The Audacious Plan to Launch a Solar-Powered Rocket Into Interstellar Space (arstechnica.com) 41
Ars Technica glimpsed a possible future at the Johns Hopkins University Applied Physics Laboratory: a solar simulator "that can shine with the intensity of 20 Suns..."
"They think it could be the key to interstellar exploration." "It's really easy for someone to dismiss the idea and say, 'On the back of an envelope, it looks great, but if you actually build it, you're never going to get those theoretical numbers,'" says Benkoski, a materials scientist at the Applied Physics Laboratory and the leader of the team working on a solar thermal propulsion system. "What this is showing is that solar thermal propulsion is not just a fantasy. It could actually work."
In 2019, NASA tapped the Applied Physics Laboratory to study concepts for a dedicated interstellar mission. At the end of next year, the team will submit its research to the National Academies of Sciences, Engineering, and Medicine's Heliophysics decadal survey, which determines Sun-related science priorities for the next 10 years... In mid-November, [APL's] Interstellar Probe researchers met online for a weeklong conference to share updates as the study enters its final year. At the conference, teams from APL and NASA shared the results of their work on solar thermal propulsion, which they believe is the fastest way to get a probe into interstellar space.
The idea is to power a rocket engine with heat from the Sun, rather than combustion. According to Benkoski's calculations, this engine would be around three times more efficient than the best conventional chemical engines available today. "From a physics standpoint, it's hard for me to imagine anything that's going to beat solar thermal propulsion in terms of efficiency," says Benkoski. "But can you keep it from exploding...?" If the interstellar probe makes a close pass by the Sun and pushes hydrogen into its shield's vasculature, the hydrogen will expand and explode from a nozzle at the end of the pipe. The heat shield will generate thrust. It's simple in theory but incredibly hard in practice.
A solar thermal rocket is only effective if it can pull off an Oberth maneuver, an orbital-mechanics hack that turns the Sun into a giant slingshot. The Sun's gravity acts like a force multiplier that dramatically increases the craft's speed if a spacecraft fires its engines as it loops around the star... The big takeaway from his research, says Dean Cheikh, a materials technologist at NASAâ(TM)s Jet Propulsion Laboratory, is there's a lot of testing that needs to be done on heat shield materials before a solar thermal rocket is sent around the Sun. But it's not a deal-breaker. "Additive manufacturing is a key component of this, and we couldn't do that 20 years ago. Now I can 3D-print metal in the lab."
"They think it could be the key to interstellar exploration." "It's really easy for someone to dismiss the idea and say, 'On the back of an envelope, it looks great, but if you actually build it, you're never going to get those theoretical numbers,'" says Benkoski, a materials scientist at the Applied Physics Laboratory and the leader of the team working on a solar thermal propulsion system. "What this is showing is that solar thermal propulsion is not just a fantasy. It could actually work."
In 2019, NASA tapped the Applied Physics Laboratory to study concepts for a dedicated interstellar mission. At the end of next year, the team will submit its research to the National Academies of Sciences, Engineering, and Medicine's Heliophysics decadal survey, which determines Sun-related science priorities for the next 10 years... In mid-November, [APL's] Interstellar Probe researchers met online for a weeklong conference to share updates as the study enters its final year. At the conference, teams from APL and NASA shared the results of their work on solar thermal propulsion, which they believe is the fastest way to get a probe into interstellar space.
The idea is to power a rocket engine with heat from the Sun, rather than combustion. According to Benkoski's calculations, this engine would be around three times more efficient than the best conventional chemical engines available today. "From a physics standpoint, it's hard for me to imagine anything that's going to beat solar thermal propulsion in terms of efficiency," says Benkoski. "But can you keep it from exploding...?" If the interstellar probe makes a close pass by the Sun and pushes hydrogen into its shield's vasculature, the hydrogen will expand and explode from a nozzle at the end of the pipe. The heat shield will generate thrust. It's simple in theory but incredibly hard in practice.
A solar thermal rocket is only effective if it can pull off an Oberth maneuver, an orbital-mechanics hack that turns the Sun into a giant slingshot. The Sun's gravity acts like a force multiplier that dramatically increases the craft's speed if a spacecraft fires its engines as it loops around the star... The big takeaway from his research, says Dean Cheikh, a materials technologist at NASAâ(TM)s Jet Propulsion Laboratory, is there's a lot of testing that needs to be done on heat shield materials before a solar thermal rocket is sent around the Sun. But it's not a deal-breaker. "Additive manufacturing is a key component of this, and we couldn't do that 20 years ago. Now I can 3D-print metal in the lab."
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Not crazy but not really "interstellar" (Score:5, Informative)
Using solar thermal propulsion and taking advantage of the Oberoth effect is not crazy. It certainly works to some speed, at some reasonable distance from the sun.
The problem is that even their ~600Km/s is still something like 0.2% of C. so the nearest star is~2000 years away. Still, it migth provide some data on the outer parts of the solar system if any interesting targets can be identified. Not clear if there is enough science to be had out at say 1000 AUs for what looks like a pretty expensive and risky mission.
Re:Not crazy but not really "interstellar" (Score:4, Insightful)
Well, the stated goal here is to reach interstellar space. I was a bit confused at first until I realized that this thing isn't supposed to produce thrust out there, it's just a way of getting there faster.
So you could potentially launch a scientific probe to study the heliopause without having to wait forty years for the data to start coming back.
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yes it would pretty quickly get beyond any existing probes. Anyone know the science targets?
Maybe the most interesting target is to chase down one of the interstellar asteroids? Maybe have one read for the next detected asteroid?
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The website mentions "heliophysics, astrophysics and planetary science" so I'd guess we'd be studying the heliopause, studying the interstellar medium, and looking at transneptunian objects for a start.
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The interesting target, is the space faring technology itself. There are a series of logical steps to work through to make it really long distances. Consider it all practice as well as a safe way to allow return from great distances with possible alien contagions on board.
Going to use solar panels why use one tuned to work best with distant radiation sources when you should work with higher energy radioactive sources, how to maximise the energy output. The minimum radiological material with the maximum area
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so the nearest star is~2000 years away.
The best time to launch an interstellar probe is 2000 years ago. The second-best time is today.
Seriously, though, we still study doctrines that were developed 2000 years ago, so this time period is not outside the realm of keeping human interest. People may not necessarily forget that the probe is out there while those 2000 years go by.
In fact, society will likely crumble and be rebuilt in those intervening years, as has happened multiple times in the preceding 2000 years. The greater challenge than sending
Hard to imagine Project Orion? (Score:3)
Just for fun, upgrade to fusion bombs.
I *think* literally a fusion drive is gonna beat your little mirror toy, no offense. :)
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There's actually a fantastic refinement of Project Orion, called the Nuclear Salt Water Rocket. (see: wikipedia article [wikipedia.org], also this article [washington.edu])
Basically -- the idea is to have a mix of water and U235 mixed to a level _just below criticality_ stored as your fuel. You then inject it at high velocity into your rocket exhaust where it reaches critical density; and ignites. Giving you a "constant flow" nuclear explosion (i.e. not intermittent bursts like Orion). It's usable today, using todays technology.
The only ma
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Related idea is fission fragment engines, the nuclear fuel as bonded particles or sheets disintegrates by design and is ejected. 3 -5 percent speed of light might be possible that way.
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The only major disadvantage?
First you have to get the thing into orbit, including the fuel that is difficult to handle and on the verge of going critical. Safety would be difficult to say the least, and the mess if something went wrong would be pretty catastrophic.
The rocket itself would need multiple stages. A few massive conventional ones to lift the fuel and nuclear engine out of orbit so that there is no danger of the exhaust falling back to Earth. Then you have to find something to make this engine out
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Orion was a fun idea, but I wonder how well it would have worked in practice. The fusion bombs would make a lot of neutrons that would heat the thrust plate, and getting rid of heat in space is tricky.
I guess if the bombs were really huge, you could add enough neutron absorbing material, but I think that pushes you to very large bombs. (you need a meter or so of material to shield neutrons, so a few meter sphere - for each shot.
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The pusher plate was designed to weigh 1000 tons, making up 1/4 of the entire mass of the vehicle. IIRC thermopiles on the upper side of the pusher plate were going to supply all the power the spacecraft needed. Rather than a maximum payload of 130 tons for the Saturn 5 the Orion would have a payload in excess of 6000 tons. Unfortunately Freeman Dyson, a Quaker and one of the lead designers of the project, estimated that a terrestrial launch of an Orion would cause approximately one case of terminal canc
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Forgot to include their test launch using conventional explosives.
https://www.youtube.com/watch?... [youtube.com]
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I don't see how you cool the pusher plate. If you rely on radiation (really your only option) the average acceleration is going to be pretty small and its not clear orion wins over nuclear electric.
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I think they found that simple iron was a good material for pusher plate because part of the bottom would ablate and carry much of the heat off while the rest would migrate relatively slowly throughout the rest of the plate. It doesn't cool immediately, and with 1000 tons of heat sink it doesn't need to. Once it's in orbit it can sit there and radiate for as long as it needs to, or the heat can be transferred to some other process that can use it. There are plenty of uses for hot iron in space, too.
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that was my comment on neutrons. If the explosions mostly produced visible through soft X-ray, then ablation will work. .The problem is that a significant amount of the energy is in neutrons which will heat the entire plate. Since the total energy being produce is far more than the vaporization energy of the entire rocket (otherwise you'd just use nuclear / thermal) I don't see how this can work.
Don't get me wrong - I love the Orion idea, but this seems like a fatal flaw .
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I recommend 'Project Orion: The True Story of the Atomic Spaceship' by George Dyson, son of Freeman Dyson. Hopefully it's available in your library, a digital edition doesn't seem to be available unfortunately. Dyson (and others) did a pretty in-depth analysis of the interaction between the bombs and the pusher plate, neither heating nor ablation seemed to be an issue. Interestingly their primary obstacle (besides the politics, of course) seemed to be the shock absorbers between the plate and the capsule
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Do you want cheeze with your whine?
Hitchhiker's Guide to the Galaxy (Score:2)
They should call it Disaster Area, like the plutonium rock band from tHGttG, just in case it does crash into the Sun.
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I have to stick with the classics, and call it Icarus.
Just design a Bussard Ramjet (Score:2)
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Theoretically, a Bussard Ramjet won't work and can't propel itself sufficiently to keep itself fed, look it up in wikipedia and see the cited paper demolishing it.
Meanwhile, the sun at close range shining on a tube of gas and making it hotter than heck with sufficiently energized propellant is guaranteed.
Analogy would be Bussard Ramjet design that is guaranteed to make fusion but does it so well it explodes without proper materials and design. Sadly, a BR "can't get it up."
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Its really difficult to imagine how a Bussard ramjet could work. Interstellar hydrogen is mostly protons, not deuterium, so it fuses extremely slowly: under the conditions in the center of the sun it takes a billion years to fuse
If you are relativistic, the hydrogen will only be in the spacecraft for microseconds. can't imagine how to get H1 to fuse that quickly - even if you could figure out how to collect the mostly neutral hydrogen
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Read Larry Niven. Fusion drives in his Universe counted on pinch fields that required magnetic monopoles to work, and interstellar hydrogen was collected with magnetic fields hundreds of miles wide. Onboard hydrogen tanks held the fuel to get the craft up to ramjet speeds, where more could be collected to run the engine and refill the tank.
So far as I know magnetic monopole
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the solar thermal is imaginable. Bussard ramjet, antimatter propulsion etc - I just can't think of any approach to makign those work. I've looked at X-ray launch lasers, etc, and its really difficult to get beyond 0.1C . You can do almost as well with fission as with fusion (especially since you can build the spacecraft structure out of fissionable materials) but getting rid of waste heat is tough. 1e-3 G's with 0.1C max seems around the limit. (100 year acceleration time).
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So how do you get it to the Sun? (Score:2)
You need a 17km/s delta to escape the Solar system, but a 30km/s delta to launch a probe into the Sun. Even if this thing would work, it would require a conventional rocket far bigger then one required for an interstellar probe.
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You don't have to go into the sun, just close to it - and yes, you would need a bigger rocket, but the aim isn't to use a smaller rocket: It's to get into interstellar space much faster than even that bigger rocket would permit otherwise. Very useful if you want to still be alive when your probe starts returning observations.
Solar panel (Score:1)
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How do you keep it from going back in time? (Score:2)
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Didn't they also have to travel THROUGH the sun?