Whats our next generation propulsion technology?

isare · Oct 10, 2007

Evening All, I was just wondering what your guys opinions are on where we should focus for our next generation of propulsion systems, as it seems we are reaching height of chemical rocket propulsion. Personally i think nuclear powered engine should be the next to be used for propulsion considering our considerable experience with nuclear propulsion doesn't it seem to be the next logical step to anyone else? I'd be interested to know what next generation technology is currently in development. I've heard a few times that the cutting edge technology on view today is 30 years old, I'm interested by the potential in "o3" which can be harvested in large quantities off the moon althou I realise that would be a chemical rocket. Also if anyone here had to guess when do you think (in years) that A) We'll reach the moon again. B) We'll reach Mars. C) Titan. D) Nearest Star. Also which kind of engine do you see us using over these time periods and when i say reach i mean reached by a manned spacecraft. Thanks for reading.

qso1 · Oct 10, 2007

I agree that nuclear propulsion is the next step...if we finally decide to leave earth orbit. Nuclear propulsion is very expensive and not all that practical for rockets departing from earths surface. Not to mention the environmental headaches associated with the exhaust byproducts. Chemical rockets, much like their automotive counterparts...internal combustion engines...are going to be around for awhile. There was some promising research on laser light craft propulsion as an alternative to chem. But I haven't seen any new developments in LLC in years. They either shut down due to the usual funding problems or it went deep black. Nuclear for deep space is more practical than chemrocs but until we commit to human exploration of mars...not much of a future for nuclear propulsion right now. Moon: If the Bush plan is put into effect, by 2020, conventional chemical propulsion as already evidenced by the cancellation of the methane as fuel part of the program. Mars: If the Bush plan lasts...2025 to 2030 and again, chemical propulsion as funding will restrict the ability to develop nuclear. However, its possible nuclear might win out. Nuclear thermal would be a good choice except that its rather costly and heavy which partially offsets the propulsion advantage. Nuclear electric based on the VASIMR research program may be a better choice. Theoretically allowing for as little as three months transit to mars. Moon and mars projections based on conventional timelines and NASA. If the private sector really shakes things up...the equation will change and possibly allow for earlier dates, although in the case of mars, not much before 2025 I would think. Titan: Probably early to mid 22nd century with humans. Nearest star: Earliest I can see that coming is maybe 150 to 200 years and actually, these projections are from a graphic novel I have almost finished which touches upon all these destinations and s <div class="Discussion_UserSignature"> My borrowed quote for the time being:There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened. </div>

gunsandrockets · Oct 11, 2007

Unmanned robot probes work fine with NSTAR type ion thrusters, as are being used on the DAWN probe to orbit Vesta and Ceres. For manned propulsion I think two avenues should be developed, the Hall Plasma Thruster electic rocket and the Low Pressure Nuclear Thermal Rocket (LPNTR) engine. The Hall thruster was used for the SMART-1 moon orbiter. LPNTR is a natural outgrowth of earlier successful work with NERVA.

spacelifejunkie · Oct 11, 2007

A dark horse is nuclear fusion. Not tokamaks, they're way too heavy. From Focus Fusion to Dr. Bussard's IEC ideas, there might be some promise. It will be hard to get nuclear fission reactors in space. I'm not against it but the public has such irrational fears. If not fusion, I'm afraid we might be stuck with chemical rockets for a long time. An incremental improvement to space access would be scramjets. DARPA has some interesting experiments going on right now using hydrocarbon fuels. I believe there was a scramjet thread on Missions & Launches a while back with some interesting links. Scramjets would be an improvement but not a revolutionary one, especially since they don't work in space. http://www.askmar.com/Fusion.html SLJ

keermalec · Oct 11, 2007

Nuclear Thermal Rockets already exist: check out the Timberwind uper stage thrusters on astronautix.com. These have an ISP of around 1000s and a thrust to weight ratio of 30. Compare that to an advanced LOX/LH2 (chemical) thruster such as the RL-10B which has a better t/w of around 44 but a much lower ISP of 462s. Next logical step after fission is fusion but this is probably 30 years away as we are only just starting to experiment with large scale fusion reactors here on the ground (ITER experiment). However, a fusion reactor should be lighter and produce more energy than a fission reactor. First generation will be Deuterium-Hydrogen burning reactors, then Deuterium-Helium-3 and then Helium3-Helium3 which requires temperatures 10x higher than DHy but produces much more energy and no radioactive waste at all except for the walls of the reactor which must be changed every once in a while. I believe you must be referring to Helium3 as the magic fuel of the future which can be found in large quantities son the Moon, not O3. <div class="Discussion_UserSignature"> “An error does not become a mistake until you refuse to correct it.” John F. Kennedy </div>

wick07 · Oct 11, 2007

I recommend taking a look at VASIMR: http://en.wikipedia.org/wiki/Variable_specific_impulse_magnetoplasma_rocket And also the TRITON Engine: http://www.nuclearspace.com/A_PWrussview_FINX.htm Either of these could be the future of space flight. <div class="Discussion_UserSignature"> _______________________________ "If you are surrounded by those who constatly agree with you, then you're in an intellectual vacuum. If you feel like trying to make a difference, you have to BE different. How can you do that without interacting with those who are different from yourself?"- a_lost_packet_ </div>

keermalec · Oct 11, 2007

Thanks for the link, Wick. I'm glad to see the Triton engine is fully ready and functional. Borowsky talked about it in his 2002 Mars Design Reference MIssion revision-1 except it didnt have a name then. It was just a Nuclear Thermal Rocket built from Russian technology with the added capability of LOX augmentation (LANTR) or Bimodal (thrust and power generation) operation (BNTR). The VASIMR technology seems very theoretical to me and this one line really snags in my opinion: "VASIMR drives are expected to require a great deal of heavy machinery " Ion drives are already producing 4'000s ISP for a much better t/w ratio than VASIMR (see this 2002 report on the NEXT ion drive) so in my opinion VASIMR is moot... Fusion drives are probably the way of the future. This very serious 2005 study by the same Borowski from the Glenn Ressearch Center imagines that a Deuterium-Helium3 drive built 30 years from now could deliver an ISP of over 40'000 and get you to Jupiter in 118 days at a constant acceleration/deceleration of 1.68 milli-gs. To me that works out to 90 days for getting to Mars... <div class="Discussion_UserSignature"> “An error does not become a mistake until you refuse to correct it.” John F. Kennedy </div>

wick07 · Oct 11, 2007

I think saying Triton is fully functional and ready to go is a bit optimistic. In the article they say they need 800 mil to create a prototype. Most likely the prototype will need some modification before it is "field ready". It is true of VASIMR as well. Here are some more articles on VASIMR. It seems to be more than a pipe-dream. And one major advantage is that the engine can be used to create high ISP or high thrust, making it very flexable. http://space.newscientist.com/article/dn12064-plasma-rocket-breaks-endurance-record.html http://www.adastrarocket.com/home.html [pure conjecture & scifi] I am not sure but it may be possible, if you used the right fuel and got the exhaust compression just right, to induce some type of limited secondary fusion reaction. [/pure conjecture & scifi] Plus we shouldn't discount GCNR, which is still kinda "out there", but it may also provide us with a powerful engine. Also, if I am not mistaken one major downside of Ion drives is that they cannot be used to lift cargo from the Earth to LEO, which unfortunately is where we need to make the greatest improvements. I have heard it said right here on SDC the LEO is halfway to the rest of the universe. <div class="Discussion_UserSignature"> _______________________________ "If you are surrounded by those who constatly agree with you, then you're in an intellectual vacuum. If you feel like trying to make a difference, you have to BE different. How can you do that without interacting with those who are different from yourself?"- a_lost_packet_ </div>

keermalec · Oct 11, 2007

For the foreseeable future, the only type of engine that will allow us to lift from ground to LEO is the chemical rocket. Even NTRs won't make it due to their (relatively) low thrust to mass ratio. VASIMR is in the same category as ion or future fusion drives, ie low-thrust/long duration. Good for getting from planet to planet but no use whatsoever for ground to LEO. <div class="Discussion_UserSignature"> “An error does not become a mistake until you refuse to correct it.” John F. Kennedy </div>

docm · Oct 11, 2007

I posted to the Aviation forum about a tech that may bridge that gulf; a multi-mode turbo/ram/scram jet being developed by AeroJet and PyroDyne called the PyroJet TBCC (Turbine Based Combined Cycle). PyroJet PyroJet pic.... Space.com link.....(AeroJet paragraph at bottom) The idea is for Mach 0 to Mach 10 capability. Now imagine a mothership powered by one or more of these that would serve as the ultimate reusable first stage. Kind of a super White Knight. <div class="Discussion_UserSignature"> </div>

docm · Oct 11, 2007

Variable from 1,000 to 30,000 plus. http://www.adastrarocket.com/home.html They plan to test the 200 kw VX-200 ground prototype in 2008 and fly the VF-200 a within a few years if the ground tests work out. Latest press release (Oct 1, 2007): http://www.adastrarocket.com/AdAstraPressRelease100207.pdf Technology Review article (Sept. 25, 2007: http://www.technologyreview.com/Infotech/19427/ <div class="Discussion_UserSignature"> </div>

keermalec · Oct 11, 2007

I hate to be the show stopper but I just dont believe in the performance of either high-isp or low-isp VASIMR. Lets take high isp: imagine we are accelerating 0.01 kg of H2 per second with an ISP of 30'000, ie 300'000 m/s. We require 4.5x10E8 watts or 450 MW for this. Solar Concentrator Arrays, as used in Deeps Space 1, currently cutting edge solar panels, weigh 11 kg / kW. That means you'll need about 5'000 tons of solar panels. A nuclear reactor will weigh in about 7 kg/kw so you still need a 3'000-ton nuclear reactor. Assuming the drive mass is zero, which of course it isn't you will be producing 3000 Newtons of thrust for a drive+power source in excess of 3000 tons. That is a thrust-to-weight ratio of 0.0001. Assuming the whole ship weighs only 3000 tons, it will take you 1'000 seconds to accelerate to 1 m/s, and 1'000'000 seconds (12 days) to accelerate to 1 km/s. So we are talking very very low thrust here, not to mention that current VASIMR prototypes overheat after 4 hours... Note that current ion drives have been actually used in space for years at a time. I am sure that if we consider lower ISPs such as 3'000 or 4'000s, the VASIMR drive does not stand up against an existing ion drive simply because the ion drive is so simple and requires such less mass (basically two charged plates and a massive power conversion unit which must also exist in the VASIMR). I am afraid that once VASIMR really takes off it will be less interesting at low ISPs than nuclear thermal rockets, also less interesting at medium ISPS than ion drives and only possibly interesting at very high ISPs. But then we cannot produce the massive power needed at those high ISPs today, and if we wait for the advent of fusion reactors, these will necessarily be more efficient when accelerating the products of their own fusion (ie fusion drives), instead of converting heat to electricity and then to kinetic energy: which is necessarily very inefficient. <div class="Discussion_UserSignature"> “An error does not become a mistake until you refuse to correct it.” John F. Kennedy </div>

docm · Oct 11, 2007

And what about SAFE-400? A 512kg 51cm core/reflector generating 400 kw. Even scaled up it would have less mass to accelerate, but still enough to cut months of a Mars transit. <div class="Discussion_UserSignature"> </div>

qso1 · Oct 12, 2007

Keermalec: Nuclear Thermal Rockets already exist: Me: To the best of my knowledge, the only nuclear rocket that ever actually existed as a functioning rocket was NERVA. The NERVA engine tests of the 1960s validated the NTR concept. Timberwind was in development when it was canceled. None of the nuclear upper stages ever became operational and IIRC, none of them even reached the testing phase. <div class="Discussion_UserSignature"> My borrowed quote for the time being:There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened. </div>

keermalec · Oct 12, 2007

qso, you must be right. It seems the Timberwind never flew before it was cancelled in 1992... The Triton engine, though, seems quite advanced in terms of design, if not actual testing, from Borowski's report on the subject. The SAFE-400 is a nuclear reactor designed for producing electricity in space. It can be used to power an electrical drive (ion, HAL, VASIMR) but given the advances in solar panel technology, it will probably only be used for missions to the outer solar system, if ever. <div class="Discussion_UserSignature"> “An error does not become a mistake until you refuse to correct it.” John F. Kennedy </div>

wick07 · Oct 12, 2007

Well aren't you just the party pooper <img src="/images/icons/wink.gif" /> Realistically though, I think chemical will be the only Earth to LEO option for a long time yet. Even if TNR is build and is reliable the public won't stomach a nuclear rocket engine operating in the atmosphere, people are still untrusting of just launching nuclear material for use in thermal reactors. It is sad that most people equate nuclear with evil or dangerous. It reminds me of something I read today on MSNBC talking about a new screening device for airports that will scan people without using x-ray radiation, instead it only uses elecromagnetic waves. The general public is not able to understand even the most basic concepts in physics, and yet they want to decide what technology is safe and how to use it. <div class="Discussion_UserSignature"> _______________________________ "If you are surrounded by those who constatly agree with you, then you're in an intellectual vacuum. If you feel like trying to make a difference, you have to BE different. How can you do that without interacting with those who are different from yourself?"- a_lost_packet_ </div>

MannyPim · Oct 12, 2007

I don;t believe it is the intention of the NTR designers and promoters that it be a system for use in the Earth's atmosphere. A LATERN system has been designed at NASA using Lunar Ox mined from Lunar regolith and a refueling sation in Lunar Orbit. This system shortens the Earth to Moon and Moon to Earth trips to less than 24 hrs each (instead of the 3 days it takes to get there with conventional chemical only engines). <div class="Discussion_UserSignature"> The only way to know what is possible is to attempt the impossible. </div>

keermalec · Oct 12, 2007

MannyPim I think u meant LANTR and not LATERN. The difference in performance for lift-off from the Moon is not very important though between chemical LH2/LOX and LANTR 1 (10% LOX, 90% LH2). For a 10-ton lifter I get 5.91 tons payload using LANTR 1 and 5.25 tons payload using chemical: http://www.vrzone.org/space/high_thrust_ship.php Parameters used: Desired Delta-v: 2.05 km/s Aerobrake: NO Minimum acceleration: 0.34 Gs RCS/avionics: YES This little difference is due to the large mass of the LANTR thruster which undermines the fuel savings wrt chemical thrust. LANTR 1 will use only 2.5 tons of propellant per lift-off (0.25 tons LOX and 2.25 tons LH2) instead of 3.81 tons for the chemical thruster (3.39 tons LOX and 0.42 tons LH2) but requires much more LH2. Because Oxygen is much more plentiful on the Moon than Hydrogen, it may be much more cost effective to use a Lunar-oxygen based chemical rocket on the moon than a LANTR. Usng the same logic the 4.2 km/s transfer from LEO to LLO should probably be propelled by a chemical LH2/LOX rocket. Unless you want to get your LH2 from Earth, at 10'000'000 USD per ton... <div class="Discussion_UserSignature"> “An error does not become a mistake until you refuse to correct it.” John F. Kennedy </div>

MannyPim · Oct 12, 2007

Yes, you are correct, LANTR is the proper acronym... As for how the system is intended to be used, it is supposed to be used only for Earth-Moon and Moon-Earth transit. Surface to orbit transfers, whether from the Earth or the Moon, and also orbit to Lunar Surface, use conventional chemical engines. <div class="Discussion_UserSignature"> The only way to know what is possible is to attempt the impossible. </div>

keermalec · Oct 12, 2007

I see, so they're planning on using faster than hohmann transfers to shorten the trip time. But they're still using up more LH2 than if using conventional rockets and LH2 comes from Earth. Shortening trip time is critical in the case of a long mission such as Earth-Mars but is it worth it to get to the moon in 1 day instead of 3? I wonder. <div class="Discussion_UserSignature"> “An error does not become a mistake until you refuse to correct it.” John F. Kennedy </div>

MannyPim · Oct 12, 2007

I will have to check into how much H2 they need. I suspect that they don;t need anymore H2 or O2 then if they used conventional hohman transfer orbits. They get more energy out of the same fuel by pre-heating the O2 to about 2,000 deg using the nuclear core and then injecting H2 into the combustion chamber (similar to a jet afterburner). <div class="Discussion_UserSignature"> The only way to know what is possible is to attempt the impossible. </div>

keermalec · Oct 13, 2007

To come back to the subject of future propulsion, the Triton engine is an awesome developement: probably one of the greatest steps forward of these past few years. But let us not overestimate the importance of LOX afterburning. The Triton injects LOX into the combustion chamber after having superheated the LH (and not the other way round, as superheated oxygen tends to react with anything it encounters, including tube walls). The net effect is an increase in thrust but a decrease in ISP. high thrust is useful for minimising gravity losses (as when leaving LEO) or taking off from a small body such as the Moon. However, the ration of LH to LOX in the LANTR is always greater than that of a chemical rocket, which is 1/8, so the net advantage of using lunar Oxygen is always less for a LANTR than for a chemical rocket. <div class="Discussion_UserSignature"> “An error does not become a mistake until you refuse to correct it.” John F. Kennedy </div>

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