Details of the Ares I Upper Stage

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.