Balck Holes too soft

[raynor]

If a spacecraft the size of the shuttlecraft exited a hypothetical wormhole and found itself 100 KM from the outer corona of a star the size of our sun, what velocity would that spacecraft have to achieve in order to maintain a stable orbit around the star?

A multi-part question

1. A spacecraft the size of the shuttle approaches our sun on a course aimed directly for the 'center' of the star.
2. Take the main engines used to achieve escape velocity out of the equation.
3. Assume the spacecraft doesn't use any fuel until it reaches closest approach.
4. Assume that heat/radiation aren't a factor--robotic pilot if you want.

How close do you think the spacecraft can get to our sun before it must alter its course to try to enter an orbit around the star?

[This message has been edited by raynor (edited 30 March 2001).]

[Steve A]

Raynor,
Orbital velocity at the sun's surface is 436 km/s. Spacecraft size does not matter as long as it is significantly smaller than the sun in mass.

If a ship fell towards the sun's surface from very far away, it would be traveling roughtly at escape velocity straight towards the core when it hits the surface. That velocity is 616 km/s at the sun's surface. To get into a circular orbit at that point, you would have to reverse the 616 km/s to stop the fall and add 436 km/s sideways to enter orbit. You can do both at once (a**2 + b**2 = c**2) with a delta velocity of 755 km/s.

The game engines don't really use delta V so it's hard to answer your question. The various books and board games SE4 is loosely based on have engines that propel spacecraft at 1% to 5% of lightspeed (3000 km/s to 15000 km/s), so it should be no problem for them to hover over the surface of the sun.

Steve



[This message has been edited by Steve A (edited 31 March 2001).]

[Steve A]

capt_spoogy,
Black holes can come in many masses, from around 5 solar mass to millions of solar masses. The energy it takes to get into orbit around a 5 solar mass black hole is exactly the same as the energy it takes to get into orbit around a 5 solar mass star.

Steve

[Steve A]

Dracus,
No, our sun will eventually end up as a white dwarf unless somebody uses a stellar converter on it.

<grin>

Steve

[Suicide Junkie]

quote:

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Here is a question for you--could our sun become a black hole?

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Yes. Even Earth would become a black hole if you squeezed it down to the size of a marble (1 cm)
Will it happen naturally? Not a chance.

quote:

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A black hole has a huge mass right? So if a ship tried to orbit it, would it take lots of energy to remain in orbit?

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To remain in orbit takes zero energy. Just take a look at the sun/earth/moon.

It may take a lot of energy to get into orbit from the surface, but once you're there you're there for good until you hit something, or generate thrust.

quote:

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1. A spacecraft the size of the shuttle approaches our sun on a course aimed directly for the 'center' of the star.
2. Take the main engines used to achieve escape velocity out of the equation.
3. Assume the spacecraft doesn't use any fuel until it reaches closest approach.
4. Assume that heat/radiation aren't a factor--robotic pilot if you want.
How close do you think the spacecraft can get to our sun before it must alter its course to try to enter an orbit around the star?

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The key to getting an orbit is to have a mass whose gravitational well you happen to be in.
The Intrepid Space Pilot in your question happens to be in an orbit already, its just that that orbit happens to pass through the surface of the star In order to stay in orbit, all the spacecraft must do is miss the star. To do that, the spacecraft need only dodge sideways one star-radius. It will then skim past the edge & go flying out, slow, fall back, and zing past the opposite edge.

Now, lets say you want to orbit an object that's 30,000Km wide. Since we are heading straight for it at the moment we must move sideways 15,000Km before we hit. If our ship is one second from impact, we must accelerate to 0.1c (10% the speed of light) in one second, then we can cut engines and be in orbit.
By accelerating to 30,000Km, in one second, we average 15,000Km/s, and in the one second before we hit, we've slid one star radius to the side, and fly past.

If we are nice and far away, such as near pluto's orbit, then we will have weeks to months before we reach the (30,000Km)"sun" (light takes 7 hours to get to pluto, and we're not going to be going anywhere near lightspeed)
divide the 15,000Km by 2 months, and we have:

quote:

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No-calculator math time:
2 months= 60 days
=60*24 = 1200+240 = 1440 hours
=1500 x 60 = 60000+3000 minutes
=60000 x 60 = 3,600,000 seconds
15,000km / 3,600,000 seconds
=15 km / 3,600 s
= 15 /3.6 m/s
= about 5 m/s
= Jogging Speed.

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So, even a ship without engines coud merely open a door & vent some atmosphere, to get a boost to that speed.

All you have to do is scoot sideways the width of your target & you're in orbit. Very Hot & Very cold at times, but an orbit nonetheless.

[raynor]

Thanks!

Stupid Sci-Fi shows should try to be a bit more accurate about black holes.

[AJC]

Excellent SCI-FI book -

Light of Other days
by Arthur C. Clarke, Stephen Baxter http://images.amazon.com/images/P/08...1.LZZZZZZZ.jpg
Its about wormholes. Fascinating read.

[This message has been edited by AJC (edited 31 March 2001).]