The five-segment solid rocket motor for Ares I. Credit: NASA

Today NASA was supposed to conduct the first full-scale test of the motor for the first stage of its future space rocket, Ares I. The test, at NASA partner Alliant Techsystems, was in Utah at 3:00 P.M. EST and was intended to last two minutes. The goal was to obtain data on thrust, roll control, acoustics, and vibrations to aid engineers in designing Ares I. But the test was scrubbed 20 seconds before ignition of the 154-foot motor, which was anchored to the ground horizontally. The problem: failure of a power unit that drives hydraulic tilt controls for the rocket's nozzle, according to a local report. The static firing test of the motor has not yet been rescheduled.

While nothing appears to be wrong with the rocket itself, the failure is a setback. The Ares rocket is part of NASA's Constellation Program--a plan for new manned flights to the moon and possibly to Mars and beyond, the first of which is scheduled to launch in 2015. A test flight rocket, Ares I-X, will take place later this year.

The failure also comes at a crucial time for NASA. The independent panel charged with reviewing the future of U.S. human spaceflight is preparing to present its recommendations to the Obama administration in less than a week. One option is to simply abandon the program, which has been over budget and behind schedule.

The new motor is a 12-foot-wide solid rocket booster. Its design is derived from the space shuttle, which uses two four-segment solid rocket boosters, and it will burn the same specially formulated propellant. The added fifth segment will allow Ares I to lift more weight and reach a higher altitude.

Artist concept of Ares I upper stage. Credit: NASA

Today the committee charged with reviewing the future of U.S. human spaceflight is listening to Ares I team members describe how the rocket will work. They must convince the independent panel of experts that the rocket's design is safe and reliable, and that Ares I should be the vehicle the U.S. uses to send humans to the moon and eventually Mars.

Already, the committee has heard alternate ideas for spaceflight from private companies and even from inside NASA--John Shannon, NASA's shuttle-program manager, presented a shuttle-derived launch-vehicle concept. These ideas were well received by the committee chairman, Norman Augustine.

I spoke with Danny Davis, program manager of the Ares I upper stage, this past spring while working on an article about Ares I-X, a test vehicle to gather data for Ares I. We talked in detail about the components of the upper stage of the rocket, which will separate from the first stage shortly after liftoff. The upper stage includes the most important avionics and navigation and control systems (see PDF). Here are a few excerpts from our conversation.

Technology Review: How will the upper stage be navigated and controlled once it separates from the first stage?

Danny Davis: We are using a fairly traditional approach to that, but the avionics will be state-of-the-art; we are not using old technologies. We will input the trajectory that we want to fly and use onboard computer controls, so ground [personnel or systems] are not flying the vehicle. The computer senses the motion and chooses the guidance commands so that [the rocket] stays on the right path. Astronauts have the capability to provide input into the guidance system if need be, but it's mostly onboard computers flying instead of being an open-loop control system like the first stage.

TR: Can you explain more about what controls the upper stage?

DD: It's basically sophisticated electronics, mostly the flight computer. It is a state-of-the-art computing system that is designed to operate in the environment that you see during liftoff and flight. The instrument unit is also in a good location; it is far up the rocket, near a structure that connects the Orion capsule, [the crew exploration vehicle], to the launch vehicle. There are actually three flight computers onboard that constantly check each other. If one produces a command not understood, then it can be kicked out by the other two. [This process is called] a "voting watch." The computers manage the entire operations of the vehicle--guidance, navigation, and communications.

TR: What type of engine will the upper stage use for power?

DD: A J-2X engine that will fire as the upper stage breaks away from the first stage, [about 127 seconds after liftoff]. It draws on designs from two of the Apollo-era Saturn rockets, and is powered by liquid oxygen and liquid hydrogen. It will operate for about [465 seconds] until it reaches a certain altitude when the Orion crew capsule separates. Both the engine and upper stage will then fall back into Earth's atmosphere and not be recovered.

TR: What is truly innovative about the rocket design?

DD: Our design has a lot of heritage work: using aluminum alloy, which is extremely strong and lightweight and was developed by the space shuttle program; thermal protection systems, primers, and thruster valves for the most part that were already available, but we are developing greener versions of primer.

The innovation in our mission is to put astronauts in orbit so they get to come home. Every day we think about the safety of the machine design. It has to perform--the first stage, the upper stage all have to work together, and it has to have the right propulsion system.

Another thing is that what we are going to do is make it more affordable. The problem with the space shuttle is that it's too expensive. We have to spend NASA's budget and resources paying for transportation. We want to build a new upper stage that is more affordable, ... to enable engineers to do work on other things as well. There are lots of improvements that we can make and have made.

In my coverage of NASA's successor to the space shuttle, the Ares rocket, and the next crew capsule, Orion, I have come across a common theme: vibrations.

While it may seem like a simple concept, vibrations or shaking can have a very powerful effect on a rocket's avionics, hardware, and any humans onboard. They come from such sources as the thrust of the solid rocket motors or boosters at lift off and even during flight, the burning of rocket propellant, and the sheer speed at which the rocket travels--over four times the speed of sound.

NASA's Dan Kanigan does a great job of explaining vibrations and their effect on the Ares I-X test flight rocket in this blog post. In addition, he talks about NASA's solution to the problem.

The vibration that is produced by the burning of the solid rocket propellant in the first stage booster is called thrust oscillation. These vibrations -- or oscillations -- come in the form of waves, which travel up and down the length of the rocket like a musical note through an organ pipe. One of the biggest challenges in any rocket design is developing avionics (aviation electronics) that can function in this vibrating environment.

Vibration is not just a rocket issue, though. All electronic hardware is tested for its ability to handle shock and vibration. An MP3 player, for example, has to be tested for its ability to handle the vibrations from someone walking or jogging while holding it, placing it on a countertop, or accidentally dropping it on the floor. However, compared to the workout that Ares I-X's avionics receive, your MP3 player has got it easy. Imagine shaking that MP3 player inside an automatic paint can shaker for two minutes while continuing to play your favorite tunes. That's kind of what the electronics of the I-X are up against.

Jon Cowart, the deputy project manager for Ares I-X at Kennedy Space Center, said in an interview earlier this year, that gathering data such as aerodynamic data, stresses, strains, pressures, temperatures, and vibrations is the most important part of the rocket's mission, and it will be used to make the Ares I even better.

Yet, the Ares I-X is just one example. NASA has been fighting the vibration issue since Apollo. Then such longitudinal oscillations caused by the burn out of the first stage booster were referred to as the "Pogo effect" and were especially troublesome for Saturn V. During an unmanned Apollo 6 flight, a critical test before manned flights could be approved, vibrations actually caused the main engine to shut down.

The new launch abort systems being built for NASA's Orion crew exploration vehicle is facing the same challenges. When the capsule and launch abort tower, which sits on top of the capsule, separate, a solid rocket motor called the abort motor fires, burning the propellant very rapidly to thrust the vehicle away from the rocket. The plume of hot gases emitted by the motor are the greatest source of noise and vibrations the vehicle will experience during flight, says Henri Fuhrmann, program manager of the new launch abort system at Orbital Sciences, an aerospace company that has partnered with NASA to design and develop the escape system. Thus the engineers have developed reverse-flow nozzles that turn the flow of the gases 155 degrees, away from the capsule. This will reduce the acoustics, vibrations, and loads on the capsule that could damage the electronics and hardware. This is the first time the technology has been developed at this scale, says Fuhrmann. The launch escape system on Apollo had direct flow motors and therefore had to add extra steel structures to increase the distance between the motor and the crew capsule. The Russian's launch escape system on the Soyuz spacecraft also uses direct flow nozzles.

Kanigan says that the next challenge is to make sure you can control the rocket at such vibrations. For NASA's new launch abort system engineers built a unique motor called the attitude control motor that steers and controls the capsule. It is also the first of its kind and can fly the vehicle forward and backward, and flip the capsule over to reorient it so the heat shield is facing forward.

Both Ares I-X and the Orion crew exploration vehicle are part of the Constellation Program, a plan to send humans to the moon and, then, to Mars. Norm Augustine, the chairman of a panel charged with reviewing this plan, said in a press briefing after the committee's first meeting where it heard ideas on alternative designs to the Ares rockets that the most interesting thing was the talk of how vibrations affect rocket design.