34 ms·
NASA proposes new propulsion to cut Mars voyage to 3 days
- leecarraher 11y agoJane, Stop this crazy thing! or in other words, how do you decelerate the spacecraft once you near Mars orbit. You'd need either a ton of conventional propulsion fuel , or a mars based laser there too. Worse is that you have a limited energy sources and no one to mine them. Solar might help, but it'd take a helluva alot of planning to install them via some automated system.
- wjnc 11y agoI had the same question. One thing that crossed my mind is that if speeds like these are possible, you could let the spaceship fly a gigantic loop and slow it down on the way back to earth. Same laser for acceleration and deceleration. (Things I've learned from the Martian #1.)
- revicon 11y agoRegarding slowing down upon arrival, could they enter a low orbit and skim the atmosphere of Mars to reduce velocity?
- arijun 11y agoDefinitely not. Back of the napkin shows that to get to Mars in 3 days would need a speed in excess of 200 km/s. That is an order of magnitude larger than Mars escape velocity. Your only chance of being captured by Mars is by pancaking.
- zelos 11y agoMake the first vehicle nothing but a giant mirror, crash it into Mars and then reflect the laser off the debris to slow down the second vehicle?
- tomswartz07 11y agoI think you're having trouble grasping exactly how fast 200km/s actually is.
- dandelany 11y agoThe "debris" would a fine dust scattered over millions of square kilometers at that speed.
- jobu 11y agoMars is actually a pretty bad planet to try landing on. It has just enough atmosphere to burn up a spacecraft that enters too quickly, but not enough to use for air-braking (skimming or parachutes).
- mikeash 11y agoGiven that aerocapture and parachutes have been successfully used for Mars probes in the past, that seems unlikely to be true.
- adwn 11y agoWhat jobu probably means, is that Mars' atmosphere is too thin for parachutes to slow a reasonably sized craft down to low speeds (that's why MSL's landing required additional rocket propulsion [1]). Compare with Earth: Here, the terminal velocity of a reentering capsule is slow enough for parachutes to take over, which in turn slow it down enough for touchdown. [1] https://en.wikipedia.org/wiki/Mars_Science_Laboratory https://en.wikipedia.org/wiki/Mars_Science_Laboratory
- deleted 11y ago[deleted]
- Shivetya 11y agoI assume that all fuel taken with you could be used to stop, though at those speeds it might not be a wash. So perhaps atmospheric braking? Still I could see the value for sending problems out of the system without having to do the orbital boost tricks with gravity
- thomasmeeks 11y agoTurn the craft around halfway to your destination and burn to decelerate at the same rate you accelerated. Keeps a nice 1G on the body the entire time.
- tehbeard 11y agoPropulsion is provided from the earth /LEO/GEO (imagine blowing on a kite with giant fan). turning the kite around will not make it slow down/return to you while you keep blowing on it.
- bradyd 11y agoSail boats are able to sail into the wind. This, however, requires the drag of the keel to work. It might be possible to use a traditional rocket engine to act like a keel to allow using the laser energy to slow down the craft.
- chiph 11y agoYou use 2 kites on board the spacecraft. One gathers the transmitted beam and reflects it to kite #2, which then reflects forward again. Careful design is important to ensure the spacecraft in the middle isn't struck by the photons. And you will have significant losses by the double-reflection, so you have to turn earlier than 50% of the way there.
- falcolas 11y agoIn the story "Flight of the Dragonfly", which used the same propulsion system, they simply detached a portion of the sail, and used it to reflect the beam back at the spacecraft to decelerate it.
- alejohausner 11y agoThis doesn't make sense to me. The detached portion would be subject to radiation pressure from the ground-based propulsion lasers, and would quickly be pushed away from the spacecraft it was meant to act on.
- falcolas 11y agoYes, but it's reflecting the light back at the spacecraft. So, even though it would accelerate quickly away from the spacecraft, the light reflected back at the spacecraft would be used to decelerate the spacecraft. So long as the daughter sail never hits C (thanks, physics), it's always reflecting back photons back at the spacecraft (though red-shifted). You'd still have to account for the light coming from the source as well as from the daughter sail, but a black coating on the back of the spacecraft's reflector would take care of that; it would give you n force pushing you away from the original light source, and 2n pushing you towards the source. The coordination and planning required for such a device would not be trivial, but it would be possible.
- dexwiz 11y agoSo over-under on this being viable before fusion power? Nice idea, but we are years away from this being viable. If we visit Mars it will be with chemical rockets first? This may be viable for some sort of highway system when travel is more common.
- adwn 11y ago> So over-under on this being viable before fusion power? There's nothing magical about human-built nuclear fusion power generation that'll give you noticeably larger or cheaper power output than nuclear fission. Therefore, commercial fusion power will not bring us any closer to viability of this concept.
- RLN 11y agoWhenever I read a story about using sails for propulsion in space I'm reminded of the short story Sunjammer by Arthur C. Clarke https://en.wikipedia.org/wiki/Sunjammer https://en.wikipedia.org/wiki/Sunjammer
- rubidium 11y agoback-of-envelope: conservation of momentum: 2(num photons)h/lambda = (100 kg)*(c/3), so 5.9×10^36 photons needed to propel a 100 kg object to 1/3 speed of light. 1.5×10^18 joules of energy, which is 11% of the energy output of the US in 2001 (according to wolfram alpha). That's a 5.8 Tera Watt laser running for 3 days straight. I haven't even gotten into dispersion of a laser beam. The ludicrousness of this proposal is left as an exercise to the reader. Edit: here's their proposal with physics. Just to be clear, I don't doubt the theoretical possibility, I doubt the economic and experimental reality. http://www.deepspace.ucsb.edu/wp-content/uploads/2015/04/A-Roadmap-to-Interstellar-Flight-15-h.pdf http://www.deepspace.ucsb.edu/wp-content/uploads/2015/04/A-R...
- imglorp 11y agoI like exercise ;-) If we wanted a self-assembling orbital solar array to provide that much power, it would need to be almost half the surface area of the moon. http://www.wolframalpha.com/input/?i=1.5%C3%9710^18+J++%2F+81650+J%2Fm%C2%B2+in+km^2 http://www.wolframalpha.com/input/?i=1.5%C3%9710^18+J++%2F+8...
- venomsnake 11y agowe could use a suitable size black hole to create lensing effect - that way we could capture sizable chunk of the sun's energy
- airza 11y agoprobably making a reasonably large lens would be somewhat easier than creating and controlling a black hole
- deleted 11y ago[deleted]
- nabla9 11y agoAnother thing to consider: mirrors are never perfect. 100% of the light is not reflected. If the spaceship uses high quality laser mirror with 0.00001% absorption rate, absorption from 5.8 terawatts is still 5.8 megawatts of power to get rid of in space.
- ldpg 11y agoI think the "Mars in 3" days comment is just for scale, not a serious proposal. This is more about getting probes to whiz past other solar systems. As obviously, you can't stop the craft.
- stcredzero 11y agoyou can't stop the craft. Zubrin and someone devised a way to use magsails to decelerate starships without using onboard fuel. That's magic, as you're not subject to the rocket equation. (Really, it was a failed attempt to develop a Bussard ramjet, but they figured out you'd never overcome the "friction" with the interstellar medium. So they were like, let's go with the friction!)
- Kinnard 11y agoVery light on details
- Skunkleton 11y agoYep, that is wired for you. As far as I can tell, this plan was first proposed in the '80s. The technical challenges of a 1.21 jiggawat laser, and a gigantic sail have led to it never being attempted even though it is probably theoretically feasible.
- wmfiv 11y agoSo what changed?
- Skunkleton 11y agoNothing as far as I can tell.
- danjayh 11y agoAs much as I love the idea, it is fairly impractical for the reasons that other commentors have noted. Call me greedy, but within the constraints of a balanced budget, I would like to see an increased portion dedicated to science (be it a 'cancer moonshot' or an actual marsshot) vs social programs ... maybe we could find some real solutions to these issues. In my own life I have a tendency to skimp on the 'now' in the name of investing in the future, so this is probably just me applying my own financial philosophies at a larger scale.
- melling 11y ago"Preaching to the choir". Since the government is not going to spend significantly more on science because most citizens don't want it, can you come up with a different solution that might work? For example, a Kickstarter for science that actually works. Crowdfunding X-Prizes, YC (incubator) for basic science companies, etc. The US economy is $15 trillion. How to redirect some of that into more research?
- chriswarbo 11y ago> Call me greedy, but within the constraints of a balanced budget, I would like to see an increased portion dedicated to science (be it a 'cancer moonshot' or an actual marsshot) vs social program Note that this basically happened already. As Apollo wound down, the War on Cancer wound up https://en.wikipedia.org/wiki/War_on_Cancer https://en.wikipedia.org/wiki/War_on_Cancer Turns out it's far more difficult to cure cancer than to reach the moon.
- CapitalistCartr 11y agoTo reduce travel time from 9 months to four would be incredibly helpful to sending people. To halve that again to two months even more so. But after that, faster has lessened benefits. One month makes it easier on the human body, less than that is more convenience than anything. We'd be better served putting our money elsewhere. An Earth-Mars cycler would be a great start. https://en.m.wikipedia.org/wiki/Mars_cycler https://en.m.wikipedia.org/wiki/Mars_cycler And for unmanned missions, faster is of marginal benefit. If I were setting up such a system for planetary flybys and extra-solar missions, I'd put the laser on one of the lunar poles .
- huhtenberg 11y agoAnother back of the napkin thing - if one manages to maintain +1G acceleration for the first half of the trip and -1G for the second half, one can get to Mars in 1 to 3 days, with the top speed of about 1000 km/s.
- rubidium 11y agoWhich does provide the interesting feature that if we could method of propulsion that gets to c/3 in a day or two, we could just use the acceleration of the ship to provide artificial gravity on-board, and flip the ship around mid-trip to provide artificial gravity during the deceleration.
- mahranch 11y ago> Lubin supposes that the system could propel crafts to an "unheard of" 30 percent the speed of light. > "There is no known reason why we could not do this" Yeah, no. There is a known reason. What do you think happens to a spaceship hitting something at 30% c? What do you think happens to the front of a spaceship or craft hitting something the size of bead or pebble at 30% c? The ship will disintegrate. Granted, the ship could be shielded or employ some sort of plasma/magnetic deflector technology (still in proof of concept stages of development), but now you're talking technology that's just as far away, if not further than the propulsion system they're talking about using. It's also why things like project Orion really never got off the ground or are feasible in their current forms. Sure, we can get up to those speeds, it's surviving at those speeds that's the challenge. Also, they talk about the weight of a ship being ultra light. If you had to shield it to survive the impact of tiny particles and other space debris you'll inevitably encounter on your trip, it's no longer going to be ultra light.
- dzdt 11y agoNot sure its that bad. This thing would be mostly akin to a big mylar sail. A micrometeorite at high relative velocity will punch right through making a nice cutout. As long as it doesn't hit the (small) payload I don't think it should disintegrate. But I would worry about all the atoms and ions hitting too. Space isn't empty!
- grymoire1 11y agoSee Larry Niven's Mote in God's Eye (1974) for details..
- stuxnet79 11y agoDid Mars figure prominently in the plot? I read the book exactly six years ago and loved it, but I have no idea why you are quoting it here.
- gherkin0 11y agoNo, but the aliens were discovered because one of them built a ship based on this idea ("solar" sail with a ground-based propulsive laser) and happened to arrive in a human-inhabited system. https://books.google.com/books?id=lKt5laoj1coC&pg=PA55&lpg=PA55&dq=mote+in+god%27s+eye+laser&source=bl&ots=QTucO9WK2p&sig=fwQ9HNOZjtl4at5mi9aWZpuKpQs&hl=en&sa=X&ved=0ahUKEwjDva2m8YvLAhVEpx4KHWz0BfsQ6AEILzAB#v=onepage&q=mote%20in%20god%27s%20eye%20laser&f=false https://books.google.com/books?id=lKt5laoj1coC&pg=PA55&lpg=P...
- stuxnet79 11y agoThanks, I wasn't aware that this was the exact type of propulsion that NASA was proposing. Mote In God's Eye is a classic book! I'm going to have to re-read it sometime soon. Getting a nostalgia kick just thinking about it.
- algorithmsRcool 11y agoMinor spoilers for others The first ship sent by the moties (the aliens in the book) uses this exact type of propulsion. A huge laser pushing a solar sail ship across space. It is not a new idea i think was the GP's point.
- c54 11y agoSee also: Aurora, by Kim Stanley Robinson http://www.amazon.com/Aurora-Kim-Stanley-Robinson/dp/0316098108 http://www.amazon.com/Aurora-Kim-Stanley-Robinson/dp/0316098...
- tomrod 11y agoHow long would it take to catch up to the Voyager probes?
- TickleSteve 11y agoShooting a 100kg mass off at 30%C wouldn't be taken lightly by whoever it hit! Planet killer?
- vkou 11y agoNot quite. Considering an inelastic collision, the impact would dissipate roughly mv^2/2 worth of energy, so... 1/2 * 100kg * (10^8 m/s)^2 = 5 * 10^17 Joules of kinetic energy. In contrast, the amount of solar energy that impacts the Earth each second is 10^17 Joules. For a more relevant comparison, the Tsar Bomba (50 megatons) released ~2*10^17 Joules. So, worst-case, the probe would cause the equivalent of a ~100 megaton explosion. Hardly a planet-killer.
- mcguire 11y agoBut still pretty impressive. I say we start flinging these things at all the extra-solar planets we've discovered. Think of it as grafitti or an art project. Leaving our mark on the universe.
- dr_zoidberg 11y agoThat sounds like the kind of art that Black Hat Guy from XKCD would aprove of.
- maxxxxx 11y agoCould you make any meaningful observations if you flew through a neighboring stellar system at that speed? Seems you could reach Proxima Centauri in between 10 and 20 years that way but you could not slow down.
- boggie1688 11y agoSo if it take an array of laser to get there, how do you get back? Bring lasers with you?
- cowardlydragon 11y agoCan't pulse nuclear (Orion) get there in about as close to practicality as exists? 133 years based on what I've read. And that doesn't do antimatter-catalyzed fusion, which seems near-term practical.
- abecedarius 11y agoOrion is pretty great, but still suffers from the rocket equation. Well, you could get around that by keeping the bombs back at home base and throwing them to catch up with the craft... I wonder if anyone's worked out that variant. Too complex to be worth it, right?
- nkrisc 11y agoSo please help me out here. The article suggests a craft could be accelerated to .3c; surely this would not be for a Mars intercept!? This is just an example of the potential, right? Otherwise slowing down a craft at relativistic speeds for Mars capture sounds... difficult to say the least. EDIT: OK, after thinking it through further at .3c the trip would only take about 50 minutes, roughly. So clearly that's not what the article meant.
- dr_zoidberg 11y agoSounds like Kerbal Engineering at its best... :P
- nkrisc 11y agoRelativistic litho-braking?
- sehugg 11y agoA practical near-term application of this tech is precision formation flying of satellites -- Young Bae has been developing test systems for over a decade: https://www.nasa.gov/spacetech/niac/2013phaseII_bae.html https://www.nasa.gov/spacetech/niac/2013phaseII_bae.html (It must be annoying when the researchers studying pie-in-the-sky mission architectures get all the clickbait headlines)
- owenversteeg 11y agoFor context, some of the numbers here: c: 300,000 km/sec, 1/3c: 100,000 km/sec Fastest man-made thing in history by far, Voyager 1: 17km/sec Time it took most recent Mars mission to get there (Mars Science Laboratory, 2011): 254 days Closest Mars-Earth: 182 light-sec Farthest Mars-Earth: 1342 light-sec These scientists are proposing to send something at about six thousand times faster than anything man-made has ever gone in history. At this scale, the energies involved become absolutely insane. Guess what would be the energy of a tiny one-gram pebble floating in space hitting this spacecraft? Ten terajoules. That's approximately equal to you walking along on your way to work and getting hit by, oh, I don't know, the International Space Station (13 terajoules) or a sixth of a good sized atomic blast (63 terajoules). Space is a busy place. If you hit even one thing, you're over. But, you argue, you won't get hit by any pebbles. I'd imagine that you're wrong, but let's humor you. You argue that the largest thing to hit you would be a microscopic 0.001g object. Let's say that your microscopic object is standing perfectly still in space, somehow, even though that's incredibly unlikely. You hit this object, and instantly your craft is subjected to a ten gigajoule blast. Let's put that into context: at an incredibly small point somewhere on your craft, rocketing along at just north of 223000000 mph, you just experienced a hit equivalent to one hundred million large caliber (.45) bullets. Let's say the scientific payload of your craft is one gram, and the rest is armor. You'd be safe right? No, unfortunately 99.999kg of armor doesn't seem so strong in the face of one hundred million bullets. I don't think it's possible.
- peter303 11y agoNew Horizons is fastest chemical rocket taking 78 days to cross Mars orbit. (You'd use a different, longer path for Mars orbital/lander insertion.) New Horizons crossed lunar orbit in 9 hours, or about six times faster than Apollo flights.
- owenversteeg 11y agoSure, but my points in the article only really apply once you change the velocity in a significant way. ke=mv^2, so going 100 times faster means ten thousand times the KE and thus ten thousand times the destruction. For an example, New Horizons was at Mars around 13km/s. At 13km/s, the impact of that microscopic object, instead of being one hundred million bullets, is now 169 joules, barely a tenth of a bullet's energy. Still harmful, but with New Horizons being car-sized, slower moving, and armored, that repeated tenth-of-a-bullet impact is a problem that can be dealt with.
- zwetan 11y ago"if it works" between parenthesis, in the title ... so I'm not a scientific but even if it works at the tech level, even if the deceleration problem is solved, even if not colliding with something along the way is solved what about the impact of travelling at 1/3rd the speed of light on the human body ?
- pmontra 11y agoNothing, you'll feel only the acceleration which is is equivalent to a gravitational pull. If it's 1 G you won't feel any difference from being in a room on Earth.
- Gravityloss 11y agoYou probably need to manufacture the terawatt class space lasers from asteroid materials, at least the majority of mass. One can't afford to lift them from any deep gravity well. This is the major reason why asteroids are in total much more important than the moon or even Mars.
- amai 11y agoHow to stop a spacecraft propelled by a laser?
- amai 11y agoHow to stop a spacecraft propelled by a laser?
- gremlinsinc 11y agoOkay, so what I read from others is that stopping is gonna be a PITA -- so maybe Mars isn't the best target.. Why not send some huge telescope in the direction of that solar system that looks like it has an Alien Megastructure- - get as close as we can to that thing and take closer pictures of it to find out what's really going on (and other parts of the galaxy) -- imagine having a telescope like a couple solar systems away sending back data to us? -- we may to create some sort of galactic internet though - maybe using lasers and relay stations? (I honestly have no clue... we'd want to get data back and it to NOT take 50 years per data dump.) ..
- dalke 11y agoIt's likely very much easier to build a telescope array in this solar system than to send a telescope "a couple solar systems away". KIC 8462852 is 1480 light years away. At 10% light speed it would take over 10,000 years to get within a few solar systems of the star. On the other hand, a space-based interferometer with a baseline of 15 AU would have an angular resolution of: 1.22 * 500 nm / (15 AU) = 2.7E-19 radians giving the ability to see things at KIC 8462852 which are 1480 light years * 2.7E-19 = 3 meters across That's also fantastically advanced, but working backwards, to see objects 100km in size: (1.22 * 500 nm) / (100km / 1480 light years) = ~100,000 km I think we can pull that off within 1,000 years, much less 10,000.