Text Size

Frequently Asked Questions

This section contains answers to frequently asked questions about NASA's exploration mission and its associated programs and projects.


Why is the Administration proposing a new direction for Human Space Exploration?

In May of last year, the Office of Science and Technology Policy (OSTP) tasked an independent committee with reviewing U.S. human space flight plans and activities, with the goal of ensuring that our nation is pursuing the best trajectory in this arena – one that is safe, innovative, affordable, and sustainable. While the committee did determine that the Constellation Program was technically sound, they found it to be "be on an unsustainable trajectory" because it NASA was "perpetuating the perilous practice of pursuing goals that do not match allocated resources." In other words, the budget did not support the Constellation architecture.

What is better about the new approach?

The new approach proposed by the Administration focuses long term investments on the fundamental capabilities required for human space flight beyond Low Earth Orbit, but that we currently lack. The plan calls for technology development in areas like propulsion, in-orbit propellant storage, automated and autonomous rendezvous and docking, advanced closed-loop life support, and tele-robotic operations. It also increases funding in NASA's human research program, allowing us to better understand the potentially harmful effects the space environment might have on people and how we can best mitigate them. Most importantly, this approach is financially sustainable.

Does this mean that NASA has given up on returning to the moon?

Absolutely not. In fact, recent discoveries of water on the moon have made it more scientifically interesting that ever before. Our focus in the near term will be discovery through robotic missions, such as the Lunar Reconnaissance Orbiter, followed by robotic precursor missions, to scout the terrain for the eventual return of humans.

Why is turning over a portion of human spaceflight to commercial industry a good idea?

NASA has already committed a significant investment to commercially provided space flight services. Almost all of our satellites and many science missions are launched commercially. In addition, we recently contracted with commercial companies to carry cargo to the International Space Station commercially. The next natural step is for NASA to buy commercial flights for our astronauts to the ISS. This will free up NASA to pursue the greater challenges in the way of a trip to Mars.

Exploration Systems was the directorate that managed the Constellation program. What will its role be under the new plan?

Under the new plan the Exploration Systems Mission Directorate (ESMD) will be responsible for many research and development programs including exploration technology and demonstrations, heavy lift and propulsion technology, exploration precursor robotic missions, and human research. In addition, ESMD will manage the commercial crew and cargo spaceflight programs.


What is the feasibility of replacing the Ares I with a human-rated evolved expendable launch vehicle (HR EELV), and its first-order effect on the overall Constellation architecture according the Aerospace Study commissioned by NASA?

In July 2008, as part of a top-level strategic analysis, NASA tasked the Aerospace Corporation to determine the feasibility and cost of using a human rated Evolved Expendable Launch Vehicle in place of the Ares I in NASA's lunar transportation architecture. After reviewing the preliminary results, NASA asked the Aerospace Corporation to study in more detail the performance of potential upper stage engines for a Delta IV heavy as well as the human rating needs for the RS-68 engine, and to use that more detailed assessment to again review the cost and schedule implications of replacing the Ares I with a human rated Delta IV heavy. Additionally, Aerospace was tasked to address the infrastructure, industrial base, and ground operations aspects associated with use of a human rated Delta IV heavy vehicle.

> Download the Full PDF: Human-Rated Delta IV Heavy Study Constellation Architecture Impacts

What is the latest update on NASA's Transportation Architecture?

NASA has spent substantial effort over several years to consider many launch concepts, and the agency continues to develop the Constellation architecture, which includes the Ares I crew launch vehicle, the Ares V heavy lift vehicle and the Orion crew exploration vehicle. NASA chose these systems based upon significant analysis, and the agency believes it has the best program in place to meet our nation's future exploration needs.

Since the completion of the Exploration Systems Architecture Study in 2005, NASA has continued to mature its exploration launch system approach in conjunction with ongoing Constellation program studies. Since early 2005, the agency has conducted over 1700 launch concept analyses. The agency has evolved and refined its Lunar Mission requirements to accomplish the goals of the Global Exploration Strategy and U.S. Space Exploration Policy. The Ares I launch vehicle is heading for preliminary design review this fall. The entire transportation architecture for going to the moon and back, including the Ares V rocket, recently completed its mission concept review.

Over the last two years, NASA has performed feasibility assessments of the different DIRECT launch vehicle designs that have emerged. These feasibility assessments are summarized in the attached white paper. The charts below detail the assessments of the DIRECT 2.0 concept (April - May 2007) and the updated DIRECT 2.0 (September 2007) and provide the background for the white paper.

> Download the white paper: NASA Background on Ares Vehicles versus the DIRECT Proposal
> Download the PDF: NASA Performance Assessment of Direct 2.0

Why did NASA Choose to Utilize a Shuttle-Derived Crew Launch Vehicle (CLV) Instead of Human Rating an Evolved Expendable Launch Vehicle (EELV)?

NASA evaluated many launch vehicle options that could be utilized for human space exploration missions. The principal factors considered were the desired lift capacity, the comparative reliability, and the development and life-cycle costs of different approaches. Among these approaches, NASA considered existing vehicles, such as the EELV fleet, to meet crew and cargo transportation needs. This white paper outlines why NASA decided to move forward with the Ares launch vehicles after careful consideration and study of other launch alternatives.

Developing NASA's Exploration Architecture

NASA is developing the Exploration architecture to safely and affordably transport humans and cargo beyond low Earth orbit (LEO). This multi-purpose architecture is not simply a "ferry to the International Space Station (ISS)," or a "Shuttle replacement." Instead, by utilizing tested human space elements, it includes the Heavy Lift Launch Vehicle (HLLV) to deliver up to 70-75 metric ton (mT) of cargo to Trans Lunar Injection (compared to the Apollo/Saturn capability of approximately 47 mT).

NASA studied hundreds of commercial, Government and concept launch vehicle and architecture systems prior to 2005, culminating in the release of the Exploration Systems Architecture Study (ESAS). NASA studied Space Shuttle-derived, EELV-derived as well as "clean sheet" launch vehicle architectures in cooperation with the U.S. launch industry, and concluded that the Ares I and V system architecture provided the optimal solution for both LEO and beyond LEO applications. Figures of Merit (FOMs) used during the studies --cost, reliability, human safety, programmatic risk, mission performance and schedule --were applied to drive out the best alternative in the analysis. Additional considerations included legal requirements from the NASA Authorization Act of 2005 (P.L. 109-155), workforce skills and industrial capabilities. After a thorough analysis of the entire Exploration architecture requirements, EELV solutions were ultimately determined to be less safe, less reliable, and more costly than the Shuttle-derived solutions in development.

The ESAS concluded that NASA should adopt and pursue a Shuttle-derived architecture as the next-generation launch system for exploration missions due to their significant advantages, particularly with respect to safety, reliability, and cost. The extensive flight and test databases of currently flying hardware/software give a very strong technical and safety foundation with clearly defined and understood elements to anchor next-generation vehicles and minimize development costs and risks to flight crew. In addition, NASA's approach allows the Nation to leverage significant existing ground infrastructure investments (Kennedy Space Center (KSC); Michoud Assembly Facility (MAF), etc.) and personnel with significant human spaceflight experience. Overall, NASA's Shuttle-derived approach was found to be the most affordable, safe, and reliable approach, both by leveraging proven human rated vehicle and infrastructure elements and by using common elements across the architecture. While NASA continues to conduct trade studies aimed at refining the Ares V architecture for minimum development risks and operational costs, the Agency is committed to the fundamental Ares I/V approach established over two years ago.

The next section of this white paper explores some of the specific reasons why NASA chose the Ares architecture for future spaceflight missions, both manned and unmanned.

The Ares versus the EELV

Vehicle Performance: The EELV crew transport options examined were those of the Delta IV and Atlas V families. The study focused on the heavy lift versions of both Delta (currently flying) and Atlas families (drawings only), and confirmed that none of the medium versions of either vehicle had the capability to accommodate the Orion Crew Exploration Vehicle lift requirements. The Medium class EELVs, with no additional solid boosters, significantly under performed by approximately 40-60 percent. The option of using small, strap-on solid boosters was eliminated for safety reasons in the Orbital Spaceplane Safety Study conducted in 2004. Both EELV-heavy vehicles were assessed to require significant modification for human rating, particularly in the areas of avionics, telemetry, structures, and engine selection. Additionally, both the Atlas and Delta Heavy classes required development of new upper stages to achieve the lift performance required to launch Orion. Ares I is designed to launch the 23.3 mT Orion vehicle, which consists of the crew and service modules, into LEO.

The Ares can also launch a 20.3 mT Orion to the inclination of the ISS. The ESAS assessment showed that lunar missions requiring more than three launches dramatically reduced the probability of mission success. Therefore, NASA issued an architecture goal to minimize complex on-orbit assembly, and also placed a limit to no more than three launches for a mission. For lunar missions, this equates to a launch vehicle design with a lift capability near 100 mT or greater to LEO. Early in the trade study process, NASA identified the current EELV fleet, if used for lunar cargo missions, would require more than seven launches per lunar mission. This very high number of flights per mission is unacceptable from a mission success probability standpoint and did not meet the NASA goal of three launches maximum.

While elements of current EELVs can be utilized to develop a 100 mT LEO equivalent launch vehicle (boosters, engines, etc.), the lack of acceptable EELV boost stage performance (compared to Shuttle-derived hardware) drives the need for an additional Liquid Oxygen (LOX)/Liquid Hydrogen (LH2) stage to reach orbit. The EELV-derived solutions required two upper stages as well as additional strap on core boosters to provide the necessary lift capability to minimize launches for on-orbit assembly. These characteristics were deemed to decrease mission safety and reliability while increasing costs to unacceptable levels based on NASA requirements. NASA did not pursue "clean sheet of paper" designs because it was deemed too risky and expensive.

Crew Safety/Reliability: The current EELVs were designed to carry unmanned payloads. Modifying the EELV design to meet the Human Rating Requirements would require changes in areas such as flight termination system changes to add a time delay for an abort scenario and in-flight crew control/abort capabilities. The use of EELVs for crew transportation would also require NASA to invest significant funds into pad modifications required for crew access/emergency egress that currently does not exist at the EELV launch site. Based on ESAS assessments, the Shuttle-derived launch vehicle was highest-rated in terms of crew safety by about a factor of two over other options (Loss of Crew approximately 1/2000). This confidence for crew safety is driven by the extensive history of the Shuttle system, which far surpasses the experience base for any other existing system. To add to the reliability of the system, the Ares I hardware is recovered and inspected for any system anomalies.

In addition, Shuttle propulsion systems are already "human-rated" which mitigates one of the highest programmatic risks for a launch vehicle. Leveraging systems that are already human rated reduces the uncertainties and risks associated with human rating the new CLV. In addition, the current EELVs have a booster structural Factor of Safety (SF) of ≤1.25, where NASA requires that all structures have a 1.4 Factor of Safety (NASA Standard NASA-STD-5001). If the Agency were to accept the reduced SF of the EELVs, a large engineering and development effort would be required to validate structural integrity relative to NASA Standard and would likely eventually lead to some structural redesign of select systems. In addition, main propulsion systems would require modification, for example, the RL-10 upper stage engine would also require human rating in areas such as: Redundancy upgrades; increased subsystem robustness; fault detection; isolation and recovery; engine redlines; safe in-flight shutdown mode; and, any design changes from structural assessments. For Atlas V, RD-180 American co-production and human rating would be required adding greater challenges. From a human rating perspective, the RD-180 will require additional redundancy and increased robustness in select systems. Finally, for Delta IV, several modifications would be required to human rate the RS-68 including extensive health monitoring, increased robustness of subsystems, and elimination of the fuel-rich environment at liftoff which would pose a crew hazard.

Life Cycle Costs: The Ares I and Ares V combination for lunar missions provides significantly lower non-recurring cost than that of the current EELV launch vehicle families. The Shuttle-derived launch vehicle combination allows for a "1.5 launch" solution whereas the EELV architectures required two HLLV launches with more expensive hardware costs. It was determined that the total EELV-derived CLV plus EELV-derived Cargo Launch Vehicle (CaLV) Design, Development, Test, and Evaluation (DDTE) costs are approximately 25 percent higher for EELV-derived versus selected Shuttle-derived architecture. The launch cost for human rated, EELV-derived systems is significantly higher than the current cost of a medium-class EELV. This launch cost also does not include the non-recurring development investment required to meet the Orion's lift requirements and human rate these systems, which has been estimated to cost in the several billions of dollars. In order for the unmanned payload customers to not incur the unnecessary additional costs for human-rated systems on the EELV, the EELV providers would likely need a unique human-rated variant which would increase the costs.

NASA continued to refine its launch recommendations post-ESAS. In early 2006, NASA modified the architecture from a four-segment Reusable SRB (RSRB)/single Space Shuttle Main Engine (SSME) upper stage CLV, and a five-segment RSRB/Expendable SSME Core/J-2X Earth Departure System (EDS) CaLV to a five-segment RSRB/single J-2X upper stage CLV, and five-segment RSRB/RS–68 Core/J-2X EDS. After careful analysis, NASA elected to forgo the modification of the SSME for altitude-start and proceed directly to development a common J-2X engine for both the Ares I upper stage and the Ares V Earth departure stage, which sends the Orion crew capsule/lunar lander combination to the Moon. This new approach eliminates a top ESAS-identified risk — SSME altitude start — and addresses another risk — J-2X development — sooner thereby lowering overall Exploration risks and costs.

In addition, the inordinate expense of using five SSMEs with each cargo launch made the selection the relatively simple (and much less costly), utilizing the expendable RS-68 engine with the added advantage of using a common engine to meet both Department of Defense and NASA needs. With this approach, engine development for the Ares I provides a significant and direct "down payment" on the Ares V test and development plan. Selecting common hardware not only maximizes nonrecurring investments and reduces overall lifecycle cost; it also gets NASA closer to enabling a lunar transportation system. Concentrating efforts on two major propulsion developments rather than on five, as was originally proposed, will reduce development costs by hundreds of millions of dollars and save billions in operations costs. These combined changes represented a projected savings of over $5 billion in life cycle costs over the initial ESAS recommendations.

Infrastructure and Capability Retention: While NASA will continue to use existing U.S. expendable launch vehicles for the robotic exploration missions (five to eight launches per year), the Ares V system leverages heritage human-rated systems such as the Shuttle Solid Rocket Motor; the Solid Rocket Booster, as well as heritage infrastructure, including the MAF in Louisiana; and the Vertical Assembly Building and crawler and launch complex 39 at KSC in Florida. To sustain the manufacturing infrastructure capability required for the Ares V between Shuttle retirement and the first human lunar launch, NASA's Exploration architecture (Shuttle-derived Ares I) ensured America's industrial base for production of large solid rocket systems, high-performance liquid engine systems, large lightweight stages, large-scale launch processing infrastructure, and the current production level of solid propellant fuels is available to support the Ares V. If NASA selected the EELV-based CLV options, this would have required a significant amount of "keep alive" costs to maintain the industry and Center infrastructure and skills assets for eventual use on Ares V development.

External Reviews: Several external reviews have been conducted with regard to NASA's launch vehicle selection, with all reviews to date supporting the direction of the Agency. NASA's conclusions regarding the Space Shuttle-derived Ares I and V vehicles have received agreement by the Department of Defense (DoD) and results were validated by Congressional Budget Office (CBO) and Government Accountability Office (GAO) reports. In 2005, the DoD reviewed NASA's analysis and concurred with NASA's approach. A joint recommendation was formally submitted in a memorandum to the Director of the Office of Science and Technology Policy, Dr. John Marburger, in August 2005.

In October 2006, CBO concluded a study on the NASA's selection of the Ares I and Ares V launch vehicles ("Alternatives for Future U.S. Space Launch Capabilities Report"). The CBO report contrasted CBO's analysis with the recent NASA ESAS report and resulting implementation approach and identified a number of observations, highlighting four main points:

  1. Fewer launches per exploration mission increases overall mission reliability;
  2. NASA's Shuttle-derived launch vehicle approach is the most economical option when minimizing the number of launches;
  3. Since CBO cost results are consistent with NASA's ESAS conclusions, and since NASA also based its launch decisions on safety and reliability (not assessed by CBO), NASA's selection of a Shuttle-derived launch vehicle is further validated by the CBO study; and
  4. The CBO estimates for the NASA-selected launch vehicles are within NASA budget projections.

And the most recent report from the GAO in November 2007 ("Agency Has Taken Steps toward Making Sound Investment Decisions for Ares I but Still Faces Challenging Knowledge Gaps Report") noted that "NASA has taken steps toward making sound investment decisions for Ares I." The GAO report also noted that: "Furthermore, NASA's decision to include the J–2X engine and five-segment booster in the Ares I design in order to reduce long-term operations and support cost is in line with the practices of leading commercial developers that give long-term savings priority over short-term gains. The Ares I project was also proactive in ensuring that the ongoing project was in compliance with NASA's new directives, which include elements of a knowledge-based approach. NASA's new acquisition directives require a series of key reviews and decision points between each life cycle phase of the Ares I project that serve as gates through which the project must pass before moving forward…We found that the Ares I project had implemented the use of key decision points and adopted the recommended entrance and exit criteria for the December 2006 Systems Requirements Review and the upcoming October 2007 Systems Definition Review."

Summary: NASA is designing transportation architecture, not just a point solution for access to LEO. In deciding on this architecture, NASA considered principal factors such as performance, reliability and development and life cycle costs when comparing alternatives. NASA also took into consideration the growth path to heavy lift capability which results from the choice of a particular launch vehicle family. To grow significantly beyond today's EELV family for lunar missions requires essentially a "clean sheet of paper" design, whereas the Ares V design makes extensive use of existing elements, or straightforward modifications of existing elements, which are also common to Ares I. The Shuttle-derived launch vehicle architecture selected by NASA meets all of the goals and objectives to achieve the exploration mission, while also:

  1. Providing the best possibility of meeting stakeholder and customer requirements, including legal mandates, within the funding available and timeframe desired;
  2. Providing the safest, most reliable and cost effective launch vehicle for NASA missions;
  3. Maximizing leverage of existing, human rated systems and infrastructure;
  4. Leveraging collaboration between the retiring Shuttle Program and emerging Constellation projects by sharing lessons learned and transitioning valuable resources, ranging from a specialized workforce to a unique launch infrastructure;
  5. Creating the most straightforward growth path to later Exploration launch needs; and
  6. Ensuring the industrial base for production of large solid rocket systems, high performance liquid engine systems, large lightweight stages and critical, large scale launch processing infrastructure.

> Download the PDF: Why NASA Chose to Utilize a Shuttle-Derived Crew Launch Vehicle

What is NASA Administrator Michael Griffin's reaction to recent news reports that claim Constellation Program engineers are struggling with a potentially serious vibration problem on the Ares I rocket?

NASA Administrator Michael Griffin responds:

In my 37 years in the space industry, I've rarely seen more of a mountain made out of less of a molehill. We're not even sure yet that we have a problem. But the vibration challenge we call thrust oscillation is the type of problem we would expect to encounter in an engineering development project, which is exactly what the Ares I project is. That said, the thrust oscillation issue is a challenge we take very seriously – and we are in the midst of an exhaustive analysis to address it.

Most solid rocket motor programs have struggled with precisely this challenge, so there are plenty of experts and much data available to help us. We're considering several solutions, many of which have proven successful in the past. Before we can choose a solution, however, we must understand exactly how thrust oscillation affects our particular solid rocket motor design, if it affects it at all.

Damping vibrations in Ares I and Ares V to ensure the safety of the people and equipment we will send to the lunar surface is just one of many engineering challenges we will face as NASA implements America's plan to explore the moon. We are striving to incorporate as many flight-proven elements as we can in order to improve the safety and reliability of Ares I and Ares V, but the fact remains we are developing a new space transportation system.

Developing new spacecraft is never easy. It was difficult when we developed Apollo, and it's still difficult today. Space travel is one of the most difficult and complicated things that humans can do; it pushes the limits of our technological abilities. But pushing those limits to explore the unknown and expand our frontiers is the way that human civilizations have advanced throughout history.

What is thrust oscillation and how is NASA addressing the problem?

Thrust oscillation, also called resonant burning, is a phenomenon characterized by increased acceleration pulses that may be felt during the latter stages of first-stage powered flight. Depending on the amplitude of these pulses, the impact on the vehicle structure and astronauts may be significant.

Thrust oscillation is a characteristic of all solid rocket motors including the first stage of the Ares I launch vehicle. Vortices, created inside the solid rocket motor by the burning propellant or other flow disturbances, can coincide, or tune, with the acoustic modes of the motor combustion chamber, generating longitudinal forces. These longitudinal forces may increase the loads experienced by the Ares I during flight, and may exceed allowable loads on various portions of the vehicle and allowable forces on the astronaut crew.

During any new development program, program risks must be identified and resolved prior to hardware development. Thrust oscillation is such a risk. NASA is committed to resolving this issue prior to the Ares I Project's preliminary design review, currently scheduled for late 2008.

In November 2007, NASA chartered the Thrust Oscillation Focus Team to precisely define the frequency spectrum and oscillation amplitudes that the five segment motor is expected to produce. These analyses are being accomplished using a combination of available ground test motor data as well as early shuttle solid rocket motor flight data. Efforts are underway to update the existing data set by adding instrumentation on several upcoming shuttle flights. In parallel, the team is evaluating vehicle structural assessments in order to provide additional vibration isolation to critical launch vehicle systems and uncouple the vehicle's natural frequency from motor induced loads.

Since upper stage elements and the command/service module are not yet fully designed, this is an excellent time to factor in thrust oscillation load mitigation should that be required. The team's analysis has already led to several mitigation strategies, including the removal of a significant amount of conservatism from within existing models, correlating to significantly lower loads by a factor of almost two. Additionally the team was able to remove the first longitudinal mode as an issue – the remaining effects are now in a narrow, manageable region in the 12Hz frequency range. NASA will conduct additional analysis coupled with upcoming flight tests on the shuttle (STS 125, currently planned for August 2008 and STS-119, currently planned for December 2008) and Ares I-X (planned for April 2009) to better characterize this phenomenon, which may further reduce loads.

> View charts from the Thrust Oscillation Focus Team (4.3 MB PDF)