rocketry

Saturn V

The Saturn rocket series’ biggest brother, the culmination of America’s efforts during the Cold War Space Race against the Russians, and the paragon of human spaceflight achievement, The Apollo program’s primary tool was the mighty Saturn V, the pride of American space exploration, and NASA’s poster child. Designed by Wehrner von Braun, the massive rocket took 24 astronauts beyond Earth’s orbit, 12 of which walked on the Moon.

The Saturn V dwarfed every previous rocket fielded by America in the Space Race, remaining to this day the tallest, heaviest, and most powerful rocket ever brought to operational status and still holds records for the heaviest payload launched and largest payload capacity. On the pad, she stood 363 feet (111m) tall, taller than the Statue of Liberty by 58 feet, with a diameter of 33 feet (10m), and weighed 6.5 million pounds fully fueled. Her designed payload capacity was rated at 261,000 pounds (118,000 kg) to Low Earth Orbit and 90,000 pounds (41,000 kg) to the Moon, but in later missions was able to carry about 310,000 pounds (140,000 kg) to LEO and sent up to 107,100 lb (48,600 kg) worth of spacecraft to the Moon.

The total launch vehicle was a 3 stage vehicle: the S-IC first stage, S-II second stage and the S-IVB third stage. The first stage used RP-1 for fuel, while the second and third stages used liquid hydrogen (LH2), with all three using liquid oxygen (LOX) for oxidizer.

Originally posted by spaceplasma

First Stage

The first stage of the Saturn V is the lower section of the rocket, producing the most thrust in order to get the vehicle off the pad and up to altitude for the second stage.

The Rocketdyne F-1 engine used to propel the rocket was designed for the U.S. Air Force by Rocketdyne for use on ICBM’s, but was dropped and picked up by NASA for use on their rockets. This engine still is the most powerful single combustion chamber engine ever produced, producing 1,522,000 lbf (6,770 kN) at sea level and 1,746,000 lbf (7,770 kN) in a vacuum. The S-IC has five F-1 engines. Total thrust on the pad, once fully throttled, was well over 7,600,000 lbf, consuming the RP-1 fuel and LOX oxidizer at a jaw-dropping 13 metric tonnes per second.

The launch sequence for the first stage begins at approx. T-minus 8.9 seconds, when the five F-1 engines are ignited to achieve full throttle on t-minus 0.  The center engine ignited first, followed by opposing outboard pairs at 300-millisecond intervals to reduce the structural loads on the rocket. When thrust had been confirmed by the onboard computers, the rocket was “soft-released” in two stages: first, the hold-down arms released the rocket, and second, as the rocket began to accelerate upwards, it was slowed by tapered metal pins pulled through dies for half a second.

It took about 12 seconds for the rocket to clear the tower. During this time, it yawed 1.25 degrees away from the tower to ensure adequate clearance despite adverse winds. (This yaw, although small, can be seen in launch photos taken from the east or west.) At an altitude of 430 feet (130 m) the rocket rolled to the correct flight azimuth and then gradually pitched down until 38 seconds after second stage ignition. This pitch program was set according to the prevailing winds during the launch month. The four outboard engines also tilted toward the outside so that in the event of a premature outboard engine shutdown the remaining engines would thrust through the rocket’s center of gravity. At this point in the launch, forces exerted on the astronauts is about 1.25 g.

At about T+ 1 minute, the rocket has gone supersonic, at which point, shock collars form around the rocket’s second stage separator. At this point, the vehicle is between 3 and 4 nautical miles in altitude.

Originally posted by sagansense

As the rocket ascends into thinner atmosphere and continues to burn fuel, the rocket becomes lighter, and the engine efficiency increases, accelerating the rocket at a tremendous rate.  At about 80 seconds, the rocket experienced maximum dynamic pressure. Once maximum efficiency of the F-1 engines is achieved, the total thrust peaks at around 9,000,000 lbf. At T+ 135 seconds, astronaut strain has increased to a constant 4 g’s.

At around T+ 168 seconds, the engines cut off as all fuel in the first stage is expended. At this point in flight, the rocket is  at an altitude of about 36 nautical miles (67 km), was downrange about 50 nautical miles (93 km), and was moving about 6,164 miles per hour (2,756 m/s). The first stage separates at a little less than 1 second following engine cutoff to allow for engine trail-off.  Eight small solid fuel separation motors backs the S-IC from the rest of the vehicle, and the first stage continues ballistically to an altitude of about 59 nautical miles (109 km) and then falls in the Atlantic Ocean about 300 nautical miles (560 km) downrange. Contrary to the common misconception, the S-IC stage never leaves Earth’s atmosphere, making it, technically, an aircraft.

Second Stage

The second stage is responsible with propelling the vehicle to orbital altitude and velocity. Already up to speed and altitude, the second stage doesn’t require as much Delta-V to achieve it’s operation.

For the first two unmanned launches, eight solid-fuel ullage motors ignited for four seconds to give positive acceleration to the S-II stage, followed by start of the five Rocketdyne J-2 engines. For the first seven manned Apollo missions only four ullage motors were used on the S-II, and they were eliminated completely for the final four launches. 

About 30 seconds after first stage separation, the interstage ring dropped from the second stage. This was done with an inertially fixed attitude so that the interstage, only 1 meter from the outboard J-2 engines, would fall cleanly without contacting them. Shortly after interstage separation the Launch Escape System was also jettisoned.

About 38 seconds after the second stage ignition the Saturn V switched from a preprogrammed trajectory to a “closed loop” or Iterative Guidance Mode. The Instrument Unit now computed in real time the most fuel-efficient trajectory toward its target orbit. If the Instrument Unit failed, the crew could switch control of the Saturn to the Command Module’s computer, take manual control, or abort the flight.

About 90 seconds before the second stage cutoff, the center engine shut down to reduce longitudinal pogo oscillations (a forward/backward oscillation caused by the unstable combustion of propellant). At around this time, the LOX flow rate decreases, changing the mix ratio of the two propellants, ensuring that there would be as little propellant as possible left in the tanks at the end of second stage flight. This was done at a predetermined Delta-V.

 Five level sensors in the bottom of each S-II propellant tank are armed during S-II flight, allowing any two to trigger S-II cutoff and staging when they were uncovered. One second after the second stage cut off it separates and several seconds later the third stage ignited. Solid fuel retro-rockets mounted on the interstage at the top of the S-II fires to back it away from the S-IVB. The S-II impacts about 2,300 nautical miles (4,200 km) from the launch site.

The S-II would burn for 6 minutes to propel the vehicle to 109 miles (175km) and 15,647 mph, close to orbital velocity.

Third Stage

Now in space, the third stage, the S-IVB’s sole purpose is to prepare and push the Command, Service, and Lunar Modules to the Moon via TLI. 

Unlike the two-plane separation of the S-IC and S-II, the S-II and S-IVB stages separated with a single step. Although it was constructed as part of the third stage, the interstage remained attached to the second stage.

During Apollo 11, a typical lunar mission, the third stage burned for about 2.5 minutes until first cutoff at 11 minutes 40 seconds. At this point it was 1,430 nautical miles (2,650 km)  downrange and in a parking orbit at an altitude of 103.2 nautical miles (191.1 km)  and velocity of 17,432 mph (7,793 m/s). The third stage remained attached to the spacecraft while it orbited the Earth one and a half times while astronauts and mission controllers prepared for translunar injection.

This parking orbit is quite low, and would eventually succumb to aerodynamic drag if maintained, but on lunar missions, this can be gotten away with because the vehicle is not intended to stay in said orbit for long. The S-IVB also continued to thrust at a low level by venting gaseous hydrogen, to keep propellants settled in their tanks and prevent gaseous cavities from forming in propellant feed lines. This venting also maintained safe pressures as liquid hydrogen boiled off in the fuel tank. This venting thrust easily exceeded aerodynamic drag.

On Apollo 11, TLI came at 2 hours and 44 minutes after launch. The S-IVB burned for almost six minutes giving the spacecraft a velocity close to the Earth’s escape velocity of 25,053 mph (11,200 m/s). This gave an energy-efficient transfer to lunar orbit, with the Moon helping to capture the spacecraft with a minimum of CSM fuel consumption.

After the TLI, the Saturn V has fullfilled its purpose of getting the Apollo crew and modules on their way to the Moon. At around 40 minutes after TLI, the Command Service module (the conjoined Command module and Service Module) separate from the LM adapter, turns 180 degrees, and docks with the exposed Lunar Module. After 50 minutes, the 3 modules separate from the spent S-IVC, in a process known as Transposition, docking and extraction

Of course, if the S-IVC were to remain on the same course (in other words, if they leave it right there unattended), due to the physics of zero gravity environments, the third stage would present a collision hazard for the Apollo modules. To prevent this, its remaining propellants were vented and the auxiliary propulsion system fired to move it away. Before Apollo 13, the S-IVB was directed to slingshot around the Moon into a solar orbit, but from 13 onward, the S-IVB was directed to actually impact the Moon. The reason for this was for existing probes to register the impacts on their seismic sensors, giving valuable data on the internals and structure of the Moon.

Launch Escape System

The Saturn V carries a frightening amount of potential energy (the Saturn V on the pad, if launch failed and the rocket ruptured and exploded, would have released an energy equivalent to 2 kilotons of TNT, a force shy of the smallest atomic weapons), which luckily was unleashed as planned without incident. However, this being NASA, precautions were made to save the crew in event of a catastrophic failure. 

The LES (Launch Escape System) has been around since the Mercury Program as a way to get the crew capsule away from a potential explosion on the pad or in early launch. The idea is that a small rocket would take the capsule far enough away from the rocket that parachutes could be deployed.

The LES included three wires that ran down the exterior of the launch vehicle. If the signals from any two of the wires were lost, the LES would activate automatically. Alternatively, the Commander could activate the system manually using one of two translation controller handles, which were switched to a special abort mode for launch. When activated, the LES would fire a solid fuel escape rocket, and open a canard system to direct the Command Module away from, and off the path of, a launch vehicle in trouble. The LES would then jettison and the Command Module would land with its parachute recovery system.

If the emergency happened on the launch pad, the LES would lift the Command Module to a sufficient height to allow the recovery parachutes to deploy safely before coming in contact with the ground.

An interesting factoid is how much power the LES possesses; in fact, the LES rocket produces more thrust (147,000 pounds-force (650 kN) sea level thrust) than the Mercury-Redstone rocket (78,000 pounds-force (350 kN)) used to launch Freedom-7 during the Mercury program. 

Skylab 

Originally posted by pappubahry

After budget cuts necessitated mission cancellations and the end of the Apollo program, NASA still had at least one Saturn V rocket intended for Apollo 18/19. Luckily, in 1965, the Apollo Applications Program was established to find a use for the Saturn V rocket following the Apollo program. Much of the research conducted in this program revolved around sending up a space station. This station (now known as Skylab) would be built on the ground from a surplus Saturn IB second stage and launched on the first two live stages of a Saturn V. 

The only significant changes to the Saturn V from the Apollo configurations involved some modification to the S-II to act as the terminal stage for inserting the Skylab payload into Earth orbit, and to vent excess propellant after engine cutoff so the spent stage would not rupture in orbit. The S-II remained in orbit for almost two years, and made an uncontrolled re-entry on January 11, 1975. 

This would be NASA’s only Saturn V launch not associated with the Apollo program, and unfortunately, would prove to be the Saturn V’s last one. There were other concepts for Saturn V’s as launch vehicles, including a space shuttle design, but none of these ever came to fruition. 

Cost

From 1964 until 1973, a total of $6.417 billion ($41.4 billion in 2016) was appropriated for the Saturn V, with the maximum being in 1966 with $1.2 billion ($8.75 billion in 2016). 

Displays and Survivors

There are several displays of Saturn V rockets around the United States, including a few test rockets and unused ones intended for flight. The list below details what and where they are.

  • Two at the U.S. Space & Rocket Center in Huntsville:

SA-500D is on horizontal display made up of S-IC-D, S-II-F/D and S-IVB-D. These were all test stages not meant for flight. This vehicle was displayed outdoors from 1969 to 2007, was restored, and is now displayed in the Davidson Center for Space Exploration. The second display here is a vertical display (replica) built in 1999 located in an adjacent area.

  • One at the Johnson Space Center made up of first stage from SA-514, the second stage from SA-515 and the third stage from SA-513 (replaced for flight by the Skylab workshop). With stages arriving between 1977 and 1979, this was displayed in the open until its 2005 restoration when a structure was built around it for protection. This is the only display Saturn consisting entirely of stages intended to be launched.
  • One at the Kennedy Space Center Visitor Complex, made up of S-IC-T (test stage) and the second and third stages from SA-514. It was displayed outdoors for decades, then in 1996 was enclosed for protection from the elements in the Apollo/Saturn V Center.
  • The S-IC stage from SA-515 is on display at the Michoud Assembly Facility in New Orleans, Louisiana.
  • The S-IVB stage from SA-515 was converted for use as a backup for Skylab, and is on display at the National Air and Space Museum in Washington, D.C.

Source: Wikipedia

Solar System: Things to Know This Week

With only four months left in the mission, Cassini is busy at Saturn. The upcoming cargo launch, anniversaries and more!

As our Cassini spacecraft made its first-ever dive through the gap between Saturn and its rings on April 26, 2017, one of its imaging cameras took a series of rapid-fire images that were used to make this movie sequence. Credits: NASA/JPL-Caltech/Space Science Institute/Hampton University

1-3. The Grand Finale

Our Cassini spacecraft has begun its final mission at Saturn. Some dates to note:

  • May 28, 2017: Cassini makes its riskiest ring crossing as it ventures deeper into Saturn’s innermost ring (D ring).
  • June 29, 2017: On this day in 2004, the Cassini orbiter and its travel companion the European Space Agency’s Huygens probe arrived at Saturn.
  • September 15, 2017: In a final, spectacular dive, Cassini will plunge into Saturn - beaming science data about Saturn’s atmosphere back to Earth to the last second. It’s all over at 5:08 a.m. PDT.

4. Cargo Launch to the International Space Station

June 1, 2017: Target date of the cargo launch. The uncrewed Dragon spacecraft will launch on a Falcon 9 from Launch Complex 39A at our Kennedy Space Center in Florida. The payload includes NICER, an instrument to measure neutron stars, and ROSA, a Roll-Out Solar Array that will test a new solar panel that rolls open in space like a party favor.

5. Sojourner

July 4, 2017: Twenty years ago, a wagon-sized rover named Sojourner blazed the trail for future Mars explorers - both robots and, one day, humans. Take a trip back in time to the vintage Mars Pathfinder websites:

6. Voyager

August 20, 2017: Forty years and still going strong, our twin Voyagers mark 40 years since they left Earth.

7. Total Solar Eclipse

August 21, 2017: All of North America will be treated to a rare celestial event: a total solar eclipse. The path of totality runs from Oregon to South Carolina.

8. From Science Fiction to Science Fact

Light a candle for the man who took rocketry from science fiction to science fact. On this day in 1882, Robert H. Goddard was born in Worcester, Massachusetts.

9. Looking at the Moon

October 28, 2017: Howl (or look) at the moon with the rest of the world. It’s time for the annual International Observe the Moon Night.

10. Last Human on the Moon

December 13, 2017: Forty-five years ago, Apollo 17 astronaut Gene Cernan left the last human footprint on the moon.

Discover more lists of 10 things to know about our solar system HERE.

Make sure to follow us on Tumblr for your regular dose of space: http://nasa.tumblr.com

youtube

The sordid history of how the @SpaceX Falcon 9, the first fully reusable, orbit-class booster rocket, eventually managed to land in one piece and stay that way … maybe Falcon realized it still loved us or finally read the instructions…

- Elon Musk, Instagram

lesbianmooncolony  asked:

assuming a starship never has to travel through an atmosphere, and never has to worry about collisions with eg. asteroids or attackers' weapons (maybe some sort of forcefield, or a perfect interceptor weapon system), are there any compelling reasons for starships to be any particular shape? (let's also assume the starship can travel at relativistic speeds)

Aha! Excellent question! I love talking about spaceships.

So most of what I know comes off Atomic Rockets, which has far too much love of old whitedude science fiction novels, but also a lot of useful information, and more recently, lots of conversations with arborine, who has thought/knows a great deal about space habitats and is generally wonderful.

There are a few design considerations that constrain what shape your spaceship should have…

  1. it needs to bear the stresses of acceleration without breaking
  2. it needs to dissipate the heat generated by the crew, onboard machinery and direct sunlight into the highly insulating vacuum of space
  3. it needs to be able to manouvre correctly and, for example, not start spinning uncontrollably when the engine does a burn
  4. its rotation needs to be long-term stable in flight
  5. it needs to be able to withstand impacts with interplanetary/interstellar debris, which although consisting only of rarified gas and small particles, may (depending on the mission) may be approaching at extremely high, even relativistic speeds
  6. it needs to protect equipment and crew from space radiation (from stars or cosmic rays)
  7. it needs to protect the crew from any radiation produced by the ship’s engines, or its power source (a big issue if you use something scary like nuclear power or antimatter annihilation!)
  8. if humans are on board it needs to have pressurised compartments for them to live in, and enough space that they will be comfortable for the duration of the voyage
  9. it needs to minimise the extent of the damage if something goes wrong, e.g. part of the ship is depressurised
  10. it needs to survive for the entire length of the voyage, which probably means it needs to be self-sustaining
  11. it needs to carry enough propellant reaction mass to give it the \(\Delta v\) for whatever it’s out there to do
  12. it needs to be as light as possible, because every unit of mass of spaceship also adds a lot of units of reaction mass, depending on the mission \(\Delta v\)
  13. if you want the crew to experience artificial ‘gravity’, it either needs to be capable of accelerating near \(g\) for nearly the entire mission, or have sections of the spaceship capable of rotation to create a centrifugal force near \(g\)

I’m sure there are a lot more of them.

So while there’s no reason for your ship to be streamlined, there are a bunch of constraints!

1. make it strong, and maybe put the engine at the front to save mass

The first one depends a lot on where you position your rockets. Most designs place the propulsion at the back of the ship, pushing the ship forwards.

If you put the propulsion system at the back of the ship, you need your ship to be sturdy against compressive strength, which adds to the mass of the mission - compressive strength usually requires massive beams and so on, and it’s hard to get around that. When you’re accelerating, it will feel as if gravity is pushing down on everything on board towards the back of the ship, and like a building, your ship has to be strong enough to stand up. Otherwise, your engine will punch straight through your ship, or crush it, or tear off, or something similarly bad.

A tiny number of designs, like the Valkyrie, and in fact some of the earliest rockets ever built, have the propulsion at the front of the ship, towing the rest of the ship behind it.

If you do that, your ship needs tensile strength to not snap against the propulsion. You generally don’t need as much mass to have tensile strength as compressive strength - but putting the engine at the front does mean your crew are directly in the path of the engine exhaust! (The radiation problem is a general one for nuclear and antimatter engines, but it’s particularly severe when you’re right in the engine beam…)

The Valkyrie gets around this by having a shadow shield between the engine and the crew compartment, which absorbs radiation from the engine and casts a shadow over the crew compartment.

Another option is to have your engines not point directly backwards, but have two or more engines angled slightly out to the sides in opposite directions - this is apparently what the ship in the film Avatar does (ship’s presumably a still from the film, annotations from Atomic Rockets).

Putting the engines at the front on a flexible tether does make it much harder to change direction, though.

2. make sure it has large flat surfaces, or sprays of recoverable droplets, to act as radiators

Although space is sometimes described as ‘cold’, especially in movies, that’s kind of misleading. Certainly, if not in direct sunlight, something in space without a heat source will eventually cool down until it’s incredibly cold… but for the same reason that we use vacuum flasks to keep tea or whatever warm, it takes a very long time.

If you’ve got something like a spaceship, which is generating a lot of heat, you need to do something to dissipate that heat. The only mechanism that heat can be lost in space, with no atmosphere to carry it away, is electromagnetic radiation. To lose heat through radiation, you need a large surface area (i.e. big flat surfaces called ‘radiators’), and to carry the heat from the rest of your ship to the radiators. You heat up the radiators and they radiate away your heat into the vacuum.

The Space Shuttle would apparently open its cargo bay doors in space to help it radiate away heat (labels once again from Atomic Rockets).

Your radiators should not have their surfaces facing each other, or else they will heat each other up, and won’t radiate heat as effectively.

Another trick to cool your ship down is to use a ‘Liquid Droplet Radiator’ (picture source - apparently the ‘ICAN-II’ design from Penn State University, no idea what that stands for). This involves using your waste heat to heat up a spray of hot liquid droplets, which travel through space, steadily cooling down. As your ship is accelerating, the droplets ‘fall’ towards the back/front of the ship (depending which way you go), and can be collected, heated up and sprayed back in the opposite direction, maintaining continuous circulation.

Atomic Rockets has some really weird-looking designs, including discs, triangles, and even one that looks like a spiral (using magnetic fields).

Have a look at Atomic Rockets - there are lots of radiator designs I haven’t covered, involving bubbles, nanotube filaments, all sorts of stuff.

3. make sure the thrust vector goes through the centre of mass

If it doesn’t - if your engine is off-centre - when you do an engine burn, it will also have a nonzero moment (torque). This means your ship will start to rotate around its centre of mass when you do an engine burn. Sometimes, this is what you want, but usually only by a small amount! And typically a large engine burn would set you spinning wildly. So you will probably have separate small thrusters for turning.

(This gets even more complicated if your ship has flexible elements!)

4. make sure that, if your ship is spinning, it is spinning around its major principal axis

Every rigid body has a thing called its moment of inertia tensor that can be calculated from its mass distribution. Its eigenvalues are called the principal moments of inertia, and its eigenvectors are called the principal axes of the body.  When the engine is not burning, the ship is undergoing free precession.

I remember a series of arguments about free precession in our classical mechanics lectures that say, since a not-quite-rigid body slowly loses energy to internal stresses but the angular momentum is conserved, it precesses (the angular velocity vector moves with respect to the body coordinates, if that means anything to you) so as to end up spinning around the principal axis with the largest moment of inertia.

If your plan is that your spaceship should spin around a different axis, you should be worried, because it will slowly precess to spin around the major axis.

At the time the USA launched their first ever satelite, Explorer 1, in 1958, this was not known. The pen-shaped (shh) satellite was set spinning around its minor axis, the long axis through the middle of the spaceship. To the scientists’ surprise, the axis of rotation changed in flight, until the satellite was flipping end over end. This led to the first development of Euler rotation (the kind of thing we’re talking about) in over 200 years. But we’ve done that now, so, make sure your spaceship is spinning around its major axis if it spins!

5. if you’re going too fast, the ship needs to be safe from relativistic dust

A tiny grain of dust, when raised to relativistic speeds, can have the kinetic energy of a bullet or bomb. And, if your ship is travelling through space at relativistic speeds, every grain of dust in space will be approaching your ship at those speeds! This is bad.

One solution is to put a shield at the front of your spaceship, which will be punched up by relativistic dust, but will disperse most of its energy before it smashes anything important.

I’m going to talk about the Valkyrie again. I am maybe a bit too into this design, but their solution is really cool.

The Valkyrie sprays fluid droplets ahead of the ship. Any incoming particles can detonate harmlessly among the droplets, without touching the engine. Because the ship is constantly accelerating, the fluid droplets will ‘fall’ back down and land relatively slowly on the front of the ship, where they can be recycled. This is also used for cooling - another ‘liquid drop radiator’.

During the deceleration phase of the mission, this doesn’t work - the droplets fly off ahead of the ship instead of being recaptured. The Valkyrie’s solution is to grind its spent fuel tanks into fine dust and release them ahead of the ship as it decelerates. Travelling at a constant relativistic speed, the ground up fuel tanks will punch their way through any interstellar dust particles ahead of the ship, clearing a path.

Some dust will still enter the path ahead of the ship, so in addition to that trick, the Valkyrie extends many layers of ‘blankets’ of extremely thin material (’similar to Mylar’) ahead of the ship. Because the ship is accelerating in the opposite direction, the blankets are stretched out in front of the ship.

Obviously, nothing remotely close to this has ever been tried! So who knows if it would actually work. I haven’t seen discussion of relativistic dust in other designs on Atomic Rockets, though.

6. you also need to be safe from the ordinary kind of space radiation

Even if you’re not travelling at relativistic speeds, you will (without the protection of an atmosphere) constantly be irradiated by cosmic rays and other ionising radiation from any nearby star. This is a problem even for current astronauts, who apparently hide behind water tanks during periods particularly intense radiation. And it’s often discussed as a major danger of a voyage to Mars.

To an extent, you are protected from this by the hull of your spaceship, which absorbs most kinds of radiation even if it’s quite thin. You apparently need two layers to deal with different kinds of radiation, since charged particles entering the e.g. lead you would use for gamma ray shields can create deadly X-rays. Everywhere where people will be living, long-term, needs to be protected this way.

During periods of major radiation, such as solar flares, this may not be enough. You need a particularly well-shielded part of your spaceship to hide in at these times. One method is to use the water (that you’re carrying anyway, for the crew to drink) to protect the crew at these times. You need a way for the crew to access this area, and take anything particularly vulnerable to radiation - such as food - in there with them.

Apparently people are also considering other methods, involving things like powerful electric or magnetic fields, or bubbles of plasma. I don’t know a lot about this.

7. you also need to be safe from the radiation from your ship’s propulsion and power plant

To travel long distances in space, chemical rockets tend not really to be enough - you need something with a very high \(\Delta v\). Many such propulsion systems have been designed, but they tend to have the side effect of producing lots of ionising radiation.

This isn’t necessarily a huge problem. You don’t necessarily need to shield your entire reactor (which would be very heavy), but can instead use a shadow shield, like we discussed on the Valkyrie, to keep just your ship safe from the radiation, and let the rest of the radiation radiate away into space. But it does imply that the rest of the ship, including your thermal radiators, needs to keep itself inside the cone of safety created your shadow shield. And your shadow shield is usually still quite massive, because the main way we attenuate radiation is to make a lump of very dense materials.

Here’s an example of a NASA design which uses a shadow shield, and has to keep its radiatiors inside the shadow:

8. it needs to have pressurised areas for humans to breathe in

The pressure outside the spaceship is nothing. The pressure inside the spaceship is probably about 1 atmosphere. Your ship needs to be strong enough to contain that.

You definitely don’t want to have too many parts of your ship that would be particularly vulnerable to rupturing, so the walls of your pressurised areas are probably going to be nice and curved with minimal sharp corners.

One way to build a pressure vessel, the way we currently do, is to use lots of strong metal. But that adds a lot to your payload mass. So another possibility is to have an inflatable spaceship.

NASA has one such design called the TransHab. Which I assume means it can’t be boarded by cis people. It looks like this (source)…

(all of those weird CGI people are trans. no arguing)

arborine has generally talked about much larger, long-term designs: a big sphere or torus, containing a much more comfortable landscape built for many people (I will have to ask her to help me recreate the details though!). Spheres and toruses are good for inflatable shapes, because the tension is nice and even across the surface (well, this is complicated by rotation, but basically).

The need to have a pressurised hull and radiation shielding does introduce some limitations. Windows in a pressurised compartment generally need to be quite small and rounded, like aeroplane cabin windows, but when you’re far from a planet, there’s not really anything to see anyway. (It seems that, with sufficient engineering, you can make bigger windows, such as in the ISS’s observation bubble thingy. Even then, the bubble’s pretty small, and there’s plenty of structural stuff keeping that together.)

9. you need to be able to deal with problems with mimimal damage

Despite all your best efforts, it seems inevitable that a pressurised compartment travelling through the vacuum of space might have something go terribly wrong. For example, something punches a hole in the hull. You need to have that not end the mission, and cause as little harm to the crew as possible.

This probably means, internally, that your ship needs to be divided into separate compartments, so that if one gets depressurised, the rest of the ship is still safe. If the walls of your ship can somehow be self-sealing, even better.

10. you need self-repair and a self-renewing ecosystem for a long voyage

If you’re travelling on a very long voyage, carrying supplies for the entire journey just takes too much mass. You need to carry with you a functional, lasting ecosystem of plants etc. that won’t die off during the voyage.

Making a closed ecosystem is very hard - as far as I know, we haven’t succeeded yet. I will defer to arborine on the details of one, as I can’t remember what she said or what was in her extremely practical space habitats book off the top of my head.

In addition, parts of your ship will slowly fail and go wrong. Atomic Rockets claims the best NASA probes can last 40 years in space, and that may well not be enough for your purposes (even taking as much advantage as possible of relativistic time dilation). For a very long voyage like a generation ship or something, everything can probably be assumed to go wrong your spaceship to an extent needs to have the capabilities on board to build itself, and apply its repairs outside the safety of crew compartments.

Needing to recreate them en route might constrain the materials you can use, and hence the shapes you can make.

( breathofzephyr made an interesting point that the total computing power, data storage etc. available to the crew of a generation ship will, unless they can build more computers, go down over the course of the mission. which could have interesting social effects…)

11. you will probably need to dedicate a lot of your spaceship to storing reaction mass in suitable containers

A consequence of the rocket equation is that, for every gram (or whatever mass unit) of payload - structural elements, people, food, computers, robots, whatever - you have, you will need a certain number of grams of reaction mass to throw out the back of your rocket.

(The exception is if you are using a propulsion system such as a solar sail or a laser sail where you are propelled by collisions with material that you’re not carrying with you. Or if you’ve figured out a way to get the Bussard Ramjet, or its variants, to be practical!)

The shape of your propellant tanks depends a great deal on what kind of engine you’d use, but basically, you need a lot of pressure vessels somewhere on your ship, likely held separate from the crew modules.

12. it needs to be really really light, as far as possible

The rocket equation is a very demanding thing, and unless you somehow have vast amounts of leftover \(\Delta v\), you want to take every possible opportunity to save on mass. (’loads of leftover \(\Delta v\) is like, you’re using Project Orion to travel through the solar system or something.)

This is why lots of spaceship designs are modules held together by a lightweight framework - you want to minimise heavy structural elements as much as possible.

We’ve talked quite a bit about this already, though!

13. if you provide gravity, you either need a lot of \(\Delta v\) or something has to spin

For a long voyage, your crew’s bones and muscle will atrophy unless they’re given an environment with a source of ‘gravity’ similar to Earth’s.

There are two ways you can do this, which amount to accelerating some or all of your spaceship. One way is to have your engine burning so as to provide \(1 g\) acceleration throughout your voyage. By contrast, current space missions usually involve very short rocket burns, with the spaceship flying freely for most of its mission. To burn throughout the mission, your ship will need vastly more \(\Delta v\), and hence vastly more propellant mass per unit payload mass.

Since that’s pretty demanding, the other option is to have part of your spaceship spinning. This could be for example a toroidal ring, or a cylinder, or a sphere, or a couple of rooms on the end of long arms.

Depending on how large your rotating section is, it will have to spin more or less fast in order to maintain the amount of gravity you need. The centrifugal acceleration in a rotating reference frame is given by \(r\omega^2\), where \(r\) is the distance from the centre, and \(\omega\) is the angular speed.

Note this means the artificial ‘gravity’ in a rotating section with multiple floors, or in a spherical habitat, will vary as you get closer or further away from the centre! The further out you are, the stronger gravity will be.

A rotating habitat section has some implications about the design of the inside. ‘Level’ surfaces will be curved instead of flat, and the Coriolis effect will apply to deflect trajectories from a straight line - particularly strongly in a small, fast-spinning section.

There are lots of difficulties to overcome if only part of your spaceship is spinning. A major one is the problem of the bearing between the rotating section and the rest of the ship - it needs to be near frictionless, or your spin section will slowly spin down (and your ship will slowly spin up.

Another problem comes from spinning up your spin section without setting the rest of your spaceship rotating in the opposite direction (with possible consequences of precession, and the like). One solution is to have a flywheel inside your ship, but this implies a large mass that’s generally useless. Another is to have multiple counter-rotating spin sections, such that the net angular momentum change can be 0 without spinning the entire ship.

Or, you can just let the entire spaceship spin at once, though this makes manouevring the ship somewhat complicated because of the way gyroscopes act (it becomes forced precession, and you need to push at \(90^\circ\) from the way you actually want to turn…)

A further problem comes from the fact that, when your spaceship is accelerating, the direction of ‘down’ will change. This can be accomodated by some very complicated-looking designs involving arms that swing in and out (source), or just ignored because most of the time your ship is not accelerating.

and more stuff, probably

So, yes, there are a lot of physical demands on the shape of a spaceship, even one that never visits an atmosphere!

Building a spaceship is a lot different from building on Earth, and of course nobody actually knows how to build a spaceship for an interstellar voyage. But this is what we think, based on the physical constraints we’ve imagined so far…