A possible 'Goldilocks' planet?

[Saxman]

What you really need is a dual-purpose drive, one that has high specific impulse for fuel efficient cruise (IE, ion rockets) but capable of a high thrust output for quick acceleration (something akin to the SABRE precooled turborocket). Maybe an ion rocket for cruise with a SABRE afterburner for escape velocity and rapid acceleration.

[USRanger]

And pie.  We'll need to bring a gift.  I'm thinking cherry.

[DREDIOCK]

And pie.  We'll need to bring a gift.  I'm thinking cherry.

naa. Pies go bad.

Bring em some fruitcake instead. They seem to last forever.

[RTHolmes]

What you really need is a dual-purpose drive, one that has high specific impulse for fuel efficient cruise (IE, ion rockets) but capable of a high thrust output for quick acceleration (something akin to the SABRE precooled turborocket). Maybe an ion rocket for cruise with a SABRE afterburner for escape velocity and rapid acceleration.

well cruise for a spacecraft is unpowered so no engines required for that. but it is quicker to accelerate fast then cruise than to use constant acceleration (more time spent near c, so you get more of the relativistic benefits of time/distance contraction).

for constant 1g acceleration the whole trip to Gliese 581 takes 6yr/22yr.

using the same fuel/payload ratio as above you can burn at 2g for 5ly, cruise for 10ly then decel at 2g for the last 5ly, in which case the trip to Gliese 581 takes 3.91yr/21yr.

point is that return trips to our nearest stars are completely feasible (and quick for the astronauts), and could be completed within the lifetime of an earth observer. and this is using inertial drives - no worm holes, subspace, gravity rails, FTL etc. just using developments of existing technology (ion drives, GRASERs etc.)

like the lunar trips, this is essentially just an engineering and resources challenge

[Saxman]

well cruise for a spacecraft is unpowered so no engines required for that. but it is quicker to accelerate fast then cruise than to use constant acceleration (more time spent near c, so you get more of the relativistic benefits of time/distance contraction).

It's a matter of fuel efficiency. The problem is getting high /_sp (fuel efficiency) with high thrust (acceleration). Nuclear pulse could probably do it, but because of the problems you get into dealing with nuclear fusion it may not be all that practical.

What I meant by "cruise" is a more efficient means of acceleration. A high /_sp engine for deep-space acceleration, with a less efficient but more powerful means of propulsion for certain maneuvers and atmospheric flight (ion engines wouldn't work in atmosphere).

[RTHolmes]

yup just an engineering problem, and we have a good record of solving them

[321BAR]

Actually, the theories I've seen are that the Sahara's dryness is cyclical and has gone through several wet and dry periods. The drying is largely believed to be a result of changing patterns in the monsoon, which used to extend further north than it does today.

ive also seen this. but the problem is is that with the theory i stated there is actually proof that an event that includes a flash heat is entirely plausible. this mineral spread across the sahara and into Asia Minor has a dating to the time of the drying of the sahara and also the effect of extreme burning on them. i need to find the info again...

[Saxman]

It doesn't mean an impact DIDN'T happen, just that it's not necessarily a factor in the Sahara drying out since other geological evidence shows that the Sahara has wet and dry cycles (for one, the Sahara aquifer itself still exists, however geological changes since the last wet period cut it off from the surface).

There's also the reality that earth has suffered several severe (arguably even more extreme) impacts that aren't connected to desertification of the area in which it occurred. A good comparison is the Tunguska Event, which despite SUBSTANTIAL damage to the surface it's taken only a century for the environment to recover (and before anyone gets cute because it's in Russia: "desert" is defined by a lack of precipitation, NOT a hot climate. The largest desert in the world is actually Antarctica). For an impact event to have formed the Sahara, it would have HAD to have disrupted the weather patterns themselves. Doesn't matter if the entire continent was burned to the ground, as long as rain returned to the area vegetation would recover.

Furthermore, the Sahara is also showing signs of returning to a wet period ("green" regions have expanded northward significantly since 1982).

[321BAR]

It doesn't mean an impact DIDN'T happen, just that it's not necessarily a factor in the Sahara drying out since other geological evidence shows that the Sahara has wet and dry cycles (for one, the Sahara aquifer itself still exists, however geological changes since the last wet period cut it off from the surface).

There's also the reality that earth has suffered several severe (arguably even more extreme) impacts that aren't connected to desertification of the area in which it occurred. A good comparison is the Tunguska Event, which despite SUBSTANTIAL damage to the surface it's taken only a century for the environment to recover (and before anyone gets cute because it's in Russia: "desert" is defined by a lack of precipitation, NOT a hot climate. The largest desert in the world is actually Antarctica). For an impact event to have formed the Sahara, it would have HAD to have disrupted the weather patterns themselves. Doesn't matter if the entire continent was burned to the ground, as long as rain returned to the area vegetation would recover.

Furthermore, the Sahara is also showing signs of returning to a wet period ("green" regions have expanded northward significantly since 1982).

agreed on all parts except that tundra more specifically defines Antarctica

but they also believe that the sahara incident was so hot that it flash fried all life... there was no way things could regrow. they believe that the incident if reoccuring today would melt a city without an impact. the comet split up in the upper atmosphere but so many fragments hit the atmosphere at the same time that it actually lit the atmosphere in the area on fire itself...

[Saxman]

agreed on all parts except that tundra more specifically defines Antarctica

There is Antarctic tundra on some of the islands, but the continent itself IS considered a true desert based on precipitation levels.

I've heard there's evidence of a comet impact or airburst, but nothing ever pointing to it as the "smoking gun" even in recent research. Everything I've seen still points to the natural wet/dry cycles and changes to the Monsoon patterns.

[321BAR]

There is Antarctic tundra on some of the islands, but the continent itself IS considered a true desert based on precipitation levels.

I've heard there's evidence of a comet impact or airburst, but nothing ever pointing to it as the "smoking gun" even in recent research. Everything I've seen still points to the natural wet/dry cycles and changes to the Monsoon patterns.

ok. ill give you that one.

[Boozeman]

for constant 1g acceleration the whole trip to Gliese 581 takes 6yr/22yr.

using the same fuel/payload ratio as above you can burn at 2g for 5ly, cruise for 10ly then decel at 2g for the last 5ly, in which case the trip to Gliese 581 takes 3.91yr/21yr.

If I'm not mistaken, you need roughly 168 days of constant 2g acceleration to reach 0,95 c. That would roughly mean that in less than a years time and thus less than a ly in dictance you can acclerate and decellerate, and cruise for more than 20 ly.   

[RTHolmes]

hmm I think you've missed something quite important in yr calcs there.

hint: how fast are you after 200 days of 2g?

[Ack-Ack]

or a space elevator...

Space elevators would suck, would you want to be forced to listen to elevator muzak for that long?


ack-ack

[Ack-Ack]

you think so? its only 20ly away (proxima centauri our closest neighbour is about 4.2ly away).

sounds like a long way but it really isnt. take a space ship that accelerates at 1g up to the midway point, then decelerates at 1g to destination (so the astronauts get to experience familiar earthlike gravity for the entire trip).

any guesses on how long the trip takes for the astronauts?

and how much time has passed on earth by the time they get back?

 

I bet Han Solo can make the run in less than 12 parsecs.

ack-ack