Reentry and landing.

[Blue Ghost]

Given that gas giant atmospheric refueling is a controlled re-entry, I'm curious about how starships enter ordinary rocky world atmospheres. I'm thinking it's ordinary powered flight without all the reentry theatrics and special effects, but I've never seen it addressed in the rules.

 

[JimMarn]

Space-X has been doing it recently with an engine exhaust first landing.

A Free Trader would likely glide in to the runway and do a skids down landing.

Is here some sort of heat shield on a free trader ? Otherwise how does it handle the heat buildup ?

Spiraling in, multiple times circling a planet to slow down, wouldn't be stealthy and some scenarios wouldn't work.

So I am also somewhat confused as to how a ship coming in could land in a short space, like on one continent, without flying over the rest of the globe.

 

[nobby-w]

Today's spacecraft use an unpowered re-entry (i.e. one that uses atmospheric braking to slow down) because they simply don't have enough delta-V available to burn off a significant fraction of their orbital velocity. Atmospheric braking is hard on spacecraft.

If you have more delta-V available, you could slow down to 1000-2000 m/sec before you re-enter the atmosphere (a powered re-entry), which would be much easier on your spacecraft. This is the basic assumption I make about re-entering in a spacecraft in a sci-fi game.

 

[Blue Ghost]

Er, I mean for all the gaming sessions I was ever in or ran it was never an issue. We just assumed it was "Star Wars" like, where the ship probably rides some grav cushion, doesn't need to go through reentry as such, and just sets down.

But I've never seen anything in the rules to address it, so I'm wondering what people's thoughts are on it.

 

[kilemall]

Er, I mean for all the gaming sessions I was ever in or ran it was never an issue. We just assumed it was "Star Wars" like, where the ship probably rides some grav cushion, doesn't need to go through reentry as such, and just sets down.

But I've never seen anything in the rules to address it, so I'm wondering what people's thoughts are on it.

I think it's left open so you the ref can decide.


With a grav landing you hardly scorch the paint. Could be you literally can make ship hulls out of steel, long as the grav field never fails....


I happen to do both. The hard hot landing does cause me to envision an approach that is very long- Phoenix Down for instance might start somewhere over the Pacific Ocean. Not optimal for use of airspace and limits number of craft landing, but allows for rougher ships that operate beyond 1000D.


I also have tailsitters, because I have limited artificial gravity tech and leveraging the acceleration for 'normal' Gs is desirable. They would land SpaceX style.




The grav landing ships I call Whisperliners and are a sales pitch to attract high end customers to a smooth landing, where their drinks never spill. I'm thinking maybe I need to increase their M-drive price too given the flexibility and High Passage DMs.

 

[Xerxeskingofking]

pretty much what you just said, that the ability to make weeks long burns means it isn't necessary to aerobrake.

A Free Trader would likely glide in to the runway and do a skids down landing.

Is here some sort of heat shield on a free trader ? Otherwise how does it handle the heat buildup ?

Spiraling in, multiple times circling a planet to slow down, wouldn't be stealthy and some scenarios wouldn't work.

So I am also somewhat confused as to how a ship coming in could land in a short space, like on one continent, without flying over the rest of the globe.

well, it would work very much like a airplane coming into land, with a controlled decent that started quite some distance form the landing point (like hundreds of miles in the case of a ship form orbit). as its under power the whole way, If needed it could make a very "steep" decent while relying on its grav drive to keep the gained speed down to a acceptable level. Hell, it could come in almost vertically on most worlds, especially with 2G+ drives.

The nature of orbital mechanics mean that it would need to break to a "halt" first, which requires a delta-V of around 10Km/s. I'm not a whiz at math, but you can do the sums and work out how far form the starport a 1G would need to start "Braking" in order to reach it. at a guess, it would be a case of starting your decent for New York somewhere near London.


that said, even "unarmoured" ships have sturdy hulls and rad shielding, so a element of aerobraking is not impossible. Heat shielding is a design option for ships in MgT2e, which allows for full speed unpowered decents like modern spacecraft (its clearly intended for use by lower tech planets that don't have grav drives).


as for landing, it wouldn't need to glide for a skids landing in many cases, as it has enough drive power to just plain hover. it could operate in a VTOL manner, like the ships of star wars.

 

[aramis]

Space-X has been doing it recently with an engine exhaust first landing.

A Free Trader would likely glide in to the runway and do a skids down landing.
.

Probably not, actually. As drawn in all editions, the standard Class A is not an aerodynamic lift shape. Further, skids-down at speeds for a lifting body is not healthy for the ship; it would need pretty large wheels on at least 3 "bogies" to survive the high-subsonic stall speed. (Landing an aircraft is essentially slowing down to stall speed while low enough that the loss of lift doesn't break the plane, crew, nor cargo.)

The Type R is a winged ship; it should have wheels. Unfortunately, the design sequences don't cover landing gear at all, and only TNE, T4, and T20 give a consistent method for airframe designs; T20's is my addition, which Hunter accepted and incorporated, and I didn't argue successfully for adding landing gear (and I didn't push that hard on landing gear, anyway). In at least one illo, we see it has four bogies of 4. We can estimate the stall speed from the proportions — which are close to those of the NASA STS Shuttle — about 300-350 km/h.

 

[Timerover51]

I assume reducing the ship speed to slightly more than the planet's rotational velocity at the latitude I am landing, and then descend at about a mile a minute with a bit of forward speed. Once I am where I am supposed to land, I kill all forward speed, and set down on the ship's bottom, just like a nautical ship in dry dock. As long as I do not exceed about 6 tons mass per square meter of ship bottom, there should not be too much sinkage at all, unless the soil is quite soft.

I do assume streamlining for all of my ships, unless clearly stated otherwise. If a ship is built on a planet's surface where there is a planetary atmosphere, I assume streamlining is standard with no additional charge for the hull. If built in space or on a planet with essentially no atmosphere, then a streamlining charge would be added. Building in space does increase ship cost by 25% and building time doubles.

 

[infojunky]

The nature of orbital mechanics mean that it would need to break to a "halt" first, which requires a delta-V of around 10Km/s. I'm not a whiz at math, but you can do the sums and work out how far form the starport a 1G would need to start "Braking" in order to reach it. at a guess, it would be a case of starting your decent for New York somewhere near London.

Note this assumes a ship needed to be in orbit in the 1st place. Which isn't necessarily so... Especially if some sort of contragravity is being used...

 

[Xerxeskingofking]

true, but I would not want to be the space traffic controller trying to juggle a orbital zone that has stations and ships orbiting at 10Km/s and other ships sat at 0Km/s, or at whatever "ground" speed is for the spaceport.

while it is perfectly possible for a ship under constant thrust to just make a direct landing straight in form the 100D line, that requires a fairly narrow set of parameters in terms of relative positions at jump exit (to give an example off the top of my head, a direct shot to the moon from a point on the ground has a launch window of only a minute or two a day). It is very likely that a ship would need to use some sort of parking orbit in order to actually reach the starport, which might be on the other side of the planet form the incoming ship. however, the ship would not need to be a full orbital speed, as it doesn't need to complete a full orbit. also, it could drop to a altitude below the karman line
, as it doesn't need to orbit, so it could de-conflict with orbital traffic that way as well, as well as atmospheric traffic below it.


taking off is easier for a trip to the jump limit, as you only need to get to a point outside the 100D line that has line of sight to the target system, but it still might influence the ships preferred take off time, and a route though orbital space would need to be de-conflicted with any other ships in orbit or transiting orbital space.



now the fact that a traveller ship has, effectively, unlimited delta V means it doesn't care as much as a present day spaceship about such things, but its still a factor.

 

[GypsyComet]

Note this assumes a ship needed to be in orbit in the 1st place. Which isn't necessarily so... Especially if some sort of contragravity is being used...

The only ships that need to be in proper orbits are those either parked mid- to long-term over a world with no High Port facilities, or which are on a rendezvous track with a station in stable orbit. Stations would be really expensive to keep in powered non-stable orbits, so they are most likely to be in stable orbits.

The only ships for which orbit and de-orbit operations are going to be a challenge are TNE's HEPlaR ships that frequently have *very* little extra fuel for messing around. All Traveller ships have, or are implied to have, the technology to make orbit/de-orbit , landing and take-off a routine operation set. Even 1G is a lot of thrust.

 

[Xerxeskingofking]

its less that 1g is a lot of thrust (after all, any rocket is able to go this, just to get off the ground), but that a traveller M-drive can keep up that acceleration for weeks if it wants to, whereas modern rockets have burn times measured in minutes.

Thus, a traveller ship can be "lazy" and take direct, thrust-inefficient routes that a chemical rocket ship cant due to the sheer amount of fuel it would need to attempt it.

 

[wellis]

Would most orbital transfers, done for a setting where gravitic thrust is either difficult or non-existent, instead use spaceplanes to transfer stuff?

 

[Brandon C]

Would most orbital transfers, done for a setting where gravitic thrust is either difficult or non-existent, instead use spaceplanes to transfer stuff?

2300AD uses several methods, from catapults to rockets to beanstalks. And yes, spaceplanes are in there

 

[Blue Ghost]

its less that 1g is a lot of thrust (after all, any rocket is able to go this, just to get off the ground), but that a traveller M-drive can keep up that acceleration for weeks if it wants to, whereas modern rockets have burn times measured in minutes.

Thus, a traveller ship can be "lazy" and take direct, thrust-inefficient routes that a chemical rocket ship cant due to the sheer amount of fuel it would need to attempt it.

Yeah, which is sort of why I brought up the thread. I mean YTU and YMMV and all, and like I say, I think it's implicit that Traveller uses standard space opera "the ship flies into the atmosphere and lands gently" kind of stuff. But since gas giant refueling requires that parabolic beyond hypersonic thing, it just got me to wondering what the justification, if any, there was for whatever landing mechanics might be defined in some version.

In short, I was just curious.

 

[starship_captain62]

Getting to orbit

On a related note, I came up against a similar problem yesterday with grav vehicles. It seems that they can reach orbit after several hours ascent, adding delta-V the whole time. Descent is similar in reverse. I was looking at this specifically in Cepheus Engine, bit I seem to recall something similar in Classic Traveller. I was able to explain this, then it was pointed out that the grav car could only do a couple of hundred Km/h planet side, yet could still have enough delta V to get to orbit - 8hrs as per CE rules at about 3.4m/s squared gets about 11.2Km/s to escape Earth.

Hmm I said.. Clearly your universe might vary, but there seems to be something a bit inconstant with the rules here.

 

[infojunky]

On a related note, I came up against a similar problem yesterday with grav vehicles. It seems that they can reach orbit after several hours ascent, adding delta-V the whole time. Descent is similar in reverse. I was looking at this specifically in Cepheus Engine, bit I seem to recall something similar in Classic Traveller. I was able to explain this, then it was pointed out that the grav car could only do a couple of hundred Km/h planet side, yet could still have enough delta V to get to orbit - 8hrs as per CE rules at about 3.4m/s squared gets about 11.2Km/s to escape Earth.

Note you might want to reread the AirRaft & Speeder descriptions in Book 3 again. The 1 hour per Planet Size class to orbit is for a 100 kph AirRaft, while the 1000 kph Speeder gets to orbit in under a hour...

 

[mike wightman]

On a related note, I came up against a similar problem yesterday with grav vehicles. It seems that they can reach orbit after several hours ascent, adding delta-V the whole time. Descent is similar in reverse. I was looking at this specifically in Cepheus Engine, bit I seem to recall something similar in Classic Traveller. I was able to explain this, then it was pointed out that the grav car could only do a couple of hundred Km/h planet side, yet could still have enough delta V to get to orbit - 8hrs as per CE rules at about 3.4m/s squared gets about 11.2Km/s to escape Earth.

Hmm I said.. Clearly your universe might vary, but there seems to be something a bit inconstant with the rules here.

There is a big difference between going up and reaching an orbital altitude and actually being in orbit.
A rocket achieves orbit and stays there, a grav vehicle reaches an orbital altitude and switches off its drive and falls back to the planet.

There is a but of course - an air/raft relies on its grav modules for lift and thrust, as it rises the atmosphere gets thinner and so it can go faster. Once in a vacuum there is no resistance to forward motion so it can just keep accelerating until it achieves an orbital velocity.

Grav vehicles and maneuver drive equipped ships do not need to worry about delta V since they have enough power to accelerate for days.

 

[JimMarn]

Probably not, actually. As drawn in all editions, the standard Class A is not an aerodynamic lift shape. Further, skids-down at speeds for a lifting body is not healthy for the ship; it would need pretty large wheels on at least 3 "bogies" to survive the high-subsonic stall speed. (Landing an aircraft is essentially slowing down to stall speed while low enough that the loss of lift doesn't break the plane, crew, nor cargo.)

The Type R is a winged ship; it should have wheels. Unfortunately, the design sequences don't cover landing gear at all, and only TNE, T4, and T20 give a consistent method for airframe designs; T20's is my addition, which Hunter accepted and incorporated, and I didn't argue successfully for adding landing gear (and I didn't push that hard on landing gear, anyway). In at least one illo, we see it has four bogies of 4. We can estimate the stall speed from the proportions — which are close to those of the NASA STS Shuttle — about 300-350 km/h.

The one I was thinking of is a Type A Beowulf class free trader.

The drawing shows a somewhat delta shape with fuel being in the wings. Doesn't look like it would be able to land. It does carry a small landing craft in the stern on Deck A.

 

[kilemall]

The one I was thinking of is a Type A Beowulf class free trader.

The drawing shows a somewhat delta shape with fuel being in the wings. Doesn't look like it would be able to land. It does carry a small landing craft in the stern on Deck A.

Type A doesn't have wings or a craft, sounds very much like an R.


Just another idea I've tossed out before, the conformal lift heat shield.


To wit, if you have the technology to operate a fusion bottle, you can extend that to shielding a ship on reentry, since it is very much the same sort of thing, managing hot plasma.


At higher TLs more powerful shields can be formed, which allow for virtual lift bodies formed out of energy and the associated plasma, alternately allowing for gliding, fast transit or slowing down, and for the semi-streamlined hull designs to 'land hot'.