Cupid's Arrow: a small satellite to measure 

noble gases in Venus atmosphere

1Sotin C,2Avice G, 1Baker J, 1Freeman A, 1Madzunkov S, 3Stevenson T., 1Arora N, 

1Darrach M, 3Lightsey G , 4Marty B,

1

Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA; 2California Institute of 

Technology, Pasadena, CA; 3Georgia Institute of Technology, Atlanta, GA;. 4CRPG, Universite de Lorraine, 

Vandoeuvre-les-Nancy, France.

Selected by NASA Program PSDS3 (Planetary 

Science Deep Space Small Sat Studies)

• Science question

• Small satellite answer

• Mission design

© 2018 California Institute of Technology. U.S. Government sponsorship acknowledged.
Noble gases are tracers of the evolution of planets 

(Pepin et al., 1991; Chassefiere et al., 2012)

© 2018 California Institute of Technology. U.S. Government sponsorship acknowledged.
Noble gases are tracers of the evolution of planets 

They trace:

• The supply of volatiles from the 

solar nebula

• the supply of volatiles by asteroids 

and comets

• the escape rate of planetary 

atmospheres

• the degassing of the interior 

(volcanism)

• the timing of these events

(Pepin et al., 1991; Chassefiere et al., 2012)

© 2018 California Institute of Technology. U.S. Government sponsorship acknowledged.
The Xenon case

Xe (9 isotopes):

• Depleted / Kr

• Isotopically fractionated

•

129I decaying (half life of 16 Ma) 

in 129Xe 

•

244Pu fission (half-life of 80 Ma) 

producing 131-136Xe isotopes 

with a diagnostic yield

• extant fission of 235-238U (4.5 & 

0.7 Ga) producing Xe isotopes 

with different yields

• Comparative planetology will 

help determine the processes 

involved in the distribution of 

noble gases 

© 2018 California Institute of Technology. U.S. Government sponsorship acknowledged.
–

40Ar is a good tracer of the amount of outgassing since it comes from the 

decay of 40K and it does not escape on Earth and Venus.

– 25% of the interior has been outgassed based on 40Ar (Kaula, 1999)

– The upper mantle is about 25% of the total mantle in mass

Amount of outgassing from Ar

Venus Earth Mars

40Ar in atm (kg) 1.6 (±0.5) 1016 6.6 1016 5 1014

40Ar (kg/kg planet) 3.3 10-9 1.11 10-8 7.9 10-10

40Ar/Si 1.7 10-8 5.2 10-8 4.1 10-9

potential 40Ar(kg) 6.8 1016 1.4 – 1.56 1017 1.6 1016

40Ar atm / potential 24 (±10)% 42-56 % 3%

Is the recent resurfacing due to plumes raising from the 

Core/Mantle boundary (CMB) ?

© 2018 California Institute of Technology. U.S. Government sponsorship acknowledged.
Goal I: Atmospheric formation, 

evolution and climate history

© 2018 California Institute of Technology. U.S. Government sponsorship acknowledged.
Objective IA: How did the atmosphere 

of Venus form and evolve

This objective is responsive to all three crosscutting science themes of the DS and 

to all three Inner Planets Research Goals described in the DS.

Measuring noble gases is the most important investigation of this objective 

CA can also determine the escape rate of Xe in particular (Investigation # II-A-2)

© 2018 California Institute of Technology. U.S. Government sponsorship acknowledged.
Atmospheric Entry Conditions

• Skim through Venus atmosphere below the homopause where samples are collected

• Analyze the samples and the calibrant - send data direct to Earth

• Build the probe around the instrument – 2 pieces: the instrument tray and the probe 

• Use additive manufacturing for 3D printing

• Partner with universities (Caltech and Georgia Tech)

© 2018 California Institute of Technology. U.S. Government sponsorship acknowledged.
Cupid’s Arrow miniaturized Quadrupole Ion Trap Mass Spectrometer 

(mQITMS) is a miniaturized version of the compact QITMS

Compact QITMS 

• No discrete wires to make 

electrical connections to 

mass spectrometer parts. 

• 7.3 kg mass; 4U volume

• Extremely robust against 

shock/vibe loads

• Very stable measurements

QITMS Isotopic Precision is 3-5 times better than required 

© 2018 California Institute of Technology. U.S. Government 

sponsorship acknowledged.
Instrument Requirements vs. Performance

Performance versus requirements for noble gases ratio

*1/sqrt(counts)

**Chassefiere et al., 2012

Expected Intensity (cnts)

Isotopic Ratios Assumed Fractional 

Abundance Major Minor Statistical Precision* [%] Requirement**

3He / 4He 0.0003 1.08E+08 1.08E+04 1 5 to 10

20Ne / 22Ne 12 7.56E+08 6.41E+07 0.014 1

36Ar / 40Ar 0.16 5.78E+08 3.56E+09 0.006

36Ar / 38Ar 0.18 5.78E+08 3.21E+09 0.024 1

82,83,86Kr / 84Kr 0.16-0.48 2.70E+06 0.4-1.3E+06 0.3 1

129, 136 Xe / 132Xe 1,0.3 2.05E+05 2,0.6E+05 0.4 1

124-128Xe / 132Xe 0.003-0.07 2.33E+04 0.7-14E+03 4 5

Measurements integrated during one hour

Ongoing work to calibrate the mQITMS and determine accuracy and compare it 

with the statistical precision

© 2018 California Institute of Technology. U.S. Government sponsorship acknowledged.
Test on the Allende meteorite

• The users (science team) are independent of the instrument providers (instrument team). 

• The measurements of Xe isotopes on the Allende meteorite show remarkable agreement 

within the error bars. See poster #1158 (location #345) on Thursday by Avice et al. “A 

New Quadrupole Ion Trap Mass Spectrometer for Measuring Noble Gases in Planetary 

Atmospheres”

• A comprehensive plan has been developed to certify the performance model

© 2018 California Institute of Technology. U.S. Government sponsorship acknowledged.
Density profile

The values of density, temperature and pressure at 110 km. A velocity of 10.5 km/s is used 

to calculate the dynamic pressure. (1Torr=133 Pa)

© 2018 California Institute of Technology. U.S. Government sponsorship acknowledged.

Values at 110 km 

altitude

Molecular density 

(molecule/cm3)

Density 

(kg/m3)

Temp 

(K)

Static pressure 

(Pa)

Dynamic Pressure 

(1/2.ρ.v2) (Pa)

30-60 deg - AM 1.06x1013 3.54 10-6 195.5 0.139 195

30-60 deg - PM 1.55x1013 5.53 10-6 186.1 0.207 305
© 2018 California Institute of Technology. U.S. Government sponsorship acknowledged.

Wet mass is less than 70 kg, including 23% dry mass margins on average 
Different options have been looked. Cost is well below the cap for DTE 

communications and VOI. Flyby mission saves an additional $7M. 

Trade space – mission design

© 2018 California Institute of Technology. U.S. Government sponsorship acknowledged.

Scenario Launch 

Strategy

Carrier 

stage

DTE or Relay 

Communication

VOI or 

Flyby

SRM?

Comments

1a Dedicated L/V No DTE Flyby No

1b Dedicated L/V No DTE VOI Yes

1c Dedicated L/V Yes Relay via Carrier Flyby No Cost too high

1d Dedicated L/V Yes Relay via Carrier VOI Yes Cost too high

2a Secondary P/L No DTE Flyby No

2b Secondary P/L No DTE VOI Yes

2c Secondary P/L Yes Relay via Carrier Flyby No Cost too high

2d Secondary P/L Yes Relay via Carrier VOI Yes Cost too high

3a Piggyback No DTE Flyby No Elevated approach velocity 

3b Piggyback No DTE VOI No Few flight opportunities
MarCO actuals

Team Xc study

Grassroots

NICM for instrument 

Cost

© 2018 California Institute of Technology. U.S. Government sponsorship acknowledged.

Basis

1 Project Management MarCO

2 SE MarCO

3 S&MA MarCO

4 Science Grassroots

5 Payload NICM

6 Flight System

Mgt & SE GeorgiaTech estimate

Power TeamXc

C&DH TeamXc

Telecom MarCO

Structure/Mech TeamXc

Thermal TeamXc

Propulsion propulsion embeded in structure

ACS TeamXc

Cabling MarCO

Software TeamXc

M&P TeamXc

Testbeds MarCO - GaTech testbeds

7 MOS MarCO

8 Launch TeamXc

9 GDS included in 7.0

10 ATLO MarCO

12 MDNav included in 7.0

Total Less than $50M

WBS
Conclusions

• Understanding how Earth and Venus have diverged in their geological 

history is key to understanding the habitability of earth-like planets

• Measuring the concentrations of noble gases and isotope ratios in 

Venus atmosphere would provide key information on the formation 

and evolution of Venus

• A free-flying SmallSat probe with mass < 70 kg could deliver highpriority science at Venus for a fraction of the cost of a conventional 

Discovery mission

• Same approach could be adapted to other environments: Titan’s 

atmosphere, Enceladus’ plume, possible plume at Europa, ... 

© 2018 California Institute of Technology. U.S. Government sponsorship acknowledged.