From: Johnson Space Center
Posted: Thursday, March 4, 2010
National Aeronautics and
Lyndon B. Johnson Space Center
2101 NASA Parkway
Houston. Texas 77058-3696
March 1, 2010
Reply to Attn of: CB-10-026
TO: CA/Director, Flight Crew Operations
FROM: CB/Chief, Astronaut Office
SUBJECT: Commercial-Crew Vehicle Transition Concepts
The President's 201 1 Budget Proposal which was unveiled on February 8, 2010, places an emphasis on commercial vehicles "to provide astronaut transportation to the International Space Station (ISS), reducing the sole reliance on foreign crew transports and catalyzing new businesses and significant new jobs." The following paper provides recommendations for the transition to a commercial-crew vehicle to the ISS which leverages the experience gained in the operation of the Space Shuttle, the ISS, and in the design of Constellation.
Commercial transportation of astronauts to the ISS may afford NASA the opportunity to dedicate its resources to exploration beyond Low Earth Orbit (LEO). This bold proposition places an enormous responsibility on commercial industry to preserve US. access to space following the retirement of the Space Shuttle. It is imperative that NASA's broad experience base in human spaceflight to LEO be used as a resource to expedite this transition to the commercial market, as well as, preserve the human capital and knowledge base required to conduct ascent and entry operations for the day when NASA once again conducts operations beyond Earth's orbit.
As trips to LEO become largely the responsibility of commercial providers, NASA will initially serve as the foundation of their customer base. These commercial operators will likely serve other paying passengers with their own vehicle and certified operator-astronauts to LEO destinations. Conversely, the NASA customer would he well served by leveraging the breadth of 1SS experience brought by its current operator-astronauts in the complexities of operating in close proximity to the ISS with these commercial-crewed vehicles. The Astronaut Office developed the following transition concepts that we believe will maximize the likelihood of success for the ISS as well as the commercial endeavor.
Key Design Drivers for Commercial-Crew Transport to the ISS:
Assured Crew Return (ACR)
While on the ISS, each crewmember requires a path to return to the Earth in the event of a catastrophic station failure or medical emergency. A ready vehicle (lifeboat) attached to the ISS, in lieu of a ground based launch-on-need vehicle is required for ACR. A de-orbit in this ready vehicle must be executed to a targeted ground site capable of post landing support.
The ACR function can be provided by leaving the crew transportation vehicle docked to station throughout the full expedition, or by developing a dedicated vehicle to serve that purpose (similar to the X-38 Assured Crew Return Vehicle concept). Whether the crew vehicle or a separate, dedicated vehicle is selected as the mechanism to provide ACR, the number of docking and berthing ports (currently two of each) is a consideration for vehicle traffic (H-I1 Transfer Vehicles (HTV's), commercial cargo carriers, and crew rescue/transport), as is "direct-handover" of ISS expedition crews. In direct-handover, the on-coming and off-going crews are on board ISS simultaneously in order to conduct a face-to- face exchange of control. Direct-handover is required if all US. crews are rotating on the same vehicle, since the limited user-level training provided to the Russian crewmembers would he inadequate to support ISS operations in off-nominal situations. In addition, the continuous presence of a U.S. crewmember on hoard ISS is stipulated in the memorandum-of- understanding between the U.S. and ISS partner nations. Alternative indirect handover options are feasible, but must he designed to ensure continuous U.S. presence on board the station.
If the crew transport vehicle is used to provide ACR, it must provide an on-orbit stay time equal to the ISS increment duration. The Soyuz on-orbit stay time of 210 days enables ISS increment durations of approximately 6 months. However, shorter increment durations may be feasible based on programmatic trades of science return vs. crew logistics. The ACR crew vehicle decision also drives flight crew training to ensure that the crew can operate the vehicle through undocking, de-orbit, and landing. The flexibility of relocating the ACR crew vehicle to any number of docking/berthing ports should he integral to the design.
If the crew vehicle will also perform the ACR function, two basic operational philosophies are possible. The first utilizes the expedition crew as the operators of the vehicle going to and from the ISS, and is analogous to a "rental car" operations model here on Earth. The second uses a commercial operator-astronaut to ferry the required station crewmembers (3 in the current rotation plan with 6-month increments), which more closely approximates a "taxi" operations model. In the "taxi" model, the operator(s) would transport new expedition crewmembers to the station and then return to Earth.
The "taxi" option poses some distinct logistical disadvantages. Specifically, it uses valuable un/down mass to support the dedicated vehicle operator(s) who fly the vehicle to/from the ISS. Also. one additional vehicle must be procured and flown at the beginning of the program, in order to position the initial rescue craft. This additional vehicle would either be an additional crew vehicle or a separately developed, dedicated ACR vehicle.
In either the "taxi" or "rental car" models, the crews will need to be trained on undock and entry procedures for emergency cases that require ACR. One drawback of the "rental car" option is the requirement for additional training of the ISS expedition crews in the ascent phase. Historically however. ascent training comprises less than 20% of the overall mission training requirement (based on Shuttle/Soyuz training). The "rental car" option does not require the initial flight to position the ACR vehicle, and would maximize the up/down mass capability of the vehicle for scientific payloads.
Given ACR, the "rental car" model is preferred over the 'taxi" model to maximize upldown mass, optimize handover, and leverage recent NASA operating experience in close proximity to the ISS.
Along with the key design drivers listed above, several operational assumptions also play a role in the commercial vehicle development and operation. These can be grouped into three categories:
- Government collaboration in the development process
- Crew collaboration in the design process
- Flight Operations
Government Collaboration in the Development Process
As commercial providers become integrated with NASA flight operations, questions pertaining to Federal Aviation Administration (FAA) versus NASA certifications and standards arise. Currently, FAA (Office of Space Transportation) standards are only designed to protect the public from over-flight hazards associated with a launch. In contrast, NASA's Human-Rating Requirements (HRR) for Space Systems (NPR 8705.2B) and Flight Rules have evolved over decades and are set in place to protect both the flight crew on board the vehicle and the public. It is anticipated that NASA and the FAA would collaborate in the future to determine rules and regulations for space control and commercial space vehicle licensing. Even with collaborative efforts amongst licensing agencies that evolve for human space vehicles, the NASA Human-Rating Requirements are the only current benchmark standards and should be used as the controlling document for certifying human rating of crewed spacecraft.
While the Human-Rating Requirements are the only benchmark in existence today for the certification of spacecraft, in the NASA Human-Rating Benchmark Study (December 2009), the NASA Aerospace Safety and Advisory Panel (ASAP) acknowledged that the HRR may not be inclusive enough to cover future space systems. Specifically, with regard to failure tolerance, the HRR specifies a "minimum of one failure tolerant, with specific level of failure tolerance (one, two or more) derived from an integrated design and safety analysis." While acknowledging that over-prescribing specific levels of failure tolerance may stifle innovation, it must also be acknowledged that under-prescribed levels may leave too much open to "engineering judgment" and exploitation of exactly what constitutes a level of redundancy. While a highly robust, well-tested, single failure tolerant system may be better than a two-failure tolerant systems in some cases, new commercial developers must ultimately meet the intent of the HRR which states that the "overall objective of human rating is to provide the safest design given the constraints imposed on the program." Additionally, the vehicle must provide a graceful degradation in capability as failures occur to allow the crew the time and ability to manage them to support mission success and ensure a safe return. Single failure tolerance is the minimum design criteria. Fail operational (the vehicle can incur a single failure and still perform its mission) and Fail Safe (the vehicle can incur a second failure in the same system and still safely return the crew) for failures which can lead to a loss-of-crew should be considered the standard when evaluating competing commercial-crew designs.
NASA representation at the commercial developer's facility is highly encouraged. Similar to major military acquisition programs, the presence of government representatives (customers) at the contractor facility to provide input throughout the development and build phases optimizes the potential for delivery of a successful product. In this type of model (like the Defense Contract Management Agency), contract managers collaborate with industry counterparts to ensure that government products and services are delivered on time, at projected cost, and meet all performance requirements.
Crew Collaboration in the Development Process
Planning and Development of Crew Interface
NASA flight crews have been integral to the development and testing of human-spacecraft interfaces for every US. spaceflight program. Incorporating the insights and lessons from this experience early in a new commercial development program has obvious benefits. Current NASA flight crews and operation engineers should collaborate with commercial developers of human-vehicle interfaces, and should be key stakeholders in the areas of vehicle operability and habitability.
In the absence of flight history to support reliability claims, test results are essential. It is envisioned that a "Combined Test Force (CTF)"-type approach would serve the needs of the commercial operator and ensure that the desires of NASA are met. This CTF approach would integrate commercial crews with NASA crews in an organization which performs Developmental Test (to determine if the system or vehicle meets the requirements and specifications set forth by the government) and Operational Test (to assess the ability to perform the mission). A Combined Test Force approach is recommended in order to leverage the depth of systems knowledge provided by the commercial operator with the breadth of experience brought by ISS experienced flight crews.
Experience since the Mercury program has shown the advantage to both operations and safety-of-flight which is afforded by hands-on training with flight hardware to the greatest extent possible. This covers a wide gamut of opportunities, from subsystem and hardware handling, to familiarization with vehicle wiring and plumbing, to interfacing and integrating hardware in the vehicle, to a full dress rehearsal in the vehicle for a launch count and simulated emergency operations. Pre-flight access and hands-on training of NASA flight crews with flight hardware is expected.
Crew vehicle training will be conducted to ensure proficiency in the necessary skills for flight. Only a small portion (percentage-wise) of training required for an ISS mission will be on the crew vehicle. Station crews will train primarily at the Johnson Space Center (JSC) for increment mission tasks such as robotics, extravehicular activity (EVA), ISS systems operation, and U.S. payloads. While the training location for the crew vehicle is still to be determined, there is a strong case to locate that training at JSC from an efficiency perspective. The commercial provider can leverage JSC facilities and training expertise to efficiently provide high quality training. This would not preclude conducting basic spacecraft and systems training at a location which makes the most logistical sense. Regardless of the location for basic vehicle system training, at least one vehicle simulators hould he located at JSC for astronaut proficiency.
Flight Operations and Crew Protection
Memorandum CB-04-044, Astronaut Office Position on Future Launch System Safety, was released in May 2004 by the Astronaut Office after the Columbia disaster, precipitated by a reexamination of all operational aspects of human spaceflight and focusing on launch vehicle safety for any next generation of human rated spacecraft. Although flying in space will always involve significant risk, an order of magnitude improvement during ascent compared to Space Shuttle, is achievable with current technology and represents a minimum safety benchmark for future systems. It is highly recommended that any human-rated launch system include a booster with ascent reliability at least as high as the Space Shuttle's and an abort system which, together with the booster, yield a predicted Loss of Crew (LOC) number of 1/1000. This number assumes a loss of one vehicle per 100 launches and a crew escape system providing a 90% probability of survivable crew escape.
Some boosters are designed to highly loft their ascent trajectory to optimize the capability of their propulsion system and the amount of mass the booster can deliver to orbit. For expendable vehicles, these trajectories are efficient and transparent to the payload. For a crewed vehicle however, aborting from a lofted trajectory puts the crew at a significant survival risk in some scenarios due to high G loads and heating. These pans of the trajectory, where an abort is non-survivable, are called black zones. A commercially crewed vehicle must have full envelope abort/escape capability with no black zones.
In order to mitigate the risk of unknowns associated with the technical challenges of putting humans in space, it is imperative that NASA's lessons learned, with loss of life and at great expense to the taxpayers, be effectively transmitted to those commercial providers. Mechanisms for continuous collaboration between these providers and NASA's experts must be built into the contract processes in order to optimize for success throughout design, construction, test, and flight. This commercial crew transition concept is our attempt to begin sharing some of these lessons learned.
original signed by:
Peggy A. Whitson, Ph.D.
// end //