How do you find direction in space. is the Sun a reference point?

Question

for space probes travel ling in space , how do they make sure they are in the right path?

Thanks

Answer 1

they define coordinate systems to suit the job at hand. look for names like ecef and fk5.

Answer 2

Gyroscope.

A gyro retains its direction of rotation invariant irrespective of gravity.

Answer 3

In general terms, whatever you're orbiting is the reference. When our space craft are traveling to other planets in the Solar System, the Sun is used as the reference point, as they are at that time in orbit around the Sun.

Orbits have lots of variables required to completely describe them, but the main ones are apoapsis (greatest distance from "center"), periapsis (smallest distance), inclination (how tilted the orbit is to the reference plane), period (how long does it take to complete an orbit), eccentricity (how elliptical or circular is the orbit), and mean anomaly (in which direction is the eccentricity pointing).

Most of our probes make use of Hohman transfer orbits - orbits with the perihelion (periapsis) distance being the Earth's distance from the Sun, and the aphelion (furthest distance) being the distance the target planet is from the Sun.

When in orbit, burning the engine to accelerate the spacecraft has the effect of "raising" the orbit's height above center at the OPPOSITE side of the object. Since the probe wants to raise its aphelion to the distance of, say, Jupiter, then the craft must burn its engine when at the opposite side of the Sun from where it plans to meet Jupiter.

Timing is another huge factor in space travel. You've heard of "launch windows" before. I used to wonder "why can they only do it at certain times?" Imagine the solar system like a clock face. Suppose you plan to rendezvous with Jupiter at the 12 o'clock position (relative to the Sun of course), then you should leave Earth and burn your engine roughly at the 6 o'clock position so you get as far out as Jupiter when you're at the 12, and that's when Jupiter will be at the 12 as well - then Jupiter's gravity can capture the probe.

Imagine launching 3 months later, but performing the exact same engine burn... you would be launching at the 3 o'clock position (the planets go counter-clockwise around the sun). This means when you get to Jupiter's distance from the Sun, you'll be at the 9 o'clock position, but Jupiter's at the 12. Whoops!

Of course you could still technically fly straight to Jupiter even from the 3 o'clock position, but you would have to burn a LOT more fuel to do so, and chances are, you don't have a big enough rocket sitting on the pad for all that extra fuel, and even if you had one laying around, you wouldn't have the budget to fill 'er up anyway.

That's the very basic picture of how they plan and navigate space flights. If you're really interested, check out the document I'm linking in the sources section. It gets more technical, but it's where I learned all this stuff.

(yes, I'm a geek and read this for fun, but space flight is awesome!)

Answer 4

The Sun is not a very good reference point, because it is too big.  Space probes need high accuracy directions.  Trying to aim at the center of the sun would result in a large error.

So what they actually do, is aim at certain stars.  Stars are points (unless you have a very good telescope, and the star is very close to the solar system).  By detecting a bright few stars, the probe can find its directions.

To get in the general close direction of a star they are looking for, the probes have a gyroscope system.  But they can't use the gryos all the time, because they drift off course after a few hours.  So the probe uses the stars to reset the gryos.

Answer 5

Stars are used as reference points.  The stars do move around slowly; the ultimate reference frame is set by quasars.

For crude pointing, a lot of satellites and scientific instruments have "sun seekers".