This has been bothering me for a while:
Sence=Since
:ditto:
....Break lockup is easier to accomplish with lower gravity, but most aircraft/spacecraft (at least that I know) don't have big enough break disks to lock up the wheels. However, since there is no atmosphere, I'd be more concerned with overheating the breaks than locking them up....
If you lock up the breaks on Earth, they wouldn't heat up either.
It's the friction in the break that causes the heat.
By the way, locking the breaks is not the most efficient way of breaking (even if your tires wouldn't blow up). If the wheels start to slide, the friction is lower then the force of static friction. If the wheels rotate and you're squeezing the breaks just hard enough for them not to lock up, your breaking force will be larger, however heating will be greater.
:thumbup:
The engineering definition of a
brake is; a machine that converts motional energy into heat energy (
based on that, we'd need another term for those magnetic brakes). When I first posted about brakes locking up, I assumed that everyone already knew this was not efficient. Seems that one of us did not....
That said, TCR 500's original comment about brake temperature is valid. It is for this reason that most aircraft brakes (for anything heavier than a Cessna) are "Maxorette" type, not unlike a "dry" version of a wet multi-disc clutch found in automatic gearboxes. They better deal with heat build.
The cooling problem in a vacuum, in reality, could possibly be solved by ducting nitrogen over the brakes, to disipate the heat. Or as already pointed out in the posts, using more advanced (maybe even superconductive?) material, like carbon fibre.
Now, the Moon landings. Maybe I have been getting the concept of what you are trying to do wrong... Are you attempting to touch down at ORBITAL PERIAPSIS VELOCITY? (1650 odd m/s?) :dry: You really will have a "Hopper" and a half. I thought you were at least slowing down to a "normal" touch down speed first, an assumption on which I based my own experiments. That really seems a
bit ridiculous. I am sorry to say it.
An example: (1700 / (4 * 0.85)) * (1700 * 0.5) = 425000 meters (light the retros at 425 km from the base).
Why the 85% and not 100%? I use part of the retro thrust to generally arrest the rate of descent, by incrementally pitching the nose down as velocity bleeds off (I don't use the hovers untill the end). The average horizontal retro thrust component over the trajectory works out at about 85% of the total available....
Done some more tests with this. 93% to 96% of retro thruster acceleration is right for low angle approaches (avg nose pitch down over trajectory is 15º). The 85% was for my original high angle approaches, to arrest a high ROD.