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Paper ID : 1b001
TTC NETWORK COSTING AND OPTIMISATION FOR
LEO MISSION OPERATIONS
P Ramalingam, P Soma, O Chiranjeevi and S Rangarajan Peenya Industrial Estate, Bangalore-560058, India ABSTRACT
ISRO Telemetry Tracking and Command Network (ISTRAC) has established an integratednetwork of S-band TTC stations to support both launch vehicle and satellite missions. The costsinvolved in establishing these stations and operating them are significant. ISTRAC has workedout an approach for costing of TTC services which considers the costs of all relevant elements ofthe network. This, however, does not include non performing elements. The detailed costs areworked out based on capital investments, fixed costs and variable costs taking into accountdepreciation and arriving at a cost function. A study was made to arrive at cost effective TTCnetwork configuration for supporting ISRO’s LEO/IRS missions upto 2002. ISTRAC will besupporting 10 spacecraft missions simultaneously in this time frame. Based on the requirementsfor nominal and contingency support as well as global payload operational needs, the networkconfiguration should be optimised for minimum cost of operations. This paper presents detailsof the costing methodology and analysis in arriving at the cost effective TTC network for IRSmission support in normal phase.
1. INTRODUCTION
The concept of cost forms an integral part of any meaningful economic analysis. Spaceactivities are essentially high technology, capital intensive and high risk demanding allocation oflarge chunk of national revenue. Besides scientific research, the space technology has by nowcome to offer innumerable benefits to mankind in a variety of fields. Benefits of space technologymust reach not only to nations or consortiums who directly participate in space activities , butalso who are unable to participate in it at the moment. It certainly makes sense to space powers toensure a reasonable return on their high investments. Hence it is a necessary requirement thatspace based services are operated as cost-centers with a comprehensive database on costs.
ISRO has been operating so far remote sensing satellites since 1988 beginning with the firstoperational Indian Remote Sensing Satellite IRS-1A. So far ISRO has launched six remotesensing satellites, the latest one being IRS-1D with the state of art remote sensing payloads. ISROTelemetry Tracking and Command Network (ISTRAC) is responsible for the TTC operations andMission control.
Paper ID : 1b001
ISTRAC has established a network of S-band TTC stations at Bangalore, Lucknow, Mauritiusand Bearslake to support the TTC requirements of IRS satellites. The costs involved inestablishing these TTC stations are significant.
Considering the satellite support profile upto 2002 (Table 1), a study was made to arrive at asuitable TTC network configuration that will provide cost effective support in the multi-missionenvironment. The choice of the network is based on the health monitoring requirements fornominal and contingency support including payload operation requirements for national andinternational users. Optimisation of support schedule and costing of services are some of theimportant aspects considered. This paper provides details of the study with specific emphasis oncosting.
2. TTC NETWORK FOR LEO MISSIONS
TTC and Mission Control of LEO Satellite operations can be distinctly divided into two phases Launch and early orbit phase support needs extensive monitoring of spacecraft health and alsocommand support to carry out critical operations such as solar panel deployment, three axisacquisition, orbit corrections, qualification of all subsystems, payload operationalisation etc.
These activities demand TTC station visibilities and support during all orbits in a day, to meet theoperational requirements. This type of support is a one time peak requirement during any satellitemission.
Normal phase spacecraft operations require ground station visibilities for spacecraft healthmonitoring and command operations such as payload operations programming, orbit correctionand also to support other day-to-day sub-system maintenance requirements. While it is preferableto monitor the health of the satellite once in every revolution, in order to recover the satellite fromany anomaly, nominal health monitoring requirements are worked out for each of the satellitesbased on the following considerations : · Satellite reliability and on orbit performance · Built-in onboard redundancy and automatic switch over in case of any failure · Onboard built in safety logics, which when activated keep the satellite in power safe · Onboard health data storage capacity for analysing and resolving the anomalies · Payload operation requirements and the memory available onboard for storing · Orbit determination and orbit correction requirements IRS spacecraft, by design, have provision to store onboard health data for 1 orbit duration insome spacecraft (IRS-1A, 1B) and 4 orbits for others (IRS P2, P3, 1C). All IRS satellites havebuilt-in safe mode logic, which when activated keep the spacecraft in power safe mode in case ofattitude loss. Built-in provision to switch over to redundant system in case of failure detection in Paper ID : 1b001
the main system exists in IRS-P2, P3 and 1C as a standard feature. These features have beenincorporated for keeping the spacecraft ‘safe’ during non-visible periods in an orbit and alsowhen the spacecraft is left unattended continuously over some orbits (3 to 4) due to visibility gapsin the chosen network. Hence, normal phase TTC support is planned on the basis of spacecraftconfiguration constraints, safety logics built into the spacecraft, orbit maintenance activities,payload operations plan etc. Table-1 and Table-2 provide the details of IRS satellites to besupported up to 2002 and TTC Network support requirements worked out for different satellites.
TABLE-1: IRS Satellite missions up to 2002 A.D
Spacecraft
Altitude
Repetivity
TABLE-2: TTC Network support requirement for satellite Operation
Network support
Satellites
requirement
For optimising TTC Network for IRS Satellite missions, all ISTRAC stations and stations ofexternal agencies such as ESA, DLR, CNES, NASA/NOAA were included in the study.
3. COSTING OF SUPPORT SERVICES - METHODOLOGY
In a complex facility like a TTC Station , all costs cannot be distinctly identified as either fixedcost or variable cost. For example it would be difficult to identify the exact percentage ofdepreciation charges to be allocated to variable costs. However the distinction is of great value inpricing decisions and break-even analysis. Precisely for this reason that all costs have beenclassified as either fixed or variable. The different elements of fixed and variable costs per annumfor a typical TTC Station are given in Tables 3 and 4.
Paper ID : 1b001
Table 3: Expected Life and Depreciation for elements of a typical TTC Facility
Facility Costs
% of Total
Expected
Facility Cost
Equipment(Mechanical &E-M)Replacement & The total fixed cost is the sum of depreciation , one time costs amortized over life time ,recurrent Replacement and Developmental costs and Capital cost of investment. The depreciationis computed based on the historical costs of different elements of TTC facility. The historicalcosts have been arrived at after normalizing the cost of all imports to constant January 1998US$ prices and all indigenous elements to January 1998 WPI. General Price Level Accountingis done by periodically computing the costs using GNP implicit price deflator or the inflationindices published by accredited agencies. NASA HQ inflation indices for US $ and WholesalePrice Index of Ministry of Finance , Government of India for Indian Rupee have been used asprice deflators.
The total variable cost is the sum of the cost of consumables and spares, energy andcommunication charges , manpower cost etc which are listed in Table 4.
Table 4: Elements of variable costs
Variable Costs
Cost Units
% of Total variable cost
Paper ID : 1b001
3.1 EVOLUTION OF COST FUNCTION:
The basic cost function is of the form T = F + V V is the variable annual cost of operations The basic assumptions for the cost function are: § consumables and spares are assumed for a peak activity level of 75% and hence the cost function is liable to vary if any higher levels of activity are contemplated.
§ costs worked out are for constant INR 1998.
§ all equipment costs including redundant ones are accounted for meeting performance § manpower deployment is exclusively for shift operations For evolving the cost function , three different scenarios are considered. They are the number ofshifts of operation per day as the cost functions basically hinge on the facility operation andmanpower deployment thereon. The problem boils down to formation of three linear costfunctions representing the scenarios.
where a is the fixed cost per day and b and H are variable cost per hour and hours of operation From the above , daily cost functions for the three scenarios are deduced as under: § 108.2 + 1.91h (upto 8 hours of operation per day) § 108.2 + 2.07h (from 9 hours to 16 hours of operation per day) and § 108.2 + 2.52h ( from 17 hours to 24 hours of operation per day) With the aid of regression techniques, the following envelope function which is a third orderpolynomial is obtained:Tc =107.32+ 3.06h -0.099h2 + 0.0022h3 where h varies from 1 to 24( The constants appearing in the above equations are monetary units )The average cost function Ac is given by Tc/H , The marginal cost function Mc is given by the equation Paper ID : 1b001
When Ac and Mc are plotted over a 24-hour scale (Fig. 1) , we find that they are asymptoticindicating very high fixed costs. It helps us in concluding that the point where the Ac-Mc gap isthe least , will be the most ideal situation.
COST CU RVES
COST UNITS
HOURS OF OPERATION
Figure 1 COST CURVES
4. TTC NETWORK OPTIMISATION
Radio visibility analysis was carried out for different TTC network stations considered forNetwork optimisation. Table-5 provides the visibility time bounds for descending and ascendinggroups of passes for IRS satellites from the selected TTC stations. Visibilities were generated forall the ground stations for one cycle.
TABLE-5: Visibility time bounds (UT) for Ground Stations
S/c considered : IRS-1B, 1C, P2, P3, P4, 1D, P5, P6, IRS-2A Descending
Ascending
Ground Station
Start End
Start End
Paper ID : 1b001
Optimum network configuration is arrived at by analysing i) Satellite visibility from atleast one TTC station in the network in every orbit for healthmonitoring.
ii) Visibility gap not exceeding one orbit over a day with the selected TTC network.
Even though a single station at a latitude above 78O provides radio visibility in all orbits over aday, a network of stations is considered to fulfil the mission operations requirements. Table-6provides the combinations of TTC stations and corresponding visibility gaps over a typical24-day cycle.
TABLE-6: Visibility Gaps for TTC Network Combinations
Considered
A second level analysis was carried out by simulating scenarios for different TTC networkconfigurations using Multi-satellite Scheduling Software (MSS) developed by ISRO. On theanalysis of results, a set of TTC network combinations were found to meet the requirementsstipulated. Using costing methodology as described in section-3, the cost effectivecombinations are chosen.
5. CONCLUSION
ISTRAC has evolved an approach for costing of TTC stations and control centre elements.
Based on the ISRO profile for LEO spacecraft operations until 2002, a cost effective TTCnetwork configuration for supporting 10 spacecrafts is worked out. This network comprises ofthe TTC stations at Bangalore, Lucknow, Mauritius, Bearslake and Biak.

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