A Deep Space Primer

phil reed writes "With the latest Mars missions still in the news, people might be curious about what it takes to actually run a deep space mission: how a spacecraft is designed, how the communications are handled, what kind of project management is in place to make it all work. The Jet Propulsion Laboratory has a primer online that gives broad general coverage of all aspects of putting a satellite into orbit and how to manage it once it's there. Fascinating reading, with lots of links to more detail."

Re:No thanks

[Anonymous Coward]

Whoever wins the X-Prize [xprize.com] will write it.

Re:how the communications are handled

[nathanliesch]

your ping pong ball example is essentially how a electrical wire works. The electrons don't actually travel the length of the wire, they just "push" the ones next to them. Yet this is still limited by the drift velocity of electrons which is slower than the speed of light.
I think the only way to do speed up the conversation would be quantum entaglement but that's not been done outside the laboratory.

Re:how the communications are handled

[another_henry]

I thought of that too ;) Sadly, it doesn't work. The balls at the far end of the tube don't 'know' to move until the signal, in this case a pressure wave, reaches them. In fact in this case the limit is the speed of sound in the ping pong balls.

I hope we can beat relativity some day. At the moment though, it doesn't look promising.

Re:how the communications are handled

[Shut the fuck up!]

Something that works like a very long tube filled with ping pong balls for example. Push one into one end and one pops out the other instantly, no matter how long the tube

why that won't work [ucr.edu]

Re:how the communications are handled

[Anonymous Coward]

These are called gravitational waves, with the theory being that although light only travels so fast, gravitational effects are instantaneous, and their effects can be seen immediately. What we need is the ability to use gravitational properties (gravitons anyone?) to communicate with deep space missions.

Re:JPL

[rk]

Erm, JPL is part of NASA. Caltech manages JPL, and therefore a part of Caltech, but it's also as much a part of NASA as KSC, JSC, or any of the other NASA facilities.

Re:how the communications are handled

[GigsVT]

Push one into one end and one pops out the other instantly

Well, that's sorta how electromagnetic signal propagation already happens. :)

Re:how the communications are handled

[Shut the fuck up!]

Gravitational effects travel at the speed of light. Here is a decent explanation [ucr.edu]

Re:Deep Space?

[Detritus]

Most NASA satellites are in low-Earth orbit. Some are in geosynchronous orbit, like TDRSS. Some, like satellites that study the solar wind, are in unusual orbits that take them far away from the Earth. JPL handles the satellites that leave the vicinity of the Earth and the Moon.

NASA's satellite tracking and communication systems are adequate for spacecraft in the vicinity of the Earth and the Moon. They are not good enough to handle spacecraft at larger distances. That is why JPL's DSN (Deep Space Network) has much larger antennas, super low-noise preamps, and higher performance receivers and transmitters. Their systems are designed and optimized to work with very weak signals.

The difference between near space and deep space is more a matter of operating conditions than of geography.

Re:how the communications are handled

[phil reed]

but what happens if you simply move the stick? Doesn't the whole stick move at the same time?

No. If you push the end of the stick, that push travels down the length of the stick as a shock wave, moving at the speed of sound.

Tweaking vs. robustness

[G4from128k]

Not true. To design something very complicated like an aircraft or Mars rover there are *many* models and experimentation done, because almost all textbook equations are only approximations of reality.

Excellent point. My heat transfer prof warned us that the equations in the textbook would get answers that had as much as 30% error (if you were lucky). And, IIRC, some theories in material science only yield answers that are within an order of magnitude (factor of 10) of the true value.

But what I was alluding to was robustness -- designs that aren't affected by approximation errors (or the inevitable measurement errors when you build and test a prototype). Some of this is a matter of factors of safety (overdesign) but the truely great engineers create designs that are insensitive to encountered variations. At some level the ability of the Rover team to correct the recent faults represents this type of robustness. Yes, they are tweaking and hacking, but it was only because of a robust, remotely fixable design that let them do this.

Re:how the communications are handled

[Anonymous Coward]

No quantum entanglement will not work either. There is no known way around relativity.

In case of quantum communication, to read the message being sent to you, the sender needs to send you a classical bit which travels, like all other information, at the speed of light or slower. See for example: Nature 398, 189 - 190 (1999) (and related refereces)

As for the recent news of superluminal transport in nanomaterials and such, it is important to remember that is only the phase velocity > c. Information velocity is still c. See for example:
Nature 422, 271 - 272 (20 March 2003)

This disregard for Einstein is disturbing in a community that is supposed to be interested in science.