What is the climb rate of a Air/Raft?
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AnotherDilbert
SOC-14 1K
According to LBB3 a basic air|raft can reach Earth orbit (let's say 100 km) in 8 h, that is 100 000 m / ( 8 * 3600 s ) ≈ 3.5 m/s ≈ 12 km/h, or approximately thereabouts.
By some happy coincidence that is about the same as a Cessna 172, at about the same airspeed, according to wiki.
So, quite nippy for a raft...
By some happy coincidence that is about the same as a Cessna 172, at about the same airspeed, according to wiki.
So, quite nippy for a raft...
Strictly LBB3 + Striker, 1m/sec2 up to its drag-limited airspeed. Horizontally, it's 120kph, vertically it's 30kph (assuming it stays horizontal and thus presents 4x the drag in vertical ascent as it does in horizontal travel).
In vacuum (or close to it -- for Earth, above 100km altitude), use the spacecraft speed/time formulae from lbb2 with 1/10G as the acceleration.
Straight Striker, assume it's 1.1g fully loaded and calculate the speed after determining available acceleration after subtracting local gravity, but adding the difference between the 4000kg rated payload and what it is actually carrying.
In vacuum (or close to it -- for Earth, above 100km altitude), use the spacecraft speed/time formulae from lbb2 with 1/10G as the acceleration.
Straight Striker, assume it's 1.1g fully loaded and calculate the speed after determining available acceleration after subtracting local gravity, but adding the difference between the 4000kg rated payload and what it is actually carrying.
Size hours to LEO; Earth LEO is 2000 km and size 8, so that implies 2000/8 .... 250 km per hour... assuming it's not an exponential nor log function...
Plus probably a good bit of horizontal speed, since it's to LEO, not to LEO Altitude. And that's 25,000 km/h, in 8 hours, so about 3,125 kmh per hour... but the "horizontal speed" is definitely going to be exponential due to the decreasing drag with altitude.
Condottiere
SOC-14 5K
Depends on whether the gravitational motors exude a field, or thrust forwards.
In which case, tailsitter mode.
In which case, tailsitter mode.
Remember 2000 km is the outer limit of LEO. Also note the lower limit of the Van Allen Radiation belt is around 700 km, so effectively that probably would be the altitude under which something LEO would be at.
Timerover51
SOC-14 5K
The following is what Book 3, 1981 Edition of Classic Rules states.
If you assume that Low Earth Orbit is meant, then the height would be about 200 kilometers, so with the Earth being Size 8 for the UPP, that would mean 8 hours to achieve 200 kilometers, or roughly 25 kilometers per hour. Dividing 25,000 meters by 60 would give you a climb rate of 416.67 meters per minute, which is the normal rate to list climb rate for aircraft. That would give a climb rate of 1367 feet per minute. Nothing comparable to say an F-15 on full afterburner climb, but perfectly reasonable. The climb rate might be higher at low altitudes because of the higher efficiency of the contra-gravity modules, so say something on the order of 1500 to 2000 feet per minute. My brain still thinks in Imperial Units.
I was working on a 6G small craft for rapid passenger transport from Surface to Orbit and discovered some sad facts relevant to this discussion.
For MY SMALL CRAFT ... 6 G vs 1 G is a pointless difference.
For the AIR/RAFT, 8 hours to orbit is crazy slow!
Given Orbital Velocity = 8000 meters/second and 1G = 10 m/s2, the times to accelerate to orbital velocity (ignoring drag since atmosphere thins with altitude and we are not using wings for lift) ....
6G = 134s [2.3 min]
5G = 160s [2.7 min]
4G = 200s [3.4 min]
3G = 267s [4.5 min]
2G = 400s [6.7 min]
1G = 800s [14 min]
0.5G = 1600s [27 min]
0.1G = 8000s [134 min = 2.3 hrs]
For my Small Craft, upgrading the 2G drive to 6G (1 G to 5 G performance at takeoff) reduces the flight time from 14 minutes to 3 minutes ... all that cost to save 11 minutes on a flight that will spend 15 minutes boarding and 15 minutes deplaning.
For the Air/Raft, even at 0.1 G horizontal thrust, it should reach orbital velocity in less than 2.5 hours ... so no 8 hours!
Spinward Flow
SOC-14 5K
Think of it in terms of cycles per {insert useful unit of time here}.
The 2G drive would take 15 minutes to unload/load, 15 minutes to orbital velocity, 15 minutes to unload/reload and finally 15 minutes to return to the surface parking. That approximates out to 1 round trip shuttle run per hour on a 2G drive (more or less).
The 6G drive would take 12 minutes to unload/load (smaller revenue tonnage in same displacement), 3 minutes to orbital velocity, 12 minutes to unload/load and finally 3 minutes to return to surface parking. That approximates to 2 round trip shuttle runs per hour on 6G drive (more or less).
Additionally, you need to decide "how far up into orbit" are you planning to go?
Are you just going to low orbit? If it's just low orbit, then the lower powered 2G shuttle service is probably all that you're going to need (realistically). Less drive power means more transport capacity per trip in the same hull size form factor (the "we make it up in volume" answer).
If you're planning on going all the way out to geosynchronous orbit (potentially necessary for some balkanized worlds) the journey is going to be longer than just needing to reach escape velocity. Not only do you need to reach escape velocity, you actually need to GO to a specific location (which can take time).
Using Terra as an example, geosynchronous orbit is at an altitude of 42,164km on the semi-major axis.
At orbital escape velocity (11km/s) it will take 3833.1 seconds to reach that distance above the surface "going straight up" at +11km/s the whole way (space elevator style) at a constant velocity ... which is 1 hour, 3 minutes, 53.1 seconds. However, with a more powerful lift/maneuver drive you can reduce that transit time from surface to geosynchronous orbit and do more round trip cycles within {insert useful unit of time here}.
Needless to say, there's going to be more than one inflection point for these computations.
There's going to be the "load/time" calculation, that determines how much revenue tonnage can be mobilized per 24 hour day (for example) based on how many round trips can be made within that time frame. There's going to be a "profits/time" calculation, that determines how much revenue profit gets generated after accounting for overhead and expenses (craft with bigger drives tend to have higher annual overhaul maintenance costs that need to be paid for).
So while 6G may make for the FASTEST option, it isn't necessarily going to be the most economical one, in terms to "throw weight" to/from orbit over time. Moving 100 tons per day in 10 round trips is not as valuable as moving 150 tons per day in 3 round trips (for example).
Bottom line being that you need to determine the MINIMUM acceptable performance thresholds that your business model is willing to tolerate and then work your way on up from there as necessary. If you only need to make a few round trips per day with a "lot of stuff" during each trip, you want less drives and more revenue tonnage capacity. If you need rapid response for "on call" quick turnarounds, you're going to want more drives to be able to "snipe" opportunities away from your competition (because if you arrive before them, you get the contract and they miss out on the tickets you've scooped up and prevented them from earning a profit on).
All of which is a rather long winded way of saying you need to determine what the Market Demand™ is ... and then build something which can meet that demand profile most efficiently.
Condottiere
SOC-14 5K
Capital outlay, operating costs, return on investment.
for the air/raft I've gone with the book description (hours to orbit = planet size). the grav modules IMTU for non-starships do not have infinite acceleration. At some point (as per Striker really if I recall as there is a max speed based on grav tech. But I'll admit to not looking in the last decade or two...) there is a max speed they can obtain, and air/rafts hit that limit fairly early on.
But I am more a Classic Traveller player. I just borrow a lot from other editions.
But I am more a Classic Traveller player. I just borrow a lot from other editions.
AnotherDilbert
SOC-14 1K
Yes, that is my general experience for civilian craft. 1 G will get you there fast enough, unless you are competing with microjumps on long planetary routes.
2 G is great for take-off and landing, unless contra-grav is involved. Anything more is luxury...
Yes, yet that is the only explicit data point about orbiting we have in CT at least.
If we want to keep grav vehicles as planetary vehicles, not competing with spacecraft on interplanetary routes, that is the way it should be? If an enclosed air/raft is all we need to orbit/deorbit (or go to the moon for lunch) quickly and efficiently, why would we bother with huge and expensive (comparatively) smallcraft?
Condottiere
SOC-14 5K
1. I'm falling towards the centre of the Earth.
2. I'm onboard a rocket that accelerates straight up at one gee towards orbit.
3. Presumably, I'm not going anywhere.
4. But is my body now experiencing two gravities?
5. The difference between a rocket and a manoeuvre drive is that one runs out of fuel rather quickly, so getting into orbit while you still have something in the tank becomes rather urgent.
6. If not, you may want to pack a parachute.
7. Vehicle grav motors, might not be accelerating at one gee, since they just ignore the local gravity field, so felt acceleration would be anything above that (acceleration minus local gravity field).
8. Inertial compensation, currently, seems an inherent property of spacecraft manoeuvre drives.
9. So, if you really want, or need, to get up there fast, you probably would want to take a manoeuvre driven spacecraft.
2. I'm onboard a rocket that accelerates straight up at one gee towards orbit.
3. Presumably, I'm not going anywhere.
4. But is my body now experiencing two gravities?
5. The difference between a rocket and a manoeuvre drive is that one runs out of fuel rather quickly, so getting into orbit while you still have something in the tank becomes rather urgent.
6. If not, you may want to pack a parachute.
7. Vehicle grav motors, might not be accelerating at one gee, since they just ignore the local gravity field, so felt acceleration would be anything above that (acceleration minus local gravity field).
8. Inertial compensation, currently, seems an inherent property of spacecraft manoeuvre drives.
9. So, if you really want, or need, to get up there fast, you probably would want to take a manoeuvre driven spacecraft.
mike wightman
SOC-14 10K
1. If you are falling then you are weightless.
2. The rocket is accelerating relative to what?
3. All depends on your answer to 2
4. No
8. Inertial compensation is a separate system (CT S7 et al, MT, TNE, T4, T5, GT) it is just urually below the resolution of the ship construction set - the same as artificial gravity plates and heat sinks.
9. TNE etc allow for inertial compensators to be added to grav craft (something missing from Striker).
2. The rocket is accelerating relative to what?
3. All depends on your answer to 2
4. No
8. Inertial compensation is a separate system (CT S7 et al, MT, TNE, T4, T5, GT) it is just urually below the resolution of the ship construction set - the same as artificial gravity plates and heat sinks.
9. TNE etc allow for inertial compensators to be added to grav craft (something missing from Striker).
Spinward Flow
SOC-14 5K
Au contraire!
LBB2.81, p11:
TYPICAL DISTANCES
World Surface to Orbit | 10,000 km |
Satellite | 400,000 km |
Close Neighbor World | 45,000,000 km |
Far Neighbor World | 255,000,000 km |
Close Gas Giant | 600,000,000 km |
Far Gas Giant | 900,000,000 km |
In other words, your Air/Raft needs to rise not JUST to "low" orbit (~200 above the surface) but potentially all the way up to 10,000km.
IS that the correct assumption?
Are you going to only 200km ... or are you going all the way out to 10,000km to reach "orbit"?
If it's the latter, then 8 hours doesn't sound quite so unreasonable.
After all 10,000km in 8 hours is ... {uses calculator} ... an average speed of 1250km/hour for 8 hours to traverse 10,000km ... which is actually rather close to the 1200km @ 1G result from Striker B4, p5 for Grav Vehicle Speeds (when not needing to subtract 1G for lift from performance, because ... orbital).
Note that 10,000km doesn't necessarily have to ipso facto mean 10,000km of "straight up altitude" either, since it could include needing to maneuver "around" the world to rendezvous at some position other than "directly overhead" ... in which case that 10,000km number includes both vertical AND horizontal translation (relative to the rotating surface below) in order to dock with something in orbit somewhere. So look at that 10,000km number as including a lot of "fudge factor" to cover an incredibly wide variety of orbital scenarios. Remember, you're talking "all aspect use cases" as an aid to Referees, rather than merely looking at the most favorable alignments of timing and positioning.
So if you need to lift off in your Air/Raft and get to orbit to rendezvous with your ship in orbit (somewhere) at a time that isn't "most convenient" for the orbital ephemera and positioning of both craft, it could easily take up to 8 hours for an Air/Raft to maneuver into a rendezvous position with a ship that isn't accelerating under its own power to go anywhere (else). After all, if your Air/Raft makes a break for orbit when your ship is "on the wrong side of the world" for a rendezvous, your Air/Raft is going to have to "chase down" your ship in order to link up with it ... which could be a journey of ~10,000km "sideways" even if you only need to go 200km "up" in order to leave the atmosphere.
I think the biggest problem with the Air/Raft is the illustration ...
I read the description and saw the picture and imagined "Convertible" like THIS:
... so why can't it travel anywhere fast?
I think the old LITERATURE and text actually imagined something more like a "flying forklift" like THIS:
... Now it MAY be possible to reach Mach 1 with that or throw on a vacc suit and haul a ton of cargo to orbit standing on THAT, but I would not be the guy to test that flight envelope.
I read the description and saw the picture and imagined "Convertible" like THIS:
... so why can't it travel anywhere fast?
I think the old LITERATURE and text actually imagined something more like a "flying forklift" like THIS:
... Now it MAY be possible to reach Mach 1 with that or throw on a vacc suit and haul a ton of cargo to orbit standing on THAT, but I would not be the guy to test that flight envelope.
No, it is still unreasonable.Are you going to only 200km ... or are you going all the way out to 10,000km to reach "orbit"?
If it's the latter, then 8 hours doesn't sound quite so unreasonable.
initial velocity (u) = 0 m/s
distance to midpoint (s) = 5000 km = 5,000,000 m
acceleration (a) = 1 m/s2
Velocity at midpoint = 3162 m/s
time to midpoint = 3162 seconds = 53 minutes (call it 1 hour)
Time to decelerate to rest at end point = 2 x 53 minutes = 106 minutes (less than 2 hours)
That Striker maximum speed is only applicable in atmosphere ... and universes with Space Ether.
There is no top speed in vacuum (well, SPEED OF LIGHT, but we are not close to dealing with relativistic mass and time dilatation).
At 1 m/s2 vertical acceleration (0.1G), you will exit the atmosphere (100 km) in 8 minutes at 450 m/s velocity ... then Atmospheric Drag is a non-issue.
If we accelerate for the full 10,000 km, we arrive in 75 minutes with a velocity of almost 4.5 km per SECOND.
If we accelerate for another 45 minutes, we will have traveled a total distance of 25,700 km and will be moving at 7.1 km per SECOND to overtake our target in Geostationary orbit (traveling at 3 km per second orbital velocity).
Still just 2 hours - not 8 hours.
FYI, the ISS orbits the Earth in 1 hour ... so it should take less than 1 hour coasting in LEO to get into position for a Geostationary orbit intercept (less for powered flight).
All this at 0.1 G (1 m/s2) ... imagine if we get to use a full 1G (10 m/s2) because we are above orbital velocity and no longer need to counteract gravity!
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