Question about Streamlined warships
- Thread starter Badenov
- Start date
Can't speak for Mongoose. "Grounding" was what they used in CT Adventure 7 when they wanted to land a perfectly lovely sphere with four obvious landing legs on a terrestrial world despite rules saying a sphere was only partially streamlined and therefore unable to land. It was undefined and has been the source of much speculation and debate ever since.
Condottiere
SOC-14 5K
For Mongoose, as long as you have a gravitational based manoeuvre drive, you can do atmospheric reentry without heat shields.
Dead slow, supposedly, with a dispersed structure.
Dead slow, supposedly, with a dispersed structure.
casquilho
SOC-13
For some reason the way you said this reminded me of the moment in the original Stargate Movie when Ra's ship lands. Slow and steady, not fast at all.
Condottiere
SOC-14 5K
You can include planetoids.
In theory, a pyramid is made of stone.
In theory, a pyramid is made of stone.
In the MgT2e 2022 Core Rulebook, the wording for atmospheric operations doesn't mention type of manoeuvre drive is needed.
Partially streamlined ships entering Atmos 4+ get a -2 DM on all pilot checks.
Unstreamlined ships get a -4 DM on all pilot checks, have to make a check to enter any atmosphere and then for every minute until landing - you could take your time for the atmospheric entry to negate the -4 DM, but you'd still suffer it for the every-minute check (you can't take your time for those); depending on the size of the planet you'd be looking at at least 3 checks (entry, 1 minute of flight, landing) and the same in reverse when attempting to leave. That would need a very good pilot to avoid the ship breaking up with all those chances of failing a roll.
AnotherDilbert
SOC-14 1K
CT A7:
So essentially partially streamlined, as in LBB5.
Of course you can put an unstreamlined ship on the ground, landing inside a streamlined ship. It is not explicitly stated it landed itself, in contravention of the rules.
The problem is that in A07, the Broadsword has grounded on Garda-Vilis which has Atmos 7, which it shouldn't be able to do.
mike wightman
SOC-14 10K
Traveller authors ignoring the rules as written, whoever would have thought 
And then you get me, using minimal drop tanks to meet jump fuel requirements for a legal LBB2-drives ship build, then ditching the tanks and borrowing fuel from the power plant allocation to make up the difference. See here for the design, and see here for the drop tank design exploit.
(Don't worry about the spoilers there.)
As argued to death in that thread and elsewhere, it's not R.A.W. compliant, but it's fully functional according to the rules mechanics. Call it house rules if you need to.
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Condottiere
SOC-14 5K
1. A ship without a functioning gravitic drive that attempts re-entry without heat shielding will burn up.
2. Said gravitic drive would also allow hovering in place.
3. Hovering in place means you don't move.
4. If you don't move, or dead slowly, means that streamlining isn't really relevant in calm conditions.
2. Said gravitic drive would also allow hovering in place.
3. Hovering in place means you don't move.
4. If you don't move, or dead slowly, means that streamlining isn't really relevant in calm conditions.
AnotherDilbert
SOC-14 1K
Of course it can be on the ground, it just can't land itself. It can be transported by another ship.
To be picky, a dispersed structure may well be reinforced enough to tolerate hurricane winds (240+ kph), without having any real notion of "streamlining". Just don't want the radar dishes blown off. If a ship is strong enough to handle the G loads, it may well be able to handle the atmosphere.
Granted, that's "slow". It's a 1-2hr trip from orbit to landing. But it may be doable.
That makes it pretty untenable then. If its a roll every minute, and catastrophe if they fail the roll, there's a lot of rolls involved, and the bell curve will kill you.
Spinward Flow
SOC-14 1K
This is essentially what I'm doing with my SIE Clipper design using external load towing (homebrew) rules.
The starship IS streamlined (Configuration: 1, Needle/Wedge).
The 20 ton Box container modules it can be loaded up with are PARTIALLY streamlined (Configuration: 4, Close Structure).
Maneuvering around in vacuum, it doesn't matter if a hull is unstreamlined or not.
However, for transfers between orbit and world surface through atmosphere, streamlining is preferred.
So the starship has a hangar bay that can accommodate 8x 20 ton Boxes for atmospheric entry transfers to/from orbit to/from surface.
Any "extra" Boxes can be left in a parking orbit (guarded by the Escort Fighter) while the starship makes multiple orbit to surface to orbit relays to bring all the Boxes down from orbit to the surface (or the reverse when staging for departure).
By putting the partially streamlined Boxes INTO the fully streamlined starship, it's possible to offer surface/jump/surface transport services available ... even though the "containers" being transported are themselves only partially streamlined (being, basically, rectangular blocks, essentially).
I'm not clear on why a Rating 1 grav drive gives thrust differently than a rating 1 reaction drive?
Current spacecraft need heat shields, as I understand it, because they use air resistance to slow them down from orbital velocity rather than thrusters. They don't save half a tank of fuel for the return trip. If you had a M-Drive of whatever sort to kill that velocity, you wouldn't need the air resistance, would you? You might need to turn around backwards and burn your engine to decelerate, but that's different from gliding in like current spacecraft do.
Why would a reaction drive not give you the same performance as a grav drive?
The big difference in landing adriotly seems to me to be the drive rating. A Thrust 1 drive can only exactly counter gravity. Thrust greater than 1 can do fancy tricks. But on a rating 1 drive you can set it to nearly 100% and float down safely, I think. At least as long as you keep your thrust opposing gravity. If that slips, you'd have no way to kill any velocity you gained, you'd need 100% of your drive to prevent further acceleration.
Also, what consititues 'heat shielding'? Armor 1? Armor 4? I dug up a chart at https://space.stackexchange.com/que...mb-for-the-mass-of-thermal-protection-systems -> https://i.sstatic.net/w7OQ2.png and I don't pretend to grok it all, but it looks like heat shielding is about 10-15% of the mass of the entry vehicle. At TL7, in Mongoose, Armor 4 would be 10% of the mass of the ship. In CT at TL7, I think 10% of the hull mass would be like 1.5 points, as 1 point is 8% and 2 points is 12%. That said, Armor and heat shielding are not the same thing, and I don't know of any Traveller rules on heat shielding. On the other hand, Heat Shielding is for preventing damage to the ship, that sounds like exactly what armor's job is.
Yes
Sort of.
The trick is finding calm conditions. Surface winds are easy, calm happens all the time. At 10-30,000 ft, winds can vary wildly. 60-120 knots are both common values in my area. Below 60 kts is kind of rare in my experience. Aerodynamic would help a lot with this.
Condottiere
SOC-14 5K
I don't write the rules - I have the dubious pleasure of interpreting them.
Gravitic based drives are either field or thrust effects, possibly both, though that's never been established.
Current rules say spacecraft manoeuvre drives are vector thrust, with diminishing returns, so if the thrust method is being utilized, that means you're reentering atmosphere ass first at factor one.
Gravitic based drives are either field or thrust effects, possibly both, though that's never been established.
Current rules say spacecraft manoeuvre drives are vector thrust, with diminishing returns, so if the thrust method is being utilized, that means you're reentering atmosphere ass first at factor one.
AnotherDilbert
SOC-14 1K
Rule 0?Traveller authors ignoring the rules as written, whoever would have thought
Rule 00?
AnotherDilbert
SOC-14 1K
Agreed, of course it is.
Spinward Flow
SOC-14 1K
It's a question of efficiency ... and "danger space" ...
- Gravitic thrust = fuel > fusion > electricity > gravitic thrust = high efficiency of fuel to amount of work needed
- Reaction thrust = fuel > plasma > dump overboard > reaction thrust = lower efficiency of fuel to amount of work needed
There's also the simplicity factor.
The amount of fuel consumed during a gravitic maneuver to enter atmosphere is so negligible as to be (functionally, for our purposes) "free" when it comes to accounting for fuel tankage before/after. However, this is NOT the case for reaction thrust, which consumes "relevant quantities" of fuel while in use. So as a "generic ruling" it's easier to say that gravitic drives can do this maneuver "at no cost" (effectively) but detailing what it will cost reaction drives (in fuel expended) is a non-trivial problem ... so it gets omitted (and with it, the reaction thrust option for the same maneuver).
CAN it be done with reaction thrust instead of gravitic thrust?
Yes it can ... however, there are ... side effects ... to consider when using that option.
This is basically a legacy of the fact that CT was written in the mid-late 70s, when the Space Shuttle program was the "new high tech shiny" thing for space vehicles.
The idea was that atmospheric entry would be done "shuttle style" using intertial aerobraking ... which requires a (more or less) streamlined shape to be able to withstand the plasma heating due to atmospheric compression forces. That's why the original CT rules require streamlining to enter atmospheres of 2+.
However, that notion is founded upon a specific fallacy ... that the craft in Traveller do not have what amounts to "nearly unlimited delta-v" maneuvering capability due to the efficiency of their fusion powered drives.
With sufficient thrust/acceleration, particularly when sustained ... a craft in space can effectively CHOOSE its geostationary orbit altitude.
If a craft is moving on inertia alone (zero delta-v) then geosynchronous orbit is going to be at a specific altitude over surface ... but with "nearly unlimited delta-v" (because fuel consumption is just that low relative to the thrust produced, because fusion power) geosynchronous orbits can be "any altitude you want" (including in contact with terrestrial surface, if you want).
It's the classic CTOL versus VTOL debate.
CTOL = land then stop
VTOL = stop then land
The energies involved in CTOL landings are tremendous (it's equivalent to defusing a BOMB) and those energies have to be dissipated AFTER touching down (by braking and thrust reversing, etc.).
The energies involved in VTOL landings are comparatively mild, because you "bleed off" all your excess energy (in the air) BEFORE touching down.
So the whole "streamlining to enter atmosphere" thing is predicated on the notion of inertial aerobraking with no maneuvering power thrust being used (ala the Space Shuttle) ... and for that, you need a streamlined hull shape.
However, as soon as you realize that you can use your maneuver drive to "geosync to anywhere" using thrust BEFORE descending into atmosphere, you're no longer entering atmosphere at a high (multi-mach hypersonic) velocity relative to the motion of the atmosphere and therefore do not run into atmospheric compression heating in any way akin to what you would have happening in an aerobraking context. However, doing this maneuver requires continuous thrust from the maneuver drive ... which with fusion power, most craft have. It's just the chemical and fissile "nuclear teakettle" reaction drives that may encounter difficulties pulling off the same stunt due to their lower efficiency in fuel consumption rates making "nearly unlimited delta-v" continuous maneuvering somewhat impractical from a rate of fuel consumption perspective.
Clipped. I had a big long technical reply written out and a power flicker rebooted my copmputer. Short version is grav drives are entirely space magic, so they can do space magic. But people have realistic expectations of reaction drives and I think the complication is arising from this.
I will note that the Mongoose time tables to a 10,000km orbit assume that a thrust 1 ship accelerates at 1G, ignoring planetary gravity, halfway to the listed distance, then reverse thrusts the rest of the way, thus arriving at 0 velocity, and presumably ready to dock or interact with a 0 velocity space station or whatever. I have recreated the Travel times table (apart from the typo where the travel times got copypasted into the wrong column and the adjacent column's values were pasted in to cover the gap) with the above math, except the table assumes 1G=10m/s^2 to get the numbers they got. Not sure if other versions use the same chart?
Thrusting straight up that entire time would get you to nearly 4 times that altitude, but with a velocity of 9.8 m/s^2*2000s or about 19,600m/s. Thrusting upward for half that 33 minute time, like a grav drive, would get you to 10,000km and at 9,800 m/s velocity, which is actually much faster than the velocity needed to maintain orbit at 10,000km, which is 6,317 m/s. The burn time to achieve a velocity of 6,317 m/s is about 645 seconds, or about 10 minutes 45 seconds, although that's not including the turn to change your upward thrust to horizontal thrust.
Short version is the table in Mongoose, at least, is specifically for grav drives that can then run them continuously for stationkeeping and the times to orbit are for geostationary orbits, and it's completely wrong for reaction engines (though Mongoose is way too generous with the capabilities of reaction engines anyhow, so it may cancel).
Short short version: Reaction engines (in Mongoose, at least) are space magic, too. Do no rocket science here.
