4
$\begingroup$

My idea was to use 2 stages for an interstellar spacecraft (particularly the Orion Drive) and use it in a way similar to Project: Daedalus. Phase 1 would involve accelerating to cruising speed following assembly in orbit, and that cruising speed is 0.04 c, which will then slow down as we approach the Wolf 1061c (the target planet) system. There is a problem: is this appropriate and if not, what are some issues I need to concern myself with?

EDIT: I am also going to provide a link for those of you who do not know what "mission profile" is by giving you a hands-on interplanetary or orbital example. Mission Profile Description, Definition and Example

$\endgroup$

This question asks for hard science. All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See the tag description for more information.

  • $\begingroup$ @AndreiROM I just need the profile and how the mission is to be planned from Earth, not events that occur during the mission. That will be left up to me. $\endgroup$ – Future Historian Apr 7 '16 at 15:33
  • $\begingroup$ So apparently I'm confused about what a "profile" is. Do you mean the acceleration/speed of the craft and when to slow down? $\endgroup$ – AndreiROM Apr 7 '16 at 15:34
  • $\begingroup$ @AndreiROM Fixed. $\endgroup$ – Future Historian Apr 7 '16 at 15:38
  • 1
    $\begingroup$ @AndreiROM And I found a good simple definition of what a "mission profile" is. A mission profile is the planned route and goals, and what mission hardware that requires. $\endgroup$ – Future Historian Apr 7 '16 at 15:45
  • 1
    $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. Future Historian and @WhatRoughBeast, I moved the comments to chat for posterity (they're productive), though the conversation seems to be over now, because they were getting too long. If you want to continue, that's the place to go. $\endgroup$ – HDE 226868 Apr 7 '16 at 21:54
8
$\begingroup$

Wolf 1061c is about 13.8 light years from Earth. Cruising at 0.04c, your ship will take, oh dear, 345 years. 0.04c is too slow for significant time dilation, so the ship will experience the whole 345 years. Just keeping the ship running for 345 years in interstellar space is a problem. Space is not a pleasant place, and it's really bad at 0.04c.

Over those 345 years, if humanity survives and continues advancing technologically, it's entirely they'll launch a faster ship and overtake yours rending the whole thing moot. If 50 years of advancement meant an increase to 0.05c they'll beat you. (I'm sure there is a name for this dilemma).

Whether or not they'll moon the older, slower expedition as they pass by could be a plot point of your story.


Then there's the question of the payload. What's the point of sending a ship to another star system if it just sits dumbly when it gets there? This leaves you with three sci-fi options:

First is full automation. Humans are very expensive on resources, it's cheaper to send robots. But Earth won't even know the ship has reached Wolf 1061c for nearly 14 years, and any commands will take 14 years to reach the ship. The ship and all its systems will have to be fully automated. We could get a fully automated ship to Wolf 1061c, maybe, but dealing autonomously with what is found there (because we don't know) is well beyond our current capabilities. Project Daedalus is supposed to carry surveying equipment and start sending back information to Earth, but if humans are in the decision loop the delays on analyzing that information will mean even after waiting 345 years for the ship to reach Wolf 1061c there's still generations of work to come.

There's also the problem of maintaining communication and tracking facilities and interest and budget on Earth for 345 years. This is longer than any space agency and most countries have existed and is kind of out of your control.

If you're sending humans they'll obviously die before they get there. One option is to put them in hibernation, but we haven't solved that yet. If you can solve it, you'll have all the extra problems of how to keep those hibernation systems running and powered for 345 years in interstellar space. Even nuclear fuel won't last, and there's not enough solar power between star systems.

The final option is to figure out how to create a generation ship. This is now deep into the realm of sci-fi. Not only will 10-15 generations have to live on the ship, you'll have to figure out how to create a sustainable, sealed biome capable of supporting them for 345 years. We barely know how to do this for a few days.


Normally a ship has to slow down once it reaches its target. Project Daedalus "solves" the problem of slowing down when you get there by releasing probes which start decelerating quite early using the gentle shove of ion engines. This saves the tremendous amount of fuel needed to slow the whole ship down (and the fuel to carry that fuel, and the fuel to carry that fuel...), but it sacrifices the bulk of the mass of the ship in the process and adds extra bulk of carrying probes with all their own computers and engines and shielding.

The Project Daedalus plan is to jettison the main ship... what about the humans and all their stuff? Do they all go into the probes? These much lighter probes use ion engines to very, very, very slowly slow down and achieve orbit. These will have to carry humans, and all their food, water, air, equipment, and shielding they'll need to presumably start a colony, because they're not going back to Earth. That much extra mass defeats the point of using light probes with ion engines instead of having to slow down all the mass of the original ship. The now much heavier probes with all that cargo cannot slow down using small, efficient ion engines.

So no humans on the Project Daedalus plan.

$\endgroup$
  • $\begingroup$ If you do send probes, what are they supposed to do for the best-case 27.6 Earth years between when they send data and they receive a response? You could streamline the process by having the probes explore for the first 13.8 years, receive the responses to the initial data and start going back, but that still comes with a host of problems. No, remote control really isn't going to cut it, and full automation... well, I'm not siding with the 1061c team on this one at this time. $\endgroup$ – a CVn Apr 7 '16 at 19:15
  • $\begingroup$ One thought for an Project Orion based probe was to make the pusher plate out of Uranium instead of steel. This gives the crew a ready source of Uranium for refining once they get to the target star. But they would still need to refine it to get the $U_{235}$ they needed. $\endgroup$ – Jim2B Apr 7 '16 at 20:22
  • 1
    $\begingroup$ @FutureHistorian You asked if it's an appropriate mission profile and what it's concerns are, but you didn't say appropriate for what. You clearly have something in mind. Rather than try to patch it up in the comments, how about asking a new question about that mission? Include the time and tech period, what the in-universe goal is, as well as the out-of-universe goal. $\endgroup$ – Schwern Apr 8 '16 at 15:50
  • 1
    $\begingroup$ @Schwern Fair enough. $\endgroup$ – Future Historian Apr 8 '16 at 15:51
  • 1
    $\begingroup$ @Schwern Done: worldbuilding.stackexchange.com/q/39713/12238 $\endgroup$ – Future Historian Apr 8 '16 at 16:47
2
$\begingroup$

To maximize your mission profile, you will need to use a few tricks. The rocket equation is in effect even with ORION drives, and every gram counts. Using rocket power to decelerate means you have to initially accelerate that fuel, so you should also take measures to minimize the use of powered deceleration.

The ship will need to dive towards the sun and use the gravitational slingshot effect to maximize the efficiency of the propulsion burn (deep in the sun's gravity well), in order to minimize the mass of fuel that you ned to carry.

The ship will coast for most of the journey, and on approaching the target deploy a magsail to decelerate. Since the magsail has minimal mass and uses interaction with the local medium, there is no need to carry a great amount of fuel for deceleration. Indeed, the magsail can be used for manoeuvring within the target system, another great saving in mass for the ship.

Other mass saving tips would be to rotate the ship after the Orion burn and use the drive plate as protection against interstellar dust and radiation. Repurposing like this reduces the overall mass of the ship, and the knock off effect of every gram saved provides a huge saving in the amount of fuel needed to boost to cruise velocity and for a smaller magsail needed to decelerate.

$\endgroup$
  • $\begingroup$ Hmmmmm. I suppose I never thought of it this way before. Interesting. $\endgroup$ – Future Historian Apr 7 '16 at 21:19
  • 1
    $\begingroup$ hard-science, please. $\endgroup$ – HDE 226868 Apr 7 '16 at 21:53
  • $\begingroup$ A low thrust propulsion like a sail cannot stop a Project Orion scale craft in time. At 0.04c you'll be in and out of the Wolf 1016 system in days. Even enormous magnetic or solar sails produce maybe 100 N of thrust, and that's close to a star. With some very optimistic thrust and mass assumptions... 1000 ton spacecraft at 100 N thrust decelerates at 10^-4m/s^2 so that's 3500 years to decelerate from 0.04c. $\endgroup$ – Schwern Apr 8 '16 at 3:58
  • $\begingroup$ I think you will find your calculations are a bit off: erps.spacegrant.org/uploads/images/images/… $\endgroup$ – Thucydides Apr 8 '16 at 14:55
  • $\begingroup$ @Thucydides That paper says 200 N of thrust for a truly enormous 200 km sail. So, 1750 years to slow down. That paper seems to be about measuring sail thrust and doesn't appear to discuss spacecraft mass or acceleration. Could you point out how my calculation is off? $\endgroup$ – Schwern Apr 8 '16 at 15:54

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.