Martin J Dougherty
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      • The Society for the Study of Swordsmanship >
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Reaching Orbit

A great SF writer remarked that if you can reach orbit, you’re halfway to anywhere in the solar system.

It has taken humanity a long, long time to reach that halfway point. This section is about how we clawed our way up the steep sides of the gravity well to do it - and how we might do it more efficiently in the future.

A Launch Vehicle is the means by which a payload (A satellite, a nuclear warhead, a small dog, a team of astronauts or a section of space station, to give a few example payloads) can be delivered into orbit. At present, most of the cost of a space mission is taken up by the launch vehicle. For many years scientists have been trying to reduce this cost by developing reusable launch vehicles which can deliver several payloads in their lifetime.

Depending upon its mission the payload may fall back to Earth immediately, may be placed in a transfer orbit to begin transition to its operational station, or it may break orbit on an exploration mission to Mars, Venus or the outer planets. Some day the orbital vehicle may be departing for a Scientific Conference at Proxima Centauri.

Another section on this channel will deal with what happens once the payload reaches orbit - orbital, transorbital and deep space operations - and the drive systems used to provide motive power for these operations.

But first, we need to reach orbit.

Rockets

Rocket propulsion has been in existence for centuries. The ancient Chinese discovered that a tube, closed at one end and filled with black powder, could be made to propel itself by igniting the powder. Several centuries later the principle behind these fireworks was used to propel the Congreve rockets used by the British army. Without any form of guidance beyond a few crude fins, these early military rockets were unreliable to the point of being dangerous to the user, even when they did not explode on the launcher.

Despite its inherent disadvantages - inaccuracy and a tendency to explode - the rocket remained attractive to the military as a means of dumping a great deal of explosive on an area or of delivering a large payload over great distances.

The first application led to short-range and relatively light rockets which are the forerunners of many modern systems - the massed artillery rockets of the US MLRS system, shipborne anti-submarine rocket launchers and a plethora of combat missiles, for example the Sidewinder air-to-air missile.

The second, heavy, rocket was developed as a means to carry an explosive warhead far into enemy territory without risking an expensive aircraft and its trained pilot. Becoming famous as the second of Hitler’s terror weapons - the V-2 - this concept was refined over many years. The ballistic missiles designed to carry nuclear warheads on their intercontinental flight are developed from the V-2, as are the shorter-ranged "tactical" ballistic missiles (such as Pershing) and cruise missiles (e.g. Shipwreck or Tomahawk).

Yet from this destructive beginning came the launch vehicles that place in orbit our weather and communications satellites, and the missions that put men on the moon, in peace for all mankind.


Rocket Science for Beginners

Rockets generally use one of two types of propellant - solid or liquid. Liquid fuel is far easier to make, and was used for many years. However, it is corrosive, explosive and prone to leaks. Solid fuel is expensive and difficult to manufacture, but has the advantage that it is stable and thus far safer to use.

The principle of rocket propulsion has not changed since the Ancient Chinese. A propellant burning in a tube which is open at one end only will produce an outrush of hot gas. Whatever type of propellant is used, Newton’s laws tell us that the exhaust gas, escaping backward, exerts a force on the container which will cause the rocket to accelerate forward according to the formula f=ma, where f is the force, m is mass and a is acceleration.

This means that the acceleration of a rocket (in meters per second) is given by the force applied (in Newtons) divided by the Mass of the rocket (in Kg). The principle involved is no different to what happens when you let go of a blown-up balloon. Air under pressure can escape from the balloon in only one direction, so the balloon moves in the opposite direction. Because the neck of the balloon can flap about, the path of a balloon is somewhat erratic. While this is an amusing effect with a balloon, it is somewhat less desirable in an orbital vehicle, so a means of controlling the path of the rocket must be employed.

A tube shape with a pointed nose reduces air resistance, allowing the rocket to slide through the atmosphere at high speed. A system of fins on the body of the rocket can be used to control the flight path while air is flowing over the surface. Once out of atmosphere, some other means must be employed.

The thrust accelerating the rocket must be balanced. If it is not, one side of the rocket will accelerate more quickly than the other, producing an out-of-control corkscrew effect that is alarming in fireworks and tragic in manned missions. Minor imbalances in thrust can be corrected for using the control surfaces (the fins). Major ones must be found in calculations or tests.

Launching a rocket is usually undertaken with one of three goals. It may be intended that the rocket will follow a ballistic path and fall back to Earth, or leave orbit and fly off into deep space. Somewhere between these two extremes is the goal for most space missions - the rocket will go into orbit and stay there.

Ballistic missiles use the first method, accelerating rapidly until fuel runs out then behaving like a projectile. The missile is slowed by gravity and begins to drop back towards the ground once it reaches zero velocity in an upward direction, gaining speed towards the ground as it falls. Of course, gravity does not affect the missile’s horizontal speed, so the missile is still moving fast relative to the Earth’s surface. It will come down a very great distance from the launcher. This is desirable with nuclear warheads on board. Calculating the point at which the missile will impact is tricky, so large warheads are substituted for accuracy in some missile types.

A launch vehicle that was travelling fast enough would escape Earth’s gravity field before being slowed to a stop. It would then travel outward with whatever velocity was left over until some other force stopped it.

A launch vehicle which reaches a velocity of around 8000m/sec will begin to fall towards Earth’s’ surface at the same rate at which the curvature of the Earth causes the surface to "fall away" beneath it. Above 200km, where there is no air resistance, the rocket will continue to orbit in this manner indefinitely. Higher and lower orbits require different speeds to be maintained. Usually the orbit is fine tuned by motor firings, but even so some very precise calculations are required to enable an object to be launched into an orbit close enough to fine tune from. These calculations are often confused by the fact as a rocket burns its fuel its mass constantly changes. For space launches, vast amounts of fuel are used up. Once the fuel is gone, the tanks required to carry it are just so much dead weight so a system of stages is used, where the early, lower stages of a rocket burn through their fuel very quickly and are jettisoned, leaving the lighter upper stages to continue the orbital journey. Mass changes again when boosters and fuel tanks are jettisoned. There is no room aboard a rocket for spare fuel to be used in seat-of-the-pants corrections, so the calculations must be absolutely correct or the mission will fail - expensively and perhaps tragically.

Rockets are launched straight up for a reason: they rely on thrust alone to overcome gravity, where an aircraft uses air flow over a specially-shaped wing surface to generate "lift" (the wing is pushed upwards by air pressure under the wing into an area of lower pressure above). A rocket has no such lifting surfaces. Guidance fins are not sufficient to create lift. So while an aircraft engine may develop far less power than the weight of the aircraft - or even the engine - yet be sufficient to power a light aircraft, a vehicle without lifting surfaces must generate enough thrust to overcome its weight (weight is the mass of the craft multiplied by the acceleration due to gravity) just to stand still. Any surplus thrust translates to acceleration of the craft, providing that thrust is acting against gravity. Gravity pulls the rocket down, so the direction of the thrust must be such as to push it upwards. A rocket engine which is producing a lot of sideways thrust is just wasting fuel.

So, all that is necessary to place a vehicle into orbit is to calculate the velocity it will need to reach, set a curving trajectory such that the rocket reaches that velocity at the right height, and build a vehicle capable of surviving the experience while carrying motors, fuel, boosters and whatever you actually want to launch. Then control it through the liftoff, boost, separation and orbital insertion phases, fire the motor to adjust and stabilise the orbit, and finally deploy the payload.

With gravity, weather conditions and changing mass to take into account, the complexities of guidance systems and mechanisms to jettison used stages, stresses on materials and equipment and only one attempt to get it right....

This really is rocket science.

Post-War Experiments

Examining captured German V-2 rockets after the Second World War, members of the British Interplanetary Society suggested that such a rocket could be used to carry a capsule containing a test pilot out of Earth’s atmosphere. There were no funds available for what must have seemed at the time to be an outrageous experiment, and the idea was quietly shelved.

Indeed, there were no funds anywhere in the post-war world for frivolities like space exploration. Projects such as the Rand Corporation’s Experimental World-Circling Spaceship or the US Navy’s High Altitude Test Vehicle were technically sound and had a good chance of success. But there as no money to be had and, like other such projects, they finally died.

It required another war to jump-start the space race. In the wake of the Korean War, the Convair company managed to convince the US government of the feasibility of a long-range ballistic missile designed to deliver a nuclear bomb halfway around the world. This project emerged in 1954 as the Atlas missile. The ballistic trajectory required to hit distant targets would carry the missile and its payload almost into the low orbital reaches. Visionaries began to speculate on the possibility of placing a smaller rocket atop an Atlas missile, to break away at the high point of the Atlas’ flight and complete the journey into orbit.

As scientists in the US worked towards a 1957 satellite launch using this method, their counterparts in the Soviet Union dramatically demonstrated that the theory was sound - by launching Sputnik I into orbit using a similar technique.

The space race was on.

Current launch vehicles

Early launches from the US used an Agena rocket (a small rocket only 6m in length) atop one of a number of powerful first-stages derived from military ballistic missiles. Following the Atlas/Agena combination came a succession of other combinations - the Centaur upper stage and Thor or Titan first stages. All launch vehicles were the subject of constant improvement and modification, yet the overall theme remained the same - a large and immensely powerful first stage, possibly with boosters strapped on to it, hurled a lighter, smaller upper stage upwards then fell away with fuel exhausted. The upper stage then continued to orbit. This process is very wasteful, of course, and alternatives are constantly being sought.

Launch vehicles are subject to continual update and improvement in propulsion and guidance systems, integration of boosters and reliability of hardware, but the launchers in use around the world belong to the same generation as the earliest Atlas/Agena launchers.

Many nations have or are developing their own space launch capability, often with assistance from the pioneers of space flight. Details and pictures of many of the major space launch systems can be found at the following sites:

An overview of the world’s expendable and reusable launch vehicles:

http://www.spaceandtech.com/database/vehicles/sd_athena.htm

Ariane launch systems

http://www.ariane-info.com/

Atlas, Titan and Delta launch vehicles:

http://ncst-www.nrl.navy.mil/LACE/Rockets.html

Delta Launch Systems

http://www.boeing.com/defense-space/space/delta/deltahome.htm

The European Space Agency’s launch systems: http://www.esrin.esa.it/htdocs/esa/progs/mstp.html

Indian Space Research Organisation (SLV family of launchers)

http://www.isro.org/launch.htm

Various launch vehicles for orbital and suborbital

missions

http://www.orbital.com/Prods_n_Servs/Products/LaunchSystems/index.html

Launch Vehicles for small satellites

http://www.gsfc.nasa.gov/gsfc/small_sat/launchers.html

Launch systems under development or study

http://www.orbireport.com/DevLV.html

Russian Space Vehicles

http://solar.rtd.utk.edu/~jgreen/ruvehicl.html

Sea Launch

http://www.boeing.com/defense-space/space/sealaunch/index.html

Titan and other launch vehicles

http://www.spacecom.af.mil/usspace/fblaunch.htm

Current Launch Vehicles By Nationality

British Launch Vehicles

Britain was the sixth nation to achieve orbital launch

Black Arrow Developed from the Black Knight launcher, Black Arrow used liquid-fuelled first and second stages with a solid-fuelled third stage. After second-stage jettison, Black Arrow could coast to orbital insertion point, then enter stable orbit by firing the 3rd stage motor.

http://solar.cini.utk.edu/~mwade/lvs/blaarrow.htm

Chinese Launch Vehicles

Much of China’s early space technology was developed from Soviet systems, in a similar way to the development of many Chinese weapons systems. China’s first satellite was placed in orbit by a liquid-fuelled SS-2 IRBM based upon a Soviet missile.

Long March Chinese launcher available with various configurations of boosters

http://www.spaceandtech.com/database/vehicles/sd_longmarch.htm

http://solar.cini.utk.edu/~mwade/lvfam/lonmarch.htm

 

CZ-2F Recent Chinese launcher used to deploy the Shenzhou craft.

http://solar.cini.utk.edu/~mwade/craft/shenzhou.htm

http://solar.cini.utk.edu/~mwade/graphics/p/p921lvf2.jpg

European Launch Vehicles

The European Space Agency (ESA) is a collaboration between the major nations of Europe to create an independent space capability. Much ESA activity is, however, undertaken in conjunction with NASA.

http://www.esrin.esa.it/htdocs/esa/progs/mstp.html

 

French Launch Vehicles

France was the third nation to achieve space capability, after the USSR and the United States.

Ariane A series of medium-heavy launch vehicles which first flew in 1998. Ariane 4 uses a liquid-fuelled core unit, mated to various booster combinations. Ariane 5 is a new version intended to replace Ariane 4. A liquid oxygen/hydrogen fuelled first stage is augmented by two solid fuel boosters.

http://www.spaceandtech.com/database/vehicles/sd_ariane4.htm

http://www.spaceandtech.com/database/vehicles/sd_ariane5.htm

http://www.ariane-info.com/

Diamant The first French launcher was Diamant, a 3-stage launcher, using a liquid-fuelled first and solid-fuelled second and third stages. Diamant achieved the first three orbital launches outside the USSR and US.

http://solar.cini.utk.edu/~mwade/lvs/diamant.htm

International Launch Vehicles

As space technology enters the commercial marketplace, international corporations are beginning to compete for a place in the field.

Eurockot A small launcher built by a joint German-Russian consortium.

http://www.spaceandtech.com/database/vehicles/sd_eurockot.htm

Sea Launch Using a Zenit launch vehicle, Sea Launch is an international company. Russian, Ukrainian, Norwegian and US companies are all partners in this venture.

http://www.boeing.com/defense-space/space/sealaunch/index.html

Indian Launch Vehicles India uses the SLV series of launchers.

http://www.isro.org/launch.htm

 

Israeli Launch Vehicles

Shavit Like much Israeli military equipment, the Shavit launcher is similar to a South African system.

http://solar.cini.utk.edu/~mwade/lvs/shavit.htm

 

Japanese Launch Vehicles http://yyy.tksc.nasda.go.jp/index_e.html

Japan achieved orbital capability after France, taking fourth place in the space race. Delays were caused by running two rival space projects simultaneously.

H2 The Japanese NASDA is available in various configurations, intended to make it competitive in the international marketplace.

http://www.spaceandtech.com/database/vehicles/sd_h2a.htm

J-1 An unsuccessful 3-stage launcher developed from the H2.

http://www.spaceandtech.com/database/vehicles/sd_jvehicle.htm

Lambda-4S An early Japanese launch vehicle, comprising a 4-stage solid fuelled launcher utilising 2 strap-on boosters.

Mu-4S A more developed 4-stage solid-fuel launch vehicle.

http://solar.cini.utk.edu/~mwade/lvs/mu3s.htm

 

South African launch Vehicles

RSA-3 and RSA-4 Similar to Israeli Shavit launchers, the RSA launchers were developed from ballistic missiles.

http://solar.cini.utk.edu/~mwade/lvs/rsa3.htm

http://solar.cini.utk.edu/~mwade/lvs/rsa4.htm

Soviet (and Former-Soviet) Launch Vehicles

The Soviet Union was the first nation to place a satellite in orbit, with Sputnik 1 in 1957. Soviet launch vehicles are essentially military rockets developed from those used by the Strategic Rocket Forces.

http://solar.rtd.utk.edu/~jgreen/ruvehicl.html

Luna Upper stage first used for the Soviet Luna missions.

http://solar.cini.utk.edu/~mwade/lvs/luna8k72.htm

Proton A 2-stage rocket capable of launching heavy loads into orbit. Protons are the main vehicle in the Russian space programme, and are available on the international market.

http://www.spaceandtech.com/database/vehicles/sd_proton.htm

Soyuz Developed from the earliest Soviet launch vehicles, Soyuz launchers are being further developed by a Russian/French consortium.

http://www.spaceandtech.com/database/vehicles/sd_soyuz.htm

Tsyklon Soviet family of launchers which includes the R series and Kosmos launchers.

http://solar.cini.utk.edu/~mwade/lvfam/tsyklon.htm

Vostock I An early Soviet ICBM with 4 strap-on booster rockets made up the first 2 stages of this launcher. Upper stage was a Luna rocket. The combination could place nearly 5000kg in low Earth orbit

http://solar.cini.utk.edu/~mwade/lvs/vosk8a92.htm

Zenit A two or three stage launcher which forms the basis of the Sea Launch vehicle

http://www.spaceandtech.com/database/vehicles/sd_zenit.htm

 

US Launch Vehicles

The United States was the second nation to place an object in orbit. The search for a suitable launch vehicle was complicated and slowed by inter-service rivalry, as Navy, Army and Air Force projects competed for funds and recognition.

Agena An upper-stage used on top of Thor, Atlas, Thor and Titan first-stage launchers.

Athena A solid-fuel rocket first launched in 1995. Athena I is a 2-stage vehicle, while Athena II is a 3-stage launcher.

http://www.spaceandtech.com/database/vehicles/sd_athena.htm

Atlas The earliest US first-stage launch vehicle, developed from ICBM. Used with various upper-stages. Atlas was used for the later, orbital, Mercury flights.

http://ncst-www.nrl.navy.mil/LACE/Rockets.html

Atlas II Developed in the 80s for large payload launches, Atlas II has seen continual upgrades but is now being replaced by Atlas III.

http://www.spaceandtech.com/database/vehicles/sd_atlas2.htm

Atlas III A replacement for Atlas II, incorporating several improvements

http://www.spaceandtech.com/database/vehicles/sd_atlas3.htm

Atlas V Developed for USAF purposes, the Atlas V is a heavy payload launcher

http://www.spaceandtech.com/database/vehicles/sd_atlas5.htm

Beal BA-2 A privately-financed highly-advanced 3-stage launcher currently under development.

http://www.spaceandtech.com/database/vehicles/sd_beal_ba2.htm

Centaur Upper-stage first used with Atlas to place a 4500kg payload in orbit.

Delta Versatile launch vehicle developed from Thor. Can be used in 2 or 3 stage mode, with up to 9 strap-on booster rockets. Variants include TAD (Thrust Augmented Delta), LTTAD (Long Tank Thrust Augmented Delta) and Thorad, which is an improved TAD.

http://www.boeing.com/defense-space/space/delta/deltahome.htm

Delta II The current standard US launch vehicle.

http://www.spaceandtech.com/database/vehicles/sd_delta2.htm

Delta III An Improved Delta II.

http://www.spaceandtech.com/database/vehicles/sd_delta3.htm

Delta IV A USAF improved version of Delta II.

http://www.spaceandtech.com/database/vehicles/sd_delta4.htm

Redstone A US Army-Developed rocket used for the early, sub-orbital Mercury manned space missions.

http://solar.cini.utk.edu/~mwade/lvfam/redstone.htm

Saturn A 3-stage launcher. Saturn I placed the first Apollo Command Module in orbit in 1964. This launcher was developed into Saturn V, developing nearly twice as much thrust.

http://solar.cini.utk.edu/~mwade/lvfam/saturnv.htm

Scout A small solid-fuel 4-stage rocket, used to place payloads of less than 200kg in orbit and for various re-entry experiments.

http://solar.cini.utk.edu/~mwade/lvfam/scout.htm

Taurus A 4-stage launcher designed for small/medium payloads

http://www.spaceandtech.com/database/vehicles/sd_taurus.htm

Thor Developed from an IRBM (Intermediate Range Ballistic Missile), Thor is fuelled by liquid oxygen and kerosene. A Long-Tank Thor forms the first stage of the first stage of the Delta launcher. Another variant is the Thrust-Augmented Thor.

http://solar.cini.utk.edu/~mwade/lvs/thor.htm

Titan A 4-stage launcher used with 2 boosters, mainly by the US Air Force for military launches. Titan can place over 10,000kg in orbit. http://www.spacecom.af.mil/usspace/fblaunch.htm

Vanguard A 3-stage launcher developed by the US Navy for early satellite launches.

http://solar.cini.utk.edu/~mwade/lvfam/vanguard.htm

The Search For Alternatives

Alternative means to reach orbit have been postulated for as long as orbital rockets have been a possibility. Von Braun put forward ideas for a winged space vehicle capable of making a controlled re-entry as early as 1951. His design looks remarkably like the modern Space Shuttle.
The Space Shuttle is one possible alternative to conventional rockets. It is somewhat less wasteful than traditional launch vehicles, in that the main vehicle can be used repeatedly. However, the shuttle still requires a vertical launch using strap-on boosters (these can be recovered and re-used) and an enormous belly fuel tank, which is jettisoned some time after the boosters.

The shuttle is a good start; a reusable vehicle capable of spreading its cost over many orbital missions - though that cost is much higher than a conventional rocket. But in order to achieve truly cost-effective orbital operations, a fully reusable vehicle is required.

Several ideas have been proposed. Most revolve around a "Spaceplane" concept, using atmospheric lift to reach high altitude like a conventional aircraft, then either launching a rocket capsule to make the final orbital transition or deploying a different type of engine to power the craft to orbit. Descent is a powered or unpowered aerodynamic landing similar to that made by the Space Shuttle.

Several vehicles have been designed to prove these technologies, including Dynasoar, a crew return vehicle demonstrated in the 1950s. Dynasoar was a radical departure from the usual method of crew return - a parachute-retarded plunge into the ocean - in that the vehicle had small wings to generate lift for a horizontal landing.

Information on the search for reusable space vehicles http://www.nas.edu/cets/aseb/rlv1.html

Experiments in gun launch systems: http://www.islandone.org/Propulsion/GeraldBullInfo.html


Speculative Technologies

A number of experimental technologies are being developed around the world. The means varies but the intent is the same in each case - to create an affordable, reliable means of placing a payload in orbit.

Combination Vehicles
Aircraft can reach very high altitudes using only conventional jet engines, and can do so far more cheaply than a rocket by using atmospheric lift over a conventional wing. This is the theory behind the High-Altitude Takeoff Platform concept. A large aircraft carries the orbital vehicle to the maximum possible height and releases it.

This has three main advantages: first, the orbital craft makes its takeoff much closer to orbital distance, with its full fuel supply aboard. Second, the craft is already moving at high speed when takeoff occurs. Finally, gravity diminishes with distance according to an inverse square law - so doubling the distance from the earth’s center would cause a fourfold decrease in the gravitational attraction on the orbital craft.

There are, however, considerable dangers associated with high-altitude separation, and the heights reachable by launch vehicles do not result in a great enough advantage to be worth pursuing.

A combination craft which functioned both as an atmospheric craft and orbital vehicle is a possibility, but the requirement to carry two types of engine - air-breathing jet engines and rocket motors for the extra-atmospheric component of the mission - results in a great deal of dead weight. Only if the two types of engine could be combined into one would this concept become workable.

That combination seems likely to happen in the near future.

Combination Engines
Several research groups are working on combination engines, which will use oxygen from the air while within the atmosphere, then operate like a conventional rocket at orbital altitude.

In the air-breathing mode, the combination engine combines fuel with air drawn in from the atmosphere to drive a conventional jet engine. At high enough speeds (over 800kph), engines of this type can function as ramjets or scramjets ("supersonic combustion ramjets"), which provide greater thrust due to the volume of air being forced through the combustion chamber.

Once into the upper reaches of atmosphere, there is insufficient oxygen to sustain the air-breathing engine, so the air intakes are closed and the fans withdrawn to allow the engine to function as a conventional rocket. Rocket fuel contains its own oxygen, so does not need an outside supply.

Lifting Bodies
A combination engine allows the construction of a true spaceplane - an aircraft which can take off and land like any other, yet can switch to rocket propulsion to climb out of the atmosphere. Such a craft will be almost as reusable as any jet airliner, and could conceivably become as common.

Most designs for spaceplanes use a Lifting Body concept. This is a vehicle whose underside surfaces provide much of the lift required for horizontal flight. Only a small wing surface is thus required, which cuts air resistance considerably and enables the craft to survive extremely high-speed atmospheric flight. Lifting Body craft look a little tubby and even ungainly beside conventional aircraft, but in reality they are far more efficient.

Other Launch Systems
Many early science-fiction movies and stories depicted space vessels being accelerated on a wheeled sled, along a railway-like launch track ending in a ski-jump affair. Achieving any sort of useful launch speed by this method is difficult - friction, small irregularities in the track and gaps between rails (which must be left to allow for thermal expansion), would combine to slow the vehicle or rattle it to pieces. A launch railway is not really a workable concept.

But in recent years the concept has been revived. It is possible to use a maglev (magnetic levitation) track as a launcher. Maglev uses magnetic repulsion to "float" an object in an invisible force field. Craft hovering on a magnetic "magic carpet" are cushioned against irregularities in the track and are not subject to friction except air resistance.

Spacecraft could be accelerated along the track - possibly also by magnetic means - to reach high speeds before commencing the climb to orbit.

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