August 21, 2013
Future Space Missions Could Rely On Pulsars For Navigation
Lee Rannals for redOrbit.com - Your Universe Online
Scientists at Commonwealth Scientific and Industrial Research Organization (CSIRO) are developing a new GPS method for spacecraft using pulsars.
Pulsars are small spinning stars that emit regular pulses of radio waves and sometimes X-rays. CSIRO astronomers measure when these pulsar pulses arrive in our Solar System. This data can be used to give clues about the behavior of a pulsar itself or whether it is orbiting another star.
Dr George Hobbs of CSIRO said they can use information from pulsars to precisely determine the positions of telescopes.
"If the telescopes were on board a spacecraft, then we could get the position of the spacecraft," Hobbs said.
The team determined they would need observations of at least four pulsars, every seven days, each of which would have to be observed for about an hour.
"Whether you can do them all at the same time or have to do them one after the other depends on where they are and exactly what kind of detector you use," Hobbs explained.
Currently, spacecraft are being tracked and guided from the ground through things like CSIRO's Canberra Deep Space Communication Complex. However, the farther out these spacecraft go, the less accurately scientists are able to measure their locations. Pulsars could be a key to this deep space navigation.
"Navigating with pulsars avoids these problems," said Deng Xinping, PhD student at the National Space Science Center in Beijing, who is first author on the paper describing the system, published in the journal Advances in Space Research.
The researchers made a very detailed simulation of a spacecraft navigating autonomously to Mars using a combination of technologies and software they developed.
"For deep-space navigation, we would use pulsars that had been observed for many years with radio telescopes such as Parkes, so that the timing of their pulses is very well measured," said CSIRO's Dr Dick Manchester, a member of the research team. "Then on board the spacecraft you'd use an X-ray telescope, which is much smaller and lighter."
Hobbs said that the simulated spacecraft is able to determine its position to within about 12 miles and its velocity within about four inches per second.
"To our knowledge, this is the best accuracy anyone has ever been able to demonstrate," Hobbs said. "Unlike previous work, we've taken into account that real pulsars are not quite perfect, they have timing glitches and so on. We’ve allowed for that."
Previously, the team used an earlier version of the software to "weigh" the planets out as far as Saturn. The movement of the Earth traveling around the sun affects exactly when pulsar signals arrive. In order to remove this effect, the team calculated when the pulses would have arrived at the Solar System's center of mass.
"If the pulsar signals appear to be coming in at the wrong time, we know that the masses of the planets that we are using in the equations must be wrong, and we can correct for this," Dr Hobbs explained.
With the latest version of their software, astronomers can rule out unseen masses, including undiscovered planets.
"Even if a planet is hard to see, there's no way to disguise its gravitational pull," Dr Hobbs said. "If we don’t detect the gravitational pull, then there’s no planet there. Full stop."