The SES-14 satellite will carry NASA's Global-scale Observations of the Limb and Disk (GOLD) instrument as a hosted payload. Credit: Airbus Defence and Space

WASHINGTON — A NASA instrument to study the interaction of the Earth’s upper atmosphere with space weather is ready for launch later this month as a payload on a commercial communications satellite.

The Global-scale Observations of the Limb and Disk (GOLD) mission is a hosted payload on the SES-14 communications satellite, scheduled for launch Jan. 25 on an Ariane 5 rocket that will also carry the Al Yah 3 communications satellite. The satellite arrived at the spaceport in Kourou, French Guiana, last month for launch preparations.

GOLD marks the first time NASA has flown a science mission as a hosted payload on a commercial satellite. Such payloads are designed to take advantage of excess payload capacity on commercial satellites to fly various communications, scientific and technology demonstration payloads for government agencies.

Hosted payloads offer, in theory, more frequent flight opportunities and at lower costs than dedicated spacecraft. In practice, though, only a handful of hosted payloads have flown for military and civil agencies to date because of the difficulties finding suitable satellite hosts and contractual challenges, among other issues.

For GOLD, a hosted payload made sense since the goal of the mission is to get a global view of conditions in the ionosphere as it interacts with the solar wind and geomagnetic storms, which is not possible with a satellite in low Earth orbit. “What we wanted to do is get the big picture,” said Richard Eastes, principal investigator for GOLD at the University of Central Florida, during a Jan. 4 NASA briefing. “That lets us put things into context, things that we can’t understand when we’re just looking at one little piece.”

With GOLD in geostationary orbit, he said, scientists will be able to see conditions in the ionosphere over an entire hemisphere, with observations planned for every half hour. “That allows us to follow the evolution in time, over the day, of the upper atmosphere,” he said. By contrast, missions in low Earth orbit pass over different locations at different times of day, making it difficult to separate changes in geography with changes in time.

Eastes said a hosted payload on a communications satellite made the most sense for a mission like GOLD. “Communications companies are flying lots of satellites, so that was the place to go,” he said. “So we started talking to some of the communications satellite companies, including SES.”

Getting GOLD launched has been years in the making. “SES has been working with Richard and the GOLD team for the good part of a decade, dozens of people company-wide,” said Todd Gossett, senior director of hosted payloads at SES Government Solutions, at the NASA briefing. “Now we finally get to realize the fruits of that labor.”

Eastes and other scientists will have to wait a while after launch before getting data from GOLD. SES-14 is an all-electric satellite built by Airbus Defence and Space, and will take several months to reach its final position in geostationary orbit. Eastes said it will likely be late September or early October before GOLD starts operations.

Despite the challenges that hosted payloads have faced, Gossett played up the benefits, such as the steady stream of potential opportunities for payloads as well as the use of other satellite infrastructure, such as ground stations and mission control centers, to operate those payloads.

Gossett said SES, which has worked on several other hosted payloads, is learning to find ways to make the process more efficient, such as coordinating schedules and synchronizing contracts. “Every time we go through the process, we learn a little something on how to take that process and apply it forward,” he said.

GOLD is not the only hosted payload science mission NASA has on the books. The Tropospheric Emissions: Monitoring of Pollution (TEMPO) instrument, selected as part of NASA’s Earth Venture program in 2012, is planned for launch no earlier than 2020 to measure air quality. The Geostationary Carbon Cycle Observatory (GeoCARB), selected by NASA as part of the Earth Venture program in late 2016, will measure vegetation and atmospheric carbon starting in the early 2020s. The host satellites for both TEMPO and GeoCARB have not yet been selected.

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...