W

E ARE in the second half of the opening decade of the space age. Soviet and U.S. achievements have made this a familiar, accepted fact. However, the military uses of space are still undefined. We face three forms of skepticism in determining the role of space in our defense:

(1) Is manned space flight technically feasible?

(2) Do military space operations have any military worth?

(3) Do they fill any strategic need?

Our technical strategy in answering these three questions is to confine our efforts in space to research and development. In large measure, we are concentrating on the first question only. Presumably, the effort to answer the others will follow.

In a historical context, we are in a period analogous to the decade immediately preceding World War I. In that period extensive research and development was accomplished in an effort to answer Question 1, about manned flight. Some limited demonstrations were conducted to answer Question 2 about manned air operations. For example, the United Kingdom fired the first machine gun in an aircraft (1911), used the radio for air/ ground communications (1911), and flew some support during army maneuvers (1912). The U.S. dropped the first bomb (1911). The Italians were the first to use the airplane in war (the capture of Tripoli from the Turks in 1911).

There was one underlying theme in the ferment of this early experimentation and demonstration-individual initiative. All these events did not just happen. They were made to happen by men with imagination, curiosity, foresight, and energy. These pioneers were "self-starters." They were not pushed out onto the frontiers of technology, operations, and strategy. They went there early. To get there, they had to use a new world of knowledge, of principles, and of data and had to apply it to specific projects, inquiries, and demonstrations. Dihedral, camber, chord, aspect ratio, lift/drag became their language. Meteorology

took on new importance. Understanding of the internal combustion engine became critical.

Today we are in a period of experimentation in space. Demonstrations of the use of space are off in the future. Efforts to answer Questions 2 and 3 are not under way. We in the Air Force must be ready to try to answer them when the time comes. This means that we, as individuals, must have the knowledge of the principles underlying space operations. We must know the language of space, understand it, and be able to apply it.

Most of the principles of space operations come from astronomy and celestial mechanics. They have evolved over the centuries. Others, such as Newton's laws, are basic to any understanding and use of the physical environment. As we acquire additional knowledge of the phenomena of space, such as radiation belts, solar flares, and meteorites, we will have to know their effects on space operations. Let us look at a few of these principles and data and then examine how they apply to space operations.

Among the fundamentals of space operations are the notation and orbit orientation depicted in Figure 1. Terms such as apogee, perigee, true anomaly (sometimes called merely "anomaly"), lines of apsides and nodes, and orbit plane are the ordinary, working language of those involved in space activities. The inclination of the orbit plane (i) will nearly always be a consideration because launchings into equatorial orbits will be fairly rare. This inclination is expressed in degrees. The inclination of the Mercury orbits, for example, has been approximately 28°. Launchings from Vandenberg have put our Discoverers into polar orbit, 90° inclination.

Some of the fundamental laws and equations of orbital mechanics shown in Table 1 are, of course, the same laws used in physics, or derivations therefrom. A few observations are nonetheless interesting. For instance, the velocity of a satellite in a circular orbit 300 nautical miles above the earth is precisely 24,888 feet per second, while that of a circular orbiting satellite 200 nautical miles lower

(with 5000 pounds of propellant) used to propel a 15,000-pound spacecraft would provide only about 2500 feet per second velocity increment. The comparison here between V required and V available is somewhat exaggerated but serves to emphasize two points: first, orbit plane changes should always be made at the higher altitude (lower t,); and second, higher values of I, will almost certainly be required for appreciable increases in AV available from maneuvering engines.

A few other words used in space operations, defined in Table 3, were chosen to point up the discussion which follows. Transfer will be basic to space operations whether circumearth or circumlunar. Dogleg is used in most changes of orbit plane, although another method is described later. Also, note that rendezvous names a fairly gross maneuver as compared with docking.

Figure 2 illustrates a particular type of transfer, the Hohmann transfer. This is the path which is followed to change from a lower altitude to a higher altitude in the same orbital plane with the minimum expenditure of energy when time required to reach the new altitude is not a primary consideration.

Holding in a parking orbit at an altitude of about 100 nm will generally precede transfer to higher altitude orbits, particularly when rendezvous with an orbiting satellite is required. Because of the earth's rotation, a launch site such as Cape Canaveral passes

through orbital planes inclined greater than about 30° twice a day. However, in order to launch into a plane of 45° from Canaveral without doglegging, for example, as much as a 16-hour delay can be encountered. And even after waiting 16 hours for the launch site to rotate into the plane of the orbit, it is very likely that a satellite with which rendezvous is required will not be in the proper location for direct-ascent rendezvous. In fact, when Canaveral passes under the 45° plane, a satellite in that orbit could be over Australia. Instead of waiting several days (or perhaps weeks) until the orbiting satellite is in the right position, we will simply launch into a coplanar parking orbit and wait until the two

intercept.

either by direct ascent from launch site or by transfer from parking orbit.

Maneuver by which a spacecraft makes soft physical contact with a target vehicle.

Maneuver by which a spacecraft is placed at a specific point (target vehicle) in space at a specific time, executed as a continuous trajectory from launch site or parking orbit.

vehicles are in the correct position relative to one another for the execution of a Hohmann transfer.

The dogleg is not the only maneuver that can be used for a change of orbit plane. The synergetic plane change shown in Figure 3 is a maneuver available only to spacecraft with hypersonic lift-to-drag ratios greater than one. By making this maneuver, the astronaut can change his orbit with as much as 50 per cent reduction in the amount of energy required up to altitudes of about 600 nautical miles. Aerodynamic lift available during the precisely controlled turn at low altitude (about 35 nm) to the desired orbit plane accounts for the reduction in energy required as

Figure 3. Synergetic plane changing