Systems engineering and program management can generate a lot of documentation. Useful documents include interface control documents, system block diagrams, work breakdown structures, Gantt charts, and PERT charts. Many tools exist, like NASA’s Software Tools for Project Management which bundles the Work Breakdown Structure (WBS), budgeting, task plans, and analysis. These tools can also be found separately, individually, or created from scratch by the user.

Technology Readiness Levels

Technology readiness levels (TRLs) are used to estimate the maturity of technologies, first developed by NASA in the 1970s. The Department of Defense and European Space Agency have adopted this standard for their technology assessment as well. There are nine different levels of TRL where TRL 1 is the lowest maturity and TRL 9 is the highest maturity. I visit NASA’s definition of the TRL website so often I may as well bookmark the page. Although this standard is widely adopted and used, multiple people may evaluate a technology at different TRLs based upon their interpretation of maturity. TRLs may be attached to any level of technology, from a component as small as a bolt to the entire spacecraft system. Software may even be attached with a TRL. This standard’s primary purpose is to help make decisions concerning the development and transitioning of technology [Wikipedia]. TRL definitions also help technologists understand the capabilities necessary to mature the technology toward spaceflight.

Interface Control Documents

Interface control documents specify interfaces between mating systems, which include mechanical, electrical, and data interfaces [Akin]. If the interfaces must be connected into a cohesive system before the flight, these interfaces must be checked and caught before it’s too late. But if the interfaces are disconnected until after flight and are expected to be assembled in orbit, the interface errors would cause critical catastrophes for an immensely expensive project that could have been fixed with a simple check. Here’s an example of an interface control document and all the ICDs of our kit can be found here.

Akin’s Laws of Spacecraft Design #15

System Block Diagrams

System block diagrams are visual aids to show the relationships between projects, systems, subsystems, and/or components. These diagrams can help subsystem leads catch interface errors or communicate the partitioning of responsibilities. The following diagram is a spacecraft system diagram, which does not include the larger picture of ground stations to control centers. This diagram includes components in each subsystem but not the individual constituents of each component or interface connection. That level of detail can be portrayed in a separate or embedded system block diagram.

Artemis CubeSat Kit System Diagram. Image courtesy of Amber with Hawaii Space Flight Laboratory.

Work Breakdown Structure

“A [Work Breakdown Structure] is a product-oriented family tree that identifies the hardware, software, services, and all other deliverables required to achieve an end project objective. The purpose of a WBS is to subdivide the project’s work content into manageable segments to facilitate planning and control of cost, schedule, and technical content” [NASA WBS]. In the project development cycle of initiating, planning, executing, controlling, and closing, the WBS occurs in the task of defining the work during the planning phase.

Akin’s Laws of Spacecraft Design #24

However, at the lowest level, a WBS generally has tasks of the form such as “test gizmo” rather than nouns. This helps in one of the important tasks of the WBS, which is to track costs during the project. The Agency’s Core Financial System currently limits the ability to capture costs to a maximum of seven levels. These seven levels of the WBS are defined below.

• Level 1 is the entire project.
• Level 2 elements are the major operational product elements along with key common, enabling products (as defined in NPR 7120.5, NPR 7120.7 (NID 7120.99 Interim Directive), and NPR 7120.8 standard WBS templates).
• Level 3-7 contains further definable subdivisions of the products contained in the level 2 elements (e.g., subsystems, components, documents, functionality).

WBS elements should be identified by a clear, descriptive title and by a numbering scheme as defined by the project that performs the following functions:

• Identifies the level of the WBS element.
• Identifies the higher-level element into which the element will be integrated

Gantt Charts

A Gantt chart is a “bar chart depicting start and finish dates of activities and products in the WBS” [NASA SE Handbook]. This document aids systems engineers and project managers in gauging the level of progress with respect to schedule and milestones. Gantt charts can be made in Microsoft Excel or with custom online tools, like Lucidchart, team gantt, canva, etc. Gantt Charts can help track resources and show interdependency between the WBS tasks (e.g., Task A must be completed before Task B is started). This Gantt chart was made by our structures lead over the summer to communicate his progress to our systems engineer and program manager, Amber Imai-Hong.

PERT charts

Program Evaluation and Review Technique, PERT, Charts are graphical representations of a project’s timeline. They reveal task dependencies and the critical path for scheduling. A short tutorial to find a critical path is given in Akin’s lecture slides. Tools to create a PERT chart include SmartDraw and LucidChart.

Mass and Power Estimation

Over the design process, the spacecraft’s estimated mass and power will grow until those mass and power allocations converge to the final design at delivery. The overall spacecraft may be separated into the payload and the supporting spacecraft subsystems. A study by NASA and the Aerospace Corporation assessed the historical mass, power, cost, and schedule growth for multiple NASA spacecraft buses from the last twenty years. Generally, the modification of existing designs or the addition of new designs naturally leads to greater overall uncertainty in the design and potential for the growth of spacecraft resources over time. The authors provided more nuance in that the instrument’s relative lack of maturity to spacecraft technology contributed to larger growth of mass, cost, and schedule.

Contingencies are allocated at different design stages to account for this growth. For mass and power, the NASA Green Book, Goddard Gold Rules, JPL Design Principles, and AIAA Standard guidelines are compared to the historical growth. For instruments, “Historical Mass & Power growth percentage at Phase B Start typically higher than guidelines while PDR & CDR are more in line”. Whereas for the spacecraft, “guidelines appear mostly adequate compared to historical mass & power growth”. By subsystems in the spacecraft, “interconnected” systems appear to have the highest growth: Thermal, EPDS (Harness), SMS (Brackets/Support Structure), and “Box-like” systems appear to have the lowest growth: C&DH, TT&C, ADCS.

For 1U cube satellites, the mass and volume standards are pre-determined: 1.33 kg and 10 cm³.

Cost Estimation

Cost is a huge driver in a space mission, as the funding agency or customer will hold you accountable and may end the program if the budget is overrun. Spacecraft missions are typically very expensive, due to launch costs and labor costs in the rigor of development/testing to meet critical requirements. Funding agencies and customers will use cost to justify the value of the mission and the expectation of rigor to execute a mission. A linear depiction of the cost estimation process is given in the figure below, although a note of application is that this process is an iterative process with the incorporation of new data [NASA Cost Estimating Handbook].

Much like mass and power, contingencies must be allocated for cost. The same NASA and Aerospace Corporation study found that instrument Historical Cost & Schedule growth percentages are significantly higher than guidelines at most milestones whereas the spacecraft recommendations were adequate.

The NASA Cost Estimating Handbook is a detailed reference to walk through the steps of cost estimation. Other tools include software packages, like PCEC, MOCET, CET, CDB, and NICM (alphabet soup!):

• Project Cost Estimating Capability (PCEC) develops cost estimates/models for space systems, created by Marshall Space Flight Center. This technology combines an Excel add-in with a simple, robust, and transparent collection of NASA cost-estimating relationships (CERs), statistics, work breakdown structures, and cost-estimating algorithms.
• Mission Operations Cost Estimation Tool, MOCET, provides a new capability to generate cost estimates for the operational, or Phase E, a portion of NASA science missions and was created by Ames.
• The Data Service Provider Cost Estimation Tool (CET) and Comparables Database (CDB) package provide NASA’s Earth Science Enterprise (ESE) the ability to make lifecycle cost estimates for the implementation and operation of the data service providers that are required to support its science and applications programs. The Data Service Provider CET and CDB package were developed by Goddard Space Flight Center.
• NASA Instrument Cost Model (NICM) is a probabilistic cost and schedule estimating tool. NICM has proven instrument cost and schedule modeling capabilities that provide probabilistic estimates at both the system and subsystem levels for many different instrument types.
• SMAD’s Mission Operations Cost Prediction Spreadsheet