Another reason we didn't go to Mars?

[PeterB]

Pierre1985 said:

Well, let's change argument.

Nasa engineers say their probes navigate in the deep space looking at position of stars by a powerful software.

It is not possible:
Suppose you take as reference in your bedroom the 8 vertex of the room. If you move up and down going straight forward like a probe you can notice that the 8 vertex have moved and with that powerful software made in Nasa you can know where you are because you have gone nearer to a vertex and more distant from another.

In the solar system, if you cover 500 million kilometres (those covered by going to Mars) you have not gone nearer a star and more distant from another because they are many light years distant (practically at infinite distance).

It is like if you had moved 1/1.000.000.000… millimetre in your bedroom.

Your eyes and your Nasa software can't notice any difference.

It would be as you had remained stationary in your position.

What's so hard?

In order to leave the Earth to travel to Mars, you need to fire your engines while the spacecraft is facing in a particular direction. Aligning the spacecraft against the stars is an excellent way to do it. The same when you fire your engine to slow down into orbit around Mars.

[Data Cable]

Put another way, the stars are used to determine the craft's orientation, not its position.

[JayUtah]

Right, it can't be said any more simply than that.

Star fixes give you orientation. Since a typical spacecraft incorporates direction-dependent elements such as thrusters, antennas, and heat shields, being able to detect and control a spacecraft's orientation is very important. Star fixes are not used to locate a spacecraft in space, merely to tell which direction it's pointing -- wherever it is. The relative lack of apparent motion in the stars as the spacecraft travels the solar system is exactly what makes this method work. The stars are assumed to be fixed points.

Finding a spacecraft's location within the solar system, and its velocity and direction of travel, is a matter of observing its direction from some reference point over several iterations. That's usually done with radio, and the reference point is usually the Earth. For solar-system navigation we consider the Sun to be a fixed point in space and all the coordinates are reckoned relative to it. The direction from the sun to some small set of fixed stars establishes the geometric basis for the coordinate system.

You can also use star occlusions to navigate. When a star just slips behind some object whose location is known, this establishes a line along which the spacecraft must be located at that instant.

But usually it's a matter of detecting the spacecraft's radio signal from Earth and seeing exactly the direction along which it was detected. The Doppler distortion gives its velocity along that direction, which can then give the spacecraft's orbit.

[pierre1985]

Is Mars a cucumber?

Spirit can move its head at 360 degrees around and up and down to see if there are some obstacles.

Why does it use wide angle lens?
To mask false images, to create mistery about Mars.

[Jason Thompson]

Why does anyone use a wide angle lens? To get a wider field of view in a single image.

It's not complicated, surely?

There is nothing mysterious about a wide angle image. And if they wanted to create mystery why then send back all those thousands of 'normal' images?

[pierre1985]

"Why does anyone use a wide angle lens? To get a wider field of view in a single image.

It's not complicated, surely?"

No, Nasa buffoons say wide angle lens is useful to see obstacles close to Spirit.
But Spirit can see at 360 degrees around and up and down and does not need fisheye lenses.

[sts60]

What is your basis for making that decision? What are your design parameters? What trade-offs have you considered?

In other words, what effort have you made to understand the problem before pronouncing judgment on it?

Since you have abandoned your claim that fisheye lenses can't cause such a curved horizon, I assume you acknowledge that your claim was incorrect, belying your assertion of being an "expert" in such matters. Do you know claim expertise in other areas of engineering design? Please be specific.

[Jason Thompson]

>>No, Nasa buffoons say wide angle lens is useful to see obstacles close to Spirit.
But Spirit can see at 360 degrees around and up and down and does not need fisheye lenses.<<

But using a wide angle lens gets the greatest extent of vision in the fewest possible images. Spirit does not relay video, therefore you cannot simply pan around and observe the surrounding ground in one smooth pass. With the narrow view 'normal' camera you would have to pan down, then take a picture, move across a few degrees and take another, and so on and so on. Then the images must be relayed to Earth, downloaded, analysed by the people in mission control and acted upon. With the wide angle lens this process is quicker because fewer images need to be taken and transmitted to cover the entire 360 degrees.

[scooter]

Hello Pierre...

If I read your original post correctly, you are talking about parallax...that is, how your "angle on things" shift as you move about.
The reason satellites and probes use starfinders for orientation and direction is the fact that stars are light-years away...trillions upon quadrillions of miles distant. While a trip to Jupiter or Saturn may seem an enormous distance to us, it is infintesimal in the scheme of the galaxy, much less the universe.
The "shifting" of the apparent position of stars during the multi-year voyage to Saturn is virtually nil...they are seen from Saturn as we see them from earth...the perfect, unchanging interplanetary reference points.

Are there any other questions we can help you with? It all make sense if you have a grasp of the basic science involved..

Sincerely,
Dave

[LunarOrbit]

You won't get a reply from pierre1985... he was banned along with a couple of his alter egos.