Two years ago, Ars was invited to Huntsville’s Marshall Space Flight Center to watch a team of engineers from NASA and Aerojet Rocketdyne fire up some 50-year old rocket components—specifically, the gas generator of an enormous Rocketdyne F-1 engine. Watching the gas generator shoot out 31,000 lbs of thrust (more than an F-16 puts out at full afterburner) was amazing, but it was even more amazing to realize that in the full F-1 engine, all that thrust and power was used just to run the turbopump that pushed fuel into the combustion chamber.

It wasn’t all for show, either—Huntsville-based Dynetics, working with Aerojet Rocketdyne, was pitching a gigantic new F-1 based rocket engine called the F-1B as a contender in NASA’s Advanced Booster Competition. Dynetics hoped that NASA would choose its F-1B-powered "Pyrios" concept as the preferred strap-on booster for the upcoming Space Launch System heavy-lift rocket (referred to as "SLS") that NASA is building.

But that was two years ago, and time and political pressure have shaped and extended the Advanced Booster Competition—which has morphed into an activity now called the Advanced Booster Engineering Demonstration and/or Risk Reduction, or just "ABEDRR." And it’s looking like a more conventional shuttle-style solid fuel strap-on booster will be powering NASA’s SLS rocket to orbit—at least at first.

There are of course many questions about whether SLS will ever even fly, and if it does, whether it will see more than one or two missions before being canceled. The launch vehicle’s initial scheduled launch date has slipped several times and currently is targeted for somewhere around November 2018; the second launch isn’t planned until six years after that.

Ars caught up with Andy Crocker of Dynetics via e-mail last week to get the straight dope on what’s going on with the F-1B engine concept, and Crocker echoed much of what was said in the linked NasaSpaceFlight.com articles above. The company is working steadily on cryogenic tankage manufacturing for the ABEDRR contract, but Pyrios doesn’t look like it’s going anywhere.

"In the near term, NASA is clearly focused on developing the Core Stage of the SLS first," Crocker explained. "For the first several missions, the baseline solid-fueled boosters will suffice. But to achieve bolder missions—like missions to Mars—the vehicle will need more performance, so the boosters will have to be upgraded. Both advanced solid booster and liquid boosters are options."

If the current SLS schedule isn’t accelerated, Mars missions could be quite far out indeed—in the 2030s, at the earliest—so that’s a long time to sustain a development effort.

Concerning the engine itself, Crocker painted a positive picture: "The F-1B engine work has gone very well. Although parts of our contract have been cut along the way, the parts left intact have all gone very well. We (with Aerojet Rocketdyne as the lead) have completed successful, full-scale, affordable manufacturing demonstrations of key engine components. We believe we have proven the concept that an affordable F-1B engine is possible today. We do have one major F-1B activity remaining: In the next few months, we will be testing a full-scale gas generator injector that was additively manufactured (i.e., 3D printed). This is a major engine component test, and it will prove that the 3D-printed part achieves similar performance to the heritage component."

The test-firing of 3D printed rocket parts is something NASA has been doing more and more of, though this type of "3D printing" is very different from the plastic-based sort familiar to most home users. NASA and Dynetics use much more robust techniques that involve forming components by blasting metal powder with lasers. Much as with home 3D printing, it allows the quick, low-volume construction of complicated parts—and with rocket engines, that means you can get through the prototype and test stages a lot faster.

Additionally, the work on the F-1B has branched out into general work on how to make large liquid-fueled rockets–with the possibility of producing an engine to ease NASA’s reliance on purchasing the Russian-manufactured RD-180s that currently power the workhorse Atlas V vehicle used in so many US launches.

Two years ago, Ars had hoped that we’d be returning to Huntsville some time in 2014 to witness a test-firing of a resurrected F-1 engine’s "powerpack"—that is, both the gas generator and the main combustion chamber. However, that didn’t come to pass—budgetary and political realities almost certainly mean that if SLS flies, it will fly initially with solid fuel boosters strapped to its sides.

But Crocker remains optimistic about the concept of the F-1B and liquid-fueled boosters in general. "We are still moving forward with all the technology demonstrations and risk reduction activities we can. Like I said, we think we’ve demonstrated that the F-1B engine concept is viable and affordable," he said. "And when the time comes to give the SLS the performance it needs to deliver the Mars or other deep-space missions, we think the Pyrios concept will be in the running."