4

Secondary Payloads

This chapter of the report focuses on the types of secondary payloads that are suited to an agile rideshare program. The ideal candidates lie at the intersection of the scientific value of the measurement and ease of implementation of the payload (which includes aspects of standardization and hardiness). Scientifically valuable payloads facilitate one or more of the three types of observations that enable science as described in Chapter 3—that is, temporally continuous, spatially distributed, and novel. These different types of scientifically valuable measurements benefit from different types of secondary payloads.

There are a number of complex factors involved in determining which types of secondary payloads are suitable for rideshare opportunities. This is not surprising owing to the variety of instruments, launch vehicles, and host platforms that could be involved, and also because scientific priorities will change over time. Even though no single measurement will work in all cases, it is possible to provide a framework to decide the factors most relevant to programmatic decisions.

SECONDARY PAYLOADS WITH STANDARD INSTRUMENTATION

Standard measurements might be obtained by a subset of secondary payloads that are well known, are heavily relied upon, and have high heritage. The same standard payloads may be useful for continuous or distributed measurements, depending on whether they are deployed to span time or to span space. The benefits and specifications of standard instrumentation types are well understood, and as such could be built far in advance of a launch opportunity. The committee notes that standard instrumentation does not imply a one-size-fits-all instrument for all orbits and platforms. The committee refers to these as instruments that could be stocked and stored for a limited time, or “kept on the shelf.”¹

Finding: Continuous and distributed observations often employ standard instrumentation types that can be stocked and stored for some time before a rideshare opportunity emerges.

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¹ The committee did not develop a list of these types of instruments; however, an example is networks of GPS receivers that measure total electron content, such as those used on the COSMIC mission. See NASA, “Constellation Observing System for Meteorology Ionosophere and Climate (COSMIC),” updated August 7, 2017, https://www.nasa.gov/directorates/heo/scan/services/missions/earth/COSMIC.html.

SECONDARY PAYLOADS WITH PROPULSIVE CAPABILITY

There are several types of free-flyer payloads, both remote sensing and in situ, that need specific pointing or orientation in order to obtain the desired measurements. These may require a form of propulsion. Additionally, science that requires observations made from one or multiple specific vantage points may necessitate secondary payloads with propulsive capability to reach their desired locations or orbits. Examples include constellations designed to populate LEO for ionosphere-thermosphere system science, formation-flying spacecraft designed for high-precision solar observations, and in situ monitors spaced along the Sun-Earth line. Such multipoint payloads provide benefit far in excess of the sum of their individual parts.

Finding: Some of the science enabled by rideshare opportunities may require secondary payloads that are free-flyers with propulsive capability.

SECONDARY PAYLOADS THAT DEMONSTRATE NEW TECHNOLOGY

Novel payloads aimed at exploratory science may need flight opportunities to raise their technological readiness and obtain flight heritage for new types of instrumentation. In addition, technology developments such as miniaturization of the payloads, standardization of interfaces, and modernization of communication and propulsion systems could have wide-reaching benefits. Capabilities in some of these areas are rapidly advancing in both commercial and civil space arenas. To minimize accommodation challenges (e.g., pointing requirements versus field of view, electrostatic and magnetic cleanliness), the development of technologies to mitigate less than ideal accommodation of instruments would also be helpful to enhance the utility of future standard instrumentation and speed up deployment times (see also the section “Strategic Investments,” in Chapter 5).

Finding: Technology demonstration benefits exploratory science through novel instrument development and modernization of interfaces.

SECONDARY PAYLOADS THAT ARE RAPIDLY INTEGRATED WITH HOST PLATFORMS

The ideal rapidly integrated secondary payload is one flexible enough to fit on multiple types of host platforms. There are few industry-wide, well-established rideshare program standards for power, data, command, and mechanical interfaces between secondary payload and its host platform, leading to long and costly development times. Improvements in interface standardization will speed integration while minimizing the chance of unintended impacts on the primary payload. Moreover, the development of physical and electrical interface standards will eliminate the need for consideration of variability in launch dispensers. NASA is in a position to work with industry to consider best practices and come to agreement on standard interfaces.

Finding: Standardization of interfaces between host platform and secondary payload can accelerate integration, especially for payloads that rely on host resources.

Taken together, these findings support the committee’s conclusion, as follows:

Conclusion: Secondary payloads, either ridealongs or free-flyers, that lend themselves to an agile rideshare program include technology demonstrators as well as standard instrumentation types that may be stocked and stored for limited periods. Free-flyers with propulsive capability can also expand the scientific potential of rideshare opportunities. Investments in standardization and other

technologies facilitating rapid integration and general accommodation adaptation can expand the scientific potential of rideshare opportunities.