Advanced Space propulsion systems in the 1990s

[Warringer]

I have a question for all the space enthusiasts around here.

What sort of advanced propulsion system that is not a NERVA style nuclear engine or a simple ion thruster could possibly developed during the 1990s?

Something akin to the VASMIR? A Fission Fragment Engine?

What would be realistic?

 

[LostCosmonaut]

Orion's always an option, if you can get people not to worry about the fallout (which while significant, isn't as bad as most think). Use of pure fusion instead of fission munitions for propulsion could help, although I'm not sure if that's feasible during the 90s. (I'm guessing you're going with a POD in the 60s).

Gas core fission designs, such as the Nuclear Lightbulb, are another alternative, although I am again unsure if they are feasible in this timeframe.

Other than that, and what you mentioned, the only other thing I could think of is improving chemical rockets' performance (possibly using fluorine based fuels). That's not very exciting to most, though .

 

[Michel Van]

Orion's always an option, if you can get people not to worry about the fallout (which while significant, isn't as bad as most think). Use of pure fusion instead of fission munitions for propulsion could help, although I'm not sure if that's feasible during the 90s. (I'm guessing you're going with a POD in the 60s).

Gas core fission designs, such as the Nuclear Lightbulb, are another alternative, although I am again unsure if they are feasible in this timeframe.

Other than that, and what you mentioned, the only other thing I could think of is improving chemical rockets' performance (possibly using fluorine based fuels). That's not very exciting to most, though .

Waringer ask for NON nuclear engines,

there is one, never test in space high energy engine called: Solar Moth.
it use sun light and heat by focusing it with large mirrors into engine were hydrogen goes plasma. with ISP 917 sec v. 440 sec of Lox/Hydrogen
but beyond orbit of Mars the engine work not so good anymore


Another is Solar sail aka Photon Sail
using the pressure of Solar light on huge sail from thin aluminium film (30 to 100 nanometres thick)
up to 1 km size
the japanese IKAROS probe is first operational Solar sail for moment with size of 20 meter.

NASA JLP wandet to use Solar sails for space mission in 1980s Halley Comet and Mars mission
but the Reagan administration stop that by budget cuts...

 

[Archibald]

As Michel said: solar sail is the best bet.
Solar thermal is kind of NERVA-without-the-nuke (which get replaced by a solar concentrator).

 

[phx1138]

As Michel said: solar sail is the best bet.
Solar thermal is kind of NERVA-without-the-nuke (which get replaced by a solar concentrator).

There's a better option, but I'm not sure exactly how it'd be implemented. (I'm thinking a variation on solar sail.) Namely, couple solar power satellite to solar sail... Satellites at Mercury with powerful lasers or microwave transmitters could produce powered missions throughout the Solar System.

 

[Michel Van]

There's a better option, but I'm not sure exactly how it'd be implemented. (I'm thinking a variation on solar sail.) Namely, couple solar power satellite to solar sail... Satellites at Mercury with powerful lasers or microwave transmitters could produce powered missions throughout the Solar System.

A Microwave Sail Starwisp ?

feasible with technology of 1990s, but the cost and other problems:
you need a solar power satellite in orbit
Forward original proposal for Interstellar Probe needed a SPS with 56 gigawatt power output and microwave lens of 560 km ø
to bring a 100 x 100 meter mesh of fine carbon wires, with mass of 1 kg and payload of 80 GRAMS on speed of 10% speed of light.
Even scale down for flights true Solar system, the Payload is still under kilogram, with prize tag of hundred billion dollars...

A Solar Sail is much cheaper...

 

[Jeeves]

While you've ruled out nuclear thermal propulsion, what about nuclear electric?

Maybe work for SDI leads to a greater focus on space-based reactors as a power source for laser satellites? With the end of the Cold War the whole system is repurposed as a power source for a large Jupiter probe like JIMO. Hook up the reactor, radiators and a Brayton turbine for power conversion to an array of Ion or Hall Effect Thrusters. Might be ready by the end of the 90s, but where is the money coming from?

Even with greater enthusiasm for VASIMR, I doubt that you could speed up it's development enough to get even a demonstration unit into space during the 90s.

 

[Warringer]

I'm seeking something good enough to send a ship to Saturn in a reasonable time frame, following a Mars gravity assist. At the moment my option is a HOPE derivate with a nuclear reactor (thorium based peddle bed (is something like that even possible in space?)) with a 100N MDP thruster block...

 

[asnys]

I'm seeking something good enough to send a ship to Saturn in a reasonable time frame, following a Mars gravity assist. At the moment my option is a HOPE derivate with a nuclear reactor (thorium based peddle bed (is something like that even possible in space?)) with a 100N MDP thruster block...

Thorium PBRs are definitely possible in space, but they're probably not the best choice. In particular, the use of thorium will add considerable mass to the system unless you're able to make in-pile breeding work, and is fundamentally unnecessary since you can just use highly-enriched uranium. The extra cost of weapons-grade fissiles will be negligible compared to the cost and mass of the processing equipment or the R&D to do in-pile breeding.

Not sure if a PBR is the best architecture for the task, though you could certainly do a lot worse. You might look at some of the SNAP designs. An MSR might be a good choice too if you don't mind doing a lot of extra research.

 

[Warringer]

Thorium PBRs are definitely possible in space, but they're probably not the best choice. In particular, the use of thorium will add considerable mass to the system unless you're able to make in-pile breeding work, and is fundamentally unnecessary since you can just use highly-enriched uranium. The extra cost of weapons-grade fissiles will be negligible compared to the cost and mass of the processing equipment or the R&D to do in-pile breeding.

Not sure if a PBR is the best architecture for the task, though you could certainly do a lot worse. You might look at some of the SNAP designs. An MSR might be a good choice too if you don't mind doing a lot of extra research.

The decision for Thorium is largely for security reasons. If the launch vehicle blows up on the pad or during ascent, it's much less likely to irritate large areas.

 

[Delta Force]

The aerospike engine was proposed for the VentureStar.

 

[Michel Van]

Thorium PBRs are definitely possible in space, but they're probably not the best choice. In particular, the use of thorium will add considerable mass to the system unless you're able to make in-pile breeding work, and is fundamentally unnecessary since you can just use highly-enriched uranium. The extra cost of weapons-grade fissiles will be negligible compared to the cost and mass of the processing equipment or the R&D to do in-pile breeding.

Not sure if a PBR is the best architecture for the task, though you could certainly do a lot worse. You might look at some of the SNAP designs. An MSR might be a good choice too if you don't mind doing a lot of extra research.

During SDI they work on SP-100 nuclear reactor for use in Space
the prototype had output of 100 kw power, but was design for 2 mega watt output power

The decision for Thorium is largely for security reasons. If the launch vehicle blows up on the pad or during ascent, it's much less likely to irritate large areas.

Most* nuclear power source designs, had fail save system in case the launch vehicle blows up.
the casing protected the reactor core for explosion and impact in ocean.

especially the radioisotope thermoelectric generators used on Mars and deep space probe.
Famous case was the RTG of Apollo 13, who re-entry into the Earth's atmosphere with 11 km/s hit the ocean and sank in tonga trench, 6,500 m deep.
the RTG a SNAP-27 remain intact because, no release of plutonium has been detected in the area.

* note NERVA engine and soviet Topas Reactors have non failsafe system for this problem!

Waringer, what have you in mind for Saturn Mission, something like JIMO or even a Manned Mission ?!

 

[Archibald]

During SDI they work on SP-100 nuclear reactor for use in Space
the prototype had output of 100 kw power, but was design for 2 mega watt output power

An MSR might be a good choice too if you don't mind doing a lot of extra research.

After a long search I've recently tracked down some papers discussing MSR reactors for lunar bases - after the author recognized the limits of the solid-core SP-100 design.
The author, David Buden had a very long nuclear / aerospace career that spanned from the nuclear aircraft of the late 50's (he was at General Electric) to the SP-100 (Los alamos), including NERVA NRX tests (he worked at Aerojet in the mid-60's).

As for the fuel, a lot of advanced electric thrusters (VASIMR is best known, but according to wikipedia there's a whole bunch of others) works well with ammonia, which is much easier to store than hydrogen over long periods of time.

Molten salt reactor + electromagnetic thruster + ammonia => perhaps the best combination on hand as of today.

 

[asnys]

The decision for Thorium is largely for security reasons. If the launch vehicle blows up on the pad or during ascent, it's much less likely to irritate large areas.

The radiation risk from launching reactors into space is seriously overblown. Uranium, even highly-enriched uranium, is not a serious radiation risk - you don't want it in your house, but it's not very mobile and it's half-life is hundreds of millions of years; if I recall correctly it's more dangerous as a heavy metal toxin. It's the fission product "ash" that builds up during the fission reaction that's the real health risk, not the uranium itself, so as long as you don't turn it on until you're in orbit you'll be fine. Moreover, thorium is also radioactive; not as radioactive as U-235, but still.

There's a theoretical risk with HEU of accidental criticality if the rocket blows up and falls into the ocean, but that's why you use numerous redundant safety rods during launch. And thorium isn't immune to this problem because you'll need at least some U-235 mixed in there to act as a seed for the breeding process. And using thorium will add a LOT of expense and mass if you can't make in-pile breeding work. I mean a LOT - you're talking about shipping a small chemical plant up with the reactor to periodically reprocess the fuel elements, as well as requiring a reactor with a significantly larger mass.

 

[Warringer]

Well, its better to be safe than sorry, isn't it?

I think that a MSR could be used. Smaller pressure vessel for one and its not that much hotter than a comparable peddle bed. And with the salt as fuel, its less of a problem to keep the fuel in place and the stuff has to be pumped around anyway. In combination with a Baryton cycle or two it should yield a good amount of power.

As for the thrusters. VASMIR was not the thin in the 1990s and like I said, I'm partial for the MPD thrusters, mainly because of their relatively high thrust and very high ISP. The downside is that the MDP thruster NEEDs a full known nuclear reactor in the hundreds of kW to few MW.