|Imagine a technology that would allow space travelers to transmit gigabytes of data per second over interplanetary distances or to navigate to Mars and beyond using powerful beams of light emanating from rotating neutron stars.
The concept isn’t farfetched.
In fact, Goddard astrophysicists Keith Gendreau and Zaven Arzoumanian plan to fly a multi-purpose instrument on the International Space Station to demonstrate the viability of two groundbreaking navigation and communication technologies and, from the same platform, gather scientific data revealing the physics of dense matter in neutron stars.
Principal Investigators Keith Gendreau (seated) and Zaven Arzoumanian are fine-tuning their Modulated X-ray Source, which will play a pivotal role in the demonstration of the world’s first X-ray communication system.
Selected for development by NASA’s Office of the Chief Technologist, the X-ray Navigation Demonstrator (XNAV) will include 56 X-ray telescopes, silicon detectors, and a number of other advanced technologies in a package about the size of a large recycling bin. Gendreau and his team say they plan to deliver the payload to the orbiting outpost in 2015 to begin the disparate, yet related, investigations.
“It’s rare that you get an opportunity to develop a crosscutting experiment,” Gendreau said. “This technology touches seemingly disjointed things: X-ray astrophysics, navigation, and new techniques to communicate over interplanetary distances. The time is right for this experiment. This is one that we can do now.”
Stellar Lighthouses Show the Way
The instrument demonstration is the first step in realizing pulsar-based navigation — a concept advanced after the discovery of these unusual celestial objects in 1967, Gendreau said. Pulsars are a subgroup of neutron stars. They rotate rapidly, emitting powerful beams of light from their magnetic poles that sweep around as the star spins, much like a lighthouse. On Earth, these beams are seen as flashes of light, blinking on and off at intervals from seconds to sub-milliseconds.
Because of their predictable pulsations, “they are highly reliable celestial clocks” and can provide high-precision timing just like the atomic clock signals supplied through the 26-satellite, military-operated Global Positioning System (GPS), Arzoumanian said. Although GPS offers highly reliable location and time information to anyone with a GPS receiver, it is geared to Earth-based applications. As a result, GPS signals weaken the farther one travels out into the Solar System. “Pulsars, on the other hand, are accessible in virtually every conceivable flight regime, from low-Earth orbit to interplanetary to deepest space,” Gendreau said.
To demonstrate the viability of pulsar-based navigation, Gendreau and his team, including the Massachusetts Institute of Technology, the Naval Research Laboratory, the National Institute of Standards and Technology, and others, will develop the XNAV experiment as a payload on the International Space Station’s Express Logistics Carrier, an unpressurized payload platform. The instrument will use its 56 telescopes to detect X-ray photons in these powerful beams of pulsated light to estimate their arrival times. With these measurements, the system will stitch together an on-board navigational solution using specially developed algorithms.
If an interplanetary mission were equipped with such a navigational device, it would be able to calculate its location autonomously, independent of NASA’s Deep Space Network (DSN), Gendreau said. DSN, considered the most sensitive telecommunications system in the world, allows NASA to continuously observe and communicate with interplanetary spacecraft. However, like GPS, the system is Earth-centric. Navigational solutions also degrade the farther one travels out into the Solar System. Furthermore, missions must share time on the network, Gendreau said.
“To better explore new worlds beyond low-Earth orbit, we will need additional navigational solutions. XNAV enables deep-space missions that are not feasible with Earth-based tracking,” he added.
The multi-purpose payload also will enable a demonstration of the world’s first X-ray communication system. This test will feature Goddard’s Modulated X-ray Source (MXS), which turns on and off many times per second to encode digital bits for transmitting data. Since developing the MXS with Goddard and Defense Department R&D funds, Gendreau has demonstrated 500 kilobyte-per-second data rates using the device. The goal is to one day transmit gigabytes of data per second with minimal power.
Clouds of charged particles move along the pulsar's magnetic field lines (blue) and create a lighthouse-like beam of gamma rays (purple) in this illustration.
His plan is to fly the MXS on a supply spacecraft. As the craft approaches the Space Station, MXS will transmit data via the modulated X-rays, which the XNAV hardware would then receive.
Should the first space-based demonstration succeed, Gendreau said it would be laying the foundation for a more powerful way to transmit data across vast distances. “This is a baby step toward interplanetary X-ray communication,” Gendreau said. “We understand these technologies,” Arzoumanian added. “We understand how to build the payload. We need to show what is feasible. This experiment will tell us what we can do.”
The Office of the Chief Technologist is involved in a variety of projects, missions, and technologies.