The fastest moving spacecraft in our Solar System is currently Voyager 1, which is moving at 61,419 kilometers per hour, a figure that works out to 17.06 kilometers per second. It’s always interesting to weigh such speeds against the hypothetical upper limits we would get from certain kinds of propulsion. Geoffrey Landis told me years ago, when we were talking in his office at Glenn Research Center in Cleveland, that a reasonable Sun-diver maneuver (a close pass by the Sun to get the ultimate gravitational boost) might result in a properly designed solar sail getting up to 500 kilometers per second. Quite a jump from Voyager 1.
On the other hand, contrast it to a journey to the nearest stars. Moving at 500 kilometers per second (assuming they could withstand the acceleration of the maneuver), the occupants of our solar sail starship would travel some 2580 years before reaching Centauri A and B. I’ve seen some extrapolations that get travel time to the Centauri stars down to about 1100 years using the same kind of Sun-diver maneuver, but I can’t find anything faster via solar sails unless we start talking about beamed propulsion, in which case all bets are off. One of Robert Forward’s designs reached 50 percent of lightspeed but assumed construction projects to build the necessary infrastructure that made the interstellar journey seem like the least of our problems.
Voyager 1 is also the most distant human object, at a distance from the Sun of 16,962,908,475 kilometers (as of this morning), or just above 113 AU. Voyager 2 is a distant third at 92 AU, with the no longer communicative Pioneer 10 at 100.7 AU. As for New Horizons, our doughty mission to the Pluto/Charon double dwarf planet, it’s now 16.629 AU out, moving at 16.2 kilometers per second. You can find a handy chart of these facts on Daniel Muller’s site, which draws on data from JPL/NASA, ESA and other space agencies and organizations.
Trouble on Voyager 2
Speaking of Voyager 2, a flurry of concern arose late last week with the news that the spacecraft has been put into a troubleshooting mode after changes were detected in the pattern of returning data. Most spacecraft systems seem healthy enough, with the problem arising in the flight data system responsible for data formatting before transmission to Earth. We talked last week about round-trip light travel times, which make dealing with onboard issues a problem for distant spacecraft. Ponder that Voyager 2, as of May 10, has a round-trip signal time of 31 hours 13 minutes and it’s still (barely) inside the Solar System.
Because of its problems, Voyager 2’s data are at present unavailable for decoding as mission team members work to troubleshoot the problem. I always think back to all the work that went into the Galileo mission’s high-gain antenna as engineers tried to get it operational after it failed in 1991. In 1995, working with an eighty-minute round-trip signal time, they were able to reprogram Galileo’s software to work with the low-gain antenna that was the only option left. Engineers also had to fix a major problem with the spacecraft’s digital tape recorder just before Jupiter orbital insertion, a problem that would reappear later in the mission.
The Galileo mission was still a success despite major limitations on data return because of the loss of the high-gain antenna. As to the Voyagers, there’s no doubt of the success of their mission. Diagnosis of the current problem continues, and we’ll have to hope for the best. We need as much data as possible as the spacecraft work their way through the heliopause and out into interstellar space. Their journey tells us how far we have come and offers a daunting look at how challenging it will be as we push our explorations out into the Kuiper Belt.
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This definitely makes it clear that we’ll need an extraordinary level of system robustness and redundancy if we are going to get a science return on Kuipper-Belt (and eventually Ort-Cloud and Interstellar) class missions lasting 50 years or more. Now, if we could only find a way of achieving this level of robustness without adding extra weight to the craft — that will be the real challenge!
I recall that the Space Shuttles have many fail-safe systems, some even fail-operational (some even have up to 3 levels of redundancy built in!) — and yet these (at times) have been put to the test (e.g. when 2 of 3 main engine computers failed due to an electrical short during one launch). But these things all add weight to the vehicle — that’s really not an option with a craft that’ll need to reach speeds in excess of 100 km/s.
If these construction projects are simply aggregates of identical units, as a phased array for a microwave beam would be, the construction project would consist of a high-volume transmitter factory on Earth, a steady stream of heavy lift launches, and an automated procedure to attach the transmitters to a growing spider-web like assemblage in space. All well within range of present technology, I think.
It would be expensive, but then, it could also be used to beam energy down to Earth.
Forward’s Epsilon Eridani mission (manned, no less) called for not only the power installation and transmitting facilities, but a vast Fresnel lens deep in the outer Solar System. Here he was pondering laser propulsion rather than microwave, of course. His novel Rocheworld works out a fictional treatment of the idea.
Paul: Microwaves make things a lot easier. The vast lens would be replaced by an even larger phased array, but power installation and transmitting facilities would go away entirely. The array would have to be in the inner solar system, where solar energy is plentiful. Perhaps a Lagrange point of Mercury. Depending on the interplay of power, wavelength and aperture, the array elements might be small and low power, like cellphones, or larger and medium power, like microwave ovens. Perhaps even flimsy, substrate-less microchips that could be launched by the billions. Individual elements would be linked together by hooks or threads to form a vast fabric stabilized by rotation. No structural elements, and no limits to size other than the number of units that can be made and attached in reasonable time.
I think the sail will be a tougher engineering challenge than the transmitter, in this scenario. I would still be interested to hear the argument why a superconducting mesh could not be 100% reflective. It would not be hard to keep a mesh superconducting passively in interstellar space where the equilibrium temperature is 4K. A maximum velocity would be dictated by ISM impact heating, but with HTc superconductors that could be a pretty good fraction of c, I believe. ISM impact erosion could be a very serious problem for any sail approach, as there is really no way to shield the sail.
Eniac, so true about ISM impact erosion. Some of Forward’s sails were hundreds of kilometers in diameter, and we can only imagine what they would look like after a few years at half of lightspeed!
These sturdy Voyagers have provided insight into performance well past their ‘warranties’. They have not only brought new understanding of remote parts of our neighborhood, they provide real cases of hardware and software durability in their current paths in the frigid outer system. When they do finally go silent, the last data we get will be the real-world capability of technology in these realms.
Should Voyager 2 never be rectified, it should still be monitored to determine the limits of everything from the computer to the radioisotope generator. This can help with designs for missions intended to join this cosmic vanguard.
Ad Astra per Aspera.
To ScottG, the New Horizons mission is already headed for Pluto and the Kuiper Belt. The planned duration is around 15 years, although presumably it will be kept going as long as possible:
The proposed Innovative Interstellar Explorer mission would use current technology to get out to 200 a.u. 30 years after launch. It might take longer than that to develop some of the exotic technologies discussed on this blog, even if they’d get to their destinations a lot faster.
I’m most hopeful of a sundiver solar sail mission which could reach near-interstellar space a few years after launch, and might be feasible within maybe 20 years.
Out of interest, anyone got any info on the generalization of Lagrange points to elliptical orbits? Are they even relevant for an orbit as eccentric as Mercury’s?
Going off on a tangent here …
What I find sad is how little public appreciation there is of the wonderful Voyager missions. My friends and family are well aware of my enthusiasm for astronomy & space exploration – and I have been asked more than once what the human race’s greatest achievements in space were. My response of the Voyagers (which I consider may actually be the human race’s greatest achievement so far), and the Mars rovers never fails to surprise – as people always seem to expect me to say Apollo 11 or even the recovery of Apollo 13 (thanks, no doubt, to the movie). On the other hand, people seem to be dimly aware of the Mars rovers and to have long since forgotten that Voyagers 1 & 2 ever existed.
Sadly, our cause seems to suffer from a severe lack of appreciation & support amongst the general public. I believe it falls on sites like this and organisations like Tau Zero to try to improve on that that miserably low profile, and enthusiasts like myself to do everything we can to talk positively about the benefits of space exploration and counter the “what has it ever done for me?” mindset.
Here is the JPL news release on Voyager 2:
Voyager 2 has had tough going from practically the moment it was launched
into space in 1977. But it has managed to overcome all these obstacles while
exploring the four gas giant worlds and their systems in the process. I know
the probe is aging (if you consider something born in the 1970s old), but it
has been predicted to last until 2025 so let’s hope for the best.
Engineers Diagnosing Voyager 2 Data System
Updated May 17, 2010 at 5:00 PT.
One flip of a bit in the memory of an onboard computer appears to have caused the change in the science data pattern returning from Voyager 2, engineers at NASA’s Jet Propulsion Laboratory said Monday, May 17. A value in a single memory location was changed from a 0 to a 1.
On May 12, engineers received a full memory readout from the flight data system computer, which formats the data to send back to Earth. They isolated the one bit in the memory that had changed, and they recreated the effect on a computer at JPL. They found the effect agrees with data coming down from the spacecraft. They are planning to reset the bit to its normal state on Wednesday, May 19.
The rest is here:
You’d think they’d use ECC memory with error detection and correction on these missions. How could a bit just flip? Funny…