Study of New architecture needs for AOCS / Avionics Abstract. Abstract

Transcription

1

2 The ESA "Study f New architecture needs fr AOCS / Avinics" was perfrmed in parallel t the study Attitude estimatin systems, Requirements n sensr suite. Bth studies have the cmmn bjective t derive a develpment plan fr AOCS sensrs and actuatrs. The present study cncentrates n the architectural aspects while the parallel study cncentrates n functinal aspects. The study has fr bjective: T make an inventry and analyse the emerging Technlgies r Units develpments (freseen r currently in prgress) that will be mature within the timeframe, and that will cntribute t evlutin f current Avinics architecture slutins. T thrughly examine and streamline all aspects f satellite develpment experiences, frm initial design phases, unit prcurement phases, t AIT and in flight peratins. This will allw identifying pssibilities fr mre efficient AOCS and Avinics architectures, given the expected benefits frm the abve inventry f emerging develpments, and the trends int new missin requirements. T demnstrate clearly the expected benefits and pssible limitatins f such new architectures slutins. This shall be dne frm a system pint f view in a tp dwn apprach, where the verall ptimisatin, including End t End cst and develpment issues, supersedes lcal ptimisatins at a lwer level. As a final step, t determine the architectural derived requirements applicable t future AOCS units, s as t derive the necessary develpments and updates t be incrprated int the Medium and Lng Term AOCS Sensr and Actuatr Develpment Radmap in preparatin fr the next rund f harmnizatin Emerging Technlgies In the frame f the Eurpean technlgy harmnisatin activities lead by ESA, several dcuments define the freseen evlutin f AOCS and data handling systems. In additin, supprt is prvided by ECSS and CCSDS standards. The main fllwing general technlgy gals are defined: Having at least ne Eurpean ITAR free surce fr all sensrs and actuatrs cmmnly used, Miniaturize units taking benefits fr higher achievable integratin level, increase radiatin hardening with mre usage f custm ASICs and large capacity FPGAs, Standardizatin f interfaces, Develp high prcessing pwer radiatin hardened DSP, Develp high speed serial links, Develp new generatin slid State Memries and high speed lw pwer ADC and DAC. Critical Review f current AOCS/Avinics Architecture Three missins have been selected fr an in depth review: An interplanetary Science institutinal spacecraft: ROSETTA (D), A middle class LEO exprt market spacecraft: THEOS (F) and finally a large LEO institutinal spacecraft: SPOT 5 (F). 2

3 Efficient Architecture Design and Justificatin On Bard Data Management Aspects: N stringent DHS issues have been identified during the critical review. The trend and recmmendatin is t merge DHS and AOCS cmputer, leading t simpler and efficient architectures. The decisin f IO segregatin has t be made functin f the prgram cntext (Need fr adaptatin frm prgram t prgram; gegraphical return cnstraint). The LEON prcessr impses itself as the next prcessr. ITAR issues can be minimized by develpments f Rad Hard ASICs. Cncerning the Data bus, MIL-STD-1553B was a very satisfying slutin but is nw t cstly and cmplex fr new generatin f sensrs. N real replacement is currently available. It is prpsed t keep the same prtcl n tp f a RS485 physical layer (1553-NG) allwing seamless integratin f new units int legacy architectures. Equipments Issues & Imprvements: The trend is tward increasing the autnmy f the sensrs. Autnmus Star tracker enabled lts f simplificatin f the avinics and AOCS; this will be als true with APS Sun sensrs and carse Earth sensrs which will replace simpler but mre cnstraining sensrs (Sensitivity t thermal, straylight ). There is hwever a price t pay which is rbustness. Star tracker rbustness is nt sufficient and shall be imprved with the next generatin (Slar flare, straylight, Mn ). FDIR being still a surce f high cmplexity, MEMS gyrs are expected t be a ptential surce f simplificatin, allwing dedicated lw cst/mass safe mde rate detectin. Wheels are still a majr surce f disturbances sme cncern like the frictin trque stability ( Oil jg ) shall be handled at equipment level by imprving the technlgy. Micr-vibratins are nt expected t be reduced any mre at equipment level (except by a technlgy break like magnetic bearing) and slutins shall be searched at islatin level (active/passive). Prpsed Develpment plan Frm the analysis perfrmed in bth study ( Attitude Estimatin Systems Optimized Requirements n Sensr Suite» and Study f New architecture needs fr AOCS / Avinics ) we can derive the fllwings trends: Standardizatin f slutins and architectures Miniaturizatin f sensrs Perfrmance imprvements. Cncerning sensrs, the trend is tward miniaturisatin f sensrs. We shall hwever distinguish tw types f sensrs: The sensrs which can be dwnsized with lw penalty n the perfrmances (Magnetmeters, Accelermeters, GNSS receivers, Sun sensrs, Earth sensrs ) and the sensrs which cannt due t the limits impsed by physics (Star trackers and gyrmeters). Fr the sensrs which can be miniaturized, the penalty f standard interfaces (1553 bus and unregulated pwer supply) becmes mre and mre dminant leading t select new interfaces. Fr thse types f sensrs, standardizatin f lightweight interfaces is cnsidered a mandatry preliminary step. New generatin 1553 bus has been prpsed as Astrium preferred slutin, minimizing sftware impact, reusing the quality f the well knwn 1553 prtcl fr platfrm cntrl purpses and allwing lw cst minimum ftprint f the HW implementatin. The pwer interface f such sensrs shuld als be redefined having in mind t minimize verall system cst while satisfying necessary interface 3

4 design rules t ensure failure tlerance n redunded avinics and nt nly n single string µsat avinics. Anther trend culd be t grup several functins int the same husing (e.g. MEMS gyrs in STR). This is cnsidered t be a gd idea if the functin f the hsting sensr takes benefit f this cmbinatin. If nt the preferred ptin wuld be t minimize interface verhead as stated previusly and keep the flexibility t chse the mst apprpriate sensr cmbinatin fr a given system design. Amng the sensrs which can be miniaturized, GNSS receivers are the nes which will require mst innvative develpments. First the Galile Eurpean GNSS cnstellatin deplyment will enable new perspectives fr Eurpean space missins and allw achieving new level f accuracies. New level f integratin with the AGGA4 will enable small size highly integrated receiver design and pen the dr t new markets like launchers and GEO missins. Fr the sensrs which cannt be miniaturized further withut lss f perfrmances (Star tracker and gyrmeters) the trend is t minimize the requirements n them (Gyrless r carse gyr AOCS). Star trackers are a special case as they becmes the reference sensr fr any medium t high perfrmance AOCS. The trend is t pursue the imprvement f perfrmances thrugh mre sphisticated algrithms (e.g. autcalibratin), mre integratin f electrnics (fewer parts) and imprve rbustness. Cncerning actuatrs, the trend is mre n perfrmance imprvement: minimizatin f disturbances and higher agility. Cncerning angular mmentum transfer actuatrs (wheels and CMGs) we shall distinguish high agility and medium agility missins. CMG are the actuatr f chice fr high agility missins but may be t cstly fr lw end class f missins where agility is desirable but d nt justify the cst and cmplexity induced by CMG technlgy. Fr these classes f missins (especially mini/µsat range) availability f high trque/high efficiency wheels is desirable. Obviusly this will be at the cst f mass penalty but will keep cst and cmplexity lw. Minimizatin f induced disturbances is the next subject f cncern. Cntinuus imprvement f wheel perfrmances (lwer µvibs and remval f fast variatin f frictin trques) shall therefre be fllwed while efficient methds f cancellatin f residual disturbances shall be develped (passive/active islatin). 4

5 (1) Assuming a Safe mde using Carse earth sensr and carse gyrs (2) Fr FDIR purpse (3) ITAR free Figure 1: Missins needs versus sensrs and actuatrs expected evlutins An attempt has been made t priritize identified develpments, althugh in an ideal wrld we wuld recmmend t develp simultaneusly all identified new equipments! The pririty being given t develpment fr which n current alternative exist: High precisin LEO GNSS receiver (<1m) Carse gyr and accelermeter IMU (MEMS based) Sun sensr n the chip (APS based) Lw Cst Carse Earth Sensr 5