A solar-powered rocket might be our ticket to interstellar space:
If Jason Benkoski is right, the path to interstellar space begins in a shipping container tucked behind a laboratory high bay in Maryland. The setup looks like something out of a low-budget sci-fi film: one wall of the container is lined with thousands of LEDs, an inscrutable metal trellis runs down the center, and a thick black curtain partially obscures the apparatus. This is the Johns Hopkins University Applied Physics Laboratory solar simulator, a tool that can shine with the intensity of 20 Suns. On Thursday afternoon, Benkoski mounted a small black-and-white tile onto the trellis and pulled a dark curtain around the setup before stepping out of the shipping container. Then he hit the light switch.
Once the solar simulator was blistering hot, Benkoski started pumping liquid helium through a small embedded tube that snaked across the slab. The helium absorbed heat from the LEDs as it wound through the channel and expanded until it was finally released through a small nozzle. It might not sound like much, but Benkoski and his team just demonstrated solar thermal propulsion, a previously theoretical type of rocket engine that is powered by the Sun's heat. They think it could be the key to interstellar exploration.
[...] The concept has a long way to go before it's ready to be used on a mission—and with only a year left in the Interstellar Probe study, there's not enough time to launch a small satellite to do experiments in low Earth orbit. But by the time Benkoski and his colleagues at APL submit their report next year, they will have generated a wealth of data that lays the foundation for in-space tests. There's no guarantee that the National Academies will select the interstellar-probe concept as a top priority for the coming decade. But whenever we are ready to leave the Sun behind, there's a good chance we'll have to use it for a boost on our way out the door.
(Score: 2, Funny) by Anonymous Coward on Monday November 23 2020, @12:41PM (5 children)
The billionaires are preparing for the offworld event. UFOs are shuttles. Mars is habnitable, your money worthless, and earth is done. They know it is a game. Biden president.
(Score: 1) by Only_Mortal on Monday November 23 2020, @01:57PM (2 children)
Have you been reading Stark: https://en.wikipedia.org/wiki/Stark_(novel) [wikipedia.org]
(Score: 0) by Anonymous Coward on Monday November 23 2020, @03:28PM (1 child)
> The narrative also pokes fun at religion, place names and foreigners
Pokes fun at foreigners? Sounds like racist drivel. I stopped reading there.
(Score: 2) by turgid on Monday November 23 2020, @08:25PM
I seem to remember the TV series was quite good, but that was a very long time ago.
I refuse to engage in a battle of wits with an unarmed opponent [wikipedia.org].
(Score: 1) by fustakrakich on Monday November 23 2020, @02:14PM (1 child)
Send them into the sun with Rosie O'Donnell
Clang clang clang went the trolley...
La politica e i criminali sono la stessa cosa..
(Score: 0) by Anonymous Coward on Tuesday November 24 2020, @09:29PM
Just don't send them at night.
(Score: 4, Insightful) by Muad'Dave on Monday November 23 2020, @12:56PM (25 children)
'Solar powered' and 'interstellar' don't really mix, unless you're willing to not have any propulsive capability until you're at your destination. Your navigation better be perfect and you better not need any planetary slingshots that require large Isp burns.
Imagine a theoretical trip - Sol to Alpha Centauri. Here at LEO, you get 1 SU* of solar flux. Off you go, accelerating until the sun's luminosity is insufficient. You coast for quite a while, then as you approach Alpha Centauri, you begin to decelerate. As long as the destination star is at least as bright as the star you left at full acceleration, you can stop. If the destination star is dimmer, then you must limit your initial acceleration so that you have enough power to stop when you reach the destination.
* SU means Solar Unit
(Score: 3, Informative) by PiMuNu on Monday November 23 2020, @01:26PM (1 child)
FTFA
> And the APL team is studying a probe that would go three times farther than the edge of the solar system,
> a journey of 50 billion miles, in about half the time it took the Voyager spacecraft just to reach the edge.
They are not trying to go to another star system
(Score: 2) by bart9h on Monday November 30 2020, @06:40PM
so that would be six times the speed of a spacecraft made 43 years ago.
unimpressive.
(Score: 1) by khallow on Monday November 23 2020, @01:26PM (17 children)
It's also a matter of the temperature of the star. Cooler stars have much less energy influx.
A dimmer, cooler, lighter star can still be reached, it just takes a different propulsion approach on the other end, decelerate more using a mode that doesn't depend on solar power to work. Or you might be able to just get much, much closer (like skimming the star's outer surface) to get the necessary combo of energy influx and delta-v at the bottom of a gravity well.
(Score: 4, Interesting) by Immerman on Monday November 23 2020, @02:26PM (15 children)
I'm dubious about the real-world effectiveness of the Oberth effect using the sun. If you're harnessing solar power that could certainly change the balance, but in general...
If you're slinging around a planet that you're passing it works great, no question - you enter the gravity well on a trajectory that will bring you close to the planet, and away you go. Or if you start close to the planet you can blast yourself onto an increasingly elliptical orbit over one or more passes, making your burns at the the lowest point.
But if you're starting out on a circular orbit far from the sun, then before you can harness the Oberth effect to efficiently raise your orbit, you have to inefficiently expend an enormous amount of propellant reducing your delta-V in order to pass close to the sun in the first place. It's going to be really hard to get enough added Oberth efficiency to compensate for all the delta-V you threw away.
I suppose it could still work well, from the ship's perspective at least, if you have a refueling depot on the intermediate elliptical orbit, but in general it seems like a losing proposition.
(Score: 1) by khallow on Monday November 23 2020, @03:04PM (14 children)
For example, theoretical max delta-v for a solar sail starting from the point near the Sun where most stuff would melt, is about 0.1% to 1% of the speed of light (300-3000 km/s) with the Orberth effect being a measurable part of that. That's enough to get you around.
Depends how much it costs to launch additional propellant or whatever (if you can launch one spacecraft, then you can launch a whole bunch of them in a group with some serving as propellant depots for the rest). There's an exponential increase in propellant required with each additional unit of delta-v demanded. But it might work.
(Score: 3, Insightful) by turgid on Monday November 23 2020, @03:44PM (7 children)
In order to get the spacecraft close to the Sun, you've got to get rid of a lot of velocity. That's very expensive. Then you are proposing to add it all back on again using sunlight. I think the overall efficiency of this operation would be much less than 1.
I refuse to engage in a battle of wits with an unarmed opponent [wikipedia.org].
(Score: 1) by khallow on Monday November 23 2020, @04:35PM (6 children)
(Score: 2) by turgid on Monday November 23 2020, @08:25PM (5 children)
Optimised in what way?
I refuse to engage in a battle of wits with an unarmed opponent [wikipedia.org].
(Score: 0) by Anonymous Coward on Monday November 23 2020, @11:14PM (3 children)
Extra weight?
Kidding, but some solar sail tugs would be cheap on fuel.
(Score: 3, Informative) by Immerman on Tuesday November 24 2020, @02:14AM (2 children)
Can solar sails be used to lower a solar orbit? I know they can't tack (accelerate towards the sun like a sailboat sailing into the wind) since that requires the interplay of the forces on both the sail and keel/hull - and there is no water analogue in space to provide that counter force.
They can't even accelerate perpendicular to the sun, since that would require that photons bounce off the sail at an angle mirrored around the perpendicular axis - which means the sail has to be perpendicular to that axis, and thus edgewise to the sun so it can't generate any thrust
Which means the only option is accelerating "up and backwards" so you would be simultaniously trying to raise your semimajor axis and lower your periapsis - but it's not immediately obvious to me whether there's a range of angles where the periapsis lowering would win out.
Hmmm, something half-remebered is nagging at me... up is back, back is down... okay, found this diagram https://space.stackexchange.com/questions/44608/what-happens-to-orbit-after-a-radial-burn#44611 [stackexchange.com]
That says a radial-out acceleration will raise the apogee 90* in front of you, while lowering the perigee 90 degrees behind you, I think without significantly altering the semimajor axis. While a retrograde burn both reduces your semimajor axis and lowers your perigee 180* away. I suppose that would mean a combined up-and-back burn would try to raise apogee about 90* in front of you, while lowering perigee somewhere between 90 and 180 degrees behind you, so the net effect of sustained thrust should be a slight raise in apogee and a substantial lowering of both perigee and semimajor axis, with I thing a retrograde twist to the orbital ellipse's semimajor axis.
So I guess yeah, solar sails could actually lower your orbit quite effectively. Go figure!
(Score: 1) by khallow on Tuesday November 24 2020, @02:39AM (1 child)
Actually, they can tack since the acceleration is versus the momentum of the sail. By positioning the sail so that it is angled (for example, 45 degrees would be sufficient and it would intercept ~70% of the light of a full on position) to the solar influx, they can generate acceleration along or opposite the velocity of the vehicle. That raises or lowers the orbit respectively.
So to outline such a scheme as I see it. Use a bunch of solar sails to lower the vehicles, propellant, solar shield (since you don't want this stuff exposed to direct sunlight), etc. It's all mass. Lowering the orbit to Mercury is fairly easy since you can do most of the work with gravity slingshots (which can be used to take away velocity rather than add it). Past that, solar influx is roughly 5-10 times (due to Mercury's elliptic orbit) as intense as it is in Earth's orbit. So solar sails should really shine and lower your orbit to whatever you desire. It make take many years to move the mass to the desired final orbit (perhaps 5-10 years?), but once you get it started, it's just an assembly line process and more solar sails means you can move more mass. Particularly important payloads (like the actual spacecraft and replacement equipment) may come on expedited trajectories with a much faster arrival time. Even with those years of lag, with enough logistics you could launch a mission extremely frequently (like once a day), should that be something desirable.
So in particular, once this sort of logistics are in for one mission, they can be reused many times for additional missions.
(Score: 2) by Immerman on Tuesday November 24 2020, @03:51AM
Unless I'm badly misunderstanding what you're describing, that's not tacking (or as I review the details, I guess "tacking" is technically the direction change as you zigzag back and forth, while "beating" is the act of sailing into the wind. Seems it's a common point of confusion)
If I understand what you're describing... let me describe it as seen from "above", with the sun far to the "south", and the initial circular orbital motion to the "east"....
The solar wind is traveling due north, and the sail's perpendicular axis (the front of the ship) is pointing at 45 degrees north-west, so that its tangential acceleration is west, against its orbital direction. Does that sound right?
That means the wind will come in traveling north, hit the sail and get reflected across the sails axis, to depart going due east, and your sail will be pushed north-west. Agree?
That's sailing across the wind, but it's not tacking. I mean beating.
For beating, you have to be accelerating *south*, towards the sun. And you can't do that with a mirror. You can point the ship more westward to reduce northward acceleration, but as you approach due west the exposed surface, and thus acceleration, drops to zero. And as you begin to point south-west the wind starts hitting the front of the sail instead of the back, and and pushes you backwards, north-east.
A sailboat on the other hand can sail southwards since the water provides resistance that causes the wind to flow across the surface of a properly oriented sail rather than bouncing off it, causing it to act as a wing that generates lift and pulls the boat towards the south. You can't sail due south, but you can get pretty close to south-west or south-east, and tacking is the act of switching back and forth between the two so that your net direction of travel is due south (or whatever other angle you want)
I think we agree that you can actually lower your orbit by sailing across the wind and taking advantage of the peculiarities of orbital mechanics - I did my breakdown at the end of my previous comment - but it's a very different mechanism beating and tacking.
As for not including the sails in the mission propulsion efficiency - sure. I've got no problem with that. They're valuable, (hopefully) robust, solar-powered infrastructure that can be used for lots of things, most of them completely unrelated to interstellar missions. Without a heavy attached payload they could be moved around the solar system relatively quickly to wherever they might be needed.
(Score: 1) by khallow on Tuesday November 24 2020, @04:00PM
For cost, for example. Anything actually going on that interstellar spacecraft has to be heavily optimized for mass reduction and longevity. That's not need for systems that bring the spacecraft to a near Sun orbit.
(Score: 3, Interesting) by Immerman on Monday November 23 2020, @07:19PM (5 children)
Sending a bunch of rockets is energetically equivalent to sending one big one with multiple stages - worse actually, since you've got a lot more "wrapper" around the same amount of propellant. After all, you can't be a propellant depot unless you've matched speed and trajectory with the ship, so you may as well be along for the ride from the beginning.
The core question is - for a given amount of propellant, is it more efficient to launch outwards from Earth, gaining delta-V the entire way? Or launch inwards towards the sun, shedding a massive amount of delta-v, before trying to gain it back using Oberth efficiency and solar powered propellant heating?
Keep in mind, a Hohmann transfer from Earth's orbit that grazes Mercury's requires 7.5km/s of delta-V, versus the 12.3km/s to escape the sun from Earth's orbit.
So, a Mercury-grazing solar-powered launch to interstellar space would require:
7.5km/s to graze mercury's orbit
+ 7.5km/s to regain the original orbital energy
+ 12.3km/s to escape the sun
= 27.3km/s to escape the sun, rather than 12.3
So to be worth it, that solar heating phase has to increase the overall effective impulse of the total propellant used by a factor of 2.2, despite the fact that thanks to the rocket equation, much/most of that propellant will be expended on the inward leg.
Actually though, I think I may have done the math wrong, I think delta-v might not add add linearly, so my calculations would be way off.
(Score: 1) by khallow on Tuesday November 24 2020, @02:42AM (3 children)
My thinking is that you don't need any propellant to get to a near Sun orbit. Just use solar sails. And since these sails aren't part of the extrasolar mission, they don't need to be subject to the same efficiency requirements.
(Score: 0) by Anonymous Coward on Tuesday November 24 2020, @07:39PM (2 children)
How do you use solar sails to drop delta-vee to get an orbit that goes close to the Sun?
(Score: 2) by Immerman on Tuesday November 24 2020, @08:16PM
I actually did a breakdown at the end of another comment somewhere nearby. I was surprised, but it should work.
(Score: 1) by khallow on Wednesday November 25 2020, @02:15PM
By angling the solar sail relative to the velocity of the orbit around the Sun. When the acceleration is in a direction that mostly opposes the direction of velocity, you will drop in orbit.
(Score: 1) by khallow on Tuesday November 24 2020, @04:14PM
Also the necessary escape velocity increases as the inverse square root of the radius while the solar influx increases as the inverse square of the radius. Available power increases as the fourth power of the escape velocity.
So not only we not need to expend any propellant on the inward leg, we get a huge increase in the available power for accelerating that propellant. For a crude example of how that could work, the liquid helium could first be heated to an ionized plasma by a first stage solar heater creating substantial thrust in the process and then put through a solar-powered microwave heater and/or electric propulsion system to greatly increase the escape velocity of the plasma.
(Score: 2) by Immerman on Monday November 23 2020, @04:06PM
I imagine a much closer approach to a cooler star would do the job just fine - I mean even a small, cool, red dwarf is far too hot to get anywhere close to grazing the atmosphere. Worst case scenario you have to carry more propellant since it'll be heated to a lower temperature. Or you can travel more slowly between stars to reduce the deceleration propellant needed.
It doesn't really matter what the relative mass of the stars is, since all the delta-V needed to escape our sun has already been lost before we begin crossing interstellar space. And the lighter the target star is, the less new delta-V we gain entering its shallower gravity well.
(Score: 0) by Anonymous Coward on Monday November 23 2020, @01:34PM (2 children)
I'm assuming there is a good reason to use helium as a working medium, but remember that hanging on to helium for any length of time is pretty difficult--it has a way of worming itself through all kinds of materials.
(Score: 3, Insightful) by Immerman on Monday November 23 2020, @02:45PM (1 child)
In general, the lower the molecular weight, the higher the efficiency as a propellant because of the interplay of temperature and momentum.
With a given thermal rocket engine, you can get your propellant to roughly the same temperature regardless of what it is (the thermal and mechanical stresses from the pressure and temperature of the gas don't care about molecular weight). But the average RMS speed of molecules in the gas at a given temperature is proportional to sqrt(1/molecular mass), so the lower the mass, the higher the molecular speed, and thus the greater the momentum per pound. If you reduce the molecular weight by a factor of 4, you double the molecular momentum within your gas at the same temperature. The rocket bell then converts that chaotic momentum into linear momentum as it's expelled, imparting equal-and-opposite momenum to the rocket since momentum is conserved.
And if you're going for low molecular mass, helium is the second-best propellant available since it's a monoatomic gas with an atomic mass of 4.
Hydrogen is better, since H2 gas has a molecular mass of only 2, and if you get it hot enough to dissociate into a monoatomic plasma you can lower that all the way to 1. But hydrogen is *really* hard to contain, helium is downright easy in comparison.
(Score: 4, Informative) by Immerman on Monday November 23 2020, @04:10PM
Sorry, I phrased that inaccurately, that should be:
Since the molecular mass reduces faster than the speed increases, per-molecule momentum will be lower. It's momentum per pound of propellant that doubles.
(Score: 1) by fustakrakich on Monday November 23 2020, @02:18PM
So you store it in a big capacitor. How many Farads is 1 SU?
La politica e i criminali sono la stessa cosa..
(Score: 2) by Immerman on Monday November 23 2020, @02:57PM
I don't know of *any* interstellar plans that involve accelerating while in transit.
Virtually all rocketry does all the acceleration at either end - mainly because you just cant carry enough propellant to keep burning for more than a few minutes, and also because the deeper you are in a gravity well, the more delta-V you get per pound of propellant due to the Oberth effect.
Ion drives are the exception - but that's only because we haven't yet developed an ion drive powerful enough to rapidly expend all its propellant, and they're so much more efficient than thermal rockets that even without being able to harness the Oberth effect they're still a huge improvement anyway. But even they're not efficient enough to keep running continuously for the many centuries it's likely to take to cross interstellar distances. Even laser-powered solar sails can only provide significant acceleration when relatively close to the laser. We could build lasers all the way out to Pluto, the Oort cloud, and the beam would spread so much as to be completely useless before the ship had gotten a few percent of the way to the nearest star.
Basically, you're going to be doing all your your acceleration at the endpoints regardless. So if you can harness the sun to greatly increase the efficiency of of your propellant, that's a huge win.
(Score: 0) by Anonymous Coward on Monday November 23 2020, @12:57PM (3 children)
Interstellar. Right.
So you're going to use a star-powered drive for a voyage through interstellar space, which, by its very existence, does not contain any stars.
What are you going to do, put a few tons of shiny-brighty in the trunk to take it along, driving your ship?
Now, inter-orbital tugs where delivery time is not very relevant and distance to star is somewhat constant, I can entertain that thought. Not buying any stock yet, but sounds remotely plausible.
Interstellar, though? You need either less meds or more, current dosage is bad for you.
(Score: 4, Insightful) by Immerman on Monday November 23 2020, @03:00PM (2 children)
You always do virtually all your acceleration at the endpoints anyway. You just can't carry enough propellant to keep a rocket engine running even for even hours, much less the years or centuries involved in interstellar travel.
(Score: 2) by cmdrklarg on Monday November 23 2020, @10:33PM (1 child)
Unless you build Project Daedalus https://en.wikipedia.org/wiki/Project_Daedalus [wikipedia.org]
The world is full of kings and queens who blind your eyes and steal your dreams.
(Score: 2) by Immerman on Monday November 23 2020, @11:39PM
Even project Daedalus.
3.8 years sounds like a long time - but it's only 7.6% of the duration of the projected 50-year journey, and considerably less than that by distance.
(Score: 5, Insightful) by Runaway1956 on Monday November 23 2020, @01:33PM (10 children)
In essence, they want to slingshot a giant tank of liquid helium around the sun, to superheat the helium, then use that helium for reaction mass. So, they haven't solved the conventional rocket's problem of eventually running out of reaction mass. Which means that they need a nice pool of helium at the other end of the journey from which to "refuel". Not even the Sci-Fi idea of building a powerful laser here in the solar system to aid in acceleration helps much, as it transfers no reaction mass to the tanks.
Unlimited energy does not automatically translate into unlimited reaction mass.
“I have become friends with many school shooters” - Tampon Tim Walz
(Score: 4, Insightful) by Immerman on Monday November 23 2020, @03:11PM
Obviously they haven't solved the tyranny of the rocket equation - nothing short of a reactionless drive that violates known physics will do that. Though, I did hear some promising noise about a paper awaiting peer review exploring sublight versions of the Alcubierre warp drive - apparently at sublight speeds there's no need for negative energy densities, so it might be physically possible.
Moreover, they're talking about launching into interstellar space, a la the Voyager probes, not necessarily traveling between stars.
Even if they were trying to stop at the other end, just save some of the propellant for deceleration at the far end, where it can once again be superheated by the destination star. Even interplanetary travel is so demanding of propellant that nobody has a realistic plan that doesn't involve refueling at the far end if you want to return a significant amount of mass. Heck, you can't even fly a plane across the country and back without refueling at the far end.
(Score: 2) by turgid on Monday November 23 2020, @04:17PM (8 children)
Photons are massless but they do have momentum. A photon rocket is theoretically possible.
I refuse to engage in a battle of wits with an unarmed opponent [wikipedia.org].
(Score: 2) by Runaway1956 on Monday November 23 2020, @04:29PM (7 children)
True - but a photon sail (light sail) might prove more efficient.
“I have become friends with many school shooters” - Tampon Tim Walz
(Score: 2) by turgid on Monday November 23 2020, @04:43PM (6 children)
A light sail is just a big mirror. When you're close to the Sun it works really well. When you're far away from the Sun you would have to take your own light source with you. It would have to be some sort of nuclear power. Warp drives are pure science fiction, but photon drives actually have a basis in existing physics. They're not reactionless but they don't work by emitting mass.
I refuse to engage in a battle of wits with an unarmed opponent [wikipedia.org].
(Score: 2) by Runaway1956 on Monday November 23 2020, @05:32PM (2 children)
Would that necessarily be true? The Voyager craft were noted to have picked up some extra inertia, most easily explained as pressure from the sun. Apparently, I'm using poor search terms, because I'm not finding what I remember reading. However, this hit seems to support the idea of bringing your own light source:
https://www.space.com/16648-pioneer-anomaly-spacecraft-mystery-solved.html [space.com]
“I have become friends with many school shooters” - Tampon Tim Walz
(Score: 2) by turgid on Monday November 23 2020, @07:28PM (1 child)
Correct. So shine your bright light out the back to accelerate forwards.
I refuse to engage in a battle of wits with an unarmed opponent [wikipedia.org].
(Score: 2) by coolgopher on Tuesday November 24 2020, @01:25AM
Certain people could be spaceships themselves, seeing as they think they have the sun shining out their asses...
(Score: 3, Informative) by Immerman on Monday November 23 2020, @08:02PM (2 children)
If you're taking your light source with you, the light sail becomes useless. It's essentially the cartoon scenario of blowing on your sailboat's sails to make it go faster. Technically it works, but even with 100% sail efficiency you just barely reach the same acceleration you'd get if you just turned around and blew backwards. Which would be back to a photon rocket for our solar-sail example, and the sail would just be dead weight until we slow down using the star at the other end.
And unfortunately photon rockets still aren't that great for interstellar journeys because they do in fact emit mass and are still bound by the rocket equation. Photons have no *rest* mass, but they still have mass in flight proportional to their energy, and that mass comes from the mass lost by the matter fueling your reactor.
In this sort of conversation, E=mc^2 might be more informative in its original form:
m = E/c^2 : mass is an invariant property of energy, with matter being a solid form of energy.
The common claim that you can convert between mass and energy is actually false. You can convert between _matter_ and energy, but the energy will still have exactly the same mass as the original matter did.
Anyway - photon rockets are still bound by the rocket equation, since you're basically converting your reactor fuel to energy and throwing it out the back end, and you're back to looking at specific impulse. And the momentum per unit mass isn't that great. According to Wikipedia the maximum speed of a fusion-powered photon rocket is 0.02% of c (H-H fusion I would assume, I think that has the highest matter-conversion rate), while a fission rocket which converts much less of its fuel to energy increases asymptotically to only 0.005% of c - actually slower than Voyager 1's current speed of roughly 0.0058% c https://en.wikipedia.org/wiki/Photon_rocket#Maximum_speed_limit [wikipedia.org]
(Score: 2) by turgid on Monday November 23 2020, @08:23PM (1 child)
Yes.
Indeed. So your spacecraft becomes less and less massive while still pushing just as hard, so the acceleration goes up.
I used to work at a nuclear power station. We could calculate how much mass of fuel we turned into energy. Those were the days...
Well, according to me, a chemical rocket can run for hours. A nuclear engine can run for about 30 years without refuelling. So which would be more useful?
We'll go places with nuclear engines long before "warp drives" are invented, which require completely novel Physics yet to be discovered.
I refuse to engage in a battle of wits with an unarmed opponent [wikipedia.org].
(Score: 3, Interesting) by Immerman on Monday November 23 2020, @09:02PM
>So your spacecraft becomes less and less massive while still pushing just as hard, so the acceleration goes up.
Yes, exactly like any other rocket
>Well, according to me, a chemical rocket can run for hours
Are you, like Wikipedia, on average more accurate than any printed encyclopedia?
>We'll go places with nuclear engines long before "warp drives" are invented
Nuclear engines, yes - I'm really looking forward to seeing what sort of things we come up with now that nuclear rockets are being seriously considered for in-space use.
Nuclear powered photon rockets - not so much. The specific impulse of photon rockets just sucks. Sure, it can run almost forever, but almost no thrust times a very long time, is still not much change in speed. As I recall nuclear powered ion drives offer several orders of magnitude better specific impulse.
There might be some interesting potential in hybrid drives though - after all, once you've fused your hydrogen to produce energy you've got a bunch of useless helium lying around. Instead of just dumping it overboard to lighten the load you might use it as propellant in an extremely high-impulse ion drive, potentially greatly increasing the specific impulse over a photon drive of the same power.
There also might be potential for antimatter powered photon rockets - the specific impulse looks a lot better when over 99% of your fuel mass isn't just dead weight along for the ride.
And since you mentioned warp drives - still science fiction, but I recently heard of a group exploring the properties of sublight Alcubierre-style warp drives. Apparently at sublight speeds you no longer need negative energy densities, which puts them much more firmly in the realm of things that might actually be possible.
(Score: 3, Informative) by PiMuNu on Monday November 23 2020, @01:52PM (1 child)
FTFA
> And the APL team is studying a probe that would go three times farther than the edge of the solar system,
> a journey of 50 billion miles, in about half the time it took the Voyager spacecraft just to reach the edge.
They are not trying to go to another star system, just to look at what's in the gap. Extrasolar would be a better word.
(Score: 4, Touché) by Immerman on Monday November 23 2020, @03:15PM
I don't know - there's a well accepted name for the space between stars: interstellar space.
And if you can reach interstellar space, then you can reach other stars - it'll take an enormously long time at Voyager speeds, but so long as you pick the right trajectory you'll get there eventually. Once you've escaped the Sun's gravity, you'll wander the galaxy, occasionally slingshotting through other star systems, until something destroys you.