Posts Tagged‘reaction wheel’

Cubli: This is How Reaction Wheels Work.

One of the most important parts of any spacecraft is their attitude control system. This is the part which is responsible for keeping the craft pointed in the right direction something which is of the ultimate importance when you’re trying to do things like fine tuning manoeuvres or trying to monitor a specific part of the sky for an extended period of time. The most common of these kinds of systems are reaction control systems which typically use a hypergolic fuel (ignites on mixure, no external ignition source required) however they’re limited by the amount of fuel you can bring with you. Whilst there are many alternatives reaction wheels are the best in terms of weight, size and precision and they can make for cool systems like these:

Cubli isn’t the first reaction wheel controlled robot I’ve seen but it is most certainly the most elegant and precise. It’s also probably the best demonstration I’ve seen of how reaction wheels work, showing aptly how rotational momentum can be translated into an angular force on the objects that the reaction wheel is coupled to. Whilst most space craft won’t ever use the jumping and walking functions (that’s what station keeping boosters are for) the rest of the demonstrated capabilities are identical to what many modern space craft use.

As for uses for things like this on earth? Well there aren’t as many as there are out in space, mostly thanks to us having other means by which to stabilize and rotate things, but they do make for a cool technological demonstration.

Kepler May Be Down But It’s Far From Out.

The Kepler Mission is by far one of the most exciting things NASA has done in recent memory. It’s goal was simple, observe a patch of stars continuously for a long period of time in order to detect the planets that orbit them. It’s lone instrument for doing so is a highly sensitive photometer designed to detect the ever so subtle changes in brightness of a parent star when one of its planets transits in front of it. Whilst the chances are low of everything lining up just right so that we can witness such an event the fact that Kepler could monitor some 145,000 stars at once meant that we were almost guaranteed to see a great deal of success.

Indeed we got just that.

Kepler Space TelescopeThe first six weeks of Kepler’s operation proved to be highly successful with 5 planets discovered, albeit ones that would likely be inhospitable due to their close proximity to their parent stars. The years since then have proved to be equally fruitful with Kepler identifying thousands of potential exoplanet candidates with hundreds of them since being confirmed via other methods. These discoveries have reshaped our idea of what our universe looks like with a planetary system like our own now thought to be a relatively common occurrence. Whilst we’re still a long way from finding our home away from home there’s a ton of tantalizing evidence suggesting that such places are numerous with untold numbers of them right in our own galaxy.

However earlier this year Kepler was struck with an insurmountable problem. You see in order to monitor that field of stars precisely Kepler relied on a set of reaction wheels to ensure it was pointed in the right direction at all times. There are a total of 4 of them on board and Kepler only needed 3 of them in order to keep the precision up at the required level. Unfortunately it had previously had one fail forcing the backup wheel to kick into motion. Whilst that had been running fine for a while on May 15th this year another reaction wheel failed and Kepler was unable to maintain its fix on the star field. At the time this was thought to be the end of the mission and, due to the specialized nature of the hardware, likely the end of Kepler’s useful life.

However, thanks to some incredibly clever mechanics, Kepler may rise again.

Whilst there are only 2 functioning reaction wheels NASA scientists have determined that there’s another source of force for them to use. If they orient Kepler in a certain way so that its solar panels are all evenly lit by the sun (the panels wrap around the outer shell of the craft) there’s a constant and reliable force applied to them. In conjunction with the 2 remaining reaction wheels this is enough to aim it, albeit at a different patch of the sky than originally intended. Additionally it won’t be able to keep itself on point consistently like it did previously, needing to reorient itself every 3 months or so which means it will end up studying a different part of the sky.

Whilst this is a massive deviation from its original intended purpose it could potentially breathe a whole new life into the craft, prolonging its life significantly. Considering the numerous discoveries it has already helped us achieve continuing its mission in any way possible is a huge boon to the science community and a testament to NASA’s engineering prowess. We’re still at the initial stages of verifying whether or not this will work as intended but I’m very confident it will, meaning we’ll be enjoying Kepler aided discoveries for a long time to come.