Questions about Space Travel

Page 2 - Seeking answers about space? Join the Space community: the premier source of space exploration, innovation, and astronomy news, chronicling (and celebrating) humanity's ongoing expansion across the final frontier.
The calculations above are easier than I had originally assumed. I stumbled across an article about shooter video games and it was pointed out that the vertical velocity of both the target and the bullet/missile had to always be the same. This makes for an easy calculation for the impact point and time.
 
  • Like
Reactions: dave123
IMO, the ability of any ship to guide itself to a star system would be the least of the problems. [Of course, one can dream-up a host of mechanical complications with a ship trying to slow down, etc.]

Our Sun is traveling at around the galaxy at about 230 km/s. This is very fast for speeds on Earth, but will be slow for any rocket ship, which should be between 100x to 1000x that speed, more if possible for relativistic time dilation effects.

Also, the star will be easy to see. Any exoplanet would also be easy to see with a simple(?) mask, like modern telescopes use to kill the host star's glare.

Keep in mind what happens when you travel toward any light, including an exoplanet's light. The faster you travel, the faster the flow rate is received. Standing in a river will give you one flow rate, but traveling up river will give you a faster flow rate. Photons behave similarly. The result is that the greater flux of photons will produce a brighter object. [Astronomers know to adjust for such things, when necessary.]
 
  • Like
Reactions: dave123
Jun 10, 2022
28
10
35
Thank you for all the great replies. Yes, Helio, I'm still here. I've been out awhile as I've dealt with a serious illness in my extended family, but I'm back now. Rest assured that all the replies here are read and carefully considered.

I'd like to run a paragraph from my rough draft by you gentlemen. Am I exagerating the difficulties here? Do you agree with the paragraph? Thanx again.

""Ponder for a moment the variables that must be taken into account. Although it wasn’t too difficult to plot exactly where Ross 128b would be located at any time, the real difficulty was to plot where it would be when Excalibur arrived. The incredible speeds at which planets, and even stars moved through the galaxy was one thing, but the effects of the many gravities acting on the ship as she moved through space were daunting to say the least. A variance of a foot on earth could extrapolate to millions of miles by the time Excalibur entered the solar system of star Ross 128. As difficult as this was, an even bigger problem was estimating the Excalibur’s speed accurately throughout every moment of her journey. Just how fast would she accelerate? How fast would she decelerate? And just what would be her maximum speed?""
 
Jun 10, 2022
28
10
35
Thanx Helio. Wow, I messed this thread up. I didn't realize that my latest post had posted, so I redid the post, then deleted the wrong one, as it had, in fact posted (refreash!).

Anyway, yes, the net result is that your answer preceded my question.

Good points, you make. I see that the math is not that big a deal as the computers can just recalibrate the course on a regular basis. Well, I feel silly, but that's why I'm here. I'm off to fix that paragraph for sure.
 
Jun 10, 2022
28
10
35
I'm still running into the question of what passengers on such a ship would be capable of doing during the voyage. I'm thinking that the answer is to harness acceleration to a point where humans can function somewhat, but then I'm adding (years?) of travel time...
 
Jul 13, 2022
16
8
15
Humans (as the way we are) won't ever be able to travel at such speeds, they will most probably die in an instant. It's not about acceleration or deceleration, humans are a misfit for such a spacecraft, only if humans themselves are modified foremost.
 
I'm still running into the question of what passengers on such a ship would be capable of doing during the voyage. I'm thinking that the answer is to harness acceleration to a point where humans can function somewhat, but then I'm adding (years?) of travel time...
V=a x t, ; 1 g =9.8 m/s^2

So, using t = 180 days, and a=g, then vel = 50% of light speed, roughly. Faster speeds will see more and more relativistic effects that will require more and more energy, but with the reward of huge time dilation effects when beyond 90% c.

Travelers are often placed in cryo tubes of some kind since little is required. Planet of the Apes used this fictional approach, as did Passengers. Note that if the former had been watching where they were going, they may have all survived. The latter shows that the two awoken were able to save the ship...just barely, of course.
 
Last edited:
  • Like
Reactions: dave123
Jun 10, 2022
28
10
35
Thank you, Helio. I had considered cryo tubes, and I'm beginning to lean towards using them for my long trip just to avoid the above issues. Either that, or I cheat on the math hoping that nobody notices that .9 light speed would actually turn humans to Jell-O.

But now I'm thinking, 'Hey, won't those people in cryo tubes turn to Jell-O as well?

Perhaps I'm overthinking this, as these issues aren't central to the story; but rather stem from my desire to keep things scientifically plausible..
 
Nov 19, 2021
480
218
560
Cryo is no good past about 1000 years. No human can survive longer than that due to DNA damage from decaying Potassium-40 in the body. Each human contains about 140 grams of Potassium, of which about .02 grams is radioactive Potassium-40 producing about 4,300 decays per second, emitting a 1.3 MeV electron or, in about 10% of cases, a 1.4 MeV gamma ray.
It might be possible to separate out the radioactive isotopes, raise food with them and feed the person over their lifetime thus eliminating the radioactive component. This would be rather expensive but is not out of the question.
 
Jun 10, 2022
28
10
35
Thank you, Billslugg.
As my spaceship will be capable of reaching .9 light (yes, I'm going to fudge science on this part), my uneducated time estimate for the trip to Ross 128 is 20-25 years. Of course, my main reason for my visit to Space.com was to ask how long it would take with acceleration and deceleration at such a pace to allow humans to stay alive. I'm open to a longer voyage if that would make it more believable. This number (whatever it is) would be just that – a number in the story that is believable.

Much more crucial to the story is the time my fantasy ship would need to get to Neptune for its trial voyage. My current draft has it at 22 days. Please tell me if this is reasonable.
 
Nov 19, 2021
480
218
560
Acelleration rate is not going to be the problem. One can reach very near light speed (3e8 m/s) in just 3e7 seconds at one G force (10 m/s^2). This is but one year.
The problem is where are you going to get the energy?
Ignoring relativistic effects (which make it worse), a single kilogram at .9 c requires an energy input of 1/2mv^2 joules to get there.
1/2 * 1 kg * (2.7e8 m/s)^2 = 4e16 joules.

A kilogram of matter converted to energy equals 9e16 joules. You would need to convert half the mass of your spaceship to energy in order to power the rest of it.

This is completely out of the question:

- using chemical energy (rocket fuel) convertes about one millionth of a percent of the mass into energy.

- Using fission energy (uranium) converts about .3% of the mass into energy.

- Using fusion of hydrogen into helium gives about .7% conversion.

- Fusing helium into heavier elements all the way up to iron gives you about 1% conversion into energy.

- Using antimatter annilhiation will convert only 25% of its mass into usable energy as 75% of that reaction is emitted as unusable neutrinos that fly off in every which direction and cannot be intercepted except by a thickness of lead light years thick.

Any scheme to acellerated a spaceship must rely upon external application of energy to it. Such a thing as a laser on Earth pushing against it only works to acellerate on the outward journey and decellerate on the return. You still have to stop at the destination and turn around.

The only scientifically plausible option you have is to blast your spaceship with a laser beam to push it away from Earth, loop around a black hole at the destination and then use the laser beam to brake it back at home. Or just make it a one way trip.

Energy needs again become a problem. You need about ten Newtons of force to accelerate a one kilogram mass at one G. Each Newton of force requires 5e15 watts of laser beam reflected off your target. The entire energy output of the World is about 1e13 watts. So for a 100 ton spaceship you need ten times 5e15 times 100,000 watts which is 5e21 watts which is 500 million times the current human energy output. This may take some work.
 
  • Like
Reactions: SIDexplorer

Catastrophe

"There never was a good war, or a bad peace."
Dave, re: lightsails, you need to see this: my post #34

Laser propulsion system - is it possible to tack? | Page 2 | Space.com Forums

This relates to a real project called "Breakthrough Starshot.

Here is a relevant extract:

the barrage of laser light to drive a few grams??
"Mass is the bane of accelerating objects to great speeds. To significantly increase the velocity of a heavy object takes a tremendous amount of energy. So, if the goal is to reach a distant star in a reasonable amount of time, say within a generation, a spacecraft must be extremely tiny and, therefore, robotic. Plus, it still requires an insanely energetic boost to get up to speed."
" . . . propelling a lightsail-equipped nanocraft, or Starchip, would require hundreds of individual lasers ,spanning roughly 200 acres (1 square kilometer). The array would also need access to enough energy to fire a coherent 100 gigawatt laser beam for several minutes during each . . . launch.
That's roughly the amount of power generated by all the nuclear power plants in the U.S. in a given year."

See also:
Breakthrough Starshot - Wikipedia

Cat :)
 
Last edited:
Jul 13, 2022
16
8
15
Acelleration rate is not going to be the problem. One can reach very near light speed (3e8 m/s) in just 3e7 seconds at one G force (10 m/s^2). This is but one year.
The problem is where are you going to get the energy?
Ignoring relativistic effects (which make it worse), a single kilogram at .9 c requires an energy input of 1/2mv^2 joules to get there.
1/2 * 1 kg * (2.7e8 m/s)^2 = 4e16 joules.

A kilogram of matter converted to energy equals 9e16 joules. You would need to convert half the mass of your spaceship to energy in order to power the rest of it.

This is completely out of the question:

- using chemical energy (rocket fuel) convertes about one millionth of a percent of the mass into energy.

- Using fission energy (uranium) converts about .3% of the mass into energy.

- Using fusion of hydrogen into helium gives about .7% conversion.

- Fusing helium into heavier elements all the way up to iron gives you about 1% conversion into energy.

- Using antimatter annilhiation will convert only 25% of its mass into usable energy as 75% of that reaction is emitted as unusable neutrinos that fly off in every which direction and cannot be intercepted except by a thickness of lead light years thick.

Any scheme to acellerated a spaceship must rely upon external application of energy to it. Such a thing as a laser on Earth pushing against it only works to acellerate on the outward journey and decellerate on the return. You still have to stop at the destination and turn around.

The only scientifically plausible option you have is to blast your spaceship with a laser beam to push it away from Earth, loop around a black hole at the destination and then use the laser beam to brake it back at home. Or just make it a one way trip.

Energy needs again become a problem. You need about ten Newtons of force to accelerate a one kilogram mass at one G. Each Newton of force requires 5e15 watts of laser beam reflected off your target. The entire energy output of the World is about 1e13 watts. So for a 100 ton spaceship you need ten times 5e15 times 100,000 watts which is 5e21 watts which is 500 million times the current human energy output. This may take some work.
I think the breakthrough starshot project is good and instead of sending laser guided tiny instruments towards proxima or other system, they should be directed towards our black hole sagittarius A, black hole exploration must be the first priority, since there is very much to learn and know about black holes. We already have plentiful of information about stars and planets abd their moons.
 
Nov 19, 2021
480
218
560
I guess I'm just stuck in the olden days!! I don't like the idea of self driving cars, I didn't even like the automatic transmission, cruise control or auto dimming lights.
I like to do things myself, not have a computer do them for me. I like the computer to make it easier for me to do it myself, not for the computer to do it.
I learned to drive tractor trailer on an unsynchronized 23 speed Spicer transmission. Double clutch up and down. Push in the clutch, shift to neutral, let out the clutch, rev the RPM's 1500, push in the clutch, move to the new gear, let out the clutch. Once learned it becomes second nature, you don't even think about what you are doing. There is no need for an automatic transmission. In fact, you can't push start one. Can't put one in gear on a hill. Can't move one off a railroad track with the starter motor. More expensive, more parts, less efficient. The automatic transmission was a solution looking for a problem.
 
  • Like
Reactions: dave123

Catastrophe

"There never was a good war, or a bad peace."
dave123, you suggested that there are still questions relating to the Neptune element of your composition.

We have:
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?
From 3, we see that Neptune it is a return trip, and not part of the star journey, so presumably we can have different parameters relating to the space ship.

The situation under consideration must be futuristic, if we are considering star travel, so we are not limited to today's capabilities, Thus, any stopover at Neptune would probably not be important. By today's standards (possibly also applicable in the future) the Earth's movement during the stopover on Neptune might be critical. Lowest fuel consumption (if applicable) might dictate a stopover of a considerable fraction of a year. Maybe someone would like to do the calculations?

Have you seen this?
Round-Trip Mission to Neptune Using Nuclear Fusion Propulsion | AIAA Propulsion and Energy Forum

So, Dave, where do we stand here?

Cat :)
 
Last edited:
Aug 2, 2022
17
1
15
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.
Not true, dude, not true. References???? No reputable references possible.
 
Jun 10, 2022
28
10
35
Ok, just got back from my trip.

@ Billslugg - I'll bet you are fun at parties. Thanx for your input! I don't like automatic transmissions either, all my vehicles have been manual. I drive a 1967 chevy truck now. By the way, you could get your automatic transmission car to start and move off the railroad tracks if you removed the neutral safety switch ;)

On topic,

So, after reading this, I'm still at a loss. Please allow me to test your patience one more time. If someone can just toss a plausible number at me, I can make it work:

Let's forget the mode of acceleration for a moment and see what happens. Let’s also forget Ross 128 and worry just about Neptune.

So..
My spaceship will need to get to Neptune.
My ship's max speed is .9 light.
My ship will need to accelerate at a rate that will not turn passengers into jello. I could have the passengers strapped into a chair for the duration, but would prefer not to.

My ship will need to decelerate at a rate that will not turn passengers into jello.

Can I assume that ½ the journey would be acceleration and the other ½ deceleration?

Plotting the journey to arrive when Neptune and the Earth are at their closest point, how long could this journey be expected to take? Is loiter time at Neptune relevant?

If I could just figure total time of the journey to Neptune, I would have my answer.
 
Last edited:
Nov 19, 2021
480
218
560
I've tried going to parties. No one wants to talk about kinetic energy.

I did not know about the neutral safety switch. May have to look into that.

PS - I'm from south GA. When the gate goes down, the train is several minutes away. They go real slow here. I had a gate close in front of me in Oxnard, CA once. Could not see a train in either direction. Five seconds later one came barreling around the curve and shot by me about 80 mph. I never considered going around the gate but it sure put the fear of God into me!
 
  • Like
Reactions: dave123

ASK THE COMMUNITY