Are ships heat shielded?
- Thread starter whartung
- Start date
My take here is that at least those that are streamlined, and so able to enter atmospheres, are so shielded somewhat, as are those able to skim for fuel.
That is (as many things) versión dependent. Armor 1 in MT means not only unarmored, but quite fragile, while armor 1 in CT:HG means quite armored...
Again, my take is that the mínimum armor to allow a ship to keep in space (and so to keep its internal temperatura more or less constant regardless its distance to a star, up to a limit, off course) includes this shielding, at least if it ca nenter any atmosphere ,as said above.
After all, it can keep radiation off the ship too, so this mínimum armor (be 0 as in CT:HG, 40 as in MT or anything rom other versions) is quite strong a hull,
GypsyComet
SOC-14 1K
These two examples are also different scales. HG (and most editions for that matter) calibrate armor for the scale of the vehicle. Ships with "no" armor are still reasonably well protected because that zero is solely in the context of anti-ship weaponry.
MT used one armor scale for everything, growing as it did from Striker's attempt to approximate ships in an armor and infantry game. That approximation ended up doing horrible things (TM) to Traveller's technological continuity, but the immediate result is that ships start at armor 40 because they are being considered in the scale of hand weapons and armored cars.
esampson
SOC-13
For the most part ships should be able to slow down enough that atmospheric heating is not a serious problem.
Atmospheric heating tends to be caused by a ship travelling at a velocity necessary to maintain orbit entering the atmosphere (at 200 km the orbital velocity is around 24 times the speed of sound). In order to land the orbital energy of a ship has to be reduced.
Craft in real life do this through converting the immense orbital energy into heat energy because they have very limited energy supplies (craft in real life are only capable of producing a few G/hours of thrust at absolute best).
In Traveller ships have massive energy supplies (they can accelerate at 1+ G for weeks on end). As a result they can use that huge amount of energy to counter the orbital energy instead of converting it into heat.
Well that's really the crux of the question. Not so much are they shielded, but is it necessary in the first place.
Is "blazing re-entry" the norm, or do the ships slow down to where it's not necessary.
Supplement Four
SOC-14 5K
I would say, "Absolutely!" Not just heat shielded but insulated against extreme cold as well. I don't think any armor is needed. The superdense hull is enough. There are vast extremes in temperature in space, and just about any hull is rated to dive down into a Gas Giant to skip fuel, where pressure is also a consideration.
Plenty of worlds in Traveller have extreme temperatures, too, from deeply frozen rock to boiling seas. Any starship hull could handle that.
It's worth noting that, if the drag is managed correctly, and entry speed is relatively slow, one does NOT need heat shielding other than the (minimal) needed to reduce blackbody losses.
See also Space Ship 1's flights, and SpaceX and ULA reusable booster programs...all of which cross the space barrier, and return without a reentry heat shield. (SS1 on a high drag configuration, SpaceX and ULA both using thrust to prevent excessive friction heating.)
I'd imagine slow entry is most common...but slow can mean supersonic with basic streamlining.
you dont get frictional heating beyond what most alloys can take until you get in the high supersonic, hypersonic velocities. ( mach 3-7)
I know the SR-71 and other Mach-3 aircraft have issues with frictional heating ..the SR-71 was engineered in such away that some portions can expand under heating.
so realistically a streamlined hull could hit the atmosphere at mach 1 and not suffer...although unless designed for supersonic ravel the ride would be very rough do to turbulence, and shock waves piling up up on the surface, and just ahead of the ship.
those shock waves are what caused most transonic accidents.The air become so compressed the aircraft either broke up, or could not effectively control it's flight..and crashed.A starship has the raw power to defeat that problem..but there would be side effect.
A ship of 100 tons or more would generate a huge sonic boom due to the amount of air compressed in it's bow wake...Meaning if it flew to low, it could shatter windows,and scare locals/livestock, over a wide area. which would be a serous issue with the local authorities.
https://www.youtube.com/watch?v=FP-pQb3OSvw
you can see that some of the low flying aircraft int he video are actually leaving wakes as they fly low over water....
watch the new star-wars trailer in one scene a group of x-wings in formation are pulling up a wall of spray and mist as they come in low at supersonic speeds
what they didn't add in was the fact that big of a sonic boom would have knocked people off heir feet
CliffBates
SOC-12
But with anti-grav lift of M-drives or Repulser pads they could also go slow or fast... IN fact on most re-entry or take offs would be controlled, esp on TL 12+ worlds.
I'm sure there's maths to support this, but if you slow an aerodynamic object enough whilst still in exo-atmospheric flight, could it be possible to then descend under thruster control until intra-atmospheric flight is possible (enough atmosphere to support the generation of lift from aerofoil-configured wings), and pilot it in at less than mach 2, thus avoiding the superheating effects? (apologies if I haven't been too clear in what I'm trying to say!)
esampson
SOC-13
Correct. What a lot of people do not realize is that the heat is not truly caused by 're-entry'. It is actually caused by aerobraking.
As I said earlier, an object at an altitude of 200km in a circular orbit travels at around 24 times the speed of sounds. This is because at 200km the force of gravity is still something like 98% of the surface of the planet. As a result in order to stay in orbit an object has to move so fast that if it traveled in a perfectly straight line (and if the surface of the Earth was perfectly smooth) the surface of the Earth would drop away by nearly 5 meters just because of its curvature.
On the other hand an object dropped from 200km above the surface of Earth would only reach a maximum speed of a bit over 6 times the speed of sound, discounting the fact that its drag would slow it down. When you add in the effect of drag the top speed is unlikely to be much more than 2-3 times the speed of sound (Felix Baumgartner approached Mach 1, I believe, during his jump, but the human body is hardly that aerodynamic a shape).
The basic formula for atmospheric heating involves v2 x d where v is the velocity of the object and d is the density of the atmosphere. This means that an object travelling at 24 times the speed of sound will generate 16 times as much heat as an object traveling at 6 times the speed of sound, assuming the same atmospheric density.
All of which is a really long way of saying that deorbiting objects generate way more heat than objects simply entering from space. But things like meteorites hit our atmosphere and burn up and they aren't deorbiting, so how does that work? That occurs because the meteorite is zipping through space at even higher velocities than orbiting objects.
I would imagine that for approaching an Earth-like planet the physics would run something like this:
The approaching ship would begin braking well outside the atmosphere. How far out would be a factor of how fast the ship was approaching before braking and how strong the maneuver drives are. The target is to be travelling at about 4.5 times the speed of sound when you reach 200 km above the surface.
At that speed a ship would only generate about 3.5% of the energy of a deorbiting ship. 4.5 times the speed of sound would still generate a lot of heat at normal atmospheric pressure but at 200 km the density of the atmosphere is so low that the ship probably would have no issues.
The ship would continue to decelerate at about 1/2 a G. It will take a ship around 5 minutes to decelerate from 4.5 times the speed of sound to 0 at 1/2 G and that will coincidentally cover around 200 km.
I chose 1/2 G because that gives ships a good safety margin. If they find they are coming in a little bit 'hot' they can just increase thrust briefly to adjust. Additionally if they use a greater thrust then they will hit the atmosphere at higher speeds.
My guess is that decelerating from 4.5 times the speed of sound there won't be any issue with the ship travelling too fast when it reaches the richer atmosphere at around 50 km (at which point its speed is a little over 2 x the speed of sound). In the case of a ship that is too fragile to handle these forces the rate of deceleration could be reduced even more, although this would require an even lower speed at 200 km and would extend the time necessary to cover the 200 km and land. However, since the original figure was 5 minutes you are still looking at relatively short amounts of time in order to land. Ships would be spending far more time just maneuvering so that they are above the landing site and moving into the landing pattern.
esampson
SOC-13
Short answer; yes.
You can slow down a ship so that its speed relative to the planet is 0 when you are 200 km above the surface. Feather the engine just enough that you begin descending at 1 cm/s and then bring the engines back up just enough to counter gravity. The ship will continue to descend at 1 cm/s all the way to the ground (far slower than the speed you would need to generate lift). To reach the higher speeds you need for aerodynamic lift you just allow the ship to descend faster.
The SR-71 had to get to mach 0.7 or so to stop leaking fuel... its titanium hull expanded enough with frictional heating in the transsonic range to be a problem. This is also why they required in-flight refueling - full on ground wasn't safe for operation.
Even high subsonic has significant heating... just not heating to material failure. The question set includes:
(1) is the drag sufficient to prevent impact
(2) how much friction heating?
(3) how much drag stress?
(4) how much thermal radiation?
(5) how much conductive transfer cooling?
The SR-71 had poor conductive cooling and (intentionally) low thermal radiation for the size and shape. By the end of a mach 3 mission, it was positively glowing in the IR ranges... but the shockwaves even at Mach 0.7 exceed mach 1 on that beast. And everything says that the major heating happens with the pressure flows exceed Mach 1, rather than the aircraft itself.
For that matter, Space Ship 1 was pretty bright on the return entry... but fairly evenly so, and well below hazard levels, and as it transitioned from shuttlecock mode to flight mode, it rapidly dissapated much of that... as it became conductively cooled due to more air mass over the surfaces.
The Shuttle and the Apollo projects are a brute force approach to drag-based reentry. SS1 is a finesse approach - manage the drag to be enough to slow and low enough to radiate and conduct the heat away fast enough that it never hits failure temps.
A balut is a hybrid approach...
I would imagine several hours at least, from start of orbital braking to rolling to a halt on the runway, or touching down vertically in a silo.
MT had much shorter times.
Canonical times from 10 diameters to Low Orbit and Low Orbit to ground are in MT's Imperial Encyclopedia.
[tc=7]Travel Times from Orbit[/tc]
[tc=6]Acceleration [/tc]
For comparison, earth is size 8, and apollo 8 timeline from CM/SM separation (146:28:48.0 MET) to splashdown (147:00:42.0 MET) is about 32 minutes unpowered.
http://history.nasa.gov/SP-4029/Apollo_08i_Timeline.htm
| world | ||||||
| Size | 1G | 2G | 3G | 4G | 5G | 6G |
| 0 | 6m | 5m | 4m | 3m | 2m | 1m |
| 1 | 13m | 9m | 8m | 7m | 6m | 5m |
| 2 | 19m | 13m | 11m | 9m | 8m | 8m |
| 3 | 23m | 16m | 13m | 12m | 10m | 9m |
| 4 | 27m | 19m | 15m | 13m | 12m | 11m |
| 5 | 30m | 21m | 17m | 15m | 13m | 12m |
| 6 | 33m | 23m | 19m | 16m | 15m | 13m |
| 7 | 35m | 25m | 20m | 18m | 16m | 14m |
| 8 | 38m | 27m | 22m | 19m | 17m | 15m |
| 9 | 40m | 28m | 23m | 20m | 18m | 16m |
| A | 42m | 30m | 24m | 21m | 19m | 17m |
For comparison, earth is size 8, and apollo 8 timeline from CM/SM separation (146:28:48.0 MET) to splashdown (147:00:42.0 MET) is about 32 minutes unpowered.
http://history.nasa.gov/SP-4029/Apollo_08i_Timeline.htm
esampson
SOC-13
Those times are based on 10 times the diameter of the planet. That far, far exceeds the distance of the atmosphere. For reference the Earth has a diameter of about 12,700 km. By the time you reach 200 km (.015D) above the surface atmospheric density is 4.9721301537547236x10-11 that of the surface.
Just doing some back of the envelope calculations tell me that you reach atmospheric density of 1% at around 38.8 km. If I calculate a steadily decreasing velocity and assume a speed of mach 1 at 38.8 km the craft needs to be decelerating at 1.3 m/s/s. With that as a constant rate of deceleration it takes 554 seconds, or 9 minutes 14 seconds, to reach the ground from 200 km. That should be a pretty slow and cool reentry.
On the other hand if you are doing a full 2G deceleration it will only take 2 minutes, 22 seconds to reach the ground from 200 km. You would be going at 3.86 times the speed of sound when you reached 38.8 km which would probably still not be a fiery hot reentry, but it probably would warm up the skin of the ship a bit.
Just doing some back of the envelope calculations tell me that you reach atmospheric density of 1% at around 38.8 km. If I calculate a steadily decreasing velocity and assume a speed of mach 1 at 38.8 km the craft needs to be decelerating at 1.3 m/s/s. With that as a constant rate of deceleration it takes 554 seconds, or 9 minutes 14 seconds, to reach the ground from 200 km. That should be a pretty slow and cool reentry.
On the other hand if you are doing a full 2G deceleration it will only take 2 minutes, 22 seconds to reach the ground from 200 km. You would be going at 3.86 times the speed of sound when you reached 38.8 km which would probably still not be a fiery hot reentry, but it probably would warm up the skin of the ship a bit.
