Wave Propagation Animations

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Wave Propagation Animations

Overview and Explanation

The avoidance of predicted large space debris and satellite encounters by means of sending a large transverse wave up the elevator is one of the schemes that has been proposed by space elevator engineers. Such a wave is envisioned as being created at the anchor location by moving the anchor base. This is possible since the base will be an ocean platform capable of a relocation-maneuver by a tug-system, or, under self-propulsion.

Satellites and other tracked debris are characterized by a very predictable arrival times and locations along their orbital track. If such an event, that would put the elevator ribbon in jeopardy of collision, is predicted to occur, then a ribbon avoidance maneuver may be in order.

The avoidance maneuver is characterized by the anchor's executing a translation so as to create a transverse wave (ie. a horizontal kink in the ribbon) that will propagate vertically very predictably up the ribbon in compliance with the physics of string-dynamics. This traveling wave propagation-velocity occurs at a highly predictable value, thus it is possible, knowing the time-of-arrival and position of space debris to initiate a wave in advance that would arrive at the predicted impact point at the predicted time of impact. However, this wave (say it is 1 km in magnitude), upon its arrival, will displace the ribbon sideways so that there will be no ribbon present at the predicted collision point and time and the satellite will have passed harmlessly by.

Since such waves travel at significant vertical speeds, it is possible to react on a fairly timely basis with debris that may be detected using over-the-horizon radar scanning for just such events. For instance "time to LEO" for such a wave is on the order of 6.8 km/ sec (about 15,000 mph), so it takes about 30 sec total to reach LEO; if threatening debris in LEO were spotted, say, "15 minutes out", a transverse wave generated at the anchor could easily reach LEO in time to produce an avoidance; likely one of the limiting factor in this scheme will be the time it takes to actually generate a wave by moving the anchor.

This section illustrates some basic attributes of transverse wave propagation in the elevator ribbon by example of simulating the above space debris avoidance operation. Such a wave will be viewed from many perspectives, including it interaction with the ballast mass residing at 100,000 km altitude.

Animation Descriptions

In general the displacements of the transverse waves are highly exaggerated. Typically, such a wave may have a peak amplitude of about a km; for most of these animations, this displacement, if displayed on the same scale as the vertical scale, would be difficult to detect without significant displacement scaling exaggeration.

These animations are viewed with a wide variety of eye-points in 3-D perspective

While the anchor appears to be positioned on the South American continent, this is for presentational effect only; actually the anchor would be fully at sea

Note: the above QT movie was made using the application "Space Animator", created by Paul Snow (you can contact Paul in the Seattle area at "psnow10 -at- comcast -dot- net")

Wave Creation Details

- This animation shows a low altitude side view of the ribbon with the anchor-base being moved to start a wave propagating up the ribbon.

Time sped-up x1000; Near ground planar-view of wave creation

View from 780 km, Looking down onto Anchor

- Note that the ribbon at this high LEO altitude experiences the full avoidance translation well before the anchor has returned to its original location.

REAL TIME; displacements scaled x10

View at High LEO Altitude

Time sped-up x1000; Viewed from afar

Wave as Seen at MEO Ribbon location

- This animation places the eye-point near the ribbon at MEO; this eye point simulates the location in space at which a debris object is predicted to pass (putting the ribbon in jeopardy).

- Note that when the wave arrives at the "eye-point" on the ribbon, it produces an evasive sideways displacement, thus avoiding the location through which the debris will have passed.

-This illustrates the importance of timing" in this type of debris avoidance maneuver.

Time sped-up x1000; Eye is very near to ribbon

Wave Reflecting Off Of Ballast

- This animation illustrates a basic classical aspect of string wave propagation, namely the reverse-reflection of waves off of boundaries.

Time sped-up x1000; Close up view near ballast

Wave Reflecting Off Of Ballast

Time sped-up x1000; View of entire ribbon

Effects of Climber at LEO

- The low mass density and high tension of the ribbon is what produces such high velocities for wave travel; they absence of either ingredient and disrupt wave propagation speed.

- Here a climber residing at LEO, represents a drastic deviation from the otherwise low mass density of the ribbon, and becomes an important ingredient in determining net wave transmission time up the ribbon.

- This disruption is predictable, and can be factored in to the maneuver timing, albeit, representing a net retardation of the time to transmit a given avoidance displacement to a given point along the ribbon.

Time sped-up x100; Close up View

Effects of Climber at LEO

Time sped-up x100; Far off View