Always blows my mind.
Voyager 1 has just ticked off another milestone: on Tuesday it reached 138 astronomical units from Earth, or about 20,600,000,000km from the planet on which you're (presumably!) reading this story. It's not an achievement that will be widely noticed or celebrated, because every kilometre it travels sets a new record for the …
Even if you have a simple gigabit network cable in which the signals travel at roughly 2/3rds of light speed, you end up with many bits in flight even on the cable between your desktop and your switch.
If you had an analogue TV, you could sometimes get multipath reception. You could literally see signals just having a few kilometres more way to get to you.
It's not too slow. Well, when mixed with acceleration and time dilation. The interesting thing about how it works out, is if you assume 1g constant acceleration, it takes about 30-60 years to reach ANY destination in the universe.
That is of cause assuming you have infinite fuel. Which is rather difficult. And a big shield to protect you while travelling at 0.9999999(9)% the speed of light. But even without the likes of cryogenics, time dilation takes care of the rest of the problems once your close enough to the speed of light.
Problem being, even if you leave now, you won't make it to that party at the other end of the galaxy in time!
PS, also it's funny calling it "too slow" as it is by *definition* "the fastest speed possible". :P
Voyager 1 has just ticked off another milestone: on Tuesday it reached 138 astronomical units from Earth, or about 20,600,000,000km from the planet on which you're (presumably!) reading this story.
..and is probably still wondering whether it locked the front door before it left.
Way to go, l'il fella :)
We're only 8.0e-21% of the way across the Universe?
Less than that. About a third of it, in fact.
we think that the Universe is about 27 billion light years across
Except that the universe has been expanding at an increasing rate for 13.8bn years, so it's about 92bn light-years across by now. There's also some evidence that the rate of expansion may vary, slowing down a little, then speeding up before slowing down again, with a wavelength of (currently) about 2bn years. The universe may be ringing like a bell from the impact of the Big Bang.
Putty. Putty. Putty.
Green Putty - Grutty Peen.
Grarmpitutty - Morning!
Pridsummer - Grorning Utty!
Not even a particularly
Nice shade of green.
As I lick my armpit and shall agree,
That this putty is very well green.
Vogons. El Reg must have one on the forums.
Well there's me. I used to work for Vogon International many years ago. I wrote data recovery/forensic software for them. Also did a few data recoveries. Oddly enough I happen to be wearing one of the T-shirts they gave us today.
Lol! Their old website (or parts of it) are still around :)
I'm not sure the "rate of expansion" effects that observation. Because the light is also travelling through the expansion as it moves, thus being red shifted accordingly etc. For example " Light that is emitted today from galaxies beyond the cosmological event horizon, about 5 gigaparsecs or 16 billion light-years, will never reach us, although we can still see the light that these galaxies emitted in the past"
It's hard to define objects we can only see the past of, and not even the present. Are they even "in our universe" anymore? Or have they ceased to exist? Thus leaving the "edge of the universe" still at the 14-16~billion light years?
Ah, found the details, it's about 46 light years across "now". https://phys.org/news/2015-10-big-universe.html
However I'd still argue that due to relativity etc we can say that it is now 14 billion across, and once the other light reaches us we could describe it as 46 light years across... at which point it would have expanded even more! ;)
Couldn't recall how old these were, so checked:
The Voyager spacecraft launched in August and September of 1977 and spent more than 11 years exploring the likes of Jupiter, Saturn, Uranus and Neptune before officially heading off toward interstellar space in 1989.
Not bad for forty year old hardware.
Yeah, it's getting away from Mr Sun and all his radiation. But it's also getting away from Mr Sun's protective magnetic field, so it's getting hit by interstellar radiation instead. Which, by definition, creates an even more interesting class of mutated superhero.
It's also a bit worrying that I'm older than these spacecraft, even though they've travelled an unimaginably long way, although admittedly not so unimagineably long as to have actually got anywhere yet.
The universe really is quite spacious.
Does anyone fancy a piece of fairy cake...
From Nasa's Voyager mission FAQ found here:
"Question: What kind of computers are used on the Voyager spacecraft?
Answer: There are three different computer types on the Voyager spacecraft and there are two of each kind. Total number of words among the six computers is about 32K.
Computer Command System (CCS) - 18-bit word, interrupt type processors (2) with 4096 words each of plated wire, non-volatile memory.
Flight Data System (FDS) - 16-bit word machine (2) with modular memories and 8198 words each
Attitude and Articulation Control System (AACS) - 18-bit word machines (2) with 4096 words each.
According to my calulations, that's a total of about 68KB, or small potatoes compared to today's microprocessors. We probably could perform all functions with one of today's boards and still have room for solid state data storage and much more fault detection software. We would still need a second unit for redundancy. Today's microprocessors are also much faster than the chips used on Voyager and a comparative system would use less electrical power. On the other hand, software might be more complicated as opposed to that used in an interrupt type system, but it would be much more capable and more flexible.
Let's look closer at the CCS. The CCS has two main functions: to carry out instructions from the ground to operate the spacecraft, and to be alert for a problem or malfunction and respond to it. Two identical 4096- word memories contain both fixed routines (about 2800 words) and a variable section (about 1290 words) for changing science sequences. The CCS issues commands to the AACS for movement of the scan platform or spacecraft maneuvers; to the FDS for changes in instrument configurations or telemetry rates and to numerous other subsystems within the spacecraft for specific actions. Fault-protection algorithms are also stored in the CCS, occupying roughly 10 percent of the CCS memory.
The main functions of the FDS are to collect data from, and controls the operations of, the scientific instruments; and to format engineering and science data for on-board storage and/or real-time transmission. The FDS also keeps the spacecraft "time" and provides frequency references to the instruments and other spacecraft subsystems.
The Voyager spacecraft computers are interrupt driven computer, similar to processors used in general purpose computers with a few special instructions for increased efficiency. The programming is a form of assembly language.
There is no clock chip, as such, in the spacecraft. The "clock" is really a counter, based on one of several electronically generated frequencies. These frequencies, based on a reference, generated by a very stable oscillator, are converted and fed to different locations in the spacecraft as synchronization signals, timers, counters, etc. The "clock" signal is part of the information telemetered to the ground and it is with ground software that we convert to day of year, time of day Greenwich Mean Time.
Voyager was built in-house at JPL; the computers were manufactured by General Electric to JPL specifications.
Question: How fast are the Voyager computers?
Answer:Not very fast compared to today’s standards. The master clock runs at 4 MHz but the CPU’s clock runs at only 250 KHz. A typical instruction takes 80 microseconds, that is about 8,000 instructions per second. To put this in perspective, a 2013 top-of-the-line smartphone runs at 1.5 GHz with four or more processors yielding over 14 billion instructions per second.
The standard reference for old NASA space computers is
Computers In Spaceflight: The NASA Experience where you'll find out all sorts of quite detailed stuff about how NASA built and ran those missions, right back to the days when the state of the are was a "cam timer," essentially the device used in old washing machines.
TTL has a rep for being power hungry, but it wasn't too bad if you kept the clock frequency down. The standard 16 and 18 pin packages used made the packing density quite good (for the time). Today we'd go surface mount and increase it 4x at a stroke.
Quite a few of these processors were bit serial, with "word length" set by width of registers (which might also be serial, being a string of ultrasound pulses in a delay line memory).
The availability of a 4 bit ALU (LS74181 and it's CMOS equivalent) made new processors easier, if you could take the clock speed limits and you can operate in chunks of 4 bits, which was OK for a lot of people.
When you control the hardware if it''s not fast enough not only can you hack the code, you can hack the instruction set as well. :-)
Then you hack the assembler to support the new instructions (no HLL, no YACC or Lex to write one)
From that era it seems only the RCA 1802 was available early enough and rugged enough for space use. It's sort of like the SPARC, a big register set and on chip DMA, DMA is very handy for space probes.
A very different world.
Today you hand BAe Systems $150K for a rad hard POWERPC board instead.
While "off the shelf commercial CPUs" might not be ok there were (outdoutably vastly more expensive) versions made that were rad-hard .... e.g. New Horizons has a MIPS processsor
As for the comms over that distance ... I did a course on error correcring codes in my maths degeree and teh lecturer talked about the level of error correction they had to use on Voyager and how he was amazed that they could actually communicate with it over that distance ... n.b. this was in 1984 when Voyager was between Saturn and Uranus!
I think the only rad-hard CPU around at the time was the RCA 1802:
A completely static design with no minimum clock frequency and you could use any register for the program counter.
The Z80 wouldn't have been released in time for this mission and certainly wasn't rad-hard.
Edit: I've just read the Wiki page and even the 1802 wasn't around in time for the Voyager. Also read:
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