this post was submitted on 15 Jun 2024
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[–] [email protected] 51 points 1 week ago (2 children)

It seems weird to me that they would measure a thruster in maximum speed and not by the force is generates. Doesn’t the maximum speed depend on the mass it is propelling and a bunch of other factors like friction and gravity?

[–] [email protected] 14 points 1 week ago

This speed is the Specific Impulse which is a measure of how effective the fuel mass is used. It is equivalent to the effective exhaust velocity, which is basically the mean exhaust velocity as the real exhaust velocity depends on the position in the exhaust. The specific impulse is more often given in seconds like in the Wikipedia page for the thruster and this representation is connected to the speed-based representation by dividing the effective exhaust velocity by the standard gravitational acceleration at sea level. Mass is not present in both of these representations because this way they are the impulse per unit mass of propellant.

Electric thrusters reach very high exhaust velocities, but the fuel mass flow is limited which leads to low thrust. Chemical engines reach high thrust, but their exhaust velocities are quite low in comparison.

[–] [email protected] 3 points 1 week ago* (last edited 1 week ago) (2 children)

No, that is the time to maximum speed. Maximum speed depends solely on exhaust speed (how fast the particles get accelerated).

And no friction in space. Well, almost none.

What's weird is that they say km/h. Space and rocket stuff is usually in m/s.

[–] [email protected] 15 points 1 week ago (1 children)

The grandparent comment is correct. There is no such thing as engine-specific “maximum speed”. If you add more fuel, you can always go faster (until the speed of light).

[–] NoSpotOfGround 3 points 1 week ago* (last edited 1 week ago)

Even "until the speed of light" has a caveat (hear me out). Would you call getting from A to B in 1 hour on your watch instead of 2 as "faster"? If your answer is yes, then there's no limit to how "fast" you can go. You could get from here to the Andromeda Galaxy in one minute. It's just that for the Andromeda and the Milky Way a LOT more time would have passed.

[–] Eheran 3 points 1 week ago

You are incorrect. If I am traveling at 90 % speed of light, take a stone and throw it out the back... I am now faster.

[–] [email protected] 39 points 1 week ago (1 children)

Any sort of long continuous thruster can do that in deep space, assuming there's enough fuel / fuel to weight ratio. And ion engines are simply extremely fuel efficient, but also extremely weak in their actual output.

[–] [email protected] 6 points 1 week ago (1 children)

So it's not likely it has the force for entry and exit

[–] [email protected] 29 points 1 week ago

Nah, it's for masses out in microgravity, not a lift off / landing type thing.

Source: Played a lot of KSP and read a couple of books by astronauts

[–] [email protected] 12 points 1 week ago* (last edited 1 week ago)

only take ya 3375 years to travel a light year in with one of those (edit: somebody downvoted math)

[–] clearedtoland 7 points 1 week ago* (last edited 1 week ago) (2 children)

I was going to joke and say: that’s like, what, warp 0.0001.

In the Star Trek universe, warp factors are a way to measure faster-than-light travel. The speed of light is approximately 299,792 kilometers per second (km/s). To convert your given speed of 32,000 km/hr into a warp factor, we need to use the formula that relates warp factor to the speed of light:

v = c * (w^(10/3))

where:

•	v is the speed in multiples of the speed of light (c),
•	w is the warp factor.

First, convert 32,000 km/hr into kilometers per second (km/s):

32,000 km/hr = 32,000 / 3,600 km/s ≈ 8.89 km/s

Now, find the warp factor using the speed of light:

w = (v / c)^(1 / (10/3))

w = (8.89 km/s / 299,792 km/s)^(1 / (10/3))

Calculate the fraction inside the parentheses:

8.89 / 299,792 ≈ 0.00002967

Now raise this to the power of 3/10:

0.00002967^(3/10) ≈ 0.000657

So, approximately:

w ≈ 0.000657

Therefore, a speed of 32,000 km/hr corresponds to a very low warp factor, approximately Warp 0.000657 in the Star Trek scale.

[–] Eheran 6 points 1 week ago

You are missing a zero. Also, that formatting. Either remove it or use code that can be displayed.

[–] someguy3 4 points 1 week ago* (last edited 1 week ago) (1 children)

Speed of light is 1,080,000,000 km/hr.

*Or 1.08 terametres/hr.

[–] [email protected] 4 points 1 week ago

So 0.03% of C?