Cost & Mass

NASA Mars Mission Mass & Engine Power Estimates

NASA Mars Mission Mass & Engine Power Estimates

For researching, developing, constructing, testing, and supplying the USS Enterprise, along with putting in place the infrastructure on earth and in space needed to support the Enterprise, the cost goal for the Gen1 Enterprise is this: it will cost no more than $1 trillion spent over twenty years.

The Enterprise will be built entirely in space. Thus each component must be launched from earth. This is expensive, and around 35% of the Gen1 Enterprise program budget will be to pay for heavy lifter launch costs (when including both non-recurring costs and recurring costs). These launches will transport not only the Enterprise components into space but also test hardware, Enterprise supplies, and various items needed for space infrastructure.

At the bottom of this webpage is a table showing the detailed cost goals for all components, supplies, infrastructure, and heavy lifter launches for deploying the Gen1 Enterprise. Also included are detailed mass goals for everything making up the operational Enterprise spaceship. But before going into these details, first the overall mass of the ship and its most basic systems needs more discussion.

For the overall wet mass of the Gen1 spaceship Enterprise, a goal is needed. For setting this goal, it’s desirable to be able to tie the goal to some reference point, to something concrete and easy to keep in mind. So we will set the goal as this: Its wet mass (meaning that when the propellant tanks are fully filled) will be no more than the aircraft carrier USS Enterprise back here on earth which weighs 187 million pounds (84,822 metric tons).

The 187 million pound goal may seem arbitrary, but this is not really so. Early roll-ups for estimating the Gen1 Enterprise’s mass were coming in around 200 million pounds. The amount of propellant needed was nearly 100 million pounds of this. As a goal it is very desirable to reduce the amount of propellant needed as a percentage of total ship wet mass because this saves cost and ship mass. Also, reducing propellant as a percentage of the total ship mass frees up room in the mass budget for other ship components. This desire to reduce propellant as a percentage of the ship’s mass creates a program goal for engines to use propellant more efficiently meaning that each engine should have a much higher high specific impulse than typical ion propulsion engines today. So after removing some propellant from a 200 million pound ship mass, 187 million pounds seems like a reasonable goal.

To gain some perspective on a mass of 187 million pounds, consider that a Saturn 5 rocket had a wet mass before launch of 6.6 million pounds. Thus the Gen1 Enterprise will have a wet mass equivalent to 28 Saturn 5 rockets. This is quite large, but it’s also comprehendible. The Enterprise is a big ship, and if its mass is the same as 28 Saturn 5 rockets, that seems about right.

The next figure below includes the same table as at the top of this page which gives three mission scenarios investigated by NASA. These three missions are for taking humans to Mars, using a small ship in each case, and using electric ion propulsion engines with nuclear reactors to supply the electrical power. To set the mass goals for major systems in the Gen1 Enterprise, nearly the same mass ratios will be used as derived from the leftmost column of the NASA table. In other words, for the Gen1 Enterprise, since we are striving to show feasibility, we will use nearly the same mass ratios as have been estimated to be plausible in NASA studies for Mars-bound spacecrafts carrying a human crew. The only exception is that the propellant will be 30% of the ship’s wet mass rather than the 54% used in the left column of the NASA table. (It’s important to note that if during research it’s found that engines cannot be improved enough and 30% of the ship’s mass does not provide enough propellant to support a round trip to Mars, a robotic supply depot carrying propellant will be in orbit around Mars to refill the Enterprise’s propellant tanks. This depot will exist no matter how efficiently or inefficiently the Enterprise uses propellant because the depot is required to be in place to be prepared for emergency situations.)

At the top of the figure below in the yellow box are shown the top-level goals for the mass of the Gen1 Enterprise’s major systems. These goals are derived from the NASA table by scaling up the mass of the major systems summarized in the orange box.  It can be seen that 93.2 million pounds are available for the Enterprise ship components, cargo, and supplies. This is challenging, due to the Enterprise’s large size, and will likely require extensive use of light-weight, space-worthy composites. (Below, NEP stands for nuclear-electric propulsion and this includes the mass of the nuclear reactors and ion propulsion engines in the ships being compared. MT stands for metric tons.)

Gen1 USS Enterprise Mars Mission Mass Estimates

Gen1 USS Enterprise Mars Mission Mass Estimates

From the calculations above, it can be seen that the Gen1 Enterprise will have a mass 438 times greater than the spacecraft in the leftmost column of the NASA table. Since the NASA ship requires 6MWe of electrical power, the Enterprise will require 6MWe x 438 = 2628MWe, that is, 2.628GWe. This sets the electrical output power goal for the nuclear reactors for supplying power to the ion propulsion engines and the rest of the Enterprise. (To simplify, it will be assumed that the Enterprise main reactor will be 1.5GWe and each of the two aux nuclear reactors will be .5GWe. GWe stands for Giga Watts electrical power.)

The table below gives a summary of allocated goals for the mass of everything contained in the Gen1 Enterprise. The goals are allocated based on the Enterprise having a grand total wet mass of 187 million pounds. The mass number shown for each item making up the Enterprise serves as both a goal for that item and as a preliminary estimate for that item. To see the basis for the mass estimates for the 60 million pounds of hull structures (line 6 in the table below) that make up a large part of the Enterprise total mass, see this spreadsheet. Also shown in the table below is the cost goal for each item assuming $1 trillion for the total ship and infrastructure costs. These cost goals also serve as preliminary cost estimates for the items shown. Here is a link to the excel spreadsheet for this table in case some readers would like to take a stab at coming up with their own mass and cost estimates.

Gen1 USS Enterprise Cost & Mass Roll-ups

Gen1 USS Enterprise Cost & Mass Roll-ups