Statement to
Subcommittee on Space and Aeronautics
Committee on Science
On
NASA's Integrated Space Transportation Plan and Orbital Space Plane Program
By Jerry Grey
Director, Science and
Technology Policy
American
May 8, 2003
Introduction
My name is Jerry Grey. I am Director
of Science and Technology Policy for the American Institute of Aeronautics (AIAA)
and Visiting Professor of Mechanical and Aerospace Engineering at
As you requested, I focus my testimony on the questions you posed.
(1) What key factors should be considered when evaluating human space transportation architectures?
There are two principal factors: safety and cost. Included in "safety" are avoidance of failures, tolerance of failures (i.e., no injury to the crew) should a failure occur, and adequate life-support systems and provisions. Note that "tolerance of failures" implies consideration of crew escape systems. Included in "cost" are development and operational costs, broken down into annual budget requirements and life-cycle cost.
(2) Is the proposed ISTP an overly optimistic or overly conservative approach to meeting NASA's needs? What areas of the proposed approach pose the greatest risk? What recommendations do you have to reduce these risks?
NASA's needs.
It is first necessary to define NASA's needs. By far the most critical current need is to meet the International Space Station's transportation requirements. Prior to the loss of Columbia, the Shuttle fleet provided the large-payload capability needed to transport major elements of the International Space Station (ISS) and carried ISS crew members to and from the station, along with sizable amounts of both technological cargo (e.g., experiment apparatus) and expendables (e.g., water). Once the remaining Shuttle fleet returns to flight status, those functions can resume. When that will be, however, is still uncertain.
Additional provisions and emergency crew return capability for up to three ISS crew members have been provided by Russian Soyuz and Progress vehicles. The Russians are committed to provide Soyuz crew-return capability until 2006, and although funding for the number of Progress vehicles needed to continue ISS supply flights without Shuttle support has yet to be identified, there are "workarounds" that are likely to allow the station to function at least minimally until the three Shuttles return to flight status. These include measures already implemented; i.e., using Soyuz lifeboat-replacement flights to transport ISS crew members up and down and reducing the ISS crew to two; finding ways to finance an increase in Russian Progress operations; and using the European Automated Transfer Vehicle (ATV), whose initial launch aboard an Ariane-5 is planned for late next year (assuming the Ariane-5 will have successfully returned to routine service by then). The main near-term concern is that if no source of funding for additional Progress flights can be found, it may become necessary to mothball the ISS late in 2003 or early in 2004 until the Shuttle fleet returns to flight status.
NASA's other
needs for space transportation, other than one more servicing mission to the
Hubble telescope, do not require the Shuttle's unique capabilities and can be
met by the existing Expendable Launch Vehicle (ELV) fleet. Hence the principal
requirements for the ISTP, as far as NASA's specific needs are concerned, are
(1) to provide an alternative to the Shuttle fleet for servicing the ISS,
especially after the next Shuttle failure occurs (at least one such failure is
highly likely if the Shuttle is required to operated until 2015 or perhaps even
2020), (2) to provide ISS crew rescue capability after the Russian Soyuz
commitment expires in 2006, and (3) perhaps most important, to provide rescue
capability for an ISS crew larger than the present 3-person complement. This
latter requirement is critical in order for the ISS to fulfill its purpose as a
viable research facility. Cancellation by NASA of the original Crew Return
Vehicle (CRV) program in February 2001 created this new requirement, which is
of major concern to our foreign ISS partners as well as to the
There is another
important function for the ISTP, however: to provide the technology advancement
and demonstration necessary to support major improvements in future
The ISTP.
The amended ISTP proposal has essentially three primary elements: a Shuttle Service Life Extension Program (SLEP), the Orbital Space Plane (OSP), and development of Next-Generation Launch Technology (NGLT), the latter two of which constitute a revised Space Launch Initiative (SLI).
Next-Generation Launch Technology.
The expansion of the former Generation 3 technology program into the NGLT, as well as the increased emphasis placed on this type of effort in the amended proposal, should be strongly supported. For many years the AIAA has decried the lack of an ongoing program to advance and upgrade space transportation systems; i.e., to have each successive generation of launch systems "in the pipeline" to succeed the current generation. This is relatively standard practice in both the automotive and the aviation industries. It is the lack of such a program in the past that has led to the current crisis in space transportation. The NGLT also incorporates technology advances being pioneered by the DoD, including those of the Director of Defense Research and Engineering's (DDRE) National Aerospace Initiative (NAI) and the Air Force Space Command's Operationally Responsive Spacelift (ORS) program, thereby strengthening not only the NGLT's technical base but also the potential user base for future launch systems.
One area for concern, however, is the NGLT's focus on hydrocarbon-fueled first-stage designs for the future Reusable Launch Vehicle (RLV). Although some offices of the Air Force (mainly the laboratory community) also favor hydrocarbon fuels, a definitive summer hypersonics study conducted by the Air Force Scientific Advisory Board in 2000 concluded that a hydrogen-fueled first stage would be optimum for both rocket-powered and airbreathing-propelled designs.
The planned NGLT also reduces the emphasis on rocket-powered launch systems in favor of airbreathing combined-cycle propulsion. Hence an excellent propulsion prospect, the robust high-thrust, high-pressure, high-performance expansion-cycle engine, a derivative of the ultra-reliable RL-10 (which has employed an expansion cycle with great success for four decades), will receive little or no attention in the NGLT.
Shuttle Service Life Extension Program.
The Shuttle SLEP should also be supported, because for the foreseeable future the Shuttle will be essential to ISS operations. With the loss of Columbia, we now have only three remaining orbiters to conduct these operations through at least 2012 [and possibly much later, because (a) the OSP is likely to encounter development problems that will delay its initial operational date and (b), as I will discuss later, Shuttle capability will be needed even after a successful OSP system is deployed]. Moreover, with this extended operational period, as I mentioned earlier, the likelihood of another Shuttle failure cannot be ignored. One key capability that ought to be explored in the SLEP (I don't know if NASA is planning this) is conversion of at least some missions to fully automated flight operations. More on this later.
Orbital Space Plane.
Now, the OSP. In effect, the OSP and its expendable launch vehicle have been moved chronologically ahead of the Generation-2 program in NASA's original SLI; that is, development of technologies for, and selection of, a reusable system that was to have replaced the Shuttle's function of carrying crew and cargo to and from the ISS at lower cost and with higher reliability. Elements of the old Gen-2 program now appear in the NGLT array of system applications, but the new plan postpones a decision on developing an RLV to 2009 - well into the development phase of the OSP. The OSP also replaces the function of the original CRV that was cancelled in 2001, as I've noted earlier.
So, does the proposed OSP/Evolved Expendable Launch Vehicle (EELV) architecture meet these needs of NASA's?
If we assume successful, on-time development of the OSP, that architecture does indeed meet those needs (except that the proposed initiation date for crew return capability [no later than 2010] is four years beyond the Russian commitment to provide that capability).
But that's a big "if." Let's look at the background.
X-33. NASA's termination of the X-33 single-stage-to-orbit technology demonstrator was certainly a correct decision (although as I told this Subcommittee on April 10, 2000, I really regret the expenditure of over $1 billion and several years on a program that, like the National Aerospace Plane, was doomed to failure by its overambitious goals right from the beginning).
Space Launch Initiative (SLI). NASA's subsequent decision to focus on a much more realistic two-stage-to-orbit architecture for the original SLI was also a wise one. As mentioned earlier, NASA has proposed to continue the evaluation of a reusable hydrocarbon-fueled first stage in the NGLT program, with significant cooperation from DoD. This evaluation could have some effect on the OSP development, in that the new ISTP proposal identifies the possibility of "OSP bridge to a new launcher" in 2016, but its major influence will be on the future (2009) NASA decision regarding a reusable booster. Contrary to NASA's and the DoD National Aerospace Initiative's focus on a hydrocarbon-fueled first stage, however, as I mentioned earlier, the Air Force Scientific Advisory Board's Summer Hypersonics Study in 2000 concluded that a hydrogen-fueled first stage, whether rocket-powered or airbreathing, is better than a hydrocarbon-fueled one. Hence consideration of hydrogen-fueled boosters should not be dropped from the NGLT.
Reusability. NASA should not, however, be blamed for postponing to 2009 a decision on development of a reusable launch system. The basis for that decision was sound: neither the commercial launch market nor the government launch market, even in combination, can support the estimated price tag of a new reusable launcher. Fortunately, while NASA was obeying the August 1994 Presidential directive to spend its time and money pursuing a too-ambitious reusable launch concept, the Air Force and its EELV contractors were able to develop two new expendable launcher families that now open up real possibilities to help solve NASA's near-term needs.
OSP/EELV Suitability. Back to the big "if." First, although the EELV program has demonstrated highly successful initial launches, it is still too early to tell if the EELVs can reliably support a major ongoing NASA requirement such as is posed by the ISS. The prospects are certainly good, and having two widely different vehicles rather than a single one is definitely a "plus." I'll return to this point later. Next, the OSP itself isn't even a "paper" vehicle yet. Although NASA has stated that it will be based on low-risk, current or near-current technology, we won't be able to evaluate its risk until there is better system and subsystem definition. Again, the concept makes good sense, but there is still much to be determined before one could place a soundly based bet on its success. NASA's record for on-budget, on-schedule development of new space transportation systems leaves some doubt as to whether the OSP will really become available on the proposed dates.
Cost. One troubling fact is the current OSP development cost estimate, which, although admittedly premature, ranges from $9 billion to $13 billion. Whatever happened to the $1.2-billion CRV, which was to have performed at least one of the OSP's missions - and the much more critical one at that, in terms of near-term ISS needs? NASA might be better off to focus solely at first on the ISS crew rescue requirement, which is urgently needed both to succeed the Russian Soyuz commitment beyond 2006 and to increase the size of the ISS crew to a viable complement, and put off adding the ISS access function (for both crew and cargo) until the OSP can demonstrate its ability to meet this first milestone. Certainly planning for the access function can begin, but it might make budgetary sense to conduct OSP development in an evolutionary manner, one step at a time, starting with the most critical ISS need. I will discuss this later.
Commercial Launch System Support.
One further point on the ISTP: the original Gen-2
program in the ISTP was also to have provided the technology basis and risk
reduction for a new reusable launcher that could begin to serve the entire
space launch market - commercial, civil, and military - by the end of this
decade. The OSP/EELV does not do that, and the new NGLT postpones possible RLV
risk-reduction efforts to 2004 - 2009. In essence, NASA has proposed to delay
its responsibility for risk reduction of low-cost reusable launch systems to
succeed the EELV and the Shuttle, postponing any decision on proceeding with
RLV development until 2009 at best.
Indeed, if conditions such as the commercial launch market, DoD interest, and budget concerns at that time are not
suitable, NASA may simply choose to put off any
consideration of reusable launch-system development until longer-term NGLT
program efforts are able to re-set the stage. This would leave the
Summary. In short, the revised ISTP is neither overly optimistic nor overly conservative. It is soundly based and should be supported. NASA's thinking in proposing the new OSP/EELV architecture as a second source to the Shuttle for access to and from the ISS does make sense. However, it is too early to assess the risk involved in implementing OSP development or the soundness of its cost estimates.
The highest risk in the OSP element of the ISTP is in the budget and schedule for full-scale OSP development to meet both the crew rescue and ISS transport functions. The highest risks in the NGLT element of the ISTP are (a) postponing RLV risk reduction research to support a go-no go decision in 2009, (b) over-emphasis on hydrocarbon-fueled first stage designs rather than a mix that includes hydrogen-fueled concepts, and (c) the reduced emphasis on advanced expansion-cycle rocket-powered launch systems. The highest risk in the SLEP element of the ISTP is the ability to provide crew safety for all flight modes over an extended period of operations.
To reduce these risks, I recommend (1) an evolutionary approach to OSP development, focusing first on the ISS crew return requirement and then on the transport function; (2) inclusion of hydrogen-fueled first-stage designs and expansion-cycle rocket technology development in the NGLT program, and (3) including in the SLEP (a) a method for reducing the Shuttle crew to four and designing the flight deck as an escape capsule for all flight modes, (b) providing an on-orbit thermal-protection-system inspection and repair capability, and (c) equipping the orbiters for optional fully autonomous operation.
Further considerations are discussed in my response to your subsequent questions.
(3) How might the
OSP alter NASA's reliance on, and the flight rate of the Space Shuttle? Should crew and cargo delivery be addressed
by separate systems? If the OSP and a
separate cargo delivery capability for logistics re-supply were developed,
would it be necessary to continue to fly the Space Shuttle? If so, what missions could not be
accomplished without the Space Shuttle?
If the Shuttle is required for the duration of the Space Station, is an
OSP that performs both crew rescue and crew transportation required?
NASA's Needs
Assuming the OSP/EELV architecture is demonstrated successfully by the proposed date of 2012, it is again necessary first to project NASA's needs for space transportation at that time. Those needs will continue to fall into two categories: robot spacecraft missions and those involving human crews. The latter category, at least for the foreseeable future, is almost wholly focused on servicing the ISS. Robot spacecraft will almost certainly continue to be launched primarily by ELVs, including EELVs for the more demanding missions. Hence the primary motivation for continuing Shuttle operations after the (assumed) initial successful operation of the OSP is its role in servicing the ISS.
Rationale for Continuing Shuttle Operations
There is one overriding reason for NASA to maintain the ability to conduct Shuttle fleet operations even if the OSP is initially successful. Space transportation will remain a high-risk activity for the foreseeable future, so reliance on a single system for ISS servicing (the OSP/EELV) could once more precipitate a crisis much like the present one should the OSP/EELV system fail or otherwise be grounded for an extended period. In simple terms, maintaining a viable second source of access to the ISS ensures its continued operation in the event of a launch system failure. The Russian and European access capabilities could conceivably help to ameliorate this need, but neither can be counted upon, and even if NASA were to resurrect the Alternate Access to Station program, its designs could be a useful supplement, but not the primary ISS delivery system.
Other subsidiary reasons for maintaining Shuttle operational capability are:
(1) It may become necessary to replace one or more of the major ISS elements (e.g., a solar-panel wing), which cannot be carried by any conceivable OSP design;
(2)
The sensitive economic situation in
(3) The Shuttle can provide services and facilities to the ISS that would not be available from an OSP; e.g., extra crew members for major repairs or replacement operations and to help conduct science experiments, water from Shuttle fuel cells, auxiliary equipment for short-term use on ISS research experiments, greater cargo capacity both up and down, etc.
NASA has also pointed out that with an operational OSP the Shuttle could focus on cargo missions to ISS, especially an automated version (discussed later), and could serve as a heavy lifter for future space exploration missions.
The only real negative, of course, is a big one: the additional cost of maintaining the Shuttle fleet in operational status. With a successful OSP available, the Shuttle could be pared down to perhaps one or two flights per year, and possibly even be maintained on a standby basis, flying only when its special capabilities are needed. However, not only would that raise safety concerns, but it doesn't reduce the required Shuttle infrastructure, which absorbs the bulk of Shuttle manpower and costs.
The safety issue could be somewhat ameliorated by having the Shuttle SLEP program explore reducing the number of crew members and providing the Shuttle with a suitable flight-deck escape capsule, which has been estimated to double the probability of crew survival. The best way to address both cost and safety issues of maintaining Shuttle capability, however, would be to equip the orbiters for fully autonomous operation, including automated docking at the ISS, as the Progress modules now do, and autonomous landings, as the old Soviet Buran did. For those missions in which a crew is needed at the ISS, they could be carried as passengers, as is planned for the OSP.
However, the real justification for continuing Shuttle operations is that the optimum implementation plan for the OSP would be an evolutionary one, as I will discuss later. Hence the Shuttle would be needed at least until the phased implementation of the OSP has been completed. The annual cost impact of Shuttle plus OSP for the next decade under such a plan needs to be established, of course, but the prospect of automating the Shuttle could conceivably reduce that impact, along with annual OSP evolutionary development budgets that are likely to be lower than the annual cost of implementing a fully capable OSP by 2012, if the present high OSP development cost estimates are to be believed.
Costs subsequent to 2012 are wholly dependent on the operating cost of the OSP/EELV architecture, which has yet to be even estimated, plus the cost of maintaining the Shuttles in flight-ready condition. Again, the operating cost benefits of a fully autonomous Shuttle should be factored into any trade study of parallel vs serial OSP development, as should all viable alternatives such as dependence on Russian, European, and commercial transport capabilities for both crew and cargo. But until NASA has some idea of the OSP/EELV operating cost, it does not make sense to commit to a full OSP developmental effort aimed at complete Shuttle replacement as soon as the OSP becomes operational.
Summary. In short, both the Shuttle and the OSP (or an equivalent Shuttle substitute) are required for assured access to, and egress from, the ISS. Second-level design requirements for the OSP could focus on either a common vehicle for both crew and cargo or, more likely, different versions having a common technology base. The Shuttle SLEP should include autonomous operation of the Shuttle for cargo functions and possibly also for ferrying crews to and from the ISS.
(4) Given that the
OSP program has not yet progressed beyond establishing the Level I
requirements, do you think NASA's plan for spending approximately $750 million
on technology demonstrations between FY03 and FY06 is justified? What technologies are the most critical to
demonstrate before proceeding to full-scale development?
The primary risk-reduction measure in mission assurance is elimination of single-point failure modes, which is best accomplished by a combination of heritage technologies, proven integrated system health-management techniques, and redundancy, substantiated by test or demonstration and other means of independent verification. A flight demonstration is by far the most effective mission assurance tool. Hence the planned X-37 demonstration program would be highly valuable to OSP development, provided it does indeed address the critical technologies NASA has identified. These include, among others, the thermal protection system; an autonomous, fast-response flight control system; an integrated health-management system, preferably embedded in an fault-tolerant vehicle architecture; and a crew rescue system. The proposed Demonstration of Autonomous Rendezvous Technology (DART) and pad-abort demonstrations are also of high value to OSP development.
It will not be easy to establish which of these technologies are mandatory, to what level of development they need to be brought, the level of development risk, and whether they are consistent with cost goals and OSP operational objectives.
Note that it is not necessary for NASA to wait until the X-37 technology demonstration program is complete before initiating OSP development, especially if the phased development approach I have suggested is used. [Indeed, the NASA plan calls for full-scale development of the OSP to begin in 2004, long before the scheduled completion of X-37 orbital testing]. However, in contrast to Shuttle development, the OSP development program should be structured so that useful technologies and processes demonstrated by the X-37 and the other planned demonstration programs can be readily inserted; i.e., the program should be "drop-in friendly" for new technologies. Again, this is best accomplished via a phased OSP development program.
(5) What design alternatives should NASA examine as it performs its concept studies for the OSP? What changes to the OSP program would you recommend to reduce the cost or accelerate the schedule?
Conceptual Designs.
NASA has already suggested that the design trade space for the OSP is essentially open; that is, it could be one or more reusable winged vehicles with passive or active thermal protection and powered or unpowered landing capability, or one or more expendable capsules employing ablative heat shields much like the Apollo capsule, or anything in between. Specific design options must await the formulation of second-level requirements; e.g., mass and dimensions of payload facilities; propulsion and power requirements; the nature of required medical care equipment and supplies; life-support requirements; integrated vehicle health-management system needs; ground facilities; crew escape system requirements; ISS docking, interface, and separation requirements; etc.
Design Approach.
NASA level-1 requirements specify that the OSP system must accommodate both rescue and transportation capability for no less than four crew members, although different versions of the system design might be used to perform these two functions. The rescue function must be available no later than 2010; the transport function no later than 2012. NASA's current proposal suggests that development of both functions be implemented in parallel, at an (admittedly premature) estimated cost of $9 - $13 billion. In the interest of reducing that cost, or at least stretching it out over a longer period to minimize the annual budget impact, it would seem to make sense to develop the required OSP functions serially rather than in parallel.
The urgent need
is for ISS crew rescue (which is actually needed by 2006 rather than the
specified 2010, in view of the end of
Although it might turn out that the transportation capability might indeed require different design features than the rescue capability, NASA should at the very least conduct trade studies on the parallel and serial design approaches before committing to full-scale development.
This
evolutionary development option, as well as NASA's proposed plan, requires an
operational Shuttle fleet until the OSP transport function is demonstrated, so
the trade study comparing the two approaches should include the Shuttle SLEP
options I mentioned earlier, such as fully autonomous operation and a crew
escape system. Also implicit in this trade study would be the viability of some
means for persuading
In conducting this (and other) trade studies NASA faces the challenge of "requirements creep;" that is, allowing requirements for technical demonstration of the transport phase to affect low-cost rescue options. NASA needs to re-establish cost credibility, and a properly phased, evolutionary program has the potential to do that.
Other Trade Studies. Other trade studies that should be conducted before proceeding to full-scale OSP development include the following:
Basing a Shuttle at the ISS. A temporary cost-saving option that should be explored is to extend the on-orbit lifetime of some of the Shuttle fleet so as to allow an orbiter to remain at the ISS for extended periods, thereby serving both functions required of the OSP. This approach has obvious disadvantages; i.e., it only postpones the requirement for a Shuttle replacement or supplement such as the OSP; it reduces Shuttle operational availability by keeping a third of the remaining fleet inactive for long periods; and it exacerbates the disruption that would occur following another Shuttle loss.
However, it would remove the time pressure on OSP
development, especially the 2006 deadline for ISS crew rescue capability, and
the presence of the Shuttle crew along with that of the ISS would provide full
crew capability for both ISS maintenance and science research; e.g., 10 crew
members (or 7, if the SLEP program recommends reducing the Shuttle crew to 4 so
as to facilitate crew escape). Also, NASA could reconsider its decision to
cancel the low-budget Alternate Access to Station program, whose designs could
be evaluated for their ability to supplement ISS cargo transport requirements
in lieu of more frequent Shuttle deliveries, especially after
Replacing Shuttle
Use of Modified Experimental Vehicles. Modifications that would be needed by the X-37 technology demonstrator or the Air Force's Orbital Maneuvering Vehicle (OMV) should be costed and evaluated for potential risks as interim solutions to each of the two OSP functions, including the use of multiple vehicles to accommodate the 4-person minimum requirement. Should either provide significant cost reductions vs the OSP without introducing unacceptable risk, this option could reduce the pressure on near-term OSP development. Note, however, that the cost of incorporating a crew compartment could turn out to be prohibitive, even for multiple vehicles.
Other experimental vehicles that could be evaluated for the cost and risk of performing part or all of the OSP function would be NASA's HL-20 and X-38 or the Air Force's X-24C. The Air Force has also contemplated developing a generic transatmospheric vehicle, which could be considered as a potential means for augmenting OSP functions.
Evaluation of Apollo-type Systems for both Crew Return and ISS Transport. A top-level assessment of this approach, completed in March 2003, suggests that it might be the lowest-cost option to meet OSP requirements in the shortest time, especially if development of return and transport capabilities were to be conducted serially, as I have suggested. The initial assessment report states, "The (assessment) team concluded unanimously that an Apollo-derived CRV (crew return vehicle) concept appears to have the potential of meeting most of the OSP CRV Level-1 requirements. An Apollo-derived CTV (crew transport vehicle) would also appear to be able to meet most of the OSP Level-1 CTV requirements with the addition of a service module." This option clearly needs to be evaluated in further detail.
(6) How does the decision to proceed with a design that is totally reusable, partially reusable, or expendable drive design complexity, development schedule, cost, and safety?
Reusability almost certainly implies increased design complexity, a longer development schedule, and increased development cost. The effect of reusability on safety, vis-à-vis expendable systems, has yet to be evaluated. Also, increasing the degree of reusability may or may not reduce operational costs, depending on specific design attributes. It is possible that reusability will, in the long term, prove to be a valuable attribute in terms of operating cost, turnaround time, and reliability, but there is as yet no evidence to support its nearer-term benefit. The often-cited concept of "aircraft-like" operations to realize these benefits requires a full understanding of what is meant by "aircraft-like." Airplanes are basically designed for cruise conditions while space launch vehicles are designed solely as accelerators. Comparing them without defining the basis of comparison is not realistic.
(7) Can the OSP
schedule be accelerated significantly without introducing unwarranted
risks? If so, what recommendations do
you have?
Once the Shuttle fleet returns to flight status, the urgent need is for crew return capability from the ISS. The evolutionary OSP development program I have suggested would accomplish this goal at the earliest possible time with low risk. The transport capability is not urgently needed as long as the Shuttle fleet is operational, and hence could be developed according to NASA's proposed schedule, or even stretched out somewhat to reduce both risk and annual budget impact,
(8) What challenges may NASA face in using an Expendable Launch Vehicle (ELV) as the boost vehicle for the OSP? Does the use of an ELV for human spaceflight pose an unacceptable risk?
Safety. The primary challenge is, of course, safety, but that is true for any launch system, not just expendables. The current failure rate (loss of mission) of the partly reusable Shuttle is now 2 in 114, or about 1.75%. The current failure rate of the Delta-2 ELV is 3 in 125, or about 2.4% and of the Atlas 2 - 5 ELV family (including 2A, 2AS, 3A, 3B, and 5) is zero in 64. (That is formally 0%, which is meaningless, but note that the Atlas-5 design failure rate is 0.45% compared with the Atlas-2AS design failure rate of 1.28%, with zero actual failures).
Single-point-failure tolerance is the key factor in launch-vehicle mission assurance. At least one of the EELV systems, the Atlas-5, is claimed to have full single-point-failure tolerance with the exception of its two main engines, the RD-180 first-stage engine and the RL-10 upper-stage engine. However, the RD-180 is probably the most robust large rocket engine ever built (its Russian designers claim it is even reusable), and the RL-10 has proven its robustness over 40 years of operations. Moreover, for components such as engines that are not subject to safe redundancy management, the use of "safe-life" designs and criteria can be implemented, as is common practice for aircraft jet engines (i.e., ground testing to certify design margins with appropriate safety margins). Finally, there are design options for the heavy-lift EELVs which provide engine-out redundancy that would eliminate even these single-point failure modes.
Note that any residual safety risk imposed by using an ELV can (and should) be ameliorated by incorporating an effective crew escape system in the OSP. Such a system (which may turn out to be the whole OSP itself) is likely to be specified in the second-level OSP requirements.
Hence safety is a challenge, but the risk of flying people on an ELV is certainly not unacceptable compared with the partly reusable Shuttle. Also note that the Russian Soyuz launcher, upon which we now rely for all crew-carrying operations to and from the ISS, is expendable, as were the Atlas, Titan, and Saturn rockets used for the Mercury, Gemini, and Apollo programs without a single launch failure.
Recurring Cost. A second potential challenge in using ELVs is the recurring cost per launch (after all, cost reduction was the prime motivation for developing the Shuttle and for creating the X-33 program and the original ISTP). Current estimated launch cost levels released by the Air Force's EELV System Project Office range from $80 million for the MLV models to $150 million for the HLV models. Although these costs could certainly increase if any special provisions need to be incorporated for OSP operations (e.g., human-rating, if NASA decides not to rely wholly on the OSP crew-escape system), the EELV cost range remains well within the Shuttle's cost-per-launch envelope.
Booster availability. A third, although lesser, challenge is booster availability. Having two widely different EELV families rather than a single one is definitely a "plus" in avoiding major downtime problems, although there are some cost implications (fortunately not major ones) associated with ensuring OSP compatibility with both families. It will also be necessary to coordinate launch manifesting of the EELV systems with both military and commercial customer demands, but this has never been a serious problem with prior ELV families.
Flight Control Issues. If the OSP design turns out to be a lifting-body or
winged configuration, adequate control authority of the EELV booster during
transonic flight could become an issue, especially if NASA's current plan to
launch the X-37 technology demonstrator inside a fairing is pursued. The Titan
vehicle that was to be used to launch DynaSoar back in the 1960s required the
addition of fins for the necessary control authority and a strengthened
structure to accommodate higher bending moments. If the EELVs will require
comparable "fixes," there will be cost and schedule implications, which could
be exacerbated if no information is available from an encapsulated X-37 flight
demonstration. If the OSP design ends up as a ballistic Apollo-like capsule,
there will be cross-range restrictions on the return-to-Earth launch window.
*******************
That completes my answers to the questions posed in your invitation. However, I have a recommendation for the scenario that NASA should pursue for optimum servicing of the ISS through the completion of its mission, which is estimated to be 2020 - 2025..
The first task, of
course, is to resolve the issues surrounding the failure of
The Shuttle SLEP effort
should be initiated immediately, and should include the following elements, to
be implemented as soon as possible without excessive disruption of service to
the ISS: (1) Converting the 4-person flight deck to an escape capsule suitable
for egress during all flight modes; (2) Providing the orbiters with the option
for fully autonomous operation; (3) Providing a method for inspecting and, if
necessary, repairing the thermal protection system on orbit; and (4) Equipping
two orbiters for orbital stays of at least four months. Depending on the
availability of adequate budget resources, a replacement could be built for
As soon as one orbiter is equipped for long-term stays on orbit (which should be prior to 2006), that orbiter should be flown to the ISS and based there for four or more months. Until the OSP crew-return version has been demonstrated, the two orbiters suitably equipped should continue to provide that capability, alternating with each other.
Meanwhile, the NGLT program should be pursued and trade studies followed by evolutionary development of the OSP should be conducted, beginning with the crew return function and subsequently proceeding to the crew transport (and possibly cargo transport) functions. (Pending results of the design trade studies, of course, the lowest-cost, nearest-term option is likely to turn out to be an Apollo-derived design). OSP flights to the ISS should begin as soon as the crew return function has been demonstrated, relieving the Shuttles of the need for on-orbit stays.
When the OSP transport function has been demonstrated, the Shuttles should be placed on a standby basis for autonomous operation, to fly if and when needed for lifting large payloads to the ISS, for crew-carrying and cargo-carrying during any OSP standdown, and also for ambitious NASA science and exploration missions in the Solar System.
END OF STATEMENT
AIAA
American
BRIEF BIOGRAPHY: JERRY GREY, PhD
DIRECTOR, SCIENCE AND TECHNOLOGY POLICY
Dr. Grey received his Bachelor's degree in Mechanical Engineering and his Master's in Engineering Physics from Cornell University; his PhD in Aeronautics and Mathematics from the California Institute of Technology.
He was Instructor in thermodynamics
at Cornell, engine development engineer at Fairchild, Senior Engineer at
Marquardt, and hypersonic aerodynamicist at the GALCIT 5-inch hypersonic wind
tunnel. He was a professor in
Dr. Grey is the author of twenty books and over 400 technical papers in the fields of space technology, space transportation, fluid dynamics, aerospace policy, solar and nuclear energy, spacecraft and aircraft propulsion, power generation and conversion, plasma diagnostics, instrumentation, and the applications of technology. He has served as consultant to the U.S. Congress (as Chairman of the Office of Technology Assessment's Solar Advisory Panel and several space advisory panels), the United Nations (as Deputy Secretary-General of the Second UN Conference on the Exploration and Peaceful Uses of Outer Space in 1982), NASA (as a member of the NASA Advisory Council), the Department of Transportation (as Vice-Chairman of the Commercial Space Transportation Advisory Committee), the Department of Energy (as a member of the Secretary of Energy Advisory Board), and the U.S. Air Force, as well as over thirty industrial organizations and laboratories. He was Vice-President, Publications of the AIAA, Chairman of the Coordinating Committee on Energy of the American Association of Engineering Societies, a Director of the Scientists Institute for Public Information, Vice-President of the International Academy of Astronautics, and President of the International Astronautical Federation.
He is listed in over twenty biographical publications, and has received national awards from the Aviation/Space Writers Association and the American Astronautical Society.
Phone 703/264-7500 - FAX 703/264-7551 - Web Site: http://www.aiaa.org
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