August 01, 2012
Credit: Credit: Boeing, Imaging Services STL
ATLANTA — Progress in new U.S. launch systems has slowed because rocket technology has virtually reached its limits and the time is ripe for the privately funded development of an all-new, liquid-fueled engine in the 500,000-lb.-thrust class, according to Antonio Elias, head of advanced programs at Orbital Sciences Corp.
Speaking at the Joint Propulsion Conference here, Elias says the physics of chemical rocket propulsion makes a Moore’s Law-type improvement rate impossible for engine development. “What makes Moore’s law possible is that there is tremendous headroom in the fundamental physics of micro-electronics. We have several flips to go before we start hitting the uncertainty principle.”
Elias adds that when it comes to launch vehicles there are two main measures of progress: specific impulse (ISP), which rates overall rocket efficiency, and mass fraction, which is the mass of the vehicle’s propellant divided by the total mass of the rocket. “We have reached 98% to 99% in both areas in rocketry.”
Compared to the rapid rate of apparent progress in other technologies, particularly consumer electronics, the pace of rocket technology improvement seems sluggish at best. “That’s what the public doesn’t understand. They don’t see us advancing at the same rate,” Elias says.
From a new engine perspective, he adds that growing signs of an uptick in demand for a medium-lift vehicle are creating “a number of healthy opportunities in the Delta 2 class or lower end of the Evolved Expendable Launch Vehicle (EELV). However, we have lost a bit of hope that the U.S. government will put a priority on developing new liquid rockets, so private industry will have to develop one,” he suggests.
Proposing a target thrust of around 500,000 lb., Elias says the dwindling number of current-production engines in the thrust bracket makes such a new development potentially viable. On the solid motor side the ATK-made Castor, Orion and space shuttle heritage-derived solid rocket boosters provide limited options. “You can cluster Castor 120s, and nobody can beat solids for simplicity. The disadvantage is how many can you stack? You could use elements of the space shuttle solid booster and a three-segment SSRB has performance equal to a Delta 2. With five segments you have performance in the upper range of the EELV,” he says. However, Elias adds there are inherent difficulties associated with ground infrastructure to support SSRB assembly, and adds the economics for using solids could become challenging as applications become nonreusable.