[Liquid oxygen rocket]

I suppose its possible for an ISRU project to generate excess O2.  In which case we would be looking for uses for it.  Most other gasses are lighter and thus better for propulsion.

In the case of Mars it might be possible to build an SSTO that runs on carbon monoxide and oxygen.

[Imperial versus metric]

13 hours ago, Kermann Nolandung said:

To be consistent, a statute mile subdivision should be chosen among the furlong, chain, rod, yard, foot, etc.

A Roman mile is 1000 double paces of a Roman soldier.

[Why is it better to destroy the ISS than to elevate it to a graveyard orbit?]

I hope we don't build another station for several decades.  There are more important objectives like the Moon and Mars.

But... eventually there will be another station.

What should be the priorities of the next station?  Centrifugal habitats for 1/3 and 1/6 g.  Repositionable to the Moon, Mars or Venus.  Inflatable and huge in size.  ...

[Cleaning up Kessler syndrome]

https://www.nasa.gov/smallsat-institute/sst-soa/deorbit-systems/

"

In addition to drag sails, an electromagnetic tether has proven to be an effective deorbit method. This technology uses a conductive tether to generate an electromagnetic force as the tether system moves relative to Earth’s magnetic field. Tethers Unlimited (now Amergint Technologies) developed terminator tape that uses a burn-wire release mechanism to actuate the ejection of the terminator’s cover, deploying a 70 m long conductive tape at the conclusion of the small spacecraft mission. There are currently two main modules. The first, NSTT for NanoSats has a mass of 0.808 kg. The second, CSTT, is made for CubeSats and has a mass of just 0.083 kg."

[Cleaning up Kessler syndrome]

What I'm hearing is that you need to nearly match the orbit of each piece of junk you want to catch.  Nets are not going to work at high velocity.  

 

Now there is a graveyard orbit just above geostationary orbit.  This junk is all moving with roughly the same velocity including direction.  It's too far out to easily deorbit, (easier to crash into the Moon in fact)  Out there a net that collects debris and keeps it concentrated makes some sense.

[Save the ISS!]

im not downloading but id love to see some screenshots

[Cleaning up Kessler syndrome]

I wasn't specific enough.  The cannons are in orbit.  They don't need high muzzle velocity, because you get around 14 km/s relative by counter orbiting the target.  Any hit is likely to shatter the target, but all the fragments will be going the same direction which happens to be the direction you need to deorbit.  

[What If We Could Weaken Or Stop Entropy Within A Scifi Field?]

4 hours ago, darthgently said:

 

Actually, in the extreme,  I'm pretty sure this is just another way to describe the "time stopping device" that has been in sci-fi many times.  Entropy is the arrow of time.  Time cannot pass without it

I can at least imagine this.  A time stopped bubble in an otherwise normal universe.  Other alternatives are difficult to imagine.

[Cleaning up Kessler syndrome]

What are some of the proposed methods for clearing orbital debris?

My favorite idea is a cannon that shoots blocks ice H20 or dry ice CO2.  With this the projectiles evaporate.  Whereas using metal bullets limits the angles where you can safely use it without orbiting your projectiles.  You need a cannon going in each direction, clockwise and counterclockwise as viewed from north pole.  Use a cannon going opposite direction to the target.  The cannons themselves need not be very powerful in terms of projectile speed.  We try to intersect space junk near it's apogee and shoot it with a block of ice.  Relative velocities will be in excess of 14km/s.  The target could shatter, but all the small fragments will deorbit faster.  Everything will be reduced to a lower perigee, I think.  A miss is expensive in terms of payload cost, but not dangerous because it will ablate away into gas on its own.

 

What else?  Giant nets, magnets, radioactive tracers...  Use tritium ice so at least you can easily track your projectile and tell how it disintegrates.

[Why is it better to destroy the ISS than to elevate it to a graveyard orbit?]

30 years and what do we have to show for it?  We can't even breed mice in zero-G.  Has there been any great discovery from this program?

[Why is it better to destroy the ISS than to elevate it to a graveyard orbit?]

According to wikipedia the altitude of ISS decays by 2km per month.  There is still some air up there at 420km.   So we have 13 years to wait before it de-orbits itself.  Supposing we want it over the pacific ocean, we could wait till the last minute and do it on the cheap.

[Why is it better to destroy the ISS than to elevate it to a graveyard orbit?]

How many tons of fuel would it require to move the ISS into a lunar orbit?

[Why is it better to destroy the ISS than to elevate it to a graveyard orbit?]

3 hours ago, ColdJ said:

Personally I reckon we take up a deconstruction crew and solar powered furnace. Strip out as much as possible from the interior. Melt down metal parts into ingots that you can use as raw materials. Remove the solar panels and deconsruct them down to a compact package. Then calculate and push the remaining station so that it eventually ends up in orbit of the moon. Then as we progress with future construction on the moon, dismantle, recycle materials for construction. It is already outside the main gravity well so it requires far less energy to move. We should be now be in the age of recycling, rather than push it at the earth and hope it doesn't go horribly wrong or just throw it away in space.

That's way more practical than any asteroid mining mission I've heard.

[If backwards time travel were possible in Sci Fi]

In my model it's not like Back to the Future, where you disappear if you prevent your own birth.  Einstein has a model where you can be your own grandpa.  Your grandparents might not meet each other and have you, but they are likely to have other kids.  Why be selfish?   You're not allowed to become a serial killer who goes back a forth fixing your own screw ups, because hand waving argument.

WWII might happen anyway.  The Soviets and the Japanese were committed expansionists.  It would just be different.

I'll stick with my plan to save Abraham Lincoln, as I'm most confident he could improve things slightly compared to what actually happened.

Orson Scott Card has an interesting story called Pastwatch:  The Redemption of Christopher Columbus.  In which by empowering the Native Americans just prior to Columbus' arrival, it is possible to avoid ecological devastation in our near future.  A very good read.

I also thought about saving the life of Jesus.  We get way more parables and teachings.  But a few things would be different.

[If backwards time travel were possible in Sci Fi]

My thought was to save Abraham Lincoln.  Reconstruction would have gone much better.  Our political landscape today would be quite different.

Suppose Alexander lived to conquer all of India and beyond.  Indian religion, philosophy, and mathematics would have permeated the western world early and completely.

 

 

[Why is it better to destroy the ISS than to elevate it to a graveyard orbit?]

In a way I'll be glad when we don't have a space station or a low orbit shuttle.  The priorities are the Moon and Mars.  Lets go already.  No more distractions.

[If backwards time travel were possible in Sci Fi]

It is cliche to say that a time traveler could go back in time and kill Hitler thus stopping WWII.  

Let's juxtapose the question.  If you could save the life of someone in order to change history for the better, who would you save?

 

 

[Why is it better to destroy the ISS than to elevate it to a graveyard orbit?]

Scott says the problem of space debris is more severe in higher orbits.  Micrometeors and such a likely to break off pieces of the station compounding the problem.  Too bad we can't push it past Earth's sphere of influence into it's own solar orbit.

[Is a revolutionary advance in spaceflight imminent?]

1 hour ago, sevenperforce said:

Who's to say that hypersonic jet transport is any more feasible -- as a business case -- than hypersonic rocket transport?

Obviously it does better by not carrying oxidizer.  Surely that's cheaper.

[The Analysis of Sea Levels.]

Holistic grazing management could help save the permafrost.   Snow is an insulating layer that prevents permafrost from forming in the winter.  With trees removed and snow trampled more permafrost will grow.  Grassland can sequester carbon in soil much faster than forests.  Bring back the mammoth!

[The Analysis of Sea Levels.]

Spruce is good for seaplanes

 

[Did we discover nuclear technology “too early”]

Do we have breeder reactors 50-100 years too late?

Just like the development of fission, it depends on a small number of people with a huge amount of funding.

Renewed interest in thorium reactors is 99.9% due to Kirk Sorenson.  But we won't get it because U233 is WG.

[Did we discover nuclear technology “too early”]

Without Marie Curie, I think nuke tech would be delayed at least 50 years

 

[Fun Fact Thread! (previously fun fact for the day, not limited to 1 per day anymore.)]

Correcting one of my mistakes on a lost thread:

There is some evidence of communication between the ancient Polynesia and the Americas.  The sweet potato is thought to have originated in South America and made it to the Pacific Islands.  

[Appreciate y'all]

Not sure what the current hullabaloo is, and don't care to know in detail.  This forum is already heavily moderated for anything political or personally offensive.  There is a relatively small group of regulars who a comfortable around here.