h a l f b a k e r y
Crust or bust.
idea:
add, search, annotate, link, view, overview, recent, by name, best, random
meta:
news, help, about, links, report a problem
account:
Browse anonymously,
or get an account
and write.
Login
Create account.
|
|
|
COM Shifting
Adjusting the Centre of Mass to Aid Manoeuvrability | |
In outfitting a space-craft, a number of thrusters need to be applied in order for the craft to manoeuvre.
Traditionally, pairs of thrusters are set up about an axis in order to impart spin, and central thrusters added to apply directional thrust. To combat different loading configurations, each
thruster may have a certain amount of directional adjustment.
To aid manoeuvrability, this idea is to install a central structure within the craft (or rather, to build a craft about this structure) that contains weights that can be moved about along axis of direction. The structure should have at least 3 lengths, each at 90 degrees to one another, stretching into the x,y and z axis. In or perhaps instead, a circular configuration might be used to provide a different set of properties.
Now when a manoeuvre is performed, the weights within the structure can be shifted in order to provide the maximum turning force for a single or pair of thrusters.
Control is assisted by computer, so that the spacefarer only requires traditional flight controls.
Since weight is an important factor in space travel, the weights themselves should serve a dual purpose, perhaps them also being employed as fuel, oxygen, or some other storage. Using lighter materials can be offset (for turning purposes) by using longer dimensional lengths.
In addition to aiding turning and manoeuvrability, the COM shifting principal can also be applied to assist in balancing ships of a non-uniform shape.
N.B. The Other:Spacecraft:Propulsion category was chosen due to this idea being related to the movement of spacecraft.
Diagram 1
http://www.spoadfoo...images/cogshift.gif
[zen_tom, Oct 05 2004]
Diagram 2 (alternative)
http://www.spoadfoo...mages/cogshift2.gif
[zen_tom, Oct 05 2004]
Foam Hulls
http://www.halfbake...Hulled_20Spacecraft
Shameless link [zen_tom, Oct 05 2004]
Using Tethers in Space to Control Center of Mass
http://www.sciam.co...FA-89FB83414B7F0000
.. COM control for artificial gravity and use of tether for propulsion .. [bpilot, Oct 05 2004]
[link]
|
| |
I don't understand how altering the centre of gravity will aid manoeuvrability or balance. |
|
| |
Are there any required assertions that you haven't stated? eg, that thrusters are too weak for ideal manoeuvring, and/or too strong for ideal balancing? And that swifter rotational manoeuvres are desirable? |
|
| |
[half] yes you're quite right - edited name/description accordingly (from gravity to mass). and [benjamin] yes, I suppose the core requirement here is for swift rotational movements - or rather providing an improved performance for such moves. No, it's not a huge breakthrough, craft have been rotating succesfully for years, rather, just a possible improvement. |
|
| |
One thing I'd like to point out is that moving a weight around is conceptually identical to moving the thruster around. In both cases, there are two objects that are being moved in relation to each other with the thruster being attached to one of them. In your case, the object with the thruster attached is much more massive than the other object. In the case were we would say that the thruster is being moved, the object with the thruster is much smaller than the other object. |
|
| |
This is probably a good way to look at the problem. It could make a lot of sense to mount the fuel tanks on the same object as the thruster to avoid flexible fuel lines. It may even be desireable to have the crew compartments on that object as well. The only limitation is that as the object with the thruster gets more massive, the distance that the other object must move to get the same effect gets larger. At the same time, the required strength of this connection is less as the object without the thruster gets smaller. |
|
| |
[contracts] the purpose is primarily to help with orientation - inertial trajectory really shouldn't be affected. It's the adjustment of the centre of mass coupled with the position of the thrusters that allows you to, for example, spin about face, or perform some other manoeuvre (I hate spelling that word) with slightly more agility than might otherwise be possible. |
|
| |
In other words, providing agility and grace of movement as an alternative to the 2001 Blue Danube/lander style 'gently does it' imagery of space-flight is the main goal of the idea. |
|
| |
[scad m] Yes, you could consider having the thrusters themselves able to slide along an extended axis - and the effect would be the same. Using both (by having the centre of mass moved along one axis, while the thruster moves to the opposite end of that axis) would provide the maximum benefit. |
|
| |
If a single thruster is used with the thrust vector offset from the CG, the thruster will exert a torque on the structure dependent on the distance from the CG, as well as a lateral thrust in the direction of the thrust vector. This lateral component is usually undesireable, so a pair of thrusters is used, so that the lateral components cancel each other, and the ship experiences only a net torque. When two thrusters are used in this manner, the position of the CG is not an issue. Only the relative offsets of the pair of thrusters has any effect. |
|
| |
What about using large mobile weights on a spacecraft to change its angular 'heading' without using thrusters at all? |
|
| |
See link for an excellent Scientific
American article on use of tethers in
spacecraft for artificial gravity, power
generation, propulsion and orbit
control. The artificial gravity application
is most directly connected to
adjustment of
COM. |
|
| |
I can't see this working with the linear channels. You mention circular channels for the counter masses to run through (which implies a spherical spacecraft) and that might work, but you'll consume the same amount of energy. |
|
| |
Also, thrusters can alter trajectory. These counter masses will only allow you to change orientation. This probably wouldn't matter to the Hubble, but probably wouldn't be practical for a spacecraft. |
|
| |
[bpilot] I couldn't access your link
without subscribing to SA. |
|
| |
Also, there appear to be two (or more?)
schools of thought forming here: |
|
| |
The traditionalists, like me, who are
considering using COM shifting,
coupled with thruster use, to increase
the agility of a space-craft. |
|
| |
And a bold new school, where no
thrusters are used, but the ship is able
to shift itself into different orientations
by moving mass around - a bit like
trying to spin on an office chair without
touching the floor. Is this right? Or have
I missunderstood something? |
|
| |
Big revolving masses are indeed used to reorientate spacecraft without the need for external thrusters. |
|
| |