Orbits:

The direction a body travels in orbit can be direct, or prograde, in which the spacecraft moves in the same direction as the planet rotates, or retrograde, going in a direction opposite the planet's rotation. True anomaly is a term used to describe the locations of various points in an orbit. It is the angular distance of a point in an orbit past the point of periapsis, measured in degrees. For example, a spacecraft might cross a planet's equator at 10 degrees true anomaly. Nodes are points where an orbit crosses a plane. As an orbiting body crosses the ecliptic plane going north, the node is referred to as the ascending node; going south, it is the descending node.

To completely describe an orbit mathematically, six quantities must be calculated. These quantities are called orbital elements, or Keplerian elements. They are: (1) semi-major axis and (2) eccentricity, which are the basic measurements of the size and shape of the orbit's ellipse. Recall an eccentricity of zero indicates a circular orbit. The (3) orbit's inclination is the angular distance of the orbital plane from the plane of the planet's equator (or from the ecliptic plane, if you're talking about heliocentric orbits), stated in degrees: an inclination of 0 degree. means the spacecraft orbits the planet at its equator, and in the same direction as the planet rotates. An inclination of 90 degrees indicates a polar orbit, in which the spacecraft passes over the north and south poles of the planet. An inclination of 180 degrees indicates an equatorial orbit in which the spacecraft moves in a direction opposite the planet's rotation (retrograde). The (4) argument of periapsis is the angular distance of periapsis from the ascending node. Time of periapsis passage (5) and the celestial longitude of the ascending node (6) are the remaining elements. Generally, three astronomical or radiometric observations of an object in an orbit are enough to pin down each of the above six Keplerian elements.

The semi-major axis of an orbit is determined by the kinetic energy acquired by the rocket at burnout. This is equivalent to the burnout velocity. For low burnout velocities (below 25,000 ft/sec) the orbit is ballistic, meaning it does not escape the surface of the Earth. Burnout velocities above 25,000 ft/sec achieve stable orbit. At 35,000 ft/sec, the orbit reaches the distance of the Moon.

The amount of burnout velocity also determines the orbit type, an ellipse, a parabola or a hyperbolic path.

Satellites:

Satellites use a wide variety of orbits to fulfill their missions. The orbit chosen for a satellite is a compromise between the mission requirements, the capabilities of the rocket used to launch the satellite and orbital mechanics.

• The orbital period. This increases with the mean altitude of the orbit, so a satellite in a low earth orbit moves faster than a satellite in a geostationary orbit. Also the velocity of a satellite in an eccentric orbit varies along the orbit, being fastest at perigee & slowest at apogee (Keplers second law of equal areas).
• Inclination. The angle between the plane (major axis) of the satellite orbit and the equator
• Eccentricity: A perfectly circular orbit has an eccentricity of zero, an elliptical orbit an eccentricity of 0< to <1, a parabolic orbit an eccentricity of 1 and a hyperbolic orbit of >1. The low point of an orbit is known as perigee, whilst the high point is apogee. The major axis is the vector connecting the perigee to the apogee.
• The ascending node is where the orbit crosses the equator in a northbound direction (i.e.. the direction of the satellite motion). Likewise, the descending node is where the orbit crosses the equator in a southbound direction.

Where is the International Space Station Right Now?

Low Earth Orbit:

Landsat 7 is an earth resources spacecraft which images the earth's surface in visible and infrared light. Therefore this satellite orbit is optimized for earth observation, i.e. close to the Earth's surface and moving so that it can cover the entire surface of the Earth in a short time. For this reason a near polar orbit of 700km, 98.8 inclination, 98 minute period is used which ensures that the satellite can (at least in theory) observe the entire globe. Several other features of this orbit make it especially useful for remote sensing satellites.

• Circle of visibility = yellow circle around satellite indicating the region of the earth visible from the satellite.
• Part of orbit in sunlight = yellow.
• Part of orbit in shadow = red.
• Wayside of earth = light blue.
• Nitride of earth = dark blue, after the terminator three lines indicate the boundaries of civil, nautical & astronomical twilight.
General view of Landsat 7 orbit.

Left: View perpendicular to plane of orbit
Right: View of orbit from ascending node

In theory an orbit should remain fixed in space whilst the earth rotates beneath the satellite. In reality the earth is slightly bulged and the effect of this bulge is to shift the point of perigee and the ascending node for any orbit which has an inclination other than 90. This effect is known as nodal regression, the result of which is that the plane of the orbit rotates or precesses.

Ground tracks. Red dots along the ground track show the position of the satellite at regular intervals. Closely spaced dots indicate slow speed, widely spaced dots high speed.

However, this effect is used to advantage here to shift the orbit at exactly the same rate as the daily change in position of the sun over any point of the earth. So the satellite always passes over the earth on the sunlit part of its orbit at the same local time of day (for example at 9 am local time). This ensures that lighting conditions are similar (ignoring seasonal differences) for images taken of the same spot on the earth at different times. Additionally the orbit is resonant with the rotation period of the earth, meaning that the satellite passes over the same point on the earth at the same time of day at regular intervals (which may be daily or every 2 or more days depending on the resonance). In the case of Landsat there are 14.5 orbits per day or 29 orbits every 2 days.

Geosynchronous Orbits (GEO):

A geosynchronous orbit is an orbit which has an orbital period close to that of the earths rotation. A geostationary orbit is a special case of the geosynchronous orbit where inclination = 0 and the period is equal to the rotation period of the earth (approx 1436 minutes), corresponding to a circular orbit of approx. 35,700km altitude. A satellite in this orbit appears essentially stationary in the sky, which is why this orbit is used extensively for telecommunications & weather satellites. In reality lunar & solar gravitational influences perturb the satellites orbit, so that through the day the satellites position shifts slightly.

Below is shown the orbit of the TDRS-7 satellite, one of a series of NASA satellites which used to provide a near continuous communications link with the Space Shuttle, International Space Station & other spacecraft such as the Hubble Space Telescope.

General view of TDRS-7 orbit

View of orbit from ascending node

Compared with the LEO orbit of Landsat, a much larger portion of the earth's surface is visible from the TDRS-7 spacecraft. The zone of visibility of the spacecraft has been highlighted by a cone. Approximately 40% of the earths surface can be viewed at any one time from geostationary altitude. Additionally, the spacecraft orbit is sunlight apart from a small zone which passes into the earths shadow. Actually, geostationary satellites only experience eclipses at two periods of the year - for a few weeks at a time at the spring and autumn equinoxes. The reason for this is simple. The earths rotation axis is inclined with respect to the ecliptic, hence the earth's shadow cone misses the plane of a zero inclination geostationary orbit apart from the times when the suns declination is close to zero. This occurs twice a year, once at the spring equinox and once at the autumn equinox.

Ground tracks. Red dots along the ground track show the position of the satellite at regular intervals. Closely spaced dots indicate slow speed, widely spaced dots high speed.

As can be seen from this graphic a perfectly geostationary satellite stays over the same spot on the equator all day. However, if we were to look closely we would see that the satellite does appear to change position, generally describing a small figure of 8 or an arc due to the effect of lunar / solar perturbations dragging the satellite into a slightly elliptical, slightly inclined orbit. There are many non operational satellites in "graveyard" orbits slightly above or below a true geostationary orbit. Since the orbital period is slightly more or less than the earths rotation period these satellites appear to drift slowly around the earth.

Geosynchronous Transfer Orbits (GTO):

There are many rocket boosters which are observable in "transfer" orbits. These are the orbits used to transfer the satellite from an initial low earth orbit to the final orbit. The orbit used for transfer to geostationary orbit is named appropriately enough a "geostationary transfer orbit" (GTO). A standard GTO is an orbit which requires the minimum energy to reach geostationary altitude (A Hohmann transfer ellipse). The perigee corresponds to the altitude of the initial low earth orbit parking orbit, the apogee the geostationary orbit altitude and the inclination is usually the inclination of the initial parking orbit. At apogee the payload usually fires an on-board motor to circularize the orbit and adjust the inclination to zero. The GTO orbit of the Intelsat 4-2 rocket (An Atlas-Centaur) is shown below. This is a 600x35 km,700x28 km inclination orbit Note that the orbit is very elliptical. The perigee is in the southern hemisphere, so it is possible for observers over a narrow latitude range (centered on -28) to see this object at a range of only a few hundred kilometers. However, the satellite spends most of its time, due to the "equal areas" rule of orbital dynamics at high altitudes. The apparent trajectory of Intelsat 4-2 rk with respect to Alt / Azimuth is shown below. The rocket appears to trace out a hairpin loop - the shape is a combination of the orbit & the rotation of the earth as can be seen from the ground trace.

Intelsat 4-2 rocket orbit

Ground Trace of 4 orbits of the Intelsat 4-2 rocket

In recent years modified versions of the GTO orbit have been used. A supersynchronous orbit is one where the apogee is significantly greater than geosynchronous altitude. Why send the payload higher than the target orbit altitude? The reason is because the payload still has to adjust its inclination from the launch inclination (anything from 5 to 51) to 0. This maneuver is very expensive in terms of energy, much more so than an in plane change of orbital altitude. The energy required to do this maneuver decreases with orbital altitude, so it requires less fuel to perform this plane change at high altitude (e.g.. 60,000 or 70,000 km) and then descend to a geostationary orbit rather than do the plane change at geostationary height. Many supersynchronous transfer orbits also have very low perigee altitudes, to accelerate their decay and reduce the amount of debris in orbit. Subsynchronous transfer orbits also exist where the rocket only sends the payload part of the way to geostationary height, the payload then uses its own propulsion system to reach the final orbit.

Molniya orbits:

Many Russian cities are at high northern latitudes where it is impractical to use geostationary satellites for telecommunications since the satellite would appear either low on the horizon on not visible at all. To overcome this problem Molniya satellites are used for communications in these regions. The orbit used by these satellites is a 12h, high inclination elliptical orbits. The orbit of Molniya 3-47 is shown below. This is a 1470 x 38900 km, 63.4 inclination orbit. Again this orbit has special features which make it well suited for telecommunications. First the period is 12h, so there are 2 orbits per day.

General view of the orbit of Molniya 3-47 with cone of visibility

As a result the ground track of the orbit repeats at the same time of day each day. Since the orbit is elliptical, the satellite spends most of it's time near apogee (where its velocity is slowest), so for 11h of each orbit the satellite is above the horizon for high northern latitudes. Additionally, for several hours per day the satellite moves only very slowly across the sky (as can be seen from the ground track), making it easy to follow with a communications antenna. There is a special reason for the 63.4 inclination. Normally, as described above for the sun-synchronous orbit of Landsat 7, the oblate shape of the earth causes a gradual shift of the orbits perigee along the orbit. As a result the perigee of this orbit would shift from the southern hemisphere into the northern hemisphere. However, the rate of shift depends on the inclination of the orbit and at certain inclinations the perigee does not move. For 63.4 inclination orbit with a perigee in the southern hemisphere the position of perigee remains fixed, which is why this inclination is used for Molniya orbits.

Ground track of Molniya 3-47 over 6 orbits

Mid Earth Orbit:

Mid earth orbit (MEO) is a term used to describe 12h period, medium inclination orbits generally used for Global Positioning Satellites. With a constellation of 24 appropriately spaced satellites in approx 20,000 km near circular orbits it is possible to ensure that at least 4 satellites are visible from any one location at any time to ensure reliable navigation using signals from these GPS satellites.

The orbit is resonant with the earths rotation period (2 orbits per day) so the orbit track repeats itself each day.

General view of orbit of GPS2-12 satellite

Ground trace of GPS2-12 satellite over 6 orbits

Hohmann Transfer Orbits:

To launch a spacecraft to an outer planet such as Mars, using the least propellant possible, first consider that the spacecraft is already in solar orbit as it sits on the launch pad. Its existing solar orbit must be adjusted to cause it to take the spacecraft to Mars. In other words, the spacecraft's perihelion (closest approach to the sun) will be Earth's orbit, and the aphelion (farthest distance from the sun) will intercept the orbit of Mars at a single point. This is called a Hohmann Transfer Orbit. The portion of the solar orbit that takes the spacecraft from Earth to Mars is called its trajectory.

To achieve such a trajectory, the spacecraft lifts off the launch pad, rises above Earth's atmosphere, and is accelerated in the direction of Earth's revolution around the sun to the extent that it becomes free of Earth's gravitation, and that its new orbit will have an aphelion equal to Mars' orbit. After a brief acceleration away from Earth, the spacecraft has achieved its new orbit, and it simply coasts the rest of the way. To get to the planet Mars, rather than just to its orbit, requires that the spacecraft be inserted into the interplanetary trajectory at the correct time to arrive at the Martian orbit when Mars will be at the point where the spacecraft will intercept the orbit of Mars. This task might be compared to throwing a dart at a moving target. You have to lead the aim point by just the right amount to hit the target. The opportunity to launch a spacecraft on a transfer orbit to Mars occurs about every 25 months.

To be captured into a Martian orbit, the spacecraft must then decelerate relative to Mars (using a retrograde rocket burn or some other means). To land on Mars, the spacecraft must decelerate even further (using a retrograde burn, or spring release from a mother ship) to the extent that the lowest point of its Martian orbit will intercept the surface of Mars. Since Mars has an atmosphere, final deceleration may be performed by aerodynamic braking, and/or a parachute, and/or further retrograde burns.

To launch a spacecraft to an inner planet such as Venus using the least propellant possible, its existing solar orbit must be adjusted so that it will take it to Venus. In other words, the spacecraft's aphelion will be on Earth's orbit, and the perihelion will be on the orbit of Venus. As with the case of Mars, the portion of this orbit that takes the spacecraft from Earth to Venus is called a trajectory. To achieve an Earth to Venus trajectory, the spacecraft lifts off of the launch pad, rises above Earth's atmosphere, and is accelerated opposite the direction of Earth's revolution around the sun (decelerated) to the extent that its new orbit will have a perihelion equal to Venus's orbit. Of course the spacecraft will end up going in the same direction as Earth orbits, just a little slower. To get to Venus, rather than just to its orbit, again requires that the spacecraft be inserted into the interplanetary trajectory at the correct time to arrive at the Venusian orbit when Venus will be at the point where the spacecraft will intercept the orbit of Venus. Venus launch opportunities occur about every 19 months.

Gravity Assist Trajectories:

The planets retain the vast majority of the solar system's angular momentum. It is this momentum that is used to accelerate spacecraft on so-called "gravity-assist" trajectories. It is commonly stated in newspapers that spacecraft such as Voyager and Galileo use a planet's gravity during a flyby to slingshot it farther into space. How does this work? In a gravity-assist trajectory, angular momentum is transferred from the orbiting planet to a spacecraft approaching from behind. Gravity assists would be more accurately described as angular-momentum assists.

Consider Voyager 2, which toured the Jovian planets. The spacecraft was launched on a standard Hohmann transfer orbit to Jupiter. Had Jupiter not been there at the time of the spacecraft's arrival, the spacecraft would have fallen back toward the sun, and would have remained in elliptical orbit as long as no other forces acted upon it. Perihelion would have been at 1 AU, and aphelion at Jupiter's distance of about 5 AU.

However, the spacecraft's arrival was carefully timed so that it would pass behind Jupiter in its orbit around the sun. As the spacecraft came into Jupiter's gravitational influence, it fell toward Jupiter, increasing its speed toward maximum at closest approach to Jupiter. Since all masses in the universe attract each other, Jupiter sped up the spacecraft substantially, and the spacecraft slowed down Jupiter in its orbit by a tiny amount, since the spacecraft approached from behind. As the spacecraft passed by Jupiter (its speed was greater than Jupiter's escape velocity), of course it slowed down again relative to Jupiter, climbing out of Jupiter's gravitational field. Its Jupiter-relative velocity outbound was the same as its velocity inbound. But relative to the sun, it never slowed all the way to its initial approach speed. It left the Jovian environs carrying an increase in angular momentum stolen from Jupiter. Jupiter's gravity served to connect the spacecraft with the planet's huge reserve of angular momentum. This technique was repeated at Saturn and Uranus.

The same can be said of a baseball's acceleration when hit by a bat: angular momentum is transferred from the bat to the slower-moving ball. The bat is slowed down in its "orbit" about the batter, accelerating the ball greatly. The bat connects to the ball not with the force of gravity from behind as was the case with a spacecraft, but with direct mechanical force (electrical force, on the molecular scale, if you prefer) at the front of the bat in its travel about the batter, translating angular momentum from the bat into a high velocity for the ball.

Gravity assists can be also used to decelerate a spacecraft, by flying in front of a body in its orbit, donating some of the spacecraft's angular momentum to the body. When the Galileo spacecraft arrived at Jupiter, passing close in front of Io in its orbit, Galileo experienced deceleration, helping it achieve Jupiter orbit insertion.

Three Body Problem:

The problem of determining the motion of three celestial bodies moving under no influence other than that of their mutual gravitation. No general solution of this problem (or the more general problem involving more than three bodies) is possible.

As practically attacked, it consists of the problem of determining the perturbations (disturbances) in the motion of one of the bodies around the principal, or central, body that are produced by the attraction of the third. Examples are the motion of the Moon around the Earth, as disturbed by the action of the Sun, and of one planet around the Sun, as disturbed by the action of another planet. The problem can be solved for some special cases; for example, those in which the mass of one body, as a spacecraft, can be considered infinitely small, and in the Lagrangian and Eulerian cases.

U.S. Post WWII Rocket Research

Although somewhat of a genesis of modern rocketry research had been established in the United States prior to the end of World War II, certainly the greatest impact in modern U.S. rocketry occurred when the bulk of German rocket scientists surrendered to U.S. forces. As early as January, 1945 Wernher von Braun met secretly with his senior staff members to decide whether or not to remain at Peenemunde and most certainly eventually surrender to Soviet forces or head southward to meet and surrender to U.S. forces.

With the German war effort crumbling and German military leadership showing a state of confusion, official orders for von Braun remained vague. Different orders reached him from Berlin, local army and navy commanders, the SS as well as Nazi party bosses. Some ordered von Braun to stay and defend Peenemunde, while others ordered him to retreat to a more secure site. In general, von Braun decided to ignore the orders to stay while considering the best of the orders to abandon the site. Since escape to U.S. forces was his goal, he needed an official plan that best aided this objective.

An official order was eventually given to von Braun which involved a relocation of the Peenemunde operation to the town of Bleicherode in the Harz Mountains. This plan was obeyed to an extent. Although the relocation order was obeyed, von Braun arranged for tons of sensitive documents to be moved, as well as the families of his associates. Arrangements were made for Wernher von Braun and his team to cross German lines and stay with U.S. troops.

By the close of World War II, the U.S. military had already begun rocketry research that would aid in the development of future rocket and missile programs. Although U.S. rocketry research paled in comparison to developments made in Germany, a test bed was established that would prove fruitful in the development of long-range rockets after the war. The Private rocket program was initiated at the Jet Propulsion Laboratory, an Army-sponsored research arm of the California Institute of Technology. The Private A rocket was 8 feet long and had a diameter of 2.8 feet. The Private A was powered by an Aerojet solid-propellant sustainer engine, with liftoff thrust provided by four modified 4.5-inch barrage rockets attached by a steel casing. The Private A had four guiding fins at the rear and sported a tapered nose. The rocket was launched from a rectangular steel boom employing four guide rails. A total of 24 Private A rockets were tested. The maximum altitude achieved by a Private A rocket during these tests was 11.3 miles.

Wac Corporal:

Perhaps the most significant World War II research rocket was the Wac Corporal. The Wac designation stood for "Without Any Control", with Corporal being the next rank above Private. Wac Corporal development began in 1944 when the Army Signal Corps requested a rocket capable of carrying a 25-pound scientific payload to altitudes approaching 100,000 feet. The full-scale Wac Corporal was 21 feet long, had a diameter of 12 inches and sported three tailfins. The Wac Corporal employed a solid-propellant first stage nicknamed "Tiny Tim" which could produce a liftoff thrust of 50,000 pounds. A solid-fueled Aerojet second stage could produce a thrust of 1,500 pounds. Wac Corporal rockets were launched from a launch tower similar to those used for tests conducted by Dr. Robert Goddard. Test launches of the Wac Corporal were conducted at the White Sands Proving Ground in New Mexico, although tests of the rocket did not occur there until September, 1945 after World War II had ended.

Results from the Wac Corporal program were significant, with one of the rockets reaching a maximum altitude of 43.5 miles. The Wac Corporal program also yielded a second stage for captured German V-2 rockets, with the two-stage V-2 called Bumper-Wac. A Bumper-Wac became the first rocket to carry an object into space and also became the first type of rocket to be launched from Cape Canaveral.

The V-2 research program moved fairly quickly, with flights scheduled at the White Sands Proving Ground, New Mexico. The first static engine test firing of a German V-2 on U.S. soil occurred on March 14, 1946. The missile used for this engine test became the first German V-2 launched in the U.S. on April 16, 1946. The U.S. V-2 series of launches concluded in 1952. Some of the launches employed V-2 missiles equipped with scientific instrumentation designed to study the upper atmosphere. These types of V-2 launches were managed by the V-2 Upper Atmosphere Research Panel, which was established in January, 1947 and evolved into the Upper Atmosphere Rocket Research Panel in March, 1948.

A number of scientific objectives were met, including measurement of the ionosphere, solar radiation, cosmic radiation, micrometeorites and sky brightness. Biological research and Earth photography were also conducted. Early V-2 research employed missiles entirely of German design, but U.S. performance enhancements were introduced as early as 1947. These included the lengthening of the V-2 by about five feet, resulting in an increase in available payload space from 16 cubic feet to 80 cubic feet.

Another important modification was the addition of a second stage. Eight V-2 missiles were outfitted with Without Any Control (WAC) Corporal rockets as a second stage, with the resulting vehicle called Bumper-Wac. These were used to test stage separation under a variety of operational conditions. The first five Bumper-Wac rockets were launched from White Sands, New Mexico where achieving the highest altitude possible was the goal. On February 24, 1949 the second stage of Bumper #5, the fifth rocket launched in the Bumper-Wac series, became the first man-made object placed in space.

Bumper-Wac tests moved to the virgin Long Range Proving Ground at Cape Canaveral in 1950, where the rockets were intended to test rocket staging at a near horizontal flight. These tests required a greater flight range than was available at White Sands. Bumper #8 became the first rocket launched from Cape Canaveral on July 24, 1950. This was followed by the launch of Bumper #7 on July 29, 1950 which became the second rocket launched from the Cape.

Hermes:

The Army knew its supply of V-2 rockets would eventually run out, so a number of other ballistic missiles were designed to augment or replace the V-2 for the purpose of carrying our certain research objectives. Some were designed as a part of Project Hermes, a joint venture of the Army and General Electric. A number of V-2 scientific launches, including the entire Bumper-Wac series, were conducted under Project Hermes.

The first of the new vehicles was called the Hermes A1, a small rocket similar in design to the German Wasserfall surface-to-air missile. The Hermes A1 was powered by an engine that burned a combination of liquid oxygen and alcohol, and was capable of a maximum altitude of 15 miles, maximum range of 40 miles and maximum speed of 1,850 m.p.h.

Project Hermes gave the von Braun team the resources it needed to design more advanced weapons, like the Hermes II. This was a ramjet-powered second stage designed to be mated to a V-2 first stage. It employed a complex engine design, and a full-scale version of the ramjet stage was actually test fired from a V-2. General Electric designed the Hermes C, a large three-stage rocket powered by a six-booster first stage, a one-booster second stage and a glider-type third stage. The Hermes C had a desired range of 2,000 miles but was never built.

Redstone ICBM:

Army ballistic missile research activities outgrew the facilities at Fort Bliss, Texas by the late 1940's. A search was made to select a more suitable site. The Redstone Arsenal in Huntsville, Alabama was selected. It featured ample electricity from the Tennessee Valley Authority and convenient transportation access to the new Long Range Proving Ground at Cape Canaveral. The transfer from Fort Bliss to the Redstone Arsenal was approved on October 28, 1949 and the move, which included the entire von Braun design team, was completed between April and November, 1950. About 500 military personnel, 130 Germans, 120 civil servants and several hundred employees of General Electric made the move to Huntsville.

Upon the outbreak of the Korean War in June, 1950 the Army design team at the Redstone Arsenal was given the responsibility of designing a ballistic missile capable of achieving a range of 500 miles. After unofficially being called Ursa, then Major, the missile was named Redstone in honor of the Redstone Arsenal on April 8, 1952. Development of the Redstone ushered in the most important period of rocket development in U.S. history, with Redstone-based rockets ultimately assuming the duty of carrying both the first U.S. satellite and first U.S. astronaut into space.

Although great scientific accomplishments were associated with the Redstone missile, development of vehicles at the Redstone arsenal were driven by military concerns, especially a fear that the Soviet Union had succeeded in the development of advanced, long-range ballistic missiles capable of delivering nuclear weapons.

Jupiter

The joint Army-Navy missile was named Jupiter. Although Army-Navy cooperation on the Jupiter missile would not last, the Jupiter program led directly to the launch of the first U.S. satellite, Explorer I, on January 31, 1958. The resulting Jupiter missile itself became the free world's first intermediate-range ballistic missile. Jupiter missiles were also employed as the first stage of the Juno II rocket. ABMA designed follow-up rocket concepts through Juno V. The Juno V concept closely resembled the Saturn I, a vital vehicle in the NASA Apollo program.

Although the Air Force had chosen specifically not to pursue the development of ballistic missiles following World War II, the advent of small, high-yield nuclear weapons and an ever-increasing Soviet threat facilitated the most massive peacetime weapons development program in U.S. history. The MX-774 ballistic missile research program funded by the Army Air Corps and canceled in 1947 did provide technical information that would prove fruitful later. In December, 1952 the Air Force Scientific Advisory Board set up a committee to review the Air Force position on the delivery of nuclear weapons.

The ARDC Western Development Division was redesignated the Air Force Ballistic Missile Division (AFBMD) in June, 1957. By this time, the foundation was securely laid for long-range ballistic missile programs like the Thor intermediate-range ballistic missile (IRBM) and ICBM programs like Atlas, Titan I, Titan II and Minuteman. As was the case with missiles designed by the Army, Air Force missiles also became instrumental in the U.S. space program. The Thor-based Delta rocket family remains in use today, as do space launch variants of the Atlas, Titan and Minuteman.

Jupiter-C, a direct descendant of the German A-4 (V-2) rocket, was designed, built, and launched by the Army Ballistic Missile Agency (ABMA) under the direction of Dr. Wernher Von Braun. The Jupiter-C has its origins in the United States Army's Project Orbiter in 1954. The project was canceled in 1955, however when the decision was made to proceed with Project Vanguard. The Jupiter-C rocket was originally developed to test the ablative re-entry nose cone of the Jupiter IRBM, although its satellite-launching capabilities were recognized at the time it was designed.

The vehicle consists of a modified Redstone ballistic missile topped by three solid-propellant upper stages. The tankage of the Redstone was lengthened by eight feet to provide additional propellant. The instrument compartment is also smaller and lighter than the Redstone's. The second and third stages are clustered in a "tub" atop the vehicle, while the fourth stage is atop the tub itself. The second stage is an outer ring of eleven scaled-down Sergeant rocket engines; the third stage is a cluster of three scaled down Sergeant rockets grouped within. These are held in position by bulkheads and rings and are surrounded by a cylindrical outer shell. The webbed base plate of the shell rests on a ball-bearing shaft mounted on the first-stage instrument section. Two electric motors spin in the tub at a rate varying from 450 to 750 rpm to compensate for thrust imbalance when the clustered motors fire.

Soviet Secret Missile Program

While the Soviet Union suffered somewhat of an embarrassment as U.S. forces removed the lion's share of German V-2 hardware from the Mittelwerk plant literally under their noses, the Soviets did not conclude World War II empty handed. While most of the German scientists and hardware were gone, the Soviets were able to secure tons of equipment and key German scientists Helmut Grottrup, Erich Putze and Werner Baum. These scientists were experts in guidance, production and propulsion, respectively. The Soviets also secured hundreds of lower echelon workers. Most importantly, the Soviet Union already possessed its own experts in rocketry, an equation that was lacking in the U.S. These scientists included A.G. Kostikov, inventor of the World War II Katyusha rocket, and Sergei P. Korolev, considered to be the father of modern Soviet rocketry.

Following World War II, the Soviets supervised renewed V-2 production at the Mittelwerk plant, which continued well into 1946. The Soviets also used V-2 rockets for initial post-war rocketry research. On October 22, 1946 all of the German scientists working for the Soviets were transported without warning by truck and train to Russia. A German Rocket Collective was soon established outside Moscow. There, the Germans went to work refining and improving the V-2 to create a similar, yet new, rocket. On March 15, 1947 a State Commission was formed to study the feasibility of producing long-range ballistic missiles. The State Commission recommended that the first logical step was an improved version of the V-2, which was already under development at the German Rocket Collective. The improved V-2 was first launched from Kapustin Yar on October 30, 1947 and achieved a range of 200 miles. The improved V-2 was followed by the Pobeda, a mobile ballistic missile with an impressive range of 500 miles. From that point on, German participation in the Soviet missile program declined rapidly. Most of the German scientists and workers were repatriated to Germany by the early 1950's. The last to be repatriated was lead scientist Helmut Grottrup, who returned to West Germany in November, 1953.

Many of the Germans were interrogated by U.S. intelligence, but the Soviets were very careful to restrict access of the Germans to only the missile programs they were directly involved in. In fact, next to no insight was given to the U.S. by the repatriated Germans into the state of Soviet rocketry. It was not well known in the U.S. exactly how advanced the Soviet missile threat actually was. Soviet ballistic missile research progressed quickly after World War II, and was in fact by the late 1950's dangerously ahead of the U.S.

The Soviet advantage over the U.S. was based on two major factors. First, the Soviet military settled on the development of ballistic missiles from the early days after World War II, and wasted no effort designing guided winged missiles which ultimately proved for the U.S. to be ineffective in light of advances in improved interceptor aircraft and anti-aircraft defenses. Simply stated, the Soviets had about a decade's head-start over the U.S. in the development of ballistic missile weapons. In addition, the Soviets were undeterred by the fact that nuclear weapons payloads were heavy and bulky. They simply developed huge rockets that could carry these heavy payloads.

Soviet ICBM's, R-1 through R-5

The R-1 was the Soviet production copy of the German V-2. Despite the threatening supervision of the program by Stalin's secret police chief, Beria, and the assistance of German rocket engineers, it took eight years for the Geman technology to be absorbed and the missile to be put into service. A resolution to put into production a Soviet-built copy of the V-2, the R-1, was issued on 14 April 1948. Aleksander Shcherbakov was responsible for seeing that a fifteen year technology gap was bridged. To accomplish this the resources of 13 research institutes and 35 factories were tapped. Glushko was tasked with producing the RD-100 copy of the V-2 engine. Prototypes had already begun factory tests at the end of 1947, with stand tests beginning in May 1948. R-1 test flight trials were accomplished swiftly - ten in 1948 and 20 in 1949. On 25 November 1950 the missile was accepted for service, with the first operational unit the 92nd brigade (BON RVGK) at Kapustin Yar. Things seemed to be going well, but getting the missile in production would be another matter.

Aside from the service version of the missile, variants were used for technology and scientific tests. From the fifth flight of the R-1A these were equipped with ejectable lateral containers

• R-1A for test of separable warheads for use on future ballistic missiles (the R-2 and R-3). The last two launches were vertical scientific flights to sample the upper atmosphere.
• R-1B and R-1V for study of cosmic rays, the upper atmosphere, solar radiation, recoverable biological payloads, and recovery of the entire missile by parachute for reuse.
• R-1D for study of the atmosphere; aerodynamics of test shapes at high velocities and altitudes; wind in the upper layers of the atmosphere; the ionosphere; and recoverable biological and instrument payloads.
• R-1Ye for study of the atmosphere, solar spectrum, aerodynamics; wind in the upper layers of atmosphere; ionosphere; ozone layer; recoverable biological specimens, and recovery of the entire missile by parachute.

In field service the rocket required twenty vehicles and four kinds of liquid propellants for the main engine, turbines, and starter (liquid oxygen, alcohol, hydrogen peroxide, permanganate catalyst). Six hours were required to prepare the rocket for launch, and CEP was only 1500 m. Another major objection of Red Army Generals - they didn't dare let the troops work with a rocket using alcohol for a propellant.

Nevertheless in December 1950 the first field R-1 unit was formed - the 23th brigade (BON RUGK). Each brigade was equipped with six launchers. In January 1951 the 23rd deployed to Kamishin in Volgograd oblast. Further deployments of this pathfinder unit were to Belokovorovich, Ukraine; Shyalyay, Lithuania; Dzhambul, Kazakhstan, and Ordzhonikidze, the Far East, the Primorsk area. The 77th and 90th brigades were formed at Lvov, Khmelnitskiy, and Zhitomir, Ukraine. In August 1958 they were transferred to the Land Forces. The number of units fielded were small, reflecting the long delay in getting the R-1 into production. The field equipment was designed to also be used for R-2 missiles, which quickly replaced the R-1 in the field units.

1951 The first launch of the "geophysical" rocket carrying live animals onboard.

The R-2 doubled the range of the R-1 and was equipped with a deadly radiological warhead. The ethyl alcohol used in the V-2 and R-1 was replaced by methyl alcohol in the R-2, eliminating the problem of the launch troops drinking up the rocket fuel. Aside from the basic military service version of the R-2, specialised variants included:

• R-2E: Prototype rocket with characteristics of both the R-1 and R-2 used to test the integral fuel tank and separable warhead planned for the production R-2 missile.
• R-2R: Evidently used to test the advanced radio controlled cut-off system being developed for the R-3. However this may also just identify certain R-2A flights with this payload. No launch dates conclusively known.
• R-2A: This was the main variant for scientific work, used to continue the experiment series of the R-1 to a height of 200 kilometres. Instruments were carried to study the atmosphere over 150 km; ultra-violet observation of the sun; ultra-violet astronomy; the ionosphere; and recovery of biological payloads (dogs and rabbits) from double the altitude of the R-1.

Versions of the R-2 for suborbital manned flights were studied by Korolev in 1956-1958, but it was decided instead to move directly to orbital flights of the Vostok. However some equipment tested on the R-2 found its way onto canine flights of Sputnik and Vostok.

The G-2 design objective was to create the first IRBM - to deliver a 1000 kg payload over a 2500 km range. The missile would use three V-2 derived engines with a total thrust of 100 tonnes. A variety of alternate configurations (R-12A through R-12K) were considered by the German team in Russia. These included parallel and consecutive staging, gimballed motors, and other innovations. The R-12K was particularly interesting because it represented a concept later used on the US Atlas missile - jettisoning of the two outboard engines at altitude to significantly improve range. The G-2 was given the secret designation R-6 and overt designation R-12 by the Russians.

Development of the long-range R-3 missile was authorised at the same time as the V-2-derived R-1 and R-2 rockets in April 1947. Supplemental authorisation was contained in a government decree of 14 April 1948.The specification was an order of magnitude leap from the other vehicles - to deliver a 3 tonne atomic bomb to any point in Europe from Soviet territory - a required range of 3000 km. To achieve this objective innovative technology was needed in every area of the missile design. Korolev was again in direct competition with the design to the same specification of the captured Germans (Groettrup's G-4).

In 1956, the Soviet of Ministers of the USSR approved the development of the scientific satellite. This project, Sputnik will use an R-7 ICBM to enter the space age by lifting a 50 lb payload into orbit.

Topical Questions:

• How are orbits defined? What is the primary determinate to the major axis of an orbit?