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ISAS/JAXA Small Scientific Satellite Series Program with Flexible and Reusable Bus Design
T. Nakagawa (ISAS/JAXA)S. Sakai (ISAS/JAXA)
26th ISTS @Hamamatsu [2008-f-17]
S.Sakai: ISAS/JAXA Small Scientific Satellite Series Program with Flexible and Reusable Bus Design 2
ISAS/JAXA small scientific satellite series
• The Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (ISAS/JAXA) has recently started to develop a series of small scientific satellites, and has a plan to launch three to five minisats (300-400 kg) per five years.
• The series aims at ‘cheaper and faster realization of unique space experiments’ as a complementary program of mainstream medium-class scientific satellites.
• In order to shorten the period of satellite development with low cost, it is considered to be reasonable to employ standard bus architecture, where the bus and payloads are clearly separated in a modular manner.- The modular configuration is
attained in exchange of resources like mass.
Mission payload
Standard bus
The mission payloads are on the roof of the bus system.
S.Sakai: ISAS/JAXA Small Scientific Satellite Series Program with Flexible and Reusable Bus Design 3
Working Groups for small scientific satellites
Scientific missions:
TOPS Tele-observation of planetary plasma
FFAST X-ray observation w/ formation flight
PPM-Sat Precise positioning w/ GPS occultation
CAST Gamma-ray burst observation
DPF Gravity wave observation
DIOS X-ray observation (dark baryons)
ELMOS Seismic Electromagnetism
ERG Plasma observation in Geospace
POLARIS X-ray polarization observation
Engineering missions:
Tether Tether technology demonstration
SPS Solar power generation
SLIM Lunar lander
Venus balloon Venus balloon
MAGSAIL Pure magneto-sail
EGG Gas-balloon re-entry
First flight (2012)
S.Sakai: ISAS/JAXA Small Scientific Satellite Series Program with Flexible and Reusable Bus Design 4
This presentation
• The missions for small scientific satellites have various kinds of requirements:- three-axis/spin-stabilized attitude control, - a wide range of power (50 to 300 W), - a variety of orbit (LEO, SSO, HEO, etc), ...
-> A traditional rigid standard bus will be unable to satisfy the diversity of mission requirements.
• In this presentation, several concepts to enhance flexibility of the standard bus are introduced:- Layers of standardization- Semi-custom-made bus system - Tradeoff between integration and modularization
S.Sakai: ISAS/JAXA Small Scientific Satellite Series Program with Flexible and Reusable Bus Design 5
Layers of standardization
• Specifications of most conventional standard buses are strictly regulated for a particular mission in the whole system/subsystem of satellites. (e.g., communication satellites on GEO)- Effectiveness of the rigid standardization depends on the number of satellites
with the particular mission.
• Traditionally, medium-class scientific satellites in ISAS/JAXA were dedicatedly developed in order to satisfy various requirements and pursue resource-optimal design, so that fruitful achievements would be brought.- Optimization of satellite-by-satellite consumes relatively large cost and long
development time.
-> ‘layers of standardization’ concept
scientific satellites with a wide variety of requirements
S.Sakai: ISAS/JAXA Small Scientific Satellite Series Program with Flexible and Reusable Bus Design
SpaceWire as standard data network•Promising technology because of high speed, simplicity, and testability•RMAP (Remote Memory Access Protocol) over SpaceWire is a powerful method, which enables one component to read and write directly from memory and registers of another component over the network.
6
Layers of standardization [Cont’d]
The Layer (IV): Configuration- Similar to the conventional rigid standard buses
- Possible to omit mechanical/thermal model tests
- Applicable to most scientific observation missions by adding selectable or alternative options
The Layer (III): Instruments- Advantageous for engineering missions where
the satellite configuration itself is hard to be standardized (e.g., the small lunar lander with a large-scale propulsion system)
- Valuable concerning economics of bundling order
The Layer (II): Interfaces- Essential for higher levels of standardization
The Layer (I): Design Methods- Standard method of modeling satellites
-> reuse of GSE software, etc
S.Sakai: ISAS/JAXA Small Scientific Satellite Series Program with Flexible and Reusable Bus Design 7
Semi-custom-made bus system
• Consideration of the bus specifications using a requirement matrix- Three categories:
Core, alternative option, and selectable option
• The alternative and selectable options are crucial for the flexible standard bus to realize diverse missions with time- and cost-saving strategies.Semi-custom-made bus system
For small scientific satellitesReady-made standard bus
full-custom-made medium-class scientific satellites
• The idea is similar to Product Line or Product Platform engineering in development of commercial products.- The capability of adding or replacing options is based on recent progress in
technology of modular design and Plug and Play.- A tradeoff between the number of options and effectiveness of the
standardization should be carefully investigated.
S.Sakai: ISAS/JAXA Small Scientific Satellite Series Program with Flexible and Reusable Bus Design 8
Semi-custom-made bus system[Cont’d]
Selectable options•solar array drive assembly (SADA)•GPS receiver•X-band transmitter•monopropellant propulsion system•design for EMC (Electro-Magnetic Compatibility) Alternative options
•number of solar panels (one, two, or three panels
per wing)•capacity of Li-ion batteries (35Ah/50Ah)•accuracy of attitude sensors such as a star tracker and an inertial reference unit (corresponding to requirements)•size of reaction wheels (corresponding to requirements of perturbation immunity)
Note: Nominal specifications are underlined.
S.Sakai: ISAS/JAXA Small Scientific Satellite Series Program with Flexible and Reusable Bus Design 9
Tradeoff between integration and modularization
Conventional Integration Modularization
Cost analysis says that present satellite cost has strong correlation with the number of onboard components. -> Common functions which belong to different components have to be integrated into a single component.The integrated architecture is intrinsically appropriate for small satellites because it will consume less resources such as mass, size, and electric power.
The integrated architecture, however, has latent difficulties in testability and reusability. -> Modularization is attempted in the next step.The modular architecture seems preferable in many cases, if a resource budget including cost allows it.
What is important is to standardize interfaces between modules. -> The standard interfaces will facilitate change of architecture from integration to modularization, and vice versa.
S.Sakai: ISAS/JAXA Small Scientific Satellite Series Program with Flexible and Reusable Bus Design 10
Tradeoff between integration and modularization [Cont’d]
WDE4WDE3WDE2
IRU
SMU (Satellite Management Unit)
APR
SAP1
Mission Payload64bit CPU (MIPS) +
PROM/ EEPROM/ RAM
DHFS
DC/ DC converter
MTQ-Z
MTQ-XMTQ-Y
SAP1
SADA1
DreamCubeSAt
各Heater(24ch max)
Data Handling Network(DH-N/ W) 100Mbps×n max
DR(2Gbytes)
RCS
3N thruster
S-H
YB
S-RTM(S-band Routing module)
S-ANT1
50V Primary Power from PCU
TCIM(ON/ OF
)
NIC (Network Interface Circuit)
SAP2
SAP2
SADA2
64bit CPU (MIPS) + PROM/ EEPROM/ RAM
ACFS TCFS
ADC/ MUX
(Temp)
DRUS-TRP1、S-TRP2
WDE1~WDE4STT-E, IRU
unregulated 50 voltage
ACIM(MW)
ADC/ MUX
Avionics Control Network (AC-N/W)
S-ANT2 S-ANT3
Space Packet only on NW
TCIM(TLM/ C
MD)
S-TRP1
S-TRP2
To WDE1~WDE4、STT-E、IRU Power ON/ OFF
PCUMission × 2ch
NEA
NEA× 4ch
× 4ch
STT-E
STT-S
SPS
STT
CSAS1
CSAS2
SPS
from Temp. Sensors (64ch max)
GFD
PFD FLT
TNK
LV
RCSHeater
ODC
Li- ion BAT35AH
ACIM(Sensor)
SpWRouter(12port)
Analog TLM(32ch max)
ACIM(STT)
SpWRouter(12port)
SADA Driver
Heater Driver × 3ch
Thruster Driver
MTQ Driver
DRU(Drive Unit)
ACIM(STT)
PRE
1 2 3 4
Valve Module 2
Valve Module 1
S-DIP2
S-DIP1
S-SW
AC-NW
DH-NW
WDE1
RW1~RW4
Valve Driver
SMOS(RealTimeOS)
RD TLMSA SEP
System block diagram of the standard bus for small scientific satellites
(baseline)
The functional integration is considerably pursued.
S.Sakai: ISAS/JAXA Small Scientific Satellite Series Program with Flexible and Reusable Bus Design 11
Tradeoff between integration and modularization [Cont’d]
System block diagram of the standard bus
for small scientific satellites (modification)
Now studying to modify the architecture to more modular one so as to enhance testability and reusability
WDE4WDE3WDE2
SMU (Satellite Management Unit)
APR
SAP1
Mission Payload
64bit CPU (MIPS) + PROM/ EEPROM/ RAM
DHFS
MTQ-Z
MTQ-XMTQ-Y
SAP1
SADA1
DreamCubeSAt
Data Handling Network(DH-N/ W) 100Mbps× n max
RCS
3N thruster
50V Primary Power from PCU
NIC (Network Interface Circuit)
SAP2
SAP2
SADA2
64bit CPU (MIPS) + PROM/ EEPROM/ RAM
ACFS TCFS
DRUS-TRP1、S-TRP2
WDE1~WDE4STT-E, IRU
unregulated 50 voltage
Avionics Control Network (AC-N/W)
Space Packet only on NW
PCUMission × 2ch
NEA
NEA× 4ch
× 4ch
STT-E
STT-S
SPS
GFD
PFD FLT
TNK
LV
ODC
Li- ion BAT35AH
ACIM(STT)
PRE
1 2 3 4
Valve Module 2
Valve Module 1
AC-NW
DH-NW
WDE1
RW1~RW4
SMOS(RealTimeOS)
DR(2Gbytes)
S-H
YB
S-RTM(S-band Routing module)
S-ANT1 S-ANT2 S-ANT3
TCIM(TLM
/ CMD)
S-TRP1
S-TRP2S-
DIP2
S-DIP1
S-SW
RD TLMSA SEP
TCIM(ON
/ OFF)
DC/ DC converter
SpWRouter(14port)
STT
CSAS1
CSAS2SPSIRU
ACIM (Avionics Control Interface Module)
μ HCE
μ HCE
μ HCE
SpW Router (14port)
S.Sakai: ISAS/JAXA Small Scientific Satellite Series Program with Flexible and Reusable Bus Design
“Semi-order-made” approach[e.g. AOCS]
So, now “semi-order-made” approach is considered. Example: what is the appropriate attitude &
orbit control system (AOCS) configuration to implement this concept. IRU
Type-A (Fine, larger, expensive) Type-B (Coarse, small, cheaper)
Reaction Wheel ….Um… IRU should be Type-B for
my mission…
Example of “semi-order-made” approach
To achieve this concept, one important thing is to distinguish and separate the AOCS into two categories: one which is independent of the AOCS components selection, and ones dependent on components.
S.Sakai: ISAS/JAXA Small Scientific Satellite Series Program with Flexible and Reusable Bus Design
New Architecture for AOCS Data Interface
For slightly difference component configuration…
Conventional ISAS approach
• Monolithic AOCS computer unit.+ Effective to minimize weight, size, number of parts, …– Component change affect wide area in the unit.
S.Sakai: ISAS/JAXA Small Scientific Satellite Series Program with Flexible and Reusable Bus Design
New Architecture for AOCS Data Interface [Cont’d]
New approach
• Distributed AOCS computer unit.+ Minimize the are influenced by the component change.– Weight etc. are not minimum.
S.Sakai: ISAS/JAXA Small Scientific Satellite Series Program with Flexible and Reusable Bus Design
New Architecture for AOCS Data Interface [Cont’d]
• In this novel approach, function to interface each component is distributed in the individual ACIM (attitude control interface module), not implemented in the computer unit.
• Thus the connection between ACIMs and the computer unit should behaves just like local bus.
• Then, what is the appropriate data interface for this purpose?
• “SpaceWire” is assumed to be a solution, because of- Speed,- Simplicity,- Open standard, - …
S.Sakai: ISAS/JAXA Small Scientific Satellite Series Program with Flexible and Reusable Bus Design
Architecture for ground test equipments
For software development & test, flight operation simulation, etc.
For static closed loop test, etc.
S.Sakai: ISAS/JAXA Small Scientific Satellite Series Program with Flexible and Reusable Bus Design 17
Conclusion
• A standard bus system for the ISAS/JAXA’s new series of small scientific satellites has been presented. Some ideas and concepts to enhance flexibility of the bus system have been shown.
• The TOPS project which is the first satellite of the series will proceed to the Phase B soon.
• On and after the second flight, the development time will be no more than two years from determination of mission interfaces to the launch including integration tests.
• As the estimated cost is worldwide competitive, the standard bus has potential to be applied to earth observation or disaster monitoring missions in the future.
Thank you very much for your attention.
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