The Air Force has canceled funding for future phases of its Reusable Booster System (RBS) Pathfinder program to develop a flyback reusable lower stage. Above: a concept by Lockheed Martin, one of three companies what won funding for initial concept design work for the program. (credit: Lockheed Martin) What is the future of the RLV?

A decades-long goal of the space community, from engineers to policymakers to advocates, has been the development of reusable launch vehicles (RLVs). From an operational perspective, this emphasis makes perfect sense: after all, in most other modes of transportation, like cars, planes, and ships, we don’t throw away vehicles after a single use. A reusable launch vehicle could allow for far lower per-flight costs than existing, expendable rockets, as the manufacturing costs could be amortized over dozens or even hundreds of flights. This, in turn, could dramatically alter the economics of spaceflight by opening up markets not accessible at current launch costs or those that require transportation to and from orbit. Within the last year, RLV development has achieved a rather ignominious milestone: the US government has, in effect, gotten out of the RLV business. In practice, though, the promise of RLVs has remained just that: a promise as yet unfulfilled. The Space Shuttle demonstrated that it was technically possible to build a launch vehicle that is at least partially reusable. The external tank, of course, was not reused, and some might argue that it’s more accurate to call the shuttle orbiter and its solid rocket boosters refurbishable rather than reusable given the large amount of labor required to prepare then for flight again. However, the shuttle fell fall short of the high flight rates and low per-flight costs bandied about during its development. During the three decades that the shuttle flew, both NASA and the US military supported various projects to develop next-generation RLVs that might come closer to realizing the goals of low-cost space access. This resulted in an alphabet soup of acronyms and designations, including NASP, DC-X, X-33, X-34, and SLI. All of these programs, though, died of technical, budgetary, or other programmatic reasons, falling far short of those space access goals. And now, within the last year, RLV development has achieved a rather ignominious milestone, one that has largely escaped the attention of the space community: the US government has, in effect, gotten out of the RLV business. For the first time since the Space Shuttle program’s inception more than four decades ago, neither NASA nor the US military is operating or actively developing anything that could be considered a reusable launcher, with no firm prospects for such efforts to resume for the indefinite future. The highest profile event in this RLV anti-development, if you will, is the retirement of the only active orbital RLV, the Space Shuttle, last year. But long before Atlantis rolled to a stop on the runway at the Kennedy Space Center last July at the conclusion of the final shuttle mission, RLV activities within NASA had also come to a halt. Back in 2001, NASA started the Space Launch Initiative program—after the demise of the earlier X-33 and X-34 RLV vehicle programs—with the goal of developing a “second generation” RLV (the shuttle being the first generation). NASA’s plan for SLI was to develop technologies and system architectures for such a vehicle that would result in a recommendation of a “final architecture” of such a vehicle by 2006 and “operations by early next decade”—in other words, by about now. SLI, though, fell victim to the change in direction at NASA precipitated by the Columbia accident and subsequent development of the Vision for Space Exploration. With a focus on a return to the Moon, development of a second-generation RLV didn’t fit. The launch vehicles NASA has worked on since then—the Ares 1 and 5 rockets under Constellation, and, more recently, the Space Launch System (SLS)—have not required reusability. Ironically, while the initial variants of SLS will make use of Shuttle-heritage hardware designed for reusability, such as the Space Shuttle Main Engines, those components will be thrown away after each launch. While NASA retired the shuttle and ended other RLV efforts, the Air Force kept up RLV development, albeit at a very low level, with some small technology development programs, most notably the Reusable Booster System (RBS). That program sought to develop a reusable lower stage—launching vertically and landing horizontally on a runway, using a “rocketback” maneuver to land back at the launch site—and an expendable upper stage by the end of the decade. Last December the Air Force Research Laboratory (AFRL) awarded RBS Pathfinder contracts to Andrews Space, Boeing, and Lockheed Martin to begin initial design studies of such a system. The RBS effort, though, ended not long after it started. In October, the Air Force announced that it had zeroed out funding for the program as part of service-wide budget cuts. “The funding resources for Pathfinder were cut from the future Air Force budget, not diverted to other programs,” according to AFRL. The program is scheduled to wrap up in December, after which Air Force personnel involved in the project will be reassigned to other programs. Even before that October announcement, AFRL officials indicated that the RBS Pathfinder program would not proceed beyond its initial phase. “Phase two has been discontinued,” said Jeffrey Zweber of AFRL at the AIAA Space 2012 conference in Pasadena, California, in September. “The Air Force has decided not to proceed with the subsequent phases of the program.” Those subsequent phases were intended to support development and testing of RBS technology, with a particular emphasis on demonstrating the rocketback maneuver needed to bring the first stage back to the launch site. Zweber said the decisions were based on broader budgetary uncertainty and not out of any concerns about the technical feasibility of an RBS system. The three contractors “presented a level of fidelity in their designs that is beyond what would be considered a typical conceptual design,” he said. “The program team was satisfied that we were going to get at least one proposal that was a feasible solution” that would allow the program to proceed to the next phase. With the discontinuation of RBS Pathfinder, there is no major RLV development effort in progress by either NASA or the US military today. The Air Force’s decision not to proceed with the RBS effort came around the same time as the release a National Research Council report on the program. The report raised several concerns about the program, including uncertainties in the business case for an RBS system and technology risks. It concluded that because of those issues, “it is premature for Air Force Space Command to program significant investments associated with the development of a RBS capability,” although it did “strongly endorse” continued R&D work on advanced launch technologies. With the discontinuation of RBS Pathfinder, there is no major RLV development effort in progress by either NASA or the US military today. There are, to be certain, R&D efforts underway that could be applicable to future RLVs. The Air Force is working on hypersonics technology, but, as Aviation Week noted in its current issue, that effort is intended to support future missiles and aircraft, and not explicitly launch systems. And the X-37B, whose third flight is now scheduled for launch next month, has drawn parallels to the shuttle. However, it’s more accurate to call it a reusable spacecraft, since it’s entirely reliant on other, expendable vehicles—namely, the Atlas V—to reach space. Barring another change in direction in military or civil space programs, the future of the RLV may depend on efforts in the commercial sector. (Other nations have thus far shown little interest in reusable launchers; India has proposed developing an RLV by 2025 but many treat those plans skeptically, given the challenges India has encountered building more conventional launchers.) And, fortunately for RLV advocates, there is some work—or, at least, plans for such work—by several companies. Perhaps the most ambitious effort is by SpaceX. Last fall, the company announced plans to develop a reusable version of its Falcon 9 rocket. In animations released by the company, the reusable Falcon 9 would look similar to the existing, expendable version. However, the two stages would each be able to reenter, deploy landing legs, and touch down vertically under rocket power. As part of its RLV development efforts, SpaceX has developed a demonstration vehicle called Grasshopper: a Falcon 9 first stage outfitted with landing legs and a single Merlin rocket engine. On September 21, the Grasshopper made its first, very short test flight at SpaceX’s rocket test facility near McGregor, Texas, briefly rising off the pad before setting back down. It made a second, higher test flight on November 1, rising 5.4 meters off the pad during the eight-second flight. The company said a hover flight to an altitude of about 30 meters is planned “in the next several months.” “There are a bunch of entrepreneurs out there, some of them with a lot more money than the Air Force has,” quipped AFRL’s Jess Sponable. Some reusable suborbital vehicle developers also have their eyes on evolving their designs into orbital RLVs. XCOR Aerospace, for example, has hinted it has plans for an orbital vehicle as a follow-on to its Lynx suborbital spaceplane it is currently building. Company representatives, responding to media reports that the company has long-term plans for suborbital point-to-point passenger travel, said their interest is instead on orbital flight, which has similar energy requirements but a better business case. “You make a lot more money flying to orbit than you do flying from Europe to Shanghai,” said Jim Muncy, who represented XCOR at the SpaceVision 2012 conference in Buffalo, New York, earlier this month. “We would prefer to be in the profitable industry of flying people to orbit.” “There are a bunch of entrepreneurs out there, some of them with a lot more money than the Air Force has,” quipped AFRL’s Jess Sponable, a veteran of several RLV development efforts, at the Space 2012 conference. He cited work by SpaceX, Virgin Galactic, and Blue Origin, all of whom have aspirations for reusable vehicles. “You’re going to see AFRL work really hard in the future to work with these kinds of companies and try and accelerate the progress that they can make.” Lest people be relieved that the future of the RLV is in the safe hands of entrepreneurial companies, recall that, about 15 years ago, an earlier wave of companies were making similar plans for RLVs. Those vehicles, like the Rotary Rocket’s Roton, Kistler Aerospace’s K-1, and Space Access LLC’s SA-1, among others, failed to get off the ground (excluding very low altitude test flights by Rotary’s Roton ATV, which was effectively a helicopter.) Funding for these ventures dried up because of a mix of technical issues and disappearing markets, as the numerous low Earth orbit satellite systems that were to be the main customers for these vehicles failed to materialize. Could the same problems happen again? Sponable noted that current efforts aren’t going as smoothly as these companies originally promised. “They’re all overbudget, they’re all spending more money than they thought, and they’re all taking longer to get the hardware and flight systems built than they claimed, and by large amounts,” he said. “This is a tough problem.” However, the approach many of these new companies are taking—starting suborbitally and then incrementally moving to orbital vehicles—may be more sustainable, allowing them to gradually retire technical risk while generating revenue from suborbital markets like tourism and research. SpaceX is taking a different technical approach—taking an existing orbital vehicle and retrofitting reusability into it—but also has the potential for incremental progress rather than developing a full-fledged orbital RLV from scratch. The future of the RLV—assuming there is one—is more likely to involve some degree of cooperation between the public and private sectors. Rather than a single, monolithic RLV development effort by NASA or the Air Force, these organizations may instead help support private-sector RLV efforts through technology development as well as the stimulation of markets big enough to close the business case for orbital RLVs. Charles Miller, former NASA senior advisor for commercial space, has argued that markets are a bigger issue than technologies for RLVs, and that delivering propellant to orbital depots to support deep space exploration or other missions might be the ideal initial market for such vehicles (see “How the US can become a next generation space industrial power”, The Space Review, November 5, 2012). One thing is clear: in an era of constrained budgets and competing priorities, there seems to be little appetite within government for another large RLV development program as has been attempted several times over the preceding decades. The future of the RLV will, by necessity, be very different from its past. 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