Hello Richard Aiken,

One of my habits, I'm not sure whether to consider it good, bad, or indifferent (probably annoying is more accurate), is filling in a blank. The "uncertainty in the duration of jump" was a blank that I have an answer to so I unthinkingly filled in the blank.

Drat, I recall and can not find the source, that in at least one Traveller rule set dropping out of Jump space automatically occurs at the 100-D limit of the nearest object or after the variable time period of 168 +/-10% hours in jump space.

Even if my recollection is half right or totally wrong, I do agree that there is a chance that the calculations will put your ship in the wrong spot at the right time for the defenders or possibly making a new feature in the landscape.

Tom R

From: "Richard Aiken" <xxxxxx@gmail.com>
To: "TML" <xxxxxx@simplelists.com>
Sent: Friday, February 19, 2016 5:25:41 AM
Subject: Re: [TML]Tracking spaceships in Jump TU, was: Instant city

On Fri, Feb 19, 2016 at 8:00 AM, <tmr0195@comcast.net> wrote:

Jump duration: 168 +/-16.8 hours

Tom R

From: xxxxxx@shadowgard.com
To: "TML" <xxxxxx@simplelists.com>
Sent: Thursday, February 18, 2016 11:55:33 PM
Subject: Re: [TML]Tracking spaceships in Jump TU, was: Instant city

On 12 Feb 2016 at 22:57, Richard Aiken wrote:

> Since a ship exiting jump retains it's initial vector and velocity,
> that just makes using an xboat as a WMD a matter of somewhat chancy
> timing. If you can manage to have the ship emerge somewhere/when
> ahead of the planet along it's orbital path, then it's going to hit
> the surface *somewhere.*

Nope. You forgot the uncertainty in the duration of jump.

Earth's orbital velocity is about 30 km/sec. so in an hour it moves
108,000 km. That's 13.5 diameters.

Given that jump duration varies a lot more than *just* an hour....

Actually, I didn't forget the uncertainty in the duration of jump. That's why I said "a matter of somewhat chancy timing." The planet's orbital path is fixed. The ship's emergence *point* is also fixed . . . at least within a relatively small scale, since ships can make coordinated jumps in close formation and emerge at the far end without colliding. The unpredictable variable is the exact *time* at which emergence will occur. But if you plot jump emergence to occur (for Earth) 1.8 million miles or more ahead of the planet's position on it's orbital path at the time you enter jump, you should emerge *somewhere* ahead of it.

Of course, the closer you make emergence, the less time the planet's defenses will have to react to you as a threat. Which means that if you try to shave it too close, you might overshoot and emerge behind the planet.

Richard Aiken

"Never insult anyone by accident." Robert A. Heinlein

"I studied the Koran a great deal. I came away from that study with the conviction there have been few religions in the world as deadly to men as Muhammed." Alexis de Tocqueville (1843)

"We know a little about a lot of things; just enough to make us dangerous." Dean Winchester

"It has been my experience that a gun doesn't care who pulls its trigger." Newton Knight (as portrayed by Matthew McConaughey), to a scoffing Confederate tax collector facing the weapons held by Knight's young children and wife.

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