49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083)

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CUPID’S ARROW: A SMALL SATELLITE CONCEPT TO MEASURE NOBLE GASES IN VENUS’
ATMOSPHERE. C. Sotin1, G. Avice2, J. Baker1, A. Freeman1, S. Madzunkov1, T. Stevenson3, N. Arora1, M. Darrach1, G. Lightsey3, B. Marty4. 1Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr.,
Pasadena, CA 91109, USA; 2California Institute of Technology, GPS division, 1200 E. California Blvd, Pasadena,CA 91125, USA; 3Georgia Institute of Technology, 270 Ferst Drive, Atlanta, GA, 30332, USA; 4CRPG-CNRS, Université de Lorraine, 15 Rue Notre Dame des Pauvres, 54501 Vandoeuvre Cedex, France.

Introduction: Getting reliable measurements ofnoble gases in Venus’ atmosphere with a CubeSatderived mission concept is very challenging. But if
feasible it could change how we make this fundamental
geochemical measurement in planetary atmospheres
and other gaseous environments (e.g., plumes emanating from icy moons or dwarf planets) across the solarsystem. Venus poses the most urgent and nearby targetfor such measurements, to fill in a key piece of thepuzzle of Venus’ origin, evolution, and divergencefrom Earth’s geophysical history. Understanding Venus’ geophysical evolution is also key to interpretingobservations of “Earth-like” exoplanets in order toassess whether they are Earth-like or Venus-like, which
has obvious implications for their habitability potential.
Noble gases are tracers of the evolution of planets.
They trace physical processes such as the original supply of volatiles from the solar nebula, delivery of volatiles by asteroids and comets, escape rate of planetaryatmospheres, degassing of the interior, and its timing in
the planet’s history. However, a major observational
missing link in our understanding of Venus’ evolution
is the elementary and isotopic pattern of noble gases
and stable isotopes in its atmosphere, which remain
poorly known [1]. The concentrations of heavy noble
gases (Kr, Xe) and their isotopes are mostly unknown,
and our knowledge of light noble gases (He, Ne, Ar) is
incomplete and imprecise. The Cupid’s Arrow mission
concept would measure those quantities below thehomopause where gas compounds are well mixed.
Science objectives: The objectives of the Cupid’s
Arrow mission are to determine (1) the origin of thevolatiles, (2) the atmospheric loss mechanisms, and (3)the history of volcanic outgassing. These objectives
would be achieved by measuring noble gases concentrations and their isotope ratios below the homopause.
These objectives partially address two of the five science goals in Planetary Science as they are described in
the NASA’s 2014 Science Plan. Moreover, the measurements that would be made by Cupid’s Arrow correspond to the highest ranked investigation in the number
1 objective of Goal 1 “Atmospheric formation, evolution and climate history” of the VEXAG’s Goal, Objectives and Investigation document published in 2014.
The measurements will be made by a miniaturized
quadrupole ion trap mass spectrometer (QITMS) thathas been developed at JPL. We have conducted measurements in the lab in order to validate the performancemodel. We demonstrate that the performances exceed
the requirements with ample margins [2].
Mission architecture: The mission concept would
send an atmospheric probe that skims Venus atmosphere below the homopause to collect samples of Venus atmosphere. These samples are then analyzed by
the miniaturized QITMS once the probe is outside ofVenus atmosphere. The trade space for the architecturegoes from a skimmer that is piggy-backed to Venus(single pass) to an autonomous mission that realizes aVenus orbit insertion (VOI) allowing for multiple passes below the homopause.The nominal mission concept
assumes that the spacecraft would approach Venus withan excess velocity of 2.7 km/s, with a closest approachof 250 km. Venus orbit insertion (VOI) would be conducted by the STAR8 motor at periapsis. The spacecraft would then be in a nominally 30 day orbit with aperiapsis altitude of 250 km and an inclination of 82°.
The high inclination was chosen to minimize the timein which the spacecraft is eclipsed by Venus, and results in an aeropass latitude of approximately 30°. Using a 3σ VOI delta-V error of 6 m/s, the initial orbit
period is expected to be between 580 and 915 hours, or24.2 to 38.1 days. Once the orbit has been refined, theprobe would use the ACS thrusters to perform a periapsis lowering maneuver at apoapsis, with a maximum
expected delta-V of 0.90 m/s. This will lower the periapsis to 110 km, which is well below the homopause torealize the first atmospheric sampling.
The probe would collect the atmospheric samples atperiapsis at 110 km altitude within a few seconds. The
probe is below the lowest level of the homopause during more than 100-s leaving plenty of margin for collecting the sample. After the aeropass, the probe would
be in a shorter orbit, between 13.3 and 240.5 hours.
The large uncertainty in this period is primarily due tothe uncertainty in the density of Venus’s atmosphere.
The probe would perform another apoapsis maneuverwith the ACS thrusters to raise the orbit periapsis outof the atmosphere, to 200 km, requiring a maximum of
9.1 m/s. The probe would remain in this orbit while itanalyzes and downlinks the collected data from the first
aeropass. Once all of the collected data have been returned and the batteries are recharged, the probe would

49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083)

lower its periapsis back to 110 km for the second andfinal aeropass.

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dynamic pressure. For each of the four samples (thefourth one is the QITMS chamber in Fig. 2), theQITMS first removes the main components of the atmosphere (CO2 and N2) before measuring first He isotopes and then all other noble gases and their isotopes.
The performance model suggests integration times of
120 s. A reference gas would also be measured for calibration. The total time for the measurements is about
20 minutes but can be extended to several hours if neccessary.

Figure 1: Artist concept of the Cupid’s Arrow probe with theSTAR 8 motor which would be ejected after VOI.

Spacecraft concept: The Cupids Arrow probe wasdesigned as a modular but highly integrated unit resulting in a compact and lower mass spacecraft (70 kg withmargins) that can sample the atmosphere, analyze thesamples, and transmit the data to Earth. It consists of
two modules, connected by a Lightband separation
ring: the probe itself and a detachable STAR 8 solid
rocket motor (SRM) that enables orbit insertion aroundVenus. The probe is a completely self-contained spacecraft and has all the required functionality and performance to fly itself to Venus or be carried to Venus withanother spacecraft. The design is flexible and allows
for a solid motor, in this case a STAR 8, and its supporting structure to be mated to the probe using an18.25” Lightband. In the standalone flight mission profile, the probe and the motor remain connected
throughout the cruise phase to Venus. The STAR 8
would then be used for the Venus orbit insertion burn,after which the motor and the supporting structure aredecoupled from the probe by the Lightband, leaving
the smaller upper Lightband ring attached to the probe.
Concept of operations: The nominal mission puts
the probe in orbit around Venus with periapis at 110km, several scale heights below the homopause which
has an altitude between 119 km and 138 km dependingon the time of day [3.4]. It is higher on the night side
past the morning side of the terminator. At this altitude,
the ambient pressure is about 0.14 Pa and the dynamic
pressure is 1500 times higher due to a velocity of 10.5
km/s. The atmosphere enters the tanks and the QITMS
by an inlet located at the stagnation point of the probe.
The design is such that one could collect samples ateither the ambient pressure or the dynamic pressure
which provides an enhancement of 1500 times. The
analysis of these different samples would allow us todetermine whether fractionation happens due to theFigure 2: Schematic design of the QITMS and the different
tanks in the probe. Using different valves, one can tailor thesampling strategy to best determine the concentration innoble gases in Venus’ atmosphere.

Conclusions: The mission concept that has beendeveloped during the present study funded by thePSDS3 NASA program would cost less than the$100M cost cap. Although Venus is the most urgent
application, it could also be applied to other places
such as Titan where the probe could be piggy-packed
by mission such as the Dragonfly mission that was recently selected as one of the two finalists for NewFrontiers 4. It could also be used to analyze plumes
emanating from icy moons such as Enceladus, Europa,
and other icy moons in the outer solar system.
Acknowledgments: This work has been performedat the Jet Propulsion Laboratory (JPL), California Institute of Technology (Caltech), under contract to NASA.
The information in this paper is predecisional and ispresented for planning and discussion purposes only.
The cost information contained in this document is of abudgetary and planning nature and is intended for informational purposes only. It does not constitute a
commitment on the part of JPL and/or Caltech.
References: [1] Chassefière et al. (2012) Planetary& Space Science, 63-64, 15-23. [2] Avice G. et al.
(2018) LPSC 49. [3] Limaye S. et al. (2017) Icarus,294, 124-155. [4] Mahieux A. et al. (2012 J. Geophys.
Res. 117. doi: 10.1029/ 2012JE004058. [5] Mahieux,A. et al. (2015) Planet. Space Sci. 113-114, 309–320.