[FPSPACE] FW: Centauri Dreams - Project Longshot

[LARRY KLAES]

>From: Centauri Dreams <gilster at mindspring.com>
>Reply-To: Centauri Dreams <gilster at mindspring.com>
>Subject: Centauri Dreams
>Date: Wed, 6 Feb 2008 14:04:31 -0600 (CST)
>
>Centauri Dreams
>
>///////////////////////////////////////////

>Project Longshot: Fast Probe to Centauri
>
>Posted: 06 Feb 2008 01:55 PM CST

>http://www.centauri-dreams.org/?p=1708
>
>
>Project Daedalus, discussed frequently in these pages, was the first 
>in-depth design study of an interstellar probe. Its projected fifty-year 
>flyby mission to Barnards Star at 12 percent of the speed of light was 
>beyond contemporary technology (and certainly engineering!), but not so far 
>beyond as to render the design purely an intellectual exercise. I bring up 
>Daedalus again because I keep getting asked about Project Longshot, which 
>some have mistakenly seen as a successor to Daedalus with a NASA pedigree. 
>And wasnt Longshot a far more advanced design?
>
>Actually, no. But the other day I again ran into Longshot in the form of an 
>online post describing it as a hundred-year mission to Alpha Centauri (true 
>enough), evidence that NASA had the technology right now (not true) to get 
>us to the nearest stellar system in a century, which would be faster by far 
>than the thousand years Ive always used as an absolute minimum for getting 
>there with the technology we have today. Even that 1000 years is deeply 
>problematic. I mentioned it several years back to Les Johnson at NASAs 
>Marshall Space Flight Center and he said, If we can get to Alpha Centauri 
>in a thousand years, Ill take it! Meaning we were, in his view, not even 
>that far along.
>
>So what is this Project Longshot? The first thing to do is to untangle its 
>origins. This design for an unmanned interstellar probe grew out of the 
>NASA/USRA University Advanced Design Program, which ran between 1984 and 
>1994. The idea of the program was to help integrate future NASA design 
>projects into university curricula. Engineers from the agency would work 
>with students and faculty from US engineering schools, thus fostering 
>engineering design education and adding synergies to NASAs own efforts in 
>the area of advanced space design. Project Longshot was a concept that grew 
>out of this programs involvement with the U.S. Naval Academy, including 
>seven first class midshipmen, faculty advisors and two visiting professors, 
>one of whom was NASA representative Stephen Paddack, a visiting professor 
>based at Goddard Space Flight Center.
>
>As for using current technologies, the Longshot team made no such claim. 
>This is what they had to say:
>
>Our probe will be a completely autonomous design based upon a combination 
>of current technology and technological advances which can be reasonably 
>expected to be developed over the next 20 to 30 years. The expected launch 
>date is in the beginning of the next century with a transit time of 100 
>years.
>
>The expected launch date, in other words, would have been about now, but 
>the technologies anticipated for it to occur still have a long way to go. 
>Longshot was conceived as being built with modular components on the ground 
>and then launched to low-Earth orbit for assembly at the space station 
>presumed to be operational there. The enabling technologies included a 
>pulsed fusion micro-explosion drive (Im quoting from the Project Longshot 
>report) with a specific impulse of 1 million seconds, along with a 
>long-life fission reactor with 300 kilowatts power output.
>
>The differences between this concept and Project Daedalus are profound in 
>both emphasis and execution. Daedalus was to be a fast flyby of Barnards 
>Star, scattering smaller probes as it entered the system to explore any 
>planets found there. Longshot, audaciously enough, was intended to carry 
>enough fuel to actually brake as it entered the Centauri system and go into 
>orbit around Centauri B, which the report erroneously calls Beta Centauri 
>(Beta Centauri is another star altogether, the components of Alpha Centauri 
>being Centauri A, B and Proxima Centauri). That last just reminds us that 
>the pooled light of the three Alpha Centauri stars makes it appear to be a 
>single star, so that the second brightest object in Centaurus came to be 
>known as Beta Centauri.
>
>Needless to say, including enough fusion fuel to slow an object traveling 
>at these speeds to brake into orbit around Centauri B would require an 
>engine far more efficient and powerful than anything envisioned for 
>Daedalus. Thats because youre carrying, when you begin the journey, not 
>just the fuel to get you up to cruising speed, but all the fuel needed for 
>the deceleration. The numbers quickly start running away with you here  
>while Daedalus offered a first-step flyby that strained every technological 
>resource we would possess in the near future (including the need to mine 
>for helium-3 in places like the atmosphere of Jupiter), Longshot pushed 
>credibility to the max by insisting that a similar design could stay in the 
>Centauri system and do useful science, reporting the results via a laser 
>beam communications system that seems workable.
>
>Where Longshot was perhaps closest to technological realization was in the 
>area of autonomy. Heres what the report says on this subject:
>
>Due to the great distance at which the probe will operate, positive control 
>from earth will be impossible due to the great time delays involved. This 
>fact necessitates that the probe be able to think for itself. In order to 
>accomplish this, advances will be required in two related but separate 
>fields, artificial intelligence and computer hardware. AI research  is 
>advancing at a tremendous rate.  Progress during the last decade has been 
>phenomenal and there is no reason to expect it to slow any time soon. 
>Therefore, it should possible to design a system with the required 
>intelligence by the time that this mission is expected to be 1aunched.
>
>All of which seems reasonable enough. The Longshot report was compiled 
>between 1987 and 1988, and we have certainly seen our share of computer 
>advances in the time since. Indeed, I am now and again told by its 
>partisans that the Singularity event could happen any time now, but 
>certainly within the next few decades, in which case AI systems to run such 
>a probe would be plentiful, one assumes, although whether intelligent 
>hardware would not want to re-design the whole spacecraft remains an 
>unanswered question.
>
>I, for one, appreciate the reports attention to long-term thinking. In 
>discussing the human side of the infrastructure supporting Longshot, the 
>authors note that given the time for design, procurement, in-orbit assembly 
>and transit, the likely time before return of data would be more on the 
>order of two centuries than one. And they go on to say this:
>
>the greatest challenge comes with the caretaker portion of the mission  the 
>century of travel time when very little data will be transmitted. The 
>problem here is not the number of people required, since it will be small, 
>but rather the time involved. There has never been a similar project in 
>modern history carried out over such a long time scale. However, there have 
>been organizations which have lasted for such a time. In fact, some have 
>lasted longer! Some examples include: the militaries of nations such as the 
>U.S. and the U.K., various research institutions like the National 
>Geographic Society and the Smithsonian Institution, and private 
>organizations such as the Red Cross and the Explorers Club.
>
>Robert Forward used to worry about precisely this point. In considering one 
>of his mind-boggling lightsail designs, he wondered what political will 
>might be needed to keep the power supplied to the huge lasers that drove 
>the lightsail over spans of a century or more. You can see the subject 
>entertainingly explored in his novel Rocheworld (1990), expanded from his 
>1984 work The Flight of the Dragonfly. Weve clearly got the patience to 
>work with probes that are thirty years old and more, as witness our 
>Voyagers and Pioneers, but a century or longer imposes more challenges, 
>especially given the political changes that might take place in the 
>interim.
>
>The Longshot team pondered the possibility of laser lightsails for its work 
>as well, but ended up with pulsed fusion. And again, the report points out 
>that such a drive is not a current, but rather an enabling technology. The 
>concept is to fire high energy particle beams at small, fusion-able pellets 
>whose implosion and subsequent channeling out the nozzle would drive the 
>vehicle. Helium-3 is deemed necessary, as with Daedalus, with atmospheric 
>mining of Jupiter being just one of the methods discussed for gathering 
>sufficient quantities. [T]he collection of fuel will be the most difficult 
>and time consuming portion of the building, says the report, and thats 
>something of an understatement.
>
>Project Longshot, then, should be seen as a gutsy academic exercise that 
>never proceeded to the intricate analysis given to Daedalus, lacking the 
>resources of time and expertise that the British Interplanetary Society was 
>able to deliver to the latter. Even so, the Longshot report is a fun read 
>that places many of our current interstellar concepts in context. The rough 
>sketch of an interstellar probe called Project Longshot: An Unmanned Probe 
>to Alpha Centauri can be downloaded here.
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