DESIGN OF GROUND SEGMENTS FOR SMALL

Guy Mac_

HATRA NARCONI SPACE I I 31, Rue des Cosmonautes, Z.I. du Palays 31077 Toulouse Cedex - France

ABSTRACT Small missions usually consist of one or two instruments aboard a small New concepts must be implemented when thanks to technology progress. The designing a Ground Segment (GS) for small development time frame and the programme satellites to conform to their specific mission costs are major drivers that will have to be characteristics : low cost, one main instrument, fully considered for the definition of Ground spacecraft autonomy, optimised mission return, Segment development and operations. The etc... This paper presents the key cost drivers main driver to optimise the design while of such ground segments, the main design considering the cost constraints is thus to features and the comparison of various design consider the space system (Figure 1) as a options that can meet the user requirements. whole and to think integrated system.

Key words • Small satellites, Ground Segment, Mission Control, Data Acquisition.

I- Introduction :q

The Ground Segment for control of the spacecraft and for exploitation of their data represent a growing part in the space mission budgets. Therefore it has been considered important by Industry and by such Agencies as ESOC (1) and CNES (2) to review the state of the art for the Ground Segments that support the Small Missions, to understand the possible :{ii!ii':_ degree of optimisations and the cost implications. Figure 1 : Concurrent Engineering for Ground Segment design

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The paper presents the cost drivers to be For a typical observation small mission (Table examined when designing a Ground Segment, 1), the GS design must consider with specific the typical overall Ground Segment design attention all requirements that may impact the characteristics and the main latitudes for number and definition of the Ground Stations optimisation. Finally the emphasis is placed on and the Flight Dynamics functions on-ground. the definition of major Ground Segment In this example, the and Flight elements, the Mission Control System and the Dynamics elements have a sizing costs within • 2 '_ il Ground Stations to highlight where an the Ground Segment costs. i_:_ii;_i_ optimum design can stand. The accuracy of restitution needed for data processing is a characteristic of 2- Mission related cost drivers this mission that directly impacts the flight dynamics processing on-ground. The ground Since the cost constraints must be considered station is a unique S-band station that supports from the beginning, it is necessary to analyse both the Payload and the TM/TC housekeeping where lay the cost drivers for ground segments. data. The other elements have a lower The cost drivers may vary from one mission to importance since either based on reuse of the other, may depend a lot on the category of existing components or based on a limited service proposed by the mission : data for development for a simple mission : for

2 scientists, commercial service for example, the mission planning function is telecommunications. However some general limited due to only one payload instrument trends have been highlighted from examination with no direct interaction with the users who of a number of conventional missions and of require a systematic observation. small missions.

SMALL SATELLITE MISSION Ground Comlns Mission Control GS DEVELOPMENT COST Stations Infrastruct. Flight Mission TFC Other (Most sizing cost driver graded 5) Dynamics Planning :processing functions USERS REQUIREMENTS Mission purpose Permitted mission outage Availability of payload data MISSION REQUIREMENTS Mission Lifetime Satellite Pointing requirement RF Payload constraints SATELLITE DESIGN Orbit control 1 /: iili¸I•_i Attitude control 2 TM/TC interfaces 1 RF design 3 Data rates/response times 4 Number/complex Ops modes Table 1 : Typical Cost Drivers for a small satellite mission (Observation)

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The methodology followed was to identify interfaces definition, data rates and response what are the requirements that can impact the times, RF links characteristics and link budget, :?}/L ¸i:_i_:: Ground Segment Design. In relation with the number and complexity of operations modes

• •>! Users, the following requirements are identified that will have to be handled from the ground. as having a significant impact : the Mission Purpose that defines mainly coverage (image For comparison an observation conventional size, trajectory), resolution and duration of mission is considered : the GS costs are equally :ii!_ i,.. i: :. L • !_ "i•' observation, the permitted mission outage shared between the Ground Stations and expressed in possible interruptions of on-board Comms development, the Mission Planning service or observations, the availability of and the Satellite Control Centre. For such a payload data criterion corresponding to the conventional mission, the main cost drivers delay between the observation on-board and were impacting most elements in a more the time of reception of data at user site. The distributed fashion as shown per Table 2. Mission Analysis then considers these The above elements must be given full requirements and the characteristics of a space consideration, when performing the necessary system to derive such characteristics as the iterations between the Ground Segment design, mission lifetime, the satellite pointing the costs, the operations and satellite definition. requirements or the RF payload constraints (e.g. number of ground stations, RF band The main Ground Segment design selection). From the Mission Analysis a characteristics for a small mission are now Spacecraft design will also impact the Ground highlighted. Segment design with such requirements related to orbit control, attitude control, TM/TC !i . <

Conventional SATELLITE MISSION Ground Comlns Mission Control GS DEVELOPMENT COST Stations Inflastruct. Flight Mission TFC Other (Most sizing cost driver graded 5) Dynamics Planning processing functions i : USERS REQUIREMENTS Mission purpose 3 2 Permitted mission outage 2 1 Availability of payload data 1 1 MISSION REQUIREMENTS Mission Lifetime 1 Satellite Pointing requirement 2 RF Payload constraints 2 !/711_: SATELLITE DESIGN Orbit control 1 Attitude control 2 TM/TC interfaces 1 RF design 3 Data rates/response times 3 Number/complex Ops modes Table 2 : Typical Cost Drivers for a conventional satellite nussion (Observation)

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:U%I / ':_ ?!i _ iii_:!!i¢_!ii_i_ 3- Ground Segment design To design a Ground Segment with building 151, ii :i _ blocks will be more easily achieved if the The Ground Segment design for a small system is built as a distributed system. And mission must be such as to support the overall since cost efficiency for operations is an other mission, but with much emphasis placed on major criteria, the collocation of the Ground costs aspects both for development and for the Segment facilities must be enforced. Therefore

.... , iil typical 3 years mission duration (2 to 5 years a typical Ground Segment design for a small depending on the mission). mission will be based with its components '<; collocated around a Local Area Network A first major trend of the design will be to (Figure 2) : Ground Station, Satellite Control maximise the use of existing components in the System, Night Dynamics, Mission Planning, ground infrastructure : this trend limits the Payload Preprocessing with the capabilities to development costs and the maintenance effort communicate payload data to users either by since the hardware is based on off-the-shelf mail or by communication links. items and the software is flight proven in other programmes. This is why an important design For small missions, the availability effort will be dedicated to the overall requirements can be less stringent than in architecture definition to identify the building conventional missions. No hot redundancy will blocks, to define their interfaces and the be implemented as a rule : as experienced in missing elements, and last but not least to react conventional missions, it is costly since it on requirements whenever it is felt to simplify requires more hardware, automatisms, specific the design while meeting the overall mission procedures adding to the complexity of objectives. operations, documentation, training and maintenance.

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P-JGHT DYNAMIC_ ! SATELU]_ CONTROL PAYLO/_ 8YgTEM 8'I_T_M PRE-PROOE_BINQ

OPERAT_ONg ROOM

Figure 2 : Typical design for a Small Satellite Ground Segment

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The other main features of the GS design for attached to a conventional mission. The Lower ! ,!:i(ii!_ • , small missions are : collocation of facilities, Risk option will mainly differ from the LOw reduced staffing, use of proven off-the-shelf Cost option in the operations concept that will hardware and software, of routine provide a higher security level for operations

i _ operations, compliance to standards (e.g. and a higher mission availability. CCSDS and ESA COES) to enforce further How the Lower Risk option can best meet the commonalties for reuse. Table 3 hereafter i /i_i_i:_,_ overall mission requirements and what are the compares the main features for a Low Cost possible risks attached to a Low Cost option ground segment option, for a Lower risk are given a preliminary answer in the following ground segment option and for the design section.

OPTION OPTION CONVENTIONAL Low Cost Lower Risk MISSION i / MISSION 80-90% : normal > 90% : 7 days/week + > 99.9 % :7 days/week + AVAILABILITY working hours on-call at night 24 Hours/day (+ on-call for w.e.) STAFFING 2 or 3 for all tasks 3 for ops + 6 shift x 2 for ops + part support important part support FACILITIES Con t 1 or 2 sites Several sites DISTRIBUTION STATION Design Standard products, Idem + reuse New development small antennae of a station network MCS Design Reuse existing packages Reuse existing packages New development Minimum adaptations More tailored to ops Many ops requirements Table 3 : Main features for the overall GS Design

4- Ground segment optimisation In the conventional mission example, the Ground Stations costs were important due to the number of The allocation of costs for a Ground Segment must antennae considered and to a 11 meter antenna

r • be carefully considered to select design options that supporting accurate angular measurements. The _i:i_iii_ will maximise a mission return criteria, i.e.. the ground station cost for the small mission was amount & quality of data versus the investment. limited since VHF/UHF data links were considered both for payload messages (less than 20 Kbps) and Typical costs allocations are shown for a for housekeeping TM/TC with no ranging Telecomms conventional mission (Figure 3) and requirements imposed on ground other than iI _:ilI for a Small Mission (Figure 4). The total GS cost processing the on-board GPS transmitted data. • i(ii includes the following costs : Ground Stations & Comms, Mission Control System, Prelaunch With these characteristics a significant cost of the operations (Flight procedures preparation, MCS small mission Ground Segment corresponds to the definition and validation, ground and operations costs. Therefore it is important to flight operations validation and rehearsals) and a analyse how these costs can be reduced and how normalised period of 3 years operations. this reduction can impact the GS availability and the risks for operations.

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_ii,i'i/!i__ ._:i GS & Operations costs

(3 yea's) 23% Crou-d slogans& Cam-s L; Pre_Ol:S 43% 11%

?i Msslon Card 23%

Figure 3 : Cost break-down for a Telecomms Conventional mission

Telecomrns : Lowcost option

9 Ops (3 years) @round Slalions 49% & Corrms

sion 9_11rol

PrelaLr_ch ops 29% 13%

• _ _ii__ Figure 4 : Cost break-down for a Telecomms Small mission

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:i i _i_i Figure 5 below presents a typical example of a the design is different when the staff is GS availability as a function of the GS total available day and night, including week-ends to i _ cost for typical GS options with different react to any ground failure detected with spare design, maintenance and staffing orientations. equipment available for ground equipment.

" i_i_ '_ The availability was computed using i/! iiii! i equipment failure rates and mean time to repair The Low Cost option is interesting since it as checked during several years of operations presents a substantial cost advantage of about and the time for intervention considered for 3 MAU with respect to the other options and a exploitation. The main difference between higher mission return per cost unit (defined as options availability characteristics proceeds the amount of data a user can expect over the from this time for intervention, i.e. time spent mission duration, and therefore proportional to ii between the occurrence of a failure and the the GS availability figure). From the user staff performing failure detection, investigation perspective the mission return is 2% lower but and replacement of the faulty equipment. With the sensibility of theses availability figures and today's GS equipment high reliability figures, it their statistical meaning show that this will is the exploitation characteristics that mainly have little effect on the user satisfaction wrt the drive the GS availability. amount of data acquired over the 3 years. Therefore the 24 Hour Manning Low cost _L In the Low Cost option, staff is only available option does not bring a significant advantage to during working hours. In the other option (Low be considered. cost/24 Hours, ESOC reuse, Low risk) only

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100 Low cost/24 H n-ar_ng • ESOC r_use

99,5

A a_ _9 Low risk

i ¸•• i N _ill ii _ Low cost

97.5

96,5

95,5

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Figure 5 : Staffing & Maintenance impact on GS availability and cost

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ii _ _:_ i)/_ An alternative could be to change some The beginning of spacecraft lifetime would H characteristics so that the mission return be lead to less data availability, what could be much lower at a significant saving. From the accepted since a first period is often considered cost drivers analysis this orientation would for calibration and with full support of the bring a minor cost saving with a substantial spacecraft engineering team. However it is degradation of mission return and a higher risk: slrongly recommended to keep the sinmlator

'::i / _ iiI for example operators only working upon even in a low cost option, since the foreseen automatic anomaly detection could be felt more benefit for operations security is important risky without a significant advantage. with regards to the cost of such a recurring _!_i)_i_ i_! product which represents less than 3 % of the This is why it is of the utmost importance to ;iii'ii i: total mission cost. appreciate the risks induced by the Low cost approach in comparison with the more Each of the GS components are further conventional approaches. The following examined with emphasis on the major design elements contribute to the risk specific to the options. Low Cost option and not supported by the other options :

_!iili: il 5- Mission Control System - The whole expertise (spacecraft and ground) is supported by a 3 engineers staff coming The Mission Control System (MCS) is from the spacecraft development team. In the composed of the following functions : TM/TC other options an operations support function with real time control and satellite infrastructure is identified that support performance analysis, flight dynamics and _i+ i_ _ spacecraft contingency analysis or such mission planning. The main outcome for small expertise domains as flight dynamics, or nfissions will be the reuse of existing software ground equipment maintenance. The difficulty packages. Most packages are running now on consists in the level of skills required from this Unix workstations and the integration can be 3 engineers team and whether they can limited when only exchanging few data files. efficiently support contingency cases. The typical spacecraft autonomy of 1 week, the on- An important trend to reach additional cost board securities and the expertise gained by the saving for small missions, will be to consider staff during spacecraft development should all Ground Systems needed in a programme : compensate most of the risk. with reuse of existing EGSE and MCS - The simulator is not foreseen in the low cost building blocks, it is now envisaged to build a option and limited testing will be performed "Universal Test Bench" that can be used in all with the spacecraft (or its engineering model) stages of the satellite development and on ground. A number of operations will not operations. have been tested prior to launch : this could be accepted if the spacecraft is safe, robust to Figures hereafter (Figures 6 to 8) examine the ground errors and that a number of spacecraft relative development costs for observation specialists are available at the beginning of life missions : a Conventional mission, a Sea so that operations imperfections be detected Altimeter small satellite mission and a quickly and correct procedures be validated. Cartographic small satellite nfission.

832 iii:ii _ _ ii_; _-_ Ground S egment Development costs

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F llght Management Mlssion Dynamics & Integra_on planning 3% 1 2% 25% Ground

Caroms statlons24% (2)& _! ; i:::, ii ¸¸

MCS :T M/T C 36%

Figure 6 : MCS costs for a conventional mission (Observation)

G,,_ Development for Small Sea Altimeter satellite

Mar-ogt & Ir'rlegrall on

F IlglYr Dynamics li%

Msslon PlanrV

3%M£3 :T M/IC Slalon45%&COTrT_ 12% i, if?: _v: •

Figure 7 : MCS costs for a Sea Altimeter small mission

GS Development for Small Earth Observatlon satellite

F light Dynamics Managt & i1% Integration /i i _:iI Mission 28% Planning __

M CS I:T%M/T C 1_i_li_ Stafion & Comms 36% i

Figure 8 : MCS costs for a cartographic small mission

/ 833 housekeeping operations. The choice of the The above examples show that with this frequency (X band, S band or lower strategy of reuse with minimum adaptations, band such as UHF) and the mission orbit the amount of the Mission Control System in characteristics will then make the price of the the overall development costs is lower than for antenna. A common characteristic of many conventional missions. Depending on the small missions is that only one antenna system ground station characteristics, the MCS can is used for communications of both payload weight 36% to 44% of the Ground Segment and housekeeping data of the satellite platform. development cost. The RF equipment and equipment 6- Ground stations and Communications are then to be considered in the cost but they are usually off-the-shelf equipment with high The Ground Stations and the ground reliability figures : the Monitoring & Control Communications part of a Ground Segment is equipment can limit itself to the set-up of usually a sizing ratio of the total development equipment configuration and to support cost. Therefore special attention must be investigation and no longer as a procedure granted to the characteristics that contribute to driven system to act on the redundancies and the costs (Table 4). switches. In addition, for a low cost solution, a new range of VSAT equipment is available at The Antenna itself in the ground station can be a lower cost with possibly lower reliability the sizing cost element when high performances that can be adequate for small performances are required from the specified missions. As for other elements of the Ground bandwidth and data rates. This is why a Segment, a major contributor to costs, as ground and board optimisation must take place experienced in passed conventional to review the data rates with respect to user programmes, is the development of specific requirements, to review then the budget link equipment or of new technology when off-the- requirements, to retain only one system of shelf equipment exists. communications both for payload and

COST DRIVERS SMALL MISSION CONVENTIONAL OFF-TIlE-SHELF Systematic cost of technology changes EQUIPMENT ANTENNA & RF Only 1 station Network of stations for payload and data Sizing costs RANGING Use of GPS Can be costly on _round Interface with existing network LEOP Transportable Trc station Specific requirements S/C autonomy wrt LEOP COMMUNICATIONS Collocation on LAN as baseline Usually low relative costs Files transfer at low data rates Table 4 : Cost drivers for Ground Stations and Communications

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7- Conclusion An other important cost item can be related to 15! . _ , the requirements imposed on ground to Small missions constraints enforce a new perform the ranging. In conventional missions approach for development of both the satellite these requirements imposed range equipment in and its associated ground systems. With due the station, or large antenna with complex consideration to existing technology and ::: 2!.:'/. mechanics for accurate angular measurements. products, the project team must review in an For small missions these requirements are iterative way the requirements, design and alleviated either by lower performance costs implications on both the satellite and the requirements on orbit determination or by the ground systems for satellite testing and for availability on-board of GPS or other operations. This new approach can be equipment that provide orbit measurements. summarised as the Integrated System i?" • Approach relying on a new ground system Finally communications can be achieved more means, the "Universal Test Bench" which simply than in conventional missions with building blocks will be used according to relaxed requirements for data timeliness that satellite development and operations stages. :ii ' i?: defines the time spent to provide the user with ? data. Depending on missions, simple mail ACKNOWLEDGEMENTS ili?/ii _ procedures can be accepted or an electronic file Mr. Van der Ha (ESOC), Mr. Oberto (MMS) transmission system using standard networks i/' (e.g. INTERNET or other national or REFERENCES international networks) can be used. To (1) Small Satellite for Ground Segment and decrease the communications costs, one Operations : ESOC study conducted in 1993- solution if feasible may consist of having users 1994 under Mr. J. Van der Ha's responsibility collocated at Ground Segment site and (2) Ellips study : CNES study conducted in receiving their data on the LAN. The 1994 communications analysis can impact the place • ? _i: where the data demultiplexing can be performed : either at Station or at Control Ground System level.

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