Palamede, more than a microsatellite. Workshop on University Micro Satellites in Italy Rome, July 27, 2005

Transcription

1 Palamede, more than a microsatellite The Palamede Team (represented by Franco Bernelli and Roberto Armellin) Workshop on University Micro Satellites in Italy Rome, July 27, 2005

2 Outline Mission and educational objectives Palamede Project stats Main subsystems overview with an historical insight Project status Complementary activities Conclusions

3 Mission Objectives Palamede is a project started in 1997 by the at Politecnico di Milano with the aim to design and put in Low-Earth orbit a Microsatellite entirely designed by students Mission goals Take pictures of the Earth by means of a CCD colour camera Validate new triple junction solar cells to be used for future space missions Palamede is designed to be a basic platform to test new concepts for future small and cheap satellites The subsystems are made by standard components mostly not space qualified Palamede will be a multipurpose bus for a wide range of payloads

4 Educational Objectives Important chance for students to apply in practice what they have learned in theory Offer students a unique opportunity to face complex spacecraft subsystem design and the typical resources shortage of space environment Introduce students to team work and to concurrent design, a standard approach in aerospace field Allow students to cooperate with aerospace companies resulting in an easier insertion in the job market Pave the way for the Aerospace System Design graduate course

5 Stats At the moment 2 full professors, 3 researchers, 1 research fellow, 1 postdoc, 7 Ph.D. students, 3 engineers and 5 students are involved in the project Over 9 years ~ 50 students worked at the project ~ 40 thesis works and ~ 15 scientific papers have been produced Many industrial partners (A.S.I., Carlo Gavazzi Space, Galileo Avionica, CESI, Eurotech) cooperate at the project About 50% of the theses have been developed in industrial environment and a good percentage of authors are currently working in these companies

6 History of Mission Goals Throughout the design process some guidelines have been maintained unchanged Microsatellite configuration in order to be launched as secondary payload Multipurpose bus for a wide range of payloads and launchers compatibility Use of commercial components mostly not space qualified Test new cheap technologies for future space missions Mission goals have been changed during the design process Test-bed for deployable structure useful for payload reentry on Earth Earth-Imaging using a CCD color camera and test-bed for attitude determination using GPS sensor Earth-Imaging using a CCD color camera and test-bed for new kind of triple junction solar cells.

7 Configuration vs. Goals Microsatellite reentry demonstrator (Palamede forerunner, 1992) : Sphere configuration, 450 mm diameter, + deployable aero-braking device Overall mass 50 kg Earth imaging + GPS for attitude determination: Parallelepiped shape 600x400x400 mm to maximize solar array area (terrestrial solar cells were used) Overall mass 32 kg Earth imaging + triple junction solar cells Cubic shape 400x400x400mm Overall mass ~20 kg

8 Orbit The spacecraft orbit is constrained by the launcher Pervious choice: Ariane 5 piggyback e = 0, a = 7038 km, i = 65 Actual choice (TBC) Dnepr e = 0, a = 7038 km, i = 98.7 Midday-Midnight

9 Structure - Thermal Structure Previous choice Aluminum alloy panels with 4 vertical beams Aluminum alloy panels were substituted by aluminum alloy honeycomb ones Actual choice Thermal External Aluminum alloy honeycomb structure with no vertical beams Base plate and secondary structure made by aluminum alloy 7075 Passive thermal control

10 Communication Previous choice Dedicated Ground Station + radio modem Logistic problems: Ground station installation and maintenance Technical problems: Actual choice Shift Doppler Loss due to different polarization of the waves Antennas depointing and dimensions High power consumption Orbcomm low cost, reliable solution Satellite constellation for data relay standard communication

11 GPS Previous task Attitude determination Problems High Power consumption (the GPS system should be on for the entire life time) Base dimension to place antennas required too large in order to acquire desired accuracy Actual task Correlate photo with GPS data to post-process the scientific data Refresh position and velocity data of the on board orbital propagator

12 ADCS Attitude determination Previous choice 6 sun sensors 2 accuracy GPS ~0.2 accuracy Must be operative for the whole mission duration Too large antenna aperture required Actual choice 6 sun sensors 2 accuracy Attitude control Previous choice 3 magneto-torquers 1 Momentum wheel 3 axis stabilized satellite High power consumption Costly solution & procurement problems Actual choice 3 magneto-torquers 2 axis stabilized and angular rates below 2 /s

13 Power Previous configuration Bus 24 volt Body mounted solar array using silicon terrestrial solar cells (13% efficiency) Solar array area incompatible with satellite dimensions Pick Power Tracker AGM Ion Lithium, 5 Ah capacity Actual configuration Bus 14 volt solar arrays power output maximization Body mounted solar array using triple junction solar cells About 23% cells efficiency Compatibility with cubic shape 25 W power delivery No Pick Power Tracker due to compatibility with AOCS philosophy SAFT Ion Lithium, 6 Ah capacity Battery Charge Regulator with Charge Profile CCCV developed by

14 CCD color camera CCD features Variable focal length (5-40 mm) lens It requires pitch angular velocity under 2 / s and the roll velocity under 2.5 /s Observed area of 72 x 96 km Maximum resolution of meters with high contrast and meters with medium or low contrast Frame grabber board resolution of 754x480 pixels and able to digitalize the images in real time Image size between 300 Kbyte and 13 Kbyte according to the compression factor

15 Electronics Standard Pc 104 selected for Computer Acquisition (housekeeping and photo) Power management AOCS management Operative system Linux RTAI developed at Software Completely in house developed

16 Project Status (1/2) Launch Dnepr launcher is not yet confirmed Satellite will be ready for launch within the end of 2006 ADCS Sensors and actuators have already been bought and tested Control law is currently in a tuning stage Communication Orbcomm transponder has been bought Communication antennas are under construction (delivery is foreseen at the end of August 2005) Communication philosophy (utilization of Global Gram or Message) is under investigation Electronic & Software All electronic boards have been bought and under test Assembly is foreseen in October 2005 Software requirements have been set Software is under development

17 Project Status (2/2) Power Solar array under construction Bus definition completed Battery charge regulator under design Structural Main structure available Secondary structure (electronic box, battery box) under construction Thermal Passive thermal control subsystem under test in the thermal vacuum chamber facility at AIV activity Foreseen at the end of October 2005

18 Complementary activities (1/3) Set up of laboratory facilities A new thermal vacuum chamber has been designed to test Palamede components

19 Complementary activities (2/3) Technology development Production technologies to manufacture structural components have been assessed

20 Complementary activities (3/3) Practical training Palamede components are used as test specimens for regular laboratory course work Lucky students have unique opportunities (e.g. manufacturing of solar panels at Galileo Avionica)

21 Conclusions Palamede is a useful project for both technical and educational reasons The project involves a wide numbers of students, researchers and industrial partners Palamede is now ~80% completed and it will be the milestone for other missions entirely designed at