#### dave123

Hello.

I'm writing a story about a manned spacecraft capable of leaving the solar system. In my story, the vessel must complete a trial run to Neptune, then be sent on a one way trip to colonize Ross 128B; so I have questions about both trips. I've chosen a Photonic laser thruster system as the means of travel, and I will need the vessel to reach .9 light speed. I realize that the math for this really does not work out, but I've decided to postulate that future science will overcome the current impossibilities and modify the system that Young Bae has researched to make the trip feasable.

I have some questions for the experts here and would really appreciate knowledge as well as opinions you may wish to share. My goal is not perfection, but rather to craft a story that won't sound completly silly to someone who has a broad knowledge of such things.

I hope I'm not dumping too much into one thread, but certianally don't want 20 threads cluttering up the place; so several questions follow:

1. What would be the fastest that a spacecraft could accelerate/decelerate without turning humans into Jello?

2. I've read that a trip to Neptune at .9 would take just over 4 hours to reach Neptune. But how long would it take factoring in Acceleration and Deceleration
(A + D)? I would have the same question for Ross128B, which is just over 11 light years from earth.

3. Assuming the trip to Neptune was planned to reach her at her closest point to earth, would it matter much if the return trip were delayed? Let's say that the vessel planned a 3 day loiter and the time was increased a day?

4. The vessel must have the ability to see and record data (of course). Would it be correct to use the term 'Scanners', or maybe 'Sensors'?

5. I'm sure the math to send a vessel to Ross 128 would be formidable. Would it be necessary to allow the spacecraft to alter course during the trip?

Thank you very much for any input.

Catastrophe

#### Phillip Huggan

At .5c or .6c our brains will stop working. I assume some sort of suspension technology is there at +0.6c. I imagine other anomolous effects happen past then to every day future technologies. The suspension is no longer good liquid, and all our existing projected medicine is useless around 0.7c or 0.8c. I assume months for both sides of suspension fitness physiotherapy.
Your quantum sensors will conk out in the teens. Electricity might fail anywhere from .3c-.7c. I wouldn't think it matters if our first fast probes dispell the exact speeds. Quantum radar works fixed and low power, but it is fragile. Neutrinos will be there with dense/massive sensor rods or particle beams. I would think it takes time to fix a ship accelerating out of control so you'd never go too fast. Antimatter might get near 0.6c. Then you need a GUT for sci-fi stuff.

dave123

#### Catastrophe

##### "There never was a good war, or a bad peace."
4. The vessel must have the ability to see and record data (of course). Would it be correct to use the term 'Scanners', or maybe 'Sensors'?
5. I'm sure the math to send a vessel to Ross 128 would be formidable. Would it be necessary to allow the spacecraft to alter course during the trip?
4. Either seems fine.
5. Since you are going to a star, it should be literally straight forward. You can check with Google or a star atlas as to whether there are any close stars en route. Of course, there may be uncharted hazards, such as dark stars, interstellar rocks (rogue asteroids), et cetera. You will need to refine course close to destination, but this will be included in deceleration. Again, at very high speeds even minute particles, even large space dust, can be a serious hazard. Check the following (look through all thread).

Cat

Helio and dave123

#### Phillip Huggan

Photon travel permits slowing down. But tacking left or right is difficult. Steering away from hazards mid-course will require heavy rockets or something. You can clear away the debris from the solar system but in plane is tough. I'd suggest going through the bottom of the south pole for 20 or 30 AU mildly away from the asteroid belt below the Sun. Then a straight line to 20 or 30 AU below Neptune, then up to Neptune. That is three or four photon sources unless you can tack well from the Cis-Lunar source.

#### dave123

Thank you both for the replies. The link on diamagnetism will be super helpful.

I can see I'm totally out of my league here (even worse than I thought) as I try to understand Phillip's reply. I'm just a regular guy who like to write SF. Even after a google, not sure what .6c means (I'm guessing 6/10ths of light?). Assuming I'm correct, all the SF I've ever read has just been trashed when you state that electricity won't work at speed.

So, if I can impose a bit more - I'm not looking for perfection, just trying make something that's not crazy off in the science department. My main goal here is just to have realistic timetables. For example my rough draft goes like this:

Although the time to Neptune at the ships maximum speed of .9 light was less than a day, the time it took to accelerate and decelerate lengthened the trip to a still incredibly fast 22 days.

So, are there calculators, or ways for me to estimate travel times to Neptune and Ross 128?

Oh, the "Sensors" would only be used while at Neptune and almost stationary. Is that what they really call them?

Catastrophe

#### Catastrophe

##### "There never was a good war, or a bad peace."
And . . . . . . check Google Ross128B:

Imgur: The magic of the Internet

Wait 35,000 years and Ross 128 will only be less than 3 light years away!

Cat

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Helio

#### Helio

1. What would be the fastest that a spacecraft could accelerate/decelerate without turning humans into Jello?
V= a*t (Newton)
So, ~43 days at 1 g acceleration. [actually longer, I think, given that high of a relativistic speed.]

2. I've read that a trip to Neptune at .9 would take just over 4 hours to reach Neptune. But how long would it take factoring in Acceleration and Deceleration.
s=a*t^2/2 , so... t=(2s/a)^1/2. — s is distance to Neptune. You will need to use 1/2 distance for both acc. and dec. This equation ignores initial velocity.

I would have the same question for Ross128B, which is just over 11 light years from earth.
time dilation effects are.... t’ = 1/[1-(v/c)^2]^1/2; v/c = .9

Speed has no bodily effects, unlike acceleration. This is the heart of General Relativity.

3. Assuming the trip to Neptune was planned to reach her at her closest point to earth, would it matter much if the return trip were delayed? Let's say that the vessel planned a 3 day loiter and the time was increased a day?
Any ship that is that powerful can do whatever you want.

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#### Phillip Huggan

Our brains use processes that won't work at the speed of light, without lots of borg brain teach. We have electrical synapses. They won't work well at .9c. The thoughts will be slowed down and entire brain regions affected.

dave123

#### billslugg

The velocity you are going has no affect on you in the the vacuum of space, you are completely unaware of how fast you are going. You are only aware of how fast you are accelerating and not much of that is required to reach significant velocities. Just three months at a constant 1 g will get you to 25% of light speed.
What is an insurmountable problem is the energy requirement. The need for energy increases by the square of the desired end velocity. If you want to get to .25 c then a single kilogram of payload will require 2.8 x 10^15 joules of energy which is the amount produced by the world's electrical generating capacity over about a 9 minute period of time. If your craft weighed 15 metric tons then you would need the world's entire electrical generating capacity all to yourself for the 90 days it would take to reach .25c. And most of that would have to be stored in batteries during the early part of the trip for use near the end where the powerequirement is highest.

#### Helio

Our brains use processes that won't work at the speed of light, without lots of borg brain teach. We have electrical synapses. They won't work well at .9c. The thoughts will be slowed down and entire brain regions affected.
No. We are traveling now at 0.9c relative to any far away distance at some point, and our brains are normal. That’s relativity. No one inertial frame wI’ll be special to any other when it comes to how physics is observed within each frame.

#### Phillip Huggan

Einstein and our HS texts posit speed 0.9c of a single static object; every molecule in the object at identical local speed. A system which has parts moving at different speeds is okay as long as the speeds of the local molecule/field are not magnitudes in order faster than the speeds of the other object, and also approaching light speed fractions. Our electrical synapses signal faster than our ionic ones. The ionic ones are a few hundred or a thousand km/hr. At 0.5c, there will start to be a degradation of our mental capacities. The fast parts of our brains, will slow down badly at 0.9c. The ion conducting synapses will only barely slow down. At 1st the effect will be a missed coffee, then maybe Salvia, then death. Our thoughts are happening left and right in our brains while we are at near c Normally the electric synapses are "x" % faster than ion ones, at 0.9c they are only x/50 % higher, the stuff travelling near light speed has slowed down while stuff travelling slower has not slowed, all in the *same* brain volume.

dave123

#### Helio

Phillip, can you provide any peer-reviewed paper on this?

GR says otherwise.

Catastrophe

#### Phillip Huggan

No. Everyone else has been wrong in ignoring the effect for a system such as batteries or brains. It is a special relativity effect. General relativity does not apply except it can be used to map the 3d space at 0.9c differently. I am the first to note the effect. It means we will need cryonics to catch an AI probe, but not a pirate. Radioactive stimulation near nerves. Nerves coated in a substance absorbing the harmful radiation. Scraped away and replenished every 100 years, to be developed within 100 yrs after commencing the 10c suspension. Fort Knox somewhere remote and cheap. Jupiter needed for North America. I noted it for decohering photons around .2c, never for systems until now.

#### dave123

Copy and paste from Helio:

s=a*t^2/2 , so... t=(2s/a)^1/2. — s is distance to Neptune. You will need to use 1/2 distance for both acc. and dec. This equation ignores initial velocity.

time dilation effects are.... t’ = 1/[1-(v/c)^2]^1/2; v/c = .9

I think this is what I'm looking for, except, despite my google efforts, I'm too dumb to use it.

Are there calculators to help? Even with this, I can't answer the question - How long for my vessel with photonic laser propulsion to accelerate and decelerate and arrive at Neptune. Initial velocity would be nil. Part of my problem is that I don't know what a realistic guess would be for acceleration and deceleration.

On the second formula, the one to Ross 128, the answer is 5/12 years, but for the life of me, I can't figure how. It's got to be tied to time dilation while on the ship. I've read a bit about that, something along the lines of arriving before you leave, if memory serves. But, how much earth time would pass?

Thanx for your patience; I'm afraid that I'm a writer, not a scientist...

Catastrophe

#### billslugg

Here is a good calculator for travel time, energy needs, etc.
Space travel calculator (simhub.online)

A realistic value for acceleration is about one g for about 30 minutes. That is at the limit of chemical rocket propulsion.

A fission rocket can best that by a factor of about 100,000.

A fusion rocket can best a fission rocket by a factor of 7.

An antimatter rocket can best a fusion rocket by a factor of 4.

There is no case where you can arrive before you left. All you can do is make your clock slow down as measured by an outside observer. You would not notice any difference in your frame of reference.

When you got back to Earth, much more time would have passed on Earth, everyone would be much older than you.

#### Helio

How long for my vessel with photonic laser propulsion to accelerate and decelerate and arrive at Neptune. Initial velocity would be nil. Part of my problem is that I don't know what a realistic guess would be for acceleration and deceleration.
So ignoring initial velocity, and just using 30AU for the total distance...

A 1g acceleration is about 8 days to get half way, then 1 g deceleration is also 8 days, assuming you want to stop for gas and hamburgers, or something. [11 days if just zipping by Neptune.]

On the second formula, the one to Ross 128, the answer is 5/12 years, but for the life of me, I can't figure how. It's got to be tied to time dilation while on the ship. I've read a bit about that, something along the lines of arriving before you leave, if memory serves. But, how much earth time would pass?
Once you see how it's done, you might enjoy playing with whatever speed you like since you have a magically powered spacecraft...

Step 1. Set the speed you'd like (time of acceleration is usually ignored as it is small, normally.) Let's use 0.9c (~ 270,000 kps). Thus, from Earth, the speed observed will be 270,000 kps

Step 2. Now we just need to now the distance see we know the ship's speed:
11 lyrs. is 9.46 trillion km/lyr. times 11 = 100 trillion km.

Step 3: Time Earthers see ship reach distination:
100 trillion km divided by 270,000 km/sec = 385,400,000 seconds. Converting seconds to years = ~ 12.2 years.

Step 4: Time for Travelers to reach (Special Relativity effects):

A: get vel/speed of light (v/c). This is our 0.9c value.
B: Square this value. 0.9^2 = 0.81
C: Subtract it from 1. 1-0.81 = 0.19
D: Take the sq. root of it. (0.19)^1/2 = 0.138 [oops. This is 0.43.{
Thus, the time dilation will be 13.8% [43%!] less time overall.

Thus, the time traveler's clocks will say they arrived in only ~ 10.5 years. [5.3 years]

These times become quite small for the travlers as they get closer and closer to the speed of light because of the exponential reduction in time with speed.

So, you might want to walk through the steps using a different value. I'm sure there are calculators on the web for special relativity effects.

Good luck

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#### Helio

If the ship must decelerate then you might calculate the dilated time by using 1/2 the distance, then double that time. [7.8 years for the above]

[Dang. The acceleration and deceleration times were to be ignored. I tend to get distracted while doing posts via my iPhone. ]

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#### billslugg

The relativistic equations look like a hockey stick, don't become significant until up around 0.8 c
What is significant is the energy requirement. At 0.8 c, a single kilogram of mass has the same amount of energy as produced by the US electrical grid in 8 hours. And that is ignoring the increased mass due to GR.

#### Catastrophe

##### "There never was a good war, or a bad peace."
IMHO, "star travel" is all up in the air (npi) at the moment. When (or if) we get transport even at 0.2c, is problematical - then we can think of going there.

Of course, the world of fiction, justifiably, has control over the rules, and many legitimate scenarios are possible, which do not stretch the imagination too far.

Cat

Helio

#### Helio

IMHO, "star travel" is all up in the air (npi) at the moment. When (or if) we get transport even at 0.2c, is problematical - then we can think of going there.

Of course, the world of fiction, justifiably, has control over the rules, and many legitimate scenarios are possible, which do not stretch the imagination too far.
Indeed.

Dave, if you're still around, you might enjoy a story regarding James Cameron. Neal Tyson once had a chance to tell him that the stars the night the Titanic sank were off in the movie. IIRC, Cameron sarcastically responded with wondering how many more millions of people would have seen the show had he been right.

Star Trek has suffered little with no known way to have warp drives.

#### Helio

FWIW, here is an illustration that explains how to calculate the travel time to stars.

Astronomers provide "proper motion" in milli-arcseconds of RA (Right Ascension) and Dec (Declination). Knowing the distance and using Pythagoras, one can convert these to a kps motion. Astronomers give radial motion (speed toward's us) in kps.

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