The Best Rocket For Landing Scifi Thrusters

[Spacescifi]

The rocket science is real for this scenario, the scifi angle is not.

 

The scenario: Due to scifi tech I won't bother explaining, a spaceship is able to jump teleport from space directly into the earth's atmosphere only a hundred feet from the ground.

 

To avoid falling and crashing quickly, the ship uses it's scifi works in space ONLY engines prior to jumping to match earth ground rotational speed and ascend. Thus upon jumping intto the air a hundred feet up from the ground,  the vessel continues ascending a bit before it starts to fall.

 

Rocket science in play: What is the optimum form of rocket and propellant to land in this scenario? Will chemical rocketry be good enough? Or do we have to do the dangerous Fluorine or nuclear rocket combo chem thing?

 

Assuming you wanted to ship max cargo payload?

 

Let's ball park figure this and assume spaceship mass is like this:

 

At 510 feet (160 m) long, a displacement of 9,200 tons, and with armament of more than 90 missiles, guided missile destroyers such as the Arleigh Burke-class are actually larger and more heavily armed than most previous ships classified as guided missile cruisers.

 

This is a cargo ship, not a warship, so it is mostly cargo and propellant.

Edited February 21, 2020 by Spacescifi

[Nightside]

Just use the rocket equation.

Assuming that you appear a 0 velocity, you won’t need to cancel too much velocity (~45 m/s) as gravity starts to accelerate the ship down.

To choose the best rocket for the task you will need to decide a couple of things about your vessel.

-What fraction of the total mass is payload
- Do you also need to lift off again (will similar payload) or can you hoverslam?

-Do you have one large thruster or many small one? - this will affect what kind of engines you can use and the ISP.

- Is your design mass limited

   or volume limited?

 

 

Edited February 21, 2020 by Nightside

[Spacescifi]

19 minutes ago, Nightside said:

Just use the rocket equation.

Assuming that you appear a 0 velocity, you won’t need to cancel too much velocity (~45 m/s) as gravity starts to accelerate the ship down.

To choose the best rocket for the task you will need to decide a couple of things about your vessel.

-What fraction of the total mass is payload
- Do you also need to lift off again (will similar payload) or can you hoverslam?

-Do you have one large thruster or many small one? - this will affect what kind of engines you can use and the ISP.

- Is your design mass limited

   or volume limited?

 

 

 

Use a reasonable payload figure I suppose.  Whatever maximizes payload while still alowing for a safe landing.

 

Liquid methalox propellant maybe? The only real concern is refueling, as I expect to burn most all of the propellant for landing once.

 

Fortunately this ship has special stuff that enables extracting moon or asteroid fuel easy. Even though alluminum oxygen is not very great propellant from the moon. It follows below:

 

Liftoff? Not required, this baby can jump teleport into space off a planet, from there it has a special constant acceleration drive that only works in space.

 

I also suppose they could use water to refuel by seperating LH and oxygen, but that would take days to extract and process It all.

So when they land, they could not refuel on earth quickly again if doing ISRU refueling.

 

I do not think moon or asteroud derived propellant is good enough for landing my hulk of a ship at 100 feet with1g gravity pull.

 

EDIT: Ship has 6 duaul axis thrusters for landing. Three for each end of underbelly.

Edited February 21, 2020 by Spacescifi

[kerbiloid]

As the ship size  is comparable to the altitude, it can just expand a plunger instead of engine and brake by the air compression.

Spoiler

Why not, Mercury had this.

[Superfluous J]

3 hours ago, Spacescifi said:

...

Welcome back

[Nightside]

I think you can get by with less than a 10% fuel/total mass ratio, with plenty of margin left over.

 

 

[Shpaget]

Pratt & Whitney T73 will beat any rocket.

[sevenperforce]

If you're that low to the ground then definitely go with an airbreathing engine every time. A turborocket with a reversible intake is ideal. 

[XLjedi]

If you have the sci-fi tech to jump into the atmosphere; I would think your spiffy anti-gravity drive would work wonderfully to gently set you down on the surface?

Seems like a pretty big technology disconnect between the two drive systems you are describing.

[Terwin]

If you are > 500 feet long and only ~ 100 feet from the ground, why not just extend some extra-long landing legs with good shock-absorbers to handle the descent?

I could see pneumatic feet telescoping out from the bottom of the vessel, then after they smack into the surface of the body(small jolt to craft), they collapse down to a 'landed' length, letting the craft gently come to rest on the (possibly uneven) surface.

100% reusable and with a small mass fraction.  Re-pressurize the extension tank and you are ready for your next landing.

[XLjedi]

8 minutes ago, Terwin said:

If you are > 500 feet long and only ~ 100 feet from the ground, why not just extend some extra-long landing legs with good shock-absorbers to handle the descent?

I could see pneumatic feet telescoping out from the bottom of the vessel, then after they smack into the surface of the body(small jolt to craft), they collapse down to a 'landed' length, letting the craft gently come to rest on the (possibly uneven) surface.

100% reusable and with a small mass fraction.  Re-pressurize the extension tank and you are ready for your next landing.

Or just beam in at 10-20ft maybe?

[Terwin]

7 minutes ago, XLjedi said:

Or just beam in at 10-20ft maybe?

I think the 100' target is a safety-measure due to accuracy issues with the teleportation technology, so less than that and you are playing Russian roulette.

That is also why the legs would need to extend after the jump, as you will 'usually' be at about 100', but may occasionally be higher or lower.

[XLjedi]

4 minutes ago, Terwin said:

I think the 100' target is a safety-measure due to accuracy issues with the teleportation technology, so less than that and you are playing Russian roulette.

That is also why the legs would need to extend after the jump, as you will 'usually' be at about 100', but may occasionally be higher or lower.

Ah...  naturally...

And the 100ft long landing gear is a backup in case the anti-gravity drive fails.   All makes sense now.

[StrandedonEarth]

Just jump in, eject your cargo, and jump out again....

 

[XLjedi]

@StrandedonEarth  That reminds me; I have to go back and finish watching that series!

[StrandedonEarth]

2 minutes ago, XLjedi said:

@StrandedonEarth  That reminds me; I have to go back and finish watching that series!

Hope that wasn't a spoiler for you then. But you had ten years to catch up...

[XLjedi]

34 minutes ago, StrandedonEarth said:

Hope that wasn't a spoiler for you then. But you had ten years to catch up...

Dang... has it been that long?   Of course I'd be watching it on my DVD set; so I guess it has been.

[Spacescifi]

4 hours ago, XLjedi said:

If you have the sci-fi tech to jump into the atmosphere; I would think your spiffy anti-gravity drive would work wonderfully to gently set you down on the surface?

Seems like a pretty big technology disconnect between the two drive systems you are describing.

Ummm... there is no antigravity tech. It is for simple explanation's sake... a jump drive in appearance to the naked eye.

 

I got rid of antigravity drives when I realized I no longer needed them. And I like the way rocket plumes look in air.

 

 

3 hours ago, Terwin said:

I think the 100' target is a safety-measure due to accuracy issues with the teleportation technology, so less than that and you are playing Russian roulette.

That is also why the legs would need to extend after the jump, as you will 'usually' be at about 100', but may occasionally be higher or lower.

 

A safety measure indeed. The teleportation invoves displacement assuming you jump into mass (air for example).

 

So jumping in 100 ft above the ground will teleport the volume of your vessel's shape into space where you originally jumped from. While your vessel trades places.

 

This can turn out badly if you teleport into the ground. Yes your vessel will displace the ground and be literally stuck in the mud.

The bad news is that the volume of your vessel stuck in the mud will have it's volume's worth falling down from space toward it, assuming wind won't blow it off course before impact.

Edited February 21, 2020 by Spacescifi

[Wjolcz]

What's with the "the ship can blink BUT needs realistic engines"?

If you're writing a sci-fi book with these kind of rules you might as well go all Harry Potter magic rules which is just... no rules.

[Nuke]

brushless motors cram a lot of power into a little motor. so provided you have a lot of power to work with, say a fusion reactor, then an array of small ducted fans would work on planets with suitable atmosphere. any other planet, probably some kind of nerva or fusion rocket, any life forms are likely protected by domes anyway.

me personally i think i would differentiate my atmospheric shuttles from non-atmo shuttles. former would likely be shuttle-like belly landers with air breathing engines. maybe some kind of multi-propellant thermal engines, which can run off the local atmosphere, or internal tankage. the latter would be much more simple craft likely with a small number of main engines in a nozzle down config. mothership would be equipped with whatever shuttles it would need for its mission. exploration type ships (sort of like the enterprise) would likely carry both and maybe other more specialized craft (like inter-vessel shuttles, gas giant fuel skimmers or sun divers that can operate close to a star or on hot planets like venus).