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by the_rosentotter 3585 days ago
How does it slow down?
4 comments

It doesn't hence its going to be used for flyby missions and not orbit/capture missions.

Many missions to the outer planets are flybys since we can't have enough fuel to actually slow down.

just curious but how would you even capture any usable signals when passing a planet at 20% lightspeed?
Well if you think about it we are capturing useful signals that move at relativistic speeds all the time.

Many galaxies we see are moving at very high speeds due to the expansion of the universe hence the doppler shift and we can take both optical and radio images of them.

I'm not an RF/Optical engineer but I would think that it would be possible to capture and send some data back to earth even its minimal it's still might be better than nothing / what we can get from earth/our solar system, at the end we only might have to account for the doppler shift.

IIRC there have been also other tricks like deploying very large sails and using them as drag chutes or using some mechanical trickery and deploying a very small probe by literally like having it on some pendulum and some other weird stuff so you would transfer most of the momentum it has to the probe and you'll release it with considerably less momentum than the rest of the spacecraft.

The planet itself could slow the probe down quite rapidly. ;)
Would it be possible to drop a payload that would enter orbit?
The payload would need to slow down to be captured by the planet just the same. Normally you could try aerobraking and the like, but we are talking about relativistic speeds here.
To get better closeup pictures, if possible, aim the probe for the planet and live stream picture home all the way to impact.

Although I'm not sure these probes are at all steerable, either autonomously or remotely.

Highly unlikely, the mass of the probes will be on the order of several grams at most, and, depending on the trajectory relative to the planet, steering could require an equally impractical amount of fuel as slowing down would.
Livestream at 20% of light speed?
There may not be any significant atmosphere for aerobraking. This likely would not be known until long after the probe arrived.
We'd also have limited knowledge of the system itself. Without more accurate data about its objects and their orbits, it'd be almost impossible to plan out orbit insertions even assuming we come up with a means of slowing a probe from relativistic speeds.

Even if your probe had the computing power to run orbital mechanics calculations, there's no guarantee that it'd be in a position to actually make it work when it got there. Of course, that's ignoring the mass constraints involved.

But that doesn't discount the value of even 'just' flyby missions. The scientific benefit would be, literally, incalculable. And the data could help with followup missions, assuming we develop a drive system that could get there and slow down.

The StarShot probes are going to be about a gram. Not much weight to make a primary probe AND a payload.
slowing down from that kind of velocity is serious business. you're talking about braking from 75000km/s to ~8km/s and not blowing up in a spectacular explosion.
I just died laughing. I'm reading all the inspiring comments on how we actually could get there, and could totally see myself being on an engineering team that builds this thing, and 100 billion dollars later you ask that question and we all go: "Oh... oh crap." On a constructive note -- does anyone have a list / book of generally smart people getting sidelined by such things?
There's a book called It Looked Good On Paper full of things a bit like that, albeit on a smaller scale.
This comment left me flabbergasted. Great thinking.

What about orbiting the planet and using the lasers when the craft is orbiting towards us in blasts to slow it down gradually?

Magsails would work.
If you're going to use magsails to slow it down, why not use a magsail to get it there? The trip is basically symmetrical.

I suppose it's possible that the laser could produce a much more stable and precise trajectory, while a magsail would just slow it's descent towards or accelerate it away from the sun. But I think it's more likely to be a case of the materials science and energy density being in favor of the laser method over sails.

What if we used lasers to send a fleet of laser ships with powerful one-time-use chemical lasers, then the front set of laser ships fired the same kind of beam back at the rearmost ship to to slow it down?

> If you're going to use magsails to slow it down, why not use a magsail to get it there? The trip is basically symmetrical.

If you launch a strong magnet in interstellar space, it will slow down relatively to plasma by deflecting charged particles.

In order to speed up, you need to spend energy.

The symmetry is broken between accelerating and slowing down relatively to interstellar plasma (Edit: or solar wind).

Ah, I had neglected the effects of interstellar plasma.

I assumed the magsail operated in a similar fashion to a solar sail, depending on the solar wind. If the destination's solar wind was sufficient to slow us down, I expected that the Sun's solar wind would be sufficient to speed us up.

Thanks for the explanation!