BIRDY–T

Daniel Hestroffer - IMCCE/Paris obs., PSL Research univ., France

M. Agnan ESEP - Odysseus Space Ltd., TaiwanJ.J. Miau - NCKU, Taiwan

G. Quinsac - LESIA/Paris observatory, FranceP. Rosenblatt - ROB, Belgium

B. Segret LESIA-ESEP/Paris observatory, FranceJ. Vannitsen - NCKU - Odysseus Space Ltd., Taiwan

hestroffer@imcce.fr – 6th iCubeSat

Small bodies

•NEO, MBAs, Trojans, ...

• Asteroid-Comet continuum

• Small and irregular satellites

• Planetary resources exploitation

• PHA threat to Earth

• Science: origins, formation and evolution physics and dynamics

•Mass, internal structure, mechanical behaviour2

hestroffer@imcce.fr – 6th iCubeSat

Small bodies •Space missions

asteroids, comets+Phobos/Deimos

3

diversity size-surface-structure

no Trojan ; no binary(*)... yet(P&G 2017)

hestroffer@imcce.fr – 6th iCubeSat

Internal structure

•Gravitational aggregates

•

4

‘small’ asteroids ‘rubble piles’

binary and multiple systems

spin-rate barrier

(Pravec, Harris)

Rotation spin-rate

hestroffer@imcce.fr – 6th iCubeSat

Internal structure

•mass for ≈50 asteroids

•average densities with taxonomic class

•variation with porosity

•variation with size

5

(Carry 2012)

hestroffer@imcce.fr – 6th iCubeSat

Internal structure

6

(Baer et al.2011)(Britt et al. 2010)

• Porosity

• Gravitational aggregates or rubble-piles

• post-collision, YORP?

fractured

NEAs

rubble-piles

coherent

P-type & comets

S-type Itokawa porosity 40% (Fujiwara et al.2016)

hestroffer@imcce.fr – 6th iCubeSat

Planetary geodesy• Mission to small body

‣ Didymos (AIDA/AIM)

‣ Phobos (MMX, Dephine)

‣ ... MBAs, Trojans

‣ interplanetary mission hosting CubeSats

• Derive mass, density, and moments of inertia +higher moments of gravity field (spherical/elliptical harmonics) test internal structure and density distribution

• Advantages of CubeSat

‣ CubeSat spacecraft dedicated to instrument (or target)

‣ autonomy in operations/orbits

‣ closer to surface (higher risks)

‣ proximity operations

• Constraints

‣ no direct link to Earth (à priori), => relying on mothercraft

‣ no example of radio-science cubesat, nor interplanetary

7

hestroffer@imcce.fr – 6th iCubeSat

Planetary geodesy•Radio-science and Imaging

•Radio-science

‣ echo(/ranging) + Doppler

‣ stellar astrometry

• Imaging

‣ shape and size

‣ rotation, landmarks attitude

• additional Delta-DOR (PRIDE, ...), Lidar or radio link to surface (MASCOT2, ...)

8

hestroffer@imcce.fr – 6th iCubeSat

BIRDY concept• BIRDY: CubeSat to small body concept

‣ piggyback, cruise or proximity operations

‣ mothercraft relay

‣ need of autonomy

‣ complementary observations by 1 or 2 CubeSats

‣ end of life: land on surface, radio operations

• Main features developed

‣ propulsion

‣ autonomous orbit navigation and control

‣ radio science (POD)

9

hestroffer@imcce.fr – 6th iCubeSat

BIRDY heritage

10

(Segret IFOD)

flying legs

• Operations - Flying legs

‣ Autonomous navigation

- astrometry and position

- orbit correction and attitude control

‣ Ground segment

- models in the loop, prepares ref. orbit

‣ Flight segment

- autonomous ΔV impulse, navigation, science, link mothercraft

• Propulsion - PPT

‣ see Quinsac et al. session B2

hestroffer@imcce.fr – 6th iCubeSat

Autonomous navigation

‣ star tracker - ‘object tracker’

‣ in-flight attitude and orbit – on-board AOCS

‣ in cruise, or in proximity

‣ see Segret et al. IFSSD 2017 see Agnan et al. COSPAR 2017 Symp. SmallSat

11

hestroffer@imcce.fr – 6th iCubeSat

Radio-science

12

Basic concept of radioscience experiment

Tracking data: 2-way radio-link between the Earth and the spacecraft orbiting the systemDoppler and range measurements

Precise Orbit Determination (POD)Dedicated orbitography software (like GINS(1)):• Calculation of orbit from least

squares fitting of a dynamicalmodel of motion to tracking data

• Determination of the parameter of geophysical interest (Mass and gravity field of primary, mass of secondary)

XbandKa-band

(1) Géodésie par Intégration Numériques simultanées, developed by the French space agency (CNES) and further adapted to planetary geodesy applications by the Royal Observatory of Belgium (ROB).

xmothercraft

xxxCubeSat

hestroffer@imcce.fr – 6th iCubeSat

Radio-science

13

• RDV flyby experiment

• object (Didymos)

‣ density 2000 kg/m3

‣ diameter 800 m

•measure Doppler

‣X-band 0.02 mm/s over 60s

‣ relative vel. 20 to 30 cm/s GM ≈ 0.03% single RDV @1km

hestroffer@imcce.fr – 6th iCubeSat

Radio-science

•Orbit (planar) stabilities around binary asteroid Didymos

•over ≈1month on resonances

•polar orbits, close to secondary

•hovering and rdvs, no perturbations

•POD and Ji coeff. determination

14

(F. Damme DLR 2012)

(Escorial GMV 2016)

hestroffer@imcce.fr – 6th iCubeSat

Radio-science• Optimising: polar orbits, close to surface

• Phobos

‣ QSO 50km, hovering ≈0.1-10km

• Didymos

‣ QSO 2-10 km, hovering 0.25-1km

• multiple rdv (Phobos case, or QSOs)

• RS assessment

‣ radio-link analysis (bands, one-or-two way, USO)

‣ one or two CubeSats

‣ external forces, accelerations

‣ orbit correction constraints

‣ POD

15

hestroffer@imcce.fr – 6th iCubeSat

Development plan

16

BIRDY–T