Comic 195 - 11 hours later ( roughly )

19th Jun 2014, 12:00 AM
11 hours later ( roughly )
Average Rating: 5 (13 votes)

Author Notes:

Centcomm 19th Jun 2014, 12:00 AM edit delete
Centcomm
The math is all sound for a 1 gee burn at a constant velocity :D
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Comments:

jamie59 19th Jun 2014, 12:10 AM edit delete reply

I think you mean accelration. The velocity is increasing a lot.
Centcomm 19th Jun 2014, 2:23 PM edit delete reply

They cant actually get to light speed but they can get a fair bit of speed :D
cattservant 19th Jun 2014, 12:29 AM edit delete reply

"Fast as fast can be.
You can't catch me!!!"
Stormwind13 19th Jun 2014, 6:58 AM edit delete reply

Puts a 200G Dog(ging) missile on cat's tail. :-D
Centcomm 19th Jun 2014, 2:23 PM edit delete reply

LOL :D
Sheela 20th Jun 2014, 1:00 AM edit delete reply

Wha- HEY!!

Why am I suddenly accelerating at 200G ??
Stormwind13 20th Jun 2014, 9:49 PM edit delete reply

::Points at the cat to Sheela:: Cat, get him!!! :-D
JacobJSebastian 19th Jun 2014, 12:52 AM edit delete reply

Jamie is right. a 1G burn is constant acceleration. constant velocity would be 0G. but this does remind me that my comments in the previous strip were a bit off. while us terrans would feel the thud of the accel at first and then get used to the 'normal' gravity, a lunan would get SLAMMED by the initial thrust, and be pinned at much more than the gravity they were used to.
plymayer 19th Jun 2014, 2:14 AM edit delete reply

Commence normal ship's routine.
Hydrargyrum 19th Jun 2014, 4:22 AM edit delete reply

Hmm, I think I'm having a hard time reproducing the math. Earth to Mars at 1 G (with no attempt at velocity matching) looks like a day and half to three days, depending on how the planets are positioned. That's a long watch on comms, or at least that's how the text comes across to me---there's nothing in it which absolutely precludes multiple watches having elapsed.
Timotheus 19th Jun 2014, 4:39 AM edit delete reply
Are you calculating it as one g continuous acceleration? The velocity adds up rather quickly. I'm waiting to see how they decelerate. (Otherwise known as flipping the ship around and point the thrusters the other way.)
Mister Black 19th Jun 2014, 9:07 AM edit delete reply

It's possible for them to 'flip' the ship without cutting the engines, but the math on that one breaks my brain, to say nothing of draining the fuel tanks making course corrections. I don't know how TPTB plan to make the flip to deceleration mode, but the most fuel efficient and simplest way would be to cut the drive and use a combination of attitude thrusters and flywheel momentum transfer to make the flip. If you limit yourself to 0.25G during the maneuver, the flip takes about 83 seconds. That's a small enough deviation from a pure brachistochrone trajectory to be recoverable, or should be.
Fairportfan 19th Jun 2014, 3:18 PM edit delete reply

I've lost track - is Mars their destination?

==============

I was wondering if the ship is basically one of Heinlein's "torch ships", which apparently run on direct matter annihilation; in Double Star, he has the ship do what is described as a "skew flip" maneuver to reverse thrust and begin "backing down".

It's been a while since i read the book last, but they are blasting at 2G and i think it takes a day or two for Earth-Mars.

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Earth-Mars distance varies considerably, depending on whether Mars is in opposition (same side of the sun) or conjunction (opposite sides of the sun - i know that sounds weird, but it refers to Mars' relative position to the Sun as observed from Earth).

If Mars is in conjunction, the distance from Earth orbit (1 Astronomical Unit radius) to Mars orbit (1.5 AU) is, therefore, 2.5 AU. Since an AU is (roughly) 150 trillion meters, and one G acceleration is 9.8 meters/sec/sec, and distance is one-half acceleration times the square of time ... hmmm ...and we assume that the trajectory is essentially a straight line (the actual size of the Sun being pretty much insignificant in this schema so the deviation from a straight line is negligible) ... roughly 76 hours Earth orbit to Mars.

Looks like a velocity of about 2700 km/sec - time dilation would not be a significant factor yet at that speed.

Still, three full days would be a long time on watch.

So lets assume opposition - where the distance would be half an AU.

Hmmm ... about 34 hours. (Square factors are a wonderful thing - five times the distance takes only a little more than twice the time. 2.24 times - square root of five - in fact.)

Velocity about 1200 km/sec.

Still a long time on watch.
Centcomm 19th Jun 2014, 3:21 PM edit delete reply

well .. for Galina its not hard for her to " exceed " Human limits on Sleep loss.. she does not need as much as a human in any case .. she also had to be "told" to go get rest... she was too wrapped up in the trip.. and pondering the signal...
Fairportfan 19th Jun 2014, 4:28 PM edit delete reply

I think the eleven hour figure forgot the square factor in calculating time to distance...
Stormwind13 19th Jun 2014, 5:39 PM edit delete reply

Yeah, Fairport I think you may be right. What I'm seeing for a straight flight to Mars (no braking) is 1 day, 7 hours, 58 minutes (found here) at the closest between Mars and Earth.
Centcomm 19th Jun 2014, 3:53 PM edit delete reply

Sorry missed the first question - Saturn is the target :D They are just passing Mars at this point..
Tokyo Rose 20th Jun 2014, 1:26 AM edit delete reply

*points wordlessly towards Mister Black, then runs away from all the math*
Stormwind13 20th Jun 2014, 5:47 PM edit delete reply

::Points all the WONDERFUL NUMBERS at Rose:: Get her! }:-D~>
Dragonrider 19th Jun 2014, 8:57 AM edit delete reply

First they are going from Luna Orbit which is higher and more ideal for positioning than earth launch. Next the constant 1G Burn is eating mass at an astronomical rate lightening the ship while the thrust stays constant. As pointed out they are going to have to flip the ship for deceleration burn very soon. Also, arriving at an intercept point where the aliens are facing three very large plasma cannons(the engines)is a fairly decent strategy for survival if the balloon goes up.
Fairportfan 19th Jun 2014, 4:27 PM edit delete reply

Since Galina says she "watched Luna as we passed it by", they probably built the ship at one of the LaGrange points, not Lunar orbit.

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Actually, if we assume that they have some sort of total-conversion torch drive, they'll be able to achieve an incredible exhaust velocity, so reaction mass needed would go down.

=========

* Earth/Luna distance is roughly one-quarter of a percent of an AU.
Hydrargyrum 19th Jun 2014, 5:51 PM edit delete reply

@Dragonrider: You seem to be mixing constant acceleration and with constant thrust. Everything we know so far indicates the former is how Luna Star is moving. Also, spend some time with the maths and you'll see the launch position within the Earth-Moon system has negligible effect on transit time.

@Fairport+Stormwind: It doesn't look to me like neglecting the square. One way of approaching this is to note the title of this page says 11 hours to Mars. Solving a = 2d / t^2 for the required acceleration for an 11 hour transit yields 7.3G at the minimum distance of 56M km and a crushing 52G at the maximum distance of about 400M km. An acceleration of 1G would require an exponent in the range of 2.19 to 2.37.

@Black: Yeah, I assumed a negligible flip time in the Earth-Saturn transits I mentioned in the previous page's comments.
Centcomm 20th Jun 2014, 7:30 PM edit delete reply

I did say "Roughly" .. and Yes they probably had a shift change .. Just Gali didn't ...
Hydrargyrum 21st Jun 2014, 1:13 AM edit delete reply

Well, if ya make it 14 hours the required acceleration drops to 4.5 to 32G. (I think the minimum typo for 1G would be 31 hours.)

-<runs off chasing Rose brandishing an integral sign>-
Stormwind13 19th Jun 2014, 7:02 AM edit delete reply

Shows how humans adjust to their environment. Galina is adjusting to the acceleration and the noise.
cattservant 19th Jun 2014, 1:11 PM edit delete reply

She must have a programmable bladder though.
I think her eyes are getting greenish!
Centcomm 19th Jun 2014, 2:25 PM edit delete reply

nope still the same color - :D its probably other lighting making it look diffrent..
Centcomm 19th Jun 2014, 2:24 PM edit delete reply

yep that she is :D
Outlaw 19th Jun 2014, 1:57 PM edit delete reply

As always, great page!
Centcomm 19th Jun 2014, 2:24 PM edit delete reply

thank you :D
DizzasterJuice 19th Jun 2014, 3:24 PM edit delete reply

Beautiful art and writing here!
Centcomm 19th Jun 2014, 3:31 PM edit delete reply

Thank you :D and Im sure Rose thanks you too :D
Hornet 19th Jun 2014, 5:31 PM edit delete reply
"flipping the ship" depends on when and at how fast your going to maintain 1G. you are from the target you cut the drive engines. Given enough time and space between cutting the engines and arrival, you could use the maneuvering thrusters to stop, place and dock with the target.
Centcomm 20th Jun 2014, 7:29 PM edit delete reply

Very correct :D
Don B. 21st Jun 2014, 1:39 AM edit delete reply
I shouldn't be surprised by Galina's poetic side...she is a master of language and communication after all. Makes me wonder if she went on to write about her experiences. I'm sure there is lots of documentation about her and her life from others, I'm unsure of how much came from Gali herself. She's an inspiration to androids of Dolly's time but how much of it is drawn from her own words as opposed to "Historical Fact", "Common Knowledge" or the opinions of others?
Stormwind13 21st Jun 2014, 9:49 AM edit delete reply

Galina has her Boswell, May, to write her words for her Don. :-)

Pity she isn't on the trip, I wonder how May would capture the moment. Fear of the unknown, excitement of going to meet the unknown, wonder at the new sights to see... and boredom of nothing going on (at the moment) but babysitting instruments. :-D
Centcomm 22nd Jun 2014, 6:05 PM edit delete reply

Actually Gali is keeping track for May and sending her regular one way comms.. that let her fill in the blanks :D
Stormwind13 23rd Jun 2014, 6:05 PM edit delete reply

Ah, good to know CentComm. :-)
mjkj 21st Jun 2014, 6:07 AM edit delete reply

I am glad Gali is enjoying herself :D

Well, after eleven hours they have covered a distance of about 15,378,396 km.
Stormwind13 21st Jun 2014, 9:35 AM edit delete reply

You sure, mjkj? I'm getting about half that myself.

Oh here, I just found this resource which might help. :-)
mjkj 21st Jun 2014, 5:42 PM edit delete reply

Ah, could be that I missed something...
PriorKnowledge 21st Jun 2014, 11:48 AM edit delete reply
All you math geeks that are questioning the travel time need to realize that this is taking place in Luna Star/Datachasers universe, not our universe. Perhaps in their universe the planets are in tighter orbits around the sun. Or maybe orbital math is completely different in the their universe. Lastly, maybe the author misplaced a decimal point.
Stormwind13 21st Jun 2014, 12:54 PM edit delete reply

I think Mr. Black (the science/math geek for the comic) misplaced the decimal point. Rose and CentComm want as little to do with math as humanly (or inhumanly) possible! :-D
Centcomm 22nd Jun 2014, 12:36 AM edit delete reply

well we do roughly try to follow "real" science principals - any errors are more likely my scripting .. :P and well math is math..
Stormwind13 22nd Jun 2014, 5:49 PM edit delete reply

Sometimes rougher than others right CentComm? :-D
Caley Tibbittz Collopy 15th Jul 2014, 8:20 PM edit delete reply

I sure hope the pilot didn't hear the captain say "rack time", as he'd surely think of an entirely different activity with the same name.
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