≡ Menu

Of Solar Sails, Bets and Optimism

I’ve been surprised by the sizable reaction to my bet with Tibor Pacher, not just in terms of comments here but in related e-mails. For those of you who missed the original post, I found Tibor’s prediction that the first interstellar mission would be launched by 2025 to be an irresistible target. Tibor posted the prediction on the Long Bets site, and the way this works is that someone willing to make a bet on the prediction puts down the money upfront and challenges the predictor to match it.

Negotiations follow, the outcome being that if the terms are worked out and the bet is accepted, it is finalized. Both parties send in their money, and the money grows over the years in a long-term investment portfolio called the Farsight Fund. Ultimately, either the Tau Zero Foundation or (Tibor’s choice) the SOS-Kinderdorf International, will enjoy the result.

Now that Tibor and I have finalized the terms, the details will go up on Long Bets as soon as our funds arrive (which should be in a few days). Until then, I thought you might be interested in some of the details we settled upon. Among other things, we have agreed that:

  • The mission can be a manned or unmanned, either a flyby probe or a spacecraft intended to be captured by the target star’s gravitational field. The mission will have been designed expressly as a mission to another star, and as not an outer-Solar System mission that simply keeps going, with a star more or less along its route of flight.
  • The allowed launch location of the spacecraft is any place in the Solar system within the orbit of Neptune, either from the surface of a Solar System body or from any orbital position.
  • The mission duration must be less than 2000 years.
  • As a minimum requirement for the mission the spacecraft shall be capable of delivering data for at least one scientific measurement.

The actual text of these details and a few other matters will be posted soon on the Long Bets site — I’ll provide the link once it’s available. And as I’ve told more than a few people, I would be delighted to be proven wrong on this matter, for it would mean that our technology is advancing at a far faster clip than I currently assume, and also that enough public support will exist to make such a mission possible. That sort of optimism (even though I think it’s premature) is a bracing tonic after the weekend’s loss of NanoSail-D, a solar sail deployment experiment.

The last time I wrote about solar sails, I noted the frustration that the team at Marshall Space Flight Center in Huntsville must have been feeling about the concept. That frustration grows out of knowing that this technology is ready for space-testing but perennially short of resources, and I suspect it is shared among NASA scientists at all centers involved in sail work. The NanoSail-D deployment experiment, involving a 100-square foot sail, seemed made to order, since it hitched a ride aboard a SpaceX Falcon rocket to which NASA Ames had already committed.

Now we’ve lost both the SpaceX Falcon and NanoSail-D, a setback to be sure, but keeping Elon Musk’s words in mind is probably good advice. In a letter to SpaceX employees, the company’s CEO noted that the Merlin 1C first stage engine worked flawlessly, the problem occurring in staging. The latter evokes the spectre of Cosmos 1, the Planetary Society’s mission, which also perished through booster failure. Musk went on to say:

As a precautionary measure to guard against the possibility of flight 3 not reaching orbit, SpaceX recently accepted a significant investment. Combined with our existing cash reserves, that ensures we will have more than sufficient funding on hand to continue launching Falcon 1 and develop Falcon 9 and Dragon. There should be absolutely zero question that SpaceX will prevail in reaching orbit and demonstrating reliable space transport. For my part, I will never give up and I mean never.

Musk means business, and that same attitude is surely felt through the community involved in solar sail activity, and in the larger community thinking about deep space missions at various space agencies, universities and private companies around the planet. Solar sails, leaving the propellant at home and hence able to significantly ramp up payload possibilities, are probably going to be key players in opening up the Solar System. Factor in beaming concepts from microwaves to lasers and you’re talking about a technology that makes sense and is workable under the laws of physics as presently understood. NanoSail-D never made it, but the more commercial possibilities we explore via companies like SpaceX, the sooner we’ll get the next sail into full space deployment.

Comments on this entry are closed.

  • Ron S August 5, 2008, 14:28

    I just have to ask why you two specified the second condition since I can’t see that it matters where the launch is from. If it’s beyond Neptune, you do still need to at least travel to that location; at best, if you start for the launch point now, you gain an extra 17 years, for a total mission time of 2017 years. I also don’t see how you can know whether data acquisition, transmission and reception is possible until it occurs (4030 AD or later); you are limited to predicting the MTBF of the spacecraft science instruments.

    Interesting bet regardless. I would vote against the eventuality of such a launch by 2025. However, I would also prefer to lose the bet.

  • Administrator August 5, 2008, 15:03

    Ron, re data return, the point is that the mission be built for it — we obviously won’t know whether or not any data are returned until it gets to target.

    Regarding launch, you’ll need to ask Tibor, who may weigh in on this here. The Neptune limitation was his idea. I’ll write him in case he doesn’t see this right away, as I’m curious myself.

  • Tibor August 5, 2008, 16:27

    Ron & Paul,

    the Neptune limitation refers simply to the planetary border of our Solar System (after Pluto’s “degradation”). The why behind this allowance of a space launch – and so not restricting the launch site to Earth – is the possibility to design a mission which would use the old technique of exploration: build bases on the way to the target and use the resources deployed there for the final step. Look at the concept of Space Adventures for their Lunar Mission (http://www.spaceadventures.com/index.cfm?fuseaction=Lunar.Details); they plan to use one launch for the manned Soyuz and use another for a rocket booster. Just imagine a small probe based on nanotech and AI, and send a booster stage some time earlier…

    I look forward to see and discuss “Crazy Ideas” like a mission design based on this possibility, and, of course, any other good ideas. Although not ready yet, You may check out the “Crazy Ideas” menu in The PI Club: http://www.peregrinus-interstellar.net


  • Tibor August 5, 2008, 17:12

    Paul mentions that “Ultimately, either the Tau Zero Foundation or (Tibor’s choice) the SOS-Kinderdorf International, will enjoy the result.”

    May I add why I have chosen SOS-Kinderdorf International:


    My rationale behind this reads so: if Paul wins, we still do not have the first interstellar mission. In this case TZF is the best place to channel the money to. If I win, R&D performance was excellent, there is a wide support for interstellar missions – so the money can go to children who needs it. Without children we do not have future.


  • ljk August 5, 2008, 22:36

    I will be blunt: The next solar sail mission must be
    launched on a proven rocket by a proven space power –
    not on a converted ICBM and not on a barely tested
    booster by a fledgling space company. No offense,
    but we will never see a solar sail mission happen
    otherwise and it is too important a concept to wait
    for so long.

    As for the first starship mission happening in 2025. If
    you asked someone in 1950 when the first men would
    walk on the Moon, they would have given you an
    answer ranging from the year 2000 to 2050 or more.
    1969 would have been considered far too soon.

  • Adam Crowl August 6, 2008, 2:16

    Hi Tibor

    Personally I think it could be done with a high performance solar-sail – if there’s a materials breakthrough allowing dielectric quarter-wave sails to dip to ~0.01 AU for a solar-fryby. Such a system should be able to get to 0.5%-1.5% c thus taking 880-293 years to Alpha Centauri.

    But does anyone want to finance such a long-term long-shot mission?

    Would a 220 year mission at 0.02 c manage to scrape up funds? A solar-sail with a reflector-collector to beam light at it for longer could do that, perhaps even get close to an 88 year mission at 0.05 c. Would that attract funds?

  • Marc Millis August 6, 2008, 9:05

    The conditions of the bet provide enough details to start student design projects, perhaps competitively. If there are any aerospace professors out there looking for a class project for their students, please let us know what you think of the idea of using this long bet mission to drive a student design project.


  • david lewis August 6, 2008, 10:31

    Perhaps a two stage system.

    First stage would be a solar sail capable of surviving a close pass to the sun as Adam mentions above.

    The second stage could be a modification of the Orion design that someone came up with. Rather than a pusher plate an umbrella shaped sail is used and nuclear explosions are exploded within that sail.

    If the sail is capable of surviving such a close pass to the sun then perhaps it’s also capable of performing the second role. The nuclear devices don’t need to be carried by the probe but can be launched years ahead of the time with them being used as the probe passes them. A thousand nuclear devices spread out over several billion kilometers should give the probe a little extra push – maybe enough to cut travel time down to 100 years?

  • John Hunt August 6, 2008, 14:04

    I think that Adam hits the nail on the head. The issue is one of fundability. For a scientific probe, several factors go into determining if something will attract funds such as:
        1) the cost,
        2) the likelihood of success,
        3) if a later craft will make it there first, and
        4) the lost value of alternative sol system discovery or development missions.

    Unless the overall pie is enlarged, I think that these factors present a mighty steep hurdle to get over.

    This is why I argue that a survival-of-the-species motivation is more likely to get funded in the nearer term since these factors look very different when viewed through that lens:
        1) Cost – The value of species survival is greater than scientific information therefore justifying greater funding,
        2) Success – Even a small possibility of success is worth attempting since the downside of species extinction is huge,
        3) The Wait Issue – There is risk in waiting to purchase “humanity’s life insurance”. If extinction does not happen it still would have been reasonable to purchase the insurance.
        4) Alternative Missions – If humanity destroys itself, Sol system discovery would have been essentialy wasted. If Sol system development is able to avoid extinction then one wonders why we see no evidence of alien civilizations having survived.

    Either we figure out how to develop a scientific mission for tens of billions of dollars at most, traveling at 0.05 c at least, and with a high likelihood of success or we need to start making the survival-of-the-species arguments and come up with such a mission design with at least a modest likelihood of success.

  • John Hunt August 6, 2008, 14:35

    I would like to question the rationale for the mission needing to be less than 2,000 years.

    Setting such a criteria seems to restrict certain propulsion methods. Also, will equipment not survive for greater than 2,000 years? Previously, Adam indicated that some studies pointed out that “
    some electronic components already have mean failure lifetimes of c. 10,000 years or so
    “. A greater than 150 or so year mission seems inappropriate for a science probe for various reasons. But the only time criteria for a survival-of-the-species mission is that it have at least a modest likelhood of suceess at the other end. Reasons to believe that biologic materials (e.g. frozen embryos and stem cells) can survive have previously been given.

  • Dennis August 6, 2008, 15:04

    A notion about student project is interesting, as a student I might try asking some prof in my University. If I get any responce, I will contact Paul.

  • Tibor August 6, 2008, 18:02


    the 2,000 years maximum mission duration – which is, of course, an almost arbitrarily set timeframe – implies that at least 0.2% c average cruising velocity must be achieved. This is in the range of the estimated possibilities of sail-driven missions (see Adam’s comment above), but still challenging enough.

    Nevertheless, I will be more than happy to loose the bet if an interstellar mission will start before the deadline but with a longer than 2000 years planned duration!


  • Administrator August 6, 2008, 21:55

    To which I’ll add that the fastest mission time I’ve seen to the Centauri stars, assuming relatively near-term technologies, is roughly 1200 years. Greg Matloff spoke about a thousand year mission using sail technologies and a close solar pass, but I don’t have my notes on that, and in any case, I’ll be speaking to Greg again soon as we’ve talked about putting up an interview here re recent developments. The 1200-year time frame comes from work that Ralph McNutt did for NIAC, and actually represents a substantial though plausible development of existing technology. Tibor, we’ll both be happy if a mission of any sort gets off by 2025.

  • Lee August 7, 2008, 12:40

    “To which I’ll add that the fastest mission time I’ve seen to the Centauri stars, assuming relatively near-term technologies, is roughly 1200 years.”

    What do you mean by “the fastest mission time”? Is it the fastest time using any conceivable technology we could use, or the fastest using technology that would realistically be employed in practice? I ask this because if nuclear technology was used (the Orion starship, for example), the mission time could be much less than 1200 years. For example, if the ship traveled 3% of light speed (which appears possible), it would get to the Centauri stars in 130+ years, not counting acceleration and deceleration. But it doesn’t seem realistic that Orion will be built in the foreseeable future because of the politics surrounding nuclear weapons (more specifically, the Nuclear Test Ban Treaty). Nevertheless, it would be interesting to know how fast we could technically go now using any method available, versus how fast we can when financial and political factors are considered.

    As I said in a post a while back, if the minimum time to the Alpha Centauri system is really 1200 years (even if only because of political problems with building ships like Orion), I don’t see how it makes sense. Think about it–if Charlemagne launched the mission, we’d be getting the data back right now! I don’t see people in 3100 saying “Hey! Only 100 more years until our ship gets to Alpha Centauri! Whoppee!!” They’ll long since have built starships to completely overtake one requiring 1,200 years to arrive. In fact, by 3200 we may well be able to approach the speed of light (using manned or unmanned probes).

    And since a 1,200 year mission would be unmanned, I don’t see how it would help to “save humanity” in any way. I say this because people frequently give this argument to justify these types of missions.

  • Lee August 7, 2008, 13:21

    Here’s another way to look at a 1,200 year mission to the Centauri stars. What if King John of England had launched a spaceship to Neptune in the year 1200 that was scheduled to arrive in 2400? What would the Voyager astronomers in the late 20th century have done in this scenario? Would they really have said “Well, we could build a faster ship right now that would get to Neptune by 1989. We have the money, and we really are interested in learning more about the planet. But no, King John’s ship will get there in 400 years, so we’ll leave getting great pictures and fascinating data about Neptune to our remote descendants who will be around then”?

    Is there any chance they would actually say that?

  • Administrator August 7, 2008, 14:37

    Lee, by ‘fastest mission time’ I’m talking about missions within a reasonable range of our technological skill, and yes, missions that are realistic possibilities. Freeman Dyson, who worked so hard on Project Orion and wrote about its interstellar implications, has long since abandoned the concept for interstellar travel, and in any case, we’re hardly likely to find ways to convert the Earth’s nuclear weaponry into a single Orion-style interstellar mission. Would Orion — if built — be faster than anything else we now have? Absolutely.

    We’ve looked at the incessant obsolescence postulate (as Marc Millis likes to call it) on occasion in these pages. Millis describes it this way: “No matter when an interstellar probe is launched, a subsequent probe will reach the destination sooner and with more modern equipment for transmitting the findings back to Earth.” See, for example, “Barnard’s Star and the ‘Wait Equation'”:


    Or “Remembering Far Centaurus”:


    It’s quite an issue — when do you launch, and how long do you wait under the assumption of faster technologies later? My guess is that we’ll accept nothing longer than about 75 years travel time for a scientific probe, but it’s interesting to speculate on what might happen if longer missions are considered. What would we do, for example, if it became necessary to preserve the human species in the event of catastrophe on Earth? Would we consider a thousand-year mission, either as a ‘generation ship’ or using, perhaps, some kind of suspended animation? Probably so, if it were the only choice. Will such a thing ever become necessary? For that we need to consider existential risks, of which there are many, and I’ll be writing about these soon in conjunction with some Tau Zero work on the subject.

    One other thing to consider: You’re assuming a constant upward progression in technology. Can we assume that? What if we launch a thousand-year probe to Alpha Centauri and, in the interval, there is a nuclear war that sets civilization back? Assuming a ‘dark ages’-style interval, would scientists of the future be interested in retrieving data from the mission when it arrived, if they had re-built the capability to do so? Surely they would, and that slow probe might get there before their own society had the capability of building anything faster. So the case is complex and capable of being approached from a number of directions.

  • Tibor August 7, 2008, 15:15

    Regarding the Wait Question – which I think is an issue – look at two simple things: first, we never know sure when – if ever – a faster ship will be built (reasons for a long pause can be numerous), second, everybody is keen to know as much as possible about the way lying ahead. I am sure, the Voyager astronomers would have been very grateful to King John of England for the data already collected by his slow, old-fashioned ship.

  • Tibor August 7, 2008, 15:20

    I just realized after having sent my comment, that I was missing Paul`s last sentences. We are telling the same.

  • hiro August 11, 2008, 14:48

    I think we have to increase to travel time a little bit, it can be up to 250 years. I agree with Lee most of the time. We really don’t want a probe which was sent in 1000 AD from Earth to Moon and receive data in 2000.

  • John Hunt August 12, 2008, 3:52

    As I have done the Wait calculations I could go either way with 200 or 250 years. The difference is a 20% vs 25% increase in speed in the following 50 years after launch.

    On the survival-of-humanity side of things the flight times can be much longer. Really it would only be limited by the viability of the frozen cells and equipment. Launching a later mission would not be determined by the Wait equation so much as by our ability to improve the likelihood of a successful mission.

    Going out on a limb here, I’m going to say that equipment protected by a magnetic field and normal micrometeorite shielding will not be the limiting consideration. Rather it will be the viability of the frozen cells. Using freezing, magnetic shielding, antioxidants, DNA repair enzymes, and numerous cells, there would be at least one viable cell at 5,000 years. So I’d say we could launch such a mission whenever propulsion could get us there in 5,000 years.

  • Tim September 6, 2008, 10:06

    ar orion thermonuclearm bomb pulse driven vehicle is actually capable of achieving up to 10 % of light velocity but 10 megaton pulse units would be needed to get debris velecity of 30,000 km/sec.
    1 megaton pulse unit gets only 10,000 km/sec because its fireball is not as hot at the core as is a ten megaton fireball.Ve scales by the sqaure root of the magnitude of the change in the temperature of the fireball .

  • Tim September 6, 2008, 10:06

    ar orion thermonuclear bomb pulse driven vehicle is actually capable of achieving up to 10 % of light velocity but 10 megaton pulse units would be needed to get debris velecity of 30,000 km/sec.
    1 megaton pulse unit gets only 10,000 km/sec because its fireball is not as hot at the core as is a ten megaton fireball.Ve scales by the sqaure root of the magnitude of the change in the temperature of the fireball .