VASIMR Engine (From Earth to Mars in 40 Days)

[vger]

Felt like this needed its own thread. I'm surprised this hasn't gotten more interest around here so far.

The main drawback seems to be that we'd need to get everyone feeling comfortable with nuclear devices in space. I know WE realize it's not as apocalyptic as the idea implies, but many aren't - for the same reasons that many aren't comfortable with nuclear power on Earth.

All that aside, this bugger is theoretically the Turbo-Charged V8 of space travel.

http://www.huffingtonpost.com/2015/04/06/vasimr-rocket-mars_n_7009118.html?ncid=txtlnkusaolp00000592

[Bill Phil]

That would be good, 40 days to Mars.

Then we could build one or two vessels and use them more than once...

[xenomorph555]

The reason it hasn't come up a lot around here is because it's old news. We've known about the VASIMR for years, waiting quietly for it's use to begin. However with NASA cancelling the ISS VASIMR test flight I guess we are going to have to wait longer.

[B787_300]

It is a rabbit hole that NASA is chasing... The tests of the earth based articles have provided nowhere NEAR the thrust and only about 50% efficiency, which is below what they need for it to work.

[Streetwind]

The VASIMR isn't a miracle engine (at least, outside of Near Future Propulsion ). There's nothing it can do that other electric engines can't.

The thing that makes it different is its power rating. The Dawn space probe uses 2 kW thrusters; it has three but that's just for redundancy. It only fires one at a time. The VF-200, in comparison, runs at 100 times that power throughput. It's that throughput that allows it to fly these shortened Mars trajectories with payload sizes suitable for human travel.

However, you could achieve the same throughput by clustering, say, two 100 kW multi-channel nested hall thrusters, like those being developed atthe PEPL at the University of Michigan. Considering that the VASIMR is at the lower end of the electric efficiency range, a hall thruster operated at the same power throughput would post similar thrust/Isp numbers... perhaps having a somewhat lower Isp but a comparatively higher thrust. It would require packing more fuel, but would also have more oomph to accelerate that extra fuel along with the spacecraft.

Of course, no power solution to drive a 200kW electric propulsion system exists today. Even the entire power output of the ISS devoted to the task wouldn't be able to run it. As such, discussing the merits of a 200kW engine is a bit moot. We should perhaps be dicsussing the power generation solution that brings us to Mars in 40 days, not the engine. Because as far as engines go, we have several different options just waiting in the woodwork. ESA just three years ago successfully tested a 19,200s Isp, 250 kW engine and then canned it and put it on a shelf because there was simply no use case for it in the foreseeable future.

(A lot of this has to do with there being a relationship between payload/dry mass, mission dV, specific power and electric engine Isp. For any given numbers of the three former, there is an ideal engine Isp for that mission profile. At our current technology levels, we're creeping around the 3000-4000 Isp range to GEO... and a lot less than that to Mars. Only better power generation equipment will let us actually use high Isp engines efficiently.)

Edited April 7, 2015 by Streetwind

[SeaDog]

The main drawback seems to be that we'd need to get everyone feeling comfortable with nuclear devices in space.

Don't underestimate the difficulties of nuclear power... Getting people comfortable might not be the most difficult part, in some sense that has already been done. And before anyone says "RTGs": that's a very different thing. We're talking a big reactor here that has to be quite effective in terms of energy to weight AND electrical energy to heat, that can't rely on gravity or massive input of coolant in the form of air or seawater in case of emergency, which humans would depend on for several years for their survival. It's probably not impossible, but I don't think we'll see it until it's actually really needed, ie, for manned missions beyond Mars.

However, a research reactor in, for example, lunar orbit, would be interesting. Basic functions could be based on solar, while the reactor either powers electric propulsion experiments or simply converts water ice to fuel. 10 years later we would have a proven system, while the experiments and fuel created would somewhat make up for the cost.

[Streetwind]

Nuclear reactors have been flown to and tested in space numerous times, particularly by the Russians. Now I couldn't tell you what those tests told them about reactor design in space, but it's definitely not a field that humanity is new at.

NASA is/was(?) experimenting with a 512 kg, 100 kW closed brayton cycle reactor called SAFE-400 (for 400 kW thermal output, conversion efficiency 25%) that is specifically designed as a state-of-the-art implementation for spacecraft use. Unfortunately there's no actual, official project to do this - that's something scientists are doing in their free time, using "discretionary" funding. In other words, spare change the lab manager scrapes together for them whenever he can. As such, the project's not going anywhere fast... but do note, the reactor WAS up and running running some 10-12 years ago.

About one ton of reactor mass to drive a single VF-200 wouldn't be too shabby. Definitely better what we can do with solar in Earth orbit (and in Mars orbit there's just no contest).

EDIT: I don't know if the weight figure includes 300 kW worth of radiator surface, but if I were to guess, I'd say no. Also don't know how long one load of fuel lasts/how long it can maintain 100 kW electric output.

Edited April 7, 2015 by Streetwind

[prophet_01]

It's nice to know that there are such engines, but as already mentioned they need to be powered by something...

As far as I know, the TOPAZ II is the most powerful generator (with a suitable mass/output ratio) that has actually been proven in orbit. It's one of the very few fission reactors that have been developed to work in space and that are more than just "near future concepts". This one has 4.5 - 5.5 kW which isn't that bad, but you can see what this is compared to the requirements of a mature electric propulsion system. Not to mention that it's doubtful at best that a western space agency would launch something with the 'n'-word... (well, beside ntg's)

http://fti.neep.wisc.edu/neep602/SPRING00/lecture35.pdf

Sure, there is the ISS with it's giant solar arrays that provide ~ 70 kW (don't quote me on that number), but they are rly heavy and are likely to ruin your leftover payload capability...

Edit: interesting, didn't know that 'NASA' still works on something like this. To bad they aren't making an official project here and invest some real money. Afterall it's one of the technologies that is more likely to be reality at some point

Edited April 7, 2015 by prophet_01

[maccollo]

We're talking a big reactor here that has to be quite effective in terms of energy to weight AND electrical energy to heat

That's quite an understatement. The 40 day trip to Mars requires a 200 megawatt reactor and specific power of 1, that is 1 kilogram per kilowatt. This reactor would have a mass of 200 tonnes.

How would you launch it even if it could be built?

Looking at the performance of actual reactors that have flown in space the specific powers is like 50 times worse. I did see a design proposal for a reactor called SAFE-400, which would have a specific power ratio of 13.5, still over an order of magnitude higher.

Ad Astra, the company behind VASIMIR, made a handy spreadsheet that shows what could actually be done with more reasonable performance characteristics.

https://dl.dropboxusercontent.com/u/22015656/Glover_1-19-11.pdf Page 25.

Even 10 kg/kw it's not possible to beat the Hohmann transfer, and the 'sweet spot' configuration takes over two years. So the idea that VASIMIR, or any electric propulsion, would allow quick trips to Mars doesn't seem realistic. It seems like it could make a very good cargo hauler beyond low Earth orbit though.

[Rakaydos]

Since Microwave Beamed power is considered something of a miracle solution to orbital lift, would it also work for a brachistone transfer?

Of course you wouldnt be using a thermal rocket- too inefficent. But the microwave rectennas could just as easilly power the same sort of applications a reactor might, without the onboard mass or political issues.

[Scotius]

Hmmm. Maybe NASA already knows something about Cannae\Emdrive\QThruster that we don't? And they don't want to sink money and time in technology that will be obsolete just in few years?

That was a joke Althought...

[Kerbart]

The main drawback seems to be that we'd need to get everyone feeling comfortable with nuclear devices in space.

In space is not the issue. The public has an issue with the process of getting it into space, aka "launch"

This may seem haggling over semantics but it's not. If you can launch the dry reactor in a normal way, and send up the fuel in an extra secure launch (likely with the director of NASA and the CEO of the nuclear contractor on board, to make sure they don't say they take safety seriously, but they actualy do) you could deal with that.

After that, not too many* people will be worried if the reactor has a meltdown halfway between mars and earth (until at least they find out that without the injection burn around mars the vessel *will* eventually meet up with earth again, I assume)

* Excluding the obvious one like crew, family of crew, nasa directors, etc.

[Streetwind]

Hmmm. Maybe NASA already knows something about Cannae\Emdrive\QThruster that we don't? And they don't want to sink money and time in technology that will be obsolete just in few years?

That was a joke Althought...

Then why did they just sign a $10 million contract with Ad Astra Rocket Company to get the VASIMR flight qualified within 3 years? It's a very fun topic though.

The Quantum thruster is at TRL 3 (on a scale of 1 to 9), according to the lead researcher of the lab entrusted with it - and that statement is from 2013, before the whole Cannae drive thing even happened. Mind you, that's a huge claim. According to what we in the public have been told, calling it TRL 1 or 2 would make more sense. TRL 3 implies that they're so confident in their preliminary research that they can try for a laboratory proof-of-concept of the underlying principles. Of course, considering the whole Cannae drive shebang, a different explanation might be that they simply skipped the theoretical science TRLs 1 and 2... because they can reproduce a thrust effect in the lab without actually having any underlying principles to work with, or understanding why.

The Cannae drive research project is not really taken seriously right now, though - there's no budget assigned for it. It operates on "discretionary" funding (whatever spare change the lab management can scrape together for them on the side) and makes only slow progress because of that. For example, they are struggling with doing vacuum tests because there is no money to buy vacuum hardened test components required for the RF excitation in the device, and they wrecked the non-hardened components they had on hand trying to get at least some scrap of vacuum data.

The VASIMR meanwhile is at TRL 6, with the contract just signed meaning to push it to TRL 8. There's at least a decade of serious development work that separates these two projects, even if we assume that developing a quantum thruster is as straightforward as developing a MPDT (which it is most certainly not). So we'll probably see VASIMR equipped spacecraft fly for a good long while before they get replaced with Q-thrusters (although, the mere fact that we can speculate on replacing things with Q-thrusters is mindblowing enough).

[TythosEternal]

I first read the following article in 1999, and it subsequently defined the trajectory of my academic career through grad school. It's worth a read even now as a layman's introduction to the field and specific devices.

https://books.google.com/books?id=RsHqYbQ6maEC&printsec=frontcover&output=html_text

At the time, VASIMR looked like a very promising technology--and the basic concept still does. For a while, though, it looked like the main export from Ad Astra had been press statements and interviews like these. A few years ago, though, they started producing some real data and (even though there were a lot of unforseen efficiency issues) things looked genuinely interesting. The ISS test was going to be a key milestone, a viability demonstration after which power would be the only major remaining hurdle (though not a small one, to be sure). Everyone in the field, regardless of their opinion or cynicism, was excited for the test.

With that test having been canceled, though, you're taking about a relatively unproved technology (compared to contemporary, flight-proven EP devices) that's been draining research resources for 45 years. Even with a sound concept and in-lab prototypes, I'm not optimistic about the project's future when the lead scientist is back to making exaggerated claims in popular publications to increase awareness in his project shortly after his main (and arguably the only realistic) roadmap to operation has, for better or for worse, been quietly guillotined. It's a sad, but common and familiar, state of a project nearing its last legs.

Putting my crystal ball glasses on (and with my tongue safely ensconced in my cheek), I predict Ad Astra will not survive. The VASIMR engine will not reach an operational status, but the technology will be sold and used to evolve existing EP devices. Over time, you will see SS/L and Boeing (etc.) come out with smaller radio-injected fuel streams and maybe even evolved virtual nozzles. Once NASA reaches a point where they release an RFP for manned interplanetary engines, there will be multiple experienced sources who will scale up their own products to deliver. In the meantime, multiple scientists from Ad Astra will go work at a fusion lab somewhere until the next big breakthrough in large-scale electromagnetic engine comes from some random shed outside of Manchester.

[nilof]

Some news:

Highlights:

1. Ions and electrons in the same plume, no neutralization needed

2. Primarily using argon, 6N thrust level achieved (estimated isp 3000s)

3. More than 10000 firings of VX-200

4. 70% efficiency with argon and ISP of 5000s.

5. With krypton, they could reach 75% efficiency.

6. CDR milestone beginning 2016.

7. ISS flight milestone beginning of 2018.

8. ISS reboost currently requires 7t of fuel and 210 million USD per year

9. Smaller 80kW unit would require 1/10 of this cost

10. various application specific animations shown

The improvement in efficiency is probably the most important thing. Its improved from low-end to fairly high-end.

----------

Regarding power, people on this thread are severely underestimating solar power, which has seen huge improvements in recent years. Essentially, nuclear reactors are never going to get better than flexible blanket or thin-film arrays in the inner solar system, period. With DSS megarosa arrays or ATK's upgraded megaflex arrays, the power can readily be scaled up to multi hundred kilowatt levels, at about 4 kg/kW.

With 2 MW of these arrays and either nested halls or Vasimr, you have faster than chemical transits to Mars, in the 4-5 month range. 800 kW is enough for ~8 month transfers with one third of the mass needed using chemical. Regarding payload, this is assuming an architecture similar to the one outlined in the Nasa DRM 5.0.

40 day transits are made of pixie dust and Ad Astra is imho ill-advised to mention them, but shorter transits with far less mass needed in LEO are definitely possible, and probably the best path to Mars at this point.

Edited May 31, 2015 by nilof

[Karriz]

Is the flight test confirmed to go to the ISS? It sounded like it's a separate test.

[Aanker]

Optimistic, it sounds indeed.

[Streetwind]

No, "optimistic" was the original plan to have an operational module on the ISS by the first half of 2014

The engine seems healtheir for the slower pace, though, so it's all good. The abysmal efficiency which had a lot of critics seems to have been addressed.

[xenomorph555]

Actually the ISS mission got cancelled by NASA. They are now weakly funding some smaller ground hot fire tests.

[DerekL1963]

Nuclear reactors have been flown to and tested in space numerous times, particularly by the Russians.

The reactors flown by the Russians are horrid little things - they have some very dodgy safety characteristics due to the "unique" design of the control rods.

[sgt_flyer]

To have good power to weight ratios in a reactor, we need something extremely efficient - not a 25% efficiency reactor. (Because the less efficient, the more radiators you'll need to keep it cooled)

So we'll have to look into direct conversion reactors - like the Fission Fragment dusty plasma reactor concept. But if we go towards this kind of direct conversion technology, it will already have more ISP in thruster configuration on it's own than using it as a reactor to power ion engines

We already have lots of researches done that would allow us to create all kind of what would be 'sci-fi' technologies - if we had the adapted dense power sources / batteries - until we have those - most of those 'sci-fi' technologies will remain on paper (or only test versions in a lab )

Edited May 31, 2015 by sgt_flyer

[SciMan]

Well, either nuclear reactors or several square kilometers of solar panels.

TBH, I think the solar panels option is more likely. Because "Nuclear is evil and a power reactor will instantly kill me from across the country in my sleep".

And yes, that's an entirely stupid and illogical reason for that outcome to be favored. It's an education and communication failure, not a logical argument.

[Scotius]

https://en.wikipedia.org/wiki/Safe_Affordable_Fission_Engine

Another great idea that is ran by scraps from the table of bigger projects 500 kg reactor producing 100 kW of energy - built and maintained on what basically is pocket change. To think what could be achieved if such projects got proper funding...

[vger]

TBH, I think the solar panels option is more likely. Because "Nuclear is evil and a power reactor will instantly kill me from across the country in my sleep".

There's also the question of weight. Uranium certainly isn't the easiest thing to put in space. How much of it would be needed?

[cryogen]

To have good power to weight ratios in a reactor, we need something extremely efficient - not a 25% efficiency reactor. (Because the less efficient, the more radiators you'll need to keep it cooled)

It goes both ways. At a higher T_cold, conversion is less efficient, hence there's more waste heat. But, radiators radiate far more heat per unit area (scaling as T⁴), so their size might shrink, for some parameters.

There's a tradeoff between efficiency and radiator size; saving radiator mass might push towards higher temperatures and hence lower efficiencies.