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SpringHeeledJack
6th Mar 2015, 15:00
BBC News - Nasa's Dawn probe achieves orbit around Ceres (http://www.bbc.co.uk/news/science-environment-31754586)

It baffles my small brain just how do you guide an unmanned craft such a distance to arrive at a given point, which itself is moving ? How come such tiny craft wouldn't be hit by particles of (God know's what) during it's long voyage and be damaged ? Come on space bods of JB, enlighten me please.


SHJ

ShyTorque
6th Mar 2015, 15:03
Unmanned? No, those little green men from Area 51 drive them there.

And they have windscreen insurance.

tony draper
6th Mar 2015, 15:11
They use Newton's sums. never been beat at space sums has our Isaac
:)

Fox3WheresMyBanana
6th Mar 2015, 15:19
Any gravitational dynamics problem with 3 or more bodies (Goggle "Three-body Problem" e.g. Earth, spacecraft, Ceres) is not absolutely solvable, so an iterative technique is used, using partial differential equations derived from Newton as Tony points out. Fortunately this is highly accurate, if you use small enough steps. Voyager 2 passed over Uranus's North Pole in 1986 only 1 second out on the original calculations back on Earth (back when NASA had one computer ;))

The path is computed to take account of all known debris fields, but there is always the risk of a rogue rock. To the best of my knowledge, no spaceprobe has been lost to this cause so far. It is possible that some failures on arrival have been caused by inflight damage to systems.

This paper puts it relatively simply
http://www.sciencedirect.com/science/article/pii/S1000936113001787

but remember, this is rocket science ;)

SpringHeeledJack
6th Mar 2015, 16:36
So, by Newtonian principles it arrives at it's destination and it hasn't been hit by a rock, small or large. But assuming that space is full of small, nay tiny particles that travel at great speed after having been ejected from some celestial body or collision, how is it statistically unlikely that in the course of 7.5 years no damage has occurred ??? Space craft are generally very light and flimsy when in contact with other things, so it makes me wonder. Same wondering also involved with how so many spacecraft surrounding the earth never get badly damaged by fast moving particles and moreso space junk….

Btw, do thy know what those shiny areas are in the crater on Ceres ?


SHJ

Fox3WheresMyBanana
6th Mar 2015, 16:52
For protection from micrometeoroids, most spacecraft use Whipple Shields. These are one or more thin layers of strong, light materials (e.g. kevlar) with spaces between. The micrometeorites tend to break up on passing through a layer, so although their energy is only somewhat reduced, the remains hit the next shield or the spacecraft spread over a much wider area, which much reduces the damage potential.
More here (including a simulation)
http://ares.jsc.nasa.gov/HVIT/index.cfm

8 possibilities for the Ceres bright spots
8 possible explanations for those bright spots on dwarf planet Ceres - CNET (http://www.cnet.com/news/8-possible-explanations-for-those-bright-spots-on-dwarf-planet-ceres/)

Linedog
6th Mar 2015, 16:54
Nah............... It's coz they got a satnav, innit? ;)

Windy Militant
6th Mar 2015, 21:33
but remember, this is rocket science ;)

Ballistics! No it's true I tell you!

Actually isn't this Astrodynamics as the Rocket Science is just the loud bit at the beginning? ;)

TURIN
6th Mar 2015, 22:35
So, by Newtonian principles it arrives at it's destination and it hasn't been hit by a rock, small or large. But assuming that space is full of small, nay tiny particles that travel at great speed after having been ejected from some celestial body or collision, how is it statistically unlikely that in the course of 7.5 years no damage has occurred ???

Because.....

http://stmlcom.s3.amazonaws.com/jamesbridle-playful.004.jpg

alisoncc
6th Mar 2015, 22:44
Any gravitational dynamics problem with 3 or more bodies (Goggle "Three-body Problem" e.g. Earth, spacecraft, Ceres) is not absolutely solvable, so an iterative technique is used, using partial differential equations derived from Newton as Tony points out. Fortunately this is highly accurate, if you use small enough steps. Voyager 2 passed over Uranus's North Pole in 1986 only 1 second out on the original calculations back on Earth (back when NASA had one computer ;))Doesn't matter how many variables are used in the calculations the answer is always 42.

Eddie Dean
6th Mar 2015, 23:16
The "lights" are MH370.
That's where the aliens left it.
Forgot to turn off the landing lights.
How's that for a segue.
http://www.pprune.org/jet-blast/557606-say-segue-please.html

thing
6th Mar 2015, 23:33
Re the asteroid belt; asteroids are very thinly distributed. NASA reckon there's about a one in a billion chance of clobbering one while travelling through. It's not like the old asteroids game ..

SpringHeeledJack
7th Mar 2015, 07:16
Speaking of which, I downloaded a version of the classic 'Space Invaders' computer game of 1980's fame and have been playing it on my laptop. Time hasn't helped my lack of skill, sadly :(


SHJ

Avtrician
7th Mar 2015, 11:32
Its all very simple really, they (Rocket Scientists)aim at where the target isnt, but most likely will be by the time package gets there, at the same time neatly missing all the other things that arent in the way yet. As for the objects that could heit the satellite, they arent there yet either and cant be seen, so obviously dont exist and therefore arent a problem..


I think that should do it. Oh, course corrections are done by letting the sattelite get close enough to some thing thats not there yet, to allow the gravity of the object to flick the satellite into a new direction..

:suspect::suspect:

Fox3WheresMyBanana
7th Mar 2015, 11:59
Exactly; it's all about errors. The satellite knows where it wasn't, isn't and won't be, generally avoids those bits of space, and so arrives at the destination. Simples!

arcniz
7th Mar 2015, 14:17
They use Newton's sums. never been beat at space sums has our Isaac

Back in the day... early 60's thru mid 80's... there were quite many embarrassing errors and slip-ups in navigation and course guidance for various space projects and programs.

More often than not, the mistakes and bad results were buried in "internal" memoranda, or "classified" to a level where few eyes saw the contents. Effects were that the Glorious launches and projects were mostly never sullied or even tarnished by abundant mistakes made.

People would have understood, one imagines. To err is human, etc.

In fact, most of the erring came from the internal architecture of the earlier mainframe computers, themselves. A known but under-appreciated little problem called "round-off error" was not handled well enough for the veery fine precision from endless iterations required at astronomical scales, speeds, and distances, resulting in certain endpoint calculations that were unpredictably wrong or inconsistent in odd ways, all due to idiosyncrasies inside the arithmetic hardware of several product lines and series of mainframe computers from prestigious manufacturers.

When newer generations of computing engines had time to cross-check results from older brains, the discordant bits hit the fan... very quietly.

RedhillPhil
7th Mar 2015, 14:36
Wasn't there a major fcku-up with a mission a few years ago when the scientists were working on metric and the engineers in imperial - or was it the other war around?

Fox3WheresMyBanana
7th Mar 2015, 14:45
Mars Climate Orbiter - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Mars_Climate_Orbiter)

The primary cause of this discrepancy was that one piece of ground software supplied by Lockheed Martin produced results in a United States customary unit ("American"), contrary to its Software Interface Specification (SIS), while a second system, supplied by NASA, that used those results expected them to be in metric units, in accord with the SIS. Software that calculated the total impulse produced by thruster firings calculated results in pound-seconds. The trajectory calculation used these results to correct the predicted position of the spacecraft for the effects of thruster firings. This software expected its inputs to be in newton-seconds.[16]

The discrepancy between calculated and measured position, resulting in the discrepancy between desired and actual orbit insertion altitude, had been noticed earlier by at least two navigators, whose concerns were dismissed. A meeting of trajectory software engineers, trajectory software operators (navigators), propulsion engineers, and managers, was convened to consider the possibility of executing Trajectory Correction Maneuver-5, which was in the schedule. Attendees of the meeting recall an agreement to conduct TCM-5, but it was ultimately not done.

The cost of the mission was $327.6 million

nomorecatering
8th Mar 2015, 10:29
Thanks Fox3, read the paper on space dynamics.........and did not understand a fricken word.:\.......Not one!

Is there a version called rendezvous dynamics for dummies?

Fox3WheresMyBanana
8th Mar 2015, 10:54
No.

There's a 'How to Handle the Fatal Accident Inquiry and PR Crisis from Rendezvous Dynamics done by Dummies' by D. Cameron. That any use? ;)