Copenhagen Suborbitals

Copenhagen Suborbitals is a Danish nonprofit space program focused on developing the capability to send a person above the internationally used 100-kilometre boundary of space on a suborbital flight. Founded in 2008 by aerospace designer Kristian von Bengtson and entrepreneur and amateur rocketry pioneer Peter Madsen, the organization operates as a volunteer and crowd-funded project rather than as a conventional aerospace company. It has publicized much of its engineering work through lectures, blogs, demonstrations, and open project documentation, giving it an unusual position in the space sector: it combines experimental launch development, citizen engineering, education, and public fundraising. The program’s work has progressed through several generations of propulsion systems, vehicles, capsules, and launch infrastructure. Early development concentrated on hybrid propulsion and the HEAT-1X vehicle, which was intended to carry the Tycho Brahe capsule. A 2010 launch attempt failed to ignite because of a problem involving the liquid-oxygen valve and its heating system. The following year, HEAT-1X Tycho Brahe lifted off from the organization’s floating Sputnik platform, but an unexpected pitch-over required an early engine shutdown. The vehicle reached approximately 2.8 kilometres rather than its planned altitude, while the uncrewed capsule was recovered after landing in the sea. The organization subsequently tested additional vehicles and propulsion concepts, including the SMARAGD sounding rocket, the HATV hybrid test vehicle, the TM-65 liquid engine family, and the HEAT-2X test vehicle. HEAT-2X was not launched after a 2014 static-fire accident caused an engine failure, a large ethanol fire, and significant vehicle damage. These experiences contributed to a strategic change from earlier hybrid and other liquid-propellant concepts toward bi-propellant engines using liquid oxygen and ethanol. The Nexø series became the principal technology-demonstration path toward a future crewed vehicle. Nexø I flew in 2016 using a BPM-5 engine, and Nexø II launched in 2018. The BPM-2 and BPM-5 engines were small liquid-propellant systems used for manufacturing, test-stand, and flight development. Copenhagen Suborbitals later concentrated on the larger BPM-25 engine class for Spica, its planned crewed rocket. Spica is designed as a 12–14 metre vehicle with a 950-millimetre diameter and a capsule derived conceptually from the organization’s earlier tubular spacecraft. Its development includes home-built guidance electronics and software, thrust-vector control, and clustered BPM-25 engines using liquid oxygen and ethanol. The group also maintains a recruitment and training dimension. Launched in 2021, the Recruits Initiative gives new participants practical experience in rocket design, propulsion, manufacturing, electronics, and project work. Its RC-A1 Recruit Rocket is a small single-stage demonstrator developed by the recruits team and uses a refined BPM-5-derived engine together with a dynamic pressure-regulation system. The project is intended both to develop future contributors to Spica and to strengthen Danish technical capabilities relevant to the space and defense industries. Copenhagen Suborbitals’ operations are organized around annual general assemblies at which volunteers elect a chair and board. As of September 2024, the program reportedly had 63 volunteers, with Jørgen Skyt serving as chairman. The organization’s launch activities take place from maritime infrastructure in the Baltic Sea near Bornholm, outside Danish territorial waters, using the mobile launch platform Sputnik and the support vessel MHV Hjortø. Its long-term objective remains a privately developed Danish suborbital human spaceflight, although the crewed Spica vehicle and its capsule had not yet reached flight readiness as of 2024.

Copenhagen Suborbitals was established in 2008 as a nonprofit, crowd-funded Danish space project by Kristian von Bengtson and Peter Madsen. From the beginning, the program sought to make its development process visible through public lectures, online writing, and technical demonstrations. Its central ambition was to develop a Danish-built rocket and spacecraft capable of carrying a human on a suborbital trajectory above 100 kilometres. The early program investigated several propulsion approaches. Between 2008 and 2012, the team worked primarily with hybrid rockets using liquid oxygen as oxidizer. The HEAT-1X vehicle was designed to carry the Tycho Brahe capsule. Early work examined paraffin fuel, but a 2010 ground test showed that the paraffin did not behave as intended. A polyurethane formulation supplied the required impulse but produced severe oscillations. The program also performed many engine tests at its Refshaleøen facility and briefly examined a nitric-acid and furfuryl-alcohol concept. In 2012, the organization decided to focus on liquid bi-propellant engines using liquid oxygen and ethanol. The first launch campaign took place in 2010 from the maritime launch area near Bornholm. The HEAT-1X vehicle and its uncrewed crash-test passenger, Rescue Randy, were carried on the Sputnik floating launch platform. The launch attempt on 5 September failed because the liquid-oxygen valve did not start properly, reportedly due to inadequate heating. The widely discussed use of a consumer hair dryer to help warm the valve became an emblem of the project’s improvised, low-budget engineering style, although the immediate problem involved the power supply for the heating arrangement. A second campaign in 2011 produced the organization’s first flight. HEAT-1X Tycho Brahe lifted off on 3 June from Sputnik, supported by the naval home-guard vessel MHV Hjortø. The rocket unexpectedly tilted toward the horizontal, so mission control commanded an early engine shutdown. It reached roughly 2.8 kilometres instead of the planned 30 kilometres. Tycho Brahe separated from the booster but its parachute system did not deploy successfully. The capsule was recovered from the sea after a high-impact landing and was partly damaged and waterlogged. In 2012, the SMARAGD two-stage sounding rocket was launched to test operational and technical systems. The group also developed HATV, a smaller hybrid atmospheric test vehicle whose booster was static-fired but not flown. The TM-65 family of approximately 65-kilonewton liquid engines was tested from 2012 onward for possible use in HEAT-2X and other vehicles. HEAT-2X was intended to carry a one-third-scale capsule mock-up toward the Kármán line, but a 2014 static test ended in an engine fire. A nozzle failure and opened weld allowed a large quantity of ethanol to escape rapidly, damaging the vehicle and rendering the engine unusable. HEAT-2X and the TM-65 were subsequently retired. The 2014 period also brought a leadership transition. The board announced that co-founder Kristian von Bengtson had left in February after a falling-out with Madsen. Madsen departed in June. The organization continued as a volunteer association and developed the BPM-2 and BPM-5 bi-propellant engine families. BPM-2 was primarily a test article for manufacturing and test-stand work, while BPM-5 powered the Nexø demonstrators. Nexø I flew in July 2016, followed by Nexø II in August 2018. These vehicles were intended to validate technologies, propulsion, guidance, and operational methods needed for a larger rocket. The main long-term vehicle became Spica, a proposed 12–14 metre crewed suborbital rocket with a 950-millimetre diameter. Its propulsion concept evolved from the BPM-100 to clustered BPM-25 engines. Although the BPM-25 has lower individual thrust than the earlier concept, it offers advantages in flow control and roll authority. Spica is planned to use liquid oxygen and ethanol, thrust-vector control, and home-built avionics and software. By late September 2024, two hardened steel tanks had been constructed and BPM-25 development was underway, while a full flight capsule remained at an early stage. A boilerplate capsule was planned as an intermediate ground-test step. Spacecraft development has included Tycho Brahe, a steel pressure-hull micro-spacecraft designed around a single occupant in a partly standing posture, and Tycho Deep Space, a larger capsule intended to place an astronaut in a horizontal position during acceleration and landing. An uncrewed Tycho Deep Space test, also called Beautiful Betty, was launched in August 2012 using a launch-escape-system test. It did not gain enough altitude for parachute deployment and was partly damaged on impact. The earlier Tycho Brahe capsule was later displayed at Copenhagen’s Tycho Brahe Planetarium; the MAX-1 capsule concept was abandoned because of concerns about human tolerance of its acceleration profile. In 2021, the Recruits Initiative added a formal educational and workforce-development component. Its RC-A1 Recruit Rocket is a five-metre, single-stage vehicle developed by new participants and uses a BPM-5-derived engine with dynamic pressure regulation. The program’s stated purpose is to create practical engineering experience and help expand Danish expertise relevant to the space and defense sectors. As of September 2024, the organization reportedly had 63 volunteers, governed through annual general assemblies that elect a chairman and board. Its maritime operations use Sputnik and MHV Hjortø, with launches conducted from an authorized Baltic Sea area near Bornholm. The organization remained active and continued developing Spica, but had not yet completed a crewed suborbital flight.

• 2021

  Recruits Initiative launched

  [2]Copenhagen Suborbitals official websitecopenhagensuborbitals.com

  The organization begins a recruitment and training program for young engineers and aspiring rocket developers.

• 2018

  Nexø II flight

  [1]Copenhagen Suborbitalsen.wikipedia.org

  Nexø II launches in August using a BPM-5 engine.

• 2016

  Nexø I flight

  [1]Copenhagen Suborbitalsen.wikipedia.org

  Nexø I flies with a BPM-5 engine as a technology demonstrator.

• 2014

  HEAT-2X test failure and leadership changes

  [1]Copenhagen Suborbitalsen.wikipedia.org

  A static-fire accident retires the HEAT-2X and TM-65 programs; co-founder Kristian von Bengtson leaves in February and Peter Madsen leaves later in the year.

• 2012

  SMARAGD launch and propulsion transition

  [1]Copenhagen Suborbitalsen.wikipedia.org

  The SMARAGD sounding rocket flies, while the organization adopts liquid oxygen and ethanol bi-propellant development as its main propulsion direction.

• 2011

  First rocket flight

  [1]Copenhagen Suborbitalsen.wikipedia.org

  HEAT-1X Tycho Brahe launches but pitches over and is shut down early at approximately 1.4 kilometres altitude.

• 2010

  First HEAT-1X launch attempt

  [1]Copenhagen Suborbitalsen.wikipedia.org

  A launch attempt near Bornholm fails when the vehicle’s liquid-oxygen valve does not operate correctly.

• 2008

  Organization founded

  [1]Copenhagen Suborbitalsen.wikipedia.org

  Kristian von Bengtson and Peter Madsen establish Copenhagen Suborbitals as a nonprofit, crowd-funded human spaceflight project.

A volunteer-driven, open and crowd-funded Danish space program emphasizing low-cost experimental engineering, public participation, and eventual indigenous human suborbital flight.

• Crewed suborbital rocket

  Spica

  Spica is Copenhagen Suborbitals’ principal planned crewed rocket. The design is approximately 12–14 metres tall and 950 millimetres in diameter. It is planned to use clustered BPM-25 liquid engines burning ethanol with liquid oxygen as oxidizer, together with thrust-vector control and home-built guidance electronics and software. By late 2024, tank construction and engine development were progressing, but the operational spacecraft capsule remained in an early development phase.

• Technology-demonstrator rockets · 2016

  Nexø I and Nexø II

  The Nexø vehicles are small liquid-propellant demonstrators developed to test propulsion, manufacturing, guidance, and flight operations before the larger Spica program. Nexø I launched in 2016 and Nexø II in 2018, both using BPM-5-class engines fueled by ethanol and liquid oxygen. The series was not intended as a crewed product line but as an engineering bridge toward human-rated suborbital systems.

• Hybrid rocket and capsule system · 2011

  HEAT-1X Tycho Brahe

  HEAT-1X was the booster intended to carry the Tycho Brahe micro-spacecraft. It used a hybrid propulsion approach involving a solid fuel and liquid oxidizer and flew an uncrewed test in 2011. The rocket pitched over shortly after launch, requiring early shutdown, while the capsule separated and was recovered from the sea after a hard landing.

• Crew capsule demonstrator · 2011

  Tycho Brahe

  Tycho Brahe is a steel pressure-hull micro-spacecraft designed for one occupant. Its original configuration placed the passenger in a half-standing, half-seated position beneath a transparent dome, with parachutes and flotation provisions for sea recovery. The first flight article carried a crash-test dummy rather than a person. A surviving capsule was later displayed at the Tycho Brahe Planetarium in Copenhagen.

• Space capsule demonstrator · 2012

  Tycho Deep Space

  Tycho Deep Space, initially known as Beautiful Betty, is a larger capsule concept designed to place an occupant horizontally relative to launch and landing acceleration. An uncrewed launch-escape-system test took place in 2012, but the vehicle did not reach sufficient altitude for parachute deployment and was partly damaged on sea impact.

• Training and technology-demonstrator rocket

  RC-A1 Recruit Rocket

  RC-A1 is a single-stage rocket developed by participants in the Recruits Initiative. It is approximately five metres long and has a fuelled mass of about 165 kilograms. The design uses a dynamic pressure-regulation system rather than a turbopump and a refined BPM-5-derived engine. Its primary role is practical training and technology development for newer members.

• 2021Recruits Initiative

  Denmark

  A recruitment, education, and practical engineering program designed to attract young participants and build Danish skills in rocketry and space technology.

  Outcome. The initiative produced the RC-A1 Recruit Rocket project and was intended to support the broader Spica program.

  Source

• 2014

  Retirement of the TM-65 and HEAT-2X programsGeneration change

  Background

  A static-fire accident caused an engine failure, major ethanol fire, and extensive damage to HEAT-2X.

  Action taken

  The damaged vehicle and TM-65 engine were retired, and development moved toward smaller BPM engines and later the BPM-25 class.

  Aftermath

  Nexø became the main near-term flight-demonstration series while Spica remained the long-term objective.

  Source

• 2014

  Co-founder departuresOther

  Background

  The board reported an internal falling-out between Kristian von Bengtson and Peter Madsen.

  Action taken

  Bengtson left in February, followed by Madsen in June.

  Aftermath

  The organization continued as a volunteer-led project under a new governance arrangement.

  Source

• 2014

  Selection of BPM-25 for SpicaGeneration change

  Background

  The original Spica concept considered the more powerful BPM-100 class, but manufacturing difficulties affected that direction.

  Action taken

  The program selected BPM-25 engines, planned in a cluster to provide the required thrust.

  Aftermath

  The BPM-25 offered greater roll authority and flow-control advantages, although it required multiple engines.

  Source

• 2012

  Shift to liquid oxygen and ethanol propulsionStrategy

  Background

  After testing hybrid systems and briefly examining other propellant combinations, the organization reassessed its propulsion architecture.

  Action taken

  Copenhagen Suborbitals adopted liquid oxygen and ethanol bi-propellant engines as the basis for its subsequent BPM family.

  Aftermath

  The decision led to BPM-2 and BPM-5 development, later Nexø flights, and the BPM-25 concept for Spica.

  Source

• 2021

  Recruits Initiative begins[2]Copenhagen Suborbitals official websitecopenhagensuborbitals.com

  Campaign · Other

  Copenhagen Suborbitals introduced a structured initiative to attract and train new participants in rocket science and related engineering disciplines.

• 2018

  Nexø II launches[1]Copenhagen Suborbitalsen.wikipedia.org

  Product launch · Product generation

  Nexø II launched in August 2018 using a BPM-5 engine, extending the organization’s series of uncrewed rocket tests.

• 2016

  Nexø I technology-demonstrator launch[1]Copenhagen Suborbitalsen.wikipedia.org

  Product launch · Product generation

  Nexø I flew with a BPM-5 liquid-propellant engine as part of the technology path toward the future Spica rocket.

• 2014

  HEAT-2X static-test accident changes propulsion direction[1]Copenhagen Suborbitalsen.wikipedia.org

  Other · Product generation

  A static test of the HEAT-2X and its TM-65 engine resulted in a nozzle failure, fuel release, and a major fire. The vehicle and engine were retired, and the organization moved away from the TM-65 class.

• 2014

  Kristian von Bengtson leaves Copenhagen Suborbitals[1]Copenhagen Suborbitalsen.wikipedia.org

  Leadership change

  The board announced Bengtson’s departure after an internal disagreement with co-founder Peter Madsen. Madsen left the organization later the same year.

• 2011

  Copenhagen Suborbitals makes first HEAT-1X Tycho Brahe flight[1]Copenhagen Suborbitalsen.wikipedia.org

  Product launch · Other

  The organization launched its first full-scale rocket and capsule combination from the Sputnik platform. The vehicle pitched over shortly after liftoff and the engine was shut down early, limiting the flight to approximately 2.8 kilometres.

1. 1Copenhagen Suborbitalsen.wikipedia.org
2. 2Copenhagen Suborbitals official websitecopenhagensuborbitals.com