juventas cubesat for hera - icubesat2019 · monostatic low-frequency radar, built from consert...

DEVELOPMENT OF THE JUVENTAS

CUBESAT FOR HERA

ICUBESAT 2019

H. GOLDBERG, O. KARATEKIN, ET.AL.

JUVENTAS: 6U CUBESAT FOR THE HERA MISSION

❑ Juventas is a 6U Cubesat developed as a daughtercraft to the Hera mothership for the purpose of contributing to asteroid research and mitigation assessment objectives of the Hera mission. The Juventas Cubesat will provide scientific contribution towards the understanding of the formation processes of binary asteroids, their interior structure, surface properties, and dynamical properties

❑ Juventas is carried to the Didymos asteroid system riding inside a deployer in the Hera spacecraft

❑ Once Hera has completed its Early CharacterisationPhase (ECP), prior to starting its Detailed Characterisation Phase (DCP 1) – approximately 2 months after Didymos asteroid arrival (April 2027), it will deploy the two 6U CubeSats: Apex and Juventas

iCubeSat 2019 - Juventas

Juventas is named for the Roman goddess of youth and rejuvenation.Her Greek equivalent Hebe is the daughter of Hera and Zeus

SCIENCE OBJECTIVES AND PAYLOADS


Science objective Investigation Measurements Instruments Mission Phase

Determine gravity field of Didymoon

Gravity field characterization outside Brillouion sphere at least up to degree and order 2

Deflection during orbit measured with ranging, line-of-sight to Hera

ISL radio link Proximity operations

Surface gravity Surface acceleration Gravimeter Surface operations

CubeSat touchdown/ bouncing

Dynamic recording of each event

IMU Landing / bouncing

Determine interior structure of Didymoon

Reconstruction of material density and largest monolithic object

Properties of (back-) reflection of transmitted signal

Low frequency radar

Proximity operations

Surface properties of Didymoon

Visible imaging Inspection of Didymoonsurface features and impact crater

Visible camera Proximity operations, surface operations

Surface strength measurement

Rebounds from the surface IMU Landing / bouncing

(Secondary) Determine dynamical properties of Didymoon

Variable surface acceleration

Surface acceleration over >1 orbit

Gravimeter Surface operations

Attitude and time dependent surface illumination

Attitude and time dependent surface illumination

Star tracker, sun sensors

Surface operations

Low-frequency Monostatic Radar

Inter-satellite link radio science

3-axis Gravimeter

Gyroscopes and accelerometers

Visible context camera

JUVENTAS CUBESAT PLATFORM CONFIGURATION


❑ 6U CubeSat form-factor, 12 kg max wet mass❑ Accommodation of low-frequency radar including

deployable dipole antenna elements❑ Autonomous operations, communications through Hera

mothercraft❑ 3-axis stabilized inertial pointing with reaction wheels

and RCS propulsion, input from star trackers and sun sensors

❑ Cold-gas propulsion system, with 14 m/s delta-V

❑ Deployable solar arrays, ~30W input at 1.8 AU❑ Nominal operations 1.3 – 1.8 AU, capable to 2.2 AU❑ Variable data rate S-band Inter-satellite link RF

communications up to 460 kbps, 2W RF transmit power❑ Navigation via ISL ranging to Hera, also used for radio

science

❑ Camera and laser altimeter to navigate relative to asteroid target for landing

JUVENTAS MISSION CONOPS


Main science objectives of radar and radio science achieved during global observations and proximity operations phases

Self-Stabilized Terminator Orbit (SSTO)

1. Pre-release checkout, <1 day

Deployment conditions from Hera: 10km

2. Release, detumbling, and commissioning, 2-4 days

Spacecraft checkout, deployments, and operational commissioning

3. Global and Proximity observations, 10 days – 3 months

Self-Stabilizing Terminator Orbits (SSTO), 2km-5km

Radar and radio science observations

4. Descent and Didymoon landing, 1 day

Monitoring of impact and/or bouncing

5. Didymoon surface operations, ~1 day

Local gravity field measurements and attitude, combined with ISL radio science

RADAR SCIENCE

❑ Monostatic low-frequency radar, built from CONSERT heritage (Rosetta/Philae)

❑ Meets science objective of determining the internal structure of Didymoon

❑ Observation of Didymoon during global observation and proximity operations phase (5 km down to 1.5 km SSTO)

❑ Complete coverage (>20 orbits) gives information to feed full tomography

❑ “Cuts” across body for few orbits (~7) allow inference of large scale structures

❑ Limited coverage (1 orbit) gives average values of permittivity, size distribution and heterogeneity


Ref. Rosetta/CONSERT (A. Herique, et.al)

SSTO RADAR COVERAGE

❑ Didymoon 5km SSTO for 60 days

❑ Unobservable zone due to Didymain shadow (system is tidally locked)

❑ Didymain 3km SSTO for 60 days

❑ Unobservable zone on poles


LOW FREQUENCY MONOSTATIC RADAR (LFR)

❑ Radar details (CONSERT heritage):

❑ Design led by Univ. of Grenoble, A. Herique

❑ Frequency: 60 MHz carrier, 20 MHz signal bandwidth

Allows deep ground penetration of the body

❑ Four deployable antenna elements

❑ Spatial resolution: 10-15m

❑ Data rate: 2-20 kbps

❑ Mass: 1.5 kg

❑ Power: 50 W


ISL FOR RADIO SCIENCE

❑ Use of line-of-sight ISL radio link between Hera mothercraft and Juventas Cubesat for radio science

❑ Mission design of flyby trajectories assist in determination of shape and gravity field for higher degree and order harmonics, allow for identification of density anomalies

❑ Degree 2 gravity field can be retrieved with uncertainty <15%

❑ Measurement derived from phase-coherent Doppler shift due to relative line-of-slight velocity differences between Hera and Juventas Cubesat

❑ Cubesat-to-Cubesat link may also be utilized

❑ Dynamical properties of Didymoon can be determined from landing position through orbital analysis augmented with attitude and illumination information from sun sensors and star trackers


Coherent transponder

Highly stable microwave carrier

ISL

VISIBLE CAMERA

❑ Context of local target body surface

❑ Used to feed GN&C and science teams,

❑ Opportunistic imaging (shape and volume of DART impact crater at closer altitudes)

❑ Camera details:

❑ 2048x1944 pixels

❑ Lens: 16mm F/1.2 (23 deg FoV)

❑ Mass: 60 g

❑ Power: 0.7 W


IMPACT/LANDING SCIENCE

❑ Impact measurements for mechanical surface properties (porosity and grain properties):

❑ Dynamic recording of impact and bouncing events with accelerometer and gyro at high sample rates

❑ Determine energetic Coefficient of Restitution (CoR), similar to Philae on 67P

❑ Surface measurements of local accelerations at Didymoon landing location with gravimeter

❑ Measurements over >1 orbit, evenly spaced temporally for tide measurements

❑ Determine surface geopotential, contributes to the understanding of subsurface structure & heterogeneity


Landing acceleration space (AIM/AGEX study)

Transfer to landing trajectory• Convert SSTO to equatorial

plane change• Hohmann transfer to

Didymoon orbit, circularize

INERTIAL MEASUREMENT UNIT

❑ High rate 3-axis accelerometer and gyro:

❑ Measurement Range: ±10g

❑ Resolution: 1.9 μg

❑ Sampling rate: up to 2kS/s

❑ Mass: 55 g

❑ Power: up to 1.5 W

❑ High rate acquisition recording triggered by landing impact events

❑ Expected impact velocity: <10cm/s

❑ Collision time estimate 7 msec for hard rock and up to 6 sec for granular bed, assuming ~1 cm pebbles


GRAVIMETER PAYLOAD

❑ 3-axis gravimeter:

❑ Measurement range: 1000mGal

❑ Sensitivity: 0.001 mGal

❑ Mass: 300g

❑ Power: 0.3 W

❑ Created by the Royal Observatory of Belgium, similar design to MMX


juventas cubesat for hera - icubesat2019 · monostatic low-frequency radar, built from consert...

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