Orbital Express: Prototype Satellites Primed for In-Flight Service
An artist's illustration of DARPA's Orbital Express spacecraft in orbit, with the ASTRO servicing vehicle (left) bearing down on NextSat.
Credit: DARPA.

Two prototype spacecraft, one wielding its own robotic arm, are poised to launch spaceward late Thursday on a three-month mission to test methods for robotically refueling satellites in Earth orbit.

A United Launch Alliance Atlas 5 rocket is slated to launch the two spacecraft, collectively known as Orbital Express, and a clutch of microsatellites at 9:37 p.m. EST (0237 GMT) from Florida's Cape Canaveral Air Force Station [image]. The planned flight is part of the U.S. Air Force's Space Technology Program 1 (STP-1) mission.

"I think we're feeling pretty good about it," USAF Lt. Col. Fred Kennedy, project manager for Orbital Express, said in a telephone interview. "We're very confident that we're going to have a nice successful mission."

Built for the Defense Advanced Research Projects Agency (DARPA), the Orbital Express vehicles are aimed at demonstrating autonomous spacecraft refueling and servicing techniques [video, image].

For military uses, such capabilities would allow reconnaissance satellites to keep station over specific areas of interest and tank up on vital propellant later, though the technology could also aid general-use spacecraft in need of periodic equipment repairs, replacements or an orbital boost, mission managers said.

"I think it's extremely valuable for the entire space arena," Kennedy said of Orbital Express' goal, adding that the mission could help ease the stringent requirements of long-life satellites. "Maybe you can accept a level of imperfection that will allow you to go up later and perform upgrades and perform repairs, and put more propellant onboard to get the job done. That will be a sea change in the way we do business."

Service via automaton

The $300 million Orbital Express vehicles come in two forms: the smaller target NextSat and the larger service spacecraft ASTRO [image].

Short for Autonomous Space Transport Robotic Operations, the ASTRO servicing satellite is a 2,100-pound (952-kilogram) vehicle laden with 300 pounds (136 kilograms) of hydrazine propellant and measuring about six feet (1.8 meters) tall and wide. Its robotic arm is designed to either latch onto NextSat and pull it close for a manual docking, or transfer replacement hardware, such as a battery, from ASTRO to the target vehicle.

The 500-pound (226-kilogram) NextSat, meanwhile, is a three-foot (about one-meter) wide prototype for a next-generation satellite designed with in-flight refueling and servicing in mind [image].

"Our goal is to demonstrate on-orbit refueling, component exchange and satellite repair--all without a human operator," James Lee, head of Automated Rendezvous and Docking Projects at NASA's Marshall Space Flight Center, which developed part of the autonomous navigation system to be used on Orbital Express.

That NASA navigation system, first flown during the space agency's DART autonomous rendezvous mission in 2005, and will be combined with Boeing-built sensors, passive detection systems and computer software to allow ASTRO to keep close tabs on NextSat, mission managers said.

"ASTRO is most often flying itself," Kennedy said, adding that the vehicle is expected to function with minimal intervention by flight controllers at Kirtland Air Force Base in New Mexico. "We are basically sitting there waiting to watch for telemetry and other data tot tell us, '"Did it work? Is there a problem? Do we need to intervene?'"

During its planned 91-day mission, the Orbital Express vehicles are expected to go through a two-week checkout period, and then test initial refueling and equipment replacement techniques -- while still mated to one another -- using ASTRO's robotic arm. A series of more complicated rendezvous, robotic arm and servicing scenarios are then due to follow throughout the remainder of the mission, DARPA officials said.

"Wrapping all this inside a software package that can understand what to do with all of it, without significant intervention, has been both the struggle and serious achievement here," Kennedy said.

Boeing Phantom Works served as the primary contractor for Orbital Express' ASTRO vehicle, while Ball Aerospace led NextSat's development.

Along for the Ride

Orbital Express' Atlas 5 booster [image] is not only expected to haul ASTRO and NextSat into orbit tonight. The rocket is also carrying four experimental microsatellites to test a multitude of technologies in low-Earth orbit for the U.S. Air Force.

  • Cibola Flight Experiment: An experimental satellite smaller than an armchair designed to test new power supplies, inflatable antennas and other technologies for future spacecraft, according to the Los Alamos National Laboratory.
  • FalconSat- 3: An experiment-laden satellite built and managed by U.S. Air Force Academy. It carries five military science experiments to study space weather, with a focus on space plasma, and spacecraft operations.
  • MidSTAR-1: A multi-experiment satellite built by midshipmen and personnel at the U.S. Naval Academy. It is carrying an experimental microdosimeter, a nano-chemical sensor, as well as tests of an Internet Communications Satellite payload and Configurable Fault Tolerant Sensor.
  • STPSat-1: A Space Test Program vehicle carrying several experiments that include testing a high-resolution ultraviolet spectrometer and studying irregularities in space-to-ground communications, according to manufacturer AeroAstro, Inc.

"We come off first and then they start popping off, each of the Air Force satellites in turn," Kennedy said of the STP-1 spacecraft deployment plan. "We are ecstatic to be here and thrilled that we're going to get an opportunity to prove out a new capability for the Department of Defense and for the nation." 

United Launch Alliance will provide a live launch webcast of today's planned space shot via the firm's website: http://www.ulalaunch.com.