NASA, DARPA to go nuclear in hopes of putting boots on Mars US research agencies NASA and DARPA are teaming up to create a nuclear thermal rocket engine in hopes the tech will one day carry crewed missions to Mars. The Demonstration Rocket for Agile Cislunar Operations (DRACO) is expected to prove nuclear thermal propulsion by 2027. DARPA has been working on an experimental spacecraft …
Dyson investigated the use of atomic explosions for rocket propulsion, as recounted in his autobiography 'Disturbing the Universe'. I don't think he was considering a nuclear thermal engine as described in the article. The team realised that the increasing level of radioactivity in the atmosphere due to airborne nuclear bomb testing made their idea unacceptable. (The experiments with chemical explosives were successful.)
I assume that there would be a pure chemical launch vehicle to Earth orbit, and the thermal nuclear engine would take over afterwards for the actual trip to Mars.
> the nuclear bit just being "payload" until it's out the atmosphere
Payload or not, even if it's not yet operating (fuel rods isolated), nobody likes being showered with several kilos of uranium/plutonium dust: If the rocket launch fails for any reason, the reactor and its highly unwelcome contents will be scattered all over the area.
From the book on Project Orion by Dyson's son the estimate was 1 additional death, somewhere on Earth, per launch. For the time at least the 'bomb' designs were relatively clean in terms of fall out as I understand it, but a lot of the project is still classified as small lightweight nuclear propulsion systems may have other non-peaceful uses...
So instead of being cooked like a pie in a microwave over a 6 month period, the Marsfarers can now be cooked instantly. We live in an age of instant gratification.
What worries me is that the NASA put out a statement without mentioning how it will help them search for extraterrestrial life on other planets. Someone needs to be sacked (or microwaved) for not reminding the world how the NASA is still relevant, even in this age, out there looking for life and keeping busy.
(It's intrigued me for a while how the NASA want to use JWST to look for signs of life on a planet 40 LY away when they can't even conclusively determine if it exists on Mars, which is here within grabbing distance).
JWST can possibly detect life if there is lots of it to the point it has modified the atmosphere to show chemical signatures that are rare for inorganic processes.
Mars is known to have very little signs of life, but we also know from extreme locations on Earth that life can survive and those have not yet been ruled out.
Every craft that's stopping arrives too fast and needs to brake. So the total loss of fuel would be fatal to any interplanetary mission. You're just screwed a bit faster if it's nuclear.
For example, here's NASA's summary of the Mars Orbiter using chemical thrusters to perform orbital insertion. And here's an ESA description of Cassini-Huygens at Saturn. To quote, "If [orbital insertion] had failed, the spacecraft would have just flown past Saturn and got lost in the outer Solar System." And that involved multiple rotations. Some to shield the craft. Some to align antenna. And some "For science!"
I'm sorry you got a downvote. What is obvious to science (or sci-fi) fans is not necessarily obvious to the general public, and one should not be penalized for asking a honest question.
The answer, simplifying just a bit, is: at some point before you get there, you rotate the vehicle 180° and fire the main engine again.
TL;DR: Argon ? Sulfur hexafluoride ? Or something else ??
If you are going to super heat some gas that is stored as a liquid, what would work best (I'm guessing that you do not want to deal with a solid, because the second phase change would waste far too much energy).
I'm guessing that it needs to be a gas with a low molar heat capacity, somewhere about ~21 J/(mol·K) or lower, which would take Oxygen, Nitrogen and Hydrogen off the table at ~28 to 30 J/(mol·K). It would need to not be corrosive (so a noble gas would fit the bill well). Next question would be which would be better a higher or a lower temperature boiling point, I'm going to guess that higher is better that you need to use less energy to raise it's temperature before it leaves the craft forever. That would make the perfect gases Xenon (boiling point 165.051 K; −108.099 °C; −162.578 °F) Molar heat capacity 21.01 J/(mol·K) or Krypton (boiling point 119.93 K; −153.415 °C; −244.147 °F) Molar heat capacity 20.95 J/(mol·K). But if you needed a few hundred tons of the stuff something that is about 0.9340% of earths atmosphere might work out much much much much much cheaper to source - i.e. Argon (boiling point 87.302 K ; −185.848 °C; −302.526 °F) Molar heat capacity 20.85 J/(mol·K) ? Krypton is about ~0.000114% and Xenon is about 0.0000087% of earths atmosphere and insanely expensive to use by the ton.
Sulfur hexafluoride would probably be better than perfect (boiling point 222.3 K; −50.8°C; −59.4 °F) but for it's ridiculously high molar heat capacity of 97 J/(mol·K).
Fuel or propellant?
Anyway, the article was short on details but the news bit at DARPA emits this:
Nuclear thermal rockets have been built before, so DRACO has a head start. About 50 years ago, the technology was tested on the ground. DRACO is now leveraging lessons learned from past NTR reactor technology, but instead of using highly-enriched uranium, DRACO is using high-assay low-enriched uranium (HALEU) fuel to have fewer logistical hurdles on its ambitious timeline. As an added safety precaution, DARPA plans to engineer the system so that the DRACO engine’s fission reaction will turn on only once it reaches space.
Fission, the same process used for nuclear power, is the splitting of atoms. It creates high levels of heat that can turn rocket propellant such as hydrogen from a liquid to a gas phase. In the NTR, that gaseous propellant is accelerated out a converging/diverging nozzle in the exact same way as a conventional chemical rocket engine. The high performance of an NTR is enabled by the reactor passing its heat along to its rocket propellant. DRACO’s proposed solid core NTR temperatures could reach almost 5,000 degrees Fahrenheit, requiring use of advanced materials.
"The Demonstration Rocket for Agile Cislunar Operations (DRACO) is expected to prove nuclear thermal propulsion by 2027"
If they had continued with the 1960s NERVA nuclear rocket engine then there would have been no need to reinvent it today. The was a great deal of optimism in the 1960s about what could be accomplished in space including project ideas like Mustard to get into Earth orbit (3 shuttles attached to each other at launch) and Project Deimos to get to Mars.
There is a very good account of those days in Philip Bono and Kenneth Gatland's Frontiers of Space book. While that book is no longer in print, copies can still be found online.
While the idea of nuclear engines are great, I think we must figure out on how to survive on the moon, with minimal help first. Mars is a bit too far away for any reasonable help to arrive in time.
You want boots on Mars, fine, but with people wearing them, not so fine. So far we have not had a long term isolated, working habitat right here on the ground on this planet. The ISS is regularly supplied, and with personal changes, so it doesn't count.
So how do they plan to deal with the demonstrators this time around? Isn't there usually a huge fuss (and news coverage) by the anti-nuclear folks every time NASA ever mentions putting nuclear material in or on a rocketship? And those were just small nuke battery warmers or something like that, not something large enough to propel a vehicle to Mars. I think this nuke engine idea has legs, but depending on the social/political winds up to launch day, it may never leave the launch pad, and may not even get that far.
An (intermittently) excellent self-published book on decades spent trying to make this happen. You even even reported on it yourselves.
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