A secondary payload, also known as rideshare, is a smaller-sized payload transported to orbit on a launch vehicle that is mostly paid for—and with the date and time of launch and the orbital trajectory determined—by the entity that contracts and pays for the primary launch. As a result, the secondary payload typically obtains a substantially reduced price for transportation services to orbit, by accepting a trade off of the loss of control once the contract is signed and the payload is delivered to the launch vehicle supplier for integration to the launch vehicle. These tradeoffs typically include having little or no control over the launch date/time, the final orbital parameters, or the ability to halt the launch and remove the payload should a payload failure occur during ground processing prior to launch, as the primary payload typically purchases all of these launch property rights via contract with the launch services provider.
While originally a US government-centric option for government-owned launches—where secondary payload slots were often given away by whatever allocation means a government agency might choose—an entire market has emerged over time to take advantage of the lower cost of access to space through secondary payload opportunities.
The small satellite segment of the satellite launch industry has been growing rapidly in recent years. Development activity has been particularly high in the 1–50 kg size range. In the 1–50 kg range alone, there were fewer than 15 satellites launched annually in 2000 to 2005, 34 in 2006, then fewer than 30 launches annually during 2007 to 2011. This rose to 34 launched in 2012, and 92 small satellites launched in 2013.
Offering of secondary launch services vary by launch provider. US commercial launcher United Launch Alliance (ULA) offers virtually no access for secondary payloads commercially, although the US military offers some secondary payload slots on ULA launchers Atlas V and Delta IV, that are then controlled by government launch slot allocation processes.
SpaceX offered a priced set of secondary payload launches on their Falcon 9 rocket beginning in 2011 with prices between US$200–325 thousand for secondary payloads delivered to low-Earth orbit (LEO). As of March 2014[update] SpaceX indicated that they continue to launch some secondary payloads, but are not doing a lot of them, as there is "not a lot of money in the secondary payload market."
ILS, a US company that markets launches of the Russian Proton rocket, does not and has no plans to launch commercial secondary payloads of smallsats or CubeSats. Sea Launch, a US-based consortium of US company Boeing and Russian company RSC Energia (RSCE) (now majority owned by RSCE), also does not currently launch commercial secondary payloads.
Standardized payload interface offerings
The EELV Secondary Payload Adapter (ESPA) is an interstage adapter ring that was originally designed for launching secondary payloads on US DoD space missions that use the Evolved Expendable Launch Vehicles (EELV) Atlas V and Delta IV. First used in the 2000s, the goal of ESPA was to reduce launch costs for the primary customer and enable secondary and even tertiary missions with minimal impact to the primary mission. The ESPA ring design has become a de facto standard, and is now much more widely used than the original intent and rockets.
ESPA was designed to support up to a 6,800 kilograms (15,000 lb) primary payload and up to six secondary payloads of no more than 180 kilograms (400 lb) each. Each secondary spacecraft is mounted radially on a 38 centimetres (15 in) diameter port and is allocated 61 cm (24 in) x 71 cm (28 in) x 97 cm (38 in) volume.
Commercial derivatives of the ESPA Grande ring are being developed. Named the Spaceflight Secondary Payload System (SSPS), the system is being developed and manufactured by Andrews Space under contract to Spaceflight Services. It includes five 61 cm (24 in)-diameter ports, each capable of carrying payloads weighing up 300 kilograms (660 lb). "The SSPS operates very similar to a standalone spacecraft with a flight computer, electrical power system, orbit determination capability, and payload power switching."
- "New Startups Are Allowing Satellites to 'Rideshare' All the Way to Space". Motherboard. Retrieved 2016-05-12.
- Perry, Bill (July 2012). "ESPA: An Inexpensive Ride to Space for Secondary Payloads". MilsatMagazine. Retrieved 22 March 2014.
- "Evolved expendable launch vehicle secondary payload adapter" (PDF). American Institute of Aeronautics and Astronautics (AIAA). 28 August 2001. Retrieved 22 March 2014.[permanent dead link]
- "2014 Nano/Microsatellite Market Assessment" (PDF). annual market assessment series. Atlanta, Georgia: SEI. January 2014: 18. Retrieved 22 March 2014.
- Foust, Jeff (22 August 2011). "New opportunities for smallsat launches". The Space Review. Retrieved 22 March 2014.
SpaceX ... developed prices for flying those secondary payloads ... A P-POD would cost between $200,000 and $325,000 for missions to LEO, or $350,000 to $575,000 for missions to geosynchronous transfer orbit (GTO). An ESPA-class satellite weighing up to 180 kilograms would cost $4–5 million for LEO missions and $7–9 million for GTO missions, he said.
- Gwynne Shotwell (2014-03-21). Broadcast 2212: Special Edition, interview with Gwynne Shotwell (audio file). The Space Show. Event occurs at 32:15–32:35. 2212. Archived from the original (mp3) on 2014-03-22. Retrieved 2014-03-22.
[Q: Are you doing a lot of secondary payloads?] not a lot, we are doing a few. There is still not a lot of money in the secondary payload market.
- Foust, Jeff (2014-03-24). "Reusability and other issues facing the launch industry". The Space Review. 2014. Retrieved 2014-04-01.
- Spaceflight Secondary Payload System Archived 2012-07-07 at Archive.is, retrieved 2012-05-10.