2. Work Breakdown Structure

2.1 Developing Organizations

The responsibilities of various organizations involved in Payload implementation are shown in Figure 24.

Figure 24. Organizational responsibilities for S-U Payload implementation.

JPL has the overall responsibility for managing development and integration of the Payload. JPL also has the responsibility for developing the Canister, the Canister Mechanisms, and the Collector Arrays. Los Alamos National Laboratory (LANL) has the responsibility to develop the Concentrator and the Monitors. Johnson Space Center (JSC) has the responsibility for providing overall guidance on contamination control. JSC will provide facilities and combine with JPL to implement final clean assembly of the flight Canister prior to shipping to Lockheed Martin Astronautics (LMA) for integration with the spacecraft, and for disassembly of the recovered Payload.

The JPL activity will be carried out by the Mechanical Engineering Section of the Mechanical Systems Engineering and Research Division, which is the same organization that has implemented many flight hardware systems including Cassini, Galileo, Voyager and many flight instruments.

The solar wind Monitors and Concentrator are being developed by the Space and Atmospheric Sciences Group at the Los Alamos National Laboratory (LANL), with collaboration from scientists at JPL, Caltech, and the Southwest Research Institute (SWRI). This Space Plasma Team has been developing, operating, and analyzing data from space plasma instruments for over 30 years and has developed over 50 space plasma Monitoring instruments for various agencies.

The S-U cleanliness requirements are equally stringent before launch and after recovery of solar wind samples. JSC, the designated NASA Center for curation of extraterrestrial materials, was selected to partner with JPL for final cleaning and assembly, and eventual disassembly of the Payload. The facilities developed under the S-U Program will remain as a national resource for future sample return missions.

2.2 Work Breakdown Structure (WBS)

The product-oriented WBS for the Payload is shown to level 4 in Figure 25. There are six major elements of the Payload WBS. Management and System Engineering (41000), residing at JPL, is provided to assure that requirements, plans, reviews and overall cognizance of the work is administered through one office. Nevertheless, development of the Payload is being carried out by a partnership, and each participating institution will carry out its assigned responsibilities according to its own institutional policies and procedures. JPL Payload elements (42000) include all the activities necessary to develop the Canister, collector arrays and mechanisms. The LANL Payload elements (43000) include a small management effort plus development of the Concentrator and Monitors. Payload integration and test (44000) is accomplished by JPL. WBS element (45000) is provided for auxiliary handling and support equipment, ground support equipment, and shipping. Final cleaning and assembly of the flight Canister will be done at JSC by a combined partnership of JPL and JSC (46000).

A more detailed WBS and a WBS Dictionary are provided at the end of Part 7 of the PIP.

Figure 25. Payload Work Breakdown Structure

3. Implementation Approach

3.1 Development Test Program

The Payload schedule is dictated by the need to conform to the overall project schedule as delineated in the LMA Spacecraft and Sample Return Capsule development plan. An overview of this plan is provided in the colored insert that follows this page.

The four key dates in the S/C and SRC plan which affect the Payload are:

Receive Payload Mass Simulator Wed 5/8/96

Receive JPL Payload STM Fri 4/18/97

Receive P/L Engineering Model Mon 6/2/97

Receive P/L Flight Hardware Tue 11/10/98

These dates were taken as constraints for the Implementation Plan for the Payload. The Payload Implementation Plan was designed principally to meet these requirements.

As in the case of the LMA Spacecraft and Sample Return Capsule, technical risks associated with the fabrication, assembly and testing of the flight S-U Payload will be substantially reduced by the planned development test program. A number of Payload development models of increasing sophistication will be built and tested, commensurate with the development models and schedule of LMA's Spacecraft and Sample Return Capsule Implementation Plan.

The development program for the Canister is illustrated in the flow chart of Figure 26. This chart depicts the assembly of the various Canister models, the design verification testing that is performed and the flow to higher levels of integration and test. The development plan for the Concentrator is shown in Figure 27 and the development plan for the Monitors is shown in Figure 28. The development plan minimizes cost and risk, provides adequate Payload test models to the higher levels of integration, and yields a completely flight representative ("form, fit and function") Engineering Model Payload to be retained on Earth after the flight model is launched.


Figure 26. Development plan for Canister models. (CG = center of mass, EM = engineering model)


Figure 27. Development plan for Concentrator


Figure 28. Development plan for the Monitors.

3.1.1 Payload Development Models

Mass and CG Emulators

Early fabrication and testing of an Engineering Development Unit (EDU) Spacecraft and Sample Return Capsule is planned by LMA. This EDU will allow LMA to obtain interface dynamic loads predictions for launch and reentry. These predictions will ultimately result in the dynamic loads requirements for environmental testing of the Payload. For these tests, JPL will provide a Mass and CG Model with a flight-representative mounting interface to obtain the required interface dynamics loads. This Model is planned to be a large aluminum toroid with the proper mounting interface and which emulates the calculated mass properties of the Payload. Mass and CG Models of the Monitors will consist of simple structures with the same mass, shape and CG as the Flight models. Foot prints, cable connections, and thermal blanket designs and attachments will also be verified.

Canister Structural-Thermal Model

More design fidelity is required for the next phase of testing at LMA, which is the "flight system" Structural/Thermal Model. The system-level testing performed with this Model will validate the design for the dynamics and solar-thermal vacuum environments. This STM Canister will be representative of the mass properties and overall stiffness of the flight unit by the inclusion of an assembled Sample Canister with the EM Array Assemblies (including launch support hardware), and mass mockup mechanisms and a Concentrator mass and cg emulator. The EM Array Assemblies must be included in the STM in order to get a high fidelity representation of the solar wind collector arrays, which must satisfy a critical temperature requirement. After system-level dynamic testing at LMA, the Payload STM is returned to JPL and the Canister structure is refurbished as the flight unit.

Although a single delivery of an EM Canister would be preferred, the need for an early Phase C delivery of the Canister Model for inclusion in the "flight system" Structural/Thermal Model left only a marginal amount of schedule time for development of the Payload mechanisms. It was decided that a more robust program would result if additional schedule time could be allocated for mechanism development. Therefore, a Canister Structural/Thermal Model (STM) which does not contain workable mechanisms, will be delivered earlier than the Canister Engineering Model (EM), which will be fully mechanized.

Because instrument thermal dynamics and target temperature are crucial to the operation and success of the Concentrator, a physical thermal model will be developed to validate the thermal model. Testing of this Structural/Thermal model will also verify that the step structure of the solid electrode will not allow concentration of solar irradiance on the target. Thermal modeling of the Monitors is well understood and straightforward, and therefore a computer model should be sufficient for this purpose. The Structural/Thermal model Concentrator is delivered to JPL for testing with the EM Canister.

Canister Engineering Model

The solar-thermal vacuum testing performed at LMA will utilize the same S/C and SRC hardware that was used in the dynamics testing. For this purpose, a Canister that merely simulates the thermal load of the electrical boxes and motors would be adequate. However, a full EM Canister is desired for these tests in order to preclude unnecessary and expensive chamber breaks (to reconfigure the Canister and Arrays). It is also of primary importance that the Canister be functionally tested in a relevant environment. Since the rather costly solar-thermal vacuum testing has to be done at the system level, it was felt that performing the same tests at JPL prior to delivery was a duplication of effort and would require the unnecessary expense of building SRC and S/C thermal simulators at JPL in order to provide a relevant test. Therefore, the EM Canister is environmentally tested to qualification levels of the dynamics and thermal vacuum requirements at JPL, and all functional deployments are verified. Although functional testing in the relevant environment of solar-thermal vacuum is deferred until the Canister is mounted in the SRC at LMA, the risk is believed to be minimal with respect to the mechanisms and deployments. Substantial cost and schedule savings are realized by this approach. Subsequent to the system-level STM testing at LMA, the EM Canister will be integrated into a fully capable Electrical Engineering Model S/C and SRC test article. All subsystems including the Canister will be tested end-to-end.

In Phase A, a prototype Array Assembly was fabricated for dynamics testing early in Phase B when the dynamics load requirements are more fully understood. In the specific case of the Arrays, deferring solar-thermal vacuum testing is perceived to have some risk, and so this environmental testing is planned to be performed early in Phase B. After completion of environmental testing at the Array level of assembly, the Arrays are integrated into the full EM Canister for qualification (design verification) testing at JPL prior to delivery to LMA. The delivery schedule incorporates a slack of three months after the planned tests to allow rework and retest if problems occur.

It should also be pointed out that another function performed by these Engineering Models is to enhance development of assembly and cleaning procedures at JSC. Both an EM Array and the EM Canister are delivered to JSC at appropriate times in the schedule to allow the JSC Facility to "pre-run" flight-representative Canister articles through the flight operations procedures such as disassembly, cleaning and verification, assembly and functional flight acceptance testing. This work will be done early enough in the program to allow further development of Canister handling fixtures or facility modifications, if necessary.

Monitors and Concentrator

The electrical models of the Monitors will be integrated with the Spacecraft for EEM testing at LMA. Commands, telemetry, ground test systems, and the DPU hardware and software will be checked and verified.

In addition, the Monitors and Concentrator will be tested at LANL to verify their functionality and viability. This will include:

3.2 Flight Model Integration and Test

The flow chart of Figure 29 depicts the Canister flight verification program. A significant difference from the development test program is that the Canister is not delivered directly to LMA, but must be delivered to JSC for final cleaning and flight acceptance testing. After final cleaning at JSC, the Canister must not be opened before on-orbit flight operations. This contamination sensitivity is a major design challenge to allow adequate verifications at the S/C level to minimize risk and yet retain a closed Canister.

Figure 29. Canister flight verification program.

The method used to accomplish this requirement is to provide ground support clamps (brightly red-anodized and obvious to operations personnel) that retain the Canister Cover in the closed and sealed position. The Array Latch can be exercised and its proper function verified by electrical telemetry as well as visual inspection. With the Array Latch in the "unlatched" position, each Array can be rotated within the Canister a small angle, and electrical telemetry will verify that this has occurred.

With the Canister Cover sealed closed by means of the ground support clamps, and the Cover disconnected from the mechanism linkage, both the Locking Ring and the Cover Mechanism can be articulated, resulting in both electrical telemetry and visual indications. Return to the stowed and launch position will be verified by proper electrical telemetry and post-test visual inspections. This verification procedure will be performed after flight acceptance thermal vacuum testing of the Canister at JPL, in which full functional deployments will be exercised. This verification procedure is also performed at JSC under ambient conditions prior to delivery of the Canister to LMA Assembly, Test and Launch Operations.

The flight verification program flowchart indicates that the flight Concentrator is returned to LANL after Canister flight acceptance testing at JPL. The reason for this is that true functional testing of the Concentrator (which requires an ion beam in a high vacuum system) cannot be performed at JPL or JSC. Therefore, after Canister environmental testing, the Concentrator is disassembled, final-gold coated and then final-cleaned at LANL. After final acceptance testing at LANL, the cleaned Concentrator is delivered to JSC, where only contamination assays are performed to verify adequate cleanliness.

3.3 Contamination Control

It is of great importance that the solar wind collectors be as pure and as free from contamination as possible. Contamination control for S-U begins very early in the design process and involves mission design, spacecraft, SRC and Canister materials selection and design, collector material selection and design, materials handling and fabrication, final cleaning and assembly, and transportation and storage.

To assure that the science requirements can be met, a Contamination Control Plan was written to provide a strategy for controlling the purity of collector materials and a cohesive contamination control strategy within the scope of the Mission Implementation Plan. JPL is responsible for implementing portions of the Contamination Control Plan involving design, fabrication, and testing of the Sample Canister, including mechanisms. JSC is responsible for providing the required facilities for the cleaning, assembly, function testing and disassembly of the Sample Canister, and the cleaning, allocation, and curation of the collector materials. LMA will coordinate the choice of S/C and SRC materials and the timing of S/C operations with the PI, JSC, and other team members to minimize the possibility that outgassed effluents will contaminate collector materials. LANL is responsible for cleaning the Concentrator.

The basic strategy used for contamination control in the Suess-Urey Payload is summarized below:

(i) Use ultra-pure collector materials to minimize impurities.

(ii) Analyze ultra-pure collector materials to assure that background levels of impurities do not exceed requirements.

(iii) Mount collectors in a Sample Canister which isolates the collectors from the spacecraft and Sample Return Capsule, providing a very clean environment for ground handling and transport to and from halo orbit at L1.

(iv) Control materials used in the interior of the Sample Canister to minimize outgassing from within.

(v) While on the ground, maintain a positive pressure of a neutral gas in the Sample Canister so there is no leakage into the Canister.

(vi) During ascent, allow the gas stored in the Canister to vent, and during reentry, refill it with filtered air.

(vii) When solar wind collector arrays are deployed at L1 halo orbit, minimize deposition of contaminants by

(viii) Close up and seal the Sample Canister prior to return from L1.

3.4 Post-Recovery Hardware Analysis

The S-U project provides a new and unique opportunity to retrieve, inspect and evaluate flight hardware exposed for 3 years to the space environoment outside the Earth's magnetosphere. There will be a sharp demarcation between surfaces exposed in the sunward and anti-sunward directions. Whereas the effects observed on the Large Duration Exposure Facility were dominated by exposure to atomic oxygen in low Earth orbit, S-U will provide materials exposure in a very different environment. Materials used on the Canister include paints, metal surface treatments, fluorocarbon seals, and lubricants. In addition to space effects on materials, S-U offers the opportunity to examine specialized hardware exposed to the space environment. This includes a variety of flight mechanisms, and the Concentrator, a flight instrument. In particular, the Collector Array Deployment Mechanism, which is expected to actuate several hundred times in space, affords a unique opportunity to inspect the active surfaces of bearings and rotary seals which have been operated in space. Return of the Concentrator offers the opportunity to not only inspect, but also to retest and recalibrate an electro-optical instrument exposed to space. This would enable demonstration of the calibration history of a flight instrument before and after the mission.

Retest and recalibration of the Concentrator is planned and costed as a post-recovery activity. However, the materials and mechanisms studies described here are not planned and costed in the S-U project. It is expected that upon recovery in 2002, the materials science disciplines within NASA will plan such activities and pursue separate funding, probably through NASA Code X.

4. Resource Requirements and Constraints

4.1 Mass and Power Allocations

Table 2 describes a history of the estimated mass of the Payload from the original values estimated in the proposal, throughout the progressive design in Phase A. The total mass estimated has not varied by more than 10% throughout Phase A, and the overall mass of the Canister has not varied by more than 13% over the entire duration from proposal preparation through Phase A. The in-depth technical design work has resulted in a significant number of changes in the estimated masses of components that make up the Payload. This is viewed as providing a healthy understanding of the true mass picture and it is considered to be a credible, fairly accurate estimate. As can be seen by inspection of the detailed components in the table, the Phase A effort has identified new mass items and a fairly significant rearranging of the magnitudes of mass items identified early in the design. Since several of the conventional methods for solving mass problems are not available to S-U, such as fabricating major components out of composite materials (contamination concerns for the Canister and Arrays), a concerted effort was made to ensure that all elements were included and that the estimates were realistic or conservative.

The mass estimate is divided into two parts because of the nature of the Payload. The Monitors reside on the Spacecraft, where the mass allocation is set by the usual overall limits on the launch vehicle to carry the entire Spacecraft, Sample Return Capsule and Payload. The mass allocation set by LMA for the Science Canister Assembly, including the Concentrator and high voltage power supply (HVPS), is 52 kg. The current best estimate results in a mass margin of slightly over 21%. The mass allocation set by LMA for the Monitors is 6.8 kg, which results in a mass margin of almost 55%.

The current power requirements for the Payload Concentrator HVPS and Monitors are unchanged from the Proposal, which were 8.5 watts and 6.0 watts respectively. In Phase A, no power allocations for the Canister mechanisms have been defined by LMA. The reason for this is that the mechanisms are short duration loads and that the current power margin for the Spacecraft is estimated as a comfortable ~67%. The S-U spacecraft solar arrays, consisting of heritage-design solar cells, are easily sized for a large power margin because of the relatively comfortable mass margin for the S/C. Again, S-U is being configured using a robust, conservative design approach to reduce potential future risk. Power summaries and allocations will be updated during Phase B as the formal Interface Control Documentation is released.

Table 2. S-U Canister Mass Estimate (kg)
Canister Mass Element
Proposal
Phase A:
Phase A:
Phase A:
Initial
Interim
Final
Can Cover
6.2
5
5
5.1
Array Latch Mechanism, Cover side (new)
0.8
1.1
1.1
0.9
Array Assy, Fixed
2.2
2.5
1.8
1.9
Canister
11.2
10.2
10.3
7.2
Canister Seal Assembly incl
0.3
0.4
0.6
Fixed Saddle
0.2
0.2
0.25
0.3
Array Latch Mechanism, Can side (new)
1.2
Array Assy, 4 deployables Total
8.6
10
8
8.5
Array Deployment Mechanism
5.1
5.5
4.5
4.5
Cover Mechanism incl linkage
2
2.2
2.7
2.8
Locking Ring
1.1
2.6
2.6
3
Locking Ring drive mechanism
0.8
1
0.3
0.3
Connector Brackets
0.2
0.2
0.2
0
Cabling & connectors
0.2
0.2
0.2
0.4
Array Deploy Mech Drive Electronics (new)
0.9
Concentrator
1.5
3.5
2
4.4
Concentrator HVPS not incl
0.7
0.85
0.9
Estimated Canister Mass Total (kg)
40.1
45.2
40.2
42.9
Canister Mass Allocation (kg)
52
52
52
52
Canister Mass Margin (%)
30%
15%
29%
21%
Monitors Mass Element
Ion Monitor
2.6
2.6
2.6
2.6
Electron Monitor
3.3
3
1.5
1.8
Estimated Monitors Mass Total (kg)
5.9
5.6
4.1
4.4
Monitors Mass Allocation (kg) not avail
6.8
6.8
6.8
Monitors Mass Margin (%)
---
21%
66%
55%
Payload Total Mass Estimate
46
50.8
44.3
47.3
Payload Mass Allocation (kg) not avail
58.8
58.8
58.8
Payload Mass Margin (%)
---
16%
33%
24%

Another constraint of significance for the Science Canister Assembly is the overall volume or envelope. The SRC has a limited size and therefore limited internal volume due to the physical limits imposed by both launch and reentry. Therefore, a significant amount of effort was expended during Phase A to understand the volume of the Canister and how it fits within the SRC. Preliminary Interface Control Drawings have been generated, first in Vellum software with dimensions and later in SDRC Master Series to be compatible with the design database used at LMA. The Payload model generated at JPL was then "plugged in" to the LMA database to verify compatibility of the Canister design.

4.2 Master Payload Schedule

The Payload schedule is dictated by the need to conform to the overall LMA Spacecraft and Sample Return Capsule development schedule as described in the colored fold-out sheet in this Plan. The four key deliveries to LMA for the Payload in the S/C and SRC schedule are:

Receive Payload Mass Simulator Wed 5/8/96

Receive JPL Payload STM Fri 4/18/97

Receive P/L Engineering Model Mon 6/2/97

Receive P/L Flight Hardware Tue 11/10/98

A detailed schedule for development of the Canister is shown in Figure 30 (not available on web). This schedule shows all major deliveries between the various participating organizations. This schedule is arranged in time sequence, with the flow of effort defined by Phase, rather than by work element. A rearranged schedule is shown in Figure 31 (not available on web) in which the tasks are arranged by work element (i.e. Arrays, Mechanisms, etc.). A network view of Figure 31 is given in Figure 32 (not available on web).

Phase B is a 9 month effort from January through September 1996. The Payload mass simulator is delivered to LMA midway through Phase B. The Payload Preliminary Design Review takes place 9/20/96, ten days after the project PDR, which occurs on 9/10/96.

Phase C/D starts at the beginning of the fiscal year in September 1996. The first part of Phase C/D is devoted to developing the Payload engineering models. The two engineering model deliveries in April and June 1997 represent the major effort in the first part of this phase. The Payload Critical Design Review occurs on 9/8/97, a week before the system CDR on 9/15/97. After the CDR, work begins on the flight hardware.

The schedule for development of the Concentrator is given in Figure 33 (not available on web). The schedules for development of the Monitors and the Ground Support by LANL are given in Figures 34 and 35 (not available on web).

4.3 Receivable and Deliverable List4.3 Receivable and Deliverable List

Table 3 shows the Suess Urey level REC/DEL list. This list has been agreed to by all team members and provides the framework for exchange of critical hardware and data between institutions. We have incorporated the REC/DEL approach into our WBS level schedule construction. This REC/DEL list starts with ICD agreements in Phase B, progresses to development model deliveries, and finally flight unit deliveries in Phase C/D. The MS Project network schedules, provide a notes feature that can be attached to any activity or milestone. This provides the Payload Team with a convenient tool for use in tracking the progress of all inputs and outputs of a given task. By incorporating the data into an existing tool, we keep the process simple. These REC/DEL data can be published in tables by date, or WBS and made available to the Payload participants via a collaborative server.

Table 3. List of critical deliverables and receivables for the S-U Payload.
Deliverable Item
From
To
Day
Date
Canister ICD input info JPLLMA Fri2/2/96
Concentrator/HVPS ICD info LANL JPLFri 2/2/96
Monitors ICD input info LANL LMAFri 2/2/96
Concentrator/HVPS ICD Prelim LANL JPLThu 2/29/96
Monitors ICD - Prelim LANL LMAThu 2/29/96
Canister ICD Prelim LMA JPLThu 2/29/96
Concentrator HVPS Elec Parts List LANL JPLFri 3/15/96
Monitors Elec Parts List LANL JPLFri 3/15/96
Collector Array ICD Final JPL CITMon 3/25/96
Concentrator & HVPS Mtls List LANL JPLMon 4/15/96
Concentrator/PS ICD Final LANL JPLFri 4/19/96
Monitors Mtls List LANL JPLThu 5/2/96
Monitors ICD Final LANL LMAMon 5/6/96
Canister ICD Final LMAJPL Mon5/6/96
Canister Mtls List JPLJSC Fri5/17/96
6 Canister/SRC I/F Trunnion Assys LMAJPL Fri5/17/96
200 Test Collector Wafers CITJPL Fri3/8/96
50 Test Collector Wafers CITJSC Fri3/8/96
Concentrator HV Feedthru Connectors JPL LANLThu 11/7/96
Mating HV Feedthru Connectors LANL LMAThu 11/7/96
Mating Monitors Connectors LANL LMAThu 11/7/96
1200 EM Collector Wafers CITJPL Fri11/22/96
Deliver EM Collector Array Assy JPLJSC Wed1/22/97
LANL Delivers EM Concentrator LANL JPLWed 1/22/97
EM Canister to LMA JPLLMA Wed6/4/97
Deliver Canister Eng Model (002) LMAJPL Fri11/14/97
Deliver Canister Eng Model (002) JPLJSC Wed1/7/98
Collector wafers, Flight Units (500) JPLJSC Tues 3/17/98
Concentrator & HVPS, Flight Models JPLLANL Thu4/16/98
Concentrator & HVPS, Flight Models LANL JSCWed 6/17/98
Return Canister Eng Model (002) JSCJPL Wed6/17/98
500 flt test Collector wafers CITJPL Mon9/29/97
500 flt Collector wafers CITJPL Wed1/7/98
Return Canister Str/Ther Model (001) LMAJPL Fri8/8/97
6 Canister/SRC I/F Trunnion Assys LMAJPL Fri1/16/98
Deliver Flt Concentrator LANL JPLTue 2/10/98
Deliver 7 Flt Array Frames JPLJSC Fri3/13/98
Deliver Flt Canister Assy JPLJSC Tue6/9/98
Return Canister EM to JPL (002) JSCJPL Wed9/2/98
Deliver Flt Model Canister to LMA JSCLMA Fri11/10/98

4.4 Schedule Reserve4.4 Schedule Reserve

Schedule slack is provided in the Payload schedule as shown in Table 4.

Table 4. Slack periods in Payload development. (Slack periods bridge the gap between "from" and "to" columns).
From
To
Slack Period
Completion of the Canister STM Delivery of this STM to LMA 6 weeks
Completion of Canister EM testing Delivery to LMA 11 weeks
Completion of Flight Canister post-clean assembly and test Delivery to LMA for integration with the SRC 13 weeks
Completion of the Flight Concentrator Delivery to JPL for integration with the Canister 8 weeks
Completion of coating the Flight Concentrator Delivery to JPL for integration with the Canister 4 weeks
Completion of the Flight Monitors Delivery to LMA 12 weeks
Reintegration of the Flight Monitors Final acceptance on the LMA Spacecraft 14 weeks

These slack periods were provided to allow for unforeseen occurrences in development of the various elements of the Payload. Of great importance to schedule risk mitigation is the 13 weeks of slack allocated between the end of the scheduled environmental qualification testing of the Canister Assembly at JSC, and delivery to LMA. This time is allocated to allow for the possibility that problems may occur during testing, and rework/retest may then be required. Additionally, six weeks of slack is provided prior to delivery of the Canister STM unit to LMA. Schedule risk for inter-partner activities is thereby reduced by the incorporation of slack in the JPL schedule.

The slack incorporated in this schedule is fully funded in our cost estimates. In other words, the cost estimate has been compiled with the assumption that the slack time is fully staffed by the workforce rate at the beginning of the slack duration.

4.5 Schedule Management

The S-U project will utilize earned value schedule variance information generated monthly by the Microframe Project Manager (MPM) software to detect, identify, and determine the magnitude of Project schedule problems. Schedule variance will be calculated monthly at the Work Element level (one level below the Cost Account) with rollups to the Cost Account and all higher WBS levels. Since the same person at JPL acts as Financial Administration Assistant for the Project and for the Payload, the Payload Team Leader will derive information on Payload issues through this process.

Another main tool for S-U Project schedule management will be the top-level task network, which contains all of the Payload's major milestones, and all of the Receivable/ Deliverable (REC/DEL) tasks across team boundaries. Once the schedule baseline is set within this network, all changes thereto must be negotiated with and approved by the Payload Team Leader. Critical Path Method (CPM) analysis of all networks will be used to evaluate schedule options when necessary. The Payload Team Leader will use CPM in a "Slack Table" as a periodic metric for slack trend analysis purposes. The Slack Table contains key milestone information showing previous period's slack, current period's slack, original task duration, remaining task duration, and a quotient which measures the relative diminution of the remaining slack versus the remaining task duration. In addition, "Milestone Trend Charts" showing cumulative milestone completions planned versus accomplished will be utilized as a periodic metric. These tools will provide continuous information on the degree to which the schedule is being met, and the amount of slack remaining to deal with future problems.

The combination of successively more realistic engineering models, together with the provision of schedule slack at critical junctures in development, provides the Payload Team leader with the assurance that the development program is on track, and the flexibility to absorb unavoidable delays during the development program. The resource-loaded MS Project Scheduling Tool will provide a "pulse" of the state of the Payload development process which can be compared with the estimated progress for the known expenditures at any point. This invaluable tool will be used routinely, for the schedule (like any variable) cannot be controlled if its position cannot be sensed accurately.

ON TO SECTION 5