Are you ready for Mars in a week?

[Moonbeam]

Here is a link to an interesting laser technique that will make speeds of 100km a sec possible, or travel to Mars in a week. Pretty cool. I think that's about 223,560 mph.

 

[Paratus]

I read that link the other day very cool. The one thing I'm not sure about it is it looks like it would shoot the beam from the ground and reflect it off the space craft and back again. That's going to require some mighty tight attitude control.

If you are interested here's another cool propulsion concept for Earth to Mars in about a month

http://en.wikipedia.org/wiki/V...e_magnetoplasma_rocket

I've actually seen the lab version of that work. Dr. Chang-Diaz was a fusion researcher who realized that while having problems containing plasma is bad for fusion it makes a good rocket. The only problem (especially from your point of view ) is that VASIMR would require tens to hundreds of megawatts which is only really possible with a fission power plant for a Mars mission

 

[Lemon law]

At least for Mars, the question is why speed matters that much? Not only does the the engine have to accelerate a given mass up to 100Km/sec, it has to be able to slow it back down in what amounts to days at those speeds. How many days would that accelerate process take? It would seem the engine cries out for longer journeys.

 

[Paratus]

LL

For a manned mission speed is essential to reduce radiation effects & musle atrophy on the crew. Powered abort options are nice too.

posted via Palm Life Drive

 

[Jeff7]

100km/sec? That's (not) 1/3 C. That'd take a damn long time to accelerate to, either without killing any human occupants (chunky salsa, anyone? Where are those intertial dampeners....), or even just exposing mechanical components to extreme G-forces.
Stupidity edit
I did a 1000 multiplication in my head there for some reason. 100km/sec is nowhere close to 1/3C. I apparently saw 100km and translated it to 100,000 kilometers per second.
Hopefully the rest of my calculations (assisted by silicon) are more accurate.

Still, they should have stuck this on the New Horizons spacecraft. It's making the 5 billion kilometer trip in 9.5 years. 5 billion kilometers at 100,000km/sec - that's about 14 hours, assuming instantaneous acceleration.

The laser generates 35 uN of thrust and is scalable to much larger amounts of propulsion.

Ok, so New Horizons has a mass of 478kg.
35 micro-newtons.
F = ma

a = 0.00000007322176 m/s^2 = 7.322 * 10^-8 m/s^2


And for x = 0.5 * a * t^2, solved for time:
t = 534,522,483.8 seconds = 16.95 years.

And then by the time it reaches Pluto, it will be traveling at:
v = at
v = 18,708.3 m/sec = 41,849.3 mph.

So it would take several years longer to get there, but by the time it would, it would be moving faster as the speed it will be at when it makes its rendezvous (27,000mph).

But of course, all that assumes it wouldn't get a kindly boost from a chemical rocket of some sort.
With that, it would be starting out at about 16,200 m/sec.
Solving for t, that's t = 244215003.68 seconds = 7.74 years

and then vfinal = 24,747.5 m/sec = 55,358.6 mph, almost twice the original speed, and in less time.

(Note, this speed is still less than 1/4th of the theoretical maximum of 100

Apparently, sticking this thing onto New Horizons would have gotten it there faster. Another possibility: a more powerful version to get the probe there even faster, combined with a chemical retro-rocket to slow it down for the flyby.
Oh well.
At least I've proven that I remembered some basic equations of motion, right? When I start doing equations for the hell of it, I know that I really need to get to sleep.

 

[1EZduzit]

That would be perfect to use from a moon base. We could do a large scale test of Einsteins theory of relativity. Send some people off on a long trip at a high speed orbit them back off something like Pluto? and then slow them up again once they get close enough.

 

[dphantom]

Sign me up. But slowing down seems to remain the problem.

 

[techs]

If someone could figure out a way for me to get crosstown during rush hour in my car at WALKING speed, that would be a REAL accomplishment.

 

[1EZduzit]

Originally posted by: techs
If someone could figure out a way for me to get crosstown during rush hour in my car at WALKING speed, that would be a REAL accomplishment.

Move!!

 

[DrPizza]

Allow me to be the first to exclaim, "Bullshit."

I'm sure the technology is real, and I'm sure that there are potential applications for the technology, perhaps in particular, maintaining precise alignment of a fleet of satellites.

However, as far as propelling a space craft to Mars using this? Not gonna happen. Why? Ohhh, just those pesky laws of physics. Let's go through it... First, we have conservation of momentum. The change in momentum of the space craft will be equal and opposite the change in momentum of the Earth. (See Newton, 3rd law.) This is no big deal though, because compared to the space craft, the earth is massive, leading to a very very small change in velocity. If a fly ran into me, I'd have a larger change in velocity as a result. This is good news though, for the space craft. Because the change in velocity of the earth is so small, so is the change in kinetic energy. Thus, most of the energy of the laser would be available for accelerating the space craft, not the earth. (Rather than the earth and satellite split the energy 50/50.)

Hey, speaking of energy, that's the important law: conservation of energy.

Let's see... earth is moving at 30km/s (slightly less, actually). So, to achieve a speed of 100km/s, a space craft would have to be accelerated "only" by 70km/s. And, this laser is going to do it in a week.

Let's see, we'll assume a 1000kg space craft... 1/2 mv^2 = 1/2 * 1000kg * (70,000m/s)^2 = 2.45x10^12 joules of kinetic energy. Let's pretend for a moment that this process is 100% efficient (yeah right, uh hum, sure.) That means, the laser needs to provide 2.45x10^12 joules of energy. It's got a week to do this? I'll also be nice to the laser, giving it the full week to get the satellite up to this speed. If you want to do it in half a week, it'll take twice as much power. Power = Energy/time. 604,800 seconds in a week.

2.45x10^12 joules divided by 604800 seconds = :shocked: Where the hell are you going to get a 4.05 MILLION WATT LASER??!

Okay. Skip the humans in the space craft. We'll just send up a probe. And, forget about it having a chance to slow down - we're going to spend the entire week just getting it up to 100km/s, a speed it will attain moments before it becomes smashed into the side of Mars. (Or missing Mars at the last second, only to be flung into space and lost forever, if Nasa and Lockheed Martin can't agree on which units to use). We can cut down the mass of this thing to, say, 100kg. Much betterer! Now we only need a 405,000 watt laser. (Assuming, of course, that the entire process is 100% efficient.)

Again, I'm certain there are applications that the technology is useful for. But, traveling to Mars in one week is not one of them. (I am actually hopeful that I made a calculation error - it would be neat to see this technology go forward for the purpose of space exploration.)

p.s. If any NASA people are reading this, and saying, "you know, he's right," kindly remit a few bucks my way as a consulting fee Or, have a pizza sent to my house. Pepperoni and mushroom. Thanks.

 

[Harvey]

Beam me up, Scotty! Link to da source.

Kewl if it works. There's more about his research in other areas on the site.

 

[XMan]

It'd turn my hair white to go that fast . . . at 1/3 C, hit a pebble and you're tomato sauce.

Hopefully they're working on some sort of force field along with their propulsion system.

 

[fuzzybabybunny]

Pshhhhh... I go that fast on my bicycle.

 

[Lemon law]

Originally posted by: XMan
It'd turn my hair white to go that fast . . . at 1/3 C, hit a pebble and you're tomato sauce.

Hopefully they're working on some sort of force field along with their propulsion system.

We may all be traveling at 1/3 C or better as it is. Unfortunately its just not relative to anything relevant in the vicinity.

But point taken from previous poster, 100Km/sec is only 1/3000 C, and hit anything with mass
and there goes your ass.

 

[XMan]

Originally posted by: Lemon law

Originally posted by: XMan
It'd turn my hair white to go that fast . . . at 1/3 C, hit a pebble and you're tomato sauce.

Hopefully they're working on some sort of force field along with their propulsion system.

We may all be traveling at 1/3 C or better as it is. Unfortunately its just not relative to anything relevant in the vicinity.

But point taken from previous poster, 100Km/sec is only 1/3000 C, and hit anything with mass
and there goes your ass.

Yeah, I read it before he fixed the mistake.

And even at the speed they're talking about, it wouldn't take much mass. A golf ball would probably do the trick. . . .

 

[techs]

Uh, wouldn't you be affected by relativity at the speeds suggested?

 

[Jeff7]

Originally posted by: techs
Uh, wouldn't you be affected by relativity at the speeds suggested?

Well sure. GPS satellites are affected by it, and they need to correct for it. But of course, it's only a difference of a few microseconds a day, or something around that, if memory serves me correctly. Since it is such a small fraction of the speed of light, relativistic effects would only be an issue for maintaining time sync, and maybe they'd affect communication channels due to Doppler shift.

DrPizza makes good points though, as usual. NASA people probably read this and thought, "Ok, great, now we just need super-powerful fission reactors in space. Noooooo problem!" But the press gets it and doesn't know any better. They just hear "Lasers in space" and run the story.

And a 100kg spacecraft wouldn't be able to do a whole heck of a lot. New Horizons is a pretty compact probe, and it was 478kg at launch. Compare that to some others:
Voyager 1 - 722kg.
Cassini - 2125kg, excluding 3132kg of propellant. (It was also the heaviest, most sophisticated probe ever launched to another planet.)
Pioneer - now you're in the right range. Some of the earlier ones were around 63kg.

I guess ion engine propulsion is a better idea right now..

And, this laser is going to do it in a week.

I think it'd need some kind of amazing chemical booster to get it to 100km/sec. With the acceleration given of only 35 microNewtons, it would fly past Pluto before reaching 100km/sec. Maybe a railgun to blast the thing out of Earth's orbit?

 

[DrPizza]

But the press gets it and doesn't know any better. They just hear "Lasers in space" and run the story.

Which is incredibly unfortunate. (Hey, this is a P&N thread, so...) Because if Bush has someone read the article to him, NASA will be told that half of their budget has to be earmarked for developing this technology. (No budget increase though.)

 

[DrPizza]

Originally posted by: 1EZduzit
That would be perfect to use from a moon base. We could do a large scale test of Einsteins theory of relativity. Send some people off on a long trip at a high speed orbit them back off something like Pluto? and then slow them up again once they get close enough.

Sounds like you're talking about the twin paradox? There'd be no point in doing the experiment you suggested. This concept from the theory of relativity has already been verified. In fact, time dilation has to be taken into account for the GPS satellites, otherwise they would be very inaccurate at this point.

 

[Lemon law]

Originally posted by: techs
Uh, wouldn't you be affected by relativity at the speeds suggested?

In a word no. At least if you are talking 1/3000 of C.

The mathematical operator in relativity is is the square root of the quantity of 1 minus V squared divided by C squared.

Even at a full 1/3 C, the operator only gets to a factor of 1.06066.

At 1/3000 of C it would amount to 5.5 parts in one hundred million.

But thats from memory and a not very good scientific calculator. I hope I am not wrong because I will get flamed by the physics police.

 

[Deudalus]

Thats going to make for a very large carbon footprint.

 

[WHAMPOM]

Originally posted by: techs
If someone could figure out a way for me to get crosstown during rush hour in my car at WALKING speed, that would be a REAL accomplishment.

Park your car and walk?

 

[Darwin333]

Originally posted by: Deudalus
Thats going to make for a very large carbon footprint.

Just write a very large check out to Al Gore and it will be just fine.

 

[piasabird]

Somewhere you have to accouont for mass in the equation. The larger the mass the more force it takes to slow it down. Also such force would require a better built structure possibly. No matter how much force you have, the ship would have to withstand the force accelerating or slowing down would create.

 

[Deudalus]

Originally posted by: Darwin333

Originally posted by: Deudalus
Thats going to make for a very large carbon footprint.

Just write a very large check out to Al Gore and it will be just fine.

That was my evil plan all along.