This article originally appeared in the Sept. 10, 2018 issue of SpaceNews magazine.

Ten years after then-U.S. Air Force Secretary Michael Wynne called for maximizing use of secondary payload adapters to launch small satellites on large rockets, the Air Force, NASA and the National Oceanic and Atmospheric Administration are working together to make that happen.

In addition to identifying flights with available room, the government agencies are looking for small satellites appropriate for piggyback flights.

“There is a lot going on,” said Joe Maly, Moog CSA Engineering’s product lead for payload launch adapter. “Everyone is talking about ESPA.”

ESPA is the Evolved Expendable Launch Vehicle (EELVs) Secondary Payload Adapter. Moog CSA Engineering developed ESPA under contract for the Air Force Research Laboratory in the 1990s. It flew for the first time in 2007 as part of the Air Force’s first Space Test Program aboard a United Launch Alliance Atlas 5 rocket.

Based on that successful mission, Wynne wrote a February 2008 memo calling for the Air Force to devote excess weight margin on future EELV flights to secondary payloads. Since then, however, only seven flights have included ESPA rings. Even on those flights, the rings, which can accommodate multiple small satellites, were rarely full.

ESPA’s popularity, however, is on the rise.

“People launching realize that rather than going by themselves, it’s to the benefit of the taxpayer to combine spacecraft” on a rocket, said Bob Caffrey, Rideshare project manager at NASA’s Goddard Space Flight Center.

People who have promoted that idea for years say it’s finally catching on. At the annual Small Satellite conference in Logan, Utah, Thomas Zurbuchen, NASA associate administrator for science, said the space agency will plan to fly an ESPA ring with every science mission.

“We’re not going to ask whether we need it,” Zurbuchen said in August. “You have to convince us that we don’t need it.”

NASA’s Rideshare office has identified 16 NASA and NOAA missions scheduled to launch between 2020 and 2026 to various orbits with room for ESPA rings. Altogether, those missions could fly 81 ESPA-class satellites, weighing 33,270 kilograms.

“This is going to change the way science missions are done,” Caffrey said. “Instead of doing one science mission at a time, we can do many missions at the same time, all with significant science.”

To fill available slots, NASA is working closely with the NOAA and other government agencies, Caffrey said.

NASA also is seeking to ensure a ready supply of secondary payloads by inviting researchers to propose small satellites appropriate for piggyback flights through its Small Explorer missions, which cost no more than $120 million, and its Earth Ventures competitively selected science campaigns.

NOAA demonstrated its interest in secondary payloads July 31, when it asked commercial firms to share information on instruments that could fly on an ESPA ring with the Joint Polar Satellite System-2, a weather satellite scheduled for takeoff in 2021.

“NOAA intends to make available these rideshare opportunities on these ESPA ring positions for experimental satellites containing instruments of future interest,” according to the Request for Information published on the website FedBizOpps.Gov.

Specifically, NOAA hopes the secondary payloads will demonstrate small satellite instruments and technologies the agency can use to “substantially lower the size, weight, power and cost of future environmental remote sensing instruments while maintaining useful performance, or substantially upgrade performance without incurring substantial size, weight, power or cost penalties,” NOAA said in the announcement.

In 2018, Defense Department, NASA and NOAA leaders have shared plans for future constellations that rely heavily on small satellites. Now, those agencies are taking steps to ensure extra launch capacity on large rockets isn’t wasted.

That hasn’t always been the case. In 2015, NOAA’s Deep Space Climate Observatory satellite traveled to Earth-moon Lagrange Point 1 on a SpaceX Falcon 9 rocket with room to spare for 2,500 kilograms. Then in April 2018, NASA sent its Transiting Exoplanet Survey Satellite to trans-lunar injection orbit without using 3,000 kilograms of lift capacity.

Why the empty flights? Caffrey likens ridesharing to carpooling. When going from Washington to New York, it’s tempting to drive a car even if trains and buses are more economical ways to transport groups of people. Plus, it takes time to find people you are comfortable riding with who are available when you are ready to go, said Joe Burt, a NASA Goddard deputy program manager. “If you pick up some stranger or some strange payload, it might hurt your payload through contamination, out-gasing, vibration,” Burt added.

Once everybody gets to know each other, they realize they don’t mind carpooling, Burt said. “The other guys aren’t so bad and we all get a really good deal,” he added.

Comfort with ridesharing in general is growing thanks, in part, to Air Force guidelines. The Air Force has defined 44 environmental activities, including pressure, materials and thermal testing, secondary payloads must complete to prove they will not harm other satellites.

“It’s nice that the rideshare payloads can say, ‘We are going to follow these guidelines and share the 44 products for each spacecraft that flies with you,’” Caffrey said. “You can go through them and make sure they meet all your requirements.

Another reason the government is embracing ESPA is its practicality, said Eric Anderson, president of And One Technologies, a consulting firm in Mountain View, California. “It’s already been tested and flight proven,” said Anderson, former chief technologist at Moog CSA Engineering.

In recent years, companies have created ESPA derivatives that offer customers greater flexibility. Initially, ESPA rings sent satellites weighing as much as 180 kilograms into the same orbit as a rocket’s primary payload. Now, ESPA rings come in various sizes and may include propulsion to carry small satellites into distinct orbits.

In April, the Air Force Research Laboratory (AFRL) launched the ESPA Augmented Geosynchronous Satellite, known as Eagle, on a United Launch Alliance Atlas 5 rocket. Eagle served as the prototype for the Orbital ATK, now Northrop Grumman Innovation Systems, ESPAStar platform, which provides propulsion, power, attitude control and communications for payloads that remain on the platform or satellites that will be sent off it.

“ESPAStar opens up many doors for small satellites,” said Carol Welsch, Northrop Grumman Innovation Systems business development director. “They can go wherever they need to for their own particular mission objectives.”

ESPAStar can accommodate as many as six payloads that remain on the ring, 12 payloads that detach or some combination of the two.

“You can envision separable payloads going where they need to go and fixed payloads staying onboard for up to five years,” said Welsch, a retired Air Force colonel and former acting director of the Air Force Space Development and Test Directorate at Kirtland Air Force Base in New Mexico. “Now you’ve gotten a very cheap launch into space and a very affordable spacecraft bus.”

Based on another AFRL program called Automated Navigation and Guidance Experiment for Local Space, or ANGELS, launched in 2014, Northrop Grumman developed ESPASat, a geostationary satellite bus designed to fly from the ESPAStar platform. The recent Eagle flight includes Mycroft, an experimental ESPASat.

The combination of Department of Defense, NASA and NOAA ESPA missions with flexible platforms is helping to spur small satellite development.

“You can design your spacecraft to the known [ESPA] interfaces, and there is a good chance you’ll be able to get your spacecraft into orbit,” Welsch said. “It’s amazing how much energy that has put into the small satellite community.”