Space and Aerospace Design in a Focus Fusion World

[Henning]

Today we already have Virgin Galactic’s SpaceShipOne programme reaching 100km sub-orbit. On the other hand we have the VASIMIR electromagnetic thruster for vacuum propulsion.

The atmospheric pressure at 100km is less than 1 Pascal (0.01 millibars) (see here). This might make it possible to use a VASIMIR as third stage.

So the configuration would be something like this:

1st Stage: Focus fusion powered ground lifter like WhiteKnightTwo.

2nd Stage: Conventional hybrid rocket motor powered sub-orbit vehicle like SpaceShipTwo.

3rd Stage: Focus fusion powered VASIMIR orbit escape vehicle.

With the two bodies of a WhiteKnightTwo we don’t even have to shield the reactors that much, giving r^-2 of neutron density. Then on the other hand you can’t take tourists up there on that second body…

One important thing here: Don’t get the misconception that we need conventional kerosine powered turbines for atmospheric plane travel. The high-velocity and high-temperature of kerosine powered turbines are actually a engineering problem for normal (sub-supersonic) modern air travel, in addition to their vibration.

Modern jet engines use the high burning temperature only for efficiently burning fuel which drives the high pressure turbine. Then a gearbox reduces the velocity and drives the main fan, see high-bypass turbofan. So today’s design trades velocity with throughput, that’s why modern jet engines get bigger and bigger fans (diameter increases).

Focus fusion will make electric powered intercontinental air travel very economic. There’s not even a reason to refill the fuel, so traveling from Europe to New Zealand (half the Earth’s circumference) without an intermediate stop is easily possible.

This implies that we don’t need to convert electricity using steam powered generators, but can use something like Powerchips for converting heat into electricity. A flying steam engine might pose a problem here, but it’s still a viable option for ground-based operation.

For more info about electric powered aeroplanes see SkySpark, Next Generation More-Electric Aircraft: A Potential Application for HTS Superconductors, and search the web for aeroplane superconducting electric turbine. Why superconducting? Because they need 3 times less mass than normal electric engines. Mostly the superconducting option is inspected, because the hydrogen is chilled anyway. Just as a start of discussion.

[Tulse]

Does VASIMR have enough thrust to act as a third stage in that manner? Could it go from suborbital to orbital?

[Henning]

Ok, you’re right. This should read LEO then. So the second stage needs to ascent from about 14km (WhiteKnightTwo) to 160km (LEO), and not just 100km (Kármán line) like SpaceShipTwo. But they’re both arbitrary definitions. So somewhat between that.

[speedplane]

You may not even need the VASMIR engine. If designed properly, you may be able to use the ion beam coming out of the focus fusion device directly for thrust. Of course there would be numerous engineering difficulties to build this, but in space’s vacuum it may work very well.

[belbear42]

The main problem of getting in space (LEO, at least) is not reaching a certain altitude, it’s reaching a certain velocity (about 7 km/sec) and once you are above an altitude where wings provide lift, you have accelerate to orbital speed within a given time with a given minimal acceleration or else you will simply fall back to Earth.

All non-chemical methods of thrust (including those hypothetical focus fusion powered ones) appear to fall short of that goal because of lack of raw thrust. That’s why I propose a vehicle with a conventional rocket upper stage (LOX-LH2 as NASA would do or a much cheaper hybrid rocket as private organisations are proposing.) That upper stage is much smaller than any single stage solution and may be re-usable.

Once you are in LEO, things are different. Motors like VASIMR or direct focus fusion beam can be used to get away from Earth and roam around the solar system.

Anyone wishing to gain some hands-on experience with spaceflight, I can recommend the ORBITER software simulator on http://orbit.medphys.ucl.ac.uk/

And the best of all is that this form of spaceflight is VERY cheap: Cost is ZERO dollars. Give it a try and find out how spaceflight REALLY works!

[vansig]

belbear42 wrote: The main problem of getting in space (LEO, at least) is not reaching a certain altitude, it’s reaching a certain velocity (about 7 km/sec) and once you are above an altitude where wings provide lift, you have accelerate to orbital speed within a given time with a given minimal acceleration or else you will simply fall back to Earth.

Yes, space ship 2 reaches its max speed of mach 3.5 after a 70-second burn and coasts up to its 110km max altitude.
This is way short of orbital velocity (~mach 24), requiring (24/3.5)²=47 times as much energy.

Consuming 200kW, one VASIMR VF-200 engine will have 5N thrust, and weigh 300kg. if you’re not already at orbital velocity, this doesn’t get you there.

[Aeronaut]

vansig wrote:

The main problem of getting in space (LEO, at least) is not reaching a certain altitude, it’s reaching a certain velocity (about 7 km/sec) and once you are above an altitude where wings provide lift, you have accelerate to orbital speed within a given time with a given minimal acceleration or else you will simply fall back to Earth.

Yes, space ship 2 reaches its max speed of mach 3.5 after a 70-second burn and coasts up to its 110km max altitude.
This is way short of orbital velocity (~mach 24), requiring (24/3.5)²=47 times as much energy.

Consuming 200kW, one VASIMR VF-200 engine will have 5N thrust, and weigh 300kg. if you’re not already at orbital velocity, this doesn’t get you there.

Yepper. That’s why so many of us are looking forward to a Space Elevator. For some missions, the SE could eliminate or greatly minimize the amount of thrust required by ‘launching’ from near the tether’s end.

[belbear]

Aeronaut wrote:
Yepper. That’s why so many of us are looking forward to a Space Elevator. For some missions, the SE could eliminate or greatly minimize the amount of thrust required by ‘launching’ from near the tether’s end.

Just a matter of finding out how to build 40000 klicks of carbon nanotube cable that weighs less than a conventional rocket can carry and you’re halfway there. Unfortunately the unique in-orbit assembly capabilities of the Space Shuttle won’t be available anymore to assemble the first geostationary satellite.
After all, now Constellation is cancelled, nobody knows when an post-Shuttle American manned spacecraft will ever fly again and how it will look like.

[Aeronaut]

Progress on the tether is incremental. Much more challenging imo is getting the popular and financial support needed. I have a hunch that FF and the SE are both going to reach the public awareness about the same time. By public awareneness, I mean when most people believe it can be done and then start asking why it hasn’t been done yet.

Now If W had directed NASA to develop the SE as the most cost-effective road to Mars and beyond, $50G would be no major problem.

[vansig]

belbear wrote:
Just a matter of finding out how to build 40000 klicks of carbon nanotube cable that weighs less than a conventional rocket can carry and you’re halfway there.

What’s this i hear about colossal carbon tubes being a better choice for tether material? they’re already macroscopic, and when you look at breaking length, they exceed nanotubes because they are less dense.

http://en.wikipedia.org/wiki/Colossal_carbon_tube

[Aeronaut]

vansig wrote:

Just a matter of finding out how to build 40000 klicks of carbon nanotube cable that weighs less than a conventional rocket can carry and you’re halfway there.

What’s this i hear about colossal carbon tubes being a better choice for tether material? they’re already macroscopic, and when you look at breaking length, they exceed nanotubes because they are less dense.

http://en.wikipedia.org/wiki/Colossal_carbon_tube

Looks good at first glance. The last sentence says it’s strong enough, and I’m reading the ability to make very long continuous lengths into the article. 69,000 miles long, though, is still going to be a BIG spool or few. But at least that would move the engineering from the tether to deploying the tether. Much nicer challenge to have.

[theanphibian]

I agree that Carbon Nanotubes have great potential for the future. But that’s the future. The specific strength needed has only dubiously been achieved in micro-materials and practically we would need about the mass of Mount Everest of this material to lift something as large as a human up. And even THEN it will only be able to slowly lift item-by-item at a rate that will not allow for quick development of space.

I’m less encouraged by the idea of a space elevator than I am of Iter.

Consider…

http://www.quicklaunchinc.com/

We have established technology that with significant but realistic investment can catapult materials into LEO. Humans remain a separate issue, but there remains much potential for revolution in that area – epically we have a separate and cheap delivery mechanism for material supplies.

The only cost limitation for such a plan is, yes, energy. Regardless of the specifics, by increasing the volume of what we send into space the price of launch will eventually approach the energy costs required to put something into orbit, most people agree with this. But… if energy suddenly became abundant by a revolutionary technology then space exploration would correspondingly become accessible.

[Aeronaut]

Looks like your chicken gun, PD 🙂

Seriously, though, it has clear military implications once the friction heating allows re-entry targeting. I favor the SE despite the engineering curve because it’s being developed to move roughly 30 ton loads at around 120 mph. This will enable a space-based economy that doesn’t require bone-jarring acceleration or aerodynamically risky re-entries.

[theanphibian]

Oh, you’re entirely right. A cannon launcher could target any terrestrial location with ease, since it’s already firing rockets that have to make accurate maneuvers to dock in space. The design calls for one-stage rockets and they would have exactly the same effectiveness as present-day ICBMs. But for that matter, anything sufficiently heavy object in LEO could be used in this manner.

Maybe there is an argument that the space elevator would reduce any malicious threats because it raises things to GSO, from where a de-orbit maneuver could be detected before someone in space sent something plummeting onto Earth. But still, putting a huge number of people into space presents a similar terrorist risk as building Quicklaunch type cannons. And in addition to that, the number of appealing terrorist plots directed at the space elevator itself are intimidating. Considering it must be tethered to Earth one could send it flying into space with an ordinary commercial jet. Then consider the other possibility, the space elevator falling down to Earth – even worse.

It’s interesting to hear what people envision for the specifics. Because even at the technically challenging speed of 120 mph it would take 7.6 days to get to GSO. Even with multiple 30 ton payloads on the tether, something like a Quicklaunch design or just conventional rocket innovation could take up ~1 ton payloads with a frequency greater than what the space elevator could theoretically do before we’ve ever manufactured a square meter of sufficient strength carbon fiber.

[Aeronaut]

Why invest in the energy to orbit the projectile? I’d just build a turntable and modify my fall of shot tables accordingly.

[Author]

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