 170 rockets forced a delay of the flight to May 22, 1980 after a decision
had been made to fly the payload aboard an Astrobee rocket instead of continuing to wait for an
Aerobee 170 to be readied.
The results from the third flight a_ee very closely with those from the second flight for both
rocket instruments and Nimbus-7 H-F measurements. The results are summarized in Table IV.
Nimbus-7 channel l0 C measured 1376 wm -2 for the dates of each of these flights and the rocket
averages for the second and third flights were 1372 and 1374 wm -2 respectively, all well within
the estimated uncertainty of the instruments.
However, the SMM ACRIM was also in space on 22 .May 1980 obtaining a value of 1368 wm -2
for the solar constant. These ACRIM instruments (now reading lower in space) had read about 0.2
percent higher than the rocket ACR IV's during mtercomparisons at Table Mountain in December
1979. This result indicated that environment, possibly pressure, might influence the measurements
of the ACR detectors. Also, the H-F during intercomparisons in April 1980 at Table Mountain
read 0.3 percent lower than the rocket ACR but during the third rocket fligt,., it read 0.3 percent
higher for a total difference of 0.6 percent. The rocket H-F, however still read about 0.2 percent
higher than the Nimbus-7 H-F for a total difference between ground intercomparisons and space-
craft values of about 0.4 percent which is very close to the difference (0.6%) observed by Willson
between ground, rocket, and space performance.
SUMMARY
Table V lists pertinent data for each of the three flights along with sunspot number_ on the
dates of the flights. Table VI summarizes the results of the measurements for the three flights.
Table VII summarizes the results from Ninabus 6 & 7 ERB and $MM ACRIM for the dates of the
flights. Table VIII presents an average value for the solar constant for the dates of each flight using
both rocket and spacecraft data. The rocket average value for the solar constant is given equal value
to the spacecraft values in a simple arithmetical average.
52
1982009140-055
TABLE IV. SOLAR MONrlTORING ROCKET FLIGHTS
Results of 3rd Flight - May 22, 1980 @ 9:00 MDT - White Sands, NM
INSTRUMENT VALUE
PACRAD 1373 wm "2
ACR A 1373 wm -2
ACR B 1374 wm"2
H-F 1378 wm"2
ESP 1385 wm"2
Mean 1377 wm"2
ERB Rocket Channel 3 1377 wm"2
ERB Nimbus--6 Channel 3 1377 wm"2
ERB Nimbus-7 Channel 3 1367 wm"2
Mean 1374 wm -2
Nimbus 7 H-F Channel 10C 1376 wm "2
S.MMACRL\I A, B, C Average 1368 wm "2
Difference ERB Channels 3
and Rocket Payload Mean 3 wm -2 or 0.2%
Difference H-F Channel 10C
and Rocket Payload Mean I wm -2 or 0.07%
Difference SMM ACRI2,1 and
Rocket Payload Mean 9 wm "2 or 0.6%
53
1982009140-056
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1982009140-059
TABLE VIII. AVERAGE VALUE OF SOLAR CONSTANT AT TIMES OF
ROCKET FLIGHTS (CAVITY SENSORS IN SPACE)
Date Sensors Value (win-2) Average Value (win-2)
29 June 1976 Rocket Payload (1367) 1367
16 Nov. 1978 Rocket Payload (1372) 1374
Nimbus 7 H-F (1376)
22 May 1980 Rocket Payload (1374) 1373
Nimbus 7 H-F (1376)
S._IMACRIM (1368)
57
1982009140-060
' A fourth rocket flight is planned for May 198 I. The experiment canister is being rebuilt so
that vacuum can be maintained prior to and after launch. Fr_hlich will also provide two PMO-6
sensors for the expex'iment payload under an international agreement which has been negotiated
recently. Plans for this flight also include 30 seconds off sun pointing after 5 minutes of data have
been taken to establish the space offset values for tile senso-¢.
, REFERENCES
1. J.R. HiekeyandA. R. Karoli, ApF.! Opts., 13,523(1974).
2. C.H. Duncan et al., Ap;,,l. Opts., 16, 2690 (1977).
58
1982009140-061


A summary of results from solar monitoring rocket flights

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