1. Preliminary Design of the eXTP Satellite Institute of Spacecraft System Engineering , CAST Hong Bin Mar 22th , 2017 , Beijing

2. Outlines
1. General Description
2. Design Evolution
3. Basic Parameters
4. Preliminary Design
5. Programme Schedule
6. Problems
7. Conclusions

3. General Description
eXTP , the enhanced X-ray Timing and Polarimetry mission, is a science mission designed to study the state of matter under extreme conditions of density , gravity , and magnetism.
It’s the next generation of the X-ray detected telescope after HXMT in China.
HXMT
eXTP

4. 2. Design Evolution
2007 The conception of XTP was put forward by IHEP; An advanced research of the XTP was carried out by ISSE; Completed the system analysis and achieved the mission’s basic parameters . The first step design of the XTP was finished; With the LAD and WFM adding into the XTP and the parameters of SFA&PFA has changed，redesigned the eXTP satellite; 2017 New launch vehicle; new orbit；new payload；So we update the design of the eXTP satellite.

5. 3. Basic Parameters Orbit 550km,0 deg Launch vehicle LM-7 Launch site
Wenchang Satellite Launch Center
Mass
Launch Mass
≤ 4500 kg
Power
Max demand
3300 W
Solar array
35 m2
Communication
Frequency Band
Ka-band
Data Volume
3.2 Tb per day
Data Rate
1500×2 Mbps
Control system
Accuracy of attitude pointing
< 0.01° (3σ)
Accuracy of attitude measurement
< 0.002° (3σ)
Attitude Stabilization
0.005°/s(3σ), 1’/500s (3σ)
Mission duration
8 years（goal 15 years）

6. 4. Preliminary Design Launch Vehicle
LM-7 launch vehicle ，has a big fairing with diameter of 4200mm a total height of mm， has maximum capacity for 550km circular orbit at 0 deg. inclination is 4500kg.
Telemetry and Control system
The TC system applies the international USB system . Low tilt angle communication is achieved through utilizing relay satellites or building new TC station.
Satellite ground application system
Data receiving is achieved by stations at Sanya. Or using the ground station at Malindi (3°S Kenya), built by Italian (LOFT team).

7. 4. Preliminary Design
Observation Mode——Pointing Observation
The –X axis point to the specific objects in the inertial space ；
The sun vector is controlled in XOZ plane and in a obtuse angle with the +Z axis；
The sun vector will perpendicular to the solar array by rotate it；
According to the user’s observation plan to carry out attitude maneuver，aiming at the burst objects to carry on the observation.
Objects

8. 4. Preliminary Design
Flight Procedure
Objects
Burst source
更新数传速率1500

9. 4. Preliminary Design
Configuration
Stowed in fairing
On orbit

10. 4. Preliminary Design
Configuration

11. 4. Preliminary Design Configuration
Service module(SVM): the SVM includes all units required to control and operate the S/C platform. The WFM and GRM are accommodated in the SVM, too.
LAD Assembly(LADA): the LADA consists of LAD panel(#1~#4), LAD sunshields, deployment mechanisms. The LADA are accomodated on either sides of the SVM.
Mirror Assembly Module(MAM): the MAM is located inside the telescope tube , contains the SFA & PFA mirror module and star trackers，with the associated supporting platform.
Telescope Tube(TT): the TT allows to maintain the SFA&PFA at the required distance from the focal planes.
Focal Plane Assembly (FPA) : the FPA hosts the 13 focal plane cameras, including thermal control hardware.

12. 4. Preliminary Design Service module(SVM) :
Hosts all platform subsystems;
-four tanks
-six reaction wheels
-two star trackers
-four sun acquisition senors
-three gyroscopes
Support the LAD，WFM and GRM;
Downside of SVM is the interface of the launch vehicle;
Inside the SVM there’s a contamination cover , it’s also the sun-shield of the WFM.

13. 4. Preliminary Design Mirror Assembly(MA) :
SFA and PFA are accomodated in the mirror platform.
Conceived as independent unit.
Can be later integrated into the telescope support structure.
Kinematic mounts :Minimising the impact of mechanical and thermal-elastic loads onto the optics alignment.

14. 20 modules each panel（TBD）
4. Preliminary Design
LAD Assembly
Two wings (each wings two panels or one panel（TBD）);
LAD support platform use the hign thermal conductivity material for the structure;
The deployment mechanisms perform the connection between LAD panel and satellite, withstand the launch loads in the stowed condition;
On orbit, the DM releases the panel reliably, and then performs the deployment of the LAD payloads, with the automatic latching at the end of its travel;
After the latching, the DM maintains the angular position and assure the stiffness.
10 modules each panel
1973(L)×1212(B)×132(H)
20 modules each panel（TBD）
2384(L)×1973(B)×132(H)

15. 4. Preliminary Design Telescope Tube(TT) :
Maintain the required focal length;
Support the solar array and ka-antenna;
Provide the catching interface for on-orbit servicing(TBD);
The ICU of the focal detectors are accomodated on top of the TT;

16. 4. Preliminary Design Focal Plane Assembly(FPA) :
Hosts the 13 focal plane cameras;
With the sun-shield to protect the detectors from the suns;
The shape is designed to minimize the envelope dimesions and fit the fairing;

17. 4. Preliminary Design TCS: Mirror assembly thermal design
The insulating washers(fiberglass) are used to limit the conductive heat transfer between the MA and MSP.
The MA are covered by 15-layer MIL to insulate heat radiation of SVM.
The external surface of TT is used for radiator of the MA.
PFA: 20±2℃
镜筒头部是否可以采用镀锗膜待确认
SFA: 20±2℃

18. Pulse-tube Cryocooler
4. Preliminary Design
TCS: SDD thermal design
The FPA is connected to the TT by insulating washers, to limit the conductive heat transfer between the SDD and FPSP.
The SDD are covered by 10-layer MIL.
The SDD heat dissipation are firstly collected by the ethane loop heat pipe, then the collected heat dissipation is refrigerated by the pulse-tube ,power 120W). Finally, the hot junction heat dissipation of refrigerator is transmitted to the individual radiator by the ethane heat pipe.
Pulse-tube Cryocooler
Ethane loop heat pipe
深冷环路热管+制冷机：大面积、多热源热收集系统
中科院理化所于2013年搭载发射的某卫星探测器上的脉管制冷机
其中对于低温乙烷环路热管的热传递系统需要进行隔热设计，包括对于环路热管安装部位的传导及辐射隔热，隔热垫和多层；其安装面与整星舱板之间设置5mm玻璃钢隔热垫，连接采用钛合金螺钉
SFA-SDD *11：
-110℃~-80 ℃
Radiator

19. 4. Preliminary Design TCS- LAD thermal design
Extensile sun-shield is used for the LAD, to insulate heat radiation from the sun.
The inside of the sunshield, covered by 15-layer MIL to insulate heat radiation.
The LAD heat dissipation(5.4W*40=216W) is radiated by itself.
Electric heaters(50W power) are applied in LAD for maintaining the -20℃ lower limit.
extensile sunshield
LAD:-20~-10℃

20. 5. Programme Schedule
Phase A: ~ , international coordination, feasibility design
~ , Subsystem interface definition document (IDS)
~ , Subsystem requirements document
~ , System feasibility design
Phase B: ~ , Preliminary design
~ , Subsystem preliminary design
~ , System preliminary design
Phase C: ~ , System critical design
~ SM delivery(30% for special test(TBD))
~ EM delivery
~ SM and TM delivery
~ QM completed
Phase D: ～ , Flight model and launch
~ FM delivery
Phase E: ～ , Science observation

21. 5. Programme Schedule Payload equipment requirements STM Deliverable
STM
Deliverable EM QM
Non-deliverable FM
FS Deliverable
as required
SFA mirror assembly (SFM) 9 - 2
PFA mirror assembly (PFM) 4 1
SFA camera assembly (SFC)
PFA camera assembly (PFC)
DHU-F  -
PCDU
LAD module 40 10
LAD PBEE  4
LAD ICU: DHU(2)+PDU(2)
 2+2
2+2
1+1
WFM Camera 6
WFM ICU  2

22. 6. Problems
LAD Assembly
The following key requirements should be confirmed:
Panels:
~The interface between panel structure and sun-shield, DM, module, PBEE.
~The requirements for strength, stiffness, alignment, thermo-stability, material, connection style.
~The technical flow about the delivery, assembly, test(How? Where?).
LAD sun-shield:
~The requirements for materials, frequency, weight, thermal control.
~Interface of the HDRM.
Deployment Mechanisms:
~The interface between DM and the panels.
~Requirements for Frequency, Accuracy, Drive torque, Thermo-stability, Weight.
~AIT process and items.

23. 6. Problems
WFM
The requirements for installation accuracy, consistency of direction (for one pair)
Can you accept the state that FoV is blocked or change the point angle(decide by the LAD panels and sunshield)？
The URF could meet the launch loads and on-orbit thermal environment？
If CAST responsibility for the design of WFM support structure:
Can you adjust the position of the three URF？(Insufficient Operation Space)
Can you redesign the position of the electrical connector？(Insufficient Operation Space for 3 pairs)

24. 7. Conclusions
We have updated the design of eXTP satellites, which could meet the requirement of the science;
Something should be confirmed to help us understanding the design and requirements of the science.

25. Thanks for your attention！
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