FEATURE

---

Goddard Engineer Demonstrates Relative Navigation During Hubble Servicing Mission

A team of Goddard technologists has demonstrated that spacecraft can operate in close proximity to one another with little or no human intervention — an important navigational capability for future science and exploration efforts. While astronauts carried out the task of rendezvousing with, grappling, and then redeploying the bus-sized Hubble Space Telescope during the recent servicing mission, Goddard engineer Bo Naasz and his team simulated the same exacting maneuvers using the Relative Navigation System (RNS). The team’s feat of engineering prowess advances the Agency’s ability to execute these precision navigational tasks in future missions, Naasz said.

Goddard engineer Bo Naasz successfully demonstrated the Relative Navigation System (RNS) during the Hubble Servicing Mission. He is pictured here with RNS, which was installed inside the Shuttle cargo bay.

Flown in the cargo bay of Space Shuttle Atlantis, RNS included three cameras with varying optical ranges, electronics to capture the camera images, the Goddard-developed Navigator GPS receiver (see related story below), and a hybrid computer system called SpaceCube that provides 15 to 25 times the processing power of a typical flight processor.

As the Shuttle approached the Hubble, the cameras gathered real-time imagery and Navigator provided GPS data. Both data streams were fed into SpaceCube, which executed two algorithms — one developed by Goddard engineers — to calculate the position and orientation of the observatory relative to the Space Shuttle.

The goal was demonstrating that space-qualified flight hardware could estimate the position of Hubble, a capability that would advance NASA’s ability to carry out these tasks autonomously using an unmanned vehicle. “I’m ecstatic we were able to acquire and track the telescope so well,” Naasz said. “SpaceCube made it possible to do the relative-navigation processing onboard and in real-time.”
 
Bright Future

Now that he has proved the viability of autonomous navigation, Naasz said the future looks bright.

It is possible that NASA will have to return to the observatory with an unmanned spacecraft at the end of the observatory’s operational lifetime to carry out a safe de-orbit — a maneuver that would require the abilities demonstrated by RNS. RNS also is a good candidate for future sample-return missions, spacecraft autonomous rendezvous, and other robotic servicing missions, Naasz said.

Work Began in 2003

Efforts to build such a capability began in 2003 when former NASA Administrator Sean O’Keefe canceled the Shuttle servicing mission, directing Goddard’s Hubble Development Project to instead investigate the possibility of executing the same repairs robotically.

While laying the groundwork for the robotic servicing, Goddard engineers realized that developing an autonomous system to estimate Hubble’s position and attitude in relation to the servicing vehicle would be difficult and would require a demonstration flight. Although former NASA Administrator Michael Griffin canceled the robotic mission two years later in favor of the tried-and-true crewed servicing mission, engineers used the technology they created to assemble the RNS experiment.

“It has been an interesting epic journey,” Naasz said. “Our experiment positions us well to do autonomous or semi-autonomous navigation in the future.”

GPS navigational devices are as ubiquitous as cell phones, freely used by commercial and government users alike to determine location, time, and velocity. These tools, however, are only as good as the signals they receive. Thanks to a team of engineers from Goddard’s Component Hardware Systems Branch, even those platforms operating in weak-signal areas — such as geosynchronous or highly elliptical orbits — will be able to acquire the precise GPS radiowave signal to determine their location. As a result, constellations of next-generation satellites will be able to fly in formation and unmanned spacecraft will be capable of autonomous navigation.

The Goddard Navigator team includes (from left to right): Bill Bamford, Steve Sirotzky, Greg Heckler, Luke Winternitz, and Rich Butler. Gerald, the team's space monkey, is perched on the shelf.

During the recent Hubble Servicing Mission, engineers demonstrated for the first time the Navigator GPS receiver, a technology Goddard engineers had begun developing six years ago with Internal Research and Development funding. During a test of the Goddard-developed Relative Navigation System (RNS), the Navigator proved highly effective at quickly finding, acquiring, and tracking weak GPS signals — contributing to the overall success of the RNS experiment, said Greg Heckler, a member of the Navigator team. The team’s work doesn’t stop with the first on-orbit demonstration, however.

Honeywell Commercializing Technology

According to Heckler, Honeywell is commercializing the technology specifically to build a receiver for the Orion spacecraft. His team provided a Navigator test unit to the GOES-R program and is now building receivers for the in-house Global Precipitation Measurement mission. The Magnetospheric Multiscale mission, a constellation of four identically outfitted spacecraft that will fly in formation to explore the interaction of Earth’s magnetic field with the solar wind, also will fly units to help maintain the constellation’s alignment.

“I am lucky I was here in the beginning,” Heckler said. “I was able to see this technology advance from TRL (technology readiness level) one to seven, from Matlab to actual flight hardware.”