![]() ![]() The next entry is ship cost, per ton of dry mass, with a unit value of $1 million, which is about what a jumbo jet costs. I used 5 tons per berth for trips of a few weeks, up to 25 tons per berth for an 18 month mission requiring long term life support. The next user entry is hab mass per passenger berth, probably several tons. This is the price to beat if you're mining He-3 from Out There somewhere. The figure I used, 2 cents per kW/h, is roughly the current cost of nuclear electric power, approximating the case of having to breed fusion fuel. The first is fuel energy cost ( not propellant cost), measured in US cents per kilowatt hour. So the dry mass is bus mass plus whatever part of the payload is 'fixed.'įinally, the right side of the worksheet permits some cost estimates. I do give a figure (also over on the right) for the mass of the bus, the ship structure minus the payload. The payload figure given is gross payload - the whole payload section, including any hab compartment, cargo bays, the cargo itself, whatever. I also don't give a figure for the dry mass of the whole ship, because this depends on the payload. The payload is simply whatever mass allowance remains once necessary mass has been assigned for the drive engine, keel, tankage, and of course propellant. It is calculated (and shown on the right hand column, just below the user cost entries). l used a generous 10 percent, since for liquid hydrogen fuel the tankage must include a cryogenics plant. The final user entry here is tankage fraction, as a percentage of propellant load. (Each section of the ship would also have its own internal bracing.) Since these are low acceleration deep space ships I used a modest 5 percent for this figure. The third user entry is keel fraction - the portion of all-up departure mass given over to the framework that holds drive engine, tankage, and payload together, along with bells & whistles such as the navigation and comms equipment. The second is drive fraction - the percentage of the ship's arrival mass (what reaches the destination) that is given over to the drive engine, including shielding, radiators, etc. The first user entry is departure mass - the ship, fully loaded and fueled. The second column is for basic ship characteristics. ![]() The worksheet computes travel time, burn time (accelerating and decelerating), mission delta v, peak travel speed, and initial and final acceleration. Acceleration is in milligees drive specific impulse is in seconds (not exhaust velocity in km/s). Note that I round off 1 g to 10 m/s/s, versus ~9.8 m/s/s, just as I round off 1 AU to 150 million km. (If you change the distance, reduce the coasting phase first - Excel will freak out if you make the trip distance less than the coasting phase.) A coasting distance of zero corresponds to a brachistochrone. Providing a coasting phase is more efficient than a brachistochrone orbit, because you aren't putting on speed only to almost immediately take it off again. Real ships don't have constant acceleration, either - acceleration increases as propellant is burned off - but this gives a decent first approximation of travel time. The ships I was modeling are fast enough, with transfer speeds in the dozens of km/s, that solar space beyond 1 AU is fairly flat for them. The mission column models a steady acceleration, coasting phase, and steady deceleration, all in flat space. User entry values are across the top, in light blue. It has no effect on this worksheet, except that the given travel distance is misleading.Įach worksheet is laid out as three columns: mission characteristics, ship characteristics, and (inevitably) cost estimates. If the ship pops through an FTL rabbit hole at the midpoint, that is between you and Albert Einstein. It is tailored for a high specific impulse drive, and trips across planetary distances conveniently measured in AU. ![]() I did this workbook for my own amusement, inspired by this recent post, then decided to offer it to an indifferently awaiting world. New! Unique! Almost worth the free download! It's the one and only Rocketpunk Manifesto Travel Planner, available in all flavors of plain vanilla Excel. ![]()
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