Manned Spaceflight - the Next 30 Years

[Eric Mc]

hidetheelephants said:

Eric Mc said:

Ion drive sounds like one solution. It's already been used a couple of times on small unmanned probes. What are the technical difficulties of using bigger and more powerful ion drive engines for manned missions?
Are there any new technologies that need to be developed to allow this or would it just be a matter of using current technology engines but just making them bigger?

Ion drives are slowly being made more efficient but the biggest obstacle is the power source; until a practical fusion reactor or perhaps a compact molten salt fission reactor is built we're stuck with powering ion drives from solar panels, RTGs or powercells, none of which have much power density compared to chemical rockets.

Does that matter if the power is applied gradually over a long period of time. From what I understand about ion drives is that you don't need a huge amount of thrust - just a small amount of thrust applied continuously over a long period of time.

[jmorgan]

A use for some nukes then.

[MartG]

Eric Mc said:

hidetheelephants said:

Eric Mc said:

Ion drive sounds like one solution. It's already been used a couple of times on small unmanned probes. What are the technical difficulties of using bigger and more powerful ion drive engines for manned missions?
Are there any new technologies that need to be developed to allow this or would it just be a matter of using current technology engines but just making them bigger?

Ion drives are slowly being made more efficient but the biggest obstacle is the power source; until a practical fusion reactor or perhaps a compact molten salt fission reactor is built we're stuck with powering ion drives from solar panels, RTGs or powercells, none of which have much power density compared to chemical rockets.

Does that matter if the power is applied gradually over a long period of time. From what I understand about ion drives is that you don't need a huge amount of thrust - just a small amount of thrust applied continuously over a long period of time.

It's the 'long period of time' bit that's the problem - with current ion technology and power supplies a manned craft would take a month or two to just get out of Earth orbit. The thrust is simply too low for a manned spacecraft which will have a considerable mass of supplies etc. aboard

[Eric Mc]

What about a hybrid using traditional rocket propulsion to boost the craft to escape velocity and then use the ion drive for continuing acceleration to the destination?

[MartG]

Eric Mc said:

What about a hybrid using traditional rocket propulsion to boost the craft to escape velocity and then use the ion drive for continuing acceleration to the destination?

Assuming you want to use the rocket to slow down at the other end, you'll have so much mass that carrying the ion drive too will make very little difference overall - possibly be worse than without it

[Dr Jekyll]

MartG said:

Assuming you want to use the rocket to slow down at the other end, you'll have so much mass that carrying the ion drive too will make very little difference overall - possibly be worse than without it

You could always use the ion drive to slow down, or at least do most of the slowing down.

There does seem to be a general problem with scaling up space technology though. Look at Virgin Galactic, stretching the spacecraft that got the X prize to take a few more seats turned out to be a massive problem whereas the equivalent for a small aircraft is straightforward.

[Eric Mc]

I wonder if anyone has seriously done the sums. Why not use the ion drive in what would normally be the "coast" phase? Surely continuous acceleration during that period would shorten the journey time substantially.

And, depending on your destination, you might be able to use some sort of non braking rocket method of deceleration - such as aerobraking.

[MartG]

You need to figure out if running an ion drive throughout the coast phase is worthwhile adding the mass of the drive and its power supply to the spacecraft - remember it will take additional fuel to accelerate the extra mass at both ends of the trip and given the large mass of a manned spacecraft and the very low thrust of an ion drive the benefits are likely to be minimal

[NNH]

I've been trying to find out what a nuclear submarine's reactor weighs to get an idea of what you might use to power an ion-drive spacecraft with. All I've found so far are typical total sub displacements (eg ~6000 tonnes for USN class, or ~7000 for RN Astute class) so I'd guess the reactor must be at least several hundred tonnes.

Does anybody have more expertise in this?

[Eric Mc]

Does the power source have to be a nuclear reactor. Solar panels are getting more effective all the time.

[Toaster]

http://www.reactionengines.co.uk/sabre.html

Probably the best new engine development to get in to orbit from my point of view it has a more realistic potential than many other options

"This advanced combined cycle air-breathing SABRE rocket engine enables aircraft to operate easily at speeds of up to five times the speed of sound or fly directly into Earth orbit.

With the Pre-cooler heat exchanger and other SABRE engine advanced technology development programmes nearing completion, the next stage of the SABRE programme is the construction of a full engine demonstrator."

[Eric Mc]

I agree. I think the Sabre is a great concept. I've chatted to Bond and his team at Farnborough a couple of times. They know what they are doing. They just need more money.

[hidetheelephants]

Eric Mc said:

Does the power source have to be a nuclear reactor. Solar panels are getting more effective all the time.

It's the power density thing, plus solar panels are fine up to about Saturn then it's too dark. RTGs are better than nothing but 5w/kg is nothing to write home about. The late Dr Bussard postulated that a polywell fusion reactor could be as little as 3m in diameter, <50 tonnes and provided you could cool it or develop sufficiently heat-tolerant materials it could make up to 250MW for as long as you fed it deuterium/boron/whatever. ORNL came up with designs for molten salt fission reactors with similar power densities in the 1970s; there's something of a renaissance happening in with this technology now, China are spending a lot of money on it with the intent of having a working reactor within 5 years and there are several commercial efforts trying to do the same. That's the kind of power needed to go mining/refining/smelting/manufacturing on the moon/Mars/wherever, solar panels won't cut the mustard.

[Eric Mc]

We don't have to hang around waiting for a "Mr Fusion"unit then ?

[Simpo Two]

hidetheelephants said:

That's the kind of power needed to go mining/refining/smelting/manufacturing on the moon/Mars/wherever, solar panels won't cut the mustard.

Very true - but I still think that the idea of mining for minerals so it can be sent back to Earth is cloud cuckoo land. OK so you have your nuclear reactor on the moon etc and have made some iron. Now you have to buy lots of rockets to get it back to Earth. Postage and packing is how much?

Given the title 'Manned Spaceflight - the Next 30 Years' we're looking at flag-planting missions - in the continuing spirit of human exploration. And you have to get a man with a flag there before you can rock up with your intergalactic 'Nostromo' nuclear mining unit.

[hidetheelephants]

Simpo Two said:

Very true - but I still think that the idea of mining for minerals so it can be sent back to Earth is cloud cuckoo land. OK so you have your nuclear reactor on the moon etc and have made some iron. Now you have to buy lots of rockets to get it back to Earth. Postage and packing is how much?

Given the title 'Manned Spaceflight - the Next 30 Years' we're looking at flag-planting missions - in the continuing spirit of human exploration. And you have to get a man with a flag there before you can rock up with your intergalactic 'Nostromo' nuclear mining unit.

I couldn't agree more, the mining/etc is for more economic manufacture of 'Nostromo' et al, with no NIMBYs to kick off about open cast mining techniques, slag heaps or smoky blast furnaces; an industrialist's paradise, especially if there are suitable tax incentives for doing it. You don't bring stuff you've made back here for the same reason it's bonkers to mine the moon for He3, it just costs too much and it's far easier and cheaper to make the stuff on earth.

[MartG]

Simpo Two said:

Very true - but I still think that the idea of mining for minerals so it can be sent back to Earth is cloud cuckoo land. OK so you have your nuclear reactor on the moon etc and have made some iron. Now you have to buy lots of rockets to get it back to Earth. Postage and packing is how much?

Getting stuff back from the moon doesn't need any rockets - just a big railgun

[Simpo Two]

Ah yes, from that handy shop 'Railgun Supplies' located just off junction 12 of the Sea of Tranquility

[Toaster]

Eric Mc said:

I agree. I think the Sabre is a great concept. I've chatted to Bond and his team at Farnborough a couple of times.

Well thats why they are there to attract serious enquires, investment and chat with the public like yourself

Eric Mc said:

They know what they are doing.

Indeed they do and this is a real step change and provide a strong challenge against other organisations

Eric Mc said:

They just need more money.

Then you cannot be aware of the BAE investment (Money and expertise) http://www.reactionengines.co.uk/news_02nov2015_re...

[Catatafish]

MartG said:

Simpo Two said:

Very true - but I still think that the idea of mining for minerals so it can be sent back to Earth is cloud cuckoo land. OK so you have your nuclear reactor on the moon etc and have made some iron. Now you have to buy lots of rockets to get it back to Earth. Postage and packing is how much?

Getting stuff back from the moon doesn't need any rockets - just a big railgun

You would only take moon materials back to earth if it was financially viable. It's likely that certain metals will spike in value when they run out down here, but in the first round of lunar mining, materials will be used to build and sustain a colony.

Once established, launches to other places in the solar system come almost for free compared to here with the far lower escape velocity. A craft that carries people beyond van allen is inherently massive to avoid the prospect of sterilised, cancer, dying or dead astronauts on arrival. The shielding could be fashioned from moon dust and epoxy fir example.

The moon will look the same if you mine the hell out of it, so we better get on with it before it's guarded by chinese nukes.