To Mars in 39 days?

[JonnyBGoode]

Popular Science has an article this month about a company that's working on a new spacecraft that, if it works, will get people to Mars in just 39 days. :blink:

 

[tblaxland]

I assume they are talking about the [ame="http://en.wikipedia.org/wiki/VASIMR"]VASIMR[/ame]. The engine works for sure (albeit not demonstrated in space yet) and should scale up quite well. The bigger problem than making it work will be figuring out how to pay for it :dry:

 

[jinglesassy]

Sounds like it uses a high-power vasmir ion engine.

 

[IgnoreThisBarrel]

Popular Science has an article this month about a company that's working on a new spacecraft that, if it works, will get people to Mars in just 39 days. :blink:

Hmm... did you just get your issue? I think I got that one a while back...

 

[jedidia]

Sounds like it uses a high-power vasmir ion engine.

Just to be a little nit-picking here, a VASIMR isn't an ion engine. Could maybe be best called a plasma engine.

39 days should be doable for a VASIMR. Also, the VASIMR is a proven, working concept of which there are prototypes, so there's no doubt about its viability. Problems are financial, as well as politcal. You'd pretty much need a nuclear reactor to power it, and getting one of those into space nowadays is not an easy undertaking...

 

[N_Molson]

Aside of the political/financial issues, a nuclear reactor is a very heavy machine (Uranium is one of the heaviest elements, you need water in the core, a thick lead layer to isolate the crew from radiations, and so on...) that has to be launched in one piece.

I'm not even sure that a very-heavy launcher (Saturn/Energia/SSLS class, around 100 tons of payload) would be powerful enough.

Progress has still to be made in the miniaturization of nuclear reactors.

For information, a Los Angeles class nuclear submarine weights 6,927 tons.

 

[thomasantony]

The submarine does weigh ~7000 tons. But just for reference, how much does a naval reactor .. ( say the S9W/S6W or the A4W reactor ) weigh? I couldn't find this information anywhere.


Now if only we had a 3 "GJ/s" Iron man style "Arc Reactor" ... things would be sooo much easier ..

---------- Post added at 01:51 PM ---------- Previous post was at 01:30 PM ----------

Just found some data on it ( though not sure how reliable ).

Source :http://kbismarck.org/forum/viewtopic.php?t=584

1. The PWR/S6G Reactor of the Los Angeles Class SSN has 35,000 shp each and the sub´s displacement is 6.930 tons.
2. The PWR/S8G Reactor of the Ohio Class SSBN has 60,000 shp each and the sub´s displacement is 18,750 tons.
3. The PWR/S6W Reactor of the Seawolf SSN sub has 57,000 shp each and the sub´s displacement is 9,140 tons.
4. The PWR/A2W Reactor for CVN-65 Enterprise Aircraft Carrier has 35,000 shp each and the flatop´s displacement is 97,000 tons.
5. The PWR/A4W Reactor for the CVN-68 Nimitz Class Aircraft Carrier has 140,000 shp each and the flatop´s displacement is 100,000 tons.

Data seems to be corroborated by this doc.
https://netfiles.uiuc.edu/mragheb/w...wer Engineering/Nuclear Marine Propulsion.pdf ( Page 16 )

Also, You may find this interesting:

http://esamultimedia.esa.int/docs/gsp/completed/comp_i_02_N54.Pdf ( Page 25)

I had taken a seminar on VASIMR as part of my undergraduate course. So I did a bit of reading up on the topic

 

[T.Neo]

The best place to go would be info on the alpha (mass to power) of various nuclear reactor designs.

According to Atomic Rockets, most reactors have an alpha of around 20 kg/kW, and an experimental 1 MW reactor had an alpha of just under 0.5 kg/kW.

At least one of the VASIMR studies used a figure (AFAIK) of 1 kg/kW. Zubrin criticised this for being fantastical, but I think that if similar performance to the aforementioned reactor could be achieved...

Unfortunately I haven't found any data on this reactor. It really sounds fancy...

 

[jedidia]

0.5 kg/kw would be truely outstanding! If you can find tangible data about it, please post!

One MW out of only half a ton of reactor would be a most thrilling perspective, since we could reasonably expect that the alpha could be scaled down a bit more for larger ones.

However, it's also always a question what you count as reactor. The submarine reactors all have shielding included in the weight figure, as far as I know, while on a spacecraft you'd probably go with a shadow shield that weights a bit less than an all-surrounding shield.

 

[thomasantony]

0.5 kg/kw would be truely outstanding! If you can find tangible data about it, please post!

One MW out of only half a ton of reactor would be a most thrilling perspective, since we could reasonably expect that the alpha could be scaled down a bit more for larger ones.

However, it's also always a question what you count as reactor. The submarine reactors all have shielding included in the weight figure, as far as I know, while on a spacecraft you'd probably go with a shadow shield that weights a bit less than an all-surrounding shield.

That is a valid point. You can stash the reactor at the back ... and shield only the side with the crew. It can irradiate space as much as it wants ... nobody need to go back there . Of course they would have to be careful bringing it near space stations and stuff ...

---------- Post added at 11:56 PM ---------- Previous post was at 11:12 PM ----------

I did a bit of googling. Found that this very thread was #3 in search results on the topic. ..

But also found this:
http://namcub.accela-labs.com/pdf/Ultralight%20Vapor%20Fueled%20Cavity%20Reactors%20with%20MHD%20for%20Powering%20Multi-Megawatt%20NEP%20Systems.pdf

In fact they are even talking about coupling it to the VASIMR in that doc.

Not sure what stage it is at or even whether it is being worked on.

 

[N_Molson]

The other problem is that you have to found a way to bring back the reactor in one piece in the case of a launcher failure. Something like a LES. Which would require a heat shield, a lot of parachutes, and a full radiation shield.

In fact, the safety rules applied for manned spaceflight also apply when you launch such a sensible payload.

And it's where a Shuttle-like design is better, since the payload stays inside the Orbiter.

 

[T.Neo]

Except, when the launch stack disentegrates, "inside the Orbiter" means very little.

RTGs are already built to survive reentry/landing and launch accidents. Since nuclear reactors are by their very nature robust and carry a lot of redundant mass (in the form of shielding) it should be quite easy to guard against such a failure.

It is also worth noting that a nuclear reactor only becomes seriously radioactive once it is turned on for the first time, which could potentially be done after the launch.

I don't see why gigantic, complex, costly, mass-eating gadgets such as a form of LES need to be used to ensure safety from launch accidents involving a nuclear payload.

 

[TMac3000]

Popular Science has an article this month about a company that's working on a new spacecraft that, if it works, will get people to Mars in just 39 days. :blink:

A heavy-water (nuclear salt-water) rocket could probably do it, if they are ever able to build such a thing.

 

[Urwumpe]

Uranium is one of the heaviest elements, you need water in the core, a thick lead layer to isolate the crew from radiations, and so on...)

You only need a few kg of Uranium per reactor, you don't need water in the core for cooling (thermoelectric energy conversion is better for high power reactors) and a thick lead layer for isolating the crew from the radiation of the reactor is actually committing suicide. Some distance and a fuel tank works much better.

Nuclear reactors in space are much lighter and smaller than their terrestrial counterparts, because you can't make the radiation in space worse by them. Many even control the reactions by opening and closing doors at the reactor vessel, letting more or less neutrons simply escape into space.

 

[Cairan]

and a thick lead layer for isolating the crew from the radiation of the reactor is actually committing suicide. Some distance and a fuel tank works much better.

It should be mentioned here that Urwumpe is referring here, I think, to the interaction of cosmic rays and beta radiation with the lead shield, not necessarily the reactor itself. It has been demonstrated that to shield against neutron fluxes or beta radiation (electron), the best element is hydrogen, and for electromagnetic radiation (x-rays, gamma rays) lead is a good, dense choice. Alpha radiation (helium nuclei) can be stopped by everything without problems...

Placing the crew forward of water/fuel/oxygen/hydrazine/coolant tanks which are all filled with arrangements of light elements (H, C, N, O) is the logical conclusion...

 

[T.Neo]

(thermoelectric energy conversion is better for high power reactors)

I've heard that thermoelectric conversion is seriously inefficient (something like 1%). Is this true?

 

[N_Molson]

Water tanks used for drinking or or washing should be put away from radiations however... The same applies for oxygen/nitrogen used to breathe...

 

[Ghostrider]

Water tanks used for drinking or or washing should be put away from radiations however

Now, remember one important thing: water is for washing and showering. For drinking, there's beer.:thumbup:

 

[T.Neo]

We definitely want intoxicated astronauts. :shifty:

 

[Ghostrider]

We definitely want intoxicated astronauts. :shifty:

Not exactly intoxicated, more like "in good spirits".