Shuttle lift off if no Gravity

[NoGravity]

Hi,

I'm a newbie here. 

My question is this.  Using the space shuttle as an example, how much fuel would be saved if gravity stopped at the moment of liftoff for 1 second, 5 seconds, 10 seconds, 30 seconds and one full minute?

I may be using this info in a SF story I am writing.

Thanks!

[The Raging Sandwich]

Well, all of it, it would just float upwards (until you got into orbit, then I don't know. There's a start)

[YNM]

"no gravity" means "no orbit".

For portion of the time... It'd be quite a boost (guaranteed at most 10x standard linear acceleration for that portion).

Edited February 22, 2017 by YNM

[StrandedonEarth]

It would experience the same number of gee's, but without gravity the actual acceleration would be increased by 9.81 m/s²

[Bill Phil]

Well... You wouldn't be able to orbit anything...

Not much fuel. You'd still have to GET to orbital velocity after or before you turn gravity back on. Unless you leave it off. But then you'd have weird stuff happening.

[munlander1]

That would definitely be interesting. If you were at a point where you where above that altitudes orbital velocity would you move up?

[linuxgurugamer]

It's an interesting question. First, your acceleration would be increased by 1g for the duration.  Second the fuel saved by not having to fight against gravity is what translates into that additional G.  Depending on how long there is no gravity, it can be pretty significant.

I'm assuming your story will have some sort of device that nullifies gravity for a short period of time.

[Bill Phil]

Another problem is that you would end up going tangential to Earth at a certain velocity, and tangential to Earth's orbit at 30 or something km/s...

[mikegarrison]

1 hour ago, Bill Phil said:

Another problem is that you would end up going tangential to Earth at a certain velocity, and tangential to Earth's orbit at 30 or something km/s...

Exactly. You wouldn't "float up". You would actually be heading on a tangent. At first it would seem like up, because of the small angle approximation. But as the angle got bigger, the sideways motion would start to become apparent.

[HebaruSan]

Are we talking all gravity? Is the atmosphere affected?

[Nibb31]

If you had no gravity during a shuttle launch, then you would have much bigger problems than the shuttle launch, like the planets flying away from the Sun for example and the Earth ripping itself to pieces.

[KerikBalm]

My guess is that he just means that gravity does not affect the shuttle temporarily.

IIRC the shuttle loses about 1000 m/s due to gravity and aero drag, and has about 9000 ms total dV.

The shuttle could "drift" up, and then expend roughly 8000 m/s to get to orbital velocity once gravity starts affecting it again.

I guess this reduces dV requirements to 8/9 what they'd be without "temporary local gravity nullification"

Edited February 22, 2017 by KerikBalm

[kerbiloid]

As without gravity the potential energy doesn't have sense, this will save GMm(1/R1-1/R2) joules of energy.

[hms_warrior]

You can test it out for yourselfe! Just put your shuttle on the pad, hit alt+f12 and deactivate Gravity

[Nibb31]

4 hours ago, KerikBalm said:

My guess is that he just means that gravity does not affect the shuttle temporarily. 

In that case, you would need zero propellant. You wouldn't even need a Shuttle. Just put the payload in the parking lot and give it a nudge. 

It's not like orbiting makes any sense without gravity anyway. 

[p1t1o]

Firstly, due to the rotation of the Earth, everything on the planet not tied down, will fly off into space, at quite a rate. Including the atmosphere which will leave quite a lot faster than everything else.

The Moon and oceans would also depart.

There would be extreme tectonic events all over the globe as various stresses were released. The Planet would expand slightly, with various effects, possibly including bad things happening to the crust.

I hesitate to say that the planet would literally explode, but there is a colossal amount of energy tied up in the gravitational potential of the Earth's mass AND in its rotation, and rock/magma/earth-material is not known for its tensile resilience.

If gravity then suddenly "switched back on" the exact reverse would occur, with the Moon being recaptured into a wider, much more eccentric orbit.

More extreme tectonics as the Earth re-compressed. Multiple quadrillion tons of dirt, rock, debris, air and water come crashing back, smoothing the surface nicely.

It would probably be the end of the world as we know it. The vast majority of people would be killed by various impacts. Most building are not attached well enough to the ground to support their own weight, and if they were, their structures would fail anyway. (they just aren't designed for this)

If it just affected the shuttle on its own, then what you would do is retire the shuttle and build a bespoke craft based on this method liftoff (does it have to re-enter normally?). If gravity comes back whilst you are in space, you are going to want enough dV to achive an orbit, but this will be significantly less dV than the current shuttle.

***

This makes a better concept for an end-of-the-world or post-apocalytic scenario (I'd read it), rather than a means of space travel (it doesn't really make sense for it just to be switched off for the shuttle, unless you just want to McGuffin-in a standard sci-fi anti-gravity drive, but that has been done to death, and makes space travel less interesting anyway).

 

Edited February 22, 2017 by p1t1o

[KerikBalm]

27 minutes ago, Nibb31 said:

In that case, you would need zero propellant. You wouldn't even need a Shuttle. Just put the payload in the parking lot and give it a nudge. 

It's not like orbiting makes any sense without gravity anyway. 

You are ignoring one key word in my post:

"temporarily"

I know it makes no sense otherwise, but that seems to be what the OP is asking:

Quote

 if gravity stopped ... for 1 second, 5 seconds, 10 seconds, 30 seconds and one full minute?

Of course... that would cause huge problems for the entire planet and probably the solar system (milky way too?)...

So... I'm trying to treat his idea in the way that makes the most sense (as people do all the time when faced with other people making statements with poor grammar).

Based on his time statements, I assume gravity will affect the shuttle shortly after "launch", and thus the shuttle will still need to achieve orbital velocity.

[NoGravity]

6 hours ago, HebaruSan said:

Are we talking all gravity? Is the atmosphere affected?

Yes, all gravity in the vicinity of earth, including the moon, but not as far as the next nearest planets.

 

[KerikBalm]

then we have a lot more to worry about than the shuttle.... It would be catastrophic. Earth would literally spin itself apart... not over the course of 1 minute, but it would be an earth quake like we've never seen.

[Nibb31]

1 hour ago, NoGravity said:

Yes, all gravity in the vicinity of earth, including the moon, but not as far as the next nearest planets.

There would be no more Earth and no more Moon. With nothing pulling it together, the Earth's crust would fly off with the centrifugal force. The Moon would fling away on a tangent into an escape trajectory.

[Snark]

3 hours ago, NoGravity said:

Yes, all gravity in the vicinity of earth, including the moon, but not as far as the next nearest planets.

Extraordinarily horrible world-wide disaster.

If it's only for a few seconds, it wouldn't noticeably affect the moon's trajectory.  The moon takes a month for an orbit; losing gravity for a minute or less would just be a minor perturbation, scarcely noticeable.

On Earth, effects due to planetary spin would also be fairly minor in terms of "rip the planet apart"-- again, because it's only momentary.  Centripetal acceleration due to the Earth's rotation is only 3.4 cm/s² at the equator (the location of maximum effect).  Even if you assume that the earth is a liquid with no tensile strength (a pretty good approximation, at planetary scale), the vertical displacement for a full sixty-second gravity outage would be 60 meters.  Hardly qualifies as "rip the planet apart"; wouldn't even be naked-eye visible from low orbit.  If the outage is shorter, the displacement would be a lot less, since it goes with the square of the outage time.  For example, a ten-second outage would be a displacement of less than two meters.

Even though it wouldn't "destroy the planet," though, it likely would cause the Mother Of All Global Earthquakes.  Like having a magnitude-10-or-worse earthquake over the whole planet.  Add some rip-roarin' tsunamis into the mix, just to add to the fun.  Not a great outlook for our modern civilization and infrastructure.

(Never mind all the "minor" personal-scale disasters that would happen.  If gravity were to unexpectedly cut out for a few seconds right now, as I sit here sedentary at my desk, and then suddenly cut back in again, I'm pretty sure I'd suffer broken bones at best, with a high chance that I'd end up falling on my head and snapping my neck and dying, even if I were lucky enough not to have anything heavy fall on me.)

As for the shuttle:  As folks have pointed out, you'd gain "free acceleration" due to not having to pile up gravity loss during the outage.  The amount of dV you'd gain would be 9.81 m/s for every second of gravity outage.  My guess would be that it would probably seriously mess up the trajectory, though.  I'm certainly not any expert on the shuttle's systems, so I don't know how steerable it is during ascent, but my guess would be "not very".  The SRBs are, well, SRBs, and can't be turned off or throttled once activated, and I don't think they're gimbaled (someone please correct me if I'm wrong).  The SSME's are liquid-fueled, so I assume they're somewhat throttleable, but they'd have to maintain the correct thrust relative to the SRBs in order not to cause torque problems to pitch the shuttle up or down.  The shuttle is, I assume, carefully engineered to follow a particular gravity curve while taking off, and giving it an extra hundred m/s or more of speed right at the start would mess that curve up; the shuttle would end up climbing more steeply than intended.  I'm not sure what the implications would be in terms of achieving a stable orbit-- i.e. whether it would be able to steer enough, after the SRBs burn out, to be able to correct for the unexpected trajectory change.  Also note that it's not just a question of whether it's physically capable, but also an issue with its guidance and control systems.  I'm pretty sure "global interruption of gravity" is not on the list of just-in-case scenarios that NASA engineers have planned for.    A sudden problem like that, totally out of left field, with only a minute or so to deal with it... bearing in mind that everyone on the ground will be in a hysterical panic and likely suffering life-threatening injuries-- seems like a pretty hard problem to recover from.  I have no idea how much ability the astronauts on the shuttle would have to understand what's going on and make the necessary corrections within the critical time window.

[HebaruSan]

3 minutes ago, Snark said:

The SRBs are, well, SRBs, and can't be turned off or throttled once activated, and I don't think they're gimbaled (someone please correct me if I'm wrong).

https://en.wikipedia.org/wiki/Space_Shuttle_Solid_Rocket_Booster#Thrust_vector_control

Quote

Each SRB had two hydraulic gimbal servoactuators, to move the nozzle up/down and side-to-side. This provided thrust vectoring to help control the vehicle in all three axes (roll, pitch, and yaw).

 

[Snark]

Just now, HebaruSan said:

https://en.wikipedia.org/wiki/Space_Shuttle_Solid_Rocket_Booster#Thrust_vector_control

Ah, thank you.

There's still the question of guidance.  How does the shuttle know its position, attitude, etc.?  Is it based on telemetry of position relative to ground stations?  GPS?  Inertial guidance?  Something else?

If it's based on inertial guidance, that will be not just useless but actively misleading, because any on-board inertial systems will have no way of knowing that gravity cut out, and will "think" that everything's fine when it's not.

If it's based on GPS, there may be other problems due to perturbations of GPS satellite orbits when gravity cuts out.

If it's based on some form of ground-based telemetry radioed to the shuttle, then maybe it might be okay in terms of knowing what its position is.

However, even if it has perfect fidelity in its guidance telemetry so that it knows there's a problem... there's still the question about whether its correction mechanisms (either automated, or from the human crew) would be able to cope with the perturbation of suddenly gaining a lot more vertical velocity than expected.

[HebaruSan]

19 minutes ago, Snark said:

There's still the question of guidance.  How does the shuttle know its position, attitude, etc.?  Is it based on telemetry of position relative to ground stations?  GPS?  Inertial guidance?  Something else?

https://spaceflight.nasa.gov/shuttle/reference/shutref/orbiter/avionics/gnc/coas.html

Quote

The crewman optical alignment sight is used if inertial measurement unit alignment is in error by more than 1.4 degrees, rendering the star tracker unable to acquire and track stars. The COAS must be used to realign the IMUs to within 1.4 degrees. The star trackers can then be used to realign the IMUs more precisely.

Unsurprisingly, it sounds like they had multiple redundant systems operating in concert. (I think there were also some gyroscopes involved.) The component I find most intriguing in this scenario is the star tracker, since the positions of distant stars would be unaffected by the gravitational anomaly. I wasn't able to find details about the star tracker beyond that page, though.

19 minutes ago, Snark said:

However, even if it has perfect fidelity in its guidance telemetry so that it knows there's a problem... there's still the question about whether its correction mechanisms (either automated, or from the human crew) would be able to cope with the perturbation of suddenly gaining a lot more vertical velocity than expected.

It might be interpreted as engine failure, if an accelerometer suddenly detected a 1 g reduction in downward force. Or I might have my vectors turned around, not sure.

[Snark]

18 minutes ago, HebaruSan said:

Unsurprisingly, it sounds like they had multiple redundant systems operating in concert. (I think there were also some gyroscopes involved.) The component I find most intriguing in this scenario is the star tracker, since the positions of distant stars would be unaffected by the gravitational anomaly. I wasn't able to find details about the star tracker beyond that page, though.

Unfortunately, the star tracker would be absolutely useless for telling them where the shuttle is or how fast it is currently going.  It will tell them the absolute orientation of the shuttle, that's it.

How do they know what their current XYZ coordinates are, or how fast they're going?

17 minutes ago, HebaruSan said:

It might be interpreted as engine failure, if an accelerometer suddenly detected a 1 g reduction in downward force. Or I might have my vectors turned around, not sure.

Except it wouldn't.  Once the shuttle leaves the ground, the accelerometer is basically telling it the product of the shuttle's own engine thrust, modified by any aero forces.  It wouldn't detect the change in the gravity field.  That's my point.