Orbit to Surface with grav equipment

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PsiTraveller
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Orbit to Surface with grav equipment

Postby PsiTraveller » Fri Jul 16, 2021 10:39 am

An air raft (Core pg 138) says it can reach orbit, but people must wear vac suits. A grav floater on pg 141 can also reach orbit.

Could a person wearing a grav belt on a vac suit launch themselves from orbit and use the grav belt to fly down onto a planet surface? The entry on page 113 does not say.

I am looking for an inconspicuous method of slipping someone onto a planet surface from orbit. I was wondering if the grav floater was the minimum size needed, or if a grav belt, or grav assisted power armor was needed.

Anyone have any suggestions for a Long Lonely Leap?
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OrdosMalleus
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Re: Orbit to Surface with grav equipment

Postby OrdosMalleus » Fri Jul 16, 2021 11:40 am

Atmospheric re-entry might be an issue
Condottiere
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Re: Orbit to Surface with grav equipment

Postby Condottiere » Fri Jul 16, 2021 12:32 pm

1. I recall that manoeuvre drives allow the option of controlled re-entry, which presumably would minimize friction, if so desired, though can't recall where i read that.

2. I'm also not quite clear as to maximum ceiling, the only one I recall at this moment is twelve hundred fifty klicks for the orbital disadvantage.
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Re: Orbit to Surface with grav equipment

Postby DarkDawning » Fri Jul 16, 2021 1:13 pm

PsiTraveller wrote:
Fri Jul 16, 2021 10:39 am
An air raft (Core pg 138) says it can reach orbit, but people must wear vac suits. A grav floater on pg 141 can also reach orbit.

Could a person wearing a grav belt on a vac suit launch themselves from orbit and use the grav belt to fly down onto a planet surface? The entry on page 113 does not say.

I am looking for an inconspicuous method of slipping someone onto a planet surface from orbit. I was wondering if the grav floater was the minimum size needed, or if a grav belt, or grav assisted power armor was needed.

Anyone have any suggestions for a Long Lonely Leap?
If he separates from a space ship that has canceled its orbital velocity, then it would be like an extended halo jump and all he would need is a space suit ( to breath) and a parachute, as he has no velocity to shed.

If leaving a space station in orbit he would need to loose all the orbital velocity. still might be able to do it but would take a lot of time given the small thrust a grav belt can generate.
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Re: Orbit to Surface with grav equipment

Postby Condottiere » Fri Jul 16, 2021 1:23 pm

The question would be if the gravitational motors have the range to tap into the local gravitational field in order to brake and control velocity.
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Re: Orbit to Surface with grav equipment

Postby AnotherDilbert » Fri Jul 16, 2021 1:46 pm

PsiTraveller wrote: Could a person wearing a grav belt on a vac suit launch themselves from orbit and use the grav belt to fly down onto a planet surface? The entry on page 113 does not say.
I would say yes. By tradition has the equivalent performance of an air/raft. Beware battery duration. Traditionally it takes a number of hours equal to the size code of the planet.

Other alternatives are:
Atmospheric Reentry Kit (CT JTAS#11, p16)

Re-entry Capsule (HG, p46)


Only the last is stealthed against military sensors, if that matters.
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Re: Orbit to Surface with grav equipment

Postby AnotherDilbert » Fri Jul 16, 2021 1:52 pm

DarkDawning wrote: If he separates from a space ship that has canceled its orbital velocity, then it would be like an extended halo jump and all he would need is a space suit ( to breath) and a parachute, as he has no velocity to shed.
You still have an orbital velocity even if you are in geo-sync, you will not fall straight down, but in a spiral around the planet.

Even without that you have a lot of potential energy from the altitude to shed, I don't think a cloth parachute will help much...
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Re: Orbit to Surface with grav equipment

Postby Condottiere » Fri Jul 16, 2021 2:01 pm

I have Earth reentry listed at a tad over twenty eight thousand kilometres per hour.
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Re: Orbit to Surface with grav equipment

Postby AnotherDilbert » Fri Jul 16, 2021 2:12 pm

Condottiere wrote: I have Earth reentry listed at a tad over twenty eight thousand kilometres per hour.
That depends on altitude. From infinite altitude, aka escape velocity, it's about 11 km/s ≈ 40 000 km/h.
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Re: Orbit to Surface with grav equipment

Postby Condottiere » Fri Jul 16, 2021 2:13 pm

Core says the air/raft is capable of reaching orbit, in it's commentary.

But how high in orbit, and if performance would be dependent on the local gravitational field, and weight of passengers and/or cargo.
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Re: Orbit to Surface with grav equipment

Postby DarkDawning » Fri Jul 16, 2021 2:48 pm

Condottiere wrote:
Fri Jul 16, 2021 1:23 pm
The question would be if the gravitational motors have the range to tap into the local gravitational field in order to brake and control velocity.
Using the ISS as an example earths gravity at that altitude is still .89g so if grav belts use contra grav like the air rafts is should be possible, but the ISS is moving at roughly 17k mph orbital velocity to avoid falling down, so the question is could it cancel the orbital speed before the suit ran out of air or the belt ran out of power,

so just have him jump out of a ship that's canceled its orbital velocity ( say preparing to land at a ground starport ) and skydive towards the ground ,then use the grav belt or a regular parachute to control final landing as a skydiver does.
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Re: Orbit to Surface with grav equipment

Postby DarkDawning » Fri Jul 16, 2021 3:06 pm

AnotherDilbert wrote:
Fri Jul 16, 2021 1:52 pm
DarkDawning wrote: If he separates from a space ship that has canceled its orbital velocity, then it would be like an extended halo jump and all he would need is a space suit ( to breath) and a parachute, as he has no velocity to shed.
You still have an orbital velocity even if you are in geo-sync, you will not fall straight down, but in a spiral around the planet.

Even without that you have a lot of potential energy from the altitude to shed, I don't think a cloth parachute will help much...
that's why i specified a ship that had canceled its orbital velocity and hovering above the planet using thrusters, so where geo orbit came from I'm not sure, if I somehow implied that it had canceled its orbital velocity and was still orbiting , I apologize

assuming earth like planet with the same gravity and atmospheric density, while falling without orbital velocity in the mix, the air as it gets thicker will slow you without burning you up till you reach "terminal velocity" roughly 150 mph, cloth chutes work for people falling at that speed every day :)
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Re: Orbit to Surface with grav equipment

Postby AnotherDilbert » Fri Jul 16, 2021 6:18 pm

DarkDawning wrote: that's why i specified a ship that had canceled its orbital velocity and hovering above the planet using thrusters, so where geo orbit came from I'm not sure, if I somehow implied that it had canceled its orbital velocity and was still orbiting , I apologize
What is "canceled its orbital velocity"? In space there is no such thing as standing still, everything orbits everything else.

I assumed you meant staying above a certain point on the planets surface. That means you are circling the planet as it rotates? That would be a forced geo-sync orbit, but not a natural geo-stationary orbit. You would continually accelerate to maintain position relative the surface. It's still an orbit, and you would move at a decent clip relative the centre of the Earth.
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Re: Orbit to Surface with grav equipment

Postby DarkDawning » Fri Jul 16, 2021 6:47 pm

AnotherDilbert wrote:
Fri Jul 16, 2021 6:18 pm
DarkDawning wrote: that's why i specified a ship that had canceled its orbital velocity and hovering above the planet using thrusters, so where geo orbit came from I'm not sure, if I somehow implied that it had canceled its orbital velocity and was still orbiting , I apologize
What is "canceled its orbital velocity"? In space there is no such thing as standing still, everything orbits everything else.

I assumed you meant staying above a certain point on the planets surface. That means you are circling the planet as it rotates? That would be a forced geo-sync orbit, but not a natural geo-stationary orbit. You would continually accelerate to maintain position relative the surface. It's still an orbit, and you would move at a decent clip relative the centre of the Earth.
By saying no orbital velocity , its speed would be the same orbital speed as a person jumping out of an airplane , or the same speed as a rock thrown upward as it just begins to fall, its not a fast firm number ,after all someone standing on the surface at the equator circles the earth once a day so has some velocity even though we would consider them not moving relative to the surface
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Re: Orbit to Surface with grav equipment

Postby Condottiere » Fri Jul 16, 2021 6:55 pm

At what altitude would an object drop straight down?
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Re: Orbit to Surface with grav equipment

Postby DarkDawning » Fri Jul 16, 2021 7:07 pm

Condottiere wrote:
Fri Jul 16, 2021 6:55 pm
At what altitude would an object drop straight down?
depends on just how straight you mean lol if you are above the equator it is moving about 1000 miles an hour . matching that still might not have you fall straight as you would be blown off straight by winds in the atmosphere, even above the poles with no atmosphere you would fall a little off of straight due to the planets speed going around the sun, but for the purpose of just getting someone to the ground in a grav belt a traveller ship with 1 or more g's to burn could briefly get to a low enough orbital speed to let him drop safely to the surface, it would depend on their tech level whether they would detect him drooping down.
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Re: Orbit to Surface with grav equipment

Postby Condottiere » Fri Jul 16, 2021 7:35 pm

I'm pretty sure that terminal velocity can be dealt with.

It's more a question when the integral anti gravity motors have enough motivation to come to equilibrium with downward movement, basically cancelling it out.
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Re: Orbit to Surface with grav equipment

Postby AnotherDilbert » Fri Jul 16, 2021 8:56 pm

Condottiere wrote: At what altitude would an object drop straight down?
In a rotating system: None.

It might affect snipers. It certainly affects artillery.
https://americanshootingjournal.com/pre ... is-effect/
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Re: Orbit to Surface with grav equipment

Postby PsiTraveller » Fri Jul 16, 2021 10:41 pm

So a grav floater and air car can reach orbit at 200-300 kph but cannot leave a ship and get back to the ground? That seems to be the implication of the re-entry pods in Highguard. And if an air raft makes it to orbit, at whatever height that is, since ships are orbiting at umpteen thousand kph an hour, what good is the air raft up in orbit anyway? How can a crew get picked up? And I am assuming that given the air raft can actually make it that high it can return to the surface and it is not a one way trip, that it might be possible to use a grav vehicle as a landing craft if you can slow down enough to let the grav unit handle the 200-300 kph limit on its speed?

I was trying to figure out what of the grav vehicles could be used as a landing craft. Can a grav based APC ferry troops to the surface or do you need a ship with an M-Drive and not a grav unit?
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Re: Orbit to Surface with grav equipment

Postby Condottiere » Sat Jul 17, 2021 10:13 am

Q: Is it possible to parachute to Earth from orbit?
Posted on January 30, 2016 by The Physicist
Physicist: Yes and no, but mostly no.

It’s certainly possible to parachute safely to Earth from the top (or nearly the top) of the atmosphere, but this question isn’t about parachuting from space it’s about parachuting from orbit. An orbit isn’t just a matter of being very high, it’s mostly a matter of being very, very fast.

Newton tried to explain orbits in terms of a progressively more and more powerful cannon.
Newton tried to explain orbits in terms of a progressively more and more powerful cannon.

When you throw something it follows a curved path that eventually intersects the surface of the Earth (technically this is already an orbit, it just gets interrupted by stuff in the way). If you use a cannon, then the curve straightens out a bit but it still intersects the surface of the Earth, just farther away. With a really, really powerful cannon (or more likely: a rocket) you can get something moving so fast that the curve of its fall matches the curve of the Earth. When this happens the object is in orbit; a closed loop around the Earth that repeats forever.

You may have noticed that the Earth isn’t terribly curved, so it may seem that you’d need to be moving impossibly fast to follow it. That’s exactly the case: above the air but near the surface of the Earth you’d need to be moving sideways at about 8km/s. This is more than 23 times faster than the speed of sound. Not slow.


A) An astronaut in low Earth orbit, who will stay there.
B) A stationary astronaut at the same height, who will be on the ground (impact on the ground) in half an hour or so.

This 8 km/s speed corresponds to the lowest, slowest (when you hit the atmosphere) orbit. Any other orbit either won’t bring you close to the atmosphere or will do so faster (at up to about 11 km/s). Being the slowest and lowest, these roughly circular “near Earth orbits” are very popular (that is to say: cheap). Near Earth orbit is probably what you’re imagining when you think of parachuting to the Earth.

Orbits at different heights. In low Earth orbit are the International Space Station, the Hubble space telescope, and most communication satellites.
Orbits at different heights. In low Earth orbit are the International Space Station, the Hubble space telescope, and most communication satellites.

So here comes the point. You can go as fast as you want if you’re doing it in space, but when you’re measuring your speed in km per second, air starts to feel like concrete (hot concrete).

The effects of air on something designed to handle it. A bag of meat (a person) would fare worse.
The effect of air on a “heat shield” designed to handle it (the bottom of the Apollo 11 crew capsule). A bag of meat (like a person in a spacesuit) would fare worse.

When an object plows through air at very high speeds it tends to burn, shatter, and shred. Parachutes are used for most entries and reentries, but not initially; most of the deceleration from orbit is handled by heat shields, which are a cross between parachutes and bricks (or a brick and another kind of brick). Once enough of a falling object’s speed has been shed by a heat shield (typically slower than sound, but up to a few times faster), it is then safe to deploy an actual parachute.

If you were to jump (fast) out of the International Space Station with the aim of entering the atmosphere and deploying your chute, you’d find it filled in short order then torn to ribbons shortly after. Like any falling star, you’d find yourself hot, dead, and profoundly luminous. Like icy meteors, you’d probably flash into steam and air burst before reaching the ground.

The reason you can’t parachute from orbit is simply a matter of engineering. We haven’t yet created parachutes that can survive being deployed, and then work properly, at speeds above around mach 2. At reentry speeds, which are in excess of mach 23, parachutes just can’t hold up. However, someday it may be possible. We know that the accelerations involved are survivable, and there don’t seem to be any fundamental limitations, we just need better materials and techniques. Also, for at least a little while, a spacesuit capable of reentry on its own (before the parachute has had a change to slow it) would be nice.

Merely falling from space is probably pretty easy. The highest jump so far was from 24 miles up. A jump from space is a mere four times higher. You’d need a rocket instead of a balloon, but aside from being a silly thing to do, there’s nothing stopping someone from doing it.

https://www.askamathematician.com/2016/ ... rom-orbit/



1. I did consider atmospheric conditions, since you wouldn't want to jump into a tornado.

2. My position has always been that lifters, and dirtside vehicle gravitational motors, need local gravity in order to gain traction.

3. Orbital disadvantage is capped at twelve hundred fifty klicks, without mentioning if this is based on a specific local gravitational field, say Earth standard, or it's net.

4. Interestingly enough, twelve hundred fifty klicks grazes Low Earth Orbit, where presumably you'd park most space stations, and the starport.

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