Medrunner Lao Dorn and his team have been given a mission. A young woman has contracted some sort of parasite that is slowly eating away at her vital organs. The doctors on Oberon are unable to do much to help her and have decided to put her into cryosleep to delay the parasite. They have contact a medrunner to ship her to a place where the doctors would know how to treat a case like this: Venus.

Due to the nature of cryosleep (in universe), emergency freezing is dangerous and at times fatal if patients are kept frozen for more then a few weeks at the most (even then, it's risky). Because of this, Lao only has a few weeks to make it to Venus before risking the death of his patient.

What kind of propulsion device would allow Lao's craft to reach Venus from Oberon in approximately 1-2 weeks real time (not Lao's possibly dilated time)?


  • Fusion power is available
  • Medrunners are publicly funded so expense isn't an issue unless it's ridiculous
  • Oberon is one of the major moons of Uranus
  • The distance between Oberon and Venus would be approximately 18.5 AU
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    $\begingroup$ For those of you Googling "What is Oberon?", it's the outermost major moon of the planet Uranus. $\endgroup$ – BrettFromLA Feb 28 at 15:25
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    $\begingroup$ It would help if you specified the distance at this point in time. The distance between Oberon and Venus depends on 3 things. 1. Oberon's position around Uranus 2. Uranus' position around the sun 3. Venus' position around the sun. $\endgroup$ – MB123 Feb 28 at 15:31
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    $\begingroup$ Ships travel at the speed of plot, or perhaps the plot travels at the speed of the ship. I would suggest you're approaching this situation backwards, you should pick a ship drive you like and change your parasite to match. $\endgroup$ – Separatrix Feb 28 at 15:33
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    $\begingroup$ This might be helpful : nathangeffen.webfactional.com/spacetravel/spacetravel.php $\endgroup$ – Morris The Cat Feb 28 at 15:35
  • $\begingroup$ On average the distance between Venus and Uranus is around 18.5 AU which is close to 1 light day (1/365 light year). If you want to make it in 1-2 weeks you are looking for 5-10% c. $\endgroup$ – Zeodyn Feb 28 at 15:41

Space travel (barring new discoveries in science) is all about propellant/propulsion. You either want a means of not carrying any with you, or you're going to be be at the mercy of the rocket equation.

So, let's assume that your Medrunners' vessel is using normal rocket propulsion, powered by fusion. It uses some sort of modified particle accelerator to accelerate its propellant to very near the speed of light. How much velocity do we need?

You want to make the trip in (at most) two weeks. 18.5 AU is 2.8 billion km, to use more useful units. That means for most of the trip, the ship needs to be travelling at about 2.3 million m/s.

That's... a bigger number than I was expecting, but as we all know, space is big. So we have another important question - do you have inertial dampeners? Because accelerating at 1 G (we'll call it 10 m/s/s, for ease of calculation), 2.3 million m/s would take 2 3/4 days - during which, he'd only travel 265 million km, rather than the half-million plus that he'd travel at the eventual top speed. So our top speed needs to be higher.

Allowing for acceleration and deceleration, in fact, it needs to be more than twice as high - 5.2 million m/s. Assuming that our fuel is also our propellant (hydrogen is fused to helium which is then flung out the back of the craft), you would need approximately four and a half times as much hydrogen (by mass) as the remainder of the weight of the spacecraft. Not impossible, but definitely a small ship perched on top of an enormous fuel tank, rather than anything like the Enterprise.

It's worth noting that 5 1/2 (2 3/4 * 2) days of acceleration doesn't eat up your entire two weeks, so the trip could be made more quickly by using lots more fuel, but presumably cost is at least partially an object.

  • $\begingroup$ Medrunner ships are basically as you described small cockpit and crew compartments and a massive fuel tank/engine $\endgroup$ – Celestial Dragon Emperor Feb 28 at 18:46

I see major issues with this idea.

Medrunner Lao Dorn and his team have been given a mission. A young woman has contracted some sort of parasite that is slowly eating away at her vital organs. The parasite is of unknown origin and the doctor's on Oberon are unable to treat her.

Rule one : quarantine.

Absolutely no one is going to transfer this woman (or anyone on Oberon) to another place. People and supplies might be sent down, but nothing going down is coming back until the outbreak is identified and a cure available.

Any other approach risks infecting the entire solar system with a potentially deadly plague.

Only freezing her will stop said parasite (the specifics of the parasite would be a later question).

If they can freeze her, what's the rush ?

Only the doctor's on Venus might be able to treat this woman. Lao has been tasked with getting to Venus as fast as possible so the woman can be put under the care of Providence.

Remember quarantine. This trip to Venus is not going to happen.

What kinda propulsion device would allow Lao's craft to reach Venus from Oberon in approximately 1-2 weeks real time (not Lao's possibly dilated time)

"kinda" is not good grammar - use "kind of" instead. :-)

Entirely depends on where they are relative to one another - planets and moons move.

The question arises as to how many other people would be affected by an unknown parasite by the time they arrived ? Likewise it's hard to see how they could tell who is in the early stages of infection and who is not ?

There's no way to know for sure and that's why you quarantine.

Note : fusion power is available Medrunners are publicly funded so expense isn't an issue unless it's ridiculous

"Fusion" doesn't mean much. Just because I can do fusion that doesn't tell me anything about mass requirements, fuel requirements, propellant requirements (and you still need propellant) and issues like acceleration limits and life support requirements. It's a medical ship which adds other complications.

Expense may not be an option, but preventing the spread of an unknown and probably lethal parasite certainly is an option. This is the reason you're going to have a quarantine imposed. It would be a hard quarantine and the ships you''ll be rushing there will be ones that can destroy any ship attempting to break out of the quarantine.

Best case scenario : a quarantine facility or a facility capable of being erected on Oberon rapidily (prefab ?) is going to brought there with medical staff on a one way trip.

So the minimum period to travel would be something around 12 days according to the calculator page provided by @Morris-the-cat in comment. But that omits the time to make decisions and plan and provision the required outfit. Politics may delay things.

And that's going to be more likely a range of 5 to 30 days for a quarantine fleet to arrive at different times around Oberon. They'll be dispatched from different places within the solar system on an emergency basis and provision for ongoing maintenance of the quarantine zone would develop over time. It would be perhaps two or three months before the quarantine system was fully in place.

But lets remember there is another option : wipe out the colony from space. Why waste money on this and take the risk of a breach of quarantine when some relatively simple kinetic weapons can wipe out the problem from orbit ?

The priority here will not be one persons life, or even the life of the colony. It will be the life of the rest of the solar system.

  • $\begingroup$ Well I stated why there is a rush and wiping out a colony isn't very ethical. I assume it would be easy to quarantine her upon freezing and setting up a quarantine zone on Venus during the flight. $\endgroup$ – Celestial Dragon Emperor Feb 28 at 18:26

Correct me if I'm wrong, but it appears to me this is a trip being made within a single planetary system. which in relativity to the universe is nominal so it shouldn't take too much to accomplish this, depending on how advanced your society is in this story.

A simple continuous fusion drive might work. It's just about the most efficient way known to man for space travel, but it's hard to carry enough fuel for a trip this long. You might run out of fuel and be drifting, just hoping your calculations were correct. Otherwise you will drift beyond Venus and we all know whats beyond that (but this could add character to your plot).

Another idea I have is an Ion drive, very weak in propulsion; However, in an environment with no resistance, something pushing very lightly will build up speed over time. so it might take a week to get up to speed but then you'd only be a week away from Venus. The bad thing about this drive is it accelerates incredibly slow. The good thing is it wont run out of fuel for a long time.

If you're intrigued by either of these ideas you can find a little bit more information and maybe some new ideas at this website: https://cosmosmagazine.com/technology/antimatter-ion-drives-nasas-plans-deep-space-propulsion


Is it feasible?

Can you actually get there in 1 or 2 weeks without FTL drive and flatting your insides due to high acceleration? That is what this question is about.

I found this little gem on SE Stack Exchange: https://space.stackexchange.com/questions/840/how-fast-will-1g-get-you-there

Using Days and AU (astronomical units) we can see 3 days will get about 2.5 AU (halfway to Jupiter). 4.5 days will get you 5 AU (halfway to Saturn). 9 days will get you 20 AU (more than halfway to the Kuiper belt)

Although you can travel 20 AU in 9 days, you actually need to accelerate until you reach ~9 AU and then decelerate for that much time also. Looking at the graph, you will need to spend 6 days accelerating to reach the half way point (10 AU) and another 6 days to slow down.

So, yes. You can get from Oberon to Venus within 2 weeks by accelerating/decelerating at 1g.

Which engine?

Chemical based engines are out of the question.

Your options are going to be some form of nuclear rocket or a pure Sci-Fi engine without any explanation of how it works. (eg NeRV Mark 5)

  • $\begingroup$ Nuclear rockets are still plausible right? I don't want anything to outlandish $\endgroup$ – Celestial Dragon Emperor Feb 28 at 20:19
  • $\begingroup$ I'm double checking some things because the plausibility of doing a trip like this seems to fall into the category of "why aren't we doing it now?". I'll update my answer regarding actual amount of fuel needed (3000 kg of LN2), ship size (space shuttle), and other things. $\endgroup$ – Michael Kutz Feb 28 at 22:07

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