SPACE ELEVATOR DEPLOYMENT FROM GEO ORBIT
This is one of many schemes that have been put forth to accomplish deployment of the space elevator. It starts with a large satellite positioned at GEO. This GEO satellite is constructed from sub-components delivered to GEO via (more or less) conventional rocket launches, and contains:
a. The Ribbon,
b. The Lower satellite; an earth-seeking guidance and control module, that delivers the bottom of the ribbon to its anchor point,
c. The Upper satellite; that manages ribbon deployment, it's own guidance and control, and is destined to become the ballast mass for the space elevator.
As the ribbon deploys downward from GEO, the two end-satellites perform a delicate guidance and control dance, to wit: as,
- the lower satellite progressively moves deeper into the Earth's gravity well of ever increasing magnitude (thus creating downward force on the system), - the upper satellite must then move to ever higher altitudes creating a correspondingly greater centrifugal force to counter the increasing gravity pull.
THE CONTROL TASK
The control task of the "upper" and "lower" satellites consists of 2 activities:
a. Altitude control, which is a combination of both vertical thrust adjustments and precise control of the amount of ribbon being deployed; this performs the "vertical balancing act".
b. Tangential thrusting (ie. thrust normal to the radial) to provide "make-up" in tangential velocity to keep each satellite's tangential velocity consistent with its altitude.
The series of animations below depict the natural tendencies of such a process, as well as portrays examples of control schemes that produce failure modes, and finally, depicts how the deployment would look when successfully accomplished.
Note 1: all these animations have highly accelerated time frames; at the bottom will be seen a digital time stamp in which the leading 2 digits represent "days into the deployment" (a normal successful deployment via such a scheme takes about 15 days).
Note 2: the eye point reference-frame for these animations is looking down on the south-pole (thus you see the Antarctica land mass and mid-Pacific ocean at the top of the globe); the eye is fixed in a frame that is rotating with the earth; this is why the earth is apparently stationary in the animation. Thus, in a successful deployment, the ribbon and its end-satellites would appear as a growing straight-line proceeding directly towards and away from earth directly along a single radial.
Note 3: the ribbon will exhibit various shades of red during deployment operations to depict tension along the ribbon.
- "High intensity red" color depicts greater (maximum) tension,
- "shades of pink" would depict intermediate tensions, and,
- "Pure white" would depict no (or very low) tension
Note: the very active pendulus motions at the beginning of some animations is indeed intended, since it is a low fuel mechanism to start initial deployment of such a system. The mechanism of tether dynamics ensures that these initial potions witl soon become of insignificnat import (the so-called "skater's effect".
1. The animation below shows the natural dynamic tendencies that will prevail if one were to simply station themselves at GEO, and start dropping the ribbon directly down towards Earth, with no compensating control interventions by the satellites at either end of the ribbon. It is seen that the entire system will progress westward, eventually plunging to earth.
2. The animation below show what would happen, if the "vertical thrusting component" of control were present, but the "Tangential Thrusting component" of control were absent.