01. Introduction

Objective

The objective of this report is to assess and give an overview of the state of the art in small spacecraft technology. It was first commissioned by NASA’s Small Spacecraft Technology Program (SSTP) in mid-2013 in response to the rapid growth in interest in using small spacecraft for missions beyond LEO, and revised in mid-2015. In addition to reporting on what is currently available, a prognosis is provided describing technologies on the horizon.

Information in this report has been collected primarily through desk research and is not intended to be exhaustive – no such assessment can be comprehensive. New technology is developed continuously, and emerging technologies will mature to become the state of the art. The authors intend to regularly update this report, and current technologies that were inadvertently missed will be identified and included in the next version. The valuable input of readers is solicited in the Feedback page.

Overview of the variety of spacecraft that fall into the small spacecraft category
Figure 1.1: Overview of the variety of spacecraft that fall into the small spacecraft category.

Scope

A spacecraft is hereafter called a “small spacecraft” when its wet mass is below 180 kg. This definition adopts the terminology set out by NASA’s Small Spacecraft Technology Program (SSTP) [1]. Figure 1.1 gives an example of the variety of spacecraft that fall into the small spacecraft category.

At the upper mass limit there are minisatellites like FASTSAT (Fast, Affordable, Science and Technology Satellite), NASA’s first minisatellite mission launched in 2010 with a mass slightly below 180 kg. On the lower mass end, there are projects such as KickSat, which aimed to deploy picosatellites the size of a large postage stamp and with a mass below 10 grams. Spacecraft are generally grouped according to their mass, where small spacecraft include minisatellites with a mass of 100-500 kg, microsatellites with a mass of 10-100 kg, nanosatellites with a mass of 1-10 kg, and picosatellites with a mass below 1 kg.

Launch dates vs mass of the small spacecraft studied in this report.
Figure 1.2: Launch dates vs mass of the small spacecraft studied in this report.

Cubesats are a standard for small spacecraft that weigh only a few kilograms and are based on a form factor of a 100 x 100 x 100 mm cube. Cubesats can be composed of a single cube (a “1U” cubesat) or several cubes combined forming, for instance, 3U or 6U units (see Figure 1.2). Due to their high market penetration and their increased usage in recent times, particular emphasis is put on the state of art of cubesat technology in this report (see also Figure 1.2). The technology tables shown in subsequent sections are not meant to be comprehensive. Their goal is to illustrate the current state of the art based on desk research in a limited amount of time.

Assessment

Cubesats with form factors of 1U, 3U, and 6U, respectively. The volume of the 1U base unit is 100 x 100 x 100 mm.
Figure 1.3: Cubesats with form factors of 1U, 3U, and 6U, respectively. The volume of the 1U base unit is 100 x 100 x 100 mm.

The state of the art assessment of a technology is performed using NASA’s TRL scale (see Figure 1.3). A technology is deemed state of the art whenever its TRL is larger than or equal to 6. A TRL of 6 indicates that the model or prototype is near the desired configuration in terms of performance, weight, and volume, and has been tested and demonstrated in a relevant environment. A relevant environment is either a high fidelity laboratory environment or a simulated operational environment [2].

A technology is considered not state of the art whenever its TRL is lower than or equal to 5. In this category, the technology is considered to be “on the horizon”. This definition of “state of the art” has been chosen because of its inherent simplicity. Clearly, old and possibly obsolete technology has a TRL larger than 6 but cannot be considered as state of the art. The bias in the definition has been recognized and care has been taken in the report to exclude obsolete technology from the study.

Overview

This report is structured as follows: in the spacecraft section the state of the art of small spacecraft technology is addressed by focusing on the spacecraft system as a whole and the current best practices of integration are presented; then, the state of the art of the spacecraft subsystems are presented in turn:

Integrated Spacecraft Platforms

Power

Propulsion

Guidance, Navigation and Control

Structures, Materials and Mechanisms

 Thermal Control

Command and Data Handling

Communications

Integration, Launch and Deployment

Ground Data Systems and Mission Operations

Passive Deorbit Systems

[1]
National Aeronautics and Space Administration, “NASA’s Small Satellite Missions.” 2015.
[2]
National Aeronautics and Space Administration, “Technology Readiness Level.” 2015.