Spaceplanes represent a fascinating intersection of aviation and rocketry, blending the horizontal takeoff and landing capabilities of aircraft with the orbital reach of spacecraft. These vehicles aim to make space access more efficient, reusable, and cost-effective compared to traditional vertical-launch rockets. While the concept dates back decades, recent advancements, particularly from companies like Polaris Spaceplanes, are pushing the boundaries with innovative technologies such as aerospike engines. This article explores the history of spaceplanes, their current developments, and the ongoing saga of Polaris’ Mira project, which has overcome early setbacks to achieve groundbreaking milestones.
A Brief History of Spaceplanes
The idea of a spaceplane – a vehicle that can fly into space and return like an airplane – emerged in the early 20th century, but practical development accelerated during the Space Race. One of the earliest operational examples was the North American X-15, a rocket-powered aircraft that flew in the 1950s and 1960s. Launched from a B-52 bomber, it reached the edge of space, achieving speeds over Mach 6 and providing valuable data on hypersonic flight.
The most iconic spaceplane remains NASA’s Space Shuttle, which first launched in 1981. Over its 30-year program, the Shuttle fleet – Columbia, Challenger, Discovery, Atlantis, and Endeavour – completed 135 missions, deploying satellites, building the International Space Station, and conducting scientific research. The Soviet Union responded with the Buran, a similar design that flew uncrewed in 1988 but was canceled due to budget constraints.
In the post-Shuttle era, the U.S. Air Force’s Boeing X-37B has become a key player. This autonomous, reusable spaceplane, resembling a mini-Shuttle, has conducted multiple long-duration orbital missions since 2010, testing technologies for future space operations. Other historical efforts, like the British Skylon or NASA’s X-33 VentureStar, explored single-stage-to-orbit (SSTO) concepts but faced technical and funding hurdles.
Today, spaceplanes are experiencing a renaissance, driven by the need for rapid, reusable access to space. Companies like Sierra Space with its Dream Chaser and private ventures are developing vehicles for cargo and crew transport, while hypersonic spaceplanes promise ultrafast global travel and on-demand satellite launches.
The Promise and Challenges of Aerospike Engines
At the heart of many modern spaceplane designs is advanced propulsion, particularly the aerospike engine – a concept theorized in the 1950s but only recently tested in flight. Unlike conventional bell-shaped nozzles, which are optimized for a single altitude and lose efficiency as atmospheric pressure changes, aerospike engines use a spike-shaped design where exhaust expands against ambient air, self-adjusting for optimal thrust from sea level to vacuum. This “altitude compensation” could eliminate the need for staging, making engines lighter and more efficient.
Despite its advantages, the aerospike remained largely theoretical due to cooling and manufacturing challenges. NASA’s X-33 program in the 1990s attempted to use linear aerospikes but was canceled in 2001. Recent breakthroughs in 3D printing and materials science have revived interest, with startups leading the charge.
Polaris Spaceplanes: From Crash to Triumph in the Mira Project
German startup Polaris Spaceplanes has emerged as a frontrunner in spaceplane innovation, focusing on reusable vehicles powered by aerospike engines. Their Mira series aims to demonstrate hybrid propulsion – combining jet turbines for takeoff and aerospike rockets for high-altitude and spaceflight – paving the way for commercial operations.
The project hit an early roadblock in 2023 when the Mira I prototype crashed seconds after takeoff during its debut flight. Caused by a crosswind and nosewheel swerve, the incident destroyed the fiberglass airframe before the AS-1 LOX-kerosene aerospike engine could ignite. Despite the setback, internal systems survived, and Polaris quickly pivoted to larger prototypes.
In contrast, the scaled-down Mira-Light, a 2.5-meter electric-powered model, completed 15 successful test flights in 2023, validating aerodynamics and controls for future iterations. This data informed the development of Mira II and III, both featuring five-meter wingspans, four jet turbines, and the AS-1 engine.
By mid-2024, Polaris received the airframes for Mira II and III, and in October 2024, Mira II achieved its first turbine-powered flight. A major milestone came in November 2024, when Mira II conducted the world’s first in-flight firing of an aerospike engine, lasting three seconds and generating 900 newtons of thrust. Further tests in December 2024 showcased a 3D-printed aerospike variant, highlighting manufacturing efficiencies.
Polaris’ ambitions extend beyond prototypes. In February 2025, they secured a German government contract from the Federal Office of Bundeswehr Equipment, Information Technology, and In-Service Support (BAAINBw) to design a hypersonic research vehicle for defense and scientific applications. In June 2025, the company raised an oversubscribed €5.3 million in funding to support development and commercial rollout. Additionally, Polaris announced an exclusive cooperation with Diehl Defence to integrate IRIS-T missiles into an unmanned airborne strike platform, expanding the vehicle’s potential for military uses.
The company plans to fly the eight-meter Nova prototype in 2026, a precursor to the commercial Aurora spaceplane. Aurora, envisioned as a 6.7-meter vehicle capable of carrying 10 tons to suborbital speeds, could begin missions by 2026 or 2027, offering payload delivery or even passenger flights.
Broader Implications for the Space Industry
Polaris’ progress underscores the potential of spaceplanes to revolutionize space access. By integrating aerospikes, these vehicles could achieve SSTO capabilities, reducing costs and turnaround times. Challenges remain, including thermal management at hypersonic speeds and regulatory hurdles, but successes like Mira II’s aerospike test signal viability.
In the wider landscape, spaceplanes could enable point-to-point Earth travel in hours, bolster national security through rapid global strike, and support the growing space economy. As Polaris and others advance, the dream of routine, airplane-like spaceflight inches closer to reality.
The Mira crash raised concerns, but Polaris’ resilience has turned it into a stepping stone. With ongoing tests, government backing, and new partnerships, spaceplanes are poised to redefine humanity’s reach beyond Earth.
