User:Matthewhburch

Matthewhburch (talk) 23:36, 17 June 2014 (UTC)

Archive of prior draft for personal reference
Propulsion methods utilizing fuel accelerated from a remote fuel source, shortened to the term 'remote fueling' for the purposes of this article, are variants of In-space propulsion methods that are defined by delivery of fuel and/or cargo to a remote spacecraft, to provide the energy the spacecraft requires to change velocity. By supplying fuel from a remote source, the need for a fuel-using spacecraft to carry it's entire fuel payload from mission beginning to mission end is eliminated.

Brief Overview
The basic concept of remote fueling is to provide fuel to a payload in transit, rather than carry all the required fuel from the beginning of the mission. Remote fueling combines the remote energy source aspect of Beam-powered propulsion methods with the fuel usage of standard rocketry methods.

The Tsiolkovsky rocket equation clearly demonstrates that if all the mission fuel needs are carried with the mission vessel from mission start, mission fuel requirements quickly become onerous as delta-v requirements grow.

The simple-seeming solution to this problem, much like the underlying principle of Beam-powered propulsion, is to deliver the fuel a small amount at a time using an energy source which is not present on the accelerating vessel. Successful remote delivery of fuel will create a scenario where fuel used to change the velocity of the accelerating vessel is only included in the mass of the accelerating vessel when said fuel is being used for acceleration.

Examples of Remote Fuel Methods
The 'pre-seeded trajectory' or 'fusion runway' concept of remote fueling is a way to improve the efficiency of Bussard ramjet propulsion. The fuel launcher pushes the fuel for a spaceship into space, where the Bussard ramjet collects it with a magnetic field used as a scoop.

The Momentum transfer concept of remote fueling is an extremely high energy transfer of kinetic energy. Projectiles are launched at extreme velocity using an electromagnetic launcher, and collected at the destination vessel with another electromagnetic launcher, configured to slow the incoming projectile. When the vessel needs to begin slowing, it uses its internal launcher to fire projectiles collected during the journey in order to slow itself.

The Robotic Refueling Mission concept of remote fueling is a very specialized Earth-launched remote fuel method. It does, however, demonstrate many technologies that a practical extra-orbital remote fueling method would require.

A Practical Remote Fuel Method Example
One practical method of implementing remote fueling requires a launcher system, a maneuverable delivery system that can carry fuel and cargo, and a capture system attached to, or part of, a vessel.
 * 1) The launcher system must impart velocity to the delivery systems (packages) that are being delivered, in order to allow them to intercept the vessel. The launcher accelerates packages containing fuel and/or cargo to a velocity which will allow the packages to perform a safe intercept with the vessel in space receiving fuel or cargo.  Any number of different technologies might perform this task of accelerating a package, for example, an electromagnetic accelerator with a solar panel power source. Another proven technology option would be to use standard rocketry as a launcher system for fuel packages.
 * 2) The launched packages must be able to intercept the vessel in order to provide fuel and/or cargo. The packages will need to be capable of adjusting velocity and trajectory. In most cases, if not all, the vessel will also be capable of maneuvering.  The packages will perform automated docking with the capture system, like what is now routinely performed in Earth orbit.
 * 3) The launched packages must be captured and secured. Once captured by the capture system, depending on the mission needs, the delivery system might use its own propulsion to accelerate the vessel,  or the vessel might draw fuel out of the delivery system,  Or perhaps some combination of both.

All of these requirements are able to be met with existing, space-proven technologies.

Efficiency Calculations
Fuel Efficiency Calculations:

Remote fueling offers fuel efficiencies which are routinely calculable. An example follows:

A 500kg vessel performing an asteroid belt survey mission has a mission requirement that it will change velocity by 1,000m/s per day, speeding up and slowing down as it investigates asteroids, looking for useful materials.

The Tsiolkovsky rocket equation proves that an ideal liquid hydrogen/oxygen fuel rocket can impart 1,000 m/s of delta-v on a 500kg vessel with 126kg of hydrogen/oxygen fuel. This is one day of activity. The chart below shows fuel use comparisons based on mission delta-v requirements for the hypothetical probe, for 1 day, 10 day, and 100 day missions.

It is clear that as mission duration increases, fuel savings increase exponentially.

Using remote fuel, each daily launch of fuel provides a set amount of delta-v. This makes fuel use in the "Mass of Remote Fuel (kg)" column linear based on mission duration, because 126kg of fuel delivered to the 500kg probe allows the probe to make 1,000m/s delta-v each day.

Using standard rocketry, the fuel requirements for each different mission duration is directly calculated by the rocket equation for the entire mission duration, rather than as a daily requirement. This makes fuel use in the "Mass of Standard Rocketry Fuel (kg)" column exponential based on mission duration, because the rocket equation is exponential.

Fuel requirements under a practical remote fuel method are governed by a linear function, while standard rocketry fuel requirements are governed by the Tsiolkovsky rocket equation which is an example of Exponential growth

Fuel use based on linear growth will quickly become insignificant compared to fuel use based on exponential growth.

Energy Efficiency Calculations:

If the component technologies for a remote fuel mission are chosen with efficiency in mind, remote fueling can be extremely efficient in a pure energy analysis as well. An example follows:

The vessel is a 500kg vessel as before. It will accelerate to 50,000 m/s and then back down to 0 m/s relative to the launcher 100,000 m/s total delta-v It will take 100 days to perform the mission. The launcher will be electromagnetic.

The fuel usage by the test vessel is the same as before. 12,600kg fuel will be required by the remote fuel system, and 2,745,985,484,033kg fuel for the standard rocketry method.

The oxygen & hydrogen reaction to create water generates 15,900,000 joules of energy per kg

Therefore, the remote fuel system uses 2.0e+11 Joules in fuel energy and the standard rocketry method uses 4.3e+19 Joules in fuel energy.

In the interest of simplicity, and to be sure that waste is well-accounted for, each of the 100 fuel launches from the electromagnetic launcher will be calculated as if it were launched at maximum velocity of 50,000 m/s. This is obviously untenable in the real world, but it establishes a great deal of built-in waste in the example.

The launcher requires (1/2)*M*V^2) joules per launch. Let us say that the fuel weighs as much as the package that carries it, 126kg fuel and 126kg of package.  It follows that the energy requirement to launch 100 of the 252kg packages containing mission fuel is (1/2)*(252*50,000^2)*100 = 3.2e+13 Joules.

Despite the inefficiency intentionally built into the launcher energy requirements for this experiment, the remote fuel method is six decimal orders of magnitude more efficient in an energy calculation than the standard rocketry method. A more rigorous experiment with boundaries defined by realistic expectations for performance of an electromagnetic launcher system would be even more efficient in comparison. Velocity is the most significant factor in energy costs for electromagnetic acceleration, and we cannot yet build a launcher on a scale sufficient to launch 252kg projectiles at anything close to 50,000 m/s. The fastest we have been able to accelerate particles in a launcher-like mechanism is 16,000 m/s

The reason for the relative efficiency between remote fueling and standard rocketry methods once again rests in the math itself. The kinetic energy equation has a linear (m) and a squared (v^2) term. The rocket equation is geometric. Based on the simple rule of comparing terms in the controlling equations, for any in-space large delta-v requirement mission where component technologies are chosen for efficiency, the total energy costs of remote fuel (both fuel and launching energy combined) will be insignificant compared to the energy cost of using standard rocketry and carrying all mission fuel from the start.