In the late 1970s, NASA and Rockwell International embarked on a groundbreaking study to design a single-stage-to-orbit (SSTO) spaceplane capable of revolutionizing space transportation. The concept, known as the Star-Raker, was an enormous horizontal takeoff and landing vehicle that aimed to carry heavy payloads to low Earth orbit while offering unparalleled operational flexibility. Although the Star-Raker never progressed beyond the conceptual stage, its innovative design and ambitious goals continue to captivate the imagination of space enthusiasts and engineers alike.
The Need for a New Space Transportation System
During the 1970s, NASA recognized the need for a more efficient and cost-effective means of transporting payloads to orbit. The Space Shuttle, which was under development at the time, represented a significant advancement in reusable space transportation. However, its two-stage design and limited payload capacity left room for improvement. The Star-Raker concept emerged as a potential solution, promising to deliver larger payloads to orbit using a single-stage vehicle.
The primary motivation behind the Star-Raker was to support the construction of large-scale space-based solar power satellites. These ambitious structures were envisioned to collect solar energy in orbit and beam it back to Earth, providing a clean and renewable source of power. However, building these satellites would require launching thousands of tons of hardware into space, a feat that was beyond the capabilities of existing launch systems.
NASA commissioned studies to explore the feasibility of various space transportation architectures that could meet the demanding payload requirements of the solar power satellite program. Rockwell International, a major aerospace contractor and the primary contractor for the Space Shuttle, proposed the Star-Raker concept as a potential solution.
The Star-Raker Design
The Star-Raker was a colossal spaceplane, measuring 94.5 meters (310 feet) in length and boasting a wingspan of 110 meters (360 feet). Its design incorporated advanced materials and propulsion technologies to enable SSTO capability. The vehicle featured a unique “wet wing” design, where the wings served as integral fuel tanks, reducing the overall structural mass.
One of the most striking features of the Star-Raker was its swing-nose design. The nose section, which housed the crew compartment, could pivot sideways to expose the payload bay for loading and unloading. This innovative approach allowed for efficient cargo handling and eliminated the need for complex docking mechanisms.
The Star-Raker’s propulsion system was a hybrid of air-breathing engines and rocket engines. It featured ten high-bypass, hydrogen-fueled, supersonic turbofan/air-turbo-exchanger/ramjet engines for atmospheric flight, and three liquid oxygen/liquid hydrogen rocket engines, similar to those used on the Space Shuttle, for the final boost into orbit. This combination of engines was intended to maximize efficiency and reduce the amount of propellant needed to reach orbit.
The air-breathing engines would operate from takeoff to Mach 6, providing efficient propulsion through the dense lower atmosphere. As the vehicle climbed and the atmosphere thinned, the engines would transition to ramjet mode, allowing the Star-Raker to reach hypersonic speeds. Once the ramjets could no longer provide sufficient thrust, the rocket engines would ignite, propelling the vehicle into orbit.
Operational Concept
The Star-Raker was designed to take off horizontally from a conventional runway, much like a large aircraft. After climbing to a high altitude, the vehicle would accelerate to hypersonic speeds using its air-breathing engines. Once the atmosphere became too thin for air-breathing propulsion, the rocket engines would ignite, propelling the Star-Raker into orbit.
Upon completing its mission, the Star-Raker would reenter the atmosphere and glide back to Earth, landing horizontally on a runway. This operational concept offered several advantages over traditional vertical launch systems, including increased flexibility in launch and landing sites, reduced weather constraints, and the potential for rapid turnaround between missions.
The Star-Raker’s impressive payload capacity of 100 metric tons (220,000 pounds) to low Earth orbit would have enabled it to support a wide range of missions, including the construction of large space structures, the deployment of satellite constellations, and the resupply of orbital outposts. Its ability to land at conventional airports and be quickly refueled and reloaded would have made it an attractive option for high-frequency launch operations.
Rockwell estimated that a fleet of 30 Star-Rakers, operating from a single runway, could deliver the 1,600 metric tons of payload per day required for the solar power satellite program. In contrast, a vertically launched two-stage-to-orbit system would have required ten launch pads and extensive refurbishment between missions to achieve the same launch rate.
Technical Challenges and Limitations
Despite its promising potential, the Star-Raker faced significant technical challenges that ultimately prevented its development beyond the conceptual stage. The most significant hurdle was the development of a practical SSTO propulsion system. While the combination of air-breathing engines and rocket engines offered theoretical advantages, the technology to make it a reality was still in its infancy.
The air-breathing engines, particularly the ramjets, required significant advancements in materials and design to withstand the extreme temperatures and pressures encountered at hypersonic speeds. The transition from turbofan to ramjet mode also presented complex control and stability challenges.
The rocket engines, while based on proven Space Shuttle technology, would have had to operate in a more demanding environment. The Star-Raker’s SSTO design meant that the engines would have to ignite at high altitudes and velocities, requiring precise timing and control.
Another challenge was the development of lightweight, high-temperature materials capable of withstanding the extreme conditions encountered during atmospheric reentry. The Star-Raker’s large size and unique design posed additional challenges in terms of structural integrity, aerodynamic stability, and thermal management.
The swing-nose design, while innovative, also presented significant engineering challenges. The mechanism would have had to withstand the stresses of launch and reentry while maintaining a secure seal to protect the payload bay. The logistics of loading and unloading cargo through the swing-nose also required careful consideration.
Cost and Feasibility
Despite the technical challenges, Rockwell estimated that the Star-Raker could achieve a cost per kilogram of payload to low Earth orbit of $22 to $33 in 1978 dollars (equivalent to approximately $100 per kilogram in 2022). This cost estimate was comparable to projections for other advanced launch systems, such as SpaceX’s Starship.
However, the development costs for the Star-Raker would have been substantial, given the need for significant advancements in propulsion, materials, and structures. The program would have required a long-term commitment and sustained funding to bring the concept to fruition.
Ultimately, the Star-Raker did not progress beyond the conceptual stage. NASA’s focus shifted to the Space Shuttle program, which was seen as a more achievable near-term solution for reusable space transportation. The solar power satellite program also faced its own challenges and did not receive the level of funding and support needed to justify the development of a dedicated launch system like the Star-Raker.
The Legacy of the Star-Raker
Although the Star-Raker never became a reality, its influence can still be seen in subsequent SSTO and spaceplane designs. The concept of a hybrid propulsion system, combining air-breathing engines with rockets, has been explored in various forms, such as the National Aero-Space Plane (NASP) and the Skylon spaceplane.
The Star-Raker also served as an inspiration for future heavy-lift launch vehicle concepts, highlighting the potential benefits of reusable, high-capacity space transportation systems. While the technical challenges of SSTO remain formidable, the vision embodied by the Star-Raker continues to drive innovation and exploration in the field of space transportation.
The Star-Raker study also contributed to the ongoing discussion about the feasibility and desirability of space-based solar power. While the concept remains controversial and faces significant technical and economic hurdles, the idea of harnessing the sun’s energy in space and beaming it back to Earth continues to capture the imagination of scientists, engineers, and policymakers.
Summary
The Star-Raker represents a fascinating chapter in the history of NASA’s pursuit of advanced space transportation systems. Its ambitious design and impressive capabilities captured the imagination of engineers and space enthusiasts, offering a glimpse into a future where spaceplanes could routinely carry heavy payloads to orbit. Although the concept never materialized, the lessons learned from the Star-Raker study have contributed to the ongoing development of reusable launch vehicles and the quest for more efficient and cost-effective access to space.
As we look to the future of space exploration, the spirit of innovation and bold thinking exemplified by the Star-Raker remains as relevant as ever. While the challenges of SSTO flight are significant, the potential benefits of a fully reusable, high-capacity space transportation system continue to drive research and development efforts around the world. The legacy of the Star-Raker serves as a reminder of the importance of dreaming big and pushing the boundaries of what is possible in the realm of space travel.
The Star-Raker also highlights the complex interplay between technological advancement, economic feasibility, and political will in the pursuit of ambitious space projects. The concept emerged at a time when the promise of space-based solar power and the need for a robust space transportation infrastructure captured the imagination of policymakers and the public alike. However, the realities of budgetary constraints, competing priorities, and the inherent challenges of spaceflight ultimately limited the scope and scale of these endeavors.
As we continue to explore the possibilities of space-based solar power and other ambitious space projects, it is important to draw lessons from the Star-Raker and similar concepts. While technical feasibility is a critical factor, it is not the only consideration. Economic viability, political support, and public engagement are equally important in determining the success and sustainability of these endeavors.
The Star-Raker may have remained a concept on paper, but its legacy lives on in the ongoing quest to push the boundaries of space transportation and harness the vast potential of space-based resources. As we continue to dream big and reach for the stars, we can draw inspiration from the visionaries who dared to imagine a future where spaceplanes like the Star-Raker could make routine access to space a reality.
