Voyager ticks one box for interstellar arrival
“Very rapid escalation” in galactic rays hints at new region of SPAAAAAACE
The venerable Voyager 1 spacecraft seems to be a little closer to leaving our Sun's neighbourhood behind and entering interstellar space, says NASA.
The space agency has outlined three criteria that must be satisfied before Voyager will be deemed to have left the heliosphere, the first of which is detection of galactic cosmic rays. Voyager apparently detected a 25 per cent increase in such rays between January 2009 and January 2012, but recent readings apparently surpass that rate of growth and represent a “very rapid escalation” in galactic ray detection.
The Voyagers are here, NASA says
The second factor NASA believes could point at crossing the threshold between solar space and interstellar space is measurement of energetic particles found near the sun. The agency's recent report on Voyager 1's progress says the probe has found a “slow decline” in the prevalence of such particles, but there's no smoking gun just yet. Indeed, NASA says if Voyager had passed beyond the heliosphere we would expect their presence to drop off “precipitously”.
The third sign that Voyager 1 has well and truly left the building would be a re-orientation of magnetic fields around the craft. There's no sign of that yet.
NASA officials nonetheless gushed about the possibility that Voyager 1 might break through into interstellar space real soon now. Indeed, it may already have done so, as the agency says it's crunching recently-arrived data in ongoing efforts to ascertain just what's going on out there.
Voyager's high gain antenna, which sends science data back to earth, is said to send data at rates “ … as high as 7.2 kilobits per second”. Recent reports suggest the probe is 17,911,000,000km from earth, so we're pretty sure there's a few packets dropped along the way. That could make ascertaining just when the craft enters interstellar space a tad tricky, you'd imagine. ®
The spacecraft were launched in 1977, 35 years ago. It was probably designed a few years before that as well (microprocessors were a little primitive in that era). If I remember correctly, the Voyager spacecraft didn't have much of a micro to speak of anyway. So, does anyone out there have a computer from that era that is in working order?
Oh, and the speed of 7200 bps was pretty fast in that era, and consider the distance the data travels, it is a few km/miles between us and the spacecraft is only a few watts of power in its transmitter.
Quite an accomplishment if you ask me!
Voyager error correction
Actually Voyage was launched with the concatenated convolution & Reed-Solomon error correction system that was not, at the time, tried and tested but the engineers expected it to deliver better performance than the then-standard long constraint length convolution codes.
It is implemented on dedicated hardware, with the choice of the dual-basis (Berlekamp) RS representation made to simplify the hardware design (in a software encoder or decoder it need an additional, though trivial, look-up transformation).
And it did work, becoming the de-facto FEC system for most space use until the rise of Turbo codes in the last decade, which provide only an extra 1-2dB of performance.
An impressive achievement!
Yes, it's a really good reminder of how vastly, hugely, mind- bogglingly big space is.