A planet you can take off from, but never land back

Question

Can there be a planet that space missions can take off from, but never land back?

It is easy to imagine that thicker atmosphere, large amounts of space debris or higher gravity could entirely stop space missions. But I'm thinking of a case where space missions could be developed, but by necessity they would always have to be one way trips.

Constraints:

• Planet should be able to support life that is similar to Earth.
• Locally evolved civilization should be able to construct rockets that can take off from the planet with enough payload to carry living beings and life support.
• It should be significantly more difficult to land back - hundreds of years difference in technological level needed.
• Some form of communication (such as radio) should be possible between surface and space.

Answer 1

Ancient planetary defense system.

The planet is in a star system with lots of asteroids. Those usually would make the planet uninhabitable. But millions of years ago the planet was colonized by a species of precursor aliens. The aliens installed a fully automatic planetary defense system which destroys anything on a trajectory heading for the surface. Mostly to protect it from asteroid impacts, but probably also to defend the planet against other spacefaring civilizations. This made the planet habitable and allowed the aliens to terraform the planet and create an ecosystem.

However, the alien civilization isn't there anymore. Circumstances that are not relevant here either killed them or caused them to abandon the planet. But although the precursor aliens are gone, they left the stable ecosystem and the automated defense system behind.

Over the past millions of years, intelligent life evolved, created a civilization and discovered spaceflight. After all that time, the defense system is still working and protects them from asteroid impacts (and occasional visitors from other spacefaring alien species). Unfortunately the system doesn't recognize the primitive vessels launched from the planet as friendly. It lets them launch, but it doesn't let them get back down. The ancient aliens might certainly have known a way to tell the system to not shoot down their own crafts, but that knowledge was lost to time. So anything that tries to return from orbit gets shot down by the defense system.

Why don't the current inhabitants try to get the defense system under their own control? The answer is that they can't. Their technological level is still far too low to understand how the system actually works. Perhaps they could destroy the system or parts of it permanently. But then they would also compromise their defense against asteroids and risk getting wiped out by the next bigger rock that comes around. So until they have the technology to provide asteroid defense themselves, that's not an option. The precursor artifacts could also be of cultural or religious significance for their society, making it politically impossible to get rid of them. They are, after all, literally a gift from their creators that protects them from harm. That's far more substantial than what other religions have to work with.

Answer 2

The planet has no atmosphere.

In a pure oxygen environment, humans can survive pressures as low as ~2PSI. The people on your planet can survive in underground pockets of gas, like we have here on earth. Unfortunately this has big ramifications for your spaceships. We use the atmosphere to our advantage during re-entry. Spaceships have massive horizontal velocities during orbit, something on the order of 8 km/s, and all of that velocity has to be removed before landing. Current spacecraft always use drag in the upper atmosphere to slow them down; and I'm not talking about parachutes. Simply ramming into the atmosphere generates tons of heat, enough to burn up most meteors. That's all the kinetic energy being converted into heat!

Without the atmosphere, though, the only way to lose horizontal velocities is to turn on those rocket engines again and propel yourself in the opposite direction. This takes nearly as much rocket fuel as it did to get into orbit! Our best existing spaceships had a payload capacity that's about 6% of the total weight of the spacecraft. The fuel can easily be over 80% of the mass.

So while obtaining orbit on your planet will be comparable to what we have today (easier in fact, because you don't have pesky air resistance or anything to deal with), landing would be pretty much impossible with anything conceivable made from today's technology. Due to the tyranny of the rocket equation, you need more rocket fuel to launch your fuel for landing (and you need to bring more fuel for that fuel, and so on, and so on), you would need incredibly efficient rocket engines that can take far more than twice as much fuel to orbit as needed while maintaining a reasonable payload fraction. Maybe some futuristic high-power ion-engines.

Answer 3

It's suffering from massive Kessler Syndrome

The problem with this planet is, that there are only two very small zones along the poles where you don't get hit by anything when you launch. You need to launch pretty straight up above the debris cloud, and only then burn sideways. The cost of launching on this absolutely worst of all paths is super high, but the only way to even get into space without a collision.

However, trying to return means you have a much flatter trajectory and need to pass through the zone of debris - and that means you are guaranteed to get hit due to the density of debris.

Answer 4

The atmosphere contains a chemical that eats away the outer layers of the rockets upon reentry, when atmospheric compression turns the gas into a plasma.

The problem doesn't happen on lift off because the velocity are lower, and shielding the rocket to withstand the reentry can only be done with materials which make the rocket to heavy to reach space, until a few hundred years of material science development find the compound which is both light and sturdy for that application.

Answer 5

Other than an alien ex machina type of answer, like Philipp answered, I can't think of any pure astrophysical reasons. However, there there could be other reasons preventing them from returning.

Contagion Reason

For the first 3 successful missions to the moon, astronauts had to quarantine for 21 days. After Apollo 14, NASA realised that there was no reason to quarantine. But what if there was a reason, for example, near your planet there is space dust that is so harmful, that the worlds governments forbid any return missions? Then astronauts who leave, can never return. There is no reason to worry about the poisonous space dust naturally entering Earth, it gets neutralised when it burn and breaks up during entry. But that process would kill all of the astronauts on board, if a spaceship tried that.

Nowadays, with all of our modern medicine, there are (typically island) countries that have no rabies. In order to keep it that way, if you want to bring your dog with you, some places require up to 6 months of quarantine. If whatever space contagion could only be discovered by dissecting the dead body, then why would anyone want to return? They would have to be killed and examined right away.

Preparing the body for space is a one way process

Liquid breathing is a process that involves filling the lung with a liquid that has a lot of oxygen inside. Surprisingly, mammals can actually survive using this. There are many scientifically, militarily, and medically ways that liquid breathing would be beneficial. But it doesn't exists outside of laboratory experiments. That is because after the lungs are filled with the liquid, it can't be reliably dried to be able to breath air afterwards. You can bet there is lots of money up for the grabs, for whoever can develop a way for liquid breathing to be viable. Yet with today's technology, that doesn't exist.

What if going to space involved a one way body transformation? Then the moment you return, you would die. Maybe there is a lot of radiation, and you can do some skin transformation to survive that radiation. But then when you return, and there is not so much surrounding radiation, you would die of reverse- radiation poisoning.

Or maybe when entering space and you experience 0 gravity, your bones get extremely fragile. In 0G space that is not a problem, but the moment you return you would be crushed under your own weight and die.

Answer 6

This is a LOT harder than you might think

I was having fun with the idea of a naturally combustible gas, maybe methane, occurring in low enough quantities in the atmosphere to allow the evolution of life but high enough quantities that, during re-entry, it would ignite. Clever technology (like really long bell housings) could conceivable allow for thrust while allowing the exhaust to cool so the atmosphere doesn't ignite on launch. But the lengthy re-entry process just dooms the planet.

Then I read @Rafael's answer (which I upvoted) and realized that the problem is easily, if not cheaply, circumvented. Just slow down, ease through the atmospheric boundary, and pop chutes.

The only idea I can think of comes from an episode of Star Trek Voyager

The episode in question is "Blink of an Eye." The gist of the episode is this: something is causing a time dilation field between the planet and the ship in orbit. Hours on Voyager are centuries on the planet. The planet evolves civilization from primitive humanoids to an advanced species that develops a way to visit Voyager.

The episode uses a technobabble cause for the time dilation: a tachyon field.

But a better solution comes from the movie "Interstellar."

The Endurance passes through the wormhole into another galaxy with a planetary system orbiting a supermassive black hole called Gargantua. The crew intends to investigate three planets, each previously explored by NASA volunteers, who shared positive reports for habitability. The first planet is an aqua planet with massive tidal waves and no dry land. Doyle drowns after failing to get into the probe and getting knocked off by one of the waves, and Amelia and Cooper fly back to the Endurance, only to find that decades have passed due to the time slippage caused by the planet's proximity to Gargantua. Romilly, having remained onboard, has aged 23 years. Cooper replays messages from Earth, learning that Murph is now his age and has become a scientist working with Brand.

Time Dilation Prohibits a Practical Return

In other words, there's a scientific basis for the kind of problem that really would make it impossible to return. The planet orbits close enough to a black hole that the simple procedure of entering orbit experiences massive time dilation. One thing the movie doesn't go into is that while the ship is on the far side of the planet compared to Gargantua (e.g., the planet is between the ship and the black hole), time on the planet moves much more slowly than on the ship. But when the ship orbits around to be between the planet and the black hole), time on the planet would move faster than on the ship.

One might conclude that orbiting the planet once would average out the time dilation and, therefore, allow a re-entry in sync with the time experienced on the planet. I don't have the equations to prove that, and I suspect it's incorrect. If I recall my astronomy correctly (I might not, it's been a honking long time), gravity is not linear with distance. It's logrithmic. That means the time dilation when the ship is between the planet and the black hole is worse than the dilation experienced when the planet is between the black hole and the ship.

While this solution may not guarantee the inability to return (or, more precisely, the meaninglessness of returning), it goes a long way toward meeting you needs in a suspension-of-disbelief manner.

Answer 7

The planet has a very treacherous surface (steep cliffs, shallow waters dotted with jagged rocks, marshes, etc) which have only sparsely been made survivable by humans at a great cost and are merely connected to each other via a network of narrow roads and tunnels.

This setting would enable civilization to arise, the roads could be used by travelers and merchants on foot or with carts - later by vehicles with internal combustion engines and locomotives. Space-capable rockets could be built from the resources available, but unless ~10 meter CEP precise landing capabilities are developed, no landing is safe enough to attempt. Crashing down on boulders, sinking in swamps, breaking up on rocks or drowning in perpertually stormy seas is all but guaranteed when landing outside man-made territories - and any "fortunate" landing on the tiny, painfully expensively prepared safe areas would result in huge damages to infrastructure and human life already present there. And thus no landing capabilities are developed at all.

Answer 8

They figured out rockets before we did

The idea behind a rocket is not difficult. You need fuel, an oxidizer, and a way of controlling the burn. Perhaps some iron aged alchemist figured out kerosine rocket fuel and maybe they have a slightly lower gravity than we do making getting to space with an imperfect fuel much more doable. So, your Leonardo de Vince, Archimedes, or Pakal like guy figures out rocket fuel, and starts launching stuff into space, but his understanding of aerodynamics and material science is still way too primitive to figure out how to make a re-entry vehicle because he cant figure out why things burn up on re-entry or how to make them heat resistant enough to survive. Maybe they blame the burn up on the wrath of God, so they assume there is no scientific problem to be solved.

So instead of making the problem of re-entry harder than it is for us, you make the problem of getting to space easy enough that your civilization needs to wait hundreds of years to catch up with the 20th century science that made 2 way travel possible.

Answer 9

Philosophically, that's easy - like Heraclitus' river, the planet continuously changes, so you can never go back to the same planet you lifted off from. Unless time on it stops as soon as you leave.

But that's not what you meant, I suppose.

So. For a single flight (like the Apollo missions), it is doable - have a deep enough gravity well that no significant payload can escape the planet's gravity unless they exhaust the fuel needed for the reentry brake. This way, also, atmosphere density increases fast enough that aerobraking from the Karman height to the ground would result in a meteoric burn.

But if the above is not doable, or potentially infinite fuel resources are somehow available in orbit, so that you can always support a Space Shuttle-style reentry, then you need a planet you can't land on, ever. Hiding the surface wouldn't work - radar, parachutes and helicopter-like propellers would allow landing anyway.

So, we need to disrupt a very large, even armored landing capsule that could split open and release a helicopter at a suitable altitude, capable of hovering and choosing the landing zone with ease; or prevent that helicopter from hovering, or at least from landing without crashing.

The only way I can think of is violent, continuous cyclonic storms over the whole planet. Like Jupiter, but worse.

You can stay safe on the ground (maybe in a deep depression) as long as you like, and wait for some brief respite, and launch just then, in the ten or fifteen minutes' of relative calm in the eye of a storm. Let's imagine there is on average at most only one such period, in any one given area, every two or three days. When leaving, that's easy: you prep for launch, and wait. And wait. And wait. When you're sure you can, you launch - and you need about three minutes to rise to safety.

But when coming back, once you've committed to reentry, you do not know whether the safe area will be or even whether there will be one.

Chances of hitting the right five-minute window in three days, if the weather is truly unpredictable, are less than 0.2%. Even aborting the landing and retrying if things look ugly won't increase that very much.

And landing in the middle of a storm means crashing almost surely. You cannot hover at high altitude (also, it would be useless), you cannot use parachutes - they might even be worse - and the landing vessel cannot fly in the weather. Given those conditions, you simply cannot land.

Of course, the plausibility of such a hellhole of a planet is debatable, to say the least.

Answer 10

Planet inside a (Kerr-)Nordströn Black Hole

Charged black holes have 'two' event horizons, both of them being before the sigularity. Thus, when tou cross the second you are inside the black hole but with the singularity spatially away from you (spacelike distance) not in your future. This means that you could theoretically enter the black hole and go about your life inside it (i.e. you '''could''' have a functional solar system inside).

Now, the important part. When you are inside you can cross again the second event horizon that you crossed, which would actually lead outside, making you go outside the black hole but in a different universe (don't quote me on this). The reason being, from the inside they are white holes, effectively.

Charged solutions are not actually of physical interest, though, because the charge would in reality equalize quickly with all the matter orbiting the black hole, closing the Cauchy horizon. The stability of the system is concerning. Inside the black hole you could also find the naked singularity, which I don't know how anyone would regard in a novel, but, hey. It's not extremely believable, but not wholly unphysical either...

i.e. white holes might be your best bet.

Answer 11

Freakishly tall mountain above the winds.

https://www.reddit.com/r/NoMansSkyTheGame/comments/mbqibg/this_is_the_highest_mountain_ive_ever_seen_in_nms/

This is where they launch from. It is up above most of the atmosphere. Wind speeds are high but the air is so thin that the wind is less able to tear things to shreds. Shredwinds is how it is lower down until you get below the surface, which is where your people live.

If you could land right on top of this mountain you would be ok. You could go home thru the tunnels, the same way you got up there. If you miss and run into the storms below, you and your ship will be torn to shreds.

Answer 12

Many little planets

A three body system is chaotic, a 20 body system is pure chaos. Once you take off the only thing to do is thrust and get out of there ASAP.

Returning home is a suicide mission, you don't know what is going to hit you from where and setting a course to your home planet becomes an impossible task as you don't have a clue where it'll be in the next day or so

Answer 13

An underwater civilization that's evolved on an airless moon orbiting a gas giant, with ocean beneath the frozen surface, like Ganymede or Europa, but bigger, with an earth equivalent surface gravity, but a tenuous atmosphere due to the temperature.

Once they breach the ice and get the idea to start launching satellites, they will have great difficulty getting them to return with negligible atmosphere to use for breaking plus most of the reasons for returning things are returning living people, who on earth can land in the ocean/taiga and wait to be picked up, even if off course, while for them the surface would be a deadlier environment than space.

Answer 14

Rapidly evolving pathogens

If the planet has really rapidly evolving viruses and bacteria, then population would evolve equally rapidly evolving immune system. But if you were to leave the planet for a months long trip, your immune system wouldn't get regularly updated, the pathogens upon your return would be too different to recognise and thus lethal.

This solution would need a planet to be on a smaller size, as otherwise even traveling on it would be dangerous. Or it should be really windy. It has to have a mechanism for whole population to be exposed to similar pathogens everywhere in small time windows.

Answer 15

The planet has catastrophic weather almost perpetually, except for a day or two every ~100 years

Even at our own level of technology, we have pretty stringent requirements for good weather in order to conduct a launch.

Suppose your hypothetical planet has horrendous weather, at least in the upper atmosphere if not on the ground, that makes launches doomed to failure a majority of the time. Due to weather patterns and seasonal changes and planetary influence and other hand waving, the weather on your planet is only safe for launches for a short window every ~100 years. Maybe it is predictable and scientists can plan for the big day, but maybe it's not and they have to keep everything ready to go at a moment's notice. After the window closes, the weather prevents any hope of landing, at least until some future advanced tech can protect their ships.

Assuming the people of your planet have a lifespan less than the frequency of these rare good launch/landing days, that's effectively a one-way trip.

Answer 16

The planet spins rapidly combined with very low gravity.

On lift off, it slings you off of the surface, facilitating easy access to space.

On re-entry there are two options, either hit it face on or try to catch it on the side.

In case 1 it would be like trying to jump from a moving truck, no way you could land safely.

In case 2 youd skip off like a rock skipping over water as gravity would be too weak to catch you.

I'm not doing the math, but I suspect a large asteroid might match the criteria. The required spin could be the result of a collision with another asteroid.

Answer 17

How about this:

High gravity planet.

It supports life and all that, just not necessarily human-friendly. The natives are short and squat but they have figured out how to get into space through fairly conventional means.

The ships that get launched from here have to be very strong. Lots of structural reinforcement. All this is unnecessary in space, though, and just adds to the cost of any maneuvers or any other travel they want to do. So one of the launch stages actually jettisons the main hull, revealing a far lighter, thinner internal structure that is fine for space but absolutely cannot land. (There could be emergency landings via parachute but the vehicle destroys itself on touchdown because it can no longer support its own weight.)

So you can, maybe, if they included the emergency parachutes, "get back down" but "landing" is not an option, in the sense of ending up with an intact ship. And if there's no parachutes, you're not getting back down at all. (Perhaps the lighter module actually does not include the heat pads necessary for re-entry at all. They can get you up, but ditching all the weight means you can't come back down.)

Answer 18

Extremely Dangerous Megafauna

Perhaps your planet has skies littered with Dragons Sky Lizards whose domain covers the entire planet, that are extremely territorial. They are vicious and hardy creatures, that can and will easily decimate anything encroaching into its territory.

By necessity outgoing rockets are moving far too fast for them to be intercepted. Rockets coming in for landing though? Either slow enough they're lizard food, or fast enough they're pancake.

Answer 19

Edge of a black hole

Your planet is very close to the photonsphere of an ultramassive black hole.

Were it a stellar black hole you and the planet would be spaghettified, but tidal forces are smaller for the bigger holes.

Due to conservation of momentum, if you take off either you or the planet will cross the event horizon (unless you do it from the poles, which might be prohibitively expensive).

In either case that will be your last contact with the planet.

Answer 20

Travelers from the planet have access to 'resources' that inbound travelers do not

Perhaps the planet is very unpredictable due to its gravitational pull, or perhaps the inhabitants have shot so much junk into space that it is very difficult to find a way through. Either way, plotting a course is very difficult and perhaps the trash is even organized in a pattern that going out is generally easier than going back in.

Fortunately you are able to overcome this with heavy calculations just before and during the launch, but this is only possible with vast computational resources which you have on the planet but not on your spaceship.

Secondly you may need to observe the situation with very accurate sensors from the perspective of the launch. Something that obviously would only exist planet side.

Lastly you may need a stable&adjustable base to even adjust the approach angle in the final seconds of the launch countdown.

In short, there may be all kind of resources needed that are available planetside, but would be very hard to make available in the middle of space.

Answer 21

Option 1

Physiology

The planet has a strong gravity, more than double than Earth gravity. Not only reaching space from there is extremely expensive, but the aliens adapted to such gravity had to develop some clever tricks to adapt themselves to the loss of gravity. Trouble is that those tricks are not reversible. Those who reach the outer space are not able to go back without suffering some mortal physical damage.

Since this is the heaviest of the planets that developed some life forms, it is too dangerous even for the inhabitants of all the other known planets.

Option 2

The magnetic cloud

A cloud of ionised gas surrounds the planed. It scatters the light and creates constants magnetic storms that affect all the electronic equipment on board, any spaceship or missile passing through is blinded for a while. It may be safe to leave because going towards outer space the likelihood of bumping into something is small. But it makes it impossible to calculate a safe return route.

Answer 22

Astronauts lose muscle-mass every day while they are in a no/low-gravity environment. Only with a strict training regime during their stay they are able keep this process in check a bit. However even with such a training regime they are not able to walk or even stand after returning to earth. Full adaption to earth-level gravity can take up to a few months.

Perhaps creatures living on a planet with a higher gravity than earth will never be able to adapt again after a few months in a no/low-gravity environment.

Answer 23

Severe Weather

Like, hurricane-severe. A dramatic axial tilt and short year gives your planet harsh, extreme, quickly changing seasons. That paired with the continental geography and atmospheric conditions cause near-constant gale force winds, monsoon rains, or hail the size of minivans. Don't forget lightning.

There are very few times a year when the weather is tame enough to launch, and the most advanced weather tracking technology can only predict those days a few days out. There is no way of knowing in advance when or where it would be safe to land.

More importantly, the lack of clear days to launch severely limits the frequency of shuttle tests and the knowledge they bring. Recovery of wrecked test craft for postmortem analysis is nigh impossible. Thus, what might take Earth a few years of progress would cost your civilization several decades.

Answer 24

You can't have such a planet naturally. If the planetary physics allows take off, it allows return. If you make it like in your question, a planet you can take off from and you can never return to -- face it, you're going to look a manic divorcee. ; )

Answer 25

I propose a very simple solution: just have the planet be orbiting its sun very quickly.

It's hard to land there because it's hard to hit a fast-moving target, especially when you have to arrive at the same velocity as the planet in order to not crash into it. But leaving the planet isn't any more difficult than usual, because "at rest" the rocket already has the same velocity as the planet does.

Answer 26

Deliberately imposed restricions

The planet is under the yoke of the Galactic Empire.

The Empire doesn't allow its subjects to get too uppity with their own spaceflight. Return trips are forbidden.