Crew Return Vehicle

The Crew Return Vehicle (CRV), sometimes referred to as the Assured Crew Return Vehicle (ACRV), was a proposed dedicated lifeboat or escape module for the International Space Station (ISS). A number of different vehicles and designs were considered over two decades – with several flying as developmental test prototypes – but none became operational. Since the arrival of the first permanent crew to the ISS in 2000, the emergency return capability has been fulfilled by Soyuz spacecraft and, more recently, SpaceX's Crew Dragon – each rotated every 6 months.

In the original space station design, emergencies were intended to be dealt with by having a "safe area" on the station that the crew could evacuate to, pending a rescue from a U.S. Space Shuttle. However, the 1986 Space Shuttle Challenger disaster and the subsequent grounding of the shuttle fleet caused station planners to rethink this concept.[1] Planners foresaw the need for a CRV to address three specific scenarios:

• Crew return in case of unavailability of a Space Shuttle or Soyuz capsule;
• Prompt escape from a major time-critical space station emergency;
• Full or partial crew return in case of a medical emergency.[2]

Medical considerations

The ISS is equipped with a Health Maintenance Facility (HMF) to handle a certain level of medical situations, which are broken into three main classifications:

However, the HMF is not designed to have general surgical capability, so a means of evacuating a crew member in case of a medical situation that is beyond the HMF's capabilities is essential.[2]

A number of studies have attempted to assess the medical risks for long-term space station habitation, but the results are inconclusive, as epidemiological data is lacking. It is, however, understood that longer periods in space increase the risk of serious problems. The closest estimates show an illness/injury rate of 1:3 per year, with 1% estimated to require emergency evacuation by means of a CRV. For an eight-person ISS crew, this results in an expected need for a CRV flight once every 4 to 12 years. These estimates have been partially corroborated by experiences on board the Soviet Union's Mir space station. In the 1980s, the Soviets had at least three incidents where cosmonauts had to be returned under urgent medical conditions.[2]

Because of its potential use as a medical evacuation method, the CRV design was required to address a number of issues that are not factors for a standard crewed space vehicle. Foremost of these are the g-loadings as influenced by reentry profiles and deceleration/landing methods upon patients with hemorrhagic shock issues. Patient security issues are more critical for injured astronauts than for uninjured personnel.

Early NASA concepts

Dr. Wernher von Braun first brought up the concept of space lifeboats in a 1966 article,[3] and then later NASA planners developed a number of early concepts for a space station lifeboat:

European Space Agency concepts

As a part of their wide-ranging studies of potential human spaceflight programs, the European Space Agency (ESA) began a six-month, first-phase ACRV study in October 1992. Prime contractors for the study were Aérospatiale, Alenia Spazio and Deutsche Aerospace.[7]

The ESA studied several concepts for a CRV:

The ESA's US$1.7 billion ACRV program was cancelled in 1995, although French protests resulted in a two-year contract to perform further studies, which led to a scaled-down Atmospheric Reentry Demonstrator capsule, which was flown in 1997.[7][11] The ESA instead elected to join NASA's X-38 CRV program in May 1996, after that program finished its Phase A study.[7]

Lifeboat Alpha

The idea of using a Russian-built craft as a CRV dates back to March 1993, when President Bill Clinton directed NASA to redesign Space Station Freedom and consider including Russian elements. The design was revised that summer, resulting in Space Station Alpha (later the International Space Station). One of the Russian elements considered as a part of the redesign was the use of Soyuz "lifeboats." It was estimated that using the Soyuz capsules for CRV purposes would save NASA US$500 million over the cost expected for Freedom.[12]

However, in 1995, a joint venture between Energia, Rockwell International and Khrunichev proposed the Lifeboat Alpha design, derived from the Zarya reentry vehicle. The reentry motor was a solid propellant, and maneuvering thrusters utilized cold gas, so that it would have had a five-year on-station life cycle. The design was rejected, though, in June 1996 in favor of the NASA CRV/X-38 program.[13]

X-38

Besides referring to a generalized role within the ISS program, the name Crew Return Vehicle also refers to a specific design program initiated by NASA and joined by the ESA. The concept was to produce a spaceplane that was dedicated to the CRV role only. As such, it was to have three specific missions: medical return, crew return in case of the ISS becoming uninhabitable, and crew return if the ISS cannot be resupplied.[14]

Orbital Space Plane

As a part of NASA's Integrated Space Transportation Plan (ISTP) which restructured the Space Launch Initiative (SLI), focus moved in 2002 to developing the Orbital Space Plane (OSP) (early on referred to as the Crew Transfer Vehicle, or CTV),[29] which would serve as both crew transport and as the CRV. In the restructuring, program priorities were changed, as NASA declared: "NASA's needs for transporting US crew to and from the Space Station is a driving space transportation requirement and must be addressed as an agency priority. It is NASA's responsibility to ensure that a capability for emergency return of the ISS crew is available. The design and development of an evolvable and flexible vehicle architecture that will initially provide crew return capability and then evolve into a crew transport vehicle is now the near-term focus of SLI."[29]

A Crew Transfer Vehicle/Crew Rescue Vehicle Study, conducted by the SLI program in 2002, concluded that a multi-purpose Orbital Space Plane that can perform both the crew transfer and crew return functions for the Space Station is viable and could provide the greatest long-term benefit for NASA's investment. One of the key missions for the OSP, as defined by NASA in 2002, was to provide "rescue capability for no fewer than four Space Station crew members as soon as practical, but no later than 2010." As a part of the flight evaluation program that was to explore and validate technologies to be used in the OSP, NASA initiated the X-37 program, selecting Boeing Integrated Defense Systems as the prime contractor.[30]

Apollo-derivative capsule

With the cancellation of the OSP, the Apollo capsule was once again looked at for use as a CRV, this time by NASA in March 2003. In the initial study of the concept, "the Team concluded unanimously that an Apollo-derived Crew Return Vehicle (CRV) concept, with a 4 to 6 person crew, appears to have the potential of meeting most of the OSP CRV Level 1 requirements. An Apollo derived Crew Transport Vehicle (CTV) would also appear to be able to meet most of the OSP CTV Level 1 requirements with the addition of a service module. The team also surmised that there would be an option to consider the Apollo CSM concept for a common CRV/CTV system. It was further concluded that using the Apollo Command Module (CM) and Service Module (SM) as an ISS CRV and CTV has sufficient merit to warrant a serious detailed study of the performance, cost, and schedule for this approach, in comparison with other OSP approaches, to the same Level 1 requirements."[33]

The study identified a number of issues with development of this option: "On the one hand, the Apollo system is well understood, and proved to be a highly successful, rugged system with a very capable launch abort system. Documentation would be very helpful in leading the designers. On the other hand, nearly every system would have to be redesigned, even if it were to be replicated. None of the existing hardware (such as CMs in Museums) was thought to be usable, because of age, obsolescence, lack of traceability, and water immersion. There would be no need for fuel cells or cryogenics, and modern guidance and communications would be lighter and less expensive. Although the flight hardware would be less expensive, and its impact on the Expendable Launch Vehicles would be minimal (it's just another axisymmetrical payload), the landing sites for the CRV may drive the Life Cycle costs high. By adding a Service Module (smaller than the one required to go to the Moon), orbital cross-range of 3000 to 5000 ft/s, might be gained, and the number of landing sites radically reduced. If land landings can be added to the system safely, another major reduction in life cycle costs would result, because the team believed that the system could be made re-usable."

Soyuz

With the cancellation of the X-38 and CRV programs in 2001, it was clear that the interim use of Soyuz capsules would be a longer term necessity. To make them more compatible with the needs of the ISS, Energia was contracted to modify the standard Soyuz TM capsule to the TMA configuration.[34][35] The main modifications involve the interior layout, with new, improved seats to accommodate larger American astronaut anthropometric standards.[36] A series of test drops of the improved capsule were made in 1998 and 1999 from an Ilyushin Il-76 cargo plane to validate the landing capabilities of the TMA.[37]

A Soyuz-TMA capsule was always attached to the ISS in "standby" mode, in case of emergencies. Operated in this configuration, the TMA had a lifespan of about 200 days before it has to be rotated out, due to the degradation of the hydrogen peroxide used for its reaction control system.[38]

Commercial Crew Development

In 2008, NASA began administering a program (CCDev) to fund development of commercial crew transportation technologies. The program funded bids to develop specific technologies with awards when milestones were achieved. The first round of recipients in early 2010 included Boeing for its CST-100 capsule and Sierra Nevada Corporation for its Dream Chaser spaceplane. Further proposals submitted at the end of 2010 for a second round of funding included Orbital Sciences Corporation for its Prometheus spaceplane and SpaceX for developing a launch abort system for its Dragon spacecraft.

External links

• ESA CRV specifications
• MSNBC Flash presentation showing construction of the ISS and placement of the CRV
• 3D Modeling for CRV design
• Timing Analysis and Scheduling of the X-38 Space Station Crew Return Vehicle and Other Space Vehicles
• CRV Interior Design
• NASA Tech Paper 3101: Numerical Analysis and Simulation of an Assured Crew Return Vehicle Flow Field
• Historic overview of space lifeboats