Suborbital Refueling

Introduction

Suborbital refuel is a concept that combines a conventional rocket launch, with a gun-launch system. The idea is to place a "delicate" payload on top of a conventional rocket. The rocket boosts to about 1/2 of orbital velocity and then follows a ballistic, suborbital trajectory. For mass efficiency, the vehicle may drop the empty propellant tanks. Meanwhile, an earth-based accelerator (or "gun") launches a projectile that contains more propellant and a docking mechanism. The gun launch is also for 1/2 of orbital velocity and along the identical trajectory. The two vehicles quickly dock while well above the atmosphere. The docking mechanism includes fuel lines, so the combined modules can reignite the rocket engine and continue to orbit. The advantage of refueling is that the mass fraction (final mass to initial mass) of the rocket is about four times better than a single-stage-to-orbit rocket. The figure below shows schematics for the systems carried by each vehicle. There are many other combinations possible. For example, the gun launched module could include a rocket engine so that hooking up propellant lines can be avoided.

It is important to realize that the vehicles are above the atmosphere during docking, and they are following what is really an orbit. It's just that the orbit eventually intersects the earth. The docking is therefore similar to a conventional orbit docking, except that everything has to be accomplished in a few minutes.


Low-G Rocket Launch Module refuel_intro_5.gif
High-G Gun Launch Module refuel_intro_6.gif
Rocket Module Transition refuel_intro_7.gif
Docked. Boost to orbit refuel_intro_8.gif
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Some links on suborbital refueling

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Studies

Introduction to Suborbital Refueling

First published; 11/28/2011. Last update: 11/28/2011

This document introduces the suborbital refueling concept and shows schematics for potential vehicle arrangements. There is a quick numerical study of the time available to perform the docking. Also, a calculation of the required gun launch-angle.

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Lift-Off mass and mass distribution for conventional rockets

First published; 12/15/2011. Last update: 12/15/2011

In order to compare mass savings for the concepts being presented, in particular suborbital refueling, I found I needed a robust method for estimating the mass of a conventional rocket, including multi-stage rockets. A package of sizing tools was written, and the study demonstrated the use of these tools under various assumptions. The includes a comparison with real-world data for a Saturn 5 rocket.

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Mathematica package
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