The Uranus Multi-Experiment Radiometer for Haze and Clouds Characterization

Space Science Re iews (2024) 220:6
h ps://doi.o g/10.1007/s11214-023-01040-3
The U anus Mul i-Expe imen Radiome e o Haze and
Clouds Cha ac e iza ion
V. Apés igue1·D. Toledo1·P.G.J. I win2·P. Rannou3·A. Gonzalo1·
J. Ma ínez-O e 1·J. Ceballos-Cáce es4·J. Azcue1·J.J. Jiménez1·E. Sebas ian1,5 ·
M. Yela1·M. So ibas1·J.R. de Mingo1·A. Ma ín-O ega1·T. Belenge 1·M. Al a ez1·
D. Vázquez-Ga cía de la Vega4·S. Espejo4·I. A uego1
Recei ed: 23 Sep embe 2023 / Accep ed: 22 Decembe 2023
© The Au ho (s) 2024
Abs ac
The ae osols (clouds and hazes) on U anus a e one o he main elemen s o unde s anding
he he mal s uc u e and dynamics o i s a mosphe e. Ae osol pa icles abso b and sca e
he sola adia ion, di ec ly a ec ing he ene gy balance ha d i es he a mosphe ic dynam-
ics o he plane . In his sense, ae osol in o ma ion such as he e ical dis ibu ion o op ical
p ope ies is essen ial o cha ac e izing he in e ac ions be ween sunligh and ae osol pa -
icles a each al i ude in he a mosphe e and o unde s anding he ene gy balance o he
plane ’s a mosphe e. Mo eo e , he dis ibu ion o ae osols in he a mosphe e p o ides key
in o ma ion on he global ci cula ion o he plane (e.g., egions o upwelling o subsidence).
To add ess his challenge, we p opose he U anus Mul i-expe imen Radiome e (UMR),
a ligh weigh ins umen designed o cha ac e ize he ae osols in U anus’ a mosphe e as pa
o he upcoming U anus Flagship mission’s descending p obe payload. The scien i ic goals
o UMR a e: (1) o s udy he a ia ion o he sola adia ion in he ul a- iole (UV) wi h
al i ude and cha ac e ize he ene gy deposi ion in he a mosphe e; (2) o s udy he e ical
dis ibu ion o he hazes and clouds and cha ac e ize hei sca e ing and op ical p ope ies;
(3) o in es iga e he hea ing a es o he a mosphe e by di ec ly measu ing he upwa d
and downwa d luxes; and (4) o s udy he cloud e ical dis ibu ion and composi ion a
p essu es whe e sunligh is p ac ically negligible (p >4-5 ba s).
The ins umen includes a se o pho ode ec o s, ield-o - iew masks, a ligh in a ed
lamp, and in e e ence il e s. I d aws on he he i age o p e ious ins umen s de eloped a
he Ins i u o Nacional de Técnica Ae oespacial (INTA) ha pa icipa ed in he explo a ion
o Ma s, whe e simila echnology has demons a ed i s endu ance in ex eme en i onmen s
while u ilizing limi ed esou ces ega ding powe consump ion, mass and olume oo p in s,
and da a budge . The adiome e ’s design and cha ac e is ics make i a aluable complemen-
a y payload o s udying U anus’ a mosphe e wi h a high scien i ic e u n.
Keywo ds Plane a y adiome e ·Ice Gian s ·U anus ·Clouds and haze
1In oduc ion
U anus and Nep une, known as he Ice Gian s, s and ou as he only plane s in he Sola
Sys em ha ha e no been he ocus o dedica ed missions. Howe e , del ing in o he s udy
Ex ended au ho in o ma ion a ailable on he las page o he a icle
6 Page 2 o 30 V. Apés igue e al.
o hese plane s is essen ial o us o g asp how ou plane a y sys em o med (Mand e al.
2015) and changed o e ime (Mousis e al. 2022), especially since ice plane sys ems a e
qui e common in o he plane a y sys ems (Bo ucki e al. 2011; Ful on e al. 2017).
Ou cu en unde s anding mainly comes om “limi ed” obse a ions made by Ea h
and space elescopes and a b ie isi by he Voyage 2 spacec a o e hi y yea s ago.
Acco ding o he ecen Decadal Su ey Repo (Na ional Academies 2022), NASA has
placed a p io i y on sending a signi ican mission o U anus, in addi ion o hei ongoing
missions o Ma s and Eu opa. Simila ly, he Voyage 2050 s udy (ESA Senio Commi ee,
2021) by he Eu opean Space Agency (ESA) aligns wi h his di ec ion, sugges ing ha ESA
should join o ces in a u u e mission h ough collabo a ion, ollowing he success ul model
o pa ne ships in Cassini-Huygens.
Du ing he las wo decades, se e al e e ence missions ha e been p oposed o each he
Ice Gian s sys em (Hubba d e al. 2010; A idge e al. 2012; Ho s ad e e al. 2017,2019;
Bayon e al. 2019). These mission p oposals aim o in es iga e he op imal a angemen o
accomplishing a numbe o scien i ic goals using he a ailable echnology a he ime. The
mos ecen and comp ehensi e s udy conduc ed o achie e he scien i ic objec i es o he
las Decadal epo is he U anus O bi e and P obe (UOP) mission (Simon e al. 2021). This
Flagship-class mission concep consis s o an o bi e and a descen p obe o be launched
p e e ably by 2031.
Fo he o bi e , he scien i ic p io i ies ex ac ed om he Decadal Su ey a e: o s udy
he plane ’s bulk composi ion and in e nal s uc u e, he magne ic ield, he a mosphe e ci -
cula ion, he ings, and he sa elli e sys em. To his end, he spacec a includes as e e enced
payload package o six ins umen s. In he case o he descen p obe, i s p ima y mission is
o ob ain he a mosphe ic noble gas abundances, noble gas iso ope a ios, and he he mal
s uc u e o he a mosphe e and winds, using ou e e ence ins umen s: an A mosphe ic
S uc u e Ins umen , a Mass Spec ome e , an Ul a S able Oscilla o , and an O ho-Pa a
Hyd ogen Senso .
Howe e , hese p obes could also be capable o s udying he hazes composed o small
pho ochemically p oduced pa icles (hyd oca bon ices) and he abundances o species ha
can condense in he a mosphe e and o m clouds, such as NH3,CH
4,H
2S, and H2O. These
ae osol pa icles a e c ucial in he adia i e hea budge o he plane , and measu ing hei
op ical p ope ies and spa ial dis ibu ion can p o ide use ul in o ma ion abou he chemis y
and dynamics o he U anus s a osphe e and oposphe e, cons aining plane a y o ma ion
models (e.g., A eya e al. 2020; Mousis e al. 2018). O bi al obse a ions could gi e pa ial
in o ma ion abou hese a mosphe ic s uc u ed laye s bu o gi e a “g ound u h” o he
e ical dis ibu ion and composi ion o he ae osols we need he use o a descen p obe
wi h dedica ed ins umen a ion and in-si u obse a ions compa ible wi h he esou ces o
he p obe’s p ima y mission.
2 Descen P obes Ae osol Ins umen a ion P eceden s
His o ically, descen p obes ha e inco po a ed ins umen a ion o he s udy o clouds based
on he op ical p ope ies o hei ae osols, and he deposi ion o sola ene gy as a unc-
ion o al i ude. The Russian Vene a p og am, in i s descen p obe o mission numbe 8,
employed a isible-ligh pho ome e . I s pu pose was o ob ain he op imal exposu e alue
o u u e su ace pho og aphs o Venus, which would be sough in he subsequen mis-
sions. Howe e , his ins umen also conduc ed he ini ial measu emen s o sola adia ion
a ia ion in Venus’ a mosphe e (A due sky e al. 1973) du ing he descen . The Vene a 9,
The U anus Mul i-Expe imen Radiome e o Haze and Clouds... Page 3 o 30 6
10, and 11 descen p obes included nephelome e s (back and mul i-sca e ing angles). They
helped iden i y h ee cloud laye s and he unde lying haze. As a esul , hey could de e mine
he mic ophysical p ope ies o he pa icles in hese laye s (Ma o e al. 1980). In 1978,
he Pionee mission, also dedica ed o he s udy o Venus, deployed a se o a mosphe ic
p obes alongside an o bi e . The Venus Sounde P obe was he la ges and mos comple e
descen module, equipped wi h 11 ins umen s, ou o which 4 we e ocused on he anal-
ysis o ae osols and he mal balance a backsca e ing nephelome e (Ragen e al. 1980),
a sola lux adiome e (Tomasko e al. 1980), an in a ed adiome e (Boese e al. 1980),
and a cloud pa icle size spec ome e (Knollenbe g and Gilland 1980). On he o he hand,
he o he h ee smalle win p obes we e ou i ed wi h 7 ins umen s, o which 2 we e also
dedica ed o cloud s udies: he same nephelome e as in he main p obe (Ragen e al. 1980)
and a minia u ized ne lux adiome e (S omo sky e al. 1980).
In 1995, he Galileo p obe conduc ed he i s in-si u explo a ion o he a mosphe e o a
gian plane . Du ing i s descen o o e 150 km, i s udied Jupi e ’s ae osols using a neph-
elome e (Ragen e al. 1992) capable o measu ing simul aneously he sca e ing p ope ies
o pa icles a 5 di e en angles, d awing inspi a ion om he Vene a nephelome e s. Addi-
ionally, he p obe included Galileo’s Ne Flux Radiome e (S omo sky e al. 1992) o he
a mosphe e ene gy balance de e mina ion.
Finally, he e is he p eceden o he Huygens p obe o he Cassini mission, de eloped
join ly by NASA and ESA, wi h he objec i e o s udying he a mosphe e o Ti an. In his
case, he Descen Image /Spec al Radiome e (DISR) was he key ins umen o he cha -
ac e iza ion o he ae osols (Tomasko e al. 2002). I encompassed he measu emen o o al
sola adia ion lux as well as measu emen s o sca e ing in wo spec al bands and ac oss
wo pola iza ion planes, along wi h wa eleng h-dependen ex inc ion measu emen s ac oss
di e en laye s o he a mosphe e. Mo eo e , i inco po a ed a came a sys em o cap u e
winds and de ails o he Ti an’s su ace.
Al hough he spa ial co e age o he p obe obse a ions is e y limi ed compa ed wi h he
o bi al obse a ions, he cha ac e iza ion o he a mosphe e (e.g., he ae osols) wi h in-si u
measu emen s is ca ied ou wi h a le el o de ail ha is no achie able om o bi e obse a-
ions. Consequen ly, a ious ins umen s ha e been p oposed in ecen yea s o he descen
p obe o a p ospec i e Ice Gian Mission. One such ins umen is he Ne Flux Radiome e
(Aslam e al. 2020), which builds upon he legacy o he a o emen ioned NFR ins umen
om Galileo’s mission. I s objec i e is o measu e he a mosphe ic hea balance and s uc-
u e, he h ee-dimensional low in he oposphe e, and he composi ions and opaci ies o
he cloud laye s. Ano he no able ins umen is he LONSCAPE nephelome e and pa icle
coun e (Rena d e al. 2020). This ins umen was p oposed o e ie e bo h he concen a-
ions and phase unc ions o ae osols in he ange o 0.2 o 50 µm, he eby cons aining hei
composi ion and o ma ion p ocess.
3Ins umen Concep
The cha ac e iza ion o ae osols in he a ious plane a y a mosphe es isi ed by descen
p obe missions has been c ucial o comp ehending hei global a mosphe ic p ocesses.
Ne e heless, due o he limi ed esou ces o he u u e mission, p ima ily esul ing om
he conside able dis ance o U anus as well as he s ingen cons ain s imposed on he de-
scen p obe in e ms o mass, olume, and powe a ailabili y, he s udy o ae osols could be
comp omised.
6 Page 4 o 30 V. Apés igue e al.
Fig. 1 The U anus Mul i-Expe imen Radiome e and i s accomoda ion in he UOP descen p obe. The Op-
ical Head is a ached o he ex e nal wall o he essel (in blue) and he P ocessing Elec onic is included
in he in e nals o he p obe (g een). Some o he Fields o View o di e en op ical channels a e shown as
examples. C edi s: Ahmad Al omeadheen o he a is ic iew o U anus’s clouds backg ound; descen p obe
inspi ed by Simon e al. 2021; UMR and inal pic u e composi ion, INTA
To p e en his signi ican loss o a mosphe ic in o ma ion om U anus, conside ing he
challenges in de eloping o he u u e missions o he Ice Gian s, and unde s anding ha
his kind o science could only be done in si u, we p opose he U anus Mul i-expe imen
Radiome e (UMR) o be included in descen p obe o he nex mission (see Fig. 1). As will
be explained in his wo k, his ins umen concep is simple, compac , lexible, and low-
powe , wi h limi ed con olled mass and olume, o e ing high scien i ic yield wi h minimal
esou ce demand (see a summa y in Table 1). Much o i s design is based on p e ious INTA
minia u ized ins umen de elopmen s o Ma s de o ed o dus and cloud cha ac e iza ion:
he Sola I adiance Senso (SIS) o he Me Ne lande mission (Ha i e al. 2017); he
Sola I adiance Senso (SIS-16), which lew on ExoMa s 2016 as pa o he DREAMS
payload (A uego e al. 2017; Esposi o e al. 2018); he Radia ion and Dus Senso (RDS),
which is cu en ly on-boa d Pe se e ance as pa o he MEDA wea he s a ion (Apes igue
e al. 2022; Rod iguez-Man edi e al. 2021); and he Sola I adiance Senso 2020 (SIS-20)
o he ExoMa s 2018 mission (A uego e al. 2016), in eg a ed in o he Me eo Package o
he su ace pla o m Kazachock (see Zelenyi e al. 2015). This app oach allows us o use
well-es ablished echnologies wi h a high Technological Readiness Le el (TRL).
The UMR inco po a es a sui e o pho ode ec o s, in e e ence il e s, ligh sou ces, and
op omechanical masks o e ec i ely con igu e i s op ical channels, which enables he in-
s umen o cap u e a ange o measu emen s a di e en heigh s, geome ies o obse a ion,
and wa eleng h bands. I akes minia u iza ion as he main design d i e , minimizing i s im-
pac on he p obe accommoda ion by di iding he ins umen in o wo uni s. An op ical head
(UMR-OH), loca ed on he ex e nal side o he p obe, includes he senso s and he necessa y
p oximi y elec onics. I can ampli y, digi alize, and send he esul ing signals o he o he
uni o elec onic p ocessing (UMR-PE), which is loca ed inside. UMR-PE has he abili y
o con ol and p ocess he signals. The communica ion be ween he wo uni s is ca ied ou
using a di e en ial- ype se ial in e ace, which u ilizes a sealed pass- h ough be ween he
ex e io and in e io o he essel. Then edundan digi al se ial and powe in e aces a e
used o connec he adiome e o he p obe’s onboa d compu e and powe subsys ems.
The U anus Mul i-Expe imen Radiome e o Haze and Clouds... Page 5 o 30 6
Table 1 UMR main cha ac e is ics
Pa ame e Value
Dimensions OH: Ø150 mm x 35 mm
PE: 102 mm x 64 mm x 24 mm
Mass OH: 350 g
PE: 220 g
(Ha ness no included)
Tempe a u e En i onmen OH: 55 K o 110 K
PE: ∼293 K
Radia ion En i onmen 100 k ad
Powe Consump ion UV-Vis-NIR: 0.75 W (a g.)
Mid-IR: 1.25 W
Hea e : 4 W
Da a a e 33 by es/s (a g.)
In e ace Redundan RS-422
@ 57.6 kbps
S uc u e >20 ba
Design li e ime 14 yea s
4 Scien ific Objec i es
The scien i ic objec i es o he ins umen all in o ou a eas including (1) o s udy he ul a-
iole (UV) ene gy abso p ion by ae osols and gases, and de e mine i s pene a ion in he
a mosphe e; (2) o s udy he size, e ical dis ibu ion, and op ical p ope ies, sou ces and
sinks o ae osols (hazes and clouds) by measu ing he sca e ed sunligh p o iles a di e en
wa eleng h bands, om he isible o he nea in a- ed (IR); (3) o s udy he he mal balance
o he a mosphe e by measu ing he up-and-down luxes om he UV o NIR; and (4) o
s udy he cloud e ical dis ibu ion, densi y and composi ion a p essu es wi h negligible
Sunligh (p >4-5 ba s) by using lash-ligh emission and de ec ion in he IR.
Table 2o e s an o e iew o he dis inc channel se s assigned o ul illing pa icula
scien i ic goals, in addi ion o hose designa ed o c ucial auxilia y measu emen s. These
auxilia y measu emen s encompass de e mining he senso ’s o ien a ion in ela ion o he
Sun and assessing he po en ial deg ada ion o channels, o example, due o adia ion expo-
su e. The speci ic placemen o each channel wi hin he UMR-OH is isualized in Fig. 2.
4.1 Ul a-Viole P ofiles
A basic objec i e o he ins umen in es iga ion is o measu e sola ul a- iole (UV) en-
e gy deposi ion in U anus’ a mosphe e and i s a ia ion wi h al i ude. This will be done
using wo pho ode ec o s poin ing a 90° wi h espec o he ins umen plane (see Fig. 2)
and wi h di e en UV in e e ence il e s ( echnical desc ip ion is gi en in Sec . 5.5). Each
pho ode ec o has a ield o iew (FOV) o 80°, which allows measu ing a each al i ude he
UV adiance coming om almos all di ec ions. To de ine he dynamic ange o he senso s,
we will make use o adia i e ans e simula ions as ollows: (1) simula e he sky b igh -
ness ( adiance ield) as a unc ion o he zeni h and azimu h angles a di e en wa eleng hs

6 Page 6 o 30 V. Apés igue e al.
Table 2 UMR channel de ini ion: scien i ic a ionale, wa eleng h, ield o iew, poin ing, and dynamic ange
Channel
Type
Scien i ic Ra ionale Channel
Numbe
Wa eleng h
(nm)
Ele a ion*
(°)
Field o View
(°)
Dyn. Range
(mW/m2)
A Sun posi ion and
ajec o y
econs uc ion
1-4 200-1100 0 120 2775
B.1 Ae osol phase unc ion
cha ac e iza ion
5-10 (3x) 560 ±10 5-10 5 97.62
(3x) 937 ±10 45.28
B.2 Spec al Ae osol
Op ical Dep h (AOD)
and UV le els
11-14 200-210 0 80 0.144
285-305 21.8
690-710 79.5
990-1010 39.3
C Ene gy Balance 15-16 (2x) 190-1100 15-30 ∼180 ×90 3100
D Ice species
de e mina ion and
heigh dis ibu ion
17-18 3200-3370 0 80 6.8
3850-3930 7.2
IR Lamp 0-4000 40
E Displacemen Damage 19-20 200-1100 N/A N/A N/A
Blind-De ec o s 3300
*Wi h ega d o he ela i e a e age sun posi ion calcula ed o he mission
Fig. 2 Schema ic design o he U anus Mul i-Expe imen Radiome e (UMR). The di e en channels a e
iden i ied based on he scien i ic goals (see Table 2) and ope a ional modes (see Table 5)
and p essu es; (2) in eg a e he adiance ield o e he senso FOV and wa eleng h band
o compu e he i adiance (uni s o W m−2); and (3) con e he i adiance in o de ec o
pho ocu en based on he senso il e s and esponsi i y ( his pa is ea ed in Sec . 6). Fig-
u e 3a shows he a ia ion o he sky b igh ness a p =0.73 ba as a unc ion o he zeni h and
azimu h angles simula ed using he NEMESIS co ela ed-k adia i e- ans e and e ie al
code (I win e al. 2008). Fo hese simula ions, we used he ae osol/gas model desc ibed in
I win e al. (2022) ( e e ed o as IRW22 he ea e ), whe e he sun is a a zeni h angle o
79.1°. By in eg a ing he adiance ield o e he senso ’s FOV and co esponding spec al
band a each p essu e le el, we de i e he i adiance expec ed du ing he expe imen . Fig-
The U anus Mul i-Expe imen Radiome e o Haze and Clouds... Page 7 o 30 6
Fig. 3 Simula ions o he sola i adiance in U anus’ a mosphe e using he NEMESIS code and he IRW22
model. In all he simula ions, he sola zeni h angle (SZA) is 79.1°. (a) Va ia ion o he sky b igh ness wi h
zeni h and azimu h angles a 0.11 ba le el and in he 700 ±10 nm wa eleng h ange. The anspa en -g ey
ci cles a e added o show he di e en ield o iew (FOV) o channels B.1, B.2, and C. (b) I adiance e ical
p o iles a 205 ±5 nm, 295 ±10 nm, 700 ±10 nm, and 1000 ±10 nm o he FOV o B.2 channels and
a poin ing di ec ion o 70° in zeni h angle and 90° in azimu h (conce ning he sun azimu h). Co esponding
colo e ical lines indica e he minimum i adiance le el de ec able o each channel (see Sec . 0). (c) same
as (b) bu o channels B.1 560 nm and B.1 937 nm. (d) in eg a ed upwa d and downwa d lux o channel C
u e 3b shows, as an example, he i adiance p o iles o di e en spec al bands (speci ic UV
bands ha e no ye been chosen) and he FOV o B.2 senso s ( ed ci cles in a adiance ield
map Fig. 3a). Thus, by doing his analysis o di e en senso o ien a ions (since he p obe
is likely o il and spin du ing he descen ), we can de ine he dynamic ange o each senso .
Me hane dissocia ion by sola UV and ene ge ic pa icles leads o a ne wo k o chemical
eac ions ha igge he o ma ion o mo e complex hyd oca bons such as C2H6,C
2H2,
o C4H2(Moses e al. 2018). These hyd oca bons can condense in o hei espec i e ices,
o ming he plane ’s s a osphe ic haze. Al hough me hane pho olysis and he subsequen
haze o ma ion ake place in he highe pa s o he s a osphe e, and hus a al i udes whe e
he p obe is no expec ed o be in measu emen mode, ques ions emain as o whe he such
p ocesses ( o ma ion o pho ochemical haze) could also occu a deepe le els in he a -
mosphe e. Fo ins ance, I win e al. (2023) showed ha Nep une’s da k spo s a e caused
by da kening a sho wa eleng hs o a deep ∼5 ba ae osol laye , and one hypo hesis is
ha his da k ma e ial is a pho ochemical p oduc p oduced by he pho olysis o H2Sby
UV adia ion. The e o e, om hese measu emen s, we will de e mine he pene a ion o
UV ligh in he oposphe e and es ablish he al i udes a which he p oduc ion o pho o-
chemical ae osols is possible. Also, by combining hese measu emen s wi h hose made by
he channels dedica ed o he ae osol (haze and clouds) cha ac e iza ions (nex sec ion), we
will de e mine whe he , in a gi en laye , he dec ease in UV adiance is mos ly due o he
abso p ion o gases o ae osols. In he ollowing sec ion, i will be explained how hese
measu emen s will also be used o cons ain he ae osol’s op ical p ope ies in he UV.
6 Page 8 o 30 V. Apés igue e al.
Table 3 P e-selec ed de ec o s o he UMR channels. Manu ac u e da a o 293 K ope a ional empe a u e
De ec o UMR
Channel
Package Sensi i e
A ea
Wa eleng h Pho o-
sensi i i y
Da k
cu en *Shun e-
sis ance
Rsh*
Noise
equi alen
powe NEP
(mm2) (nm) (A/W) (pA) (M)(W/Hz
1/2)
Hamama su
S5980
A8.8×10.6 mm 5 ×5/4
segmen s
320-1100
(960 peak)
0.72 0.002 – 1.4 ×10-14
Ce amic
Su ace Moun
Hamama su
S1337-1010
B.1, B.2,
C&E
16.5 ×15 mm 100 190-1100*
(960 peak)
0.5 200 200 1.8 ×10-14
Ce amic
2 pin e minals
12.5 mm pi ch
Hamama su
P16112-
033MF
D-E TO-46 0.7 ×0.7 3270–3330
(3300 peak)
0.0028 – 0.18 1.1 ×10−10
Hamama su
P16112-
039MF
D TO-46 0.7 ×0.7 3820–3980
(3900 peak)
0.0032 – 0.18 9.5 ×10−11
*Fo e e se ol age VR=10 mV
4.2 Dis ibu ion and P ope ies o Haze and Cloud Pa icles
Haze and cloud pa icles can di ec ly a ec he ene gy balance o U anus’ a mosphe e, and
hus he a mosphe ic dynamics, by abso bing and sca e ing he sola adia ion. Di e en
p ope ies o he haze and cloud pa icles a e impo an o unde s anding hei in e ac ions
wi h sola adia ion. The pa icle size, shape, e ac i e index, and concen a ion de e mine
he ollowing ae osol pa ame e s: (1) he phase unc ion (angula dis ibu ion o he ligh
sca e ed by an ae osol); (2) he single sca e ing albedo ( a io o sca e ing e iciency o o al
ex inc ion e iciency); and (3) he op ical dep h (measu e o he ex inc ion o he adia ion
by he ae osols) o he ae osols.
UMR will de i e many o hese p ope ies using combina ions o spec al i adiance
measu emen s om he UV o he nea IR. Six senso s wi h na ow FOVs (±5°) and a wo
spec al bands (channels B.1), om 550 nm o 570 nm and om 927 nm o 947 nm, a e
used o s udy he ae osol phase unc ion and pa icle size. To accomplish a wide ange o
obse able sca e ing angles, each pai o spec al senso s has di e en poin ing angles: 0°,
−30°, and 30° ela i e o he no mal o he ins umen plane (see Fig. 2) o ha e zeni hal
co e age. Fo azimu hal measu emen s, he ins umen capi alizes on he an icipa ed il and
spin o he p obe du ing descen . I inco po a es a ou -sec o sun senso ( e e o Table 2
and Table 3Channel A) o econs uc he ins umen ’s a i ude. A dynamic model o he
descen p obe will be de eloped o his pu pose, in eg a ing, a a minimum, da a om he
sun senso and he accele ome e included in he selec ed A mosphe ic S uc u e Ins umen
(i.e., Fe i e al. 2020). This will asce ain he Sun’s ela i e posi ion o he UMR a all
sampling poin s.
This ype o sun senso is equen ly employed o cos -e ec i e a i ude de e mina ion
in low-ea h-o bi (LEO) sa elli es (De Boom e al. 2006), wi h a p ecision o up o 0.15°
(1σ). I u ilizes a quad uple pho ode ec o de ice (e.g., Hamama su S5981), whe e sunligh
eaches he de ice’s cen e h ough an ape u e o pupil. The sec ion o he ape u e and i s
The U anus Mul i-Expe imen Radiome e o Haze and Clouds... Page 9 o 30 6
dis ance o he su ace o he pho ode ec o s de ine he sola senso ’s ield o iew (FoV).
The signals measu ed on each quad an co ela e wi h he Sun’s azimu h and ele a ion (Sun
e al. 2023) ela i e o he senso ’s no mal. The e o e, his ins umen con igu a ion ensu es
measu emen s a bo h small and la ge sca e ing angles.
A small sca e ing angles, he phase unc ion is e y sensi i e o he pa icle adius ( he
la ge he pa icles, he g ea e hei dispe sion in he o wa d di ec ion) and s uc u e (e.g.,
o agg ega es, he slope o he phase unc ion depends on he ac al dimension). Thus, he
obse a ions made by B.1 senso s a small sca e ing angles in he sola au eole will be used
o cons ain he ae osol pa icle adius and s uc u e. A backsca e ing angles (>90°), he
phase unc ion is e y sensi i e o he pa icle shape (e.g., sphe es, ac al agg ega es, o
i egula ice c ys als), and his in o ma ion is key o unde s anding unde which condi ions
he ae osols a e o med a a gi en al i ude. Fo he e ie al o he phase unc ion, di e en
ae osol shapes and sizes will be employed o s udy which ae osol model p o ides he bes
i be ween he obse a ions and simula ions. These measu emen s equi e a wide senso
dynamic ange o co e he ange ha goes om he low in ensi ies in he backsca e angles
o he di ec ligh in ensi y when he sun is wi hin he senso FOV. This will be done by
using a numbe o channel gains (see Sec . 0). Figu e 3c shows i adiance p o iles simula ed
o channels B.1. As o he UV senso s, he de ini ion o he dynamic ange will come om
he adia i e ans e simula ions.
In addi ion o B.1 channels, wo mo e senso s, poin ed no mally o he senso , wi h 80°
FOVs, and spec al bands o 700 ±10 nm and 1000 ±10 nm will be used o he ae osol
e ie als (las B.2 channels o Table 2). The analysis o hese senso s’ measu emen s, along
wi h hose om he UV senso s, will p o ide in o ma ion on he op ical dep h and single
sca e ing albedo a ou spec al bands. Because o hei wide FOV, hei obse a ions a e
less a ec ed by he phase unc ion han he B.1 channels, being he ae osol o al opaci y and
single sca e ing albedo as he main pa ame e s con olling hei measu emen s. The spec-
al ae osol opaci y and single sca e ing albedo depend on he pa icle adius and e ac i e
index. Thus, he ae osol p ope ies and e ical dis ibu ion will be e ie ed by using com-
bina ions o he B.1 and B.2 channel measu emen s. This implies ha bo h B.1 and B.2
channels mus ope a e simul aneously du ing he descen and up o 1-2 ba le el.
4.3 Sola Ne Flux
As one o he objec i es o he UMR is o di ec ly es ima e he hea ing a es in U anus’
a mosphe e, he ins umen has wo pho ode ec o s looking upwa d and downwa d o mea-
su e he sola lux in he spec al band om 190 nm o 1100 nm. The de ec o s a e poin ing
upwa ds and downwa ds wi h a FOV ha co e s abou 180° in azimu h angles and abou
90° in he zeni h (channels C, see Fig. 2) using a masked di use . Due o he pa achu e’s
blockage and he ac ha he ins umen is designed o be on one side o he p obe, hese
measu emen s canno co e all he zeni h and azimu h angles. Howe e , hey a e cap u ed
h ough successi e samples as he p obe o a es.
The ne lux is compu ed om he di e ence be ween he downwa d lux and he upwa d
lux, and he di e ence in he ne lux a he up and down bounda ies o an a mosphe ic laye
gi es he sola ene gy abso bed by i (hea ing a e). Thus, om hese measu emen s, he
plane ’s hea ing p o ile can be di ec ly es ima ed. This in o ma ion is key o unde s anding
he ole o hazes and clouds in he s a osphe e and oposphe e ene gy budge s.
Be o e using hese measu emen s, h ee co ec ions need o be made: (1) ex ending he
ange om 190 nm o 1100 nm o 190 nm o 2500 nm; (2) combining di e en obse a ions
o co e he whole ange o azimu h angles and compu e by RT simula ions he in ensi y a
6 Page 16 o 30 V. Apés igue e al.
Since he i adiance eaching he plane is almos 160 imes less han ha eaching Ma s,
a de ec o model wi h nea ly 100 imes mo e ac i e a ea has been chosen o cap u e a g ea e
amoun o ligh (Hamama su S1337-1010bq) o B and C se s. Howe e , his inc eases he
de ice’s da k cu en could po en ially comp omise he dynamic ange, bu his e ec is
nea ly insigni ican when ope a ing a such low empe a u es (50 K-100 K). In he case o A
se , we ha e selec ed a segmen ed de ice wi h 4 pho odiodes in a 2 ×2 con igu a ion. The
o i ice o i s FoV mask collec s he ligh as a beam in he middle o he de ice i he Sun’s
pa h is no mal o i s su ace. The ou senso s ecei e he same ligh in his con igu a ion.
When he ins umen u ns, he ligh spo o e he de ec o will mo e and modi y i s shape.
The ela ionship be ween he 4 senso s signals will be used o calcula e he ela i e posi ion
be ween he ins umen and he Sun. The di use ligh could in oduce some e o in his
a i ude de e mina ion bu i is es ima ed ha he p ecision could be a ound 1° bo h azimu h
and zeni h.
Simila ly o wha occu ed in he Ma s mission design, hese componen s may expe ience
deg ada ion due o exposu e o adia ion du ing he leng hy jou ney o U anus, s emming
om he damage caused by ene ge ic pa icles and cosmic ays. Consequen ly, a shielded
pho odiode has been inco po a ed, and i s da k cu en is measu ed o assess po en ial deg a-
da ions ac oss he a ious channels.
On he o he hand, he spec al ansmi ance o hese de ices will need o be ho oughly
cha ac e ized, as low empe a u es al e he p ope ies o silicon, modi ying i s in e nal ab-
so p ion and e ac i e index (Nagakubo e al. 2015). Addi ionally, ca ie mobili y is also
educed unde hese condi ions, and he combina ion o hese wo ac o s esul s in a de-
c ease in esponsi i y wi h empe a u e (Camin and G assi 2006). In he s udy by Glebo
e al. (2018), hey analyze his e ec in p e-selec ed pho odiodes by UMR (S1337-1010BQ),
ob aining esponsi i y losses o less han 6% o spec al bands a 900, 700, and 500 nm.
Howe e , hey indica e ha a 1000 nm, losses can each up o 60% a 90 K.
Fo he IR channels (G oup D), we ha e p e-selec ed new pho ode ec o de ices, Indium
A senide An imonide (InAsSb), om he Hamama su amily P16112-XXMF (see Table 3).
This de ec ion echnology is uncooled and highly sensi i e. The de ices in his amily in-
clude band-pass il e s cen e ed, among o he s, a 3.3 um and 3.9 um, which align pe ec ly
wi h he scien i ic equi emen s o de ec ing and cha ac e izing clouds (see Fig. 9a).
Di e en ypes o InAsSb s uc u es ha e been es ed o bo h ionizing and non-ionizing
adia ion e ec s. Supe la ice s uc u es appea o be qui e obus (S eenbe gen e al. 2013),
bu ba ie a chi ec u es exhibi deg ada ion in quan um e iciency (Mo a h e al. 2019). As
a en a i e selec ion, a co esponding quali ica ion campaign o adia ion and c yogenic
empe a u es will be conduc ed on hese de ices (among o he s equi alen candida es) in
he subsequen s ages o ou echnological UMR de elopmen p og am.
Fo he case o he IR emi e , we ha e p e-selec ed a nich ome (NiC )- ilamen -based
lamp (INFRASOLID HIS2000R-A300-6), ha o e s a high-op ical-powe emission (up o
620 mW, see Fig. 9(b&c)) in a e y compac de ice (Table 4). I includes a gold-pla ed
e lec o ha o e s enough na ow angula adia ion emission and a sapphi e window ha
closes he he me ic TO-8 package.
All sapphi e windows used o p o ec ing de ec o s and emi e s should include a hea e
(see Fig. 6) o p e en po en ial condensa ion o species ha each hei dew poin (e.g., CH4,
H2S) du ing descen . The aim is o sligh ly hea he ex e nal su ace o he windows abo e
he a mosphe ic empe a u e, as sugges ed in p e ious ins umen a ion o descen p obes
(e.g., S omo sky e al. 1992; Ragen e al. 1992). To achie e his, we p opose using an
Indium in oxide-based coa ing (ITO) on o below hem. These ma e ials a e comme cially
used as anspa en hea e s in he UVA-NIR egion o he ligh spec um.

The U anus Mul i-Expe imen Radiome e o Haze and Clouds... Page 17 o 30 6
Table 4 P e-selec ed IR lamp o he UMR channels. Manu ac u e da a a ope a ion empe a u e o 293 K
IR Lamp UMR
Channel
Package Radia ing
elemen
a ea
Wa eleng h Op ical
ou pu
powe
Elec ical
powe
Elec ical
esis ance
Modula ion
equency
(mm2) (µm) (mW) (W) ()(Hz)
In asolid
HIS2000R-
A300-6
A TO-8 40 2-6 620 2.5 5-6 4-10*
*50%-20% modula ion dep h
Fig. 9 (a) IR selec ed senso s amily wa eleng hs. (b) IR lamp emission spec um and (c) op ical powe
emission. C edi s: componen da ashee s
INTA has a solid ack eco d in using his coa ing o space applica ions. The ins i u-
ion de eloped he liquid-c ys al a iable e a de s included in he Sola O bi e SO/PHI
(Solanki e al. 2020) and METIS/COR (An onucci e al. 2020) ins umen s. These de ices
use ITO-deposi ed ilms o liquid-c ys al ac i e con ol (Al a ez-He e o e al. 2011)and
ha e consequen ly been quali ied o he space en i onmen (Al a ez-He e o e al. 2017).
Fo mid-IR de ec o s, we plan o explo e he use o ITO coa ings doped wi h o he com-
pounds (e.g., ZnO o Zn) ha could enhance Mid-IR ansmi ance (Gen y e al. 2011),
whe e adi ional ITO coa ings exhibi abso p ion beha io . P elimina y calcula ions indi-
ca e ha we will need 25 mW o p e en condensa ion on each window, o aling 400 mW o
powe du ing he 1 h descen phase.
Ano he po en ial cause o channels deg ada ion could be he deposi ion o pa icles on
he p o ec ion windows (which a e expec ed o be p edominan ly ice c ys als). In his ega d,
a luid dynamic s udy will be conduc ed o e alua e di e en designs o he OH shape and
windows in eg a ion, o e en o include de lec ion su aces in o de o minimize his e ec ,
which will need o be cha ac e ized on Ea h by means o wind unnel acili ies.
5.6 Elec onic Design
5.6.1 Op ical Head – UMR-OH
INTA has main ained a collabo a i e pa ne ship wi h he Ins i u e o Mic oelec onics o
Se ille (IMSE) o o e 15 yea s, ocusing on he de elopmen o mixed-signal ASICs
o space use and ex eme empe a u e condi ions. Du ing hese yea s, IMSE has de el-
oped i s own adia ion-ha dened lib a ies o he s anda d AMS CMOS 0.35 µm echnology
(Ramos-Ma os e al. 2012 and 2013). These lib a ies employ design ha dening echniques
6 Page 18 o 30 V. Apés igue e al.
Fig. 10 (a) SIS20 ASIC physical dimensions and layou . (b) SIS20 ASIC Func ional Blocks. (c) SIS20 ASIC
Digi al Block in de ail
(So do-Ibañez e al. 2014) bo h o mi iga e he e ec s o adia ion and o use i a low em-
pe a u es (323 K −148 K). IMSE has also quali ied he encapsula ions o hese de elop-
men s, compa ible wi h MIL-STD-883 s anda ds and wi h ex eme he mal cycling h ough
long-du a ion PQV (Package and Quali ica ion Ve i ica ion) es s. This e o has allowed
he ins i u e o de elop he ASIC o he wind senso s (WS) o he MEDA me eo ological
s a ion, which cu en ly ope a es in he ha sh condi ions o he plane Ma s.
Fo he ExoMa s 2018 mission, a mixed-signal ASIC (Vázquez e al. 2018)wasde-
eloped o INTA’s adiome e , he Sola I adiance Senso 20 (SIS-20). This ASIC could
no unde go adia ion es ing, bu i sha es he same building block ha was p e iously
es ed. The e o e, i can be in e ed ha i exhibi s he same adia ion-ha dened beha -
io (Ramos-Ma os e al. 2012 and 2013): (i) he echnology and lib a y we e es ed up
o 318 k ad (Si) o o al ionizing dose (TID); (ii) i is single e en la ch-up (SEL) ee
up o 81.8 MeV·cm2/mg (hea y ions); (iii) i is single e en ansien (SET) ee up o
40 MeV·cm2/mg; and (i ) i is single e en upse (SEU) ee up o 22.5 MeV·cm2/mg.
This la e de elopmen has been aken as a s a ing poin o he elec onic design o he
Op ical Head uni o he UMR (UMR-OH).
The main componen s o he UMR-OH elec onics a e a pai o mixed ASICs p e i-
ously de eloped o he SIS-20 adiome e (Vázquez e al. 2018). This de ice, Fig. 10 (a),
comp ises ou majo subsys ems (Fig. 10 b) summa ized in: i) an analog on -end ha in-
cludes 10 ans-impedance ampli ie s (TIAs) wi h wo p og ammable gains pe channel, 4
PT1000 pla inum esis ance channels, an 8-bi cu en -ou pu DAC o d i ing ligh calib a-
ion sou ces like LEDs, and 3 gene al-pu pose ol age ampli ie s wi h con igu able gain; ii)
The U anus Mul i-Expe imen Radiome e o Haze and Clouds... Page 19 o 30 6
Fig. 11 Elec ical unc ional blocks de ail o he wo uni s ha comp ise he UMR
a 16-bi ADC wi h mul iplexed inpu and a p eceding ins umen a ion ampli ie wi h con-
igu able gain; iii) a 10-bi DAC used as an inpu o he p e ious ins umen a ion ampli ie ,
p o iding sub- anging capabili ies; and i ) a digi al laye , as depic ed in Fig. 10 (c), ha
encompasses digi al signal p ocessing blocks enabling a ious au oma ic unc ions such as
o e sampling up o 256 samples a e aging, s anda d de ia ion calcula ions, a 100 Kbi s/sec
sla e SPI in e ace, con igu a ion/con ol egis e s, a Powe -on- ese (POR) ci cui y, and a
CLK signal gene a o .
As discussed in Sec . 4, o achie e he scien i ic objec i es, he UMR employs 20 op ical
channels in eg a ed in o he OH. To maximize in eg a ion, we use wo o hese ASICs (see
Fig. 11). This app oach allows o a high deg ee o in eg a ion by au oma ically condi ioning
and digi izing he da a wi h a powe consump ion o 250 mW each.
The condi ioning o bo h he Si pho odiodes and he InAsSb pho ode ec o s is based on
a solu ion in he designs o bo h RDS and SIS-16 (see Fig. 12 (a)). In his scheme, he i s
ans-impedance s age con ains he main ampli ica ion ha p o ides he dynamic ange o
he op ical channels. This i s s age allows o con igu ing wo gains, adap ing he ange o
measu e low alues o sca e ed di use ligh in ensi y o , con e sely, o si ua ions whe e
di ec sunligh may en e he FoV, causing possible sa u a ion. A second s age is added o
he analog chain, including an ins umen a ion ope a ional ampli ie in combina ion wi h a
DAC. This con igu a ion allows he applica ion o sub- anging echniques o main ain high
le els o accu acy when changing he main gain. This s age also p o ides a inal gain o he
esul o he sub ac ion con igu able wi h 1 o 50 ampli ica ion ac o s.
Due o he ac ha measu emen s a e pe o med a low equency, he equi ed ampli ica-
ion le els can be achie ed wi h he i s ansimpedance s age wi hou bandwid h limi a ion.
The dynamic ange is calcula ed based on simula ions ob ained wi h he adia i e ans e
model (las column Table 2), o wo s cases wi h he sun inside he FoV. This ampli ica ion
le els necessi a e he use o eedback esis ances (Fig. 12(a) R 1 and R 2) wi h e y high
alues ( om mega o giga ohms), making he mal noise in hese esis ances domina e o e
he elec onic noise o he ampli ie . In Fig. 12(b), we p esen an example o calcula ing
he signal- o-noise a io (SNR) as he a io o he cu en equi ed by he pho odiode o he
cu en noise calcula ed. The las is calcula ed as he oo mean squa e sum o h ee e ms:
(i) he he mal noise om he eedback esis ance R ; (ii) he he mal noise o he in insic
esis ance o he pho odiode Rshun ; and (iii) he sho noise esul ing om he pho ocu en
ecei ed by he pho ode ec o and i s da k cu en (a wo s case mission ope a ional em-
pe a u e o 120 K).
6 Page 20 o 30 V. Apés igue e al.
Fig. 12 (a) UMR pho ode ec o s acquisi ion chain shema ics. (b) Example o noise le els calcula ions o
each de ec o . In his case, we analyze channel 11 (B.2 UV) wi h co esponds o he limi o de ec ion ( e ical
line) associa ed wi h his channel in Fig. 3(b)
To in e he minimum i adiance le el o each channel, limi ed by he noise, we ha e
es ablished SNR =100 as a lowe limi (Fig. 12 (b)). Wi h he co esponding ecei ed
powe a he ecei e , conside ing i s e ec i e ac i e a ea (accoun ing o losses due o il e
ansmi ance and FoV masks), we ha e calcula ed he minimum i adiance le els o each
o he channels. These can be obse ed as e ical lines in Fig. 3(b), (c), and (d).
In he case o mid-in a ed (mid-IR) channels, a scheme iden ical o ha o Si pho odi-
odes will be employed. In his con ex , he emphasis is on he ain signal de i ed om he
backsca e ing o ae osol pa icles when illumina ed by he lamp. Noise calcula ions anal-
ogous o hose o he Si pho odiodes ha e been conduc ed o hese de ices, bu in his
ins ance, he minimum and maximum ecei ed ligh powe om he sca e ing o he lamp
ligh (Fig. 4b) a e aken as inpu . Fo Channel 17, we ob ain a signal- o-noise a io (SNR)
anging om 29 o 200 o he minimum and maximum expec ed ecei ed powe (which
depends on he species p esen du ing he measu emen ). Fo Channel 18, we ha e ob ained
an SNR anging om 20 o 271 in a simila manne . Bo h esul s could be enhanced using
he ASIC o e sampling capabili y, which could ise heo e ically he SNR up o a x16 ac o
( o 256 samples) wi h a con e sion ime o 377.5 ms.
To mi iga e backg ound noise ha may a ise om he a mosphe e and e en om he
channel housing, and o il e he desi ed signal, a digi al lock-in il e will be implemen ed.
Due o he high le els o ampli ica ion equi ed, he sou ce will be exci ed a he o de o ens
o he z, and he ASIC will be esponsible o gene a ing he ca ie by d i ing a powe d i e
ha con ols he lamp. Addi ionally, he ASIC will digi ize he signals and p o ide hem o
he mic ocon olle , which will handle he p ocessing asks. Besides elimina ing backg ound
noise, his echnique can also be employed o enhance po en ial seconda y ampli ica ion.
Once he signal is con e ed o ol age h ough he ini ial ansimpedance s age, he second
ampli ica ion is conduc ed in ol age, and hus, he 1/ noise om he ope a ional ampli ie
becomes signi ican . U ilizing a il e wi h a 10 Hz ca ie can mi iga e his noise by a ac o
o 5, depending on he ope a ional ampli ie ’s cha ac e is ics. Howe e , he inal equency
selec ed shall ha e a comp omise be ween he IR-lamp ope a ional equency capabili y, he
o e sampling selec ed in he ASIC and he inal accep able SNR igu e.
To accommoda e all hese elec onics, he UMR-OH has ou boa ds linked oge he
o ming a unique igid- lex polyamide PCB. Two o hem a e close o he uppe s uc u e ha
suppo s he h ee la e al pho ode ec o s (B.1 and C se s). The cen al igid PCB suppo s
he B.1 and B.2 pho odiodes, he sola senso (A se ), and he IR lamp and pho ode ec o s
(D se ). Finally, a he bo om o he se , we ha e he main PCB ha con ains he ASICs and
he d i e o he lamp.
The U anus Mul i-Expe imen Radiome e o Haze and Clouds... Page 21 o 30 6
5.6.2 P ocessing Elec onic Uni – UMR-PE
The UMR-PE is equipped wi h wo elec onic boa ds ha se e o wo p ima y unc ions:
(i) o adap he powe le els p o ided by he pla o m and (ii) o accommoda e a small pay-
load compu e . This design is based on he COMPACT a chi ec u e (Con igu able Minia-
u ized P ocessing A chi ec u e) de eloped by INTA (Ma in-O ega e al. 2017). The basic
idea o he COMPACT app oach is he ecu si e employmen o se e al componen s wi h
p ede ined con igu a ions, allowing o he cus omiza ion o an op imal compu e o each
applica ion based on i s speci ic equi emen s, including compu a ional capaci y, pe o -
mance, powe consump ion, and oo p in . Consequen ly, his a chi ec u e employs a ious
de ices o powe con e sion, such as isola ed DC-DC con e e s and linea egula o s, as
well as di e en componen s o signal p ocessing and cop ocessing, including mic ocon-
olle s and FPGAs. COMPACT componen s a e chosen based on hei adia ion esis ance
and unde go es ing o ensu e hei pe o mance a low empe a u es a oiding he use o
hea e s. In he amewo k o COMPACT, a ious base con igu a ions ha e been p ede ined
depending on he sys em o be con olled, wi h he simples con igu a ion o he UMR
consis ing o a mic ocon olle pai ed wi h an ex e nal p og am and massi e da a s o age
memo y (Fig. 11).
The selec ed mic ocon olle o UMR is he SAMRH707. I is a RadHa d de ice (100
k ad; LET >78 MeV·cm2/mg) based on he ARM Co ex M7 a chi ec u e de eloped by
Mic ochip, capable o eaching up o 100 DMips o p ocessing powe . I comes equipped
wi h i s in e nal memo ies, including 128 kby es o Flash, 320 kby es o SRAM, and 128
kby es o ROM. I o e s a wide ange o communica ion pe iphe als, including high-speed
(SpaceWi e), and ad anced analog ea u es: a 12-bi ADC and DAC. Addi ionally, i in-
cludes nume ous low-powe modes, allowing o ine- uning o i s compu a ional capabil-
i ies in esponse o ene gy demands. Fo he UMR, using a 10 MHz clock, he maximum
nominal powe consump ion would be 400 mW wi h a sleeping mode o ∼1mW.
The use o a mic ocon olle ins ead o low- esou ce an i- use FPGAs, as in ou p e ious
adiome e s (SIS, SIS-16, RDS, and SIS-20) ep esen s a signi ican ad ance in lexibili y
and capabili ies o he UMR. This ansi ion o e s ad an ages anging om he ease o
ha dwa e de elopmen and es ing du ing he design phases o he expanded capabili ies
ha can be impa ed o he ins umen . These capabili ies include independence om i s
ope a ion conce ning he cen al compu e , he abili y o pe o m in- ligh loa ing-poin
calcula ions, and he applica ion o comp ession algo i hms o eleme y da a, among o he s.
6 UMR Ope a ional Modes
The UMR has been designed o mee a ious scien i ic objec i es, and as a esul , i inco -
po a es di e en se s o senso s o achie e hem. Consequen ly, hese senso se s ope a e
in dis inc ways h oughou he mission, depending on he speci ic phase. We e e o hese
dis inc ope a ional s a es as Ope a ional Modes (OPM). Fo each OPM, i is c ucial o de-
e mine which channels need o be ac i a ed, iden i y he equi ed housekeeping signals,
and es ablish he speci ic sampling equency necessa y o mee he scien i ic objec i es, in-
cluding ac o s like e ical esolu ion and azimu hal da a. A med wi h his in o ma ion, we
can hen es ima e he amoun o da a needed h oughou he mission and he co esponding
ene gy consump ion o each scena io. Table 5summa izes hese es ima ions o he UMR
and pe mi s compa ison wi h he UOP mission (Simon e al. 2021).

6 Page 22 o 30 V. Apés igue e al.
Fig. 13 Mission Ope a ional Modes by mission s ages: (a) in e plane a y ip, (b) du ing he p obe descen
o e U anus a mosphe e
Fo he 1-hou whole mission, he UMR gene a es 161.9 kiloby es o aw da a (Table 5),
which ep esen s 7.5% o he o al da a budge o he en i e p obe (2.3 megaby es o 17
megabi s as pe Simon e al. 2021). Using, o example, he same del a-encoding comp es-
sion algo i hm used in MEDA o he RDS (Rod iguez-Man edi e al. 2021), hese igu es
could be educed by 55%. Rega ding ene gy consump ion, only 2.3% (2.75 wa -hou s) o
he 121 wa -hou p obe’s ene gy budge would be used by ou ins umen , which is a neg-
ligible amoun in o al.
The di e en ope a ional modes a e desc ibed below:
OPM 1: This ope a ional mode encompasses ou checkou s and calib a ions h oughou
he mission ajec o y: he i s one pos -launch (labeled “OPM 1.1” in Fig. 13 (a)), he sec-
ond one be o e he Jupi e lyby (“OPM 1.2”), he hi d sho ly a e he lyby (“OPM 1.3”),
and he inal one p eceding he sepa a ion o he o bi e capsule (“OPM 1.4”). These check-
ou s a e conduc ed o assess he ins umen ’s condi ion and moni o po en ial deg ada ion
o senso elemen s du ing he mission, wi h he expec a ion ha he mos signi ican de e-
io a ion may occu du ing he Jupi e g a i y assis maneu e . This assessmen in ol es
measu ing he da k cu en s o a ious senso s as hei alues inc ease wi h displacemen
damage (pe o med in p e ious ins umen s Jimenez e al. 2012; A uego e al. 2017;Apes-
igue e al. 2022), measu e he empe a u es o he senso s du ing all he scien i ic ope a ion
due i s ela ionship wi h da k cu en alues, along wi h moni o ing leakage cu en s om
ASICs’ ope a ional ampli ie s, which could subsequen ly a ec absolu e channel measu e-
men s. U ilizing his in o ma ion helps mi iga e adia ion-induced e ec s on channel signals.
Addi ionally, he lamp will be employed o in-si u calib a ions. This lamp will p oduce
ligh ha will e lec o e lec o s s a egically placed inside he ae oshell ( ollowing he
app oach used in p e ious missions, as desc ibed by Ragen e al. 1992). The ligh will be
de ec ed by di e en channels, acili a ing alida ion o he a ious senso chains. Despi e
being designed o minimize da a usage and powe consump ion, his mode is no conside ed
c i ical in his ega d since i is u ilized while he p obe is s ill a ached o he o bi e , and
hese da a all ou side he o al da a budge alloca ed o he descen p obe.
OPM 2: This ope a ional mode se es as a minimal calib a ion s ep jus be o e he
ae oshell is disca ded. A his poin , he p obe has al eady begun i s descen h ough he
plane ’s a mosphe e (labelled as “OPM 2” in Fig. 13 (b)), and he objec i e is o acqui e he
ul ima e o se alues o each channel, which will se e as e e ences du ing he descen
phase. Consequen ly, all UMR channels mus be measu ed unde da k condi ions du ing
OPM 2.
The U anus Mul i-Expe imen Radiome e o Haze and Clouds... Page 23 o 30 6
OPM 3: The hi d ope a ional mode begins when he p obe’s onboa d compu e igge s
he UMR, signi ying he success ul deploymen o he second pa achu e (0.1 ba ; +55 km
heigh ). Then he UMR-OH is exposed o U anus’ a mosphe e and ini ia es he scien i ic
phase (iden i ied as “OPM 3” in Fig. 13 (b)) ha will be manage by a sequence ime . Du ing
his phase, spanning om his poin un il c ossing he cloud bel a 1-2 ba s, p ecise knowl-
edge o he ela i e posi ion o he Sun becomes c i ical o achie ing speci ic scien i ic ob-
jec i es. The p obe uses a swi el mechanism o decouple i s spin om he pa achu e’s and
is also equipped wi h 3 spin anes o con ol he o a ional a e. The expe ience o Galileo,
desc ibed in Lanze o i e al. 1998, is ha he ini ial spin a e was a ound 40-35 pm and was
modula ed by he ae odynamical sys em down o 15 pm du ing he descen . This implies
ha a he beginning o he UMR mission, he p obe could o a e mo e han 180° pe second
and consequen ly, he sun senso channels should be sampled a a high a e o be able o
cap u e enough sca e ing angles. Depending on he cha ac e is ics o he ine ial senso s
in eg a ed in o he p obe, a subsequen s udy will be conduc ed o ine- une he minimum
sampling a e o hese channels, ensu ing he capabili y o econs uc he p obe’s a i ude
by combining da a om bo h senso s, bu o his i s de ini ion, we ha e conside ed 5 Hz.
The UMR’s B.1 se o de ec o s should also be sampled a he same a e as he sun
posi ion o eco d sca e ing angles as comp ehensi ely as possible. The B.2 and C se s o
channels will also be measu ed du ing his phase a a lowe a e o 0.2 Hz which co esponds
o 500 me e s o e ical esolu ion.
OPM 4: The las mode is dedica ed o cha ac e ize he clouds and he e o e i s a s a
a dep h o app oxima ely 2 ba s (∼768 seconds a e he beginning o OPM 3 see Table 5).
Se s B.2 and C con inue o be sampled as he p obe descends u he (up o 5-6 ba ), bu a
lowe sampling a es (0.07 Hz) due o a educ ion in he p obe’s speed. The D pho ode ec-
o se s will be u ilized in conjunc ion wi h he IR lamp in a lashing sequence, wi h each
lash las ing 0.5 seconds. This sequence will be epea ed app oxima ely e e y 14 seconds,
esul ing in a e ical esolu ion close o 500 me e s.
7 Calib a ion and Valida ion Ac i i ies
7.1 UV-Visible-NIR Channels Calib a ion (A, B and C Types)
The calib a ion me hod o he Si pho odiodes will be an adap a ion o he p e ious wo k
done o he calib a ion o RDS, ha is desc ibed in Jiménez e al. 2018. I is based on he
spec o- adiome ic ans e om a s anda d lamp o a s anda d de ec o in well-con olled
labo a o y condi ions (e.g., Wya 1978,1991;Hülsene al.2008; Da la e al. 2016).
In his calib a ion model i is assumed ha wa eleng h (λ), empe a u e (T) and inci-
dence angle (θele a ion, ϕazimu h senso coo dina es) can be conside ed as independen
a iables (Wya 1978 and 1991) and hus, he pho odiode ou pu signal I (A), could be
exp essed as:
I(T,ϕ,θ,ESun)=ARF (θ,ϕ)·TRF(T)·Rλ2
λ1Sun ·Eλ2
λ1Sun +o s e (T ) (1)
whe e ARF(θ,ϕ) is he angula esponse unc ion o he channel; TRF(T) is he empe a u e
esponse unc ion o channel dependence wi h he empe a u e; Rλ2
λ1Sun is he mean espon-
si i y o a channel wi h λ1−λ2 wa eleng h, i he calib a ion is pe o med wi h a sola
simula o wi h an Eλ2
λ1Sun i adiance le el.
To calcula e equa ion (1), he ollowing s eps will be unde aken du ing he calib a ion
p ocedu e: (i) O se calib a ion, s ep ha in ol es u ilizing a acuum c yos a in which he
6 Page 24 o 30 V. Apés igue e al.
Table 5 Summa y o Ope a ional Modes (OPM) o he UMR du ing he whole mission. Fo each, in o ma ion on he di e en channels used, he sampling equency, and he
da a gene a ed is p esen ed
Ope a ional Mode (OPM) Mode Ra ionale Channel Type
used*Sampling sequence
du a ion
Sampling
Ra e
Ve ical
esolu ion
Powe Requi ed Ene gy Gene a ed Da a
(s) (Hz) (m/sample) (W) (Wh) (kby es)
1 Heal h Checkou s Hea ing 1800 n/a n/a 4 2** 0.1**
All in
da kness
100 1 0.8 0.022** 2**
All ligh amp 100 1 5**
2 On-boa d calib a ion Hea ing 1800 n/a n/a 4 2 0.1
All in
da kness
100 1 0.8 0.022 2
3 Sun posi ion A 768 5 19 0.9 0.192 45
UV B.1 5 19 102
Ae osols B.2 0.2 470 0.6 0.128 3
Ne Flux C 0.2 470 1.5
T anspa en Hea e s All 0.4 0.008
4 Ae osols B.2 2291 0.07 470 0.6 0.381 3
Ne Flux C 0.07 470 1.5
Clouds D 0.07 470 1.25*** 2.7E-2 3.8
T anspa en Hea e s All 0.4 0.25
TOTAL 3.0 161.9
*Co esponding wi h Table 1classi ica ion
**No accoun ed o inal igu es due o he mission phase
***20 Hz Flash o 0.5 s du a ion, a 50% du y cycle (2.5 W maximum)
The U anus Mul i-Expe imen Radiome e o Haze and Clouds... Page 25 o 30 6
OH is exposed o da kness and subjec ed o a ull empe a u e p o ile ange (100 K−170 K);
(ii) Tempe a u e esponse unc ion calib a ion using he acuum c yos a wi h a cons an
ligh le el exposu e h ough a sun simula o , co e ing he comple e empe a u e p o ile ange
(100 K – 170 K); (iii) a e age esponsi i y calib a ion, using di e en s eps o ligh le els o
he sun simula o a cons an empe a u es (i should be epea ed o di e en empe a u es);
(i ) angula esponse unc ion calib a ion, using a collima ed and cons an le el ligh and a
gimbal obo ic s uc u e o map he angula esponse o each channel.
7.2 Mid-IR Channels Calib a ion (D Type)
The basic equa ion ela ing de ec o ou pu cu en Iou o he ex e nal adia ion lux is es-
sen ially (1). This equa ion is he esul s o adap ing equa ions in (Sebas ian e al. 2020)
(Sebas ian e al. 2021) o a pho ode ec o :
Iou =S(Td)·As·Fd− ·L +iSd (2)
whe e S(Td)is he de ec o esponsi i y including dependence on empe a u e, Tdis de ec-
o empe a u e, Asis he de ec o a ea, Fd− is he iew ac o be ween he de ec o and he
a ge (conside ing in hei calculus de ec o ela i e angula esponse), L is he i adiance
o m he a ge . Conside a la adia ion ield, as an ex ended a ea blackbody, hen L is
gi en by he Planck adiance unc ion Bλ(T ) and can be exp essed as:
L =∞
0
sλe ·Bλ(T )dλ (3)
whe e sλe is he de ec o ela i e spec al esponse a wa eleng h λand T is he a ge
empe a u e.
The e m iSd is he pho ode ec o cu en gene a ed by backg ound ligh , and i accoun s
o he lux exchange wi h he inne su aces o de ec o package and he ex e nal mechanical
assemblies con o ming he ex e nal FoV. Since he e is no il e limi ing he bandpass o he
inne luxes, hey ep esen an impo an sou ce o unce ain y (Sebas ián e al. 2011; Foo e
1999). Du ing ope a ions and descen in U anus, hese luxes will ake a non-ze o alue
because o he he mally challenging en i onmen and hei e ec will be compensa ed using
he elec onics chopping o he IR lamp.
To compu e de ec o ou pu acco ding o he abo e equa ion (1), he ollowing se o
calib a ion es s will be pe o med: (i) Rela i e angula esponse. I will use a blackbody
sou ce ope a ing abo e 500 K, a mechanical choppe o modula e blackbody signal, and a
pan-and- il sys em as an angula scanning sys em. (ii) Rela i e spec al esponse. I will be
pe o med using a 1000 K SiC global lamp, a monoch oma o o selec wa eleng hs, and
a e e ence de ec o o measu e he monoch oma o ou pu o compa ison wi h de ec o
ou pu . (iii) Rela i e esponse e sus empe a u e o each channel. The op ical head will
be moun ed on a he moelec ic coole wi hin a sealed chambe o ec ea e he mal- acuum
condi ions in which he ins umen ’s ope a ing empe a u es will be swep . The de ec o will
be exposed o an ex ended a ea o blackbody as he adia ion sou ce. Fo each de ec o op-
e a ing empe a u e, wo o mo e blackbody empe a u es will be p og ammed. In his way,
a di e en ial p ocess o a oid unce ain ies due o backg ound ligh is implemen ed (Sebas-
ian e al. 2020). (i ) Absolu e esponsi i y measu emen s. To implemen his calib a ion,
es a blackbody sou ce ha ills uni o mly he de ec o ’s ield o iew will be used. The use
o an ex ended a ea o ca i y blackbody will be s udied, aking in o accoun pa ame e s such
as FoV, uni o mi y o he adia ing su ace and appa en emissi i y. Once again, di e en ial