Free interstellar decelleration?

[Artlav]

When approaching a planet, modern spaceships often have an option to use the air for slowing them down into orbit, known as aerobraking.

What i started to think about is - suppose you're on a starship about to enter a solar system, going at 10-20% of speed of light, give or take a million mph, and you have next to no fuel/engines, how can your ship be decelerated from interstellar speeds?

Doing an aerobraking, if there is something to do it on, is out of the question - you'll be lucky if the planet stays in the same orbit.

Can something like stellar braking be done - deploy a huge solar sail (the one you were accelerated with in the first place?), and dive into the star, allowing the solar wind and light pressure to slow you down? Will that be enough for a ship of any significant mass, or it will just slam into the sun?

Any other concievable means? There are magnetic fields, interstellar hydrogen - some kind of magnetic parachute?
Bomb braking maybe - send a rock ahead of you, let it hit some planet, then brake on the debris cloud?

What do you think?

 

[TSPenguin]

I like the solar sail idea.
I don't know if it is feasible at those speeds, but maybe one can do a serious slingshot maneuver, when planets are optimally aligned, around most of them to slow down.

 

[Artlav]

maybe one can do a serious slingshot maneuver, when planets are optimally aligned, around most of them to slow down.

At such speed? zzzZZZZOOOoommm. You wouldn't have time to loose a single km/s.

 

[T.Neo]

At such speed? zzzZZZZOOOoommm. You wouldn't have time to loose a single km/s.

What about utilising a series of slingshot manuvers after most of the velocity has been lost?

 

[Artlav]

What about utilising a series of slingshot manuvers after most of the velocity has been lost?

Possibly, but you need to get there first.

 

[TSPenguin]

How about lithobraking? That will slow you down for sure!

 

[Sky Captain]

I have tried to do some slingshotting when going at only few hundred km/s and it did`t work. Even massive Jupiter affected my trajectory and speed only slightly. When coming in at 10 - 20 % c you would have to deaccelerate to few ten`s km/s first for slingshot maneuvers to be useful. As to use star`s atmosphere to slow down - it would require heatshield made of some sort of sci-fi material to withstand the heat and G forces would be extreme.

---------- Post added at 09:21 PM ---------- Previous post was at 09:19 PM ----------

How about lithobraking? That will slow you down for sure!

In Orbiter when flying at such speeds lithobraking makes you go even faster than before

 

[TMac3000]

In many directions simultaneously

 

[Linguofreak]

When approaching a planet, modern spaceships often have an option to use the air for slowing them down into orbit, known as aerobraking.

What i started to think about is - suppose you're on a starship about to enter a solar system, going at 10-20% of speed of light, give or take a million mph, and you have next to no fuel/engines, how can your ship be decelerated from interstellar speeds?

Define "about to". At that kind of speed, you'll need a whole heckuvalotta room to brake.

Otherwise, the best method of deceleration really depends on the tech that got you up to that speed in the first place, as well as whether this is a "wilderness stop" or whether your stopping in an inhabited system.

 

[Tex]

I always thought the Van Bran spacecraft in that Alien Planet show seemed realistically possible. Burn prograde halfway there turning retrograde for the second half of the trip. I guess that wouldn't be considered as free decelleration though...

 

[lalbanof]

I have seen this idea suggested, in an SF story

If I recall correctly, it is the story "The Children's Hour" in the Man-Kzin Wars III series of books by Larry Niven, Jerry Pournelle, Dean Ing and others.

The Arm (Earth and humans' Armed Forces) sent a bomber named the Yamamoto to drop kinetic projectiles onto a Kzinti (the cat-like aliens) occupied planet named Wunderland, orbiting Alpha-Centauri.

Neither the Kzinti nor the humans had interstellar travel yet.

They partially braked the bomber by grazing the Sun´s photosphere. This cloaked it, and faked its destruction. Most of the braking was done by a reaction drive which was dangerous to anything standing some millions of kilometers before the exhaust.

Then, they had some technology undistinguishable from magic. A "Slaver Stasis Field" designed by a long-dead alien civilization and built monkey-see monkey-do by humans, that simply stopped time for any object within the field, and a time switch for the field encased in neutronium.

 

[Arrowstar]

Bomb braking maybe - send a rock ahead of you, let it hit some planet, then brake on the debris cloud?

Might I suggest not doing this on the grounds that you would not appreciate it if a fleet of alien vessels decided they were going to enter the solar system by rock bombing Earth to slow down?

 

[JamesG]

Yeah, they might get the wrong idea about your intentions. lol!


Going 20% of c would take some deceleration to get within the ball park of capture velocity. But once there and within the star's heliosphere a solar wind "braking cute" would be effective in bleeding off some speed and reducing the acceleration while falling to sunward.

After that you'd do a few loops of a long elliptical cometary orbit, circularizing a bit at a time until you can match orbits with a planet. For close stars like Alpha-Centari this process might take longer than the intersteller crossing if you used up all of your Dv getting there.

Where it would get interesting is if you come in at an oblique or even 90 degrees to the local ecliptic plane. Then you'd need some precise slingshots at odd angles to the star or jovians to bend your vector down into the ecliptic.

 

[Andy44]

If you're doing .2 c there is no fancy trick for decelleration. Use your drive technology. It got you going that fast, it'sd the only thing that can slow you down again without destroying you.

Think about it: attempting any kind of aerobraking at that speed will be like hitting a brick wall. Your ship will melt before you can say "energy transfer". If it doesn't melt, it will turn you into jelly against the forward bulkhead under the massive acceleration.

Other tricks, like slingshotting, won't work, either, because at that speed your trajectory will barely even bend when rounding a Jupiter-sized mass.

 

[Jarvitä]

You're forgetting about the fact that we're not just talking about our solar system here. Consider the fact that gas giants of mass an order of magnitude higher have been discovered around several stars. Surely a retrograde slingshot, combined with aerobraking, repeated a few times over an elliptical orbit would do the trick - as long as you had a method to allow the "cargo" to survive the deceleration.

 

[the.punk]

I also think we could use a combination. The solar sail is could be used. But I think you need your engines to slow down because slingshots won't do anything on your trajectory at those high speeds. Maybe slingshots for the last step of decelleration.

 

[Artlav]

Otherwise, the best method of deceleration really depends on the tech that got you up to that speed in the first place

this process might take longer than the intersteller crossing if you used up all of your Dv getting there.

If you're doing .2 c there is no fancy trick for decelleration. Use your drive technology. It got you going that fast, it'sd the only thing that can slow you down again without destroying you.

I was thinking about a kind of interstellar probe - fill the surface of a small planetoid with lasers, attach a solar sail a few megameters wide to the probe, and accelerate it starwards. The probe will have only a little DV on it - few 100's of km/s - to maneuver around it's destination system and perform the final deceleration.

Surely a retrograde slingshot, combined with aerobraking, repeated a few times over an elliptical orbit would do the trick - as long as you had a method to allow the "cargo" to survive the deceleration.

A slingshot, in perfect conditions, can only deliver DV at the order of the orbital speed of the target planet, so it's quite useless for interstellar braking, unless we are going into a system of black holes.

 

[JamesG]

I was thinking about a kind of interstellar probe - fill the surface of a small planetoid with lasers, attach a solar sail a few megameters wide to the probe, and accelerate it starwards. The probe will have only a little DV on it - few 100's of km/s - to maneuver around it's destination system and perform the final deceleration..

The actual method you use for propulsion is really besides the point. All that really matters is the velocity of your ship and the escape velocity of the system you wind up in.
After that initial perihelion with the star if V1 > V2 you are going to go zooming off back into the darkness of interstellar space.
If you have a constant steadystate DV system (laser sail, fusion engine, warp drive, etc.) then you might get back at some point, but it would be much better to have slowed to a manageable speed prior to passing thru the system than to have loop back.

 

[Linguofreak]

I was thinking about a kind of interstellar probe - fill the surface of a small planetoid with lasers, attach a solar sail a few megameters wide to the probe, and accelerate it starwards. The probe will have only a little DV on it - few 100's of km/s - to maneuver around it's destination system and perform the final deceleration.

That's exactly the kind of information I was looking for. If you launch with a laser sail, then the most common method I've heard for deceleration at a wilderness stop involves using the beam that originally launched you. You carry more sail area than you need, and when you need to start decelerating, you detach the extra sail area and use it as a mirror to reflect the beam back to the sail that remains on your spacecraft. The extra sail is lost to interstellar space, but the spacecraft itself is decelerated and arrives at rest at the target star.

 

[Andy44]

Similar to the vessel design from The Mote in God's Eye, a laser-driven light sail. Unfortunately the alien pilot suffered a life support failure en route and didn't survive the trip.

Project Deadalus was a two-stage fusion rocket design that was meant to travel to Bernard's Star at a final velocity of .12 c.

It was to use up all of it's propellant and upon arrival in the Bernard system it was to do an instrumented flyby before sailing back into deep space.

That sounds like a similar mission profile to the one in the OP, except that there is no propellant to stop and no fancy slings or aerobrakings planned.