by Paul Gilster | May 10, 2010 | Missions |
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.
by Paul Gilster | May 7, 2010 | Missions |
Is Jupiter the best place to collect massive amounts of helium-3? The Project Daedalus designers thought so. Back in the 1970s, members of the British Interplanetary Society set out to design a starship that would use pulsed fusion propulsion, with deuterium and helium-3 as fuel. Daedalus had mind-bending requirements, for the plan was to drive it to 12 percent of lightspeed on a flyby mission to Barnard’s Star that would take fifty years to arrive. 250 pellets of deuterium and helium-3 would be detonated every second in its combustion chamber over a thrust period of four years. That calls for a lot of fuel, and therein lies the problem.
Fueling Up the Probe
We can find deuterium (an isotope of hydrogen) right here on Earth, but helium-3 is a rarity. The Daedalus team figured it needed some 30,000 tons of helium-3, so it envisioned mining Jupiter’s atmosphere, where the stuff is plentiful. Imagine floating factories in the atmosphere of the giant planet using waste heat to generate lift, so-called ‘aerostats’ that would be serviced by orbital transports. The task of mining Daedalus’ fuel was almost as daunting as the prospect of an interstellar journey, and pointed to the need for a vast solar system-wide infrastructure to support it.
Image: Project Daedalus was the first detailed study of an interstellar probe. Project Icarus aims to reconsider Daedalus in light of new technologies. Credit: Adrian Mann.
But is Jupiter the best option? The Project Icarus team, now updating the original Project Daedalus, is asking this and many other questions about the original design, including whether or not there is a case to be made for a planet like Uranus, likewise rich in helium-3 but with a much shallower gravity well. For that matter, what about mining our own Moon, now believed to have resources of helium-3? The design team is shaking down these and other ideas in what Leonard David calls an ‘exercise in theoretical engineering to the extreme.’ David writes about Icarus in this Space.com feature.
The current terms of reference for Project Icarus are as follows:
- 1. To design an unmanned probe that is capable of delivering useful scientific data about the target star, associated planetary bodies, solar environment and the interstellar medium.
- 2. The spacecraft must use current or near future technology and be designed to be launched as soon as is credibly determined.
- 3. The spacecraft must reach its stellar destination within as fast a time as possible, not exceeding a century and ideally much sooner.
- 4. The spacecraft must be designed to allow for a variety of target stars.
- 5. The spacecraft propulsion must be mainly fusion based (i.e. Daedalus).
- 6. The spacecraft mission must be designed so as to allow some deceleration for increased encounter time at the destination.
Where to Send an Interstellar Probe
One current debate involves the choice of targets. When Daedalus was being designed, Barnard’s Star was thought to have planets, a finding that later turned out to be erroneous. You pick a target based on the optimum planetary findings, but just what are they in today’s exoplanetary environment? Alpha Centauri is thought to be the closest stellar system, but the WISE mission may show us a brown dwarf even closer than this, perhaps as nearby as three light years. If that happens, does Icarus consider a brown dwarf destination, or stick with larger M-dwarfs and G- and K-class stars?
Or consider Alpha Centauri itself. We have three teams now at work on radial velocity studies that should give us an answer within three years about whether there are rocky worlds around Centauri A or B. Kelvin Long, who heads up Icarus and who is coordinating the effort between the British Interplanetary Society and the Tau Zero Foundation, is wisely keeping the options open. As design work on fusion methods and numerous other components gears up, the Icarus team will hold off until 2013 before choosing its optimum target, by which time we should have some of these questions settled. The final study reports are due in 2014.
Long an admirer of the Project Daedalus effort (my copy of that team’s final report is battered, dog-eared and crammed with notes after years of use), I’m pleased not only with the quality of the Icarus team, but with the fact that many of the Project Daedalus designers are offering their insights as well. David quotes Kelvin Long on the nature of the project:
“There is a need to maintain interest in and the capability to design interstellar probes. With many of the historical leaders in this field now nearing retirement or deceased, the Project Icarus study group wants to take up the baton and keep alive the long term vision that travel to the stars will one day be possible. This is one of the reasons why over half of the team is relatively fresh out of their university studies.”
Interstellar Mission Design in Context
An exercise like Daedalus relies upon identifying the key technological markers for an interstellar attempt. That means determining where we are today with propulsion ideas like fusion, which continues to defy our best efforts to extract useful energy here on Earth. What Icarus brings to the table that Daedalus did not have is, as primary propulsion lead Richard Obousy points out, over thirty years of new data on experimental fusion, including the interesting possibility of using tiny amounts of antimatter as fusion catalysts. As Obousy tells David, “All these technologies could certainly optimize the original Daedalus design, meaning less mass for the propulsion system and more possibilities for the payload. We hope our study will result in a faster and less massive design.”
Less massive indeed, for the original Daedalus was a 54,000 ton vehicle. If you’re interested in how the Icarus team is tackling this and other questions, have a look at the Project Icarus blog, the latest entry of which deals with measuring stellar distances and the science that an interstellar probe could return. That data return itself is a fascinating question. Do you communicate with lasers, or perhaps even something more exotic, such as a communications link based on the Sun’s gravitational lens? The energetic Icarus team is tackling these issues now and will be occupied for the next four years in refining each mission component.
A completed starship design study tells us where we are today and sparks the imagination. My own hope is that just as Icarus continues the Daedalus tradition by examining fusion alternatives, it may lead to future spinoff studies on other propulsion ideas, including beamed sail concepts. The key thing is to get serious work focused on interstellar propulsion issues so we can learn how new technologies may help us resolve seemingly intractable problems.
by Paul Gilster | May 6, 2010 | Astrobiology and SETI |
Finding life on a world in the outer Solar System — think Enceladus or Titan for starters — would be an extraordinary step forward. Martian microbes, if they exist, might be evidence of contamination, or we might be evidence of ancient contamination from Mars, given the ready exchange of materials between our planets in the last several billion years. But the outer system offers the possibility of discovering life that originated entirely separately from anything we know.
The problem is that we’re a long way from having built the spacecraft that can make these detections. That’s why places like Pitch Lake, on the island of Trinidad, are so useful. Other than the temperature, conditions here are about as close to what we might find on Titan as anything we know. The 114-acre lake is a cauldron of hot asphalt permeated with hydrocarbon gases and carbon dioxide. As you can see in the image below, it’s hardly a hospitable-looking place.
But this asphalt hell-hole defies expectation. As discussed in a recent article in Astrobiology Magazine, each gram of its black goo can harbor up to 10 million microbes. We’re looking at life that seem to feed off hydrocarbons and, while not breathing oxygen, respire with the aid of metals. Both bacteria and archaea are represented, some of the latter falling “…far enough away from known groups as to represent novel lineages.”
Image: Pitch Lake bubbles with hydrocarbon gases and carbon dioxide. Credit: Pitch Lake Research Group.
Those are the words of Steven Hallam (University of British Columbia), who is working with Dirk Schulze-Makuch (Washington State) on the project. The two scientists believe that the presence of life in Pitch Lake makes the hydrocarbon lakes of Titan look more astrobiologically promising than we have suspected. Moreover, some of Titan’s hydrocarbon reservoirs may be heated from below.
How does Pitch Lake stay alive? From the article:
Each sample contained a distinct microbial population. Most of the bacteria appear related to ones found in oxygen-depleted sediments, methane seeps or oil reservoirs…
Water levels in the asphalt are low, at or below the reported threshold for life on Earth, so the life the researchers found in the lake might be constrained to watery pockets within the surrounding asphalt, similar to what is seen bound in frozen lakes and glaciers in the McMurdoDry Valleys in Antarctica. The fact that E. coli gut bacteria can generate most of their own water and that fungus found in kerosene can extract water from light hydrocarbons could point to how life can survive even when little to no liquid water is available.
Studies like this give us a glimpse of the adaptations possible when life sustains itself with hydrocarbons and metals in asphalt. But even if we eventually find no life on Titan, we’re also getting insights into life on the early Earth before it adapted to oxygen. As to Schulze-Makuch, he is much in the news these days. We’ve already reported on his argument that the Viking lander may have found life on Mars in the 1970s (see his book We Are Not Alone), but his focus seems to be moving ever further out in the Solar System.
Some day we’ll know how far life can go in the natural laboratory that is Titan. For now, we’ll continue to seek out environments that are at the outer edge of adaptability, hoping to broaden our definition of ‘habitable zone.’
by Paul Gilster | May 5, 2010 | Astrobiology and SETI, Autonomy and Robotics |
Talk of a ‘singularity’ in which artificial intelligence reaches such levels that it moves beyond human capability and comprehension plays inevitably into the realm of interstellar studies. Some have speculated, as Paul Davies does in The Eerie Silence, that any civilization we make contact with will likely be made up of intelligent machines, the natural development of computer technology’s evolution. But even without a singularity, it’s clear that artificial intelligence will have to play an increasing role in space exploration.
If we develop the propulsion technologies to get an interstellar probe off to Alpha Centauri, we’ll need an intelligence onboard that can continue to function for the duration of the journey, which could last centuries, or at the very least decades. Not only that, the onboard AI will have to make necessary repairs, perform essential tasks like navigation, conduct observations and scientific studies and plan and execute arrival into the destination system. And when immediate needs arise, it will have to do all of this without human help, given the travel time for radio signals to reach the spacecraft.
Consider how tricky it is just to run rover operations on Mars. Opportunity’s new software upgrade is called AEGIS, for Autonomous Exploration for Gathering Increased Science. It’s a good package, one that helps the rover identify the best targets for photographs as it returns data to Earth. AEGIS had to be sent to the three transmitting sites and forwarded on to the Odyssey orbiter, from which it could be beamed to Opportunity on the surface. A new article in h+ Magazine takes a look at AEGIS in terms of what it portends for the future of artificial intelligence in space. Have a look at it, and ponder that light-travel time to Mars is measured in minutes, not the hours it takes to get to the outer system.
Where do the early AI applications like AEGIS lead us? Writer Jason Louv asked Benjamin Bornstein, who leads JPL’s Machine Learning team, for a comment on machines and the near future:
“We absolutely need people in the loop, but I do see a future where robotic explorers will coordinate and collaborate on science observations,” Bornstein predicts. “For example, the MER dust devil detector, a precursor to AEGIS, acquires a series of Navcam images over minutes or hours and downlinks to Earth only those images that contain dust devils. A future version of the dust devil detector might alert an orbiter to dust storms or other atmospheric events so that the orbiter can schedule additional science observations from above, time and resources permitting. Dust devils and rover-to-orbiter communication are only one example. A smart planetary seismic sensor might alert an orbiting SAR [synthetic aperture radar] instrument, or a novel thermal reading from orbit could be followed up by ground spectrometer readings… Also, for missions to the outer planets, with one-way light time delays, onboard autonomy offers the potential for far greater science return between communication opportunities.”
One-way light delays are obviously critical as we look at the outer planets and beyond. Voyager 1, for example, as of April 12, was 113 AU from the Sun, having passed the termination shock. It’s now moving into the heliosheath. At these distances, the round-trip light time is 31 hours 34 minutes. That’s just to the edge of the Solar System. A probe to the Oort Cloud will have much longer delays, with round-trip signal times ranging from 82 to 164 weeks. Pushing on to the Alpha Centauri stars obviously lengthens the round-trip time yet again, so that we face up to 4.2 years delay just in getting a message to a probe at Proxima, with another 4.2 years for acknowledgement. The chances of managing short-term problems from Earth are obviously nil.
Image: Comet Hale Bopp’s orbit (lower, faint orange); one light-day (yellow spherical shell with yellow Vernal point arrow as radius); the Termination Shock (blue shell); positions of Voyager 1 (red arrow) and Pioneer 10 (green arrow); Kuiper Belt (small faint gray torus); orbits of Pluto (small tilted ellipse inside Kuiper Belt) and Neptune (smallest ellipse); all to scale. Credit: Paul Stansifer/84user/Wikimedia Commons.
Just how far could an artificial intelligence aboard a space probe be taken? Greg Bear’s wonderful novel Queen of Angels posits an AI that has to learn to deal not only with the situation it finds in the Alpha Centauri system, but also with what appears to be its growing sense of self-awareness. But let’s back the issue out to a broader context. Suppose that a culture at a technological level a million years in advance of ours is run by AIs that have supplanted the biological civilization that created their earliest iterations.
Think it’s hard to guess what an alien culture would do when it’s biological? Try extending the question to a post-singularity world made up of machines whose earliest ancestors were constructed by non-humans.
Will machine intelligence work side by side with the beings that created it, or will it render them obsolete? If Paul Davies’ conjecture that a SETI contact will likely be with a machine civilization proves true, are we safe in believing that the AIs that run it will act according to human logic and aspirations? There is much to speculate on here, but the answer is by no means obvious. In any case, it’s clear that work on artificial intelligence will have to proceed if we’re to operate spacecraft of any complexity outside our own Solar System. Any other species bent on exploring its neighborhood will have had to do the same thing, so the idea of running into non-biological aliens seems just as plausible as encountering their biological creators.
by Paul Gilster | May 4, 2010 | Astrobiology and SETI |
The Stephen Hawking controversy continues to bubble, with discussion on the Larry King show and the appearance of David Brin’s essay The Other Kind of Aliens. It’s all to the good to get such discussions widely circulated, even if it can be dismaying to find that so many respondents believe the answers about how alien cultures will behave are obvious and can be readily deduced from our own cultural experiences. But maybe that’s because this is a new controversy, one that the search for exoplanets is only now bringing to a wider public in any serious way. There is plenty to ponder, and while we debate the nature of alien culture, let’s look at something more immediate.
The Protocols of SETI Success
SETI continues to look for signals of extraterrestrial civilizations. What happens if a signal is actually detected? For the answer, we can look to the SETI Post-Detection Taskgroup, created by the SETI Permanent Study Group of the IAA (International Academy of Astronautics). The Taskgroup’s job is to look at what would happen if we do get a confirmed detection. Understand that we’re talking about a group that is purely advisory in nature, but one whose insights may help scientists. It’s an impressive group whose members are listed here.
Step one is obvious. The reception of a signal would be met with the Taskgroup urging its discoverer to evaluate its authenticity beyond any shadow of a doubt. If it is genuine, the Taskgroup then advises that details be disclosed to the astronomical community first, beginning with the International Astronomical Union (IAU), which would then pass the news along to the United Nations and other govermental bodies. The discoverer would then be free to call a press conference to announce the finding, and soon the airways and computer networks would be filled with discussion.
Paul Davies runs through all this in his book The Eerie Silence (Davies is currently Chair of the Taskgroup, so he’s an unusually good source). And he notes that this calm procedure would likely be a good deal messier in practice:
The discoverer may be deliberately uncooperative or overawed and disoriented by the magnitude of events. There may be more than one person and one country involved. The news might leak out ahead of the formal diplomatic steps… Also, there is nothing to stop an astronomer who detects a signal out of the blue from going straight to the press or to her or his government, or any other organization, bypassing our Taskgroup altogether.
Handling Our Response
Davies goes on to say that despite all this, the most likely scenario is one involving a detection that occurs within the SETI community, and in that case the Taskgroup protocol is likely to be followed. You can read more in the Declaration of Principles Concerning Activities Following the Detection of Extraterrestrial Intelligence, written in 1989, which runs through the above steps. Here’s an interesting bit that bears on the debate about beaming signals to the stars. It’s in sections 7 and 8 of the protocol, the first dealing with protecting the critical frequencies:
If the evidence of detection is in the form of electromagnetic signals, the parties to this declaration should seek international agreement to protect the appropriate frequencies by exercising procedures available through the International Telecommunication Union. Immediate notice should be sent to the Secretary General of the ITU in Geneva, who may include a request to minimize transmissions on the relevant frequencies in the Weekly Circular. The Secretariat, in conjunction with advice of the Union’s Administrative Council, should explore the feasibility and utility of convening an Extraordinary Administrative Radio Conference to deal with the matter, subject to the opinions of the member Administrations of the ITU.
There follows the policy on response:
No response to a signal or other evidence of extraterrestrial intelligence should be sent until appropriate international consultations have taken place. The procedures for such consultations will be the subject of a separate agreement, declaration or arrangement.
When Speculation Runs Wild
The trick in all this is early in the detection process, when every attempt will be made to ensure that the signal is both artificial and not from this Earth. Verification could take time, and with today’s inter-connected web of communications, bogus information can spread in seconds, quickly tinged with dark hints of conspiracy when answers are not immediate. Science is deliberate and rigorous fact-checking is woven into its very being, so it’s unlikely a SETI scientist is going to make sensational claims without absolute certainty. This contrasts sharply with media expectations and can lead to an avalanche of misleading information.
And what about government in all this? If a possible detection is leaked and later proven bogus, conspiracy theorists will be all over it, claiming that the knowledge is being suppressed. I think Davies’ treatment of secrecy and SETI is to the point:
…if there are government plans to seize control of SETI following a positive result, they haven’t yet come to the attention of the SETI community, in spite of several high-profile hoaxes and false alarms. In fact, far from taking an unhealthy interest in the subject, governments worldwide seem to be completely indifferent. A member of the British House of Lords once asked me about SETI, but purely out of personal curiosity. In the US, Congress cancelled public funding for SETI in 1993, on the basis that it was a waste of money. That is hardly the action of a government that has a serious interest in ‘contact.’ As for secret government post-detection contingency plans, I have no doubt they are non-existent. When it comes to post-detection policymaking, the Taskgroup is it.
Will the Taskgroup’s recommendations ever get put into practice? The world will be utterly changed if a genuine signal is received and verified, and much will depend on its nature. Confirming an artificial pulse aimed at us raises the question of response, what to say, how to say it, whether to respond at all. But perhaps we’ll just detect the clear signs of a civilization at work, without necessarily knowing that it knows about us. The detection of an artificial construct in another galaxy comes to mind. It’s millions of light years away and we know nothing about its builders or whether they even still exist. That’s a more likely scenario, I suspect, and one that would shake up our culture without our ever having the possibility of genuine contact.
