For the rocket, the simplest type of a practical application as a means of transportation results when it climbs in an inclined (instead of vertical) direction from the Earth, because it then follows a parabolic trajectory (Figure 46). It is well known that in this case the range is greatest when the ballistic angle (angle of departure)in our case, the angle of inclination of the direction of ascent is 45° (Figure 47).
Figure 46. Inclined trajectory.
Key: 1. Parabolic trajectory; 2. Ballistic (departure) velocity; 3. Angle of departure; 4. Range; 5. Impact velocity.
Figure 47. The greatest distance is attained for a given departure velocity when the angle of departure is 45°.
Key: 1. Direction of departure; 2. Greatest distance.
In this type of application, the rocket operates similarly to a projectile, with the following differences, however: a cannon is not necessary to launch it; its weight can be much larger than that of a typical, even very large projectile; the departure acceleration can be selected as small as desired; however, such high departure velocities would be attainable that there would theoretically be no terrestrial limit whatsoever for the ballistic (firing) range of the space rocket.
Therefore, a load could be carried in an extremely short time over very great distances, a fact that could result in the opinion that this method could be used for transporting, for example, urgent freight, perhaps for the post office, telecommunication agency, or similar service organization.
The latter application would, however, only be possible if the descent velocity of the incoming rocket were successfully slowed down to such a degree that the vehicle impacts softly because otherwise it and/or its freight would be destroyed. According to our previous considerations, two braking methods are available in this regard as follows: either by means of reaction or by air drag. Because the former must absolutely be avoided, if at all possible, due to the enormous propellant consumption, only the application of air drag should be considered.
Braking could obviously not be achieved with a simple parachute landing, because, considering the magnitudes of possible ranges, the rocket descends to its destination with many times the velocity of a projectile. For this reason, however, the braking distance, which would be available in the atmosphere even in the most favorable case, would be much too short due to the very considerable steepness of the descent. As an additional disadvantage, that the main part of the descent velocity would have to be absorbed in the lower, dense layers of air.
This is equally valid even when, as suggested by others, the payload is separated from the rocket before the descent so that it can descend by itself on a parachute, while the empty rocket is abandoned. Neither the magnitude of the descent velocity nor the very dangerous steepness of the descent would be favorably influenced by this procedure.
In order to deliver the freight undamaged to its destination, braking, if it is to be achieved by air drag, could only happen during a sufficiently long, almost horizontal flight in the higher, thin layers of air selected according to the travel velocity that is, according to Hohmann's landing method (glided landing). Baking would consequently be extended over braking distances not that much shorter than the entire path to be traveled. Therefore, proper ballistic motion would not be realized whatsoever for the case that braking should occur before the impact but rather a type of trajectory would result that will be discussed in the next section entitled "The Space Rocket as an Airplane."
With an inclined ballistic trajectory, the rocket could only be used when a "safe landing" is not required, for example, like a projectile used in warfare. In the latter case, solid fuels, such as smokeless powder and similar substances, could easily be used for propelling the rockets in the sense of Goddard's suggestion, as has been previously pointed out.
To provide the necessary target accuracy for rocket projectiles of this type is only a question of improving them from a technical standpoint. Moreover, the large targets coming mainly under consideration (such as large enemy cities, industrial areas, etc.) tolerate relatively significant dispersions. If we now consider that when firing rockets in this manner even heavy loads of several tons could safely be carried over vast distances to destinations very far into the enemy's heartland, then we understand what a terrible weapon we would be dealing with. It should also be noted that after all almost no area of the hinterland would be safe from attacks of this nature and there would be no defense against them at all.
Figure 48. The greater the range, the greater the descent velocity will be (corresponding to the greater departure velocity and altitude necessary for this).
Key: 1. Departure velocity; 2. Earth's surface; 3. Descent velocity; 4. Atmosphere.
Nevertheless, its operational characteristics are probably not as entirely unlimited as might be expected when taking the performance of the rocket propulsion system into consideration, because with a lengthening of the range the velocity also increases at which the accelerated object, in this case the rocket, descends to the target, penetrating the densest layers of air near the Earth's surface (Figure 48). If the range and the related descent velocity are too large, the rocket will be heated due to air drag to such an extent that it is destroyed (melted, detonated) before it reaches the target at all. In a similar way, meteorites falling onto the Earth only rarely reach the ground because they burn up in the atmosphere due to their considerably greater descent velocity, although at a much higher altitudes. In this respect, the Earth's atmosphere would probably provide us at least some partial protection, as it does in several other respects.
No doubt, the simplest application of the rocket just described probably doesn't exactly appear to many as an endorsement for it! Nevertheless, it is the fate of almost all significant accomplishments of technology that they can also be used for destructive purposes. Should, for example, chemistry be viewed as dangerous and its further development as undesirable because it creates the weapons for insidious gas warfare? And the results, which we could expect from a successful development of space rockets, would surpass by far everything that technology was capable of offering to date, as we will recognize in the following discussion.