National Aeronautics and

Space Administration

Quick Start

Guide to

Payload Design

PAYLOAD

ENGINEERING

March 2, 2022
While engineering designs vary as widely as 

payload purposes, they are all subject to 

the physical, chemical, and mathematical 

principles understood by NASA discipline 

experts who support the ISS Program. ISS 

hardware, software, and operations are 

organized functionally into systems and 

sub-systems with leading experts that provide support in each of these areas.

NASA’s Pressurized Payloads Interface 

Requirements Document (SSP 57000) is 

the principle source for interface design 

requirements for all NASA-developed payloads operating in the pressurized volume 

of the ISS. Payload developers must verify 

the applicable requirements in this document to ensure the safety of the ISS crew, 

transport vehicles, on-orbit ISS systems 

hardware, and neighboring payloads. This 

document also provides design guidance 

that ensures the basic operation of the 

payload and affects the payload’s mission 

success. It is your responsibility as payload 

developer (PD) to design in accordance 

with the design guidance.

NASA is equipped with laboratories and 

other facilities designed to support payload projects throughout their lifecycles. Although each of these experts fulfills an important role within the ISS Program — such 

as ensuring safety or providing necessities 

for the crew — all of them have something 

to offer you as a (PD) to help you achieve 

payload mission success.

The following content draws from the 

expertise and experience of individuals 

across the organizations mentioned above. 

The sections within this chapter highlight 

specific considerations that should concern 

you while completing the engineering design, development, and verification activities associated with your payloads.

You are encouraged to coordinate closely with your Payload Integration Manager (PIM) and reach out to experts in areas 

relevant to your payload.

CONSIDERATIONS FOR 

PAYLOAD DESIGN

This section describes several aspects of 

space flight that you will need to take into 

account during the payload development 

process.

Payload

Engineering

Building a better mousetrap
Quick Start Guide to Payload Design: Payload Engineering 3

Keep in mind that payloads that use 

less of the station’s limited resources are 

more easily accommodated. Keeping resource usage to only what is absolutely 

required and finding ways of reducing 

the use of resources improves a payload’s opportunities for mission success.

Crew

Pressurized payloads share the ISS environment with the crew, whether they are 

passive/autonomous (not requiring crew 

time) or active (requiring crew time). ISS 

engineering experts are available to assist 

with the design approach and verification 

process to prepare the payload for crew 

interaction. Your PIM will conduct a payload 

Kickoff meeting where these requirements 

are introduced. The PIM is the liaison between you and various ISS experts.

Consider the number of crew absolutely 

required to complete your payload operations.

Thermal

The ISS offers payloads different types of 

thermal control: active, passive, and conditioned stowage.

The Active Thermal Control System (ATCS)

is an internal system (inside the ISS) that 

uses a closed-loop (series of tubes) that 

circulates chilled water and pulls excess 

heat from racks and payloads. In this system, there are two temperatures available: 

a 40C Low Temperature Loop (LTL) and a 

170C Moderate Temperature Loop (MTL).

The Passive Thermal Control System (PTCS)

is also an internal system that removes 

heat using forced cabin airflow across the 

payload.

When designing your payload, consider the thermal requirements and what 

would be ideal: ATCS or the PTCS.

Conditioned Stowage provides for the 

specific temperature needs for scientific 

samples and other temperature-sensitive 

payload items. This resource consists of 

several active devices, such as freezers, 

refrigerators, and incubators as well as 

passive assets like Coldbags and Ice 

Bricks. These options are available on ISS, 

plus during launch and return. Standard 

conditioned stowage temperatures are 

-32°C and +4°C. All other temperatures are 

considered a unique re- quest.

Conditioned stowage is one of the most 

limited resources on ISS. To ensure that 

your payload is accommodated for conditioned stowage, keep sample dimensions as small as possible.

Electrical

The ISS Electrical Power Distribution and 

Control (EPDC) system provides power 

to the ISS and payloads. Your PIM will 

discuss its intricacies during your Kickoff 

meeting and throughout the development 

process and will facilitate interactions with 

the Electromagnetic Effects (EME) and the 

Electrical Power System (EPS) Teams. The 

EME Team provides Power Supply and 

EMI Filter design guidance for compatibility 

with the ISS system and other payloads. 

The Electrical Power System (EPS) Team 

provides guidance on power interface 

requirements.

Engaging the help of the EME team early and often is an important practice to 

ensure success in electrical design. The 

EME team can help you understand the 

EPDC requirements and offer proven 

methods to meet them in addition to 

providing test facilities equipped to support electrical and EMI testing.

When designing your payload, take into 

consideration the following design factors:

Power Interface Design

Two-fault tolerant controls and verifications 
4 Quick Start Guide to Payload Design: Payload Engineering

are required to ensure crew safety through 

the following approaches:

Redundant or Designed for Minimum Risk 

(DFMR) Bonding of all crew accessible 

surfaces (including cables) that can be energized after a failure or electrical fault (i.e., 

test for a minimum of class H bond <0.1 

Ohm or use of double insulation).

Electrical isolation between primary power 

and chassis and secondary power.

EME Team can provide support and guidance on design and verification of all classes of bonding required for your payload.

Power Quality Testing

The EPS combines critical (ISS core systems) and non-critical loads (payloads) in 

the same power feed; therefore, additional 

systems-level requirements are in place to 

protect the system. It is important to involve 

the EME and EPS Teams early in the design of the payload.

Electromagnetic Compatibility (EMC) 

Design

When designing your payload, keep in 

mind that there are electromagnetic standards that must be met. Early communication with you PIM and the EME team will 

help lead to a successful design.

Designing for electromagnetic compatibility up front will reap dividends later in the 

process by reducing costs and schedule 

impacts from later design changes due to 

EMI issues.

Review this paper, Electromagnetic 

Compatibility Considerations for International Space Station Payload Developers, for specific guidance.

Some PDs prefer to buy Commercial-Off-The Shelf (COTS) products for 

their payloads. If a COTS product is being 

considered, EME experts can help based 

on experience with previous payloads. 

Electromagnetic Interference (EMI) 

Testing

EMI testing occurs near the end of the payload development lifecycle. This testing is a 

requirement for flight.

Be sure to account for EMI early in your 

payload design to ensure it will pass 

testing and move forward to flight.

If stated in the Payload Integration Agreement (PIA), NASA can provide testing services. Otherwise, testing can be performed 

at a commercial facility. Talk to your PIM 

about testing options.

Electrical Power Distribution and 

Control (EPDC) Design

In coordination with your PIM, the EME, 

Safety, and EPS Teams will provide assistance with initial requirements for payload 

development and design. It is important 

to engage with these teams early in the 

design phase.

In a microgravity environment, there is no 

convective cooling: objects and structures 

using electricity that heat up on the ground 

likely will get much hotter on orbit.

Example: Laptop chargers are familiar 

COTS products that tend to heat up while 

charging during ground operations. While 

on-orbit, they can heat up to temperatures 

that exceed touch temperatures, potentially endangering the crew. Additional fans 

provide a solution.

The ISS electrical system has a 32-volt 

shock limit, which is lower than what most 

payload developers expect.

By engaging with the EME Team early 

and not waiting until the Phase I safety 

review, cost and schedule impacts can 

be reduced or eliminated.

Example: If a PD up-converts from the 28 
Quick Start Guide to Payload Design: Payload Engineering 5

volts provided by the ISS, the PD could 

unwittingly introduce a situation requiring 

a two-fault tolerance. If this requirement 

is not taken into account early on, the 

payload’s electrical system will have to be 

modified.

Also consider the materials used in the 

electrical system. Polyvinyl Chloride (PVC) 

insulation is not permitted for use on the 

ISS based on its flammability risk.

Teflon-coated wiring is optimal.

Battery Design and Testing

Your PIM will assist in connecting you with 

the Safety Team for assistance with the 

battery selection process. It is important to 

understand the full implications of what is 

required to implement a design using battery power and the time required to do so.

NASA can build batteries, or COTS batteries can be used after testing.

All batteries, regardless of type, have potential risks:

Lithium ion (Li-ion) produce a lot 

energy by operating a higher capacity, 

but unique circuitry that leads to the 

potential of thermal runaway. Thermal 

runaway propagation-resistant batteries are required if the capacity is over 

80 watt-hours. With Li- ion batteries, 

rigorous safety hazard mitigation and 

safety plan documentation are requirements.

Alkaline and electrolyte batteries can 

leak and have venting issues.

Nickel cadmium batteries are easier to 

work with and do not have thermal runaway issues. The drawback is that they 

may not be powerful enough for some 

applications.

Capacitor Component Testing/Screening

When using capacitors, it is important to 

understand the hazards associated with 

wet electrolytic capacitors — particularly 

aluminum electrolytic and wet tantalum 

types — since they present the possibility 

for toxic material to reach the crew. Engage 

the Safety team early in the design phase.

Avoid aluminum electrolytic capacitors. 

Electrolytes tend to react with the dielectric material, creating a short. When 

activated after being off for some time, 

the capacitor may fail quickly. Similarly, tantalum capacitors can have unexpected failure modes. Treating them 

for moisture problems via sealing them 

or baking them out tends to help avoid 

shorts. Ask your PIM for recommendations on appropriate capacitors for your 

payload.

EEE Parts and Ionizing Radiation

The EEE part selection and the effects of 

ionizing radiation are closely monitored for 

ISS hardware.

Select parts from known manufacturers 

with an emphasis on quality and reliability.

Your PIM can help you navigate interactions with the experts on what EEE parts 

may work for your payload.

For COTS parts, it is good practice to ask 

about qualification testing and their current 

Failure-in-Time (FIT) rate when considering 

manufactures.

A FIT rate of approximately 20 is a good 

rule of thumb when selecting parts.

Ionizing radiation for internal payloads is a 

recognized but minor concern. If your payload is sensitive to radiation, the options 

for parts should include redundancy and 

proton testing.
6 Quick Start Guide to Payload Design: Payload Engineering

Consider performing a “burn- in” on the 

payload or a particular electronics assembly by simply letting it run, perhaps 

for a few weeks. This is a cost-effective 

method to identify longevity problems 

in the design.

STRUCTURES AND 

MECHANISMS

When developing your payload, it is important to engage NASA’s Structures and 

Mechanisms (S&M) experts early in the 

design phase. These experts will help you 

deter- mine how your payload and structural loads will play a factor in moving forward 

with the ISS Safety and Review Panel 

(ISRP). When designing your payload, fault 

tolerance requirements and options should 

be understood to ensure the hardware is 

created with enough flexibility to operate on 

the ISS.

Work with the S&M experts prior to entering the safety review process to determine whether your payload would be 

designated as ‘Safety Critical.’

Structural Loads

Structural loads may arise from mechanical, pressure-related, vibration-related, 

inertial, and thermal forces applied to 

structural elements. All payloads must limit 

their disrupting effects on the microgravity 

environment. Keep the following information in mind during the design phase of 

your payload:

The three categories of disruption are Quasi-Steady, Vibratory, and Transient.

Quasi-Steady Launch and Landing 

Loads

Quasi-Steady refers the state that the vehicle experiences when traveling through the 

atmosphere. In this state, the turbulence 

experienced occurs slowly and quickly 

reaches equilibrium therefore creating a 

seemingly steady state. Acceleration loads 

need to be considered for your payload.

Payloads in their launch, on-orbit, or landing configurations must provide positive 

margins of safety when exposed to accelerations.

Vibratory Loads

Your payload should be designed to withstand vibrational loads. If your payload is 

vibration-sensitive, the ISRP will recommend Protoflight Random Vibration Hardmount Testing.

Vibration testing and analysis are recommended to verify the function of any 

payload that includes electronics, close 

tolerance moving devices, or optical 

equipment.

Whenever possible, leave tolerances 

loose to enable on-orbit operations, 

such as payload installation.

Structures can change shape compared 

to their ground measurements when in 

microgravity.

Fracture Vulnerability

All payload equipment is evaluated for 

potential breakage that could cause harm 

to the crew, ISS, or visiting vehicles.

Fracture control analysis should be 

performed concurrently with the stress 

analysis early in the development of the 

payload.

Primary structural elements may be classified as low-risk, non-Fracture Critical as 

long as the working stresses are low, use 

of proper materials, and satisfactory fatigue 

life are demonstrated.

To decrease the potential of payload 

fracture, consider the parts and mate-
Quick Start Guide to Payload Design: Payload Engineering 7

rials used in the design. There should 

be no welds, castings, forgings, or additive manufacturing. Materials prone to 

shattering, such as glass, ceramics, etc., 

must be contained.

The containment of hazardous materials/fluids must be 2-fault tolerant (yielding three levels of containment). Otherwise, the primary container will become 

Fracture Critical.

Mechanisms

If your payload has mechanisms, addressing considerations early in the design process is crucial. Your PIM and S&M experts 

will help you through this process with the 

first step of developing a mechanical fault 

tolerance strategy.

Focus your efforts on incorporating mechanical redundancy wherever possible 

and determining whether to implement 

a Design for Minimum Risk (DFMR) 

strategy. (DFMR is a process that allows 

Safety Critical mechanisms to achieve 

fault tolerance through rigorous design, 

analysis, testing, and inspection practices rather than through true physical redundancy.)

Mechanical fault tolerance is always preferred, either in the form of like or unlike 

redundancy. Some examples of incorporating like mechanical fault tolerance 

include dual rotating surfaces for hinges 

and secondary sliding surfaces.

MATERIALS

The JSC Materials and Processes team 

consists of experts to assist you in the 

selection of materials for your payload. This 

team differentiates payloads into the Simple or Complex categories described below.

Payloads will need to meet the verification 

requirements set by the JSC Materials 

and Processes team. Contact your PIM for 

guidance.

Simple Payloads

Simple Payloads are those that have 

minimal ISS vehicle interfaces and little to 

no structural hardware (i.e. welded seams). 

Examples of a simple payload include 

container kits, syringe kits, consumable 

re-supply kits, and Commercial-Off-TheShelf (COTS) hardware such as cameras, 

syringes, filters, sample container bags 

to name a few. The primary concerns for 

simple payloads are flammability and toxic 

off gassing.

COTS hardware can be accepted 

through the COTS certification process. 

Contact your PIM for assistance with this 

process.

Complex Payloads

Complex Payloads are those that do not 

meet the criteria of a Simple Payload. 

These primarily include structures and will 

need to comply with the Structures and 

Mechanisms requirements.

All materials used for Safety Critical 

structural components require certification as to their composition and properties.

Structural payloads should avoid using 

complex materials processes such as additive manufacturing, welding, brazing, 

structural adhesive bonding, forging, 

casting, and structural soldering in Safety Critical structural components.

Payload Guidance

For Complex Payloads, the Materials and 

Processes Technical Information System 

(MAPTIS) contains a collection of verified 

test data on standard design materials 

that will be crucial when designing your 

payload. MAPTIS provides letter rating 

on flammability, fluid compatibility, stress 

corrosion, toxic off gassing, and vacuum 

outgassing.
8 Quick Start Guide to Payload Design: Payload Engineering

MAPTIS experts are available when you 

request assistance through your PIM.

Materials Flammability

The flammability of materials is an important consideration when designing your payload. The basic requirement for flammability is that the materials be nonflammable. 

The materials that you are envisioning for 

your payload may be tested for acceptability.

Something to keep in mind that some 

flammable materials can be accepted by 

configuration analysis, such as containment or low quantity.

Standard flammability test data typically 

used for ground applications in air environments are not conservative enough 

for the oxygen-enriched ISS pressurized 

environment. Consult your PIM to determine the appropriate expert to assist in 

choosing your material.

Common nonflammable materials are listed 

below. Talk to your PIM about any specific 

material you want to use.

Teflon (Tetrafluoroethylene (TFE), Fluorinated 

ethylene propylene (FEP), and Perfluoroalkoxy (PFA))

Nomex (HT 9040 and some additional grades, 

but not all)

Polycarbonates (Lexan, Macrolon), 1/8 inch 

or thicker

Kapton and other polyimides

Ultem

Painted metal

Common flammable materials are listed 

below. These materials are not expressly 

prohibited and may be acceptable within 

the total payload configuration. Be sure to 

discuss any materials you want to use with 

you PIM and materials experts.

Paper

Polyethylene

Polypropylene

Acrylonitrile butadiene styrene (ABS)

Nylon

Hook-and-loop fasteners (such as VELCRO® 

or similar products)

Polyvinyl Chloride (PVC)

Polyethylene terephthalate (PET)

Cotton

Polyester

Wool

Complete lists of nonflammable and 

flammable materials are avail- able. 

Please contact your PIM to discuss with 

the material experts.

Off Gassing and Outgassing

When materials release gases into the environment, this is referred to as off gassing. 

Should toxic off gassing occur on the ISS, 

it may create a toxic environment for the 

crew.

Toxic off gassing is frequently confused 

with toxic hazard ratings. The toxic hazard rating pertains to fluids only and the 

hazard that would occur if the entire 

amount of fluid were released into the 

ISS cabin atmosphere.

There are times that “off gassing” and “outgassing” terms are frequently confused. Off 

gassing typically occurs inside the pressurized vehicle whereas outgassing occurs 

outside the vehicle in a vacuum.

When navigating off gassing requirements, keep in mind that unmodified 

COTS hardware that contains less than 

20 pounds (total mass) of polymeric materials need not be tested for off gassing, with some exclusions.

Outgassing may result in contamination 

of the vehicle transporting your payload 

or the ISS. There is potential that your 

payload’s surface or near-by payloads 

could be contaminated. You can find 

an extensive list of outgassing data in 

MAPTIS.
Quick Start Guide to Payload Design: Payload Engineering 9

Fluid Compatibility and Stress 

Corrosion

Your payload materials must be compatible 

with any fluids with which they come into 

contact.

A few of the materials that are permitted 

to come into contact with the Internal 

Thermal Control System (ITCS) coolant 

loops include internal metallic materials 

made of stainless steel, materials with a 

nickel base, or titanium alloys. Aluminum 

alloys containing greater than 5 percent 

copper are not permitted.

Additional requirements to keep in mind 

with respect to materials and the ISS:

Payload materials that provide structural 

support need to meet stress and corrosion 

requirements.

Water-soluble volatile organic compounds 

are strictly controlled within the environment of the ISS. The release of methanol, 

ethanol, isopropyl alcohol, n-propyl alcohol, 

n-butyl alcohol, acetone, ethylene glycol, 

and propylene glycol are restricted in the 

ISS pressurized elements because the 

water recycling system can remove only 

limited quantities of these com- pounds 

from water condensate.

RADIO FREQUENCY AND 

SPECTRUM MANAGEMENT

If you are planning using radio frequencies 

in your payload design, it is important to 

engage the spectrum management team 

early. Your PIM will assist in helping you 

reach the experts.

Your PIM will guide you through the licensing processes (should your payload 

require it). They may seem a bit complex 

but they are necessary to minimize potential technical anomalies, interventions, and risks to mission success.

INFORMATION TECHNOLOGY 

FOR YOUR PAYLOAD

There are several options for telemetry, 

Health & Status monitoring, and commanding for your payload from the ground. Your 

PIM will connect you to the experts that will 

help determine which options will work best 

for your payload.

Separate your ISS interfaces from your 

science software as much as possible to 

facilitate pre-approvals with your software integration.

REQUIREMENTS 

VERIFICATION

Success with requirements verification can 

be achieved by following the best practices 

throughout your payload’s lifecycle:

Stay in close contact with the PIM

Openly communicate preliminary pay- load 

design data

Engage NASA experts early and often

Keep stakeholders apprised of payload 

design changes

You have access to support throughout 

the entire process of building your payload. Working together with experts will 

facilitate your success in meeting your 

scientific objectives while verifying that 

the crew and the ISS remain safe.