Navigation for Spaceships Using X-ray Pulsars: Introducing XNAV
Written by Ian O'Neill
This could be the ultimate galactic GPS system: using pulsars as an interstellar navigation tool. Rapidly spinning neutron stars emit focused beams of X-rays into space and many, with accuracy as good as an atomic clock, have been mapped by astronomers. Now these pulsars may have a very important practical use. These interstellar beacons may be used to get a fix on the position of spacecraft and guide them around space…
Ever since the first X-ray pulsar was discovered in 1967 (called Centaurus X-3, the third X-ray source discovering in the constellation of Centaurus with a period of 4.84 seconds), astronomers have been busy mapping the distribution of these rapidly spinning stellar objects. Pulsars are the embodiment of a neutron star binary system; the neutron star strips the material from its stellar neighbour, accelerating the gas to about half the speed of light, blasting hot collimated X-ray emissions from its poles. As the pulsar spins, these beams of light act like a lighthouse, and should they be directed toward the Earth, we observe a highly accurate periodic flashing of X-rays.
At the beginning of this month, the IEEE/ION Position, Location and Navigation Symposium (PLANS) 2008 conference in Monterey, California featured two interesting concepts for the use of these highly accurate X-ray sources. The first proposal called "Noise Analysis for X-ray Navigation Systems" headed by John Hanson of CrossTrac Engineering, introduces a scaled-up version of terrestrial GPS, using pulsars rather than man-made satellites. The system is called X-ray navigation, or "XNAV" for short. Primarily focusing on space missions beyond Jupiter, XNAV would use the Solar System as the base co-ordinate and then measure the phase of the incoming X-ray emission from the mapped pulsars. As the X-ray pulses are so accurate, onboard systems could measure and compare the signal from multiple pulsar sources and automatically deduce the position of the spacecraft to a high degree of certainty. I suppose it would be an advanced 3D version of the traditional sextant as used by ships to measure the elevation of stars above the Earth's horizon.
The second concept entitled "Online Time Delay Estimation of Pulsar Signals for Relative Navigation using Adaptive Filters", is headed by Amir Emadzadeh at the UCLA Electrical Engineering Department. Emadzadeh suggests that the location of two spacecraft can be worked out if both ships are looking at the same, known pulsar. The periodic emission measured by both ships will have a differential time delay proportional to the distance between the ships. In addition, the UCLA group suggest a method to derive their relative inertial position by observing a distribution of X-ray sources throughout the cosmos.
These are very interesting concepts, but until we begin routinely venturing beyond the orbit of Jupiter I doubt we'll see these ideas come to fruition any time soon…
Original source: Space.com
Additional info: IEEE/ION PLANS 2008 conference
Filed under: Observing, Space Flight
May 24th, 2008 at 5:21 pm
Steven, Stop and think about a multi-generation space trip to Alph C for a moment. Do you honesty believe that a small crew of hand picked scientists can procreate for dozens of generations without losing something genetically critical to the safety of the flight? Ok, let's assume that all of the technical and biological challenges are overcome and this imaginary flight succeeds. Then what? It the trip took a millennium to complete, how would success be communicated back to earth? Modulated EM transmissions simply won't make it. Do the math. Maybe a return trip back to earth? Who would be interested after so many generations passing on earth? Steven, there is nothing logical about an intra-galactic trip to Alph C, our closet star system neighbor. The time problem is the painfully slow speed of light. I have said this several times before, If man or any alien intelligence can not overcome the speed of light by several orders of magnitude, we ain't going anywhere outside the influence of our sun. This is the reality of space travel. Anything else is sci-fi babble.
May 24th, 2008 at 7:04 pm
Chuck - In London before the 19th century ended, people saw a problem in the future, the streets of London where going to fill up with horse dung, an expected 8 meters high level was predicted for the early 21st century then someone invented the car around the dawn of the 20th century.
All I am saying we should all keep an open mind of what is to come.
I understand your point of view, but all the relative facts will change in the future, that is what science is all about.
Further more its pointless arguing about this as nether of us will live to see who will be correct.
May 25th, 2008 at 6:17 am
Steven, My mind is open to the possibility of multi-generation deep space travel. It just will not be with human cargo. Robotics yes! Humans no! I chuckled at your reference to the late 19th century London dung problem. Just imagine for a moment having to deal with a millennium's worth of a few space travelers and their offspring's fecal matter requiring ongoing recycling. We're talking hundreds of tons of material. I'm not joking. Every molecule of material and joul of energy on a human occupied space ship has to be positivetly accounted for and dealt with very efficiently or there will be a catastrophic trip failure. The slightest miscalculation will result in disaster. I really believe most people fail to understand the technological or biolological magnitude of what is involved in space travel we are discussing. Positive "we can do anything given enough time" thinking will not make it. for human or alien intelligence deep-space travel. Space is not a human friendly place. Another thought for consideration concerning why extended space travel won't happen and that is the mind boggling cost and return on investment for a high risk prototype venture. In fact cost and ROI may be the largest single obstacle to long range space exploration. And by the way, we are not arguing, we are debating the possibility of space travel. Steven, open your eyes, it isn't going to happen with humans. Man will make it to Mars, Pluto and maybe an asteroid or two beyond pluto, but no further.
May 25th, 2008 at 10:09 am
We can solve the problem of manned interstellar trips with robotics. The main problem seems to be with sending a human body across light-years. Ok, then, don't send the human body. Remove the brain, put it in a hermetically sealed jar, and send that. Hook the brain up to a virtual reality system and you're all set.
On the way there, the only space a human would need to take up is about three liters. The ship could be the size of current day space probes. Life support and radiation protection are highly simplified, and there is no danger of going crazy because of the nearly unbounded virtual worlds that the crew would "live" in.
On arrival, use robotic bodies that have been stored along with the ship (again, very little space needed to do that).
A human body IS fragile, so it would a lot easier if we got rid of it.
May 25th, 2008 at 2:11 pm
Zeb, The human species will not survive long enough to develop the surgery and reconstituting techniques you suggest. Your second sentence should read in part . . . "sending dozens of generations of human bodies across light years of deep space." I suspect if an attempt is made to build a bio-sphere space vehicle in the next couple hundred years for a trip to Alph C; it will most likely be larger than the Merchandise Mart in Chicago. A guess is this would be a minimum size vehicle to support, say, a half dozen science engineers ready for a millennium nightmare . Hmm . . . I wonder who will put up the billions of dollars required to build this folly and who will volunteer for the mission. I sure would like to be around to see what develops.
May 26th, 2008 at 1:34 am
I suspect that once computers have achieved both superiority to the human brain both in calculating and cognitive superiority that all bets are off in what we can do. And that achievement is expected in the next 30-50 years. But I agree with Chuck that humans won't be leaving the solar system anytime soon, if ever. That doesn't mean our children (intelligent and sentient machines) won't be. Seems to be the next logical step in evolution to me.
May 26th, 2008 at 7:52 pm
Gary, It won't be we, it will be them. The thought of sentient machines scares the hell out of me.
June 6th, 2008 at 7:17 am
Guess that re-deifines the term 'Sat-Nav'
ok, crap joke
But will such a system send hordes of unwary space-travellers down dead-ends, careening into black holes, even though the darn hardware used swaers blind it's safe to proceed?