1. Mission and Description
1.1 Primary Mission: The Sprint Program is designed to service, complete, and operate the International Space Station in absence of the Space Shuttle, but assumes availability of its launch facilities and technologies. It was originally conceived after the STS-107 disaster for the possibility that the Shuttle may never fly again, and, under that premise, if started immediately, would have its first element, Delta Sprint, in service by the end of 2005.
1.2 Launch Systems: Launch systems are expensive and time-consuming to develop, and as the Mercury/Gemini program of the early 1960s handily demonstrates, use of an existing launch system is desirable in the case of a requirement for rapid entry into service. In Mercury/Geminis case, those launch vehicles were military ICBMs, in the case of the Sprint Program, those launch systems are developed commercial single use vehicles, such as Soyuz, Proton, Delta, Ariane, and Shuttle. The Sprint Program, as such, is not intended as a Shuttle replacement, but as a bridge between a shuttle stand-down and a properly developed fully reusable launch system to replace the Shuttle.
1.3 Importance of the Sprint Program: It is After Columbias stalwart position that the Shuttle should never fly again, or at the least, should fly automated without a human crew on board. Sprint Program is an option to do this designed around the ongoing requirements of the International Space Station.
2. Spacecraft General Properties
2.1 Baseline Sprint Program: There are three spacecraft concepts, each with a separate report, in the Sprint Program. All of these concepts are mandatory for the Sprint Program to succeed; unlike ISTS, this is not a pick and choose program because none of the concepts individually fulfill all of the requirements of ISS operation. Sprint Program spacecraft have future uses presented in their reports, but will not be discussed here.
2.1.1 Delta Sprint: A three person crew transfer vehicle. Its main requirement is to do so as safely as possible. Because it employs a single use launch vehicle, reliability (MSP) of the concept as a whole will be somewhat less than 99.00% (Boeings 2000 October Payload Planners Guide states 97.8% MSP) and therefore as many backups as possible need to be provided to account for ascent failures. Another major requirement is operability. The crew members are station astronauts, not Shuttle pilots, and therefore need a craft that is within their means to operate and maintain on orbit. Both of these requirements are best met by a ballistic, dynamically stable shape; a capsule. Delta II 7920 with a Fregat upper stage added in place of the more typical solid motor is currently the selected launch vehicle for this concept.
2.1.2 Ariane Sprint: Ariane Sprint is an unpiloted craft intended to meet the logistic requirements of the Space Shuttle which cannot be provided by Progress, ATV and HTV. The only significant requirement, therefore, is the ability to bring a significant cargo mass back from the International Space Station. Ariane Sprint will use Delta Sprint recovery systems scaled up to its increased size, a standard Ariane 5G launch vehicle, with, if possible, the ascent fairing in position. Ariane Sprint will also be used for upmass logistics and will supplement ATV, HTV and Progress in this role (and also partially make up for any lost ATV lift tickets that Ariane Sprint requires.) The currently preferred baseline for Shuttle-X is automation of the existing Shuttle, which should allow entry and recovery of the MPLM currently in service. The Ariane Sprint might not be necessary in this scenario.
2.1.3 Shuttle X: Shuttle X is now a subprogram intended to study several new Shuttle Derived Vehicles. For International Space Station Service, an automated version of the existing Shuttle is preferred. Shuttle X is named for Apollo X, which looked for applications for Apollo technologies and left over hardware from the lunar exploration program. It was renamed Apollo Applications, and eventually launched Skylab, with three mission watches including a spectacular repair. The originally conceived Shuttle-X concept used Shuttle ascent systems to launch several Shuttle compatible ISS assembly manifests at once. There are no significant changes to the launch system itself. Replacing the Orbiters mid-fuselage, forward fuselage, wings, and OMS pods are two large, single use 4.5m diameter payload fairings, each containing either two or three payload manifests (it was intended that one fairing has enough volume to launch two Atlantis/Endeavor manifests and one Columbia manifest. The other fairing would have two Atlantis/Endeavor manifests and an EDO (Extended Duration Orbiter) pallet to store propellants for orbital maneuvers. This way, two Shuttle X launches can be used to launch all ten manifests required to achieve US Core Complete after the failure of STS-107 Columbia. After Columbias analysis of the Mars Direct launch vehicle Ares will now be included as part of Shuttle X.
2.2 Sprint Alternatives: Each concept has certain requirements to fulfill in the Sprint Program, and in some cases, other craft may be available to fill these requirements. For example, an automated Shuttle may be able to bring a loaded MPLM back from the Station, obviating the need for Ariane Sprint.
2.2.1 Alternatives to Delta Sprint: In the case of Delta Sprint, Soyuz performs the same mission down to the letter. Delta Sprint is still required so that the two craft can provide backup for each other. A mission watch on Salyut 6 was compromised by an engine failure in a Soyuz taxi craft. The result was that the crew could not trust their own lifeboat not to have an engine failure of its own. The old Soyuz was replaced by an unpiloted taxi craft which had the modifications required to prevent the engine failure, and the old Soyuz was deorbited and landed unpiloted without incident. If Delta Sprint were present, it would be available as a lifeboat in the Soyuz place. Likewise, if Delta Sprint were to have a problem, the Soyuz would be available. Delta Sprints improved design and on-orbit serviceability reduces per capita logistics requirements by half compared to Soyuz (a Delta Sprint Descent Module need only be replaced every two years, versus six months for Soyuz.)
2.2.2 Alternatives to Ariane Sprint: Currently, the MPLM provides downmass logistics, with SPACEHAB Logistics modules available as well. The problem is that all these require the Shuttle as a recovery system. An alternative would be to provide an alternate reentry system for these modules. After Columbia believes that the most practical alternative is a medium sized (20 tonne class ascent payload) entry capable spacecraft built around the requirements of the International Station Payload Rack (ISPR) be developed and employed instead. MPLM in particular, is too heavy to be launched on a medium class (Proton or Ariane) vehicle in addition to an entry system and any useful logistics payload. Proton is an alternative launcher for this spacecraft, and Proton Sprint was briefly considered. Arianes Kourou launch site provides more flexibility for inclination, making possible future servicing of low inclination space stations (possibly hotels.)
2.2.3 Alternatives to Shuttle X: Shuttle X is required to lift the already constructed elements of the International Space Station designed for ascent on the Shuttle. Shuttle-X was selected as the primary concept for this requirement because the Shuttle Program staff are already familiar with the integration requirements of the ISS manifests and also are familiar with the ascent system. There is also some uncertainty as to whether any other launchers are capable being adapted to launch these payloads. Currently the favorite of Shuttle X is to simply automate the existing Shuttle and fly it without a crew on board.
3. Spacecraft Ascent
3.1 Baseline Ascent Systems: The Sprint Program uses existing launch vehicles as much as possible. All ascent systems chosen for the baselines of each spacecraft concept have been proven in flight, although two require extensive modification to fulfill their duties in the Sprint program (being Delta II and Shuttle.)
3.2 Fallback Ascent Systems: The Sprint program has no solidly definable fallback options for any of its ascent systems as the most basic options have already been chosen. Ariane 44L was the original preference for the concept now called Delta Sprint, but that launcher has since gone out of service.
3.3 Future Options: The future ascent options of the Sprint Program primarily revolve around ISTS, which can be utilized only for the extended missions of the Sprint Program craft. ISTS may not have the lift capability of current large single use launchers, potentially leaving a role for Shuttle-X and Ariane Sprint. Delta Sprint is intended to use ISTS for ascent during its extended mission role as a station bailout lifeboat.
3.4 Details: The Sprint Program details are available in the following spacecraft reports:
4. Spacecraft Recovery
After Columbias Summary: Piloted spacecraft crews need to be recovered. The goal is a 99.99% probability of crew recovery per mission (average of one fatal failure in 10,000 missions.) Full redundancy for all phases of the mission is desirable, but probably expensive and impractical to actually attain, and on airline class operational spacecraft, will become difficult and expensive to continue to carry. On an "operational" spacecraft/launch system, backup recovery needs to be provided for the test flight and early operational phases, but must be removable when the development of the craft progresses to a sufficiently safe and reliable level (99.99% probability of overall mission success...1 failure every 10,000 flights), and replaceable for recertification flights. Backup recovery systems should be designed to allow crew survival in 99.99% of all flights regardless of mission outcomes, and inclusive of normal mission completion (i.e. if the spacecraft has a 99.00% probability of overall mission success, the backup recovery modes have a requirement to accommodate 99.00% of mission failures, for a cumulative crew survival probability of 99.99% per mission.) As demonstrated by the close calls of the NASA 1960s manned programs, and the failures of the Shuttle program, effective management and training has a greater effect on the safety of piloted spacecraft than on-board systems. The spacecraft designer is therefore charged with providing this management with as many options and backups as practical. Some missions, such as the initial exploration of Mars, where there is a willingness to take greater personal risks, can accept more risk. I, personally, would be willing to fly a mission to Mars with an overall crew survival probability as low as 75.00%, but would expect the 99.99% overall crew survivability on the next piloted craft design for Low Energy Orbit (LEO, also known as Low Earth Orbit.)
4.1 Recovery Modes of Baseline Concepts:
4.1.1 Normal Recovery: Both Ariane Sprint and Delta Sprint are intended to use Shuttle thermal protection materials. Due to the cost of these materials, it is highly desirable that both craft be reusable, and also that their thermal protection materials be protected as much as possible during landing. Due to the ballistic nature of the craft, and the requirement to make the craft light in order to work from their selected launch vehicles, a conventional landing gear cannot be employed, therefore a parasol and airbag landing system is employed. The airbag landing gear has an advantage over the old Soyuz type rockets in that precision timing in deploying the gear is not required, and also that the airbags can protect the thermal protection system from physical contact with the landing surface. In addition to this, the crafts landing orientation is rotated from its entry orientation so that the RCC heat shield required for the leading surface during entry does not come into contact with the ground, and does not require hatches for the landing or recovery gear so that the option remains open to cure the RCC surface as a single piece.
4.1.2 Ascent Abort: Crew safety is part of the intent of the Sprint Program in replacing the Shuttle with a crew transfer system that is safer than the Shuttle. The diminutive Delta Sprint is therefore the only piloted spacecraft. It intends to carry an ascent escape system that is fired as a stage during ascent to offset its cost and mass; After Columbia calls this concept the Payload Escape Stage or PES. Details are in the Delta Sprint report. Sprint Programs other craft are not piloted, and do not have ascent abort systems.
4.1.3 Backup Recovery Modes: As with ascent abort systems, the Delta Sprint is the only craft with a requirement for backup recovery modes. Delta Sprints backup recovery modes include the crafts standard recovery system and individual crew parachutes, combined with large, easily operated side hatches, and single use backup impact systems for the possibility of landing gear failure. Paramount to Delta Sprints backup recovery ability is the protection of the thermal protection system from catastrophic damage during an uncommanded abort (the gentlest way of describing a Challenger-like explosion.) Details are in Delta Sprints report. The other craft carry entry capable recorders derived from the MADS system instrumental in Columbias accident investigation to assist in failure investigations of those vehicles, but they do not have backup recovery modes for their payloads.
4.1.4 Other Mission Emergencies: Delta Sprint has requirements to deal with station emergencies in its role as bailout craft. Details are in the Delta Sprint report.
4.2 Recovery Modes of Alternative Concepts: Various recovery options for each craft are discussed in their respective reports.
4.3 Mechanical and Thermal Loads: The thermal and aerodynamic notes for each craft are not appropriate for this report and will be found in the reports of the specific craft for the Sprint Program.
4.4 Detailed Information: Please consult the individual spacecraft reports
5. Spacecraft Mission Technologies
5.1 Baseline Mission Requirements and Systems: Mission systems, whenever possible will be selected from existing hardware. Shelters designed for mine collapse may have some hardware applicable to Delta Sprints requirements. As spacecraft, both piloted and autonomous, have been made which are larger than Delta Sprint, it is suspected that most systems can be found off the shelf, and that those which are not can be chosen from aeronautical systems. Ariane Sprint may be able to share ATV hardware and mission systems. Shuttle X will use Shuttle OMS and RCS engines and propellant systems for its maneuvering. An unpressurized docking port is required, but the Remote Manipulator System (RMS) is not, due to the presence of one on the ISS already (although Shuttle X concepts will be able to accommodate it if required.)
Options and details are contained in the spacecraft reports
6. Spacecraft Program Considerations
6.1 Positive Program Interactions: With the exception of Shuttle X, the Sprint program should reduce the cost of extending the service life of the International Space Station without the use of Shuttle. The Shuttle X is most likely to lose its usefulness the quickest, as future space stations are likely to use an 8m diameter standard module, as opposed to the current 4.5m standard. Additionally, new construction of the 4.5m standard modules can be launched on Atlas V, Ariane 5, or Delta IV launch systems more cost effectively than on Shuttle X. The new 8m standard module, which will probably be standardized by the Mars Society in the near future, can be accommodated on the Ares launch vehicle less second stage in much the same manner as an unpiloted satellite. Sprint Program elements can service these new space stations while waiting for ISTS. ISTS or its equivalent will finally render the Sprint Program obsolete, although Delta Sprint may continue to serve as lifeboat. The Sprint Program will provide manifests for Delta II and Ariane 5 launch vehicles.
6.2 Negative Program Interactions: It is reasonable to assume that Space Shuttle advocates would be opposed to the Sprint Program, as the Sprint Program basically assumes that the Space Shuttle has no further operational capability and competes for all of the Shuttles functions. Delta Sprint also competes very directly with the role of OSP in crew transfer. Interests seeking to make a replacement for the Shuttle in the role of crew transfer may want that replacement to be more elaborate, with greater mission requirements in order to make more money for the contractors involved. Delta Sprint is designed around a less than ideal world of needing to be ready on as short a schedule as possible while still advancing the state of the art somewhat (feasibility of PES-type abort systems and backup recovery modes, as well as more modern subsystems than have been used in piloted craft to date.) Ariane Sprint does compete with MPLM, but this point is moot in relation to the Shuttle issues. Ariane Sprint can be developed and built by the same interests as MPLM, who would probably be delighted to develop a stand-alone entry capable spacecraft rather than the non-separating Shuttle payloads they have become accustomed to.
6.3 New Technology Requirements: The major technological requirements of the Sprint Program are very few. Development risk of each spacecraft concept is expected to be individually slightly more than a new unpiloted spacecraft, and somewhat less than an individual piloted Shuttle manifest. Costs of Delta Sprint and Ariane Sprint development are not likely to exceed the cost of the STS-107 stand down and return to flight together. Shuttle-X is another matter, requiring a major rework of the Space Shuttle system, a considerably larger and more complex venture than Delta II or Ariane 5. This cost is then amortized over a very short program. After Columbia hopes that an alternative can be found to Shuttle X for launching ISS manifests.
6.4 The End of Sprint Program: The Sprint Program as a whole becomes obsolete when proper Shuttle replacement systems, such as ISTS, NGLT, or SLI can fulfill its requirements. Delta Sprint is likely to continue well into the future as a lifeboat, but the assembly an logistics requirements of Ariane Sprint and Shuttle-X will, hopefully, be made obsolete in the not too distant future.