Please turn on javascript in your browser to play chess.
Science Forum

Science Forum

  1. Standard member sonhouse
    Fast and Curious
    02 Aug '09 17:42 / 9 edits
    I did the math a bit more, space trips at 3 Milli G's (0.096 Feet/second squared or 0.294 Meters/second squared):

    For a 50 million mile trip (80 million kilometers) (typical Mars journey) takes 38.38 days for an average velocity of 15.07 Miles per second, 24.11 Kilometers per second and peak velocity of 30.1 miles per second, 48.1 kilometers per second.

    For a 500 million mile trip (Around Jupiter distance), takes 85 days for an average velocity of 68 miles per second, 109 Kilometers per second and peak velocity of 136 miles per second, 217 kilometers per second.

    For a 5000 million mile trip or 8000 million Kilometers (Around Pluto) takes 271 days for an average velocity of 213 miles per second, 340 Kilometers per second and a peak velocity of 426 miles per second, 680 kilometers per second.

    For a 10,000 million mile trip or 16,000 million Kilometers (the furthest so far discovered minor planet Eris, about 3000 Kilometers in diameter)
    takes 383 days for an average velocity of 301 Miles per second, 482 Kilometers per second and peak velocity of 601 miles per second, 964 Kilometers per second.

    For a 100 billion mile trip, 160 billion Kilometers (the distance to the first usable solar foci) takes 3.3 years for for an average velocity of 953 miles per second, 1525 kilometers per second and peak velocity of 1906 miles per second, 3051 kilometers per second.

    For a 4.3 light year trip, (Alpha Centauri) takes 52.4 year for an average velocity of 15,058 miles per second, 24,093 kilometers per second and peak velocity of 30,116 miles per second or 48,187 kilometers per second. That represents a peak velocity of 0.16 C! and average velocity of 0.08 C!

    Those are pretty impressive figures for a constant acceleration of 3 milli G's, eh! I wonder if you could even feel that?
    My problem I posed BTW, how long would it take to get from the front of a spacecraft to the back which is 10 meters away at 3 milliG's, is about 25 seconds!

    For comparison, a trip to Mars now in present day spacecraft takes about 6 months, for an average and peak velocity of about 3.2 miles per second, 5.1 Kilometers per second.
  2. 03 Aug '09 03:32 / 1 edit
    Originally posted by sonhouse
    I did the math a bit more, space trips at 3 Milli G's (0.096 Feet/second squared or 0.294 Meters/second squared):

    For a 50 million mile trip (80 million kilometers) (typical Mars journey) takes 38.38 days for an average velocity of 15.07 Miles per second, 24.11 Kilometers per second and peak velocity of 30.1 miles per second, 48.1 kilometers per second.
    , for an average and peak velocity of about 3.2 miles per second, 5.1 Kilometers per second.
    I would guess that even with milli g acceleration, it would take a tremendous amount of energy to maintain a low acceleration of 3 milli g's once the velocity was getting up there. Would nuclear power be enough to go 1906 miles per second accelerating at 3 milli g's?Also I wonder if the space ship hit a rice sized piece of space debris if it would be like a howitzer round going off inside, or if it would just zip right through punching holes in the life support systems?
  3. 03 Aug '09 06:17
    Originally posted by sonhouse
    For a 4.3 light year trip, (Alpha Centauri) takes 52.4 year for an average velocity of 15,058 miles per second, 24,093 kilometers per second and peak velocity of 30,116 miles per second or 48,187 kilometers per second. That represents a peak velocity of 0.16 C! and average velocity of 0.08 C!
    I am curious. What time period would be needed if we chose not to slow down at the far end but let our spacecraft accelerate all the way to Alpha Centauri.

    Could we use Alpha Centauri as a slingshot to get us to the next star we wish to visit?

    I assume that nuclear power is the only real option for sustained acceleration in interstellar space, so what amount of mass of nuclear fuel would need to be expended to keep up that acceleration for the 52 years?
  4. Standard member sonhouse
    Fast and Curious
    04 Aug '09 20:37
    Originally posted by twhitehead
    I am curious. What time period would be needed if we chose not to slow down at the far end but let our spacecraft accelerate all the way to Alpha Centauri.

    Could we use Alpha Centauri as a slingshot to get us to the next star we wish to visit?

    I assume that nuclear power is the only real option for sustained acceleration in interstellar space, so wh ...[text shortened]... of mass of nuclear fuel would need to be expended to keep up that acceleration for the 52 years?
    That depends a whole lot of the choice of rockets, or the energy supply.
    That 3 Mg accel was thought to take a 200 Mw nuclear supply, presumably fission. You do get a lot of bang for the buck. If I remember right, total conversion of mass to energy Ala E=MC^2 gives 100 MW for thirty years from 1 Kg of mass. Now fission is maybe 1/10% as efficient as total conversion so if we use that as a standard it would mean 1,000 Kg of U238 would power that much so 2000 Kg would do the job for 60 years. A bit over 2 tons. One interesting note about that: The more fuel you use up, the less there is left so the more the thrust, whatever the ratio of fuel to the rest of the mass of the ship ratio is. If the ship weighs in at 20000 Kg, then the fuel would be 10% of the mass, but that is pure conjecture.

    I can figure out how fast you are going if you accel all the way to AC:
    Well it looks like I goofed, I used 2X the distance when I should have used just the distance, the formula is T=Sqrt (2S/A). To the the right trip time, the way you do it is to accel for half the distance and decel for the other half, and that means you project a trip of half the length, then use the original full distance and double the time. So it turns out to be a two part trip, each leg taking about 37 years for a total trip time of two times that, or 74 years. The numbers I gave would be for a trip where you did not decel, so if you did full-time acceleration you would be going the velocity I mentioned, 30Kmsp or 48,000 Km/s.