Improving Stability of the Space Cable
- Paper number
IAC-08.D4.2.5
- Author
Dr. John Knapman, United Kingdom
- Year
2008
- Abstract
The proposed space cable consists of several pairs of evacuated tubes, each a few centimetres in diameter, in which fast-moving projectiles, called bolts, support the weight. It is a means of launching vehicles to orbit, as well as a platform for tourism, astronomy and communications. It stands on the ground and reaches a height of 140 km over a range of about 150 km. Like the launch loop, the space cable is a variation on the space elevator but can be built using today’s materials and technology; it has certain cost advantages over those proposals.
One of the issues with the space cable is lateral stability. As winds and other forces bend the cable, the centrifugal force on the bolts causes them to exaggerate the effect, thus creating instability. At IAC 2006, the author outlined one approach to this problem using stabilizing cables anchored to the ground. Further work has shown the feasibility of a much lighter-weight and more economical solution that employs a new technique called active curvature control. An arrangement of perpendicular and angled struts permits a local control system to adjust the curvature so as to counteract the bending effect. Moreover, it can eliminate movement in the upper part of the cable, where there is no wind and there may be scientific or other apparatus. Instead, active curvature control causes the movement and associated forces to be transmitted to the ground, where they can be handled relatively easily.
The full equation governing the motion and curvature is of the fourth order, but a more convenient second-order equation in time t and displacement x along the cable relates the curvature c directly to B, which is the bending moment per unit length of the external forces. There is also a bending moment B s caused by the local arrangement of angled struts. We get the equation
m u ∂ 2 c ∂ t 2 ± m b V ∂ 2 c ∂ t ∂ x +( m b V 2− T) ∂ 2 c ∂ x 2 = B ± B s Here, m u and m b are the respective masses per unit length of a tube and of the bolts within it. T is the tube’s tension, and V is the bolt velocity. The ± signs reflect the opposing bolt velocities in a pair of tubes. The control mechanism can adjust the curvature by adjusting B s , following a damped harmonic solution to the curvature equation. The lateral displacement z along the tube can then be computed by integrating the relationship
c= ∂ 2 z ∂ x 2 - Abstract document
- Manuscript document
IAC-08.D4.2.5.pdf (🔒 authorized access only).
To get the manuscript, please contact IAF Secretariat.