From the 20th Century Rockets, Missiles and Aircraft to Spaceplanes of the 21st Century

           The world has entered the dawn of the 21st Century. Science and technology have enabled man create enter a new form of civilization, more prosperous and comfortable that was known for thousands of years. But while there is unprecedented prosperity in many nations, yet the physical, emotional and intellectual energies of man have not been able to resolve his psychological problems; and great sorrow and suffering continues world over.

           A major accomplishment in the early part of the 20th Century was the invention of the rocket in the US (Goddard) and then USSR (Korolev); and winged flight by a heavier-than-air aircraft (Wright brothers). The oxygen-carrying rocket enabled man travel in space where there is no atmospheric oxygen available for combustion of fuel in the propulsion system. The aircraft took advantage of the atmosphere both for propulsive force as well as providing a lift force to keep the aircraft airborne. By the end of the 20th Century, man had mastered travel in both the earth’s atmosphere, and in space. Travel across continents became safe and routine for hundreds of passengers at a time; and man traveled, landed on and returned safely from expeditions to the moon.

          Even within 60 years after independence from nearly 1000 years of crushing alien invasion, conquest and rule, India has come forth with remarkable achievements in science and technology. Among the most advanced are the accomplishments in aeronautical and space science and technology that are rapidly closing the gap between India and those who had a lead in these technologies for over one century. Still, there are many in India who doubt whether we will ever master these technologies and put it to good uses for enhancing security and prosperity not only for India, but all humanity.

           However, even in the Western countries, the limitation of using rockets alone for space travel has been clearly understood. Rockets are cumbersome vehicles, vertically stacked, extremely heavy due to the large amount of oxygen (over 70% of its mass at launch) to be carried onboard. Difficult and complex to handle, prepare and launch, consume too much of fuel, uncomfortable to passengers due to high acceleration levels, still relatively unsafe, and expendable after one launch.

          On the other hand, aircraft technologies are much safes and affordable. Even gigantic transport aircraft like the Boeing 747 have magnificent safety records, and are routinely and extensively used by commercial operators. They are comfortable, highly fuel efficient, and can fly non-stop across oceans and continents.

           Hence it has been mankind’s dream to make access and travel space as safe and affordable as commercial air transportation systems. In other words, for nearly 40 years now the search is to design and build a safe, affordable, reusable space plane by a new form of aerospace vehicle that behaves like an aircraft when in the atmosphere, and a rocket in space!

Spaceplanes: A Synergy of Rocket and Aircraft Technologies Spaceplanes of Ancient India.

           Flight in the earth’s atmosphere and to space is thought to have originated in the 20th Century. However, that may not be the case. In the Vedic literature of India, recording events that occurred 12,000 to 15,000 years ago, there are many descriptions of flying machines that are generally called Vimanas. The Mahabharata speaks of "Two storied celestial chariots with many windows" "They roar off into the sky until they appear like comets." The Mahabharata and various Sanskrit books describe at length these chariots, "Powered by winged lighting...it was a ship that soared into the air, flying to the solar and stellar regions."

          Recently, an Italian scientist Dr. Roberto Pinotti at a World Space Conference (Reference http://www.hinduwisdom.info/Vimanas.htm) reported that India may have had a superior civilization and the flying devices called 'Vimanas' described in ancient Indian texts may underline their possible connections to today's aerospace technology. He held a view that 'Shakuna Vimana' described in the text 'might be defined as a cross between a plane and a rocket of our times and its design might remind one of today's Space Shuttle.' Quoting from 'Vymanika Shastra' he said the ancient flying devices of India were made from special heat absorbing metals named 'Somaka, Soundalike and Mourthwika.'

          Thus, it might appear that mankind’s dream of traveling to space; to visit planets and explore the solar system is as old as mankind itself. Why is there no physical evidence of these ‘advanced’ vehicles, if they were built thousands of years ago?

Vimanas for Space Transportation

           It was the use of Vimanas as space transportation systems that might have the clue as to why there is no physical evidence of these ancient aerospace vehicles.

The Atlanteans, known as "Asvins" in the Indian writings, were apparently even more advanced technologically than the Indians. They possessed Vailixi, similar to Vimanas, that were generally "cigar shaped" and had the capability of maneuvering underwater as well as in the atmosphere or even outer space. Other flight vehicles were saucer shaped, and could apparently travel submerged. It is recorded that between 12000 to 15,000 years ago, nations deploying Vimanas in space with lethal weapons were locked in a global war that destroyed almost all of human life and property on planet earth. Clinching archeological evidence to this effect has also been found. Thus, the weaponization of space should not be allowed to happen again.

Spaceplanes of the Modern World

           As of 2001, conceptual design of as many as 22 reusable launch vehicle (RLV) concepts were in progress in the US, UK, France, Germany, Japan and India. Eight designs were for “Heavy Lift RLVs” having a capability to deliver large payloads of 10 to 25 tonnes into space. The remaining 14 systems were designed for smaller payloads, less than 5 tonnes in low earth orbit.

          There were two basic approaches. Half of the design approaches was based using 20th century rocket propulsion systems. These were two-stage-to-orbit vehicles (TSTO), but once again, very heavy and cumbersome as the early space rockets, reaching orbit in two stages, but with one or both stages returning to earth for reuse. But, these designs have not succeeded, as the costs of building large vehicles were still very high.

          Eleven RLV design concepts were based on a combination of airbreathing and rocket engines. They fly to orbit directly like an aircraft (in a single stage), hence named single-stage-to-orbit vehicles, (SSTO). None of these is yet flying, but small scale “Technology Demonstrators” like the US X-43 has demonstrated air breathing engines and flight to Mach 10 very recently.

Design Requirements for SSTO Spaceplanes

          The basic design requirements for a fully reusable hydrogen fueled spaceplane, ascending to orbit from a runway take-off and reentering for a powered landing like any commercial transport aircraft, are as follows:

1. The hydrogen fuel weight should exceed 56% of the spaceplane’s take-off weight.

2. The time-averaged specific impulse over the flight path from earth-to-orbit should be more than 1200 secs (i.e. 1200 Kgs of propulsive thrust for ever one kg per second of hydrogen fuel flow)

3. The spaceplane’s thrust-to-drag ratio has to be more than 3.5.

4. The airbreathing engines have to be lightweight, with a thrust-to-weight ratio exceeding 14.

           The first condition ensures that adequate chemical energy is available in the spaceplane that gets converted to kinetic energy to propel the aircraft-like spaceplane to a height of at least 100 kms and a speed of 8 kms per second. The second and third ensure that the engines operate with an average overall propulsive efficiency of over 40%. The last condition ensures that the payload-to-takeoff weight ratio is maximized.

Promising Contemporary Spaceplane Design Concepts

          Out of about 22 design concepts that have been studied, small scale ground and flight tests carried out, three spaceplane design concepts are discussed here as these have the highest promise for successful development

1. A novel air-breathing liquid rocket engine rocket (also known as a LACE or Liquid Air Collection Engine) the “Sabre” engine operating at an air-to-fuel ratio of 23:1 up to Mach 5. Thereafter, up to orbital speed of Mach 26, the same engine operates as a pure lox-hydrogen liquid rocket engine with on-board liquid oxygen at a mixture ratio of 6:1. In this way, the oxygen needed to propel the vehicle up to Mach 5 is not carried on board at take-off, thus avoiding carriage of about an additional 218 tonnes of liquid oxygen at take-off [had the take-off engine been a pure lox-hydrogen rocket engine from take-off to orbit].

2. A winged-body vehicle configuration with podded-engines, that enables the vehicle to glide back and land, like the Space Shuttle. The high thrust-to-drag ratio of such a slender-body rocket configuration, and low structure weight fraction, compensate for its lower hydrogen-fraction at take-off

It is interesting to note that the “Skylon” is cigar-shaped, like the “Vailixi”.

The US “Falcon” [Late 1990’s, announced August 2003]

          The USAF has an ongoing programme for a small RLV, the “Falcon”. This spaceplane configuration is a classical hypersonic lifting body configuration.

           This spaceplane design concept is described as an unmanned hypersonic aircraft “bomber of the future”. The technology of SLV is said to lead to a SSTO spacecraft. After take-off, a supersonic turbojet engine is used to reach speeds of Mach 2 or Mach 3, then the scramjet engines take over. At max hypersonic speed, SLV would deploy, either a separate craft to reach space, in which case it would be a TSTO vehicle, or switch from its air-breathing scramjet engine to rocket propulsion to be a SSTO vehicle. The payload would be 1,000-kilogram satellite into sun-synchronous orbits.

           It is seen that the “Falcon” resembles the ancient Indian “Shakuna” and “Rukma” Vimanas.

           The main attribute of the “Hyperplane” design concept is its geometric scalability, enabling the design be built for a vehicle as small as 25-tonnes take-off weight (the weight of an advanced fighter aircraft). This is possibly the smallest weight feasible for a reusable SSTO spaceplane, and has a 4% payload ratio, enabling delivery of 1-tonne in parking orbit at Mach 26. Unlike the “Skylon”, the “Avatar” can be scaled up to heavy-lift capabilities. The major attributes of “Skylon” and “Hyperplane”/”Avatar is compared in the Table placed below