In 1935, British physicist Sir Robert Watson-Watt created the first functional radar system and in four short years, his invention was deployed all along the British coast to monitor for incoming Nazi warplanes. Today, we tend to take radar for granted – using it for everything from military applications, to surveillance, all the way to helping to catch speeders on the highway. Although each radar system in use today sends and receives microwave signals in a similar manner, not all radar systems are created equal – and NASA’s new radar application might just be the best of them all.
The radar guns you see police officers equipped with have a range of around a mile, while the much larger applications in use at international airports can reach as far as sixty miles. The United States Missile Defense Agency puts both of those applications to shame, boasting the largest phased array X-band radar installation in the world, which measures at two-hundred and forty feet wide and nearly four hundred feet long. The twenty-six-story installation is mobile – traveling throughout the Pacific Ocean via a semi-submersible oil platform and according to the agency itself, “The radar is so powerful that if it were off the East Coast of the United States near Washington, D.C., it would be capable of detecting the motion and rotation of a baseball launched into outer space from the San Francisco area.”
With such incredible credentials, how could NASA hope to top that?
“We have been able to detect NASA’s Lunar Reconnaissance Orbiter [LRO] and the Indian Space Research Organization’s Chandrayaan-1 spacecraft in lunar orbit with ground-based radar,” said Marina Brozovic, a radar scientist at NASA’s Jet Propulsion Laboratory (JPL). “Finding LRO was relatively easy, as we were working with the mission’s navigators and had precise orbit data where it was located. Finding India’s Chandrayaan-1 required a bit more detective work because the last contact with the spacecraft was in August of 2009.”
Hearing the story as Brozovic tells it, one might be tempted to dismiss this announcement as just the sort of thing one might expect NASA to be able to do… but let’s consider the scope of this development. The American Missile Defense Agency’s incredible missile detection net can find and track an object the size of a baseball from around 3,000 miles away – that in and of itself is a mind-blowing feat… but now let’s compare it to what NASA just managed to accomplish.
The Chandrayaan-1 spacecraft was launched in October of 2008 by India, and was responsible for the important discovery of water-ice on our moon’s poles. Unfortunately, in 2009, India lost contact with its probe nearly a year before its planned decommissioning, and after citing several technical issues and a failure of the thermal shielding, they were forced to declare the Chandrayaan-1 lost on August 29th, 2009. The probe itself is a fairly small five-foot by five-foot cube and telescopes are unable to locate the tiny object visually due to the relative brightness of the moon in the background of the image, leaving the orbit and state of the probe a mystery to scientists since first losing contact with it nearly eight years ago.
Using NASA’s existing interplanetary radar installations and a new technique developed by JPL, NASA was able to locate and detect the tiny, five-foot probe from 237,000 miles away.
In order to locate and identify a five-foot-wide derelict spacecraft from hundreds of thousands of miles away, NASA first turned to good old-fashioned math, using the probe’s last known orbit from eight years ago to extrapolate where it might be now. From there, they determined the right times and areas of the moon to be looking, and used their 230-foot antenna at NASA’s Goldstone Deep Space Communications Complex in California to send a powerful beam of microwaves at the portion of the moon they calculated the probe may be in. The beam impacted the lunar surface and bounced back to Earth, where it was received by the 330-foot Green Bank Telescope in West Virginia. The process was actually quite a bit more complicated than it sounds, due to the moon’s high number of mascons, which are regions with higher-than-average gravitational pull, which can have dramatic and unpredictable effects on an orbiter over time.
“It turns out that we needed to shift the location of Chandrayaan-1 by about 180 degrees, or half a cycle from the old orbital estimates from 2009,” said Ryan Park, the manager of JPL’s Solar System Dynamics group, who calculated the new orbit for the radar team. “But otherwise, Chandrayaan-1’s orbit still had the shape and alignment that we expected.”
They tracked radar echoes from the tiny ship seven times over the span of three months, coupling their radar tracking with additional input from other observatories once they had identified it. They then called on the Arecibo Observatory in Puerto Rico, which has the most powerful astronomical radar system on Earth, to confirm their discovery.
The ability to track such small objects in lunar orbit has far-reaching applications – one significant one is the ability to locate and track orbital debris that may pose a risk to spacecraft launching or already in orbit. The U.S. Air Force already dedicates a good deal of resources to that task, but NASA’s new radar application could make the process easier, and even assist in future space-junk cleaning projects such as the recently failed Japanese satellite sent up to do just that.
This long-distance radar methodology is cost-effective, as scientists established their new radar transmission and reception technique using existing platforms, and can also aid in asteroid detection from distances even greater than the moon is from us – allowing for the establishment of a more thorough early detection system for incoming asteroids and comets.
Just as a new radar development in 1935 became a staple of Britain’s defense initiative against Nazi Germany, NASA’s new radar technique could become a staple of our planet’s defenses against an even bigger threat: asteroids that put the very survival of our planet at risk.
Image courtesy of NRAO