Monday, January 31, 2011

Getting Back

Interstellar flights will need dedicated, experienced crew to transform ship to and from cruise configuration. Source of simulated gravity will transition from g-force propulsion to carefully measured longitudinal spin.

Interstellar ships must immediately initiate return portion of flight upon arrival at stellar destination.

Recurring chain of interstellar ships going to and from all stellar destinations. Perhaps a frequency of annual flights, but some periodic regularity is required.

Thus, cruise reconfiguation must become a well defined process with improvements carefully added over the years.

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The purpose of building an enormously expensive space vessel and flying for years to a neighboring star is to deliver sizeable payloads then return quickly to Sol and to do it again.

Scenario I. Retrograde cargo mass might actually size of mass dropped off.


Shakedown cruise, no need to drop off cargo (take snapshots and ASAP return)

Retrograde payloads is same size as original payload (not so far fetched, minimum plannling could accomplish this.

Not likely, and for first few missions very unlikely (unless conditions at destination were discerned as abysmal).

Scenario II. Reduce fuel load to stay in line with percentages. Donate rest of fuel to remaining travelers.

Scenario III. Most likely scenario involves quick recomputation fuel consumption rates to reflect new conditions for return leg.

Thus, the chances are overwhelming that the fuel consumption figured for destinatinon leg will be significantly different , probably a lot less.(which will greatly reduce ship's gross weight).

Background: Simple Fuel Profile
Assume: Initial GW = 100 metric Tonnes (mT)
Particle exhaust speed = .99c
Previous work: ∇ = .04%GW / day
GWt = 100mT (1 - .9996t) produces following values:
for 1724.5 days, GW = 50%
For convenience, TE assumes a round number for acceleration duration:
tAcc = 400 days.
Of course, consistent g-force would necessitate same duration for deceleration:
tAcc = 400 days.

Original GW = 1,000 mTs; fuel = 500 mTs,
GW will shrink due to fuel consumption.
Destination Leg
for t = 400 days, GW = 85.21%; thus, GW = 852.1 mT; fuel = 352 mT
for t = 800 days, GW = 72.61%; thus, GW = 726.1 mT; fuel = 226 mT

Return Leg
for t = 1,200 days, GW = 61.97%;thus, GW = 619.7 mT; fuel = 119 mT
for t = 1,600 days, GW = 52.72%;thus, GW = 527.2 mT; fuel = 27 mT

Scenario I: use same profile for dest and retn legs.
tAcc = tDec = 400 days for both destination leg and return leg.

Scenario II: Use different profile, diff fuel loads.

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