Planet-D mission toVenus in the future
Masato Nakamura, Nobuaki Ishii, Atsushi Yamazaki,
Tomoaki Toda, Ryoma Yamashiro*, Yoshifumi Futaana,
Naoki Terada, Sanjay Limaye

Example images taken by Akatsuki
cameras (IR1, IR2, UVI, LIR)

A synthesized false
color image

Venus nightside clouds atthe deep cloud layer.

Y shapestructure
clearlyappears(283 nm : blue;
365 nm : green;
0.90 µm : red. )(brightness inverted)
1.735 µm(blue) and 2.26µm (red)IR2

IR1,UVIImages

cloud top temperaturetaken by LIR. A huge bow
shape structure is seen.
LIR

IR1:

1,643

IR2:

3,201

UVI:

17,306LIR:

31,444by Jan. 2, 2020

Mission to Lagrange points

Lyapunov orbit
orLissajous orbit
orHalo orbit
around Lagrange points

Planet-D concept
VENUS
L2

L1
Spacecraft 1
UVI & LIR

Spacecraft 2
IR2 & LIR
1,000,000km

SUN
1,000,000km

Night side imaging

Day side imaging• We will be able to watch both dayside and nightside simultaneously• We need much more IR2 images at nightside ( 1643 images <<31,444 LIR images from Akatsuki)

The orbits around Venus L1 and L2
Initial position
2.5years

Lissajousorbit

SunHalo orbitzy

L1x

VenuszyL2

To make angle to the Venus 25deg, the semimajor axis
must be under 0.5M km.
Because Halo orbit has minimum length for z directionin theory, Lissajous orbit is preferable.
(The graph above is for Sun-Earth L-point)x

3.6 days (betweenpoints)

Venus

0.47M km

y25°

1M km

x

108 days in a cycle
for the x-y planeTelemetry

VenusyL125°x
1M km

0.47M kmyL2x

1M km

Plan BL1 Probe

L2 Probe

Plan B

It’s difficult to make linkage two probes simultaneously becauseof that distance.
Plan A1/A2Earth

Plan A1: to use 2 ground stations
Plan A2: to use 1 ground station and share by time
Plan B: to make linkage between probesi.e.
L1 probe has 2 HGA-T (for L2 probe & the ground station)
L2 probe has 1 HGA-T (for L1 probe)Sequence to orbital insertion
1. Insertion to elliptical orbit by Epsilon S (*1) + Kick Stage (*2)
2. Transfer to Earth-Venus interplanetary trajectory

3. Transfer to Venus L1 Lissajous orbit
4. Planet-D2 separation from Planet-D1
5. Planet-D2 Transfer to Venus L2 Lissajous orbit
6. Station keeping of Planet-D1 around Venus L1 and Planet-D2
around Venus L2*1 Epsilon S:*2 Kick Stage:

Improvement of the current Epsilon Launch Vehicle
Development started in 2020
Under development for Destiny+Launch period
The launch opportunity comes every 584 days, the period of Venus’ meeting with Earth.
However, since the orbital planes of Venus and Earth are tilted, the optimal timing comes every 8 years(about 2920 days ≒ 5 times the meeting period).

8 year cycle

targetoptimal

If sufficient development time is kept, the optimal period is autumn 2032. However, considering
the risk of development delays, the provisional target is spring 2031.
Since this is a point-to-point analysis, it is necessary to examine detailed elements such as Right
Ascension of Ascending Node.

PLANET-D Configuration (without mission devices)
PLANET-D2 : 50kg

PLANET-D1 : 430kg
Probes Separation
SystemRocket I/FOMS(for D1&D2 Orbit Maneuver）

RCS(for D1 Attitude Control)

RCS(for D2 Attitude Control)Delta V Estimation- Results of the analysis

Launch Vehicle(+ Kick Stage)

Earthorbit: alt.230 x 37000km

Payload 480kg

ΔVevt (1460m/s) by OMC

Earth-Venus transfer orbit
ΔVs (200m/s) by OMC

Attitude controlby RCS(200m/s)

Venus flyby at 400km altitude
ΔVL (520m/s) by OMC

Venus L1 Lissajous orbit
ΔVbL (1-6m/s) by RCS

Venus L2 Lissajous orbit
Station keeping in L1/L2 Lissajous orbit by RCS
ΔVsk (1-10 m/s /year)⇒ probe total mass = 480kg
ΔV = 2500～2800 m/s(ΔV by OMS = 2200～2600m/s)

ProbePropulsion

Propellant Selection for OMS
NTO/N2H4 is preferable for OMS Propellant
in the range of ΔV 2200～2600m/s.
(see right figures)

N2H4

NTO/N2H4

ΔV [m/s]

2200

2600

2200

2600

Propellant
Mass [kg]320355250

280

Dry Mass [kg]

160

125

230

200

Sum [kg]

480480

480

480

160kg

125kg

*Dry mass in this page means the mass except OMS propellant
230kg

200kg

PLANET-D1

Mass Distribution

PLANET-D2

Mass distribution based on NTO/N2H4 OMS
system is as below.

Mass [kg]D1

D2notesContentsfor OMC ΔV =2200
m/sfor OMC ΔV =2600
m/s

Mission devices

1616

LIR, UVI, LAC, PIM

Bus Structure/devices

30*30*

Power, Communication, A/O control

Propulsion devices

91

99

OMS, RCS

Propellant

294324

NTO,N2H4

D1 Sum430

469*

Mission devices

2626

LIR, IR2, LAC, PIM

Bus Structure/devices

15*

15*

Power, Communication, A/O control

Probes Separation System

11Rocket I/F

11

Propulsion devices

55

RCS

Propellant

22

N2H4

D2 Sum5050

D1 + D2 Sum

480519*Launch capacity is 480kg*necessary to improve

Current Issues
1. ΔV optimization- Acceleration timing- Swing-by- Tolerance to Z-direction amplitude in Lissajous orbit
2. Mass distribution- Refinement of bus structure/devices- Updating of devices information- Redistribution of D1/D2 function

Image by the paper: Optimization for Lissajous Orbit

Optional Instruments for ion escapeat Earth

L1
O+ ion tail• Solar EUV monitor• Fluxgate magnetometer

EUV imager

Observation can be done during L1 to L2 transfer

4 weeks

O+ distribution observed by PVO[Luhmann, 1986]

Summary• We need to plan a new generation Venus mission after Akatsuki.
• Russia is planning Venera-D in 2029 and Lagrange point mission(India plans something)• ISAS has a heritage of Akatsuki 5 cameras and easy to put them to the new mission, Planet-D.
• Planet-D consists of two spacecraft inserted into Lagrange points, L1 and L2 and look at thedayside and nightside hemisphere. UVI, LIR and IR2 are the candidate cameras onboard thespacecraft.

• Launch by Epsilon launch vehicle is assumed.
• Ion escape may be imaged during one spacecraft’s moving from L1 to L2.