Satellites: Radiation Pressure

[varungreat]

How do scientists counteract the radiation pressure of sunlight falling on artifical satellites for e.g. on solar panels? Do they use rockets or is the orbit self-correcting?

 

[Vast]

Do you mean the actual sunlight shifting the satellite itself? Because I’m not sure that would make much of a difference. Satellites have another more significant problem to deal with, and that’s the drag of the atmosphere which can extend out to 2000 km or so. (Not sure on those figures) But satellites do need to correct for atmospheric drag.

 

[varungreat]

thank you, but i do mean the actual shifting of satellites due to radiation pressure by the sun light.

 

[varungreat]

Can anyone help please?
Thank you

 

[AD]

Radiation pressure is often liable to induce roations in spacecraft as well as translations. The rotations can be compensated for with the spacecraft 's attitude control system (e.g. reaction wheels). If the translations induce a significant deviation from the intended path, these can be compensated for with a corrective burn.

 

[varungreat]

thanx. but in case of very big space station is continuous corrective burn necessary? Or can we use the impulses (of corrective burn) after regular periods??
please HELP!

 

[Garth]

In general the pressure of sunlight is insigificant except over long periods, so intermittent burns are all that are required.

However it does depend on the size and mass of the satellite, and the thrust of the thruster used. The large balloon like Echo satellite used in the early 1960's as the first experiment in satellite communications suffered considerable perturbation from its oscullating orbit because of radiation pressure and atmosphere drag, although it was actually quite high up, and was simply allowed to "go with the (sunlight) wind".

The Gravity Probe B satellite on the other hand is quite massive (3.1 tonnes) and relatively compact (~ 9 feet across) yet its orbit has to be kept free from all radiation pressure and atmospheric drag perturbations.

The central part of the experiment consisted of 4 accurate gyroscopes cooled to near Absolute zero by liquid helium in a giant dewar jar. The helium gradually evaporated away and escaped through a porous plug in the neck of the dewar.

This escaping helium vapour was then vented through a series of micro-thrusters that continuously corrected for the radiation and atmospheric forces on the satellite.

I hope this helps.

Garth

 

[Nereid]

In terms of the OP, I think it's not so much correcting for a particular cause of perturbation/drifting/whatever, but rather the ability to make corrections whenever it is deemed necessary or important to do so.

Sunlight pressure and atmospheric drag are but two of the causes of change to planned/desired/intended orbit or orientation; other causes may be micrometeorite impacts, venting/outgassing (within the satellite itself, whether planned or not), balky gyros/reaction wheels, and gravitational or magnetic torques (maybe other folk can add further possible causes).

From an engineering perspective (Enigma may give us more 'coal-face' experience and feedback), I imagine it's less a particular cause that needs to be planned for than the robustness and likely lifetime of the ability to address any causes (within broad envelopes).