SAN FRANCISCO — Spaceflight Inc. plans to send secondary payloads and the company’s new Sherpa in-space tug on a Space Exploration Technologies () Falcon 9 flight in 2014 to demonstrate the ability to move small payloads from the point where a primary mission drops them off to their desired orbital destination.
Seattle-based Spaceflight, a company established in 2009 to book rides for secondary payloads, worked with Andrews Space Inc. to develop the Sherpa tug to assist customers who were having trouble finding rides to their desired altitudes. Most of the flight opportunities listed in Spaceflight’s catalog would send payloads to high altitudes in low Earth orbit, around 600 to 700 kilometers. “Often, that doesn’t work for small spacecraft,” said Jason Andrews, president and chief executive of Spaceflight and Andrews Space. “Many of them want to be closer to altitudes of around 450 kilometers.”
Small satellites dropped off at the higher altitudes may have trouble meeting NASA’s requirement to deorbit or move to an unused orbit within 25 years of the mission’s completion, Andrews said. In addition, some Spaceflight customers have designed spacecraft featuring telescopes or other sensors designed to operate at lower altitudes, he said.
To create Sherpa, Spaceflight and Andrews added power generation and propulsion systems to the Spaceflight Secondary Payload System (SSPS), a standard adapter for small payloads that is designed to fit on the SpaceX Falcon 9, Orbital Sciences Corp.’s Antares and’s Atlas 5 and rockets. SSPS, which is scheduled to make its debut on a Falcon 9 flight in 2013, features five ports designed to carry payloads weighing 300 kilograms or less. Andrews plans to fabricate SSPS and Sherpa in its Tukwila, Wash., facility.
After a launch vehicle deploys its primary payload and secondary payloads on SSPS, Sherpa is designed to fly the secondary payloads to their desired location before deploying them. The three-axis stabilized space tug is designed to provide approximately 100 watts of power to each payload as it moves to its destination. Company officials plan to develop upgraded versions of the tug featuring higher power levels and greater pointing accuracy, Andrews said.
For the demonstration mission in mid-2014, the Sherpa tug is scheduled to travel on a Falcon 9 into sun-synchronous orbit. In late 2014, Spaceflight plans to conduct its first commercial mission of the Sherpa tug on another Falcon 9 flight to sun-synchronous orbit.
“We strongly believe in the utility of small satellites and support Spaceflight’s efforts to nurture this emerging market segment,” SpaceX President Gwynne Shotwell said in a statement.
Spaceflight plans to build two versions of the tug. The Sherpa 400, which will offer on-orbit maneuvering capability of 400 meters per second, will be designed to transport satellites to lower altitudes within low Earth orbit. The Sherpa 2200, which will offer on-orbit maneuvering capability of 2,200 meters per second, will be designed to move secondary payloads dropped off in geosynchronous transfer orbit to destinations in geosynchronous orbit, Andrews said.
Although Spaceflight developed Sherpa with secondary payloads in mind, the tug also could be used as a platform for hosted payloads. With a full fuel load, the Sherpa 400 weighs 1,000 kilograms and the Sherpa 2200 weighs 2,000 kilograms. “We can host many different types of payloads, from small sensors to larger telescopes on each of the Sherpa ports,” Andrews said. “Most of these payloads weigh between 5 and 50 kilograms, but it’s conceivable to host large payloads — weighing up to 300 kilograms. The big drivers are total power requirements and pointing accuracy.”
Small satellite builders offered mixed reviews on the idea of the Sherpa space tug. Many small-satellite builders are extremely cost-conscious and reluctant to use any service that raises the price of their overall mission, a NASA official said.
Andrews said, however, that company officials have presented the idea of Sherpa to customers who are eager to use it. Through its website, Spaceflight is offering to transport spacecraft weighing less than 180 kilograms to low Earth orbit for $4.95 million. “Unless those spacecraft have on-board propulsion, they are restricted to the launch vehicle’s destination orbit, not their desired orbit,” Andrews said. “While Sherpa will add to that cost, it provides the customer with the flexibility to be dropped off at their optimal altitude at a price that is significantly less than buying a dedicated launch vehicle. Our primary customers are people who want to deploy high-value microsatellites for specific missions or constellations of small spacecraft.”
Andrews Space also is a member of the Rocket City Space Pioneers, a Google Lunar X Prize team led by Dynetics Corp. of Huntsville, Ala. Andrews Space is leading the team’s effort to develop a lunar rover and planning to use the Sherpa tug to move the Moon-bound spacecraft from geosynchronous transfer orbit to lunar orbit.