HOTOL
Encyclopedia
HOTOL, for Horizontal Take-Off and Landing, was a British
air-breathing space shuttle effort by Rolls Royce and British Aerospace
.
Designed as a single-stage-to-orbit (SSTO) reusable winged launch vehicle, it was to be fitted with a unique air-breathing engine, the RB545
called the Swallow, to be developed by Rolls Royce
. The engine was technically a liquid hydrogen/liquid oxygen design, but by air-breathing as the spacecraft climbed through the lower atmosphere, the amount of oxidizer needed to be carried onboard, for use in the upper atmosphere and space, was dramatically reduced.
Since propellant typically represents the majority of the takeoff weight of a rocket, HOTOL was to be considerably smaller than normal pure-rocket designs, roughly the size of a medium-haul airliner such as the McDonnell Douglas DC-9
/MD-80. However, comparison with a rocket vehicle using similar construction techniques failed to show much advantage, and funding for the vehicle ceased.
s in orbit, at 300 km altitude. It was intended to take off from a runway, mounted on the back of a large rocket-boosted trolley that would help get the craft up to "working speed". The engine was intended to switch from jet propulsion to pure rocket propulsion at 26–32 km high, by which time the craft would be travelling at Mach
5 to 7. After reaching orbit, HOTOL was intended to re-enter the atmosphere and glide down to land on a conventional runway (approx 1,500 metres minimum). HOTOL was designed for automatic, unmanned flights, although later stages would reintroduce a pilot. The internal landing gear would have been too small to carry the weight of the fully fueled rocket, so emergency landings would have required the fuel to be dumped.
led by John Scott and Dr Bob Parkinson. Around the same time, the X-30 scramjet programme was announced in America.
transport aircraft
, was offered by BAe
in 1991 but that too was rejected. Interim HOTOL was to have dispensed with an air-breathing engine cycle and was designed to use more conventional LOX and liquid hydrogen.
In 1989 HOTOL co-creator Alan Bond
formed Reaction Engines Limited
which has since been working on the Reaction Engines Skylon vehicle intended to solve the problems of HOTOL.
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
air-breathing space shuttle effort by Rolls Royce and British Aerospace
British Aerospace
British Aerospace plc was a UK aircraft, munitions and defence-systems manufacturer. Its head office was in the Warwick House in the Farnborough Aerospace Centre in Farnborough, Hampshire...
.
Designed as a single-stage-to-orbit (SSTO) reusable winged launch vehicle, it was to be fitted with a unique air-breathing engine, the RB545
RB545
The RB545 was an air-breathing rocket engine that was proposed to propel a British space shuttle to orbit using a single stage. Rolls-Royce was involved; while British Aerospace worked on the vehicle.-Design:...
called the Swallow, to be developed by Rolls Royce
Rolls-Royce plc
Rolls-Royce Group plc is a global power systems company headquartered in the City of Westminster, London, United Kingdom. It is the world’s second-largest maker of aircraft engines , and also has major businesses in the marine propulsion and energy sectors. Through its defence-related activities...
. The engine was technically a liquid hydrogen/liquid oxygen design, but by air-breathing as the spacecraft climbed through the lower atmosphere, the amount of oxidizer needed to be carried onboard, for use in the upper atmosphere and space, was dramatically reduced.
Since propellant typically represents the majority of the takeoff weight of a rocket, HOTOL was to be considerably smaller than normal pure-rocket designs, roughly the size of a medium-haul airliner such as the McDonnell Douglas DC-9
McDonnell Douglas DC-9
The McDonnell Douglas DC-9 is a twin-engine, single-aisle jet airliner. It was first manufactured in 1965 with its maiden flight later that year. The DC-9 was designed for frequent, short flights. The final DC-9 was delivered in October 1982.The DC-9 was followed in subsequent modified forms by...
/MD-80. However, comparison with a rocket vehicle using similar construction techniques failed to show much advantage, and funding for the vehicle ceased.
Vehicle description
HOTOL would have been 63 metres long, 12.8 metres high, 7 metres in diameter and with a wingspan of 28.3 metres. The unmanned craft was intended to put a payload of around 7 to 8 tonneTonne
The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...
s in orbit, at 300 km altitude. It was intended to take off from a runway, mounted on the back of a large rocket-boosted trolley that would help get the craft up to "working speed". The engine was intended to switch from jet propulsion to pure rocket propulsion at 26–32 km high, by which time the craft would be travelling at Mach
Mach number
Mach number is the speed of an object moving through air, or any other fluid substance, divided by the speed of sound as it is in that substance for its particular physical conditions, including those of temperature and pressure...
5 to 7. After reaching orbit, HOTOL was intended to re-enter the atmosphere and glide down to land on a conventional runway (approx 1,500 metres minimum). HOTOL was designed for automatic, unmanned flights, although later stages would reintroduce a pilot. The internal landing gear would have been too small to carry the weight of the fully fueled rocket, so emergency landings would have required the fuel to be dumped.
Development programme
Development began with government funding in 1986. The design team was a joint effort between Rolls-Royce and British AerospaceBritish Aerospace
British Aerospace plc was a UK aircraft, munitions and defence-systems manufacturer. Its head office was in the Warwick House in the Farnborough Aerospace Centre in Farnborough, Hampshire...
led by John Scott and Dr Bob Parkinson. Around the same time, the X-30 scramjet programme was announced in America.
Problems found during development
During development, it was found that the comparatively heavy rear-mounted engine moved the center of mass of the vehicle rearwards. This meant that the vehicle had to be designed to push the center of drag as far rearward as possible to ensure stability over the entire flight regime. Redesign of the vehicle to do this cost a significant proportion of the payload, and made the economics unclear. In particular, some of the analysis seemed to indicate that similar technology applied to a pure rocket approach would give at least as good performance at lower cost.Programme shutdown
In 1988 the government withdrew further funding, the project was approaching the end of its design phase but the plans were still speculative and dogged with aerodynamic problems and operational disadvantages.Follow on programmes
A cheaper redesign, Interim HOTOL or HOTOL 2, to be launched from the back of a modified Antonov An-225Antonov An-225
The Antonov An-225 Mriya is a strategic airlift cargo aircraft, designed by the Antonov Design Bureau in the 1980s. It is the world's heaviest aircraft. The design, built in order to transport the Buran orbiter, was an enlargement of the successful An-124 Ruslan...
transport aircraft
Cargo aircraft
A cargo aircraft is a fixed-wing aircraft designed or converted for the carriage of goods, rather than passengers. They are usually devoid of passenger amenities, and generally feature one or more large doors for the loading and unloading of cargo...
, was offered by BAe
British Aerospace
British Aerospace plc was a UK aircraft, munitions and defence-systems manufacturer. Its head office was in the Warwick House in the Farnborough Aerospace Centre in Farnborough, Hampshire...
in 1991 but that too was rejected. Interim HOTOL was to have dispensed with an air-breathing engine cycle and was designed to use more conventional LOX and liquid hydrogen.
In 1989 HOTOL co-creator Alan Bond
Alan Bond (rocket developer)
Alan Bond is Managing Director of Reaction Engines Ltd and associated with Project Daedalus, Blue Streak missile, HOTOL, Reaction Engines Skylon and the Reaction Engines A2 hypersonic passenger aircraft.- Career :...
formed Reaction Engines Limited
Reaction Engines Limited
Reaction Engines Limited is a British aerospace company based in Oxfordshire, England.- History & personnel :Reaction Engines was founded in 1989 by Alan Bond and Richard Varvill and John Scott-Scott...
which has since been working on the Reaction Engines Skylon vehicle intended to solve the problems of HOTOL.
See also
- NASPRockwell X-30-See also:-References: 2. -External links:*...
- a scramjet vehicle that HOTOL would have competed with - Reaction Engines Skylon - a follow on design that seems to be more technically successful and promising
- Reaction Engines A2Reaction Engines A2|-See also:-External links:* *...
- a design for a hypersonic antipodal airliner - Liquid Air Cycle EngineLiquid air cycle engineA Liquid Air Cycle Engine is a type of spacecraft propulsion engine that attempts to increase its efficiency by gathering part of its oxidizer from the atmosphere...
- a related engine cycle that liquifies the air
Further reading
- Julian Moxon, Hotol: where next?, Flight InternationalFlight InternationalFlight International is a global aerospace weekly publication produced in the UK. Founded in 1909, it is the world's oldest continuously published aviation news magazine...
, 1 March 1986. (Two page discussion with technical description). - Rob Coppinger, Secret files reveal US interest in UK HOTOL spaceplane, Flight InternationalFlight InternationalFlight International is a global aerospace weekly publication produced in the UK. Founded in 1909, it is the world's oldest continuously published aviation news magazine...
, 23 February 2009. (Government thinking in 1984-5).