How fast is this planet moving?

[BradHann]

I noticed that this planet had biological signals, so I moved in closer to investigate. And as I approached, I couldn't help but notice that it appeared to be moving away from me. I throttled to zero to check and sure enough, it was moving fast enough to be visibly moving across the screen. The only other time I've seen that was Mitterand Hollow, which doesn't really count. So given the info the game provides, is it possible to calculate just how fast this planet is flying through space relative to its parent star?

The biologicals were braintrees, btw.

 

[varonica]

I noticed that this planet had biological signals, so I moved in closer to investigate. And as I approached, I couldn't help but notice that it appeared to be moving away from me. I throttled to zero to check and sure enough, it was moving fast enough to be visibly moving across the screen. The only other time I've seen that was Mitterand Hollow, which doesn't really count. So given the info the game provides, is it possible to calculate just how fast this planet is flying through space relative to its parent star?

The biologicals were braintrees, btw.

That's a simple problem of geometry, basically the orbital radius of the planet by how long it takes ot make a complete orbit. In this case we know it takes around 1 day to orbit the star, the semi-major axis is 0.01au, ok it's going to be an approximation because these numbers aren't going to be precise in any way, so you'll get a rough idea.

You can use the same method used to calculate the earth speed of movement from here;

How fast is Earth moving?

Earth is moving much faster than it seems.

www.space.com

First, we have to figure out how far Earth travels. Earth takes about 365 days to orbit the sun. The orbit is an ellipse, but to make the math simpler, let's say it's a circle. So, Earth's orbit is the circumference of a circle. The distance from Earth to the sun — called an astronomical unit— is 92,955,807 miles (149,597,870 kilometers), according to the International Astronomers Union. That is the radius (r). The circumference of a circle is equal to 2 x π x r. So in one year, Earth travels about 584 million miles (940 million km).
Since speed is equal to the distance traveled over the time taken, Earth's speed is calculated by dividing 584 million miles (940 million km) by 365.25 days and dividing that result by 24 hours to get miles per hour or km per hour. So, Earth travels about 1.6 million miles (2.6 million km) a day, or 66,627 mph (107,226 km/h).

You can of course apply this method to anything orbiting anything else as long as you know the radius of the orbit and how long the orbit takes. I would do the maths myself but I have to start work now, have fun.

 

[Sapyx]

Since you're there in the system, it shouldn't be too hard to measure it empirically. Simply fly up close to the planet, but not so close that you enter the planet's gravitational sphere of influence - it's a small planet, close to a star, so that shouldn't be too hard as the planet's sphere is likely to be quite small. You want to be "following behind" the planet. Match velocities with it, so that the planet is neither moving away from nor towards you. Now check your speed. That speed will be the speed the planet is orbiting the star.

 

[varonica]

Since you're there in the system, it shouldn't be too hard to measure it empirically. Simply fly up close to the planet, but not so close that you enter the planet's gravitational sphere of influence - it's a small planet, close to a star, so that shouldn't be too hard as the planet's sphere is likely to be quite small. You want to be "following behind" the planet. Match velocities with it, so that the planet is neither moving away from nor towards you. Now check your speed. That speed will be the speed the planet is orbiting the star.

Unless that speed is above around 800mps but below 30kps, a speed gap our ships simply can't get into without entering the orbital influence of the body. I suspect, with a one day orbit around a star, it's going to be quite fast, so that method may work.

 

[Zieman]

If my maths wasn't badly off, I'd reckon roughly 109 km/s.

 

[marx]

First step: check the eccentricity of the orbit, because if it's close enough to zero, we can just simplify by pretending it's a circular orbit. Eccentricity here is 0.005, good enough.

Second: we need speed, so it's the distance travelled divided by the time spent doing so. Since we simplified to a circle, the distance is simply 2 * pi * radius, and the radius here is the semi-major axis: 0.01 AU. The time is the orbital period, a nice 1 day - quite convenient.

So the orbital speed is 0.062832 AU / day. Not quite the best units though, so let's convert that... 1 AU is 149,598,000 km, so that's 9,399,541.536 km / day. One day is 86,400 seconds, so the end result would be around 108.791 km / s. There are rounding errors, of course. Especially since the system map itself rounds the numbers it displays, so that SmA might be 0.006 AU instead. The logs can help you here, they store more precise values.

 

[BradHann]

Maths was never my strong point.

Google tells me that Earth moves a bit under 30 km/s, so this is quite zippy. Curious to know how often Stellar Forge generates such racers.

 

[Arry]

That's a simple problem of geometry, basically the orbital radius of the planet by how long it takes ot make a complete orbit. In this case we know it takes around 1 day to orbit the star, the semi-major axis is 0.01au, ok it's going to be an approximation because these numbers aren't going to be precise in any way, so you'll get a rough idea.

You can use the same method used to calculate the earth speed of movement from here;

How fast is Earth moving?

Earth is moving much faster than it seems.

www.space.com

You can of course apply this method to anything orbiting anything else as long as you know the radius of the orbit and how long the orbit takes. I would do the maths myself but I have to start work now, have fun.

Nice work on the speed of the Earth.

Which poses the question: Today, can man make a space craft, that can take off and travel in the direction that is opposit the Earth's obit around the Sun. Then after a week, can the craft, turn around and catch the planet again?

 

[Orvidius]

Which poses the question: Today, can man make a space craft, that can take off and travel in the direction that is opposit the Earth's obit around the Sun. Then after a week, can the craft, turn around and catch the planet again?

Yikes. Just to cancel out your solar orbital velocity after escaping Earth, and go into an equal orbit in a retrograde direction, alone is around 60 km/s. And that's just the first part of your question. Nothing has ever been built that could do that, to my knowledge. This is where we hit the "tyranny of the rocket equation", in that going faster requires more fuel, but more fuel means more mass that has to be accelerated, requiring even more fuel, requiring even more... and so on. It gets to the point where the mass fraction of the payload would be ridiculously small.

EDIT: Edited for clarity and accuracy.

EDIT 2: The fastest spacecraft currently out there used gravity assists to get up to their current velocities (Voyagers are going about 17 km/s, and New Horizons about 16.26 km/s), and still nowhere near the speeds you're suggesting. Plus, you wouldn't have a gravity assist to turn around and "catch up". That would have to be delta-V (change in velocity) with onboard propellants.

 

[Arry]

Yikes. Just to cancel out your solar orbital velocity after escaping Earth, and go into an equal orbit in a retrograde direction, alone is around 60 km/s. And that's just the first part of your question. Nothing has ever been built that could do that, to my knowledge. This is where we hit the "tyranny of the rocket equation", in that going faster requires more fuel, but more fuel means more mass that has to be accelerated, requiring even more fuel, requiring even more... and so on. It gets to the point where the mass fraction of the payload would be ridiculously small.

EDIT: Edited for clarity and accuracy.

Yes: Von Brown, has a lot to answer for. History will show that he put back; interstelar space travel, about half a century.

 

[Orvidius]

Yes: Von Brown, has a lot to answer for. History will show that he put back; interstelar space travel, about half a century.

LOL. I think we should blame Tsiolkovsky instead.

 

[Zieman]

Yes: Von Brown, has a lot to answer for. History will show that he put back; interstelar space travel, about half a century.

Who?
If you mean Wernher von Braun, then LOLWUT?!?

 

[Zieman]

LOL. I think we should blame Tsiolkovsky instead.

And even then, it's not his fault we are too dumb to come up with more efficient engines & propellants.

 

[Arry]

Who?
If you mean Wernher von Braun, then LOLWUT?!?

Yes the guy from Peenemünde. Give it time.

If his methods of space transport, are/were the best; then why are billions being spent on other propulsion systems?

 

[iain666]

If his methods of space transport, are/were the best; then why are billions being spent on other propulsion systems?

The best we could do with 1940s engineering doesn't mean the best forever and neither scientific nor technological advance may ever be considered .

It is a bit disappointing that we've not got past big dumb boosters yet but it's a bit much to lay that solely at the door of von Braun, you might as well blame the unsung Chinese inventor of the firework.

 

[Arry]

The best we could do with 1940s engineering doesn't mean the best forever and neither scientific nor technological advance may ever be considered .

It is a bit disappointing that we've not got past big dumb boosters yet but it's a bit much to lay that solely at the door of von Braun, you might as well blame the unsung Chinese inventor of the firework.

There was too much invested in the 'concept' and therefore the man. Too much time, money and this was due more towards, his history and the amount of commitment made; to his project. To open the fields, for other ideas. Even the Russians, were 'fixed' on the same ideas; once they changed 'the director' and therefore, the fuel, they progressed faster; but for 50 years. The whole world; could only focus on; as you say: The Chinese rocket.

 

[varonica]

Nice work on the speed of the Earth.

Which poses the question: Today, can man make a space craft, that can take off and travel in the direction that is opposit the Earth's obit around the Sun. Then after a week, can the craft, turn around and catch the planet again?

As pointed out us apes have learned never to waste energy doing what the universe will do for us. The moment you fire your rockets you will lose orbital velocity and start dropping towards the sun and accelerating, a number of loops around the sun and maybe Venus as an assist and pretty soon (well maybe not pretty soon...we'll say eventually) you will be exactly where you want to be.

Here's an example, you just have to remember that all these planets are moving in relation to each other at the same time the probes are heading out there.

https://i.kinja-img.com/gawker-media/image/upload/t_original/l3vye3e2fuammmbkjqm2.png

To get back to the Earth you just do the opposite process. It's just a complicated problem in orbital mechanics.

 

[schlowi123]

Regarding Wernher von Braun: he was NOT as important in doing the research and development of rockets as he's made out to be. He actually was more of a parvenu who had luck that someone in the right places wanted to give a favor to his father (who was a big deal somewhere). He never really finished engineering education (and no, he was NO Bill Gates) and from what we know due to the records the little he did finish, he was rather bad at the important topics. That is probably the reason why the US did NOT set him to important positions but let him more than 10 years doing something … well … other.

However (!), he admittedly was extremely good in organizing rocket research! And taking into account what needs to be taken care of administrative wise in such an endeavour this is not to be underestimated. During the shortest 1000 years in history (a.k.a. the "third" "reich") that meant that he had no scruple to let prisoners work to death in the "Mittelbau Dora" concentration camp (it had one of the highest death rates). Fortunately his benevolent captors didn't allow such methods any longer.

Well, longs story short: Wernher von Braun was made to be the "space age engineer" but he wasn't in reality. He was the "organizer", which is very important but slightly less suitable for "childhood hero"-material. And he also was certainly not necessarily the "good german" history him to be.

I'm sorry for the rant, but it felt important to write that.

Anyway, we have a different method than chemical rockets to gain velocity: ion thrusters. The above mentioned rocket equation is still valid of course, but since the ions have a much larger exit speed the target velocity can be reached with a lower "fuel" mass.

For example during a (over) 5 year test at NASA, 870 kilogramm Xe provided a total impulse comparable to more than 10.000 kilograms of conventional rocket fuel.

Øhm … yes … that is also the disadvantage … you need (a lot) of time to reach the target velocity. So the "turn around after one week" boundary condition makes this an unsuitable solution.

 

[Sapyx]

Unless that speed is above around 800mps but below 30kps, a speed gap our ships simply can't get into without entering the orbital influence of the body. I suspect, with a one day orbit around a star, it's going to be quite fast, so that method may work.

Finally got around to doing some experimenting with this. I found a system, an unremarkable red dwarf system, with a bunch of planets in close-in orbits. I successfully measured the innermost planet's orbital velocity, using my method: it was moving at about 137 km/s.

The main "problem" with this method is the lack of fine speed control. The smallest increments I was getting were about 10 km/s. But after some fiddling with the controls, I finally deduced that the planet was still moving away from me (barely) while I was moving at 136 km/s (as shown int he screenshot above), but at 139 km/s it was moving towards me.

This empirical method should work in most cases where a planet appears to be "moving fast" - if it's noticeably moving fast or seems to be trying to "run away" making it difficult to catch in Supercruise, then it's certainly going to be moving above the 30 km/s Supercruise idling speed.