Weird Facts About Spacecraft Maneuvers And Orbital Maneuvers.... Am I Right Or Wrong?

[Spacescifi]

 

Sometimes reality is wilder than fiction, since it conforms to physics rather than plot.

 

Example 1: Let's say you have large a spaceship capable of constant 1g acceleration. That's great in all... for gravity, but what happens to the crew hen the ship does other maneuvers? Like pitch, yaw, and rolling?

For starters you cut off the main engines and coast for a bit before you engage the thrusters to do the maneuver, but as for the crew?

They should be strapped into their seats or hold on to something.

 

I say this because unless a big ship turns slowly, there will be g-force felt by the crew, enough to make them fall towards a nearby wall or something.

 

With that in mind it really affects the interior design of a spaceship's habitat to prevent disasters and injuries.

 

For example, no furniture that is not bolted to the floor, and likely metal dishes that stick to magnetic tables so that the chance of getting impaled by utensils is lower during a maneuver. The free floating junk that astronauts play with is to be avoided wherever possible on large spacecraft with significant crew numbers.... especially ones that include families and kids.

 

Example 2: Orbital maneuvers can be weird at times.

For example if you are in low orbit any planet and want to dock with another spacecraft orbiting some distance ahead of you what do you do? Astronauts in the early days tried the intuitive thing they would do on earth, thrust forward to meet the craft, but each time they did that they they noticed the craft got farther abd farther away until they were nearly out of fuel.

 

Turns out that the best way to get near an orbiting spacecraft that is ahead of you is to lower your orbit by retro-thrusting backward so that gravity pulls you into a tighter and faster orbit.

 

I suppose at close range this would not matter much, but at distant ranges it will... meaning retroburn at distsnt range for rendrzvous, but at close range you are probably so close that you the orbiting spacecraft simply does not have enough time to 'curve' away from you.

 

I also know that at high enough speeds of linear acceleration that you could pass up an orbiting spacecraft but you would not dock with them because if tried you would crash more than dock because of the difference in speeds.

 

 

Anything anyone wish to add?

Edited July 3, 2022 by Spacescifi

[kerbiloid]

18 minutes ago, Spacescifi said:

With that in mind it really affects the interior design of a spaceship's habitat to prevent disasters and injuries.

Spoiler

 

[Spacescifi]

21 minutes ago, kerbiloid said:

  Hide contents

 

Cute pic. Is the guy Russian? I am acutely aware that Russia has a lot of dealings with Asians since they have a country larger than several put together and border china.

Edited July 3, 2022 by Spacescifi

[JoeSchmuckatelli]

57 minutes ago, Spacescifi said:

example if you are in low orbit any planet and want to dock with another spacecraft orbiting some distance ahead of you what do you do? Astronauts in the early days tried the intuitive thing they would do on earth, thrust forward to meet the craft, but each time they did that they they noticed the craft got farther abd farther away until they were nearly out of fuel.

 

Turns out that the best way to get near an orbiting spacecraft that is ahead of you is to lower your orbit by retro-thrusting backward so that gravity pulls you into a tighter and faster orbit.

 

I suppose at close range this would not matter much, but at distant ranges it will... meaning retroburn at distsnt range for rendrzvous, but at close range you are probably so close that you the orbiting spacecraft simply does not have enough time to 'curve' away from you.

Couple of thoughts by the resident Neanderthal:

1.  The ship you are chasing / hoping to dock with is in orbit - meaning it's following a curved trajectory around the planet / moon / sun. Military pilots flying combat aircraft know that if you cut inside the target craft's turn you are shortening your path and thus closing.  Pretty sure that most pilots reduce throttle when they want a tighter turn - so the 'slow down to speed up' thing isn't that great of a leap.  Given that the first space pilots came from the military - that 'resident knowledge' should not be ignored. 

2. Most of the real world space maneuvers involve strictly limited amounts of fuel to perform any action... So techniques that can accomplish the goal with the least fuel expense are preferable.  If you can do a short burn, drop into a tighter orbit and use gravity to help you close and another couple of short burns to match your target... All the better. 

3.  If you are positing a completely sci-fi ship with effectively infinite power - your constraints will be different.  Thus the solutions are not restricted by the real world.  Example: Belter Ice Mining Tug is diving on a hard burn trajectory (burn, flip, burn) for Mars Station to cash in on the current market prices - your Pirate captain isn't going to finesse it.  She's going to cut inside the curve because of geometry - but may burn harder to get an intercept, disable the Tug, grapple it, and then burn extra hard to turn both crafts away from the waiting Martian Coasties.   Both pilots have to play the geometry game because the Belt and Mars are in ballistic, gravity controlled (and thus curved) orbits - but once she has control of her Prize, with infinite thrust she no longer has to conform to what we are currently used to. 

Edited July 3, 2022 by JoeSchmuckatelli

[Shpaget]

52 minutes ago, Spacescifi said:

 

I say this because unless a big ship turns slowly, there will be g-force felt by the crew, enough to make them fall towards a nearby wall or something.

Do your proposed maneuvering engines produce meaningful acceleration? Unless your big ship turns as fast as Vipers in BSG, your passengers won't even notice the pitch, yaw and roll. Acceleration is happening in whichever direction the ship's engines are pointing, regardless of the direction in which the ship is moving.

[Spacescifi]

Just now, Shpaget said:

Do your proposed maneuvering engines produce meaningful acceleration? Unless your big ship turns as fast as Vipers in BSG, your passengers won't even notice the pitch, yaw and roll. Acceleration is happening in whichever direction the ship's engines are pointing, regardless of the direction in which the ship is moving.

 

Video game type maneuvering?

You know, like if I wanna roll aa a big ship I roll, not necessarily super fast, but it should not take say... more than say a few seconds to do a complete revolution... those kind of speeds.

[Shpaget]

What does "big ship" mean? Are we talking a handful of passengers or a container ship size thing? If it's former, a few seconds to do a full revolution is super fast. If it's latter, it's immersion breaking fantasy land.

[RCgothic]

If you have a drive capable of constant acceleration, don't worry about fuel efficiency when catching a target ahead of you in the orbit. You can brute-force it.

Basically, you accelerate so you are going faster, so gravity is no longer enough to hold you at that radius and so your orbit would expand, but then you just thrust inwards to compensate. You'll catch the target much sooner than playing games with orbital mechanics.

Also, most rendezvous dependent on orbital mechanics assumes a cooperative target. It can be very hard to next to impossible to catch an actively manoeuvring opponent if you're fuel-limited.

Edited July 3, 2022 by RCgothic

[Spacescifi]

20 minutes ago, Shpaget said:

What does "big ship" mean? Are we talking a handful of passengers or a container ship size thing? If it's former, a few seconds to do a full revolution is super fast. If it's latter, it's immersion breaking fantasy land.

Hmmmm... how about the Python from Elite dangerous?

Dimensions

87.9m x 58.1m x 18.0m

Pilot Seats

2

Multicrew

Yes

Fighter Hangar

No

Hull Mass

350 t

And I reckon any container ship due to it's sheer size would have g-force issues with the crew during maneuvers unless they are doing it really, really slow.

Edited July 3, 2022 by Spacescifi

[JoeSchmuckatelli]

1 hour ago, Spacescifi said:

And I reckon any container ship due to it's sheer size would have g-force issues with the crew during maneuvers unless they are doing it really, really slow

Compare modern warship maneuvers vs super tankers for example.  Certainly, one has advantages over the other. 

The point above about thrust / felt-forces in line with the main engines should not be glossed over. 

You're not going to do much with bow thrusters to turn a ship - you're gonna flip the main engines around and burn

There is a few scenes in the last two seasons of the Expanse that show this 

 

Edited July 3, 2022 by JoeSchmuckatelli

[kerbiloid]

Why manage the gravity just outside, not inside.

Spoiler

 

Anyway the constant 1 g is a pure fictional engine.

[Shpaget]

Now that you have the ship size, pick an arbitrary amount of time in which you would like to make the turn and calculate the necessary angular acceleration to achieve it. Don't forget to slow down at the end of the turn.

When you have that you'll be able to calculate linear sideways acceleration felt by crew however far away from center of mass you want, calculate the resultant of that and main engine 1g.

Why do you always wait for others to do your math for you?

[Spacescifi]

32 minutes ago, Shpaget said:

Now that you have the ship size, pick an arbitrary amount of time in which you would like to make the turn and calculate the necessary angular acceleration to achieve it. Don't forget to slow down at the end of the turn.

When you have that you'll be able to calculate linear sideways acceleration felt by crew however far away from center of mass you want, calculate the resultant of that and main engine 1g.

Why do you always wait for others to do your math for you?

Math was and is a  weakness of mine.... and my current situation hardly makes studying to improve it an easy thing to do.

Edited July 3, 2022 by Spacescifi

[sevenperforce]

5 hours ago, Spacescifi said:

Example 1: Let's say you have large a spaceship capable of constant 1g acceleration. That's great in all... for gravity, but what happens to the crew hen the ship does other maneuvers? Like pitch, yaw, and rolling?

For starters you cut off the main engines and coast for a bit before you engage the thrusters to do the maneuver, but as for the crew?

They should be strapped into their seats or hold on to something.

I say this because unless a big ship turns slowly, there will be g-force felt by the crew, enough to make them fall towards a nearby wall or something.

The size of the ship doesn't really matter unless the crew cabin is far from the center of mass. Turning feels the same to the crew whether you're in a small ship or a big ship.

But why would you turn off the engines in order to pitch, yaw, or roll? That doesn't make sense. Just use the engines to provide whatever attitude change you want.

4 hours ago, Spacescifi said:

I reckon any container ship due to it's sheer size would have g-force issues with the crew during maneuvers unless they are doing it really, really slow.

A container-ship-sized spaceship wouldn't have any more trouble with g-forces resulting from turns than an actual container ship has with g-forces resulting from turns.

4 hours ago, Spacescifi said:

You know, like if I wanna roll aa a big ship I roll, not necessarily super fast, but it should not take say... more than say a few seconds to do a complete revolution... those kind of speeds.

This seems like a problem in search of a problem.

_{I would say a solution in search of a problem but it's not clear that there's a solution involved.}