Re entry in a grav vehicle

[sideranautae]

Do remember that table was given an errata. The title was changed to MAXIMUM ACCELERATION.

I wonder why? The change doesn't change anything. But, MT was such an editing CF I shouldn't ask. :lol:

 

[Anonymous]

Thanks for posting the table, most of my pre MgT books are back in London, will get them at some point... It brings up a few ideas and as ever, highlights differences in the ideas behind the different versions of Traveller but more of that another thread...

Ignoring atmospheric drag for simplicity, how long would it take for a 1G craft to accelerate to 9.4 km/s? I got this number from wiki as the velocity needed to maintain low earth orbit, tho the actual number was slightly lower at I think 7.8 km/s but they gave a reason for the higher number I don't recall.

OK, prior to the table being posted I got a number based on 1G being 9.8 m/s/s of just under 57 minutes to reach that velocity. It wouldn't take that long to ascend but if you wanted to turn your manoeuvre drive off to save power, you'll probably have completed a few orbits prior to reaching a stable altitude and velocity.

 

[Reynard]

I wish I still had the original errata printout. They were converting Thrust energy to Acceleration motion though it reads KPH which is velocity (speed). Pretty much everything thereafter points to you can't go faster rather than you can't accelerate more. I think they were trying to avoid the vacuum reference and ended up using another wrong term. It should have read Maximum Velocity.

For Mongoose simplicity though, a grav-based vehicle can reach 'orbit'. The time to reach the target in 'orbit' is the distance between them versus the vehicle's maximum listed speed. I'm not sure anyone is willing to calculate relative speeds and launch windows for optimal interception. Maneuver drives just bull their way to a target using the Travel Times table in the core book.

 

[sideranautae]

Ignoring atmospheric drag for simplicity, how long would it take for a 1G craft to accelerate to 9.4 km/s? I got this number from wiki as the velocity needed to maintain low earth orbit, tho the actual number was slightly lower at I think 7.8 km/s but they gave a reason for the higher number I don't recall.

It would take 18 minutes and you would go 5,000 KM in the meantime.

Here is a online calc for just this type of calculation: http://www.transhuman.talktalk.net/iw/AccelTime.htm

 

[sideranautae]

For Mongoose simplicity though, a grav-based vehicle can reach 'orbit'. The time to reach the target in 'orbit' is the distance between them versus the vehicle's maximum listed speed. I'm not sure anyone is willing to calculate relative speeds and launch windows for optimal interception. Maneuver drives just bull their way to a target using the Travel Times table in the core book.

This is best for an RPG situation.

 

[Infojunky]

I wish I still had the original errata printout.

Here: http://dmckinne.winterwar.org/pdfs/MegaTraveller%20Consolidated%20Errata.pdf

Page 39...

They were converting Thrust energy to Acceleration motion though it reads KPH which is velocity (speed). Pretty much everything thereafter points to you can't go faster rather than you can't accelerate more. I think they were trying to avoid the vacuum reference and ended up using another wrong term. It should have read Maximum Velocity.

Their words were wrong but the chart works.

For Mongoose simplicity though, a grav-based vehicle can reach 'orbit'. The time to reach the target in 'orbit' is the distance between them versus the vehicle's maximum listed speed. I'm not sure anyone is willing to calculate relative speeds and launch windows for optimal interception. Maneuver drives just bull their way to a target using the Travel Times table in the core book.

I would like to point out at this Juncture that in Vehicles 5-6 the speeds and endurance listed with each chassis entry are the Max speed and endurance at said max speed.

 

[sideranautae]

I would like to point out at this Juncture that in Vehicles 5-6 the speeds and endurance listed with each chassis entry are the Max speed and endurance at said max speed.

In those books what is the Grav acceleration rate in G's (for vacuum operation) let's say?

 

[Infojunky]

I would like to point out at this Juncture that in Vehicles 5-6 the speeds and endurance listed with each chassis entry are the Max speed and endurance at said max speed.

In those books what is the Grav acceleration rate in G's (for vacuum operation) let's say?

Book 5-6 Vehicles is the single replacement book for the earlier two book design system. Also it is the basis for the Vehicles SRD. And they unfortunately got give any accelerations just speeds.

 

[sideranautae]

I would like to point out at this Juncture that in Vehicles 5-6 the speeds and endurance listed with each chassis entry are the Max speed and endurance at said max speed.

In those books what is the Grav acceleration rate in G's (for vacuum operation) let's say?

Book 5-6 Vehicles is the single replacement book for the earlier two book design system. Also it is the basis for the Vehicles SRD. And they unfortunately got give any accelerations just speeds.

Doh! I didn't know they added the Vehicles to an SRD. I'll go re-download the dev pack. Thanks!

 

[Reynard]

Thank you for that PDF. I had a very old copy until my HD crashed. This one goes up to 2013 for updates!

Oh and to our inquiries:

"Page 86, Top Vacuum Speed (correction and addition): For flying vehicles, especially those that can go outside the atmosphere, top vacuum speed has no real meaning. Other than the speed of light, there really is no such thing as “top speed” in a vacuum. The craft can accelerate as long as it wants, and can attain any speed desired—limited only by its duration and acceleration. Therefore, acceleration in Gs is a more sensible and useful number than top vacuum speed, since it tells you how quickly the craft can change its speed. Once you know the craft’s maximum acceleration rate, you can compute the travel time using the basic travel time formula found in the Referee’s Companion. Therefore, Top Vacuum Speed should be replaced by MaxAccel in craft profiles.
Top Speed applies to craft operating in a standard atmosphere only. Note that wheeled, tracked, and legged vehicles are subject to the same top speed restrictions as flying craft, based on their streamlining. For example, an unstreamlined wheeled vehicle can never exceed 300 kph in a standard atmosphere. If the wheeled vehicle needs to go faster, it must be streamlined, just as any flying vehicle."

 

[sideranautae]

Thank you for that PDF. I had a very old copy until my HD crashed. This one goes up to 2013 for updates!

Oh and to our inquiries:

"Page 86, Top Vacuum Speed (correction and addition): For flying vehicles, especially those that can go outside the atmosphere, top vacuum speed has no real meaning. Other than the speed of light, there really is no such thing as “top speed” in a vacuum. The craft can accelerate as long as it wants, and can attain any speed desired—"

Ok. So on a vacuum world at least, a grav car cold eventually reach escape velocity and leave orbit altogether. Who knows what happens to it though after ...

 

[Anonymous]

In the game I'm currently playing in the GM has ruled that while an air raft can achieve orbit, the vehicle (which is open topped, a stupid idea in the first place, it never rains in Traveller, not even in the clouds you can fly thru?) itself is not made for hard vacuum/extreme cold and its gonna have something (more than just the upholstery) fail... we haven't challenged his ruling yet by trying...

Here's a question as an off shoot from that game. We're about to use Personal re entry kits to drop out of orbit and then (TL12) grav belts to fly 2 hours in NOE to a target. I am unclear why we're being told to use re entry kits when the grav belts should work perfectly well.

The challenge being thrown at us tho is that the grav belts don't have good enough endurance for the whole trip. Do you think we could free fall from low orbit from a star ship in grav held altitude and turn the grav belts on a few km from the surface or would the 0.25G they can generate be insufficient to prevent us from turning into a bowl of petunias? I guess the math could be done to see what terminal velocity would be and then how would the G be able to compensate for that... If I were any good at math...

 

[wbnc]

In the game I'm currently playing in the GM has ruled that while an air raft can achieve orbit, the vehicle (which is open topped, a stupid idea in the first place, it never rains in Traveller, not even in the clouds you can fly thru?) itself is not made for hard vacuum/extreme cold and its gonna have something (more than just the upholstery) fail... we haven't challenged his ruling yet by trying...

Here's a question as an off shoot from that game. We're about to use Personal re entry kits to drop out of orbit and then (TL12) grav belts to fly 2 hours in NOE to a target. I am unclear why we're being told to use re entry kits when the grav belts should work perfectly well.

The challenge being thrown at us tho is that the grav belts don't have good enough endurance for the whole trip. Do you think we could free fall from low orbit from a star ship in grav held altitude and turn the grav belts on a few km from the surface or would the 0.25G they can generate be insufficient to prevent us from turning into a bowl of petunias? I guess the math could be done to see what terminal velocity would be and then how would the G be able to compensate for that... If I were any good at math...

A grav Belt has to generate at least 1 Gee to hold a person in place against normal Earth gravity. to move against the local gravity it has to be able to generate at least some surplus acceleration so it would be able to safely slow you falling from orbit....as long as the batteries hold out.( 4 hours by the write up in the Traveller Core Rulebook)

However Using the reentry kit would allow you to drop from orbit at a rate faster than the very slow speed of a Grav belt in atmosphere. I think they are listed at around 300kph max speed( just a little faster than a Parachutist in free fall) ....

That leisurely descent on a grav belt would give someone on the ground plenty of time to line up a shot and vaporize your drop team.Or dispatch an armed Vehicle to fly up, wave at you,then vaporize you.

actually one of the reasons anyone would make a ballistic entry into an atmosphere would be to come in much faster than a normal slow descent on gravitics.

 

[Anonymous]

But a ballistic entry is flawed for a couple of reasons: de orbiting from a standard low orbit, the heat shield burning up is very visible and being ballistic and of limited manoeuvre you're a very predictable target.

I'm curious if the idea from earlier in this thread of a grav powered ship maintaining low orbit altitude without orbital velocity would allow a re entry kit to simply fall vertically and re enter at relatively low speeds with limited use of the heat shield?

 

[Reynard]

I was under the impression the reentry kits was a one shot emergency system, a high tech parachute. The scenario you describe sounds like you need to reach the surface quickly almost like a Hilo jump then continue traveling with normal flight capability. Sounds like any classic adventure or action movie.

 

[sideranautae]

In the game I'm currently playing in the GM has ruled that while an air raft can achieve orbit, the vehicle (which is open topped, a stupid idea in the first place, it never rains in Traveller, not even in the clouds you can fly thru?) itself is not made for hard vacuum/extreme cold and its gonna have something (more than just the upholstery) fail... we haven't challenged his ruling yet by trying...

I won't go directly against a GM but, the air/raft is standard equip on Scout Type S so is probably designed to be used by Scouts in Vacc Suits. A very utilitarian vehicle that probably has no real upholstery and what not. I have always thought that open top was a stupid idea too though.

Here's a question as an off shoot from that game. We're about to use Personal re entry kits to drop out of orbit and then (TL12) grav belts to fly 2 hours in NOE to a target. I am unclear why we're being told to use re entry kits when the grav belts should work perfectly well.

You are correct to question this. The reentry kits aren't needed if you have Grav Belts.

The challenge being thrown at us tho is that the grav belts don't have good enough endurance for the whole trip.

TL 12 grav belts have plenty of endurance. The way to go is to have the ship hover at orbital level and jump out with the belt power off. Only turn them on when you are close to the ground. In hover mode one can do this in a TL 7 space suit even. The grav belts at TL 12 can detect altitude and have their auto pilot set to go on at predetermined level based on what your velocity would be.

I suspect that your GM is not familiar enough with Trav rules yet.

 

[Anonymous]

I won't go directly against a GM

<snip>

I suspect that your GM is not familiar enough with Trav rules yet.

He's plenty familiar with the rules, he just likes to hobble us... :twisted:

 

[sideranautae]

I won't go directly against a GM

<snip>

I suspect that your GM is not familiar enough with Trav rules yet.

He's plenty familiar with the rules, he just likes to hobble us... :twisted:

Nothing wrong with that. BUT, he should have a list of house rules to give you so you know what is changed (what the PC's would know anyway). Otherwise that is just considered being a D___

 

[Reynard]

I think the original purpose for a stripped down open top air raft was it was CHEAP for player characters. Every vehicle supplement thereafter has enclosed versions of the air raft at a higher price. I think that reason it's called an air raft is the open feature. I'm sure an open cargo hauler would be a cargo raft while a weapon platform version is a weapon's raft. I've heard another term not too frequently called a sled and it may be interchangeable with a raft.

 

[sideranautae]

I think the original purpose for a stripped down open top air raft was it was CHEAP for player characters. Every vehicle supplement thereafter has enclosed versions of the air raft at a higher price. I think that reason it's called an air raft is the open feature. I'm sure an open cargo hauler would be a cargo raft while a weapon platform version is a weapon's raft. I've heard another term not too frequently called a sled and it may be interchangeable with a raft.

Yes. It was the equivalent of a Jeep (original). I had a '45 Willys jeep when I was a kid. No top whatsoever. Vacuum operated wipers, etc.