Type of tether
Space tethers
are long cables which can be used for propulsion, momentum exchange, stabilization and
attitude control
, or maintaining the relative positions of the components of a large dispersed satellite/
spacecraft
sensor system.
[1]
Depending on the mission objectives and altitude,
spaceflight
using this form of
spacecraft propulsion
is theorized to be significantly less expensive than spaceflight using
rocket engines
.
Main techniques
[
edit
]
Tether satellites might be used for various purposes, including research into
tether propulsion
,
tidal stabilization
and orbital plasma dynamics. Five main techniques for employing space tethers are in development:
[2]
[3]
- Electrodynamic tethers
Electrodynamic tethers are primarily used for propulsion. These are conducting tethers that carry a current that can generate either
thrust
or
drag
from a
planetary magnetic field
, in much the same way as an
electric motor
does.
- Momentum exchange tethers
These can be either rotating tethers, or
non-rotating tethers
, that capture an arriving spacecraft and then release it at a later time into a different orbit with a different velocity. Momentum exchange tethers can be used for
orbital maneuvering
, or as part of a planetary-surface-to-orbit / orbit-to-escape-velocity space transportation system.
- Tethered formation flying
This is typically a
non-conductive
tether that accurately maintains a set distance between multiple space vehicles flying in formation.
- Electric sail
A form of
solar wind
sail with electrically charged
tethers
that will be pushed by the momentum of solar wind
ions
.
- Universal Orbital Support System
A concept for suspending an object from a tether orbiting in space.
Many uses for space tethers have been proposed, including deployment as
space elevators
, as
skyhooks
, and for doing propellant-free orbital transfers.
History
[
edit
]
Konstantin Tsiolkovsky
(1857?1935) once proposed a tower so tall that it reached into space, so that it would be held there by the rotation of
Earth
. However, at the time, there was no realistic way to build it.
In 1960, another Russian,
Yuri Artsutanov
, wrote in greater detail about the idea of a tensile cable to be deployed from a
geosynchronous satellite
, downwards towards the ground, and upwards away, keeping the cable balanced.
[4]
This is the
space elevator
idea, a type of synchronous tether that would rotate with the Earth. However, given the materials technology of the time, this too was impractical on Earth.
In the 1970s,
Jerome Pearson
independently conceived the idea of a space elevator, sometimes referred to as a synchronous tether,
[5]
and, in particular, analyzed a
lunar elevator
that can go through the
L1 and L2 points
, and this was found to be possible with materials then existing.
In 1977,
Hans Moravec
[6]
and later
Robert L. Forward
investigated the physics of non-synchronous
skyhooks
, also known as rotating skyhooks, and performed detailed simulations of tapered rotating tethers that could pick objects off, and place objects onto, the
Moon
,
Mars
and other
planets
, with little loss, or even a net gain of energy.
[7]
[8]
In 1979,
NASA
examined the feasibility of the idea and gave direction to the study of tethered systems, especially tethered satellites.
[1]
[9]
In 1990, Eagle Sarmont proposed a non-rotating Orbiting Skyhook for an Earth-to-orbit / orbit-to-escape-velocity Space Transportation System in a paper titled "An Orbiting Skyhook: Affordable Access to Space".
[10]
[11]
[12]
In this concept a
suborbital launch vehicle
would fly to the bottom end of a Skyhook, while spacecraft bound for higher orbit, or returning from higher orbit, would use the upper end.
In 2000, NASA and
Boeing
considered a
HASTOL
concept, where a rotating tether would take payloads from a hypersonic aircraft (at half of orbital velocity) to
orbit
.
[13]
Missions
[
edit
]
A
tether satellite
is a
satellite
connected to another by a space tether. A number of satellites have been launched to test tether technologies, with varying degrees of success.
Types
[
edit
]
There are many different (and overlapping) types of tether.
Momentum exchange tethers, rotating
[
edit
]
Momentum
exchange tethers are one of many applications for space tethers. Momentum exchange tethers come in two types; rotating and non-rotating. A rotating tether will create a controlled force on the end-masses of the system due to centrifugal acceleration. While the tether system rotates, the objects on either end of the tether will experience continuous acceleration; the magnitude of the acceleration depends on the length of the tether and the rotation rate. Momentum exchange occurs when an end body is released during the rotation. The transfer of momentum to the released object will cause the rotating tether to lose energy, and thus lose velocity and altitude. However, using
electrodynamic tether
thrusting, or
ion propulsion
the system can then re-boost itself with little or no expenditure of consumable reaction mass.
Skyhook
[
edit
]
A skyhook is a theoretical class of orbiting
tether propulsion
intended to lift payloads to high altitudes and speeds.
[14]
[15]
[16]
[17]
[18]
Proposals for skyhooks include designs that employ tethers spinning at hypersonic speed for catching high speed payloads or high altitude aircraft and placing them in orbit.
[19]
Electrodynamics
[
edit
]
Electrodynamic tethers
are long conducting wires, such as one deployed from a tether satellite, which can operate on electromagnetic principles as
generators
, by converting their
kinetic energy
to
electrical energy
, or as
motors
, converting electrical energy to kinetic energy.
[1]
Electric potential is generated across a conductive tether by its motion through the Earth's magnetic field. The choice of the metal
conductor
to be used in an electrodynamic tether is determined by a variety of factors. Primary factors usually include high
electrical conductivity
and low
density
. Secondary factors, depending on the application, include cost, strength, and melting point.
An electrodynamic tether was profiled in the documentary film
Orphans of Apollo
as technology that was to be used to keep the Russian space station
Mir
in orbit.
[20]
[21]
Formation flying
[
edit
]
This is the use of a (typically) non-conductive tether to connect multiple spacecraft.
Tethered Experiment for Mars inter-Planetary Operations (TEMPO³)
is a proposed 2011
[
clarification needed
]
experiment to study the technique.
Universal Orbital Support System
[
edit
]
A theoretical type of non-rotating tethered satellite system, it is a concept for providing space-based support to things suspended above an astronomical object.
[22]
The orbital system is a coupled mass system wherein the upper supporting mass (A) is placed in an orbit around a given celestial body such that it can support a suspended mass (B) at a specific height above the surface of the celestial body, but lower than (A).
Technical difficulties
[
edit
]
Gravitational gradient stabilization
[
edit
]
Instead of rotating end for end, tethers can also be kept straight by the slight difference in the strength of gravity over their length.
A non-rotating tether system has a stable orientation that is aligned along the local vertical (of the earth or other body). This can be understood by inspection of the figure on the right where two spacecraft at two different altitudes have been connected by a tether. Normally, each spacecraft would have a balance of gravitational (e.g.
F
g1
) and centrifugal (e.g.
F
c1
) forces, but when tied together by a tether, these values begin to change with respect to one another. This phenomenon occurs because, without the tether, the higher-altitude mass would travel slower than the lower mass. The system must move at a single speed, so the tether must therefore slow down the lower mass and speed up the upper one. The centrifugal force of the tethered upper body is increased, while that of the lower-altitude body is reduced. This results in the centrifugal force of the upper body and the gravitational force of the lower body being dominant. This difference in forces naturally aligns the system along the local vertical, as seen in the figure.
[23]
Atomic oxygen
[
edit
]
Objects in low Earth orbit are subjected to noticeable erosion from atomic oxygen due to the high
orbital speed
with which the molecules strike as well as their high reactivity. This could quickly erode a tether.
[24]
Micrometeorites and space junk
[
edit
]
Simple single-strand tethers are susceptible to
micrometeoroids
and
space junk
. Several systems have since been proposed and tested to improve debris resistance:
- The US
Naval Research Laboratory
has successfully flown a long term 6-kilometer (3.7 mi) long, 2?3-millimeter (0.079?0.118 in) diameter tether with an outer layer of Spectra 1000 braid and a core of acrylic yarn.
[25]
This satellite, the Tether Physics and Survivability Experiment (TiPS), was launched in June 1996 and remained in operation over 10 years, finally breaking in July 2006.
[26]
- Robert P. Hoyt
patented an engineered circular net, such that a cut strand's strains would be redistributed automatically around the severed strand. This is called a
Hoytether
. Hoytethers have theoretical lifetimes of decades.
- Researchers with
JAXA
have also proposed net-based tethers for their future missions.
[27]
Large pieces of junk would still cut most tethers, including the improved versions listed here, but these are currently tracked on radar and have predictable orbits. Although thrusters could be used to change the orbit of the system, a tether could also be temporally wiggled in the right place, using less energy, to dodge known pieces of junk.
[
citation needed
]
Radiation
[
edit
]
Radiation, including UV radiation tend to degrade tether materials, and reduce lifespan. Tethers that repeatedly traverse the
Van Allen belts
can have markedly lower life than those that stay in low earth orbit or are kept outside Earth's magnetosphere.
Construction
[
edit
]
Properties of useful materials
[
edit
]
Tether properties and materials are dependent on the application. However, there are some common properties. To achieve maximum performance and low cost, tethers would need to be made of materials with the combination of high strength or electrical conductivity and low density. All space tethers are susceptible to space debris or micrometeoroids. Therefore, system designers will need to decide whether or not a protective coating is needed, including relative to
UV
and
atomic oxygen
.
For applications that exert high tensile forces on the tether, the materials need to be strong and light. Some current tether designs use crystalline plastics such as
ultra-high-molecular-weight polyethylene
,
aramid
or
carbon fiber
. A possible future material would be
carbon nanotubes
, which have an estimated
tensile strength
between 140 and 177
GPa
(20.3 and 25.7 million psi; 1.38 and 1.75 million atm), and a proven tensile strength in the range 50?60 GPa (7.3?8.7 million psi; 490,000?590,000 atm) for some individual nanotubes. (A
number of other materials
obtain 10 to 20 GPa (1.5 to 2.9 million psi; 99,000 to 197,000 atm) in some samples on the nano scale, but translating such strengths to the macro scale has been challenging so far, with, as of 2011, CNT-based ropes being an order of magnitude less strong, not yet stronger than more conventional carbon fiber on that scale).
[28]
[29]
[30]
For some applications, the tensile force on the tether is projected to be less than 65 newtons (15 lbf).
[31]
Material selection in this case depends on the purpose of the mission and design constraints. Electrodynamic tethers, such as the one used on TSS-1R,
[
clarification needed
]
may use thin copper wires for high conductivity (see
EDT
).
There are design equations for certain applications that may be used to aid designers in identifying typical quantities that drive material selection.
Space elevator equations typically use a "characteristic length",
L
c
, which is also known as its "self-support length" and is the length of untapered cable it can support in a constant 1
g
gravity field.
- ,
where σ is the stress limit (in pressure units) and ρ is the density of the material.
Hypersonic skyhook equations use the material's "specific velocity" which is equal to the maximum tangential velocity a spinning hoop can attain without breaking:
For rotating tethers (rotovators) the value used is the material's 'characteristic velocity' which is the maximum tip velocity a rotating untapered cable can attain without breaking,
The characteristic velocity equals the specific velocity multiplied by the square root of two.
These values are used in equations similar to the
rocket equation
and are analogous to specific impulse or exhaust velocity. The higher these values are, the more efficient and lighter the tether can be in relation to the payloads that they can carry. Eventually however, the mass of the tether propulsion system will be limited at the low end by other factors such as momentum storage.
Practical materials
[
edit
]
| The inclusion of certain items in this list
is currently being
disputed
. Please see the relevant discussion on the article's
talk page
.
(
April 2014
)
|
Proposed materials include
Kevlar
,
ultra-high-molecular-weight polyethylene
,
[
citation needed
]
carbon nanotubes
and
M5 fiber
. M5 is a synthetic fiber that is lighter than Kevlar or Spectra.
[32]
According to Pearson, Levin, Oldson, and Wykes in their article "The Lunar Space Elevator", an M5 ribbon 30 mm (1.2 in) wide and 0.023 mm (0.91 mils) thick, would be able to support 2,000 kg (4,400 lb) on the
lunar
surface. It would also be able to hold 100 cargo vehicles, each with a mass of 580 kg (1,280 lb), evenly spaced along the length of the elevator.
[5]
Other materials that could be used are T1000G carbon fiber, Spectra 2000, or Zylon.
[33]
Potential tether / elevator materials
[5]
Material
|
Density
ρ
(kg/m
3
)
|
Stress limit
σ
(GPa)
|
Characteristic length
L
c
=
σ
/
ρg
(km)
|
Specific velocity
V
s
=
√
σ
/
ρ
(km/s)
|
Char. velocity
V
c
=
√
2
σ
/
ρ
(km/s)
|
Single-wall
carbon nanotubes
(individual molecules measured)
|
2,266
|
50
|
2,200
|
4.7
|
6.6
|
Aramid
, polybenzoxazole (PBO) fiber ("
Zylon
")
[33]
|
1,340
|
5.9
|
450
|
2.1
|
3.0
|
Toray carbon fiber (T1000G)
|
1,810
|
6.4
|
360
|
1.9
|
2.7
|
M5 fiber
(planned values)
|
1,700
|
9.5
|
570
|
2.4
|
3.3
|
M5 fiber
(existing)
|
1,700
|
5.7
|
340
|
1.8
|
2.6
|
Honeywell extended chain polyethylene fiber (
Spectra
2000)
|
970
|
3.0
|
316
|
1.8
|
2.5
|
DuPont Aramid fiber (Kevlar 49)
|
1,440
|
3.6
|
255
|
1.6
|
2.2
|
Silicon carbide
[
citation needed
]
|
3,000
|
5.9
|
199
|
1.4
|
2.0
|
Shape
[
edit
]
Tapering
[
edit
]
For gravity stabilized tethers, to exceed the self-support length the tether material can be tapered so that the cross-sectional area varies with the total load at each point along the length of the cable. In practice this means that the central tether structure needs to be thicker than the tips. Correct tapering ensures that the tensile stress at every point in the cable is exactly the same. For very demanding applications, such as an Earth space elevator, the tapering can reduce the excessive ratios of cable weight to payload weight. In lieu of tapering a modular staged tether system maybe used to achieve the same goal. Multiple tethers would be used between stages. The number of tethers would determine the strength of any given cross-section.
[34]
Thickness
[
edit
]
For rotating tethers not significantly affected by gravity, the thickness also varies, and it can be shown that the area, A, is given as a function of r (the distance from the centre) as follows:
[35]
where R is the radius of tether, v is the velocity with respect to the centre, M is the tip mass,
is the material density, and T is the design tensile strength.
Mass ratio
[
edit
]
Integrating the area to give the volume and multiplying by the density and dividing by the payload mass gives a payload mass / tether mass ratio of:
[35]
where erf is the normal probability
error function
.
Let
,
then:
[36]
This equation can be compared with the
rocket equation
, which is proportional to a simple exponent on a velocity, rather than a velocity squared. This difference effectively limits the delta-v that can be obtained from a single tether.
Redundancy
[
edit
]
In addition the cable shape must be constructed to withstand micrometeorites and
space junk
. This can be achieved with the use of redundant cables, such as the
Hoytether
; redundancy can ensure that it is very unlikely that multiple redundant cables would be damaged near the same point on the cable, and hence a very large amount of total damage can occur over different parts of the cable before failure occurs.
Material strength
[
edit
]
Beanstalks and rotovators are currently limited by the strengths of available materials. Although ultra-high strength plastic fibers (
Kevlar
and
Spectra
) permit rotovators to pluck masses from the surface of the Moon and Mars, a rotovator from these materials cannot lift from the surface of the Earth. In theory, high flying,
supersonic
(or
hypersonic
) aircraft could deliver a payload to a rotovator that dipped into Earth's upper atmosphere briefly at predictable locations throughout the tropic (and temperate) zone of Earth. As of May 2013, all mechanical tethers (orbital and elevators) are on hold until stronger materials are available.
[37]
Cargo capture
[
edit
]
Cargo capture for rotovators is nontrivial, and failure to capture can cause problems. Several systems have been proposed, such as shooting nets at the cargo, but all add weight, complexity, and another failure mode. At least one lab scale demonstration of a working grapple system has been achieved, however.
[38]
Life expectancy
[
edit
]
Currently, the strongest materials in tension are plastics that require a coating for protection from UV radiation and (depending on the orbit) erosion by atomic oxygen. Disposal of
waste heat
is difficult in a
vacuum
, so
overheating
may cause tether failures or damage.
Control and modelling
[
edit
]
Pendular motion instability
[
edit
]
Electrodynamic tethers deployed along the local vertical ('hanging tethers') may suffer from dynamical instability. Pendular motion causes the tether vibration amplitude to build up under the action of electromagnetic interaction. As the mission time increases, this behavior can compromise the performance of the system. Over a few weeks, electrodynamic tethers in Earth orbit might build up vibrations in many modes, as their orbit interacts with irregularities in magnetic and gravitational fields.
One plan to control the vibrations is to actively vary the tether current to counteract the growth of the vibrations. Electrodynamic tethers can be stabilized by reducing their current when it would feed the oscillations, and increasing it when it opposes oscillations. Simulations have demonstrated that this can control tether vibration.
[
citation needed
]
This approach requires sensors to measure tether vibrations, which can either be an
inertial navigation system
on one end of the tether, or
satellite navigation
systems mounted on the tether, transmitting their positions to a receiver on the end.
Another proposed method is to use spinning electrodynamic tethers instead of hanging tethers. The gyroscopic effect provides passive stabilisation, avoiding the instability.
Surges
[
edit
]
As mentioned earlier, conductive tethers have failed from unexpected current surges. Unexpected
electrostatic discharges
have cut tethers (e.g. see Tethered Satellite System Reflight (TSS?1R) on
STS?75
), damaged electronics, and welded tether handling machinery. It may be that the Earth's magnetic field is not as homogeneous as some engineers have believed.
Vibrations
[
edit
]
Computer models frequently show tethers can snap due to vibration.
Mechanical tether-handling equipment is often surprisingly heavy, with complex controls to damp vibrations. The one ton climber proposed by Brad Edwards for his Space Elevator may detect and suppress most vibrations by changing speed and direction. The climber can also repair or augment a tether by spinning more strands.
The vibration modes that may be a problem include skipping rope, transverse, longitudinal, and pendulum.
[39]
Tethers are nearly always tapered, and this can greatly amplify the movement at the thinnest tip in whip-like ways.
Other issues
[
edit
]
A tether is not a spherical object, and has significant extent. This means that as an extended object, it is not directly modelable as a point source, and this means that the
center of mass
and
center of gravity
are not usually colocated. Thus the inverse square law does not apply except at large distances, to the overall behaviour of a tether. Hence the orbits are not completely Keplerian, and in some cases they are actually chaotic.
[40]
With
bolus
designs, rotation of the cable interacting with the non-linear gravity fields found in elliptical orbits can cause exchange of orbital angular momentum and rotation angular momentum. This can make prediction and modelling extremely complex.
See also
[
edit
]
References
[
edit
]
- ^
a
b
c
Cosmo, M. L.; Lorenzini, E. C., eds. (December 1998).
"Tethers In Space Handbook"
(PDF)
(3rd ed.). NASA.
Archived
(PDF)
from the original on 29 April 2010
. Retrieved
20 October
2010
.
See also version of
NASA MSFC
Archived
2011-10-27 at the
Wayback Machine
;
available on
Scribd
Archived
2016-04-21 at the
Wayback Machine
.
- ^
Finckenor, Miria; AIAA Technical Committee (December 2005). "Space Tether".
Aerospace America
: 78.
- ^
Bilen, Sven; AIAA Technical Committee (December 2007). "Space Tethers".
Aerospace America
: 89.
- ^
Artsutanov, Yuri (July 31, 1960).
"V Kosmos na Electrovoze"
(PDF)
.
Komsomolskaya Pravda
(in Russian).
- ^
a
b
c
Pearson, Jerome; Eugene Levin; John Oldson & Harry Wykes (2005).
"Lunar Space Elevators for Cislunar Space Development: Phase I Final Technical Report"
(PDF)
.
Archived
(PDF)
from the original on 2016-03-03.
- ^
"The Journal of the Astronautical Sciences, v25#4, pp. 307-322, Oct-Dec 1977"
.
cmu.edu
.
Archived
from the original on 3 October 2017
. Retrieved
3 May
2018
.
- ^
Moravec, Hans (1986).
"Orbital Bridges"
. Retrieved
January 8,
2023
.
- ^
Hans Moravec,
"Non-Synchronous Orbital Skyhooks for the Moon and Mars with Conventional Materials"
Archived
1999-10-12 at
archive.today
(Hans Moravec's thoughts on skyhooks, tethers, rotovators, etc., as of 1987) (accessed 10 October 2010)
- ^
Joseph A. Carroll and John C. Oldson,
“Tethers for Small Satellite Applications”
Archived
2011-07-16 at the
Wayback Machine
, presented at the 1995 AIAA / USU Small Satellite Conference in Logan,
Utah
, United States (accessed 20 October 2010)
- ^
Sarmont, Eagle (May 26, 1990).
An Orbiting Skyhook: Affordable Access to Space
(Archived copy). Anaheim, CA: International Space Development Conference. Archived from
the original
on 2014-02-22
. Retrieved
2014-02-09
.
- ^
Sarmont, Eagle (October 1994).
"How an Earth Orbiting Tether Makes Possible an Affordable Earth-Moon Space Transportation System"
. SAE Technical Paper Series (Report). SAE Technical Paper 942120. Vol. 1.
doi
:
10.4271/942120
.
Archived
from the original on 2014-02-22
. Retrieved
2014-02-09
.
- ^
Smitherman, D.V., "Space Elevators, An Advanced Earth-Space Infrastructure for the New Millennium", NASA/CP-2000-210429
[1]
- ^
Thomas J. Bogar; et al. (7 January 2000).
"Hypersonic Airplane Space Tether Orbital Launch System: Phase I Final Report"
(PDF)
.
NASA Institute for Advanced Concepts
. Research Grant No. 07600-018. Archived from
the original
(PDF)
on 24 July 2011.
- ^
H. Moravec, "A non-synchronous orbital skyhook".
Journal of the Astronautical Sciences
, vol. 25, no. 4, pp. 307?322, 1977.
- ^
G. Colombo, E. M. Gaposchkin, M. D. Grossi, and G. C. Weiffenbach, “The sky-hook: a shuttle-borne tool for low-orbital-altitude research,” Meccanica, vol. 10, no. 1, pp. 3?20, 1975.
- ^
.M. L. Cosmo and E. C. Lorenzini, Tethers in Space Handbook, NASA Marshall Space Flight Center, Huntsville, Ala, USA, 3rd edition, 1997.
- ^
L. Johnson, B. Gilchrist, R. D. Estes, and E. Lorenzini, "Overview of future NASA tether applications,"
Advances in Space Research
, vol. 24, no. 8, pp. 1055?1063, 1999.
- ^
E. M. Levin, "Dynamic Analysis of Space Tether Missions",
American Astronautical Society
, Washington, DC, USA, 2007.
- ^
Hypersonic Airplane Space Tether Orbital Launch (HASTOL) System: Interim Study Results
Archived
2016-04-27 at the
Wayback Machine
- ^
"Orphans of Apollo"
. World Press.
Archived
from the original on 21 June 2012
. Retrieved
30 January
2013
.
- ^
Foust, Jeff (July 23, 2001).
"Preview: Orphans of Apollo"
.
The Space Review
.
Archived
from the original on 5 February 2013
. Retrieved
30 January
2013
.
- ^
Wood, Charlie (29 March 2017).
"A 20-mile long 'spacescraper' dangling from an asteroid: Could it work?"
.
Christian Science Monitor
.
Archived
from the original on 31 March 2017.
- ^
Cosmo, M. L., Lorenzini, E. C., "Tethers in Space Handbook", NASA Marshall Space Flight Center, 1997, pp. 274-1-274
[
clarification needed
]
- ^
Michel van Pelt (2009).
Space Tethers and Space Elevators
. Springer Science & Business Media. p. 163.
ISBN
978-0-387-76556-3
.
- ^
"TiPS: Missuion Objectives"
. Archived from
the original
on July 8, 2007
. Retrieved
2011-10-06
.
- ^
NOSS Launch Data
Archived
2011-09-28 at the
Wayback Machine
(see NOSS 2-3, which deployed TiPS)
- ^
Ohkawa, Y.; Kawamoto, S.; Nishida, S. I.; Kitamura, S. (2009).
"Research and Development of Electrodynamic Tethers for Space Debris Mitigation"
.
Transactions of the Japan Society for Aeronautical and Space Sciences, Space Technology Japan
.
7
: Tr_T2_5 ? Tr_2_10.
Bibcode
:
2009TrSpT...7Tr2.5O
.
doi
:
10.2322/tstj.7.Tr_2_5
.
- ^
"Nanotube Fibers"
.
science-wired.blogspot.com
.
Archived
from the original on 1 February 2016
. Retrieved
3 May
2018
.
- ^
Tensile tests of ropes of very long aligned multiwall carbon nanotubes
Archived
2011-07-22 at the
Wayback Machine
- ^
Tensile Loading of Ropes of Single-Wall Carbon Nanotubes and their Mechanical Properties
- ^
NASA,
TSS-1R Mission Failure Investigation Board
, Final Report, May 31, 1996 (accessed 7 April 2011)
- ^
Bacon 2005.
- ^
a
b
Specifications for commercially available PBO (Zylon) cable:
"PBO (Zylon) The high performance fibre"
Archived
2010-11-15 at the
Wayback Machine
(accessed Oct. 20, 2010)
- ^
WO2017031482A1 (U.S. Patent #)
- ^
a
b
"Tether Transport from LEO to the Lunar Surface", R. L. Forward, AIAA Paper 91-2322, 27th Joint Propulsion Conference, 1991
Archived
2011-05-17 at the
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- ^
Non-Synchronous Orbital Skyhooks for the Moon and Mars with Conventional Materials -
Hans Moravec
- ^
Jillian Scharr, "Space Elevators On Hold At Least Until Stronger Materials Are Available, Experts Say", Huffington Post, May 29, 2013
"Space Elevators on Hold at Least Until Stronger Materials Are Available, Experts Say"
.
HuffPost
. 29 May 2013.
Archived
from the original on 2014-03-02
. Retrieved
2014-04-06
.
- ^
"NASA - NASA Engineers, Tennessee College Students Successfully Demonstrate Catch Mechanism for Future Space Tether"
.
Archived
from the original on 2010-11-26
. Retrieved
2011-03-26
.
NASA Engineers, Tennessee College Students Successfully Demonstrate Catch Mechanism for Future Space Tether
- ^
Tether dynamics
Archived
2007-07-17 at the
Wayback Machine
- ^
Mortari, Daniele (January 2008).
"Ultra Long Orbital Tethers Behave Highly Non-Keplerian and Unstable | Daniele Mortari - Academia.edu"
.
Archived
from the original on 2017-10-04
. Retrieved
2017-11-01
.
Ultra Long Orbital WSEAS TRANSACTIONS on MATHEMATICS: Tethers Behave Highly Non-Keplerian and Unstable- Daniele Mortari
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