Why Ares I
In a change from the August 12 meeting of the Review of U.S. Human Space Flight Plans Committee, NASA’s Ares I project appears to still be on the table. In their Summary Report, it is included in their Option 3: Baseline Program of Record, which projects a human return to the surface of the Moon in the mid 2020s. This option would require an additional investment of $3 billion per year in NASA’s exploration program. In the interest of evaluating this option, I’m going to review what Ares I is supposed to do and the progress it has made, and then look ahead to the likely outcome of continuing its development. I will also compare Ares I to potential alternatives.
Ares I is part of a proposed system of two launch vehicles designed to carry humans to the Moon. It evolved from the Crew Launch Vehicle (CLV) described in the Exploration Systems Architecture Study (ESAS). CLV was intended to serve two purposes. One, it was to carry the Orion spacecraft, then known as the CEV, to orbit where it would rendezvous with other components of the Earth-Moon stack. The other was to service the International Space Station (ISS). Other architectures were considered, including a dual launch of two man-rated heavy-lift vehicles (HLVs). However, one of the advantages of separating the CLV from the HLV was that the CLV could be fielded early enough to support the ISS. When this architecture was chosen, the CLV was to begin operations in 2011. It would run “taxi service” to the ISS until the HLV became available, at which point tests for the Moon mission would begin.
The CLV design selected by ESAS has other positive aspects. The study estimated that the loss of crew (LOC) risk would be roughly 1 every 2000 flights, far better than Space Shuttle demonstrated LOC. However, according to Augustine panel member Jeff Greason, “PRAs grossly overstate the reliability of an as-yet unflown system”, meaning that the CLV LOC number does not include unpredictable factors such as human error or design error. The CLV was also based on direct Shuttle-heritage hardware, including a four segment solid rocket booster (SRB) and a Space Shuttle Main Engine (SSME). This would significantly reduce development cost and risk.
The CLV eventually became Ares I. Its development would be lead by NASA, in the interest of accelerating the schedule and of reconstituting NASA’s rocket design capability. This capability had been lost in the decades after Space Shuttle development was completed. In the United States, the only organizations with orbital rocket design teams at that point were United Launch Alliance (ULA), Orbital Sciences, and SpaceX. Several changes were made to the CLV design. The CLV second stage needed an air-start capability, meaning that ignition had to be initiated by the second stage and not by ground control. Modifying SSME to be both air-startable and disposable was quickly determined to be a much larger project than NASA was willing to undertake. It was replaced by the J-2X, an engine of Saturn V heritage and shared with the Ares V. J-2X underperformance compared to SSME necessitated that the second stage be shortened and the first stage be upgraded from a four segment SRB to five segments. Due to these changes and more detailed work estimates, the initial operating capability (IOC) date was moved from 2011 to 2014. Ares I would still service ISS for 1-2 years, but a “gap” appeared in NASA’s ability to launch astronauts from Shuttle retirement in 2010 until Ares I IOC in 2014. Ares I’s ability to support the ISS was still considered to be viable, due to the high likelihood that Congress would not allow ISS to be terminated in 2016, even though the projected budget did not include an extension.
Work began on Ares I with the previously mentioned changes, while Ares I-X went on a separate path. Instead of flight-testing the Ares I first stage, Ares I-X would test the four segment SRB specified for the CLV. This would still validate that a rocket with a Space Shuttle SRB for a first stage could launch successfully. Ares I-X has remained on-schedule for its first flight in 2009. The United States Air Force, responsible for range safety at Cape Canaveral, has raised a concern that vibration caused by SRB thrust oscillation will cause failures in the Ares I-X avionics. The test launch is currently scheduled for the end of October.
The Ares I development schedule is much longer than Ares I-X. Starting in 2005, it was projected to take roughly six years to complete. Changes in 2006 from CLV to Ares I raised that to eight years. The schedule was extended a year by NASA in 2007. The Aerospace Corporation performed an independent schedule assessment in 2009 and determined that the remaining development work would take seven years to complete. In the three years from 2006 to 2009, Ares I has closed on its schedule end date by one year. The Review of U.S. Human Space Flight Plans Committee found that Ares I no longer supports the ISS, because, even with an optimistic budget projection, ISS will have to be de-orbited before Ares I IOC. This restriction is due to schedule pressure caused by operating Ares I while developing Ares V. Removing one of the two major rationales for developing Ares I illustrates why a review of the Constellation program is needed at this time.
About $8 billion dollars has been invested in Ares I development as of 2009. The project has passed two major hardware milestones: the successful tests of the abort system and the test firing of the five segment SRB. A test flight of Ares I-X seems imminent, as these things go. Some technical problems threaten the development of an operating vehicle. Ares I’s payload capacity is insufficient to launch the Orion space capsule as originally designed. This has necessitated several redesigns of Orion, and may result in future delays to both Ares I and Orion. Vibration due to thrust oscillation continues to threaten both passengers and avionics. The five segment SRB test may have retired some of the risk, but thrust oscillation severity in Shuttle SRBs has historically varied widely. These problems, plus some others, were estimated by the review panel to be solvable given enough time and money.
The main proponent of the Program of Record is former NASA Administrator Michael Griffin. In his testimony to Congress, he charged that the review panel “double-counted” the schedule reserve for Ares I development, unnecessarily extending it from 2015 to 2016. Also, in his opinion, ISS funding should be decoupled from Constellation development. This would allow Ares I to service ISS during the years 2015-2020. In Griffin’s estimation, this would cost NASA roughly $15 billion above the review panel’s unconstrained projection. Griffin also notes that a dual Ares V mission would cost hundreds of millions more per mission than the Ares I + Ares V approach.
Given enough funding, Griffin’s approach could work well. Ares I has certainly retired some technical and schedule risk in three years of development. For $45 billion above the president’s budget projection, NASA could simultaneously operate two launch vehicles, service the ISS, and accomplish its Moon mission. However, a plus $45 billion budget was investigated neither by the review panel nor by Congress. Compared against other plus $30 billion options, continuing to build Ares I means the end of ISS in 2016.
Canceling Ares I does not imply that $8 billion has gone down the drain. Ares development to date has produced several benefits which may prove useful to the exploration program. First, the recently tested five segment SRB would be used in the Ares V Light design, though not in other Shuttle-derived designs. Second, Ares I development will have been a valuable learning experience for NASA and served to reconstitute a NASA orbital rocket design team. Third, it has started work on the J-2X rocket engine, which will inform future rocket designs. Fourth, the Ares I-X test will give Kennedy Space Center practice launching rockets which are not Space Shuttles.
In conclusion, choosing to continue development on Ares I is a question of the value placed on other aspects of the exploration program. The primary loss in the Program of Record is the ISS. Alternative programs would not only extend its time on orbit, they would increase utilization and improve its return on investment. Another loss is the potential for NASA to jump-start a commercial crew launch service. The other loss in the Program of Record is the technology development program. Avoiding technology development for the next two decades means that NASA cannot hope to increase the pace or duration of exploration missions, or to extend those missions beyond the Moon. If the value placed on these aspects is minimal, Ares I in the enhanced budget Program of Record is viable and appears to expose the exploration program to less development risk than the other options.
References
- “Launch Vehicles and Earth Departure Stages“. Exploration Systems Architecture Study. National Aeronautics and Space Administration. November 2005.
- “Multi-Program Integrated Milestones“. National Aeronautics and Space Administration. Q3 2008.
- “Vibration Analysis Delays Ares I-X Stacking“. Aviation Week. July 6, 2009.
- “Summary Report“. Review of US Human Space Flight Plans Committee. September 8, 2009.
- “ Mike Griffin Lashes Out at The Augustine Committee via Email“. SpaceRef.com. September 10, 2009.
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Tags: ares, human space flight, human spaceflight, international space station, launch vehicle, nasa